Search

Study Design: In vivo validation during functional loading.Objective: To determine the accuracy and repeatability of a model-based tracking technique that combines subject-specific computed tomographic (CT) models and high-speed biplane x-ray images to measure three-dimensional (3D) in vivo cervical spine motion.Summary Of Background Data: Accurate 3D spine motion is difficult to obtain in vivo during physiological loading because of the inability to directly attach measurement equipment to individual vertebrae. Previous measurement systems were limited by two-dimensional (2D) results and/or their need for manual identification of anatomical landmarks, precipitating unreliable and inaccurate results. All previous techniques lack the ability to capture true 3D motion during dynamic functional loading.Methods: Three subjects had 1.0-mm-diameter tantalum beads implanted into their fused and adjacent vertebrae during anterior cervical discectomy and fusion surgery. High-resolution CT scans were obtained after surgery and used to create subject-specific 3D models of each cervical vertebra. Biplane x-ray images were collected at 30 frames per second while the subjects performed flexion/extension and axial rotation movements 6 months after surgery. Individual bone motion, intervertebral kinematics, and arthrokinematics derived from dynamic radiostereophotogrammetric analysis served as a gold standard to evaluate the accuracy of the model-based tracking technique.Results: Individual bones were tracked with an average precision of 0.19 and 0.33 mm in nonfused and fused bones, respectively. Precision in measuring 3D joint kinematics in fused and adjacent segments averaged 0.4 mm for translations and 1.1° for rotations, while anterior and posterior disc height above and below the fusion were measured with a precision ranging between 0.2 and 0.4 mm. The variability in 3D joint kinematics associated with tracking the same trial repeatedly was 0.02 mm in translation and 0.06° in rotation.Conclusion: The 3D cervical spine motion can be precisely measured in vivo with submillimeter accuracy during functional loading without the need for bead implantation. Fusion instrumentation did not diminish the accuracy of kinematic and arthrokinematic results. The semiautomated model-based tracking technique has excellent repeatability. [ABSTRACT FROM AUTHOR]

Quantitative in vivo biomechanical assessments are typically performed with optoelectronic motion capture (MoCap) using retroreflective markers attached to skin. This technique inherently contains measurement errors from both marker placement on palpated bony landmarks and skin motion relative to the underlying bone (i.e., soft tissue artifact (STA)). Research on lumbar spine STA is scarce and limited to young, healthy participants in static positions. This study aimed to evaluate static placement errors, lumbar spine STA from MoCap marker clusters (MMC), and linear relationships between STA and patient characteristics. Thirty-nine participants with cLBP performed three trials each of flexion/extension and lateral bending while imaged simultaneously by MoCap (120 Hz) and dynamic biplane radiography DBR (20 Hz). MMCs were placed 29.5 ± 18.0 mm and 27.1 ± 13.4 mm superior to the most prominent aspect of the L1 and L5 spinous process, respectively. L1 relative to L5 STA was larger during flexion/extension (8.6 ± 5.7°) than lateral bending (4.5 ± 2.1°) (p < 0.001). After correcting for marker placement errors, components of the L1 and L5 STA averaged as much as 16.3 mm and 11.4° during flexion/extension, but only 4.0 mm and 4.8° or less during lateral bending. On average, STA for individual L1 and L5 vertebrae increased as participants moved away from the upright neutral position. STA was participant-dependent, however, age and BMI did not model STA well. Given the inaccuracy in marker placement and wide range of patterns of STA, caution is urged when making clinical decisions or when using computational models to estimate spine tissue loading based upon lumbar spine kinematics obtained from skin-mounted markers., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA) are effective surgeries to treat end-stage knee osteoarthritis. Clinicians assume that TKA alters knee kinematics while UKA preserves native knee kinematics; however, few studies of in vivo kinematics have evaluated this assumption. This study used biplane radiography to compare side-to-side tibiofemoral kinematics during chair rise, stair ascent, and walking in 16 patients who received either TKA or UKA. We hypothesized that TKA knees would have significant kinematic changes and increased asymmetry with the contralateral knee, while UKA knee kinematics would not change after surgery and preoperative knee symmetry would be maintained. Native bone and implant motion were tracked using a volumetric model-based tracking technique. Six degrees of freedom kinematics were calculated throughout each motion. Kinematics were compared between the operated and contralateral knees pre- and post-surgery using a linear mixed-effects model. TKA knees became less varus with the tibia more medial, posterior, and distal relative to the femur. UKA knees became less varus with the tibia less lateral on average. Postoperative TKA knees were in less varus than UKA knees on average and at low flexion angles, with an internally rotated tibia during chair rise and stair ascent. At high flexion angles, the tibia was more medial and posterior after TKA than UKA. Side-to-side kinematic symmetry worsened after TKA but was maintained or improved after UKA. Greater understanding of kinematic differences between operated and contralateral knees after surgery may help surgeons understand why some patients remain unsatisfied with their new knees., (© 2024 Orthopaedic Research Society.)

Purpose: This study aimed to identify surgical parameters during reverse shoulder arthroplasty (RSA) that predict post-surgical kinematics during the hand-to-head motion (H2H) and to identify associations between kinematics and outcomes. We hypothesized that greater humeral retroversion and lateralization predict kinematics, and that more scapular upward rotation is associated with better PROs and more range of motion (ROM)., Methods: Thirty-five post-RSA patients consented to participate. All surgical parameters were recorded while operating or measured on CT. Participants performed H2H while synchronized biplane radiographs were collected at 50 images/second. Digitally reconstructed radiographs were matched to biplane radiographs to determine glenohumeral and scapular kinematics. For all rotations, the contribution, end position, peak angles, and ROM were calculated. Contact path between the glenosphere and polyethylene insert was calculated. Patient-reported outcomes (PROs), clinical ROM, and strength were measured. Multiple linear regression identified surgical parameters that predicted kinematics, and Pearson correlation identified associations between kinematics and outcomes., Results: Less humeral retroversion predicted greater peak abduction (p = 0.035). Humeral neck-shaft angle, retroversion, and glenoid tilt predicted the peak posterior contact path (p = 0.012). Better PROs were associated with more superior contact path (p < 0.001), more abduction (p < 0.001), and greater peak scapular upward rotation (p = 0.017). Greater strength was correlated with more peak external rotation (p = 0.035). Greater external rotation at 90º was associated with more abduction (p = 0.008) and upward scapula rotation ROM (p = 0.015) during H2H., Conclusion: Less humeral retroversion predicted kinematics during H2H that were associated with more favorable PROs and clinical outcomes., (© 2024. The Author(s) under exclusive licence to Biomedical Engineering Society.)

Normal biomechanics of the upper cervical spine, particularly at the atlantooccipital joint, remain poorly characterized. The purpose of this study was to determine the intervertebral kinematics of the atlantooccipital joint (occiput-C1) during three-dimensional in vivo physiologic movements. Twenty healthy young adults performed dynamic flexion/extension, axial rotation, and lateral bending while biplane radiographs were collected at 30 images per second. Motion at occiput-C1 was tracked using a validated volumetric model-based tracking process that matched subject-specific CT-based bone models to the radiographs. The occiput-C1 total range of motion (ROM) and helical axis of motion (HAM) was calculated for each movement. During flexion/extension, the occiput-C1 moved almost exclusively in-plane (ROM: 17.9 ± 6.9°) with high variability in kinematic waveforms (6.3°) compared to the in-plane variability during axial rotation (1.4°) and lateral bending (0.9°) movements. During axial rotation, there was small in-plane motion (ROM: 4.2 ± 2.5°) compared to out-of-plane flexion/extension (ROM: 12.7 ± 5.4°). During lateral bending, motion occurred in-plane (ROM: 9.0 ± 3.1°) and in the plane of flexion/extension (ROM: 7.3 ± 2.7°). The average occiput-C1 axis of rotation intersected the sagittal and coronal planes 7 mm to 18 mm superior to the occipital condyles. The occiput-C1 axis of rotation pointed 60° from the sagittal plane during axial rotation but only 10° from the sagittal plane during head lateral bending. These novel results are foundational for future work on upper cervical spine kinematics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background: Cadaver biomechanical testing suggests that the morphology of articulating bones contributes to the stability of the joints and determines their kinematics; however, there are no studies examining the correlation between bone morphology and kinematics of the subtalar joint. The purpose of this study was to investigate the influence of talar and calcaneal morphology on subtalar kinematics during walking in healthy individuals., Methods: Forty ankles (20 healthy subjects, 10 women/10 men) were included. Participants walked at a self-selected pace while synchronized biplane radiographs of the hindfoot were acquired at 100 images per second during stance. Motion of the talus and calcaneus was tracked using a validated volumetric model-based tracking process, and subtalar kinematics were calculated. Talar and calcaneal morphology were evaluated using statistical shape modeling. Pearson correlation coefficients were used to assess the relationship between subtalar kinematics and the morphology features of the talus and calcaneus., Results: This study found that a shallower posterior facet of the talus was correlated with the subtalar joint being in more dorsiflexion, more inversion, and more internal rotation, and higher curvature in the posterior facet was correlated with more inversion and eversion range of motion during stance. In the calcaneus, a gentler slope of the middle facet was correlated with greater subtalar inversion., Conclusion: The morphology of the posterior facet of the talus was found to a primary factor driving multiplanar subtalar joint kinematics during the stance phase of gait., Clinical Relevance: This new knowledge relating form and function in the hindfoot may assist in identifying individuals susceptible to subtalar instability and in improving implant design to achieve desired kinematics after surgery., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Disclosure forms for all authors are available online.

Biplane radiography has emerged as the gold standard for accurately measuring in vivo skeletal kinematics during physiological loading. The purpose of this scoping review was to map the extent, range, and nature of biplane radiography research on humans from 2004 through 2022. A literature search was performed using the terms biplane radiography, dual fluoroscopy, dynamic stereo X-ray, and biplane videoradiography. All articles referenced in included publications were also assessed for inclusion. A secondary search was then performed using the names of the most frequently appearing principal investigators among included papers. A total of 379 manuscripts were identified and included. The first studies published in 2004 focused on the native knee, followed by studies of the ankle joint complex in 2006, the shoulder in 2007, and the spine in 2008. Nearly half (180, 47.5%) of all manuscripts investigated knee kinematics. The average number of publications increased from 21.6 per year from 2012 to 2017 to 34.6 per year from 2017 to 2022. The average number of participants per study was 16, with a range from 1 to 101. A total of 90.2% of studies featured cohorts of 30 or less. The most prolific research groups for each joint were: Mass General Hospital (lumbar spine and knee), Henry Ford Hospital (shoulder), the University of Utah (ankle and hip), The University of Pittsburgh (cervical spine), and Brown University (hand/wrist/elbow). Future advancements in biplane radiography research are dependent upon increased availability of these imaging systems, standardization of data collection protocols, and the development of automated approaches to expedite data processing., (© 2024 Orthopaedic Research Society.)

The introduction of women into U.S. military ground close combat roles requires research into sex-specific effects of military training and operational activities. Knee osteoarthritis is prevalent among military service members; its progression has been linked to occupational tasks such as load carriage. Analyzing tibiofemoral arthrokinematics during load carriage is important to understand potentially injurious motion and osteoarthritis progression. The study purpose was to identify effects of load carriage on knee arthrokinematics during walking and running in recruit-aged women. Twelve healthy recruit-aged women walked and ran while unloaded (bodyweight [BW]) and carrying additional + 25%BW and + 45%BW. Using dynamic biplane radiography and subject-specific bone models, tibiofemoral arthrokinematics, subchondral joint space and center of closest contact location between subchondral bone surfaces were analyzed over 0-30% stance (separate one-way repeated measures analysis of variance, load by locomotion). While walking, medial compartment contact location was 5% (~ 1.6 mm) more medial for BW than + 45%BW at foot strike (p = 0.03). While running, medial compartment contact location was 4% (~ 1.3 mm) more lateral during BW than + 25%BW at 30% stance (p = 0.04). Internal rotation was greater at + 45%BW compared to + 25%BW (p < 0.01) at 30% stance. Carried load affects tibiofemoral arthrokinematics in recruit-aged women. Prolonged load carriage could increase the risk of degenerative joint injury in physically active women., (© 2024. The Author(s).)

This study aimed to characterize ankle and hindfoot kinematics of healthy men and women during overground running using biplane radiography, and to compare these data to those previously obtained in the same cohort during overground walking. Participants ran across an elevated platform at a self-selected pace while synchronized biplane radiographs of their ankle and hindfoot were acquired. Motion of the tibia, talus, and calcaneus was tracked using a validated volumetric model-based tracking process. Tibiotalar and subtalar 6DOF kinematics were obtained. Absolute side-to-side differences in ROM and kinematics waveforms were calculated. Side-to-side and sex-specific differences were evaluated at 10 % increments of stance phase with mixed model analysis. Pearson correlation coefficients were used to assess the relationship between stance-phase running and walking kinematics. 20 participants comprised the study cohort (10 men, mean age 30.8 ± 6.3 years, mean BMI 24.1 ± 3.1). Average absolute side-to-side differences in running kinematics waveforms were 5.6°/2.0 mm or less at the tibiotalar joint and 5.2°/3.2 mm or less at the subtalar joint. No differences in running kinematics waveforms between sides or between men and women were detected. Correlations were stronger at the tibiotalar joint (42/66 [64 %] of correlations were p < 0.05), than at the tibiotalar joint (38/66 [58 %] of correlations were p < 0.05). These results provide a normative reference for evaluating native ankle and hindfoot kinematics which may be informative in surgical or rehabilitation contexts. Sex-specific differences in ankle kinematics during overground running are likely not clinically or etiologically significant. Associations seen between walking and running kinematics suggest one could be used to predict the other., Competing Interests: Declaration of competing interest JCS, PFP, TY, SY and WA have no professional or financial affiliations to report. MVH serves on the editorial board for AAOS, AOFAS, and BOS., (Copyright © 2024. Published by Elsevier Ltd.)

Background: Reaching behind the back is painful for individuals with rotator cuff tears. The objectives of the study were to determine changes in glenohumeral kinematics when reaching behind the back, passive range of motion (RoM), patient reported outcomes and the relationships between kinematics and patient reported outcomes following exercise therapy., Methods: Eighty-four individuals with symptomatic isolated supraspinatus tears were recruited for this prospective observational study. Glenohumeral kinematics were measured using biplane radiography during a reaching behind the back movement. Passive glenohumeral internal rotation and patient reported outcome measures were collected. Depending on data normality, appropriate tests were utilized to determine changes in variables. Spearman's correlations were utilized for associations, and Stuart-Maxwell tests for changes in distributions., Findings: Maximum active glenohumeral internal rotation increased by 3.2° (P = 0.001), contact path length decreased by 5.5% glenoid size (P = 0.022), passive glenohumeral internal rotation RoM increased by 4.9° (P = 0.001), and Western Ontario Rotator Cuff Index and American Shoulder and Elbow Surgeons scores increased by 29.8 and 21.1 (P = 0.001), respectively. Changes in Western Ontario Rotator Cuff Index scores positively associated with changes in maximum active glenohumeral internal rotation and negatively associated with changes in contact path lengths (P = 0.008 and P = 0.006, respectively)., Interpretation: The reaching behind the back movement was useful in elucidating in-vivo mechanistic changes associated with patient reported outcomes. Glenohumeral joint function and patient reported outcomes improved, where changes in Western Ontario Rotator Cuff Index scores were associated with kinematics. These findings inform clinicians of functional changes following exercise therapy and new targetable treatment factors., Competing Interests: Declaration of competing interest None, (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Exercise therapy for individuals with rotator cuff tears fails in approximately 25.0 % of cases. One reason for failure of exercise therapy may be the inability to strengthen and balance the muscle forces crossing the glenohumeral joint that act to center the humeral head on the glenoid. The objective of the current study was to compare the magnitude and orientation of the net muscle force pre- and post-exercise therapy between subjects successfully and unsuccessfully (e.g. eventually underwent surgery) treated with a 12-week individualized exercise therapy program. Twelve computational musculoskeletal models (n = 6 successful, n = 6 unsuccessful) were developed in OpenSim (v4.0) that incorporated subject specific tear characteristics, muscle peak isometric force, in-vivo kinematics and bony morphology. The models were driven with experimental kinematics and the magnitude and orientation of the net muscle force was determined during scapular plane abduction at pre- and post-exercise therapy timepoints. Subjects unsuccessfully treated had less inferiorly oriented net muscle forces pre- and post-exercise therapy compared to subjects successfully treated (p = 0.039 & 0.045, respectively). No differences were observed in the magnitude of the net muscle force (p > 0.05). The current study developed novel computational musculoskeletal models with subject specific inputs capable of distinguishing between subjects successfully and unsuccessfully treated with exercise therapy. A less inferiorly oriented net muscle force in subjects unsuccessfully treated may increase the risk of superior migration leading to impingement. Adjustments to exercise therapy programs may be warranted to avoid surgery in subjects at risk of unsuccessful treatment., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Competing Interests: One or more of the authors (J.D.S.) has received funding from the Lumbar Spine Research Society. B.A.K. receives royalties from SLACK Incorporated and Elsevier, receives consulting fees from Smith and Nephew, Stryker, and Zimmer, receives honoraria from Smith and Nephew and Stryker, and received travel/meeting support from Smith and Nephew, Stryker, Zimmer, and Depuy. J.D.S. has received travel/meeting support from Stryker, Zimmer, and Depuy. The remaining authors report no conflicts of interest.

Study Design: Prospective Cohort., Objective: Quantify and compare the effectiveness of cervical orthoses in restricting intervertebral kinematics during multiplanar motions., Summary of Background Data: Previous studies evaluating the efficacy of cervical orthoses measured global head motion and did not evaluate individual cervical motion segment mobility. Prior studies focused only on the flexion/extension motion., Methods: Twenty adults without neck pain participated. Vertebral motion from the occiput through T1 was imaged using dynamic biplane radiography. Intervertebral motion was measured using an automated registration process with validated accuracy better than 1 degree. Participants performed independent trials of maximal flexion/extension, axial rotation, and lateral bending in a randomized order of unbraced, soft collar (foam), hard collar (Aspen), and cervical thoracic orthosis (CTO) (Aspen) conditions. Repeated-measures ANOVA was used to identify differences in the range of motion (ROM) among brace conditions for each motion., Results: Compared with no collar, the soft collar reduced flexion/extension ROM from occiput/C1 through C4/C5, and reduced axial rotation ROM at C1/C2 and from C3/C4 through C5/C6. The soft collar did not reduce motion at any motion segment during lateral bending. Compared with the soft collar, the hard collar reduced intervertebral motion at every motion segment during all motions, except for occiput/C1 during axial rotation and C1/C2 during lateral bending. The CTO reduced motion compared with the hard collar only at C6/C7 during flexion/extension and lateral bending., Conclusions: The soft collar was ineffective as a restraint to intervertebral motion during lateral bending, but it did reduce intervertebral motion during flexion/extension and axial rotation. The hard collar reduced intervertebral motion compared with the soft collar across all motion directions. The CTO provided a minimal reduction in intervertebral motion compared with the hard collar. The utility in using a CTO rather than a hard collar is questionable, given the cost and little or no additional motion restriction., Competing Interests: The authors report no conflicts of interest., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

Purpose: Quantitative pivot shift (QPS) testing using PIVOT technology can detect high- and low-grade rotatory knee instability following anterior cruciate ligament injury or reconstruction (ACLR). The aim of this project was to determine if preoperative QPS correlates with postoperative knee kinematics in the operative and contralateral, healthy extremity following ACLR with or without lateral extraarticular tenodesis (LET) using a highly precise in vivo analysis system. A positive correlation between preoperative QPS and postoperative tibial translation and rotation following ACLR with or without LET in the operative and healthy, contralateral extremity was hypothesized., Methods: Twenty patients with ACL injury and high-grade rotatory knee instability were randomized to undergo anatomic ACLR with or without LET as part of a prospective randomized trial. At 6 and 12 months postoperatively, in vivo kinematic data were collected using dynamic biplanar radiography superimposed with high-resolution computed tomography scans of patients' knees during downhill running. Total anterior-posterior (AP) tibial translation and internal-external tibial rotation were measured during the gait cycle. Spearman's rho was calculated for preoperative QPS and postoperative kinematics., Results: In the contralateral, healthy extremity, a significant positive correlation was seen between preoperative QPS and total AP tibial translation at 12 months postoperatively (r s  = 0.6, p < 0.05). There were no additional significant correlations observed between preoperative QPS and postoperative knee kinematics at 6 and 12 months postoperatively in the operative and contralateral, healthy extremity for combined isolated ACLR and ACLR with LET patients as well as isolated ACLR patients or ACLR with LET patients analyzed separately., Discussion: The main finding of this study was that there was a significant positive correlation between preoperative QPS and total AP tibial translation at 12 months postoperatively in the contralateral, healthy extremity. There were no significant correlations between preoperative QPS and postoperative in vivo kinematics at 6 and 12 months following ACLR with or without LET. This suggests that QPS as measured with PIVOT technology does correlate with healthy in vivo knee kinematics, but QPS does not correlate with in vivo kinematics following ACLR with or without LET., (© 2022. The Author(s) under exclusive licence to European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA).)

Cervical sagittal alignment is a critical component of successful surgical outcomes. Unrecognized differences in intervertebral alignment between supine and upright positions may affect clinical outcomes; however, these differences have not been quantified. Sixty-four patients scheduled to undergo one or two-level cervical arthrodesis for symptomatic pathology from C4-C5 to C6-C7, and forty-seven controls were recruited. Upright sagittal alignment was obtained through biplane radiographic imaging and measured using a validated process with accuracy better than 1° in rotation. Supine alignment was obtained from computed tomography scans. Coordinate systems used to measure supine and upright alignment were identical. Distances between adjacent bony endplates were measured to calculate disc height in each position. For both patients and controls, the C1-C2, C2-C3, and C3-C4 motion segments were in more lordosis when upright as compared with supine (all p < 0.001). However, the C4-C5, C5-C6, and C6-C7 motion segments were in less lordosis when upright as compared with supine (all p ≤ 0.004). There was an interaction between group and position at the C1-C2 (p = 0.002) and C2-C3 (p = 0.001) motion segments, with the controls demonstrating a greater increase in lordosis at both motion segments when moving from supine to upright. The results indicate that cervical motion segment alignment changes between supine and upright positioning, those changes differ among motion segments, and cervical pathology affects the magnitude of these changes. Clinical Significance: Surgeons should be mindful of the differences in alignment between supine and upright imaging and the implications they may have on clinical outcomes., (© 2022 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals LLC on behalf of Orthopaedic Research Society.)

Study Design: Prospective cohort., Objective: Determine if total hip arthroplasty (THA) changes lumbar spine kinematics during gait in a manner that explains the improvements in back pain seen in patients with hip-spine syndrome., Summary of Background Data: For patients with hip-spine syndrome, improvements in both hip and back pain have been demonstrated after THA; however, the exact mechanism of improvement in back pain remains unknown, as no corresponding changes in lumbar spine static radiographic parameters have been identified., Methods: Thirteen patients with severe, unilateral hip osteoarthritis scheduled to undergo THA with concomitant back pain and disability were tested at baseline and 6 months after THA. Harris Hip Score (HHS) and Oswestry Disability Index questionnaires were completed; the static orientation of the spine and pelvis were measured on standing radiographs, and lumbar spine kinematics were measured during treadmill walking using a validated measurement system that matched subject-specific bone models created from CT scans to dynamic biplane radiographs., Results: After THA, both the Oswestry Disability Index (36.3-11.3, P <0.001) and Harris Hip Score (55.7-77.9, P <0.001) improved; however, there were no changes in static intervertebral or pelvis orientation. During gait after THA, the overall lumbar spine (L1 to L5) was less lordotic from heel strike to contralateral toe off ( P <0.001), the L4 and L5 vertebra were less anteriorly tilted by 3.9° ( P =0.038) from midstance to contralateral heel strike and by 3.9° ( P =0.001) during stance, respectively., Conclusion: The decreased anterior tilt of the 2 lowest lumbar vertebrae and the corresponding loss of lumbar lordosis may reduce facet loading during the stance phase of gait after THA. This change in lumbar spine kinematics during gait is a potential mechanism to explain the observed improvements in back pain and disability after THA., Level of Evidence: 4., Competing Interests: One or more of the authors (J.D.S.) received funding from the Lumbar Spine Research Society. B.A.K. received royalties from SLACK Incorporated and Elsevier, consulting fees from Smith and Nephew, Stryker, and Zimmer, honoraria from Smith and Nephew and Stryker, and travel/meeting support from Smith and Nephew, Stryker, Zimmer, and Depuy. J.D.S. received travel/meeting support from Stryker, Zimmer, and Depuy. The remaining authors report no conflicts of interest., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

Optimal motor control that is stable and adaptable to perturbation is reflected in the temporal arrangement and regulation of gait variability. Load carriage and forced-marching are common military relevant perturbations to gait that have been implicated in the high incidence of musculoskeletal injuries in military populations. We investigated the interactive effects of load magnitude and locomotion pattern on motor variability, stride regulation and spatiotemporal complexity during gait in recruit-aged adults. We further investigated the influences of sex and task duration. Healthy adults executed trials of running and forced-marching with and without loads at 10% above their gait transition velocity. Spatiotemporal parameters were analyzed using a goal equivalent manifold approach. With load and forced-marching, individuals used a greater array of motor solutions to execute the task goal (maintain velocity). Stride-to-stride regulation became stricter as the task progressed. Participants exhibited optimal spatiotemporal complexity with significant but not meaningful differences between sexes. With the introduction of load carriage and forced-marching, individuals relied on a strategy that maximizes and regulates motor solutions that achieve the task goal of velocity specifically but compete with other task functions. The appended cost penalties may have deleterious effects during prolonged execution, potentially increasing the risk of musculoskeletal injuries., (© 2023. The Author(s).)

There is a lack of data unaffected by soft tissue artifact describing bilateral symmetry and sex differences in hip kinematics in asymptomatic individuals during activities of daily living. This study aimed to identify sex-based differences and to quantify bilateral symmetry in continuous hip kinematics during walking and bodyweight squatting using biplane radiography. Twenty-four asymptomatic young adults (13 women, 11 men; age: 21.9 ± 2.2 years) performed treadmill walking and squatting while synchronized biplane radiographs of the hip were collected at 50 frames/s. Pelvis and proximal femur bone tissue were segmented from CT images and reconstructed into subject-specific 3D bone models. Femoroacetabular kinematics were determined using a validated volumetric model-based tracking technique that matched digitally reconstructed radiographs generated from the CT-based bone models to the biplane radiographs. Symmetry was calculated as the average absolute side-to-side difference (SSD) in kinematic waveforms for each participant. Sex-based and phase-based (eccentric vs. concentric squatting) kinematic variations were assessed using linear mixed model analysis. Women were 0.2 mm more anteriorly translated and 0.1 mm more inferiorly translated than men across the gait cycle (both p < 0.04), but no sex-based or phase-based kinematic differences during squatting were identified. The maximum SSD across all movements was up to 18.6° (internal-external rotation) and 1.0 mm (superior-inferior translation), respectively. Asymmetry in internal rotation, superior translation, and medial translation was greater during squatting than during walking (all p < 0.002). This study provides a reference dataset of healthy young adults for evaluating hip kinematics and symmetry in symptomatic cohorts or in individuals undergoing surgery or rehabilitation., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: MM previously recieved roalties from Elizur LLC for an unrelated device. All other authors have no professional or financial affiliations that may be perceived to bias this presentation., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Study Design: Prospective cohort study., Objective: The aim was to identify patient factors that affect adjacent segment kinematics after anterior cervical discectomy and fusion (ACDF) as measured by biplane radiography., Summary of Background Data: The etiology of adjacent segment disease (ASD) may be multifactorial. Previous studies have investigated associations between patient factors and ASD, although few attempted to link patient factors with mechanical changes in the spine that may explain ASD development. Previous studies manually measured intervertebral motion from static flexion/extension radiographs, however, manual measurements are unreliable, and those studies failed to measure intervertebral motion during rotation., Methods: Patients had continuous cervical spine flexion/extension and axial rotation movements captured at 30 images per second in a dynamic biplane radiography system preoperatively and 1 year after ACDF. Digitally reconstructed radiographs generated from subject-specific computed tomography scans were matched to the biplane radiographs using a validated tracking process. Dynamic kinematics and preoperative disc height were calculated from this tracking process. Preoperative magnetic resonance imagings were evaluated for disc bulge. Patient age, sex, body mass index, smoking status, diabetes, psychiatric history, presence of an inciting event, and length of symptoms were collected. Multivariate linear regression was performed to identify patient factors associated with 1-year postoperative changes in adjacent segment kinematics., Results: Sixty-three patients completed preoperative and postoperative testing. Superior adjacent segment disc height and disc bulge predicted the change in superior adjacent segment range of motion after surgery. Inferior adjacent segment disc bulge, smoking history, and the use of psychiatric medications predicted the change in inferior adjacent segment flexion/extension range of motion after surgery., Conclusions: Preexisting adjacent segment disc degeneration, as indicated by disc height and disc bulge, was associated with reduced adjacent segment motion after ACDF, while lack of preexisting adjacent disc degeneration was associated with increased adjacent segment motion after ACDF. These findings provide in vivo evidence supporting early instability and late stabilization in the pathophysiology of disc degeneration., Competing Interests: A.K. receives royalties from ZimmerBiomet and NuVasive. D.O. Okonkwo receives royalties from ZimmerBiomet and NuVasive. J.S. has received a Stryker educational grant and a Lumbar Spine Research Society research grant within the last 12 months. The remaining authors report no conflicts of interest., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Dynamic biplane radiography (DBR) in conjunction with model-based tracking (MBT) has provided a suitable mechanism for biomechanical assessment of many joints but has not yet achieved widespread use at the thumb and wrist. The purpose of this work is to determine the accuracy of DBR with markerless MBT for the evaluation of thumb and wrist joint kinematics. Three 0.6 mm stainless steel beads were implanted into each trapezium, scaphoid, first metacarpal, and radius of three cadaveric upper extremities. Each specimen was manipulated in thumb abduction/adduction, thumb flexion/extension, wrist radioulnar deviation, and wrist flexion/extension while synchronized biplane radiographs were collected at 100 Hz. Specimen-specific 3D bone models were created from CT scans. MBT was performed by optimizing the correlation between digitally reconstructed radiographs, created from the volumetric CT-based bone models, and the biplane radiographs. Joint kinematics and joint space were calculated and compared between the "gold standard" bead-based tracking and markerless MBT. The MBT system accuracy (RMS error) in measuring bone position for the static and dynamic trials was 0.25 mm and 0.58 mm, respectively. The overall MBT system accuracy in measuring dynamic joint kinematics was 1.3 mm in translation and 5.0° in rotation. The MBT system accuracy in measuring dynamic joint space was 0.4 mm. DBR with MBT is a non-invasive and accurate method that can be utilized for kinematic analysis of the thumb and wrist., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

It has been suggested that subtalar and tibiofemoral kinematics are coupled, such that abnormal subtalar inversion during the impact and push-off portions of stance may affect tibial rotation, leading to abnormal compensatory knee motion. This study aimed to characterize tibiofemoral and subtalar coupled motion and to determine if sex-dependent differences exist in lower extremity coupled motion. Twenty young adults were imaged at 100 frames/s using dynamic biplane radiography while walking. Lower extremity CT scans were obtained and segmented into subject-specific 3D bone models. Digitally reconstructed radiographs generated from the models were matched to the biplane radiographs via a validated tracking process to obtain tibiofemoral and subtalar joint kinematics. Subtalar inversion/eversion was strongly associated with tibiofemoral internal/external rotation and tibiofemoral ab/adduction during impact and push-off (P < 0.001). Men reached neutral subtalar and tibiofemoral orientation at midstance, while women remained more inverted at the subtalar joint and more externally rotated at the tibiofemoral joint. The rate of tibiofemoral ab/adduction to subtalar eversion differed between sexes during push-off (P = 0.005). Women underwent subtalar inversion, as well as tibiofemoral internal rotation and adduction during push-off, while men underwent only subtalar inversion and tibiofemoral internal rotation, with effectively no tibiofemoral adduction. These results provide the first quantitative evidence characterizing subtalar and tibiofemoral coupled motion. Differences in coupled motion trajectories between men and women may be associated with the higher incidence of knee-related pathology in women. These novel findings may serve as a standard for comparison when evaluating patients with patellofemoral pain., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Biomechanical cadaver testing indicates adjacent segment motion increases after one-level anterior cervical spine arthrodesis, and two-level arthrodesis exacerbates these effects. There is little in vivo evidence to support those biomechanical studies. The purpose of this study was to assess the effects of one- and two-level cervical arthrodesis on adjacent segment motion. Fifty patients received either one-level C56 arthrodesis or two-level C456 or C567 arthrodesis and were tested preoperatively (PRE) and 1 year postoperatively (1YR-POST) along with 23 asymptomatic controls. A validated CT model-based tracking technique was used to measure 3D vertebral motion from biplane radiographs collected during dynamic flexion-extension and axial rotation of the cervical spine. Head and adjacent segment intervertebral end-range range of motion (ROM) and mid-range ROM were compared between one-level and two-level arthrodesis patients and controls. Small (2.3° or less) but non-significant increases in adjacent segment end-range ROM were observed from PRE to 1YR-POST. Mid-range flexion-extension ROM in the C67 motion segment inferior to the arthrodesis and mid-range axial rotation ROM in the C45 motion segment superior to the arthrodesis increased from PRE to 1YR-POST (all p < 0.022). This study provides in vivo evidence that contradicts long-held beliefs that adjacent segment end-range ROM increases appreciably after anterior cervical arthrodesis and that two-level arthrodesis exacerbates these effects. Mid-range ROM appears to be more useful than end-range ROM for detecting early changes in adjacent segment motion after cervical spine arthrodesis., (© 2022. The Author(s) under exclusive licence to Biomedical Engineering Society.)

Background: Clinical failure associated with nonoperative treatment of rotator cuff tears may be due to inadequate characterization of the individual's functional impairments. Clinically, restricted passive range of motion (ROM) (restrictions imply capsular tightness), limitations in muscle strength, and larger rotator cuff tears are hypothesized to be related to altered glenohumeral kinematics. Understanding these relationships, as well as the relationship between glenohumeral kinematics and patient-reported outcomes (PROs) prior to exercise therapy, may help characterize functional impairments in individuals with rotator cuff tears. The objectives of the study were to describe the baseline presentation of individuals with an isolated supraspinatus tear, including passive ROM, rotator cuff muscle strength, tear size, PROs, and glenohumeral kinematics, and to determine associations among these variables., Methods: One hundred one individuals with symptomatic isolated supraspinatus tears were recruited for the study and underwent assessments of passive glenohumeral ROM, isometric muscle strength, and ultrasonography to assess anterior-posterior tear size. Glenohumeral kinematics during scapular-plane abduction were measured using biplane radiography. Furthermore, PROs including the American Shoulder and Elbow Surgeons (ASES) score and the Western Ontario Rotator Cuff Index (WORC) score were collected., Results: Individuals presented with decreased ROM, external rotation weakness compared with the uninvolved side, and pain and disability as measured by the ASES and WORC scores. These findings were not associated with glenohumeral kinematics, with the exception of a weak positive association between glenohumeral contact path lengths and WORC scores (ρ = 0.25, P = .03). Tear size was 11.7 ± 5.7 mm, and maximum anterior translation, superior translation, and contact path length were 3.0% ± 3.8% of glenoid width, 3.5% ± 3.8% of glenoid height, and 38.2% ± 20.7% of glenoid size, respectively., Conclusion: Individuals with a symptomatic isolated supraspinatus tear presented with decreased ROM, external rotation weakness, and pain and disability as measured by the ASES and WORC scores. However, no abnormal kinematics associated with these limitations were observed. Thus, given that the tear is isolated to the supraspinatus tendon and no capsular restrictions are present, normal function of the glenohumeral joint may be possible during scapular-plane abduction., (Copyright © 2022 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

The etiology of adjacent segment disease after anterior cervical discectomy and fusion (ACDF) remains controversial. Range of motion (ROM) is typically used to infer the effects of arthrodesis on adjacent segment motion following ACDF, however, ROM only measures the total amount of motion. In contrast, the helical axis of motion (HAM) quantifies how the motion occurs and may provide additional insight into the etiology of adjacent segment pathology. Synchronized biplane radiographs of the cervical spine were acquired at 30 images per second while 62 ACDF patients and 38 control participants performed dynamic neck flexion/extension. A validated tracking process matched digitally reconstructed radiographs created from subject-specific bone models to the radiographs with sub-millimeter accuracy. The intervertebral HAM was then calculated and compared between pre and 1 year post surgery in patients, and between patients and controls at corresponding motion segments using linear mixed-effects analysis. Small differences in the anterior/posterior location of the HAM were found between the symptomatic motion segments before surgery and corresponding motion segments in controls. No changes in the HAM of motion segments adjacent to the arthrodesis were observed from pre to 1-year post-surgery. No differences in adjacent segment HAM were found between patients with one- versus two-level arthrodesis. Neither symptomatic pathology nor arthrodesis appear to change the way motion occurs in the cervical spine during flexion/extension one year after one or two-level arthrodesis. These results suggest ACDF does not alter short-term adjacent segment kinematics in a way that would contribute to the development of adjacent segment disease., (Copyright © 2022. Published by Elsevier Ltd.)

Purpose: To determine if anterior cruciate ligament (ACL) reconstruction (ACLR) with lateral extraarticular tenodesis (LET) is beneficial for restoring knee kinematics with concomitant meniscal pathology causing rotatory knee instability., Methods: Twenty patients with an ACL tear were randomized to either isolated ACLR or ACLR with LET. Patients were divided into four groups based on the surgery performed and the presence of meniscal tear (MT): ACLR without MT, ACLR with MT, ACLR with LET without MT, and ACLR with LET with MT. Kinematic data normalized to the contralateral, healthy knee were collected using dynamic biplanar radiography superimposed with high-resolution computed tomography scans of patients' knees during downhill running. Anterior tibial translation (ATT) and tibial rotation (TR) as well as patient-reported outcome measures (PROMs) were analyzed at 6- and 12-months postoperatively., Results: At 6 months, ACLR with LET resulted in significantly decreased ATT at heel strike compared to ACLR (ACLR without MT: 0.3 ± 0.8 mm and ACLR with MT: 1.4 ± 3.1 mm vs. ACLR with LET without MT: - 2.5 ± 3.4 mm and ACLR with LET with MT: - 1.5 ± 1.2 mm ATT, p = 0.02). At 6 months, at toe off ACLR with LET better restored ATT to that of the contralateral, healthy knee in patients with meniscal pathology, while in patients without meniscal pathology, ACLR with LET resulted in significantly decreased ATT (1.0 ± 2.6 mm ATT vs. - 2.6 ± 1.7 mm ATT, p = 0.04). There were no significant differences in kinematics or PROMs between groups at 12 months., Conclusion: For combined ACL and meniscus injury, ACLR with LET restores native knee kinematics at toe off but excessively decreases ATT at heel strike in the early post-operative period (6 months) without altering knee kinematics in the long term. Future large-scale clinical studies are needed to better understand the function of LET and ultimately improve patient outcomes., Level of Evidence: III., (© 2021. European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA).)

Study Design: Prospective cohort study., Objective: The aim of this study was to identify surgical factors that affect adjacent segment kinematics after anterior cervical discectomy and fusion (ACDF) as measured by biplane radiography., Summary of Background Data: Previous studies investigated the effect of surgical factors on spine kinematics as a potential etiology for adjacent segment disease (ASD). Those studies used static flexion-extension radiographs to evaluate range of motion. However, measurements from static radiographs are known to be unreliable. Furthermore, those studies were unable to evaluate the effect of ACDF on adjacent segment axial rotation., Methods: Patients had continuous cervical spine flexion/exten- sion and axial rotation movements captured at 30 images per second in a dynamic biplane radiography system preoperatively and 1 year after ACDF. Digitally reconstructed radiographs generated from subject-specific CT scans were matched to biplane radiographs using a previously validated tracking process. Dynamic kinematics, postoperative segmental kyphosis, and disc distraction were calculated from this tracking process. Plate-to-disc distance was measured on postoperative radiographs. Graft type was collected from the medical record. Multivariate linear regression was performed to identify surgical factors associated with 1-year post-surgery changes in adjacent segment kinematics. A secondary analysis was also performed to compare adjacent segment kinematics between each of the surgical factors and previously defined thresholds believed to be associated with adjacent segment degeneration., Results: Fifty-nine patients completed preoperative and postoperative testing. No association was found between any of the surgical factors and change in adjacent segment flexion/exten- sion or axial rotation range of motion (all P > 0.09). The secondary analysis also did not identify differences between adjacent segment kinematics and surgical factors (all P > 0.07)., Conclusion: Following ACDF for cervical spondylosis, factors related to surgical technique were not associated with short-term changes in adjacent segment kinematics that reflect the hypermobility hypothesized to lead to the development of ASD.Level of Evidence: 2., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

The objective was to examine the interactive effects of load magnitude and locomotion pattern on lower-extremity joint angles and intralimb coordination in recruit-aged women. Twelve women walked, ran, and forced marched at body weight and with loads of +25%, and +45% of body weight on an instrumented treadmill with infrared cameras. Joint angles were assessed in the sagittal plane. Intralimb coordination of the thigh-shank and shank-foot couple was assessed with continuous relative phase. Mean absolute relative phase (entire stride) and deviation phase (stance phase) were calculated from continuous relative phase. At heel strike, forced marching exhibited greater (P < .001) hip flexion, knee extension, and ankle plantar flexion compared with running. At mid-stance, knee flexion (P = .007) and ankle dorsiflexion (P = .04) increased with increased load magnitude for all locomotion patterns. Forced marching (P = .009) demonstrated a "stiff-legged" locomotion pattern compared with running, evidenced by the more in-phase mean absolute relative phase values. Running (P = .03) and walking (P = .003) had greater deviation phase than forced marching. Deviation phase increased for running (P = .03) and walking (P < .001) with increased load magnitude but not for forced marching. With loads of >25% of body weight, forced marching may increase risk of injury due to inhibited energy attenuation up the kinetic chain and lack of variability to disperse force across different supportive structures.

Study Design: Prospective cohort., Objective: The aim of this study was to determine the effect of graft type on residual motion and the relationship among residual motion, smoking, and patient-reported outcome (PRO) scores following anterior cervical discectomy and fusion (ACDF)., Summary of Background Data: Although most patients develop solid fusion based on static imaging following ACDF, dynamic imaging has revealed that many patients continue to have residual motion at the arthrodesis., Methods: Forty-eight participants performed dynamic neck flexion/extension and axial rotation within a biplane radiography system 1 year following ACDF (21 one-level, 27 two-level). PRO scores included the Short Form-36, Neck Disability Index, and Cervical Spine Outcomes Questionnaire. An automated model-based tracking process matched subject-specific bone models to the biplane radiographs with sub-millimeter accuracy. Residual motion was measured across the entire arthrodesis site for both one- and two-level fusions in patients who received either allograft or autograft. Patients were divided into "pseudarthrosis" (>3° of flexion/extension residual motion) and "solid fusion" groups. Residual motion and PROs were compared between groups using Student t tests., Results: Patients who received allograft showed more total flexion/extension residual motion (4.1° vs. 2.8°, P = 0.12), although this failed to reach significance. No differences were noted in PROs based on graft type (all P > 0.08) or the presence of pseudarthrosis (all P > 0.13). No differences were noted in residual motion between smokers and nonsmokers (all P > 0.15); however, smokers who received allograft reported worse outcomes than nonsmokers who received allograft and smokers who received autograft., Conclusion: Allograft may result in slightly more residual motion at the arthrodesis site 1 year after ACDF. However, there is minimal evidence that PROs are adversely affected by slightly increased residual motion, suggesting that the current definition of pseudarthrosis correlates poorly with clinically significant findings. Additionally, autograft appears to result in superior outcomes in patients who smoke.Level of Evidence: 2., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

Background: A viable treatment option for young patients with massive, irreparable rotator cuff tears is arthroscopic superior capsule reconstruction (SCR). SCR theoretically improves shoulder stability and function and decreases pain. However, no prospective studies to date have correlated magnetic resonance imaging (MRI) healing with in vivo kinematic data. The purpose of this study was to evaluate the association between graft healing and in vivo kinematics, range of motion (ROM), strength, and patient-reported outcomes (PROs)., Methods: Ten patients (8 men and 2 women; mean age, 63 ± 7 years) with irreparable rotator cuff tears underwent arthroscopic SCR with dermal allograft. Strength was measured with isometric internal rotation and external rotation (ER) at 0° of abduction, ER at 90° of abduction, and scapular-plane abduction, whereas ROM was measured during shoulder flexion, abduction, and ER and internal rotation at 90° of abduction both before and 1 year after SCR. PROs included American Shoulder and Elbow Surgeons, Western Ontario Rotator Cuff Index, and Disabilities of the Arm, Shoulder and Hand surveys that were collected before and 1 year after SCR. Synchronized biplane radiographs were collected at 50 images/s before and 1 year after SCR while patients performed 3 trials of scapular-plane abduction. A validated volumetric tracking technique with submillimeter accuracy determined 6-df glenohumeral and scapular kinematics. The acromiohumeral distance (AHD), humeral head translation, and scapulohumeral rhythm (SHR) were calculated from the in vivo kinematics. Healing at 5 locations was evaluated on 1-year postoperative MRI scans: anterior and posterior glenoid, anterior and posterior humerus, and posteriorly along the infraspinatus. Each subject was given a score from 0 to 5 based on number of sites healed., Results: Of the 10 patients, 9 (90%) had complete (n = 4) or partial (n = 5) healing of the graft whereas 1 (10%) had complete failure at the glenoid. No correlation existed between MRI healing and the AHD, SHR, strength, ROM, or PROs. American Shoulder and Elbow Surgeons, Western Ontario Rotator Cuff Index, and Disabilities of the Arm, Shoulder and Hand scores all significantly improved from before to 1 year after SCR regardless of graft healing., Conclusions: The rate of complete or partial graft healing on MRI mimics findings of prior reports in the literature. MRI healing was correlated with humeral head anterior-posterior translation but not with the static and dynamic AHDs, SHR, humeral head superior-inferior translation, ROM, strength, or PROs 1 year after SCR. All PROs improved significantly from before to 1 year after SCR regardless of graft status on MRI. In vivo kinematic changes were small after SCR and not clinically significant, and the data suggest that improvements in clinical and functional outcomes may occur in the absence of full graft healing., (Copyright © 2021 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

Background: Military personnel in combat roles often perform gait tasks with additional load, which can affect the contributions of joint mechanical work (positive and negative). Furthermore, different locomotion patterns can also affect joint specific work contributions. While mean behavior of joint work is important to understanding gait, changes in joint kinetic modulation, or the regulation/control of stride-to-stride joint work variability is necessary to elucidate locomotor system function. Suboptimal modulation exhibited as a stochastic time-series (large fluctuation followed by an opposite smaller fluctuation) could potentially affect locomotion efficiency and portend injury risk. It remains unclear how the locomotor system responds to a combination of load perturbations and varying locomotion patterns., Research Question: What are the interactive effects of load magnitude and locomotion pattern on joint positive/negative work and joint work modulation in healthy, active, recruit-aged women?, Methods: Eleven healthy, active, recruit-aged (18-33 years) women ran and forced-marched (walking at a velocity an individual would typically jog) in bodyweight (BW), an additional 25 % of BW (+25 %BW) and an additional 45 % of BW (+45 %BW) conditions at a velocity above their gait transition velocity. Joint work was calculated as the time integral of joint power. Joint work modulation was assessed with detrended fluctuation analysis (DFA) on consecutive joint work time-series., Results: Joint work contributions shifted proximally for forced-marching demonstrated by lesser (p < .001) positive/negative ankle work but greater (p = .001) positive hip work contributions compared to running. Running exhibited optimal positive ankle work modulation compared to forced-marching (p = .040). Knee and ankle negative joint work modulation was adversely impacted compared to the hip during forced-marching (p < .001)., Significance: Employing forced-marching gait while under loads of 25 and 45 % of BW reduces the ability of the plantar-flexors and knee extensors to optimally contribute to energy absorption and propulsion in recruit-aged women, potentially reducing metabolic efficiency and increasing injury risk., (Copyright © 2021. Published by Elsevier B.V.)

In vitro biomechanical studies of the osteoligamentous spine are widely used to characterize normal biomechanics, identify injury mechanisms, and assess the effects of degeneration and surgical instrumentation on spine mechanics. The objective of this study was to determine how well four standards in vitro loading paradigms replicate in vivo kinematics with regards to the instantaneous center of rotation and arthrokinematics in relation to disc deformation. In vivo data were previously collected from 20 asymptomatic participants (45.5 ± 5.8 years) who performed full range of motion neck flexion-extension (FE) within a biplane x-ray system. Intervertebral kinematics were determined with sub-millimeter precision using a validated model-based tracking process. Ten cadaveric spines (51.8 ± 7.3 years) were tested in FE within a robotic testing system. Each specimen was tested under four loading conditions: pure moment, axial loading, follower loading, and combined loading. The in vivo and in vitro bone motion data were directly compared. The average in vitro instant center of rotation was significantly more anterior in all four loading paradigms for all levels. In general, the anterior and posterior disc heights were larger in the in vitro models than in vivo. However, after adjusting for gender, the observed differences in disc height were not statistically significant. This data suggests that in vitro biomechanical testing alone may fail to replicate in vivo conditions, with significant implications for novel motion preservation devices such as cervical disc arthroplasty implants., (© 2020 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.)

In vivo knee ligament forces are important to consider for informing rehabilitation or clinical interventions. However, they are difficult to directly measure during functional activities. Musculoskeletal models and simulations have become the primary methods by which to estimate in vivo ligament loading. Previous estimates of anterior cruciate ligament (ACL) forces range widely, suggesting that individualized anatomy may have an impact on these predictions. Using ten subject-specific (SS) lower limb musculoskeletal models, which include individualized musculoskeletal geometry, muscle architecture, and six degree-of-freedom knee joint kinematics from dynamic biplane radiography (DBR), this study provides SS estimates of ACL force (anteromedial-aACL; and posterolateral-pACL bundles) during the full gait cycle of treadmill walking. These forces are compared to estimates from scaled-generic (SG) musculoskeletal models to assess the effect of musculoskeletal knee joint anatomy on predicted forces and the benefit of SS modeling in this context. On average, the SS models demonstrated a double force peak during stance (0.39-0.43 xBW per bundle), while only a single force peak during stance was observed in the SG aACL. No significant differences were observed between continuous SG and SS ACL forces; however, root mean-squared differences between SS and SG predictions ranged from 0.08 xBW to 0.27 xBW, suggesting SG models do not reliably reflect forces predicted by SS models. Force predictions were also found to be highly sensitive to ligament resting length, with ±10% variations resulting in force differences of up to 84%. Overall, this study demonstrates the sensitivity of ACL force predictions to SS anatomy, specifically musculoskeletal joint geometry and ligament resting lengths, as well as the feasibility for generating SS musculoskeletal models for a group of subjects to predict in vivo tissue loading during functional activities., (Copyright © 2021 by ASME.)

Cervical radiculopathy is a relatively common neurological disorder, often resulting from mechanical compression of the nerve root within the neural foramen. Anterior cervical discectomy and fusion (ACDF) is a common treatment for radicular symptoms that do not resolve after conservative treatment. One mechanism by which ACDF is believed to resolve symptoms is by replacing degenerated disc tissue with bone graft to increase the neural foramen area, however in vivo evidence demonstrating this is lacking. The aim of this study was to evaluate the effects of age, pathology, and fusion on bony neural foramen area. Participants included 30 young adult controls (<35 years old), 23 middle-aged controls (36 to 60 years old), and 36 cervical arthrodesis patients tested before and after ACDF surgery. Participants' cervical spines were imaged in the neutral, full flexion, and full extension positions while seated within a biplane radiography system. A validated model-based tracking technique determined three-dimensional vertebral position and orientation and automated software identified the neural foramen area in each head position. The neural foramen area decreased throughout the entire sub-axial cervical spine with age and pathology, however, no changes in neural foramen area were observed due solely to replacing degenerated disc tissue with bone graft. The neural foramen area was not associated with disc height in young adult controls, but moderate to strong associations were observed in middle-aged controls. The results provide evidence to inform the debate regarding localized versus systemic spinal degeneration and provide novel insight into the mechanism of pain relief after ACDF., (© 2020 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.)

Introduction: During cyclical steady state ambulation, such as walking, variability in stride intervals can indicate the state of the system. In order to define locomotor system function, observed variability in motor patterns, stride regulation and gait complexity must be assessed in the presence of a perturbation. Common perturbations, especially for military populations, are load carriage and an imposed locomotion pattern known as forced marching (FM). We examined the interactive effects of load magnitude and locomotion pattern on motor variability, stride regulation and gait complexity during bipedal ambulation in recruit-aged females., Methods: Eleven healthy physically active females (18-30 years) completed 1-min trials of running and FM at three load conditions: no additional weight/bodyweight (BW), an additional 25% of BW (BW + 25%), and an additional 45% of BW (BW + 45%). A goal equivalent manifold (GEM) approach was used to assess motor variability yielding relative variability (RV; ratio of "good" to "bad" variability) and detrended fluctuation analysis (DFA) to determine gait complexity on stride length (SL) and stride time (ST) parameters. DFA was also used on GEM outcomes to calculate stride regulation., Results: There was a main effect of load ( p = 0.01) on RV; as load increased, RV decreased. There was a main effect of locomotion ( p = 0.01), with FM exhibiting greater RV than running. Strides were regulated more tightly and corrected quicker at BW + 45% compared ( p < 0.05) to BW. Stride regulation was greater for FM compared to running. There was a main effect of load for gait complexity ( p = 0.002); as load increased gait complexity decreased, likewise FM had less ( p = 0.02) gait complexity than running., Discussion: This study is the first to employ a GEM approach and a complexity analysis to gait tasks under load carriage. Reduction in "good" variability as load increases potentially exposes anatomical structures to repetitive site-specific loading. Furthermore, load carriage magnitudes of BW + 45% potentially destabilize the system making individuals less adaptable to additional perturbations. This is further evidenced by the decrease in gait complexity, which all participants demonstrated values similarly observed in neurologically impaired populations during the BW + 45% load condition., (Copyright © 2020 Krajewski, Dever, Johnson, Mi, Simpson, Graham, Moir, Ahamed, Flanagan, Anderst and Connaboy.)

Knee osteoarthritis (OA) is prevalent among female soldiers, resulting in limited duty and long term adverse ambulatory effects. A proposed mechanism to the development of knee OA is the assiduous execution of load carriage tasks. Soldiers are often required to maintain a walking gait with load at velocities beyond their gait transition velocity (GTV) known as forced marching. The primary aim of this investigation is to determine the interactive effects of load magnitude and locomotion pattern on relative knee total joint moment (KTJM) in healthy recruit-aged women. The secondary aims are to determine knee total joint moment limb differences and to determine the interactive effect of load magnitude and locomotion pattern on the percent contributions of each plane of motion moment. Individuals were tasked with running and forced marching at 10% above their GTV at body weight (BW) and with an additional 25% and 45% of their BW. KTJM was analyzed at two specific gait events of heel-strike and mid-stance. At heel-strike, forced marching exhibited greater KTJM compared to run for all load conditions but running had greater KTJM than forced marching at mid-stance. The forced marching pattern exhibited larger KTJM for the dominant limb at both gait events compared to running. Lastly, at mid-stance the knee adduction moment percent (KAM%) contribution was greater for forced marching compared to running. The forced marching pattern demonstrates joint kinetics that may be more deleterious with prolonged exposure. Likewise, forced marching induced KAM% similar to those already suffering from knee OA., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The pathogenesis of lumbar adjacent segment disease is thought to be secondary to altered biomechanics resulting from fusion. Direct in vivo evidence for altered biomechanics following lumbar fusion is lacking. This study's aim was to describe in vivo kinematics of the superior adjacent segment relative to the fused segment before and after lumbar fusion. This study analyzed seven patients with symptomatic lumbar degenerative spondylolisthesis (5 M, 2F; age 65 ± 5.1 years) using a biplane radiographic imaging system. Each subject performed two to three trials of continuous flexion of their torso according to established protocols. Synchronized biplane radiographs were acquired at 20 images per second one month before and six months after single-level fusion at L4-L5 or L5-S1, or two-level fusion at L3-L5 or L4-S1. A previously validated volumetric model-based tracking process was used to track the position and orientation of vertebrae in the radiographic images. Intervertebral flexion/extension and AP translation (slip) at the superior adjacent segment were calculated over the entire dynamic flexion activity. Skin-mounted surface markers were tracked using conventional motion analysis and used to determine torso flexion. Change in adjacent segment kinematics after fusion was determined at corresponding angles of dynamic torso flexion. Changes in adjacent segment motion varied across patients, however, all patients maintained or increased the amount of adjacent segment slip or intervertebral flexion/extension. No patients demonstrated both decreased adjacent segment slip and decreased rotation. This study suggests that short-term changes in kinematics at the superior adjacent segment after lumbar fusion appear to be patient-specific., Competing Interests: Declaration of Competing Interest None of the authors have any disclosures to report. Wawrose (N), LeVasseur (N), Byrapogu (N), Dombrowski (N), Donaldson (N), Shaw (N), Lee (N), Aiyangar (N), Anderst (N)., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

'Gold standard' reference sets of human muscle architecture are based on elderly cadaveric specimens, which are unlikely to be representative of a large proportion of the human population. This is important for musculoskeletal modeling, where the muscle force-generating properties of generic models are defined by these data but may not be valid when applied to models of young, healthy individuals. Obtaining individualized muscle architecture data in vivo is difficult, however diffusion tensor magnetic resonance imaging (DTI) has recently emerged as a valid method of achieving this. DTI was used here to provide an architecture data set of 20 lower limb muscles from 10 healthy adults, including muscle fiber lengths, which are important inputs for Hill-type muscle models commonly used in musculoskeletal modeling. Maximum isometric force and muscle fiber lengths were found not to scale with subject anthropometry, suggesting that these factors may be difficult to predict using scaling or optimization algorithms. These data also highlight the high level of anatomical variation that exists between individuals in terms of lower limb muscle architecture, which supports the need of incorporating subject-specific force-generating properties into musculoskeletal models to optimize their accuracy for clinical evaluation., Competing Interests: The authors have declared that no competing interests exist.

Accurate individualized muscle architecture data are crucial for generating subject-specific musculoskeletal models to investigate movement and dynamic muscle function. Diffusion tensor imaging (DTI) magnetic resonance (MR) imaging has emerged as a promising method of gathering muscle architecture data in vivo; however, its accuracy in estimating parameters such as muscle fiber lengths for creating subject-specific musculoskeletal models has not been tested. Here, we provide a validation of the method of using anatomical magnetic resonance imaging (MRI) and DTI to gather muscle architecture data in vivo by directly comparing those data obtained from MR scans of three human cadaveric lower limbs to those from dissections. DTI was used to measure fiber lengths and pennation angles, while the anatomical images were used to estimate muscle mass, which were used to calculate physiological cross-sectional area (PCSA). The same data were then obtained through dissections, where it was found that on average muscle masses and fiber lengths matched well between the two methods (4% and 1% differences, respectively), while PCSA values had slightly larger differences (6%). Overall, these results suggest that DTI is a promising technique to gather in vivo muscle architecture data, but further refinement and complementary imaging techniques may be needed to realize these goals., (Copyright © 2019 by ASME.)

Background: Some studies have suggested that altered tibiofemoral cartilage contact behavior (arthrokinematics) may contribute to long-term cartilage degeneration, potentially leading to tibiofemoral osteoarthritis. However, few studies have assessed normal tibiofemoral arthrokinematics during dynamic activities., Purpose: To characterize tibiofemoral arthrokinematics during the impact phase of level walking and downhill running., Study Design: Descriptive laboratory study., Methods: Arthrokinematic data were collected on uninjured knees of 44 participants (mean age, 20.7 ± 6.6 years). Using a dynamic stereoradiographic imaging system with superimposed 3-dimensional bone models from computed tomography and magnetic resonance imaging of participant-specific tibiofemoral joints, arthrokinematics were assessed during the first 15% of the gait cycle during level walking and the first 10% of the gait cycle during downhill running., Results: During level walking and downhill running, the medial compartment had a greater cartilage contact area versus the lateral compartment. Both compartments had a significantly less cartilage contact area during running versus walking (medial compartment gait cycle affected: 8%-10%; lateral compartment gait cycle affected: 5%-10%). Further, medial and lateral compartment tibiofemoral contact paths were significantly more posterior and longer during downhill running., Conclusion: There was a decreased tibiofemoral cartilage contact area during downhill running compared with level walking, suggesting that underlying bone morphology may play a key role in determining the size of cartilage contact regions., Clinical Relevance: This study provides the first data characterizing tibiofemoral cartilage contact patterns during level walking and downhill running. These results provide evidence in support of performing biomechanical assessments during both level walking and downhill running to obtain a comprehensive picture of tibiofemoral cartilage behavior after clinical interventions., Competing Interests: One or more of the authors has declared the following potential conflict of interest or source of funding: This work was supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (NIH; award No. R01 AR056630); the content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. F.H.F. has received educational support from Smith & Nephew. W.J.A. and S.T. are named on a patent for the biplane radiographic imaging system used in this study. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

If intervertebral disc degeneration can be identified early, preventative treatments may be initiated before symptoms become disabling and costly. Changes in disc mechanics, such as the decrease in the compressive modulus of the nucleus, are some of the earliest signs of degeneration. Therefore, in vivo changes in the disc response to compressive load may serve as a biomarker for pending or early disc degeneration. The aim of this study was to assess the potential for using in vivo dynamic disc deformation to identify pathologic structural degeneration of the intervertebral disc. A validated model-based tracking technique determined vertebral motion from biplane radiographs collected during dynamic flexion/extension and axial rotation of the cervical spine. A computational model of the subaxial intervertebral discs was developed to identify the dynamic functional nucleus of each disc, that is, the disc region that underwent little to no additional compression during dynamic movements. The size and location of the dynamic functional nucleus was determined for 10 C5/C6 spondylosis patients, 10 C5/C6/C7 spondylosis patients, and 10 asymptomatic controls. The dynamic functional nucleus size was sensitive (significantly smaller than controls in 5 of 6 measurements at the diseased disc) and specific (no difference from controls in 9 of 10 measurements at non-diseased discs) to pathologic disc degeneration. These results provide evidence to suggest that structural disc degeneration, manifested by changes in the disc response to functional loading, may be identified in vivo from dynamic imaging collected during functional movements. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 9999:1-7, 2019., (© 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.)

Background Context: Neck pain is one of the most commonly reported symptoms in primary care settings, and a major contributor to health-care costs. Cervical manipulation is a common and clinically effective intervention for neck pain. However, the in vivo biomechanics of manipulation are unknown due to previous challenges with accurately measuring intervertebral kinematics in vivo during the manipulation., Purpose: The objectives were to characterize manual forces and facet joint gapping during cervical spine manipulation and to assess changes in clinical and functional outcomes after manipulation. It was hypothesized that patient-reported pain would decrease and intervertebral range of motion (ROM) would increase after manipulation., Study Design/setting: Laboratory-based prospective observational study., Patient Sample: 12 patients with acute mechanical neck pain (4 men and 8 women; average age 40 ± 15 years)., Outcome Measures: Amount and rate of cervical facet joint gapping during manipulation, amount and rate of force applied during manipulation, change in active intervertebral ROM from before to after manipulation, and numeric pain rating scale (NPRS) to measure change in pain after manipulation., Methods: Initially, all participants completed a NPRS (0-10). Participants then performed full ROM flexion-extension, rotation, and lateral bending while seated within a custom biplane radiography system. Synchronized biplane radiographs were collected at 30 images/s for 3 seconds during each movement trial. Next, synchronized, 2.0-milliseconds duration pulsed biplane radiographs were collected at 160 images/s for 0.8 seconds during the manipulation. The manipulation was performed by a licensed chiropractor using an articular pillar push technique. For the final five participants, two pressure sensors placed on the thumb of the chiropractor (Novel pliance system) recorded pressure at 160 Hz. After manipulation, all participants repeated the full ROM movement testing and once again completed the NPRS. A validated volumetric model-based tracking process that matched subject-specific bone models (from computed tomography) to the biplane radiographs was used to track bone motion with submillimeter accuracy. Facet joint gapping was calculated as the average distance between adjacent articular facet surfaces. Pre- to postmanipulation changes were assessed using the Wilcoxon signed-rank test., Results: The facet gap increased 0.9 ± 0.40 mm during manipulation. The average rate of facet gapping was 6.2 ± 3.9 mm/s. The peak force and rate of force application during manipulation were 65 ± 4 N and 440 ± 58 N/s. Pain score improved from 3.7 ± 1.2 before manipulation to 2.0 ± 1.4 after manipulation (p <. 001). Intervertebral ROM increased after manipulation by 1.2° (p = .006), 2.1° (p = .01), and 3.9° (p = .003) at the C4/C5, C5/C6, and C6/C7 motion segments, respectively, during flexion-extension; by 1.5° (p = .028), 1.9° (p = .005), and 1.3° (p = .050) at the C3/C4, C4/C5, and C5/C6 motion segments, respectively, during rotation; and by 1.3° (p = .034) and 1.1° (p = .050) at the C4/C5 and C5/C6 motion segments, respectively, during lateral bending. Global head ROM relative to the torso increased after manipulation by 8º (p = .023), 10º (p = .002), and 13º (p = .019) during lateral bending, axial rotation and flexion-extension, respectively, after manipulation., Conclusions: This study is the first to measure facet gapping during cervical manipulation on live humans. The results demonstrate that target and adjacent motion segments undergo facet joint gapping during manipulation and that intervertebral ROM is increased in all three planes of motion after manipulation. The results suggest that clinical and functional improvement after manipulation may occur as a result of small increases in intervertebral ROM across multiple motion segments. This study demonstrates the feasibility of characterizing in real time the manual inputs and biological responses that comprise cervical manipulation, including clinician-applied force, facet gapping, and increased intervertebral ROM. This provides a basis for future clinical trials to identify the mechanisms behind manipulation and to optimize the mechanical factors that reliably and sufficiently impact the key mechanisms behind manipulation., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Purpose: Degenerative spondylolisthesis (DS) in the setting of symptomatic lumbar spinal stenosis is commonly treated with spinal fusion in addition to decompression with laminectomy. However, recent studies have shown similar clinical outcomes after decompression alone, suggesting that a subset of DS patients may not require spinal fusion. Identification of dynamic instability could prove useful for predicting which patients are at higher risk of post-laminectomy destabilization necessitating fusion. The goal of this study was to determine if static clinical radiographs adequately characterize dynamic instability in patients with lumbar degenerative spondylolisthesis (DS) and to compare the rotational and translational kinematics in vivo during continuous dynamic flexion activity in DS versus asymptomatic age-matched controls., Methods: Seven patients with symptomatic single level lumbar DS (6 M, 1 F; 66 ± 5.0 years) and seven age-matched asymptomatic controls (5 M, 2 F age 63.9 ± 6.4 years) underwent biplane radiographic imaging during continuous torso flexion. A volumetric model-based tracking system was used to track each vertebra in the radiographic images using subject-specific 3D bone models from high-resolution computed tomography (CT). In vivo continuous dynamic sagittal rotation (flexion/extension) and AP translation (slip) were calculated and compared to clinical measures of intervertebral flexion/extension and AP translation obtained from standard lateral flexion/extension radiographs., Results: Static clinical radiographs underestimate the degree of AP translation seen on dynamic in vivo imaging (1.0 vs 3.1 mm; p = 0.03). DS patients demonstrated three primary motion patterns compared to a single kinematic pattern in asymptomatic controls when analyzing continuous dynamic in vivo imaging. 3/7 (42%) of patients with DS demonstrated aberrant mid-range motion., Conclusion: Continuous in vivo dynamic imaging in DS reveals a spectrum of aberrant motion with significantly greater kinematic heterogeneity than previously realized that is not readily seen on current clinical imaging., Level of Evidence: Level V data These slides can be retrieved under Electronic Supplementary Material.

Background: Limited in vivo kinematic information exists on managing meniscal injury during anterior cruciate ligament reconstruction (ACLR)., Hypothesis: Isolated anatomic ACLR restores knee kinematics, whereas ACLR in the presence of medial meniscal injury is associated with altered long-term knee kinematics., Study Design: Cohort study; Level of evidence, 3., Methods: From March 2011 to December 2012, 49 of 57 participants in a clinical trial underwent anatomic ACLR with successful kinematic testing at 24 months after ACLR. Twenty-five patients had associated meniscal tears: medial (n = 11), lateral (n = 9), or bilateral (n = 5). With a dynamic stereo radiography system with superimposed high-resolution computed tomography scans of patient knees, kinematics were measured during downhill running. The initial single-support phase of the gait cycle (0%-10%) was analyzed., Results: Anterior tibial translation (ATT) was the only kinematic outcome between patients' ACLR and contralateral knees that had significant interactions among meniscal groups ( P = .007). There was significant difference in ATT between patients with intact menisci and medial tears ( P = .036) and with medial tears and lateral tears ( P = .025). Patients with intact menisci had no difference in ATT, with a negligible effect size between the ACLR and contralateral knees (mean ± SEM: 13.1 ± 0.7 mm vs 12.6 ± 0.5 mm, P = .24, Cohen d = 0.15, n = 24), while patients with medial meniscal tears had an increase in ATT, with a medium effect size between the ACLR and contralateral knees (15.4 ± 1.0 mm vs 13.2 ± 1.0 mm, P = .024, Cohen d = 0.66, n = 11)., Conclusion: Associated medial meniscal injury in the setting of ACLR leads to increased ATT at 24-month follow-up. Furthermore, isolated anatomic ACLR in the absence of meniscal injury demonstrated no significant difference from native knee kinematics at 24-month follow-up during rigorous "high demand" knee activity with the current sample size. Patients undergoing anatomic ACLR in the presence of medial meniscal injury remained at a higher likelihood of sustaining altered long-term knee kinematics.

Purpose: Bone mineral density (BMD) measured using quantitative computed tomography (QCT) has been shown to correlate with bone mechanical properties. Knowledge of BMD within specific anatomic regions of the spine is valuable to surgeons who must secure instrumentation to the vertebrae, to medical device developers who design screws and disc replacements, and to researchers who assign mechanical properties to computational models. The objective of this study was to comprehensively characterize BMD in the cervical spine of young healthy adults., Methods: QCT was used to determine BMD in the cervical spines of 31 healthy adults (age 20-35). Subject-specific 3D models of each vertebra were created from CT scans, and anatomic regions of interest were identified in each bone (C1: 3 regions; C2: 9 regions, C3-C7: 13 regions). Statistical tests were performed to identify differences in BMD according to vertebral level, anatomic regions within vertebrae, and sex., Results: BMD varied significantly among vertebral levels and among anatomic regions within each vertebra. Females had higher BMD than males (p = .041) primarily due to higher BMD in the posterior regions of each vertebra., Conclusions: These data can serve as a baseline to identify BMD changes in older and symptomatic patients. This data set is also the first report of volumetric bone density within different anatomic regions of the atlas and axis of the cervical spine. The finding of higher BMD in females is in agreement with the previous QCT results but contradicts DEXA results that are known to be dependent upon bone size.

Intervertebral range of motion (ROM) is commonly calculated using ordered rotations or projection angles. Ordered rotations are sequence-dependent, and projection angles are dependent upon on which orientation vectors are projected. This study assessed the effect of calculation method on intervertebral ROM in the subaxial cervical spine (C3-C7) during in vivo dynamic, three-dimensional, functional movement. Biplane radiographs were collected at 30 images per second while 29 participants performed full ROM flexion/extension, axial rotation and lateral bending movements of their cervical spine. In vivo bone motion was tracked with sub-millimeter accuracy using a validated volumetric model-based tracking technique. Intervertebral rotations were calculated using six Cardan angle sequences and two projection angle combinations. Within-subject comparisons revealed significant differences in intervertebral ROM among calculation methods (all p<0.002). Group mean ROM differences were small, but significantly different among calculation methods (p<0.001). A resampling technique demonstrated that as group size increases, the differences between calculation methods decreases substantially. It is concluded that the method used to calculate intervertebral rotations of the sub-axial cervical spine can significantly affect within-subject and between group comparisons of intervertebral ROM., (Copyright © 2017 IPEM. Published by Elsevier Ltd. All rights reserved.)

Study Design: A longitudinal study using biplane radiography to measure in vivo intervertebral range of motion (ROM) during dynamic flexion/extension, and rotation., Objective: To longitudinally compare intervertebral maximal ROM and midrange motion in asymptomatic control subjects and single-level arthrodesis patients., Summary of Background Data: In vitro studies consistently report that adjacent segment maximal ROM increases superior and inferior to cervical arthrodesis. Previous in vivo results have been conflicting, indicating that maximal ROM may or may not increase superior and/or inferior to the arthrodesis. There are no previous reports of midrange motion in arthrodesis patients and similar-aged controls., Methods: Eight single-level (C5/C6) anterior arthrodesis patients (tested 7 ± 1 months and 28 ± 6 months postsurgery) and six asymptomatic control subjects (tested twice, 58 ± 6 months apart) performed dynamic full ROM flexion/extension and axial rotation whereas biplane radiographs were collected at 30 images per second. A previously validated tracking process determined three-dimensional vertebral position from each pair of radiographs with submillimeter accuracy. The intervertebral maximal ROM and midrange motion in flexion/extension, rotation, lateral bending, and anterior-posterior translation were compared between test dates and between groups., Results: Adjacent segment maximal ROM did not increase over time during flexion/extension, or rotation movements. Adjacent segment maximal rotational ROM was not significantly greater in arthrodesis patients than in corresponding motion segments of similar-aged controls. C4/C5 adjacent segment rotation during the midrange of head motion and maximal anterior-posterior translation were significantly greater in arthrodesis patients than in the corresponding motion segment in controls on the second test date., Conclusion: C5/C6 arthrodesis appears to significantly affect midrange, but not end-range, adjacent segment motions. The effects of arthrodesis on adjacent segment motion may be best evaluated by longitudinal studies that compare maximal and midrange adjacent segment motion to corresponding motion segments of similar-aged controls to determine if the adjacent segment motion is truly excessive., Level of Evidence: 3.

Background Context: Cervical spine segmental contributions to motion may reveal movement abnormalities associated with whiplash, disc herniation, disc arthroplasty, or fusion., Purpose: The objective of this study was to determine the cervical spine segmental contributions to head flexion\extension, lateral bending, and axial rotation during dynamic motion in young, healthy individuals., Study Design: The study design was a descriptive control study., Patient Sample: Twenty-nine young (20-35 years of age) healthy individuals comprised the patient sample., Outcome Measures: Physiologic measures of contributions from each cervical motion segment to the primary head rotation were the outcome measures for this study., Methods: Twenty-nine healthy participants performed full range of motion (ROM) flexion\extension, lateral bending, and axial rotation while biplane radiographs were collected at 30 images per second. Surface-based markers were used to determine head kinematics for each movement, and a validated volumetric model-based tracking technique was used to determine intervertebral kinematics. Contributions from each cervical motion segment to the primary head rotation were determined continuously during each of the three head movements. This study was funded by Synthes Spine (F)., Results: For each head movement, motion segments in the lower cervical spine increased their contributions to head motion near the end of the ROM. Cervical motion segment contributions to left and right lateral bending were mirror images of each other, as were contributions to left and right axial rotation. However, cervical motion segment contributions to flexion were not mirror images of the contributions to extension., Conclusions: Cervical motion segment contributions to head motion change over the full ROM and cannot be accurately characterized solely from endpoint data. The continuously changing segmental contributions suggest that the compressive and shear loads applied to each motion segment also change over the ROM. The clinical implication of increased contributions from the inferior motions segments near the end ROM is that the clinician may advise the patient to avoid end ROM positions to lessen the demand on the discs of inferior motion segments., (Copyright © 2015 Elsevier Inc. All rights reserved.)

There is substantial inter-subject variability in intervertebral range of motion (ROM) in the cervical spine. This makes it difficult to define "normal" ROM, and to assess the effects of age, injury, and surgical procedures on spine kinematics. The objective of this study was to define normal intervertebral kinematics in the cervical spine during dynamic functional loading. Twenty-nine participants performed dynamic flexion\extension, axial rotation, and lateral bending while biplane radiographs were collected at 30 images/s. Vertebral motion was tracked with sub-millimeter accuracy using a validated volumetric model-based tracking process that matched subject-specific CT-based bone models to the radiographs. Gaussian point-by-point and bootstrap techniques were used to determine 90% prediction bands for the intervertebral kinematic curves at 1% intervals of each movement cycle. Cross validation was performed to estimate the true achieved coverage for each method. For a targeted coverage of 90%, the estimated true coverage using bootstrap prediction bands averaged 86±5%, while the estimated true coverage using Gaussian point-by-point intervals averaged 56±10% over all movements and all motion segments. Bootstrap prediction bands are recommended as the standard for evaluating full ROM cervical spine kinematic curves. The data presented here can be used to identify abnormal motion in patients presenting with neck pain, to drive computational models, and to assess the biofidelity of in vitro loading paradigms., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The objective of this study was to determine the intervertebral kinematics of the young, healthy cervical spine during dynamic, three-dimensional, functional loading. Intervertebral motion was characterized by the range of motion (ROM) and the helical axis of motion (HAM). Biplane radiographs of the cervical spine were collected at 30 images/s as 29 participants (20-35 yr) performed dynamic flexion\extension, axial rotation, and lateral bending. Vertebral motion (C1-T1 in flexion\extension, C3-T1 in lateral bending and axial rotation) was tracked with sub-millimeter accuracy using a validated volumetric model-based tracking process that matched subject-specific CT-based bone models to the radiographs. Flexion\extension ROM was smallest at the C2-C3 motion segment (12.7±2.6°) and largest at the C5-C6 motion segment (19.7±3.7°). During head lateral bending and axial rotation, the intervertebral bending ROM was greater than the rotation ROM at every motion segment. The HAM demonstrated differences among motion segments and among movements. During flexion\extension, the helical axis of motion was directed nearly perpendicular to the sagittal plane for the C2-C3 through C7-T1 motion segments. During lateral bending, the angle between the HAM and the transverse plane progressively increased from the C6-C7 motion segment (approximately ±22°) to the C3-C4 motion segment (approximately ±40°). During axial rotation, the angle between the transverse plane and the HAM was approximately ±42° at the C3-C4 through C5-C6 motion segments, and approximately ±32° at the C6-C7 motion segment. This study provides valuable reference data for evaluating the effects of age, degeneration, and surgical procedures on cervical spine kinematics during three-dimensional dynamic functional loading., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Background Context: A precise and comprehensive definition of "normal" in vivo cervical kinematics does not exist due to high intersubject variability and the absence of midrange kinematic data. In vitro test protocols and finite element models that are validated using only end range of motion data may not accurately reproduce continuous in vivo motion., Purpose: The primary objective of this study was to precisely quantify cervical spine intervertebral kinematics during continuous, functional flexion-extension in asymptomatic subjects. The advantages of assessing continuous intervertebral kinematics were demonstrated by comparing asymptomatic controls with patients with single-level anterior arthrodesis., Study Design: Cervical spine kinematics were determined during continuous in vivo flexion-extension in a clinically relevant age group of asymptomatic controls and a group of patients with C5-C6 arthrodesis., Patient Sample: The patient sample consisted of 6 patients with single-level (C5-C6) anterior arthrodesis (average age: 48.8±6.9 years; 1 male, 5 female; 7.6±1.2 months postsurgery) and 18 asymptomatic control subjects of similar age (average age: 45.6±5.8 years; 5 male, 13 female)., Outcome Measures: Outcome measures included the physiologic measure of continuous kinematic motion paths at each cervical motion segment (C2-C7) during flexion-extension., Methods: Participants performed flexion-extension while biplane radiographs were collected at 30 images per second. A previously validated tracking process determined three-dimensional vertebral positions with submillimeter accuracy. Continuous flexion-extension rotation and anterior-posterior translation motion paths were adjusted for disc height and static orientation of each corresponding motion segment., Results: Intersubject variability in flexion-extension angle was decreased 15% to 46% and intersubject variability in anterior-posterior translation was reduced 14% to 33% after adjusting for disc height and static orientation angle. Average intersubject variability in continuous motion paths was 1.9° in flexion-extension and 0.6 mm in translation. Third-order polynomial equations were determined to precisely describe the continuous flexion-extension and anterior-posterior translation motion path at each motion segment (all R2>0.99)., Conclusions: A significant portion of the intersubject variability in cervical kinematics can be explained by the disc height and the static orientation of each motion segment. Clinically relevant information may be gained by assessing intervertebral kinematics during continuous functional movement rather than at static, end range of motion positions. The fidelity of in vitro cervical spine mechanical testing protocols may be evaluated by comparing in vitro kinematics to the continuous motion paths presented., (Copyright © 2014 Elsevier Inc. All rights reserved.)