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Leonard I Voronov,1,2 Krzysztof B Siemionow,3 Robert M Havey,1,2 Gerard Carandang,2 Avinash G Patwardhan1,2 1Department of Orthopaedic Surgery and Rehabilitation, Loyola University Chicago, Maywood, 2Musculoskeletal Biomechanics Laboratory, Edward Hines Jr. VA Hospital, Hines, 3Department of Orthopaedics, University of Illinois College of Medicine at Chicago, Chicago, IL, USA Introduction: Lateral mass screw (LMS) fixation with plates or rods is the current standard procedure for posterior cervical fusion. Recently, implants placed between the facet joints have become available as an alternative to LMS or transfacet screws for patients with cervical spondylotic radiculopathy. The purpose of this study was to evaluate the biomechanical stability of the DTRAX® cervical cage for single- and two-level fusion and compare this to the stability achieved with LMS fixation with rods in a two-level construct.Methods: Seven cadaveric cervical spine (C3–C7) specimens were tested in flexion–extension, lateral bending, and axial rotation to ±1.5 Nm moment without preload (0 N) in the following conditions: 1) intact (C3–C7), 2) LMS and rods at C4–C5 and C5–C6, 3) removal of all rods (LMS retained) and placement of bilateral posterior cages at C5–C6, 4) bilateral posterior cages at C4–C5 and C5–C6 (without LMS and rods), and 5) C4–C5 and C5–C6 bilateral posterior cages at C4–C5 and C5–C6 with rods reinserted.Results: Bilateral posterior cervical cages significantly reduced range of motion in all tested directions in both single- and multilevel constructs (P

Leonard I Voronov,1,2 Krzysztof B Siemionow,3 Robert M Havey,1,2 Gerard Carandang,1,2 Frank M Phillips,4 Avinash G Patwardhan1,2 1Musculoskeletal Biomechanics Laboratory, Department of Research, Edward Hines Jr VA Hospital, Hines, IL, USA; 2Department of Orthopaedic Surgery and Rehabilitation, Loyola University Chicago, Maywood, IL, USA; 3College of Medicine at Chicago, University of Illinois, Chicago, IL, USA; 4Midwest Orthopedics at Rush, Rush University Medical Center, Chicago, IL, USA Introduction: Supplemental posterior instrumentation has been widely used to enhance stability and improve fusion rates in higher risk patients undergoing anterior cervical discectomy and fusion (ACDF). These typically involve posterior lateral mass or pedicle screw fixation with significant inherent risks and morbidities. More recently, cervical cages placed bilaterally between the facet joints (posterior cervical cages) have been used as a less disruptive alternative for posterior fixation. The purpose of this study was to compare the stability achieved by both posterior cages and ACDF at a single motion segment and determine the stability achieved with posterior cervical cages used as an adjunct to single- and multilevel ACDF.Methods: Seven cadaveric cervical spine (C2–T1) specimens were tested in the following sequence: intact, C5–C6 bilateral posterior cages, C6–C7 plated ACDF with and without posterior cages, and C3–C5 plated ACDF with and without posterior cages. Range of motion in flexion–extension, lateral bending, and axial rotation was measured for each condition under moment loading up to ±1.5 Nm.Results: All fusion constructs significantly reduced the range of motion compared to intact in flexion–extension, lateral bending, and axial rotation (P

Prior to implantation, medical devices are subjected to rigorous testing to ensure safety and efficacy. A full battery of testing protocols for implantable spinal devices may include many steps. Testing for biocompatibility is a necessary first step. On selection of the material, evaluation protocols should address both the biomechanical and clinical performance of the device. Before and during mechanical testing, finite element modeling can be used to optimize the design, predict performance, and, to some extent, predict durability and efficacy of the device. Following bench-type evaluations, the biomechanical characteristics of the device (e.g., motion, load-sharing, and intradiscal pressure) can be evaluated with use of fresh human cadaveric spines. The information gained from cadaveric testing may be supplemented by the finite element model-based analyses. Upon the successful completion of these tests, studies that make use of an animal model are performed to assess the structure, function, histology, and biomechanics of the device in situ and as a final step before clinical investigations are initiated. The protocols that are presently being used for the testing of spinal devices reflect the basic and applied research experience of the last three decades in the field of orthopaedic biomechanics in general and the spine in particular. The innovation within the spinal implant industry (e.g., fusion devices in the past versus motion-preservation devices at present) suggests that test protocols represent a dynamic process that must keep pace with changing expectations. Apart from randomized clinical trials, no single test can fully evaluate all of the characteristics of a device. Due to the inherent limitations of each test, data must be viewed in a proper context. Finally, a case is made for the medical community to converge toward standardized test protocols that will enable us to compare the vast number of currently available devices, whether on the market or still under development, in a systematic, laboratory-independent manner. [ABSTRACT FROM AUTHOR]

Background: Previous clinical trials have assessed the percentage of participants who utilized further health care after a period of conservative care for low back pain, however no chiropractic clinical trial has determined the total amount of care during this time and any differences based on assigned treatment group. The objective of this clinical trial follow-up was to assess if there was a difference in the total number of office visits for low back pain over one year after a four week clinical trial of either a form of physical therapy (Exercise Program) or a form of chiropractic care (Flexion Distraction) for chronic low back pain.Methods: In this randomized clinical trial follow up study, 195 participants were followed for one year after a four-week period of either a form of chiropractic care (FD) or a form of physical therapy (EP). Weekly structured telephone interview questions regarded visitation of various health care practitioners and the practice of self-care for low back pain.Results: Participants in the physical therapy group demonstrated on average significantly more visits to any health care provider and to a general practitioner during the year after trial care (p<0.05). No group differences were noted in the number of visits to a chiropractor or physical therapist. Self-care was initiated by nearly every participant in both groups.Conclusions: During a one-year follow-up, participants previously randomized to physical therapy attended significantly more health care visits than those participants who received chiropractic care. © 2006 Cambron et al., licensee BioMed Central Ltd. [ABSTRACT FROM AUTHOR]

The analysis of current cervical collars (Aspen and Miami J collars) and cervical thoracic orthoses (CTOs) (Aspen 2-post and Aspen 4-post CTOs) in reducing cervical intervertebral and gross range of motion in flexion and extension was performed using 20 normal volunteer subjects. The gross sagittal motion of the head was measured relative to the horizon with the use of an optoelectronic motion measurement system. Simultaneous measurement of cervical intervertebral motion was performed with the use of a video fluoroscopy (VF) machine. Intervertebral motion was described as (1) the angular motion of each vertebra and (2) the translational motion of the vertebral centroid. We used surface electromyographic (EMG) signal data to compare subject efforts between the two collars and between the two CTOs. Each orthosis significantly reduced gross and intervertebral motion in flexion and extension (p < 0.05). No statistically significant differences were found between the Miami J and Aspen collars in reducing gross or intervertebral sagittal motion, except at C5-6. Both CTOs provided significantly more restriction of gross and intervertebral flexion and extension motion as compared to the two collars (p < 0.05). The Aspen 2-post CTO and 4-post CTO performed similarly in flexion, but the Aspen 4-post CTO provided significantly more restriction of extension motion (p < 0.05). [ABSTRACT FROM AUTHOR]

Background: Treatment of diabetes and its complications is a primary health care expense. Up to 25% of people with diabetes will develop diabetic foot ulcers (DFUs). Removable cast walker (RCW) boots commonly prescribed for DFU treatment, promote healing, and provide offloading and wound protection. Patient RCW removal for hygiene and wound care can lead to decreased adherence and treatment effectiveness. This study evaluated a new system for wear-time adherence measurement using multiple sensor types., Methods: An electronic wear-time monitor was developed, which included internal and external temperature sensors, an accelerometer, and capacitive proximity foot and ankle sensors. Time-stamped and date-stamped data were saved once per minute for up to 22 days. Ten healthy volunteer subjects were recruited to wear an RCW for two weeks while keeping a diary of don/doff times. Sensor data were then compared with volunteers' wear diaries using confusion matrix predictive analytics., Results: Algorithms were developed for data processing. Correlation coefficients between algorithms and diaries were calculated for individual and multiple sensor combinations. Differential temperature and accelerometer algorithms were significantly better at predicting subject wear-time than individual temperature sensor algorithms ( P = .009, P = .001, respectively). Foot proximity had significantly better correlation with subject diaries than temperature ( P = .024), and acceleration algorithms ( P = .005). Multi-sensor analysis showed high correlation (.96) with wear-time from subject diaries., Conclusions: Removable cast walker wear-time can be accurately determined using an electronic data recorder and multiple sensors. Wear-time measurement accuracy can be improved using algorithms that operate on data from multiple sensors that use a variety of sensor technologies., 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.

Background: Flatback deformity, or lumbar hypolordosis, can cause sagittal imbalance, causing back pain, fatigue, and functional limitation. Surgical correction through osteotomies and interbody fusion techniques can restore sagittal balance and relieve pain. This study investigated sagittal vertical alignment (SVA) and lumbar lordosis correction achieved through sequential procedures on human spine specimens., Methods: Human T10-sacrum specimens were stratified into 2 groups: degenerative flatback specimens had smaller L1-S1 lordosis compared to the iatrogenic group (26.1°±15.0° vs. 47.8°±19.3°, p<.05). Specimens were mounted in the apparatus in simulated standing posture with a nominal sacral slope of 45 degrees and subjected to a 400N compressive follower preload. Sequential correction of degenerative lumbar flatback deformity involved: anterior lumbar interbody fusion (ALIF) at L5-S1, ALIF at L4-5, lateral lumbar interbody fusion (LLIF) at L2-3 and L3-4, and posterior column osteotomy (PCO) at L2-3 and L3-4. In iatrogenic specimens, flatback deformity was created by performing a posterior in-situ immobilization using pedicle screw instrumentation at L4-L5-S1 followed by distraction across the pedicle screws. We then performed LLIF at L2-3 and L3-4, followed by PCO at L2-3 and L3-4., Results: Statistically significant incremental corrections were noted in SVAs and lordosis after L5-S1 ALIF, L4-5 ALIF, and PCO in degenerative flatback specimens. For the iatrogenic group, statistically significant worsening was noted in measures of standing alignment after L4-L5-S1 hypolordotic fusion. Subsequent LLIF at L2-3 and L3-4 did not significantly improve sagittal alignment. However, after PCO at L2-3 and L3-4, final alignment parameters were not significantly different than preoperative baseline values prior to hypolordotic fusion., Conclusions: ALIF cages in the lower lumbar segments significantly improved sagittal alignment in degenerative flatback specimens. In the upper lumbar segments, LLIF cages alone were ineffective at enhancing lumbar lordosis. LLIF cages in conjunction with PCO improved alignment parameters in degenerative and iatrogenic flatback deformities., Competing Interests: One or more of the authors declare financial or professional relationships on ICMJE-NASSJ disclosure forms., (© 2024 The Author(s).)

Background Context: The functional goals of cervical disc arthroplasty (CDA) are to restore enough range of motion (ROM) to reduce the risk of accelerated adjacent segment degeneration but limit excessive motion to maintain a biomechanically stable index segment. This motion-range is termed the "Physiological mobility range." Clinical studies report postoperative ROM averaged over all study subjects but they do not report what proportion of reconstructed segments yield ROM in the Physiological mobility range following CDA surgery., Purpose: To calculate the proportion of reconstructed segments that yield flexion-extension ROM (FE-ROM) in the Physiological mobility range (defined as 5°-16°) by analyzing the 24-month postoperative data reported by clinical trials of various cervical disc prostheses., Study Design/setting: Analysis of 24-month postoperative FE-ROM data from clinical trials., Patient Sample: Data from 1,173 patients from single-level disc replacement clinical trials of 7 cervical disc prostheses., Outcome Measures: 24-month postoperative index-level FE-ROM., Methods: The FE-ROM histograms reported in Food and Drug Administration-Investigational Device Exemption (FDA-IDE) submissions and available for this analysis were used to calculate the frequencies of implanted levels with postoperative FE-ROM in the following motion-ranges: Hypomobile (0°-4°), Physiological (5°-16°), and Hypermobile (≥17°). The ROM histograms also allowed calculation of the average ROM of implanted segments in each of the 3 motion-ranges., Results: Only 762 of 1,173 patients (implanted levels) yielded 24-month postCDA FE-ROM in the physiological mobility range (5°-16°). The proportions ranged from 60% to 79% across the 7 disc-prostheses, with an average of 65.0%±6.2%. Three-hundred and two (302) of 1,173 implanted levels yielded ROM in the 0°-4° range. The proportions ranged from 15% to 38% with an average of 25.7%±8.9%. One-hundred and nine (109) of 1,173 implanted levels yielded ROM of ≥17° with a range of 2%-21% and an average proportion of 9.3%±7.9%. The prosthesis with built-in stiffness due to its nucleus-annulus design yielded the highest proportion (103/131, 79%) of implanted segments in the physiological mobility range, compared to the cohort average of 65% (p<.01). Sixty-five of the 350 (18.6%) discs implanted with the 2 mobile-core designs in this cohort yielded ROM≥17° as compared to the cohort average of 9.3% (109/1,173) (p<.05). At 2-year postCDA, the "hypomobile" segments moved on average 2.4±1.2°, those in the "physiological-mobility" group moved 9.4±3.2°, and the hypermobile segments moved 19.6±2.6°., Conclusions: Prosthesis design significantly influenced the likelihood of achieving FE-ROM in the physiological mobility range, while avoiding hypomobility or hypermobility (p<.01). Postoperative ROM averaged over all study subjects provides incomplete information about the prosthesis performance - it does not tell us how many implanted segments achieve physiological mobility and how many end up with hypomobility or hypermobility. We conclude that the proportion of index levels achieving postCDA motions in the physiological mobility range (5°-16°) is a more useful outcome measure for future clinical trials., Competing Interests: Declaration of competing interest One or more of the authors declare financial or professional relationships on ICMJE-TSJ disclosure forms., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The biomechanical literature describes axial rotation occurring coupled with lateral bending and flexion in the cervical spine. Since the head is kept level during some activities of daily living, we set out to investigate the changes in total and segmental motion that occur when a level gaze constraint is applied to cadaveric cervical spine specimens during axial rotation. 1.5Nm of left and right axial rotation moment was applied to sixteen C2-T1 cadaveric specimens with C2 unconstrained and C2 constrained to simulate level gaze. Overall and segmental motions were determined using optoelectronic motion measurement and specimen-specific kinematic modeling. Without a kinematic constraint on C2, motions were as described in the literature; namely, flexion and lateral bending to the same side as axial rotation. Keeping C2 level reduced that total axial rotation range of motion of the specimens. Changes were also produced in segmental coupled rotation in all specimens. The observed changes included completely opposite coupled motion than in the uncoupled specimens, and traditional coupled behavior at one load extreme and the opposite at the other extreme. Constraining C2 during axial rotation to simulate level gaze can produce coupled motion that differs from the classically described flexion and lateral bending to the same side as axial rotation. Statement of Clinical Significance: Activities of daily living that require the head to be kept level during axial rotation of the cervical spine may produce segmental motions that are quite different from the classically described motions with implications for biomechanical experiments and implant designers., 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., (Published by Elsevier Ltd.)

Background: Soft tissue complications after Achilles tendon repair has led to increased interest in less invasive techniques. Various limited open techniques have gained popularity as an alternative to open operative repair. The purpose of this study was to biomechanically compare an open Krackow and limited open repair for Achilles tendon rupture. We hypothesized that there would be no statistical difference in load to failure, work to failure, and initial linear stiffness., Methods: A simulated Achilles tendon rupture was created 4 cm proximal to its insertion in 18 fresh-frozen cadaveric below-knee lower limbs. Specimens were randomized to open or limited open PARS Achilles Jig System repair. Repairs were loaded to failure at a rate of 25.4 mm/s to reflect loading during normal ankle range of motion. Load to failure, work to failure, and initial linear stiffness were compared between the 2 repair types., Results: The average load to failure (353.8 ± 88.8 N vs 313.3 ± 99.9 N; P = .38) and work to failure (6.4 ± 2.3 J vs 6.3 ± 3.5 J; P = .904) were not statistically different for Krackow and PARS repair, respectively. Mean initial linear stiffness of the Krackow repair (17.8 ± 5.4 N/mm) was significantly greater than PARS repair (11.8 ± 2.5 N/mm) ( P = .011)., Conclusion: No significant difference in repair strength was seen, but higher initial linear stiffness for Krackow repair suggests superior resistance to gap formation, which may occur during postoperative rehabilitation. With equal repair strength, but less soft tissue devitalization, the PARS may be a favorable option for patients with risk factors for soft tissue complications., Competing Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s) 2023.)

Background: We examined the effect of Kirschner wire (K-wire) reuse and use of oscillating mode on heat generation within cortical bone., Methods: Two trocar-tipped K-wires were drilled through the diaphysis of each of 30 human metacarpals and phalanges: one K-wire was inserted in rotary mode and another in oscillating mode. Each wire was reused once. Thermocouples placed within the dorsal and volar bone adjacent to the K-wire drill path measured temperatures throughout each test., Results: Peak cortex temperatures were 25°C to 164°C. Rotary drilling achieves peak temperatures quicker (31 ± 78 seconds vs 44 ± 78 seconds, P = .19) than oscillating drilling, but insertion time is also less, resulting in lower overall heat exposure. This effect is also seen when the K-wire is reused (34 ± 70 seconds vs 41 ± 85 seconds, P = .4). The length of time that cortical bone was exposed to critical temperatures (47°C or more) was significantly higher when a wire was reused (36 ± 72 seconds vs 43 ± 82 seconds, P = .008). Peak temperatures greater than 70°C (a temperature associated with instantaneous cell death) were observed on many occasions., Conclusions: Overall heat exposure may be higher if a K-wire is reused or inserted in oscillating mode. In the absence of external cooling, K-wire insertion into cortical bone can easily expose bone to temperatures that exceed 70°C and may increase the risk of osteonecrosis.

Background: Powered instrumentation is often used for bone preparation and/or removal in many orthopaedic procedures but does risk thermogenesis. This study compares biomechanical properties of a fluted burr and a novel fluteless resurfacing tool., Methods: Twenty cadaveric metatarsals were tested with four predetermined cutting forces to evaluate heat generation and cutting rate for the fluted burr and fluteless resurfacing tool over 40 s or until a depth of 4 mm was reached. Cutting rate was calculated from displacement transducer data. Heat generation was measured by thermocouples placed in the bone adjacent to the burring site. Assuming a body temperature of 37 °C, a 10 °C increase in heat was used as the threshold of inducing osteonecrosis., Findings: At 1.0 N and 1.7 N, the thermal osteonecrosis threshold was reached at comparable times between burrs, while the bone removed by the resurfacing tool was on average five times greater than fluted burr at 1.0 N and over twice as great at 1.7 N. Statistical analysis of these common cutting forces showed the resurfacing tool had significantly higher cutting rates (P < 0.01). As a result, the fluted burr produced higher temperatures for the same amount of bone removal (P < 0.01)., Interpretation: In a cadaveric study, the fluteless resurfacing tool demonstrated higher bone cutting rates and lower heat generation for the same amount of bone removed than a traditional fluted burr., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Adam Schiff reports a relationship with DJO Global Inc. that includes: consulting or advisory. Adam Schiff reports a relationship with RTI Surgical Inc. that includes: consulting or advisory. Adam Schiff reports a relationship with Stryker Corp that includes: consulting or advisory. Avinash Patwardhan reports a relationship with DePuy Orthopedics Inc. that includes: non-financial support. Avinash Patwardhan reports a relationship with Medtronic that includes: non-financial support. Avinash Patwardhan reports a relationship with Orthofix Inc. that includes: consulting or advisory. Avinash Patwardhan reports a relationship with Stryker that includes: non-financial support., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Background: The goal was to determine the effect of addition of oblique trajectory distal interlock screws to a retrograde intramedullary femoral nail on implant stability (stiffness), cycles to failure and mode of failure. The hypothesis was that addition of oblique screws would increase implant stability and number of loading cycles to failure., Methods: Eight matched pairs were tested; one femur implanted with a femoral nail with only transverse distal interlock screws and the other with transverse and oblique interlock screws. Axial compressive load was applied to the femoral head and the gluteal tendon was tensioned vertically to simulate standing or at 45° to the sagittal plane to simulate stair climbing. Loads were cycled to increasing amplitude until failure of fixation (10 mm displacement or 10° rotation)., Findings: In simulated standing, oblique screw specimen had greater sagittal bending (bowing) than transverse only specimen. Transverse (axial) plane motion was higher in simulated stair climbing in oblique screw specimen. Oblique screw specimen had higher sagittal plane translation at 600 N of load. At 300 N, oblique screw specimen had lower internal-external rotation than transverse only specimen. A larger number of cycles to failure were observed in four oblique screw of seven paired specimen. Failure (10 mm or 10 degrees of motion) was only achieved during simulated stair climbing., Interpretation: Our hypothesis that adding oblique screws improves fixation was rejected. Activities of daily living other than standing may constitute a challenge to fracture fixation; fixation failure occurred at lower loads in simulated stair climbing than standing., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Muturi Muriuki reports financial support and equipment, drugs, or supplies were provided by Zimmer Biomet., (Published by Elsevier Ltd.)

Study Design: This was a preclinical study., Objective: Evaluate sex-dependent differences in the bone healing response to recombinant human bone morphogenetic protein-2 (rhBMP-2) in a rat posterolateral spinal fusion model., Summary of Background Data: Minimal and conflicting data exist concerning potential sex-dependent differences in rhBMP-2-mediated bone regeneration in the context of spinal fusion., Materials and Methods: Forty-eight female and male Sprague-Dawley rats (N=24/group), underwent L4-L5 posterolateral fusion with bilateral placement of an absorbable collagen sponge, each loaded with 5 µg of bone morphogenetic protein-2 (10 µg/animal). At eight weeks postoperative, 10 specimens of each sex were tested in flexion-extension with quantification of range of motion and stiffness. The remaining specimens were evaluated for new bone growth and successful fusion via radiography, blinded manual palpation and microcomputed tomography (microCT). Laboratory microCT quantified bone microarchitecture, and synchrotron microCT examined bone microstructure at the 1 µm level., Results: Manual palpation scores differed significantly between sexes, with mean fusion scores of 2.4±0.4 in females versus 3.1±0.6 in males ( P <0.001). Biomechanical stiffness did not differ between sexes, but range of motion was significantly greater and more variable for females versus males (3.7±5.6° vs. 0.27±0.15°, P <0.005, respectively). Laboratory microCT showed significantly smaller volumes of fusion masses in females versus males (262±87 vs. 732±238 mm 3 , respectively, P <0.001) but significantly higher bone volume fraction (0.27±0.08 vs. 0.12±0.05, respectively, P <0.001). Mean trabecular thickness was not different, but trabecular number was significantly greater in females (3.1±0.5 vs. 1.5±0.4 mm -1 , respectively, P <0.001). Synchrotron microCT showed fine bone structures developing in both sexes at the eight-week time point., Conclusions: This study demonstrates sex-dependent differences in bone regeneration induced by rhBMP-2. Further investigation is needed to uncover the extent of and mechanisms underlying these sex differences, particularly at different doses of rhBMP-2., Competing Interests: The authors report no conflicts of interest., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Background: The theoretical advantages of hybrid constructs over multi-level fusion have been illustrated in clinical and biomechanical studies. However, there is no biomechanical data on hybrid constructs using load control analyses. There is also no clear data on whether there is a biomechanical difference if the arthroplasty is below or above a 1- or 2-level fusion. This work investigated the effect on segmental motion of having a cervical total disc arthroplasty implanted above or below a 1- or 2-level fusion., Methods: Segmental motions of 16 C2-T1 cervical spine specimens were measured as the specimens were tested to 1.5Nm in axial rotation and in flexion-extension under compressive preload. Tests were conducted on intact specimens, and then after arthroplasty with a 1-level and 2-level fusion. 8 specimens were in test Group 1, where the hybrid configuration had a total disc arthroplasty above a 1- or 2-level fusion. The arthroplasty was below the 1- and 2-level fusion in Group 2. Load control and displacement control analyses were conducted to determine the effect of the hybrid configurations on segmental motion., Results: In load control, compensatory motion increases were found at all non-instrumented cervical spine segments in flexion-extension and axial rotation. Flexion-extension and axial rotation ranges of motion at the total disc arthroplasty level were less than 1° different than intact.In displacement control, there was no consistent pattern of compensatory motion. Range of motion at the arthroplasty level was within 3.5° of intact., Conclusions: The total disc arthroplasty segmental level in a hybrid construct has similar amounts of motion as intact. This may shield the arthroplasty level and adjacent levels from supra-physiological motion and loading. These results suggest that a hybrid construct may be protective of adjacent segments, whether the total disc arthroplasty is above or below the fusion., Competing Interests: 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.

Introduction: Suboptimal acetabular component position can result in impingement, dislocation, and accelerated wear. Intraoperative pelvic motion has led to surgeon error and acetabular cup malposition. This study characterises the relationship between pelvic rotation and postoperative acetabular cup orientation., Methods: A device was constructed to allow cadaveric pelvis rotation along three axes about an acetabular cup in fixed orientation. The acetabular cup was fixed in space at 40° of radiographic inclination and 15° of anteversion relative to the anterior pelvic plane to represent consistent surgeon intraoperative placement. Active marker clusters were fixed to surgical equipment while the cadaveric pelvis was cemented with passive reflective markers, both identified with the Optotrak Certus motion capture system. The reamed cadaveric pelvis was rotated along three axes from -45° to 45° of roll, -30° to 30° of tilt, and -35° to 35° of pitch. The change in component inclination and anteversion was recorded at each 5° interval. Using computed tomography 3D reconstruction, the experimental setup was duplicated computationally to assess against a greater range of pelvis and implant sizes., Results: Radiographic anteversion and inclination showed a non-linear relationship dependent on pelvic roll, tilt, and pitch. Radiographic anteversion changed -0.59°, 0.76° and 0.01° while radiographic inclination changed 0.23°, 0.18° and 1.00° for every 1° of pelvic roll, tilt and pitch, respectively. Computationally, anteversion changed -0.61°, 0.75° and 0.00° while inclination changed 0.22°, 0.19° and 1.00° for every 1° of pelvic roll, tilt and pitch, respectively. These results were independent of cup and pelvis size., Conclusions: Intraoperative pelvic motion can significantly affect final cup position, and this should be accounted for when placing acetabular components during total hip arthroplasty. Based on this study, intraoperative adjustment of the acetabular component position based on pelvis motion may be implemented to improve postoperative component position.

Prosthesis design has an influence on the quantity and quality of postoperative motion after cervical disc arthroplasty. Prostheses with built-in resistance to angular and translational motion may have an advantage in restoring physiologic motion. The ability of a prosthesis to work with remaining bony and soft tissues to restore motion and load-sharing is a function of the kinematic degrees of freedom DOF, axis of rotation for a given motion, and device stiffness. How these characteristics allow the prosthesis to work with the patient's anatomy will determine whether the prosthesis is successful at restoring motion and mitigating adjacent-level stresses., Competing Interests: Disclosures and conflict of interest A.G. Patwardhan: Consultant to Orthofix Medical Inc., Lewisville, TX, USA. Institutional research funds were received from Stryker (Kalamazoo, MI, USA), DePuy Synthes (Raynham, MA, USA), Orthofix Medical (Lewisville, TX, USA) and Medtronic (Memphis, TN, USA). R.M. Havey: Nothing to disclose., (Published by Elsevier Inc.)

Alzheimer's disease is a chronic lifestyle ailment whose occurrence has come to light with the increasing life expectancy due to better healthcare. The patient burden for AD is set to double by the year 2060 and advancement in research is of utmost importance to combat this problem. AD is characterized by the pathological hallmarks of amyloid plaques and neurofibrillary tangles. The disease has been implicated to have a genetic predisposition. The current treatment strategies are at best ameliorative in nature and offer no substantive cure. Immunotherapeutic approaches employed have shown few therapeutic benefits but the accelerated approval of aducanumab by the US-FDA shows clinical benefit merit. In addition, newer therapeutic approaches are the need of the hour. This review aims to highlight the pathology of the disease, followed by an insight into newer approaches like stem cell therapy and gene editing, focusing on possible CRISPR mediated targets., (Copyright © 2021 Elsevier Inc. All rights reserved.)

We recently developed a recombinant growth factor-free bone regenerative scaffold composed of stoichiometric hydroxyapatite (HA) ceramic particles and human demineralized bone matrix (DBM) particles (HA-DBM). Here, we performed the first pre-clinical comparative evaluation of HA-DBM relative to the industry standard and established positive control, recombinant human bone morphogenetic protein-2 (rhBMP-2), using a rat posterolateral spinal fusion model (PLF). Female Sprague-Dawley rats underwent bilateral L4-L5 PLF with implantation of the HA-DBM scaffold or rhBMP-2. Fusion was evaluated using radiography and blinded manual palpation, while biomechanical testing quantified the segmental flexion-extension range-of-motion (ROM) and stiffness of the fused segments at 8-weeks postoperatively. For mechanistic studies, pro-osteogenic gene and protein expression at 2-days and 1-, 2-, and 8-weeks postoperatively was assessed with another cohort. Unilateral fusion rates did not differ between the HA-DBM (93%) and rhBMP-2 (100%) groups; however, fusion scores were higher with rhBMP-2 (p = 0.008). Both treatments resulted in significantly reduced segmental ROM (p < 0.001) and greater stiffness (p = 0.009) when compared with non-operated controls; however, the degree of stabilization was significantly higher with rhBMP-2 treatment relative to the HA-DBM scaffold. In the mechanistic studies, PLGA and HA scaffolds were used as negative controls. Both rhBMP-2 and HA-DBM treatments resulted in significant elevations of several osteogenesis-associated genes, including Runx2, Osx, and Alp. The rhBMP-2 treatment led to significantly greater early, mid, and late osteogenic markers, which may be the mechanism in which early clinical complications are seen. The HA-DBM scaffold also induced osteogenic gene expression, but primarily at the 2-week postoperative timepoint. Overall, our findings show promise for this 3D-printed composite as a recombinant growth factor-free bone graft substitute for spinal fusion. STATEMENT OF SIGNIFICANCE: Despite current developments in bone graft technology, there remains a significant void in adequate materials for bone regeneration in clinical applications. Two of the most efficacious bone graft options are the gold-standard iliac crest bone graft and recombinant human-derived bone morphogenetic protein-2 (rhBMP-2), available commercially as Infuse™. Although efficacious, autologous graft is associated with donor-site morbidity, and Infuse™ has known side effects related to its substantial host inflammatory response, possibly associated with a immediate, robust osteoinductive response. Hence, there is a need for a bone graft substitute that provides adequate osteogenesis without associated adverse events. This study represents a significant step in the design of off-the-shelf growth factor-free devices for spine fusion., Competing Interests: Declaration of Competing Interest M.A.P., S.M., J.G.L., A.G., D.E., M.H., J.Y., S.J., C.Y., K.R.B., R.M.H., M.M., A.G.P., W.K.H., S.R.S., and E.L.H. have nothing to disclose that may create a conflict of interest within this body of work. A.E.J. and R.N.S. are cofounders of the company Dimension Inx, LLC – which aims to create biomaterials, including 3D-printed biologically active materials, that induce tissue regeneration and repair – including some of the materials discussed in this paper. As of October 2020, A.E.J. is the Chief Technology Officer (CTO) and R.N.S. is the Chief Science Officer (CSO) of Dimension Inx, LLC. The trademark for Hyperelastic Bone® is owned by Dimension Inx. The study design, reporting of data, and interpretation of data in this body of work was not influenced by the interests of Dimension Inx LLC., (Copyright © 2021. Published by Elsevier Ltd.)

Background Context: Transition from standing to sitting significantly decreases lumbar lordosis with the greatest lordosis-loss occurring at L4-S1. Fusing L4-S1 eliminates motion and thus the proximal mobile segments maybe recruited during transition from standing to sitting to compensate for the loss of L4-S1 mobility. This may subject proximal segments to supra-physiologic flexion loading., Purpose: Assess effects of instrumented fusion versus motion preservation at L4-L5 and L5-S1 on lumbar spine loads and proximal segment motions during transition from standing to sitting., Study Design: Biomechanical study using human thoracolumbar spine specimens., Methods: A novel laboratory model was used to simulate lumbosacral alignment changes caused by a person's transition from standing to sitting in eight T10-sacrum spine specimens. The sacrum was tilted in the sagittal plane while constraining anterior-posterior translation of T10. Continuous loading-data and segmental motion-data were collected over a range of sacral slope values, which represented transition from standing to different sitting postures. We compared different constructs involving fusions and motion preserving prostheses across L4-S1., Results: After L4-S1 fusion, the sacrum could not be tilted as far posteriorly compared to the intact spine for the same applied moment (p<.001). For the same reduction in sacral slope, L4-S1 fusion induced 2.9 times the flexion moment in the lumbar spine and required 2.4 times the flexion motion of the proximal segments as the intact condition (p<.001). Conversely, motion preservation at L4-S1 restored lumbar spine loads and proximal segment motions to intact specimen levels during transition from standing to sitting., Conclusions: In general, sitting requires lower lumbar segments to undergo flexion, thereby increasing load on the lumbar disks. L4-S1 fusion induced greater moments and increased flexion of proximal segments to attain a comparable seated posture. Motion preservation using a total joint replacement prosthesis at L4-S1 restored the lumbar spine loads and proximal segment motion to intact specimen levels during transition from standing to sitting., Clinical Significance: After L4-S1 fusion, increased proximal segment loading during sitting may cause discomfort in some patients and may lead to junctional breakdown over time. Preserving motion at L4-S1 may improve patient comfort and function during activities of daily living, and potentially decrease the need for adjacent level surgery., (Copyright © 2020. Published by Elsevier Inc.)

Introduction: We investigated a new metric for assessing the quality of motion of the cervical segments over the arc of extension-to-flexion motion after cervical disc arthroplasty (CDA). We quantified: (1) the amount of motion contributed by individual spinal segments to the total cervical spine motion, termed segmental motion fraction, and its variation throughout the arc of extension-to-flexion motion and (2) how cervical disc arthroplasty using two distinct prosthesis designs may influence the segmental motion contributions., Materials and Methods: We tested 16 human C3-T1 spine specimens under physiologic loads; first intact, after CDA at C5-C6, and then at C5-C6 and C6-C7. The M6-C (Orthofix, USA) and Mobi-C (Zimmer, USA) disc prostheses were used in eight specimens each., Results and Conclusions: The designs of the cervical disc prostheses tested significantly influenced the variation in segmental motion fraction as the spine underwent motion between the endpoints of extension and flexion. While the mean segmental motion contribution to the total cervical motion was not influenced by prosthesis design, the way the motion took place between the extension and flexion endpoints was significantly influenced. The M6-C artificial disc restored physiologic motion quality such that implanted segments continued to function in harmony with other segments of the cervical spine as measured before arthroplasty. Conversely, the Mobi-C prosthesis, while maintaining average motion contributions similar to the pre-implantation values, demonstrated large deviations in motion contribution over the extension-to-flexion arc motion in ten of 16 implanted segments. Such non-physiologic implant kinematics could cause excessive prosthesis wear and motion and stress shielding at adjacent segments. These slides can be retrieved under Electronic Supplementary Material.

Low back pain (LBP), the leading cause of disability worldwide, remains one of the most common and challenging problems in occupational musculoskeletal disorders. The effective assessment of LBP injury risk, and the design of appropriate treatment modalities and rehabilitation protocols, require accurate estimation of the mechanical spinal loads during different activities. This study aimed to: (1) develop a novel 2D beam-column finite element control-based model of the lumbar spine and compare its predictions for muscle forces and spinal loads to those resulting from a geometrically matched equilibrium-based model; (2) test, using the foregoing control-based finite element model, the validity of the follower load (FL) concept suggested in the geometrically matched model; and (3) investigate the effect of change in the magnitude of the external load on trunk muscle activation patterns. A simple 2D continuous beam-column model of the human lumbar spine, incorporating five pairs of Hill's muscle models, was developed in the frontal plane. Bio-inspired fuzzy neuro-controllers were used to maintain a laterally bent posture under five different external loading conditions. Muscle forces were assigned based on minimizing the kinematic error between target and actual postures, while imposing a penalty on muscular activation levels. As compared to the geometrically matched model, our control-based model predicted similar patterns for muscle forces, but at considerably lower values. Moreover, irrespective of the external loading conditions, a near (<3°) optimal FL on the spine was generated by the control-based predicted muscle forces. The variation of the muscle forces with the magnitude of the external load within the simulated range at the L1 level was found linear. This work presents a novel methodology, based on a bio-inspired control strategy, that can be used to estimate trunk muscle forces for various clinical and occupational applications toward shedding light on the ever-elusive LBP etiology., (Copyright © 2020 Sharifzadeh-Kermani, Arjmand, Vossoughi, Shirazi-Adl, Patwardhan, Parnianpour and Khalaf.)

Background: Conditions requiring cervical decompression and stabilization are commonly treated using anterior cervical discectomy and fusion using an anterior cage-plate construct. Anterior zero profile integrated cages are an alternative to a cage-plate construct, but literature suggests they may result in less motion reduction. Interfacet cages may improve integrated cage stability. This study evaluated the motion reduction of integrated cages with and without supplemental interfacet fixation. Motion reduction of integrated cages were also compared to published cage-plate results., Methods: Seven cadaveric (C2-T1) spines were tested in flexion-extension, lateral bending, and rotation. Specimens were tested: 1) intact, 2) C6-C7 integrated cage, 3) C6-C7 integrated cage + interfacet cages, 4) additional integrated cages at C3-C4 and C4-C5, 5) C3-C4, C4-C5 and C6-C7 integrated cages + interfacet cages. Motion, lordosis, disc and neuroforaminal height were assessed., Findings: Integrated cage at C6-C7 decreased flexion-extension by 37% (P = .06) and C3-C5 by 54% (P < .01). Integrated + interfacet cages decreased motion by 89% and 86% compared to intact (P < .05). Integrated cages increased lordosis at C4-C5 and C6-C7 (P < .01). Integrated + interfacet cages returned C3-C5 lordosis to intact values, while C6-C7 remained more lordotic (P = .02). Compared to intact, neuroforaminal height increased after integrated cages at C3-C5 (P ≤ .01) and at all levels after interfacet cages (P < .01)., Interpretation: Anterior integrated cages provides less stability than traditional cage-plate constructs while supplemental interfacet cages improve stabilization. Integrated cages provide more lordosis at caudal levels and increase neuroforaminal height more at cranial levels. After interfacet cages, posterior disc height and neuroforaminal height increased more at the caudal segments., Competing Interests: Declaration of Competing Interest The authors do not have a financial relationship with the industry research sponsor. The first and last authors have full control of all data., (Published by Elsevier Ltd.)

Activities of daily living require the subaxial cervical spine (C2-C7) to have substantial mobility. Cervical degenerative changes can cause abnormal motions and altered load distribution, leading to pain and limiting the ability of individuals to perform activities of daily living. Anterior cervical discectomy and fusion (ACDF) has been widely used to treat symptomatic cervical spondylosis. Clinical studies have shown cervical disc arthroplasty (CDA) to be a viable alternative to ACDF for the treatment of radiculopathy and myelopathy. The benefits of CDA are based on the premise that preservation of physiologic motions and load-sharing at the treated level would lead to longevity of the index-level facet joints and mitigate the risk of adjacent segment degeneration.This review article classifies cervical disc prostheses according to their kinematic degrees of freedom and device constraints. Discussion on how these design features may affect cervical motion after implantation will provide the reader with valuable information on how disc prostheses may function clinically.The ability of a disc prosthesis to work in concert with remaining bony and soft tissue structures to restore physiologic motion and load-sharing is a function of the following design features and surgical factors: Kinematic degrees of freedom-Prostheses that allow translation independent of rotation allow, in theory, the spinal anatomy to dictate segmental motion after CDA potentially restoring physiologic motion and load-sharing. A 6-degrees-of-freedom disc prosthesis may be best equipped to achieve the intended function of CDA.Built-in stiffness-A disc prosthesis with built-in resistance to angular and translational motion may have an advantage in restoring stability to a hypermobile segment without eliminating motion.Surgical factors related to prosthesis implantation may influence cervical segments after CDA. These factors include the amount of disc space distraction caused by the prosthesis, prosthesis placement in the sagittal and coronal planes, and integrity of the soft tissue envelope., (This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2020 ISASS.)

Objective: The authors conducted a study to determine whether a change in T1 tilt results in a compensatory change in the cervical sagittal vertical axis (SVA) in a cadaveric spine model., Methods: Six fresh-frozen cadavers (occiput [C0]-T1) were cleaned of soft tissue and mounted on a customized test apparatus. A 5-kg mass was applied to simulate head weight. Infrared fiducials were used to track segmental motion. The occiput was constrained to maintain horizontal gaze, and the mounting platform was angled to change T1 tilt. The SVA was altered by translating the upper (occipital) platform in the anterior-posterior plane. Neutral SVA was defined by the lowest flexion-extension moment at T1 and recorded for each T1 tilt. Lordosis was measured at C0-C2, C2-7, and C0-C7., Results: Neutral SVA was positively correlated with T1 tilt in all specimens. After increasing T1 tilt by a mean of 8.3° ± 2.2°, neutral SVA increased by 27.3 ± 18.6 mm. When T1 tilt was reduced by 6.7° ± 1.4°, neutral SVA decreased by a mean of 26.1 ± 17.6 mm.When T1 tilt was increased, overall (C0-C7) lordosis at the neutral SVA increased from 23.1° ± 2.6° to 32.2° ± 4.4° (p < 0.01). When the T1 tilt decreased, C0-C7 lordosis at the neutral SVA decreased to 15.6° ± 3.1° (p < 0.01). C0-C2 lordosis increased from 12.9° ± 9.3° to 29.1° ± 5.0° with increased T1 tilt and decreased to -4.3° ± 6.8° with decreased T1 tilt (p = 0.047 and p = 0.041, respectively)., Conclusions: Neutral SVA is not a fixed property but, rather, is positively correlated with T1 tilt in all specimens. Overall lordosis and C0-C2 lordosis increased when T1 tilt was increased from baseline, and vice versa.

Study Design: Rat posterolateral arthrodesis model., Objective: Quantify the impact of administration of a proton pump inhibitor on spine fusion., Summary of Background Data: Proton pump inhibitors (PPIs) are widely used for gastrointestinal disorders and for ulcer prophylaxis in patients taking non-steroidal anti-inflammatory drugs. PPIs cause chronic acid suppression which has been found to result in decreased bone mineral density, increased fracture risk, and impaired fracture healing. Despite advances in surgical techniques, pseudarthrosis still occurs in up to 24% of patients requiring revision surgery following spinal fusion procedures. Thus, there are likely many unidentified risk factors. While PPIs have been hypothesized to impact fracture healing, no study has evaluated their effect on spine arthrodesis rates., Methods: Thirty-eight female rats underwent posterolateral lumbar spinal fusion. Rats were divided into two groups: normal saline control and pantroprazole, which was administered by daily intraperitoneal injections. At 8 weeks postoperative spines were evaluated with manual palpation, microCT, histologic analysis, and biomechanical testing., Results: Fusion rates of the control group and PPI group were not significantly different (100% vs. 94%). Average fusion scores were significantly lower in the pantoprazole group. New bone formation identified on microCT imaging of bilaterally fused specimens demonstrated a lower average volume of newly generated bone in the PPI group, but this difference was not significant. Biomechanical testing demonstrated no significant difference in strength or stiffness of the fusion mass between the groups., Conclusion: This study demonstrates that administration of PPIs does not inhibit fusion rates, bone formation, or affect biomechanical integrity of fusion. However, lower fusion scores in the PPI group suggest that a negative impact may still exist. Future studies will explore growth factor and protein expression in the fusion masses as well as utilize higher doses of PPI to fully discern their effect on spine fusion., Level of Evidence: N/A.

Chronic Forward Head Posture is associated with headaches, neck pain, and disability, though few studies have investigated the effects it has on the suboccipital triangle. The objective of this study was to quantitatively assess whether the biomechanical changes in the suboccipital triangle help explain the clinical manifestations of Forward Head Posture. Specifically, this study aimed to identify whether the Greater Occipital Nerve or C2 nerve root may be compressed in Forward Head Posture. Three-dimensional, specimen-specific computer models were rendered from thirteen cadaveric cervical spine specimens. The spines transitioned from neutral to Forward head posture while motion data was collected. This data was synced with the computer models to make precise measurements. In Forward Head Posture, occiput-C1, C1-C2, and occiput-C2 segments extended by 10.7 ± 4.6 deg, 4.6 ± 4.3 deg, and 15.3 ± 2.3 deg, respectively. The Rectus Capitis Posterior Major and Minor and Obliquus Capitis Superior muscles shortened by 20.0 ± 4.6%, 15.0 ± 7.6%, and 6.6 ± 3.3%, respectively. The Obliquus Capitis muscle inferior length did not change. The suboccipital triangle area decreased by 18.7 ± 6.4%, but the protective gaps surrounding the C2 nerve root and the Greater Occipital Nerve did not reveal clinically significant impingement. The C2 nerve root gap decreased by 1.0 ± 1.3 mm and the Greater Occipital Nerve gap by 0.2 ± 0.18 mm. These results demonstrate that the C2 nerve root and the Greater Occipital Nerve are protected by the bony landscape of the cervical spine. However, there is likely persistent contraction of the rectus muscles in Forward Head Posture, which suggests a secondary tension-type etiology of the associated headache., (Copyright © 2019. Published by Elsevier Ltd.)

Background: Cervical fusion is associated with adjacent segment degeneration. Cervical disc arthroplasty is considered an alternative to reduce risk of adjacent segment disease. Kinematics after arthroplasty should closely replicate healthy in vivo kinematics to reduce adjacent segment stresses. The purpose of this study was to assess the kinematics of a polycrystalline diamond cervical disc prosthesis., Methods: Nine cadaveric C3-T1 spines were tested intact and after one (C5-C6) and two level (C5-C7) arthroplasty (Triadyme-C, Dymicron Inc., Orem, UT, USA). Kinematics were evaluated in flexion-extension, lateral bending, and axial rotation., Findings: Prosthesis placement at C5-C6 and C6-C7 was 0.5 mm anterior and 0.6 mm posterior to midline respectively. C5-C6 flexion-extension motion was 12.8° intact and 10.5° after arthroplasty. C6-C7 flexion-extension motion was 10.0 and 11.4° after arthroplasty. C5-C6 lateral bending reduced from 8.5 to 3.7° after arthroplasty and at C6-C7 from 7.5 to 5.1°. C5-C6 axial rotation decreased from 10.4 to 6.2° after arthroplasty and at C6-C7 from 7.8 to 5.3°. Segmental lordosis increased by 4.2°, and middle disc height by 1.4 mm after arthroplasty. Change in center of rotation from intact to arthroplasty averaged 0.9 mm posteriorly and 0.1 mm caudally at C5-C6, and 1.4 mm posteriorly and 0.3 mm cranially at C6-C7., Interpretation: The cervical disc arthroplasty evaluated restored flexion-extension motion to intact levels and moderately increased segmental stiffness. Disc height increased by up to 1.5 mm and segmental lordosis by 4.2°. The unique prosthesis design allowed the axis of rotation after arthroplasty to closely mimic the native location., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Introduction: Anterior cervical discectomy and fusion has been associated with the development of adjacent segment degeneration (ASD), with clinical incidence of approximately 3% per year. Cervical total disc arthroplasty (TDA) has been proposed as an alternative to prevent ASD., Hypotheses: TDA in optimal placement using an elastic-core cervical disc (RHINE, K2M Inc., Leesburg, Virginia) will replicate natural kinematics and will improve with optimal vs anterior placement., Methods: Seven C3-T1 cervical cadaver spines were tested intact first, then after one-level TDA at C5-C6 anterior placement, after TDA at C5-C6 optimal placement, after two-level TDA at C5-C6 and C6-C7 optimal placement, and finally after two-level TDA at C5-C6 lateral placement and C6-C7 optimal placement. The specimens were subjected to: Flexion-Extension moments (+1.5 Nm) with compressive preloads of 0 N and 150 N, lateral bending (LB) and axial rotation (AR) (+1.5 Nm) without preload., Results: C5-C6 TDA in optimal placement resulted in a non-significant increase in flexion-extension ROM compared to intact under 0 N and 150 N preload ( P  > 0.05). Both LB and AR ROM decreased with arthroplasty ( P  < 0.01). O ptimal placement of C6-C7 TDA resulted in an increase in flexion-extension ROM with preload compared to intact ( P  < 0.05) while LB and AR ROM decreased with arthroplasty ( P  < 0.01)., Conclusion: This six degree of freedom elastic-core disc arthroplasty effectively restored flexion-extension motion to intact levels. In LB the TDA maintained 42% ROM at C5-C6 and 60% at C6-C7. In AR 57% of the ROM was maintained at C5-C6 and 70% at C6-C7. These findings are supported by literature which shows cervical TDA results in restoration of approximately 50% ROM in LB and AR, which is a multifactorial phenomenon encompassing TDA design parameters and anatomical constraints. Anterior placement of this viscoelastic TDA device shows motion restoration similar to optimal placement suggesting its design may be less sensitive to suboptimal placement., Competing Interests: R.D.G., MD: Royalties: Alphatec; Stock Ownership: Spinal Motion; Private Investments: Spinal Ventures; Consulting: DePuy Synthes; Speaking and/or teaching arrangements: Synthes; Scientific Advisory Board: K2M, Spinal Kinetics (Stock options), Nanovis, Crocker Technologies, MiMedx; Fellowship Support: OREF (Amount not disclosed, Paid directly to institution/employer), Medtronic Neurological Division (Paid directly to institution/employer). L.I.V., MD, PhD: Nothing to disclose. R.M.H., MS: Nothing to disclose. S.K., PhD: Nothing to disclose. G.C., MS: Nothing to disclose. K.R.B., MS, MHA: Nothing to disclose. S.W., BS: Nothing to disclose. J.R., BS: Employee of K2M Inc. N.P., BS: Employee of K2M Inc. A.G.P.: Funding support from K2M (Paid directly to Institution).

Background: A novel expandable lumbar interbody fusion cage has been developed which allows for a broad endplate footprint similar to an anterior lumbar interbody fusion; however, it is deployed from a minimally invasive transforaminal unilateral approach. The perceived benefit is a stable circumferential fusion from a single approach that maintains the anterior tension band of the anterior longitudinal ligament. The purpose of this biomechanics laboratory study was to evaluate the biomechanical stability of an expandable lumbar interbody cage inserted using a transforaminal approach and deployed in situ compared to a traditional lumbar interbody cage inserted using an anterior approach (control device)., Methods: Twelve cadaveric spine specimens (L1-5) were tested intact and after implantation of both the control and experimental devices in 2 (L2-3 and L3-4) segments of each specimen; the assignments of the control and experimental devices to these segments were alternated. Effect of supplemental pedicle screw-rod stabilization was also assessed. Moments were applied to the specimens in flexionextension (FE), lateral bending (LB), and axial rotation (AR). The effect of physiologic preload on construct stability was evaluated in FE. Segmental motions were measured using an optoelectronic motion measurement system., Results: The deployable expendable transforaminal lumbar interbody fusion (TLIF) cage and control devices significantly reduced FE motion with and without compressive preload when compared to the intact condition ( P < .05). Segmental motions in LB and AR were also significantly reduced with both devices ( P < .05). Under no preload, the deployable expendable TLIF cage construct resulted in significantly smaller FE motion compared to the control cage construct ( P < .01). Under all other testing modes (FE under 400N preload, LB, and AR), the postoperative motions of the 2 constructs did not differ statistically ( P > .05). Adding bilateral pedicle screws resulted in further reduction of range of motion for all loading modes compared to intact condition, with no statistical difference between the 2 constructs ( P > .05)., Conclusions: The ability of the deployable expendable interbody cage in reducing segmental motions was equivalent to the control cage when used as a standalone construct and also when supplemented with bilateral pedicle screw-rod instrumentation. The larger footprint of the fully deployed TLIF cage combined with preservation of the anterior soft-tissue tension band may provide a better biomechanical fusion environment by combining the advantages of the traditional anterior lumbar interbody fusion and TLIF approaches., Competing Interests: Disclosures and COI: The authors received no funding for this study and report no conflicts of interest.

Background: The need for posterior longitudinal ligament (PLL) resection during cervical total disc arthroplasty (TDA) has been debated. The purpose of this laboratory study was to investigate the effect of PLL resection on cervical kinematics after TDA., Methods: Eight cadaveric cervical spine specimens were tested in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) to moments of ±1.5 Nm. After testing the intact condition, anterior C5-C6 cervical discectomy was performed followed by PLL resection and implantation of a compressible, 6-degrees-of-freedom disc prosthesis (M6-C, Spinal Kinetics Inc, Sunnyvale, California). Next, a second prosthesis was implanted at C6-C7 with PLL intact. Finally, the C6-C7 PLL was resected while the disc prosthesis remained in place. Segmental range of motion (ROM) and stiffness in the high flexibility zone around the neutral posture were analyzed using repeated measures ANOVA., Results: At C5-C6, following TDA and PLL resection, FE, LB, and AR ROMs decreased significantly. Anterior and posterior disc height, segmental lordosis, and flexion stiffness increased significantly. At C6-C7, TDA with the PLL intact resulted in a significant increase in anterior disc height and segmental lordosis with no change in posterior disc height. FE, LB, and AR ROMs all decreased significantly, while flexion stiffness increased significantly compared to intact. PLL resection at C6-C7 did not result in a notable change compared to TDA with PLL intact. At the same level, flexion stiffness decreased following PLL resection compared to TDA with a value closer to intact. Two-level TDA (C5-C7) with PLL resection did not result in a loss of segmental stability., Conclusion: PLL resection did not significantly affect motion segment kinematics following cervical TDA using a prosthesis with inherent stiffness. Motion segment stiffness loss after PLL resection can be compensated for by a TDA design that can provide resistance to angular motion., Competing Interests: Disclosures and COI: This study was supported by funds from the Department of Veterans Affairs, Washington, DC, and Spinal Kinetics Inc, Sunnyvale, CA.

Purpose: In this article, we summarize our work on understanding the influence of cervical sagittal malalignment on the mechanics of the cervical spine., Methods: Biomechanical studies were performed using an ex vivo laboratory model to study the kinematic and kinetic response of human cervical spine specimens in the setting of cervical sagittal imbalance. The model allowed controlled variations of C2-C7 Sagittal Vertical Alignment (C2-C7 SVA) and T1-Slope so that clinically relevant sagittally malaligned profiles could be prescribed, while maintaining horizontal gaze, and their biomechanical consequences studied., Results: Our results demonstrated that increasing C2-C7 SVA caused flexion of lower cervical (C2-C7) segments and hyperextension of suboccipital (C0-C1-C2) segments to maintain horizontal gaze. An increase in C2-C7 SVA increased the lower cervical neural foraminal areas. Conversely, increasing T1-slope predominantly influenced subaxial cervical lordosis and, as a result, decreased cervical neural foraminal areas. Therefore, we believe patients with increased upper thoracic kyphosis and radicular symptoms may respond with increased forward head posture (FHP) as a compensatory mechanism to increase their lower cervical neural foraminal area and alleviate nerve root compression as well as reduce the burden on posterior muscles and soft and bony structures of the cervical spine. Increasing FHP (i.e., increased C2-C7 SVA) was associated with shortening of the cervical flexors and occipital extensors and lengthening of the cervical extensors and occipital flexors, which corresponds to C2-C7 flexion and C0-C2 extension. The greatest shortening occurred in the suboccipital muscles, suggesting considerable load bearing of these muscles during chronic FHP. Regardless, there was no evidence of nerve compression within the suboccipital triangle. Finally, cervical sagittal imbalance may play a role in exacerbating adjacent segment pathomechanics after multilevel cervical fusion and should be considered during surgical planning., Conclusions: The results of our biomechanical studies have improved our understanding of the impact of cervical sagittal malalignment on pathomechanics of the cervical spine. We believe this improved understanding will assist in clinical decision-making.

Introduction: A novel expandable lumbar interbody fusion cage has been developed which allows for a broad endplate footprint similar to an anterior lumbar interbody fusion (ALIF); however, it is deployed from a minimally invasive transforaminal unilateral approach. The perceived benefit is a stable circumferential fusion from a single approach that maintains the anterior tension band of the anterior longitudinal ligament.The purpose of this biomechanics laboratory study was to evaluate the biomechanical stability of an expandable lumbar interbody cage inserted using a transforaminal approach and deployed in situ compared to a traditional lumbar interbody cage inserted using an anterior approach (control device)., Methods: Twelve cadaveric spine specimens (L1-L5) were tested intact and after implantation of both the control and experimental devices in two (L2-L3 and L3-L4) segments of each specimen; the assignments of the control and experimental devices to these segments were alternated. Effect of supplemental pedicle screw-rod stabilization was also assessed. Moments were applied to the specimens in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). The effect of physiologic preload on construct stability was evaluated in FE. Segmental motions were measured using an optoelectronic motion measurement system., Results: The deployable expendable TLIF cage and control devices significantly reduced FE motion with and without compressive preload when compared to the intact condition (p<0.05). Segmental motions in LB and AR were also significantly reduced with both devices (p<0.05). Under no preload, the deployable expendable TLIF cage construct resulted in significantly smaller FE motion compared to the control cage construct (p<0.01). Under all other testing modes (FE under 400N preload, LB, and AR) the postoperative motions of the two constructs did not differ statistically (p>0.05). Adding bilateral pedicle screws resulted in further reduction of ROM for all loading modes compared to intact condition, with no statistical difference between the two constructs (p>0.05)., Conclusions: The ability of the deployable expendable interbody cage in reducing segmental motions was equivalent to the control cage when used as a stand-alone construct and also when supplemented with bilateral pedicle screw-rod instrumentation. The larger footprint of the fully deployed TLIF cage combined with preservation of the anterior soft-tissue tension band may provide a better biomechanical fusion environment by combining the advantages of the traditional ALIF and TLIF approaches., Competing Interests: This study was suppported by the Department of Veterans Affairs, Washington, DC, and Benvenue Medical, Santa Clara, CA. Bartosz Wojewnik, MD, is a consultant for Synthes Spine.

Objective: To test the following hypotheses: (i) anterior cervical discetomy and fusion (ACDF) using stand-alone interbody spacers will significantly reduce the range of motion from intact spine; and (ii) the use of a static or a rotational-dynamic plate will significantly augment the stability of stand-alone interbody spacers, with similar beneficial effect when compared to each other., Methods: Eleven human cadaveric subaxial cervical spines (age: 48.2 ± 5.4 years) were tested under the following sequence: (i) intact spine; (ii) ACDF at C 4 -C 5 using a stand-alone interbody spacer; (iii) ACDF at C 5 -C 6 and insertion of an interbody spacer (two-level construct); and (iv) randomized placement of either a two-level locking static plate or a rotational-dynamic plate., Results: Insertion of stand-alone cage at C 4 -C 5 and C 5 -C 6 caused a significant decrease in the range of motion compared to intact spine (P < 0.05). Placement of both the locking and the rotational dynamic plate further reduced the range of motion at C 4 -C 5 and C 5 -C 6 compared to stand-alone cage (P < 0.01). No significant differences in range of motion restriction at either C 4 -C 5 or C 5 -C 6 were found when the two plating systems were compared (P > 0.05)., Conclusions: Cervical stand-alone interbody spacers caused significant restriction in the range of motion. Both plates significantly augmented the stability of stand-alone interbody spacers, with similar stabilizing effect., (© 2017 Chinese Orthopaedic Association and John Wiley & Sons Australia, Ltd.)

Background: Forward head posture (FHP) may be associated with neck pain and poor health-related quality of life. Literature describes only qualitative muscle length changes associated with FHP., Objective: The purpose of this study was to quantify how muscle-tendon unit lengths are altered when human cadaveric specimens are placed in alignments representing different severities of FHP., Design: This biomechanical study used 13 fresh-frozen cadaveric cervical spine specimens (Occiput-T1, 54±15 y)., Methods: Specimens' postural changes simulating increasing FHP severity while maintaining horizontal gaze were assessed. Specimen-specific anatomic models derived from computed tomography-based anatomic data were combined with postural data and specimen-specific anatomy of muscle attachment points to estimate the muscle length changes associated with FHP., Results: Forward head posture was associated with flexion of the mid-lower cervical spine and extension of the upper cervical (sub-occipital) spine. Muscles that insert on the cervical spine and function as flexors (termed "cervical flexors") as well as muscles that insert on the cranium and function as extensors ("occipital extensors") shortened in FHP when compared to neutral posture. In contrast, muscles that insert on the cervical spine and function as extensors ("cervical extensors") as well as muscles that insert on the cranium and function as flexors ("occipital flexors") lengthened. The greatest shortening was seen in the major and minor rectus capitis posterior muscles. These muscles cross the Occiput-C2 segments, which exhibited extension to maintain horizontal gaze. The greatest lengthening was seen in posterior muscles crossing the C4-C6 segments, which exhibited the most flexion., Limitations: This cadaver study did not incorporate the biomechanical influence of active musculature., Conclusions: This study offers a novel way to quantify postural alignment and muscle length changes associated with FHP. Model predictions are consistent with qualitative descriptions in the literature., (© 2017 American Physical Therapy Association)

Devising patient-specific kinematic assessment techniques are critical for both patient diagnosis and treatment evaluation of complex biomechanical joints within the body. New non-invasive kinematic assessment techniques, such as bi-planar fluoroscopic registration, provide improved insight on joint biomechanics compared to traditional techniques, but at the expense of higher radiation exposure to the patient. The purpose of this study was to minimize the x-ray sample size required for evaluating spine kinematics, ultimately reducing radiation exposure, while maintaining a high degree of accuracy by improving upon existing 3D kinematic interpolation techniques. Existing interpolation methods were improved to account for non-uniformly sampled control points and applied to new motion descriptors, thus creating a new approach to 3D kinematic interpolation utilizing dual-quaternions. Interpolation reconstruction methods were applied to decimated gold standard ex vivo spinal kinematic data originally acquired at 30Hz. The effects of interpolation method and variables (motion descriptor, sample spacing, sampling correction factors) on accuracy were compared. Dual-quaternion interpolation methods and equal interval angular sampling showed superior reconstruction results. Accuracy also improved when using temporal correction factors. Less than 1% normalized root-mean-squared error and less than 2% normalized maximum error were achieved from 0.36% of the original data set. The new approach also demonstrated its scalability for larger movements. However, accuracy may vary when interpolating more complex motion patterns. Overall, multiple interpolation methods and factors were evaluated in reconstructing 3D spine kinematics. High accuracy at low sample sizes and advantageous scalability to motions with larger total displacement illustrate its viability for bi-planar fluoroscopy., (Published by Elsevier Ltd.)

Study Design: Analysis of prospectively collected radiographic data., Objective: To investigate the influence of preoperative index-level range of motion (ROM) and disc height on postoperative ROM after cervical total disc arthroplasty (TDA) using compressible disc prostheses., Summary of Background Data: Clinical studies demonstrate benefits of motion preservation over fusion; however, questions remain unanswered as to which preoperative factors have the ability to identify patients who are most likely to have good postoperative motion, which is the primary rationale for TDA., Methods: We analyzed prospectively collected data from a single-arm, multicenter study with 2-year follow up of 30 patients with 48 implanted levels. All received compressible cervical disc prostheses of 6 mm-height (M6C, Spinal Kinetics, Sunnyvale, CA). The influence of index-level preoperative disc height and ROM (each with two levels: below-median and above-median) on postoperative ROM was analyzed using 2 x 2 ANOVA. We further analyzed the radiographic outcomes of a subset of discs with preoperative height less than 3 mm, the so-called "collapsed" discs., Results: Shorter (3.0 ± 0.4 mm) discs were significantly less mobile preoperatively than taller (4.4 ± 0.5 mm) discs (6.7° vs. 10.5°, P = 0.01). The postoperative ROM did not differ between the shorter and taller discs (5.6° vs. 5.0°, P = 0.63). Tall discs that were less mobile preoperatively had significantly smaller postoperative ROM than short discs with above-median preoperative mobility (P < 0.05). The "collapsed discs" (n = 8) were less mobile preoperatively compared with all discs combined (5.1° vs. 8.6°, P < 0.01). These discs were distracted to more than two times the preoperative height, from 2.6 to 5.7 mm, and had significantly greater postoperative ROM than all discs combined (7.6° vs. 5.3°, P < 0.05)., Conclusion: We observed a significant interaction between preoperative index-level disc height and ROM in influencing postoperative ROM. Although limited by small sample size, the results suggest discs with preoperative height less than 3 mm may be amenable to disc arthroplasty using compressible disc prostheses., Level of Evidence: 2.

Background: A lateral approach with open reduction and internal fixation with a plate is a very effective technique for the majority of distal fibular fractures. However, this open approach for ankle fixation may be complicated by wound dehiscence and infection, especially in high-risk patients. An alternative to plating is an intramedullary implant, which allows maintenance of length, alignment, and rotation and which allows for decreased soft tissue dissection. While there has been clinical data suggesting favorable short-term outcomes with these implants, there is no current biomechanical literature investigating this technology in this particular fracture pattern. This study sought to biomechanically compare an emerging technology with an established method of fixation for distal fibular fractures that traditionally require an extensive exposure., Methods: Ten matched cadaveric pairs from the proximal tibia to the foot were prepared to simulate an Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association (AO/OTA) 44C2 ankle fracture and randomized to fixation with a distal fibular locking plate or intramedullary fibular rod. A constant 700-N axial load was applied, and all specimens underwent testing for external rotation stiffness, external rotation cyclic loading, and torque to failure. The syndesmotic diastasis, stiffness, torque to failure, angle at failure, and mode of failure were obtained from each specimen., Results: There was no significant difference in syndesmotic diastasis during cyclic loading or at maximal external rotation between the rod and plate groups. Post-cycle external rotation stiffness across the syndesmosis was significantly higher for the locking plate than the fibular rod. There was no significant difference between the rod and plate in torque at failure or external rotation angle. The majority of specimens had failure at the syndesmotic screw., Conclusions: In the present cadaveric study of an AO/OTA 44C2 ankle fracture, a modern fibular rod demonstrated less external rotation stiffness while maintaining the syndesmotic diastasis to within acceptable tolerances and having similar failure characteristics.

MRI allows non-invasive assessment of intervertebral disc degeneration with the added clinical benefit of using non-ionizing radiation. What has remained unclear is the relationship between assessed disc degeneration and lumbar spine kinematics. Kinematic outcomes of 54 multi-segment (L1-Sacrum) lumbar spine specimens were calculated to discover if such an underlying relationship exists with degeneration assessed using the Pfirrmann grading system. Further analyses were also conducted to determine if kinematic outcomes were affected by motion segment level, gender or applied compressive preload. Range of motion, hysteresis, high flexibility zone size and rotational stiffness in flexion-extension, lateral bending and axial rotation were the kinematic outcomes. Caudal intervertebral discs in our study sample were more degenerative than cranial discs. L5-S1 discs had the largest flexion-extension range of motion (p < 0.005) and L1-L2 discs the lowest flexion high flexibility zone size (p < 0.013). No other strict cranial-caudal differences in kinematic outcomes were found. Low flexibility zone rotational stiffness increased with disc degeneration grade in extension, lateral bending and axial rotation (p < 0.001). Trends towards higher hysteresis and lower range of motion with increased degeneration were observed in flexion-extension and lateral bending. Applied compressive preload increased flexion-extension hysteresis and augmented the effect of degeneration on hysteresis (p < 0.0005). Female specimens had about one degree larger range of motion in all rotational modes, and higher flexion extension hysteresis (p = 0.016). These results suggest that gender differences exist in lumbar spine kinematics. Additionally high disc loads, applied compressive preload or applied moment, are needed to kinematically distinguish discs with different levels of degeneration. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1389-1398, 2016., (© 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.)

Purpose: Patients with cervical spondylosis commonly present with neck pain, radiculopathy or myelopathy. As degenerative changes progress, multiple factors including disc height loss, thoracic kyphosis, and facetogenic changes can increase the risk of neural structure compression. This study investigated the impact of cervical deformity including forward head posture (FHP) and upper thoracic kyphosis, on the anatomy of the cervical neural foramen., Methods: Postural changes of 13 human cervical spine specimens (Occiput-T1, age 50.6 years; range 21-67) were assessed in response to prescribed cervical sagittal malalignments using a previously reported experimental model. Two characteristics of cervical sagittal deformities, C2-C7 sagittal vertical alignment (SVA) and sagittal angle of the T1 vertebra (T1 tilt), were varied to create various cervical malalignments. The postural changes were documented by measuring vertebral positions and orientations. The vertebral motion data were combined with specimen-specific CT-based anatomical models, which allowed assessments of foraminal areas of subaxial cervical segments as a function of increasing C2-C7 SVA and changing T1 tilt., Results: Increasing C2-C7 SVA from neutral posture resulted in increased neural foraminal area in the lower cervical spine (largest increase at C4-C5: 13.8 ± 15.7 %, P < 0.01). Increasing SVA from a hyperkyphotic posture (greater T1 tilt) also increased the neural foraminal area in the lower cervical segments (C5-C6 demonstrated the largest increase: 13.4 ± 9.6 %, P < 0.01). The area of the cervical neural foramen decreased with increasing T1 tilt, with greater reduction occurring in the lower cervical spine, specifically at C5-C6 (-8.6 ± 7.0 %, P < 0.01) and C6-C7 (-9.6 ± 5.6 %, P < 0.01)., Conclusion: An increase in thoracic kyphosis (T1 tilt) decreased cervical neural foraminal areas. In contrast, an increase in cervical SVA increased the lower cervical neural foraminal areas. Patients with increased upper thoracic kyphosis may respond with increased cervical SVA as a compensatory mechanism to increase their lower cervical neural foraminal area.

Study Design: A biomechanical study using human spine specimens., Objective: The aim of this study was to assess whether the presence of cervical sagittal imbalance is an independent risk factor for increasing the mechanical burden on discs adjacent to cervical multilevel fusions., Summary of Background Data: The horizontal offset distance between the C2 plumbline and C7 vertebral body (C2-C7 Sagittal Vertical Axis (SVA)) or the angle made with vertical by a line connecting the C2 and C7 vertebral bodies (C2-C7 tilt angle) are used as radiographic measures to assess cervical sagittal balance. There is level III clinical evidence that sagittal imbalance caused by kyphotic fusions or global spinal sagittal malalignment may increase the risk of adjacent segment pathology., Methods: Thirteen human cadaveric cervical spines (Occiput-T1; age: 50.6 years; range: 21-67) were tested first in the native intact state and then after instrumentation across C4-C6 to simulate in situ two-level fusion. Specimens were tested using a previously validated experimental model that allowed measurement of spinal response to prescribed imbalance. The effects of fusion on segmental angular alignments and intradiscal pressures in the C3-C4 and C6-C7 discs, above and below the fusion, were evaluated at different magnitudes of C2-C7 tilt angle (or C2-C7 SVA)., Results: When compared with the pre-fusion state, in situ fusion across C4-C6 segments required increased flexion angulation and resulted in increased intradiscal pressure at the C6-C7 disc below the fusion in order to accommodate the same increase in C2-C7 tilt angle or C2-C7 SVA (P < 0.05). The adjacent segment mechanical burden due to fusion became greater with increasing C2-C7 tilt angle or SVA., Conclusion: Cervical sagittal imbalance arising from regional and/or global spinal sagittal malalignment may play a role in exacerbating adjacent segment pathomechanics after multilevel fusion and should be considered during surgical planning., Level of Evidence: N/A.