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To determine the in vivo effects of superior capsule reconstruction (SCR) on glenohumeral kinematics during abduction and to compare those kinematics results with patient-reported outcomes, range of motion, and strength.Dynamic biplane radiography was used to image 10 patients with irreparable rotator cuff tears while performing scapular plane abduction pre- and 1-year post-surgery. Shoulder kinematics were determined by matching subject-specific computed tomography-based bone models to the radiographs using a validated tracking technique.No change was detected in static acromiohumeral distance (-0.7 ± 2.1 mm; P = .35); however, average dynamic acromiohumeral distance decreased (2.7 ± 1.2 mm to 2.3 ± 1.0 mm; P = .035) from pre- to 1-year post-surgery, respectively. The humeral head position was 0.5 ± 0.5 mm more superior 1-year post-surgery compared with pre-surgery (P = .01). Glenohumeral abduction increased from pre-surgery (150 ± 20°) to 1-year post-surgery (165 ± 10°) (P = .04) and all patient-reported outcomes improved from pre-surgery to 1-year post-surgery (all P.002). A more posterior shift in humeral head position was associated with improved American Shoulder and Elbow Surgeons Shoulder Score from pre-surgery to 1-year post-surgery (r = 0.71, P = .02).These data suggest that SCR may not depress the humeral head during functional abduction, as previously postulated, and postoperative improvements in subjective and clinical outcomes may be affected by mechanisms other than changes in shoulder kinematics.In vivo kinematics changes after SCR are small and do not correspond to previously postulated changes.

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.

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.

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.

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.

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 p0.022). 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.

Prospective cohort study.The aim was to identify patient factors that affect adjacent segment kinematics after anterior cervical discectomy and fusion (ACDF) as measured by biplane radiography.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.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.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.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.

Objectives: Patients with irreparable rotator cuff tears (RCT) exhibit functional limitations including limited ability to perform functional tasks such as combing their hair. One viable treatment is superior capsular reconstruction (SCR). SCR has been shown to restore stability of the glenohumeral (GH) joint in cadavers1, but its effect on in vivo scapular and humeral motion is unknown. The aims of this study were to determine the effect of SCR on in vivo scapular and humeral kinematics during a functional hand to head motion and to identify associations between shoulder kinematics and patient-reported outcomes (PROs). We hypothesized that moving the hand to the back of the head would be accomplished by using more GH based movement including rotation and abduction, and less scapular motion after SCR, and there would be a positive correlation between kinematics changes and improved PROs. Methods: Ten patients (8M, 2F, age 63 ± 7 years) with irreparable RCT provided informed consent to participate in this prospective IRB-approved study. American Shoulder and Elbow Surgeon (ASES), Disability of the Arm Shoulder and Hand (DASH), and Western Ontario Rotator Cuff Index (WORC) surveys were completed before (PRE) and 1-year (1YR-POST) after SCR. Participants were seated and instructed to move their hand from their lap to the back of their head while synchronized biplane radiographs of the shoulder were collected PRE and 1YR-POST at 50 images/s for 3 separate trials. Six degree of freedom GH and scapular kinematics were determined with sub-millimeter accuracy by matching subject-specific CT-based bone models of the humerus and scapula to the synchronized radiographs using a validated volumetric tracking technique3. The contributions of humeral abduction, plane of elevation and internal/external (I/E) rotation relative to the scapula, as well as scapular upward rotation, protraction, and tilt, were calculated for each subject before and after SCR. Differences in rotational contributions from PRE to POST were evaluated using a paired t-test. Variability in rotational contributions was characterized by the inter-subject standard deviation in rotational component contributions to the movement. Correlations among changes in the contribution of each rotation component and between the contribution of each rotation component and PROs were evaluated with Pearson’s correlation coefficients. Significance was set at p < 0.05 for all tests. Results: No differences in contribution to motion were identified in any of the rotational components from PRE to POST (all p > 0.15, Figure 1). Inter-subject variability in rotational contributions to the movement decreased in 5 of the 6 rotational components from PRE to 1YR-POST (Table 1; Figure 1). The PRE to 1YR POST change in contribution from GH abduction was positively correlated to the change in contribution from GH I/E rotation (Figure 2, R = 0.8, p = 0.001) and negatively correlated to the change in contribution from scapular protraction (Figure 2, R = -0.94, p = 0.001). ASES scores were negatively correlated with abduction contribution PRE (R = -0.65, p = 0.043), and positively correlated with plane of elevation PRE (R = 0.685, p = 0.03). Changes in the plane of elevation contribution were also positively correlated with changes in ASES scores (R = 0.635, p = 0.048). Conclusions: This is the first study to report GH and scapular kinematics when performing the functional task of placing the hand to the back of the head. Changes in contributions to the motion were inconsistent across subjects, making it difficult to find differences from PRE to POST. However, inter-subject variation was reduced following surgery, suggesting the participants’ movement strategy converged toward a more similar and possibly more efficient movement pattern following SCR. Increased contributions of glenohumeral rotation and abduction were offset by decreased scapular protraction and indicates SCR affects the contributions from these three rotations, partially supporting our first hypothesis. In addition, increased GH plane of elevation contribution following surgery was associated with improved ASES scores supporting our second hypothesis. This may be consistent with improved glenohumeral kinematics and efficiency of movement during a functional task following SCR. Future work will investigate GH and scapular kinematics in healthy individuals performing the hand to head movement to determine if movement strategy is closer to healthy after SCR.

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.

Objectives: Patients with irreparable rotator cuff tears (RCT) exhibit functional limitations believed to be caused by superior migration of the humerus1,2. One viable treatment is superior capsule reconstruction (SCR). SCR has been shown to restore stability of the glenohumeral (GH) joint in cadavers1, but its effectiveness at controlling in vivo humeral motion is unknown. Outcomes are typically evaluated through standard clinical radiographs to assess acromial-humeral distance (AHD), and patient-reported outcomes (PROs) such as ASES and Visual Analog Scale3. Reported changes in AHD are inconsistent, with some studies reporting an increase in AHD of 2.6 to 3.2 mm4,7, while other studies reported no significant change5,6 in AHD after SCR. Scapulohumeral rhythm (SHR), a measure of shoulder motion fluidity, has been reported at 2:1 (glenohumeral to scapulothoracic motion) in healthy individuals9, but the effects of SCR on SHR are unknown. The aim of this study was to determine the effect of SCR on static and dynamic AHD, shoulder function, and patient-reported outcomes. We hypothesized that after SCR, static and dynamic AHD would increase, SHR would approximate that of a healthy shoulder, maximum GH abduction would increase, and PROs would improve. Methods: Ten patients with irreparable RCT provided informed consent prior to receiving human dermal allograft SCR. To date, seven (6M, 1F, age 60 ± 8 years) have returned for 1 year post-operative testing. ASES, DASH, and WORC surveys were completed before (PRE), 6 months (6MO-POST), and 1-year after SCR (1YR-POST). Synchronized biplane radiographs of the shoulder were collected PRE and 1YR-POST at 50 images/s while patients performed 3 trials of scapular plane arm abduction. Six degree of freedom GH and scapular kinematics were determined with sub-millimeter accuracy by matching subject-specific CT-based bone models of the humerus and scapula to radiographs using a validated volumetric tracking technique8. AHD was calculated as the minimum distance between the acromion and the humerus at 5° increments of GH abduction. Scapulohumeral rhythm (SHR) was calculated by finding the average change in glenohumeral abduction per degree of scapular upward rotation during scapular abduction.Differences between PRE and 1YR-POST SHR and static AHD distance were evaluated using a paired t-test with significance set at p < 0.05. Changes in PROs were compared to the minimum clinically important difference (MCID). Results: There was a trend toward decreasing static AHD from PRE to 1YR-POST (average decrease: 1.5±1.6mm (p=0.06), however, dynamic AHD did not change from PRE to 1 YR-POST between 45° and 95° of glenohumeral abduction (all p > 0.11) (Figure 1). There was a trend toward increased SHR from 1.1 ± 0.5 PRE to 1.5 ± 0.3 1YR-POST (p = 0.08) (Figure 2), while the increase in maximum GH abduction during scapular abduction from PRE (76.7°±24.5°) to 1YR-POST (91.8°±14.9°) was not statistically significant (p = 0.14) (Figure 2). ASES, WORC, and DASH scores improved beyond the minimum clinically important difference from PRE to 1YR-POST (Table 1) for all patients. Conclusion: In general, SHR tended to more closely resemble that of a healthy shoulder following SCR. Althoughaverage maximum GH abduction was higher postoperatively than preoperatively, that increase was not statistically significant and may reflect that most patients in our cohort had reasonable preoperative abduction. In contrast to those quantitative measures of shoulder function, patient-reported qualitative outcomes all improved significantly. Conflicting results between static and dynamic AHD during higher glenohumeral abduction angles suggest SCR does not appear to affect AHD in higher abduction angles, though the static AHD suggests there may be a difference at lower abduction angles. Dynamic measurements of AHD at lower abduction angles will be necessary to fully characterize the dynamic changes of AHD following SCR. Figure 1. Patient-reported outcomes. Bolded scores represent changes greater than the minimum clinically important different (MCID) compared to PRE and average contact center locations ± 1 standard deviation throughout scapular plane abdjuction. Black + indicates the glenoid center with anterior (A) and posterior (P) directions indicated on the glenoid.

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.

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 (

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.

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. 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. 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. 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 V data These slides can be retrieved under Electronic Supplementary Material.

Objectives: Patients with irreparable rotator cuff tears (RCT) exhibit functional limitations believed to be caused by superior migration of the humerus1,2. One viable treatment is superior capsule reconstruction (SCR). SCR has been shown to restore stability of the glenohumeral (GH) joint in cadavers1, but its effectiveness at controlling in vivo humeral motion is unknown. Outcomes are typically evaluated through standard clinical radiographs to assess acromial-humeral distance (AHD), and patient-reported outcomes (PROs) such as ASES and Visual Analog Scale3. Reported changes in AHD are inconsistent, with some studies reporting an increase in AHD of 2.6 to 3.2 mm4,5, while other studies reported no significant change in AHD after SCR6,7. Additionally, AHD does not account for anterior-posterior translations of the humeral head and clinical radiographs cannot assess dynamic translation of the humerus during arm abduction. The aim of this study was to determine the in vivo effect of SCR on in vivo glenohumeral arthrokinematics during scapular abduction, and to compare these results to PROs. We hypothesized that static and dynamic AHD would increase, humeral head location on the glenoid would be more inferior at corresponding abduction angles after SCR, and changes in humeral head translation or AHD would correlate with increased GH abduction range of motion and improved PROs. Methods: Ten patients (8M, 2F, age 63 ± 7 years) with irreparable RCT provided informed consent to participate in this prospective IRB-approved study. ASES, DASH, and WORC surveys were completed before (PRE) and 1-year (1YR-POST) after SCR. Synchronized biplane radiographs of the shoulder were collected PRE and 1YR-POST at 50 images/s while patients performed 3 trials of scapular plane arm abduction. Biplane radiographs were also collected during a static neutral trial where the participants placed their hand on their lap. Six degree of freedom GH and scapular kinematics were determined with sub-millimeter accuracy by matching subject-specific CT-based bone models of the humerus and scapula to radiographs using a validated volumetric tracking technique8. AHD was calculated as the minimum distance between the acromion and the humerus at 10° increments of GH abduction and averaged throughout the motion. Humeral head translation, defined as the relative translation of the center of the humeral head compared to the center of the glenoid, was calculated at 10° increments of GH abduction and expressed as averages in the superior/inferior (SI) and anterior/posterior (AP) directions. Differences between PRE and 1YR-POST static AHD, average dynamic humeral head location, PROs, and maximum GH abduction were evaluated using a paired t-test. A Pearson correlation was used to determine associations between static AHD and average humeral head location, and both PROs and maximum GH abduction. Significance was set at p < 0.05 for all tests. Results: There was no difference in static AHD from PRE (5.3±1.6mm) to 1YR-POST (4.6±1.6mm) while the average dynamic AHD during GH abduction decreased from 2.7±1.2mm PRE to 2.3±1.0mm 1YR-POST (Figure 1). Static AHD was larger than the average dynamic AHD both PRE and 1YR-POST (Figure 1). The average position of the humeral head during abduction moved 1.5% of the glenoid height superior from PRE to 1YR-POST and 1.7% of the glenoid width anterior from PRE to 1YR-POST (Figure 2). ASES, WORC, and DASH scores significantly improved from PRE to 1YR-POST and maximum GH abduction significantly increased from PRE (78.1±23.1°) to 1YR-POST (93.9±12.3°) (Table 1). Interestingly, there was a positive correlation between the AP humeral head location and DASH score PRE such that a higher DASH score was associated with the humeral head being more anterior (R = 0.767). No other associations were found between either average humeral head locations or AHD and either PROs or maximum GH abduction at both time points as well as the changes in those measures between time points (all R < 0.67). Conclusions: Static AHD, as measured clinically, may not be a good representation of dynamic AHD during scapular abduction given the differences between the static and dynamic AHD measurements at similar abduction angles. Additionally, our in vivo kinematics findings are not consistent with prior results of a cadaver-based biomechanical study of SCR as we found were minute changes in the SI humeral head position, with a 0.4mm more superior humeral head position following SCR. Regardless, patient-reported qualitative outcomes and maximum GH abduction all improved significantly. This suggests clinical outcomes after SCR may be influenced by mechanisms other than restoration of humeral head translation. Future in vivo studies are needed to evaluate the kinematic mechanisms behind improved PROs after SCR. [Table: see text]

Category: Ankle, Hindfoot Introduction/Purpose: Restoration of bilateral symmetry is used clinically to evaluate surgical and conservative treatment outcomes. However, the degree of symmetry and differences between sexes in ankle kinematics in healthy individuals remain unknown. Because relative motion between the tibia, talus and calcaneus cannot be accurately measured using conventional skin- mounted motion capture systems, biplane radiography is emerging as the preferred technique to measure in vivo ankle kinematics during functional activities. Therefore, the aims of the present study were to use biplane radiography to determine the degree of bilateral symmetry in ankle kinematics in healthy individuals and to identify sex-dependent differences in kinematics during the support phase of gait. It was hypothesized that rotational ankle range of motion (ROM) during gait is not different between males and females. Methods: Twenty healthy individuals (10 male, 10 female, age 30.7 ± 6.3years) with no history of ankle injury provided consent to participate in this IRB-approved study. Each participant walked through a biplane radiography system 6 times at a self-selected pace (1.3±0.2 m/s). Synchronized radiographs of the ankle were collected at 100 images/second for 3 trials of each ankle (90 kV, 125 mA, 1 ms exposure/image). Motion of the tibia, talus and calcaneus was tracked using a validated model-based tracking process that matches 3D bone models to the radiographs. Anatomic coordinate systems were created and used to calculate ankle kinematics. All kinematics were converted to percent stance phase and averaged over all trials for each ankle. Bilateral symmetry was determined by calculating the average absolute difference between right and left ankle joint kinematics over the full support phase of gait. Differences between male and female rotational ROM were identified using unpaired t-tests. Results: The average absolute side-to-side difference in tibio-talar joint rotations was 3.3° or less, while the average absolute side-to-side difference in subtalar joint rotations was 3.0° or less (Table 1A). For males and females, at the tibio-talar joint, the largest ROM was plantar-dorsiflexion, followed by internal/external rotation and then inversion/eversion (Table 1B). At the subalar joint, the largest ROM was inversion/eversion, with similar amounts of dorsiflexion/plantarflexion and internal/external rotation, on the order of 2° to 3°. Males demonstrated significantly less ROM in subtalar dorsiflexion/plantarflexion and tibio-talar internal/external rotation (Table 1B). Conclusion: The average side-to-side differences in healthy ankle ROM during gait are small, suggesting that the contralateral ankle may serve as a reference standard to assess kinematic outcomes after conservative or surgical treatments. The difference between male and female subtalar ROM (0.6°) may be too small to be functionally significant, however, sex differences in tibio- talar ROM appear large enough to merit consideration when assessing functional outcomes and designing ankle joint replacements. The results are limited to over-ground gait performed by relatively young and healthy adults and may not be applicable to other activities or older adults.

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.