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Combined knowledge of the functional kinematics and kinetics of the human body is critical for understanding a wide range of biomechanical processes including musculoskeletal adaptation, injury mechanics, and orthopaedic treatment outcome, but also for validation of musculoskeletal models. Until now, however, no datasets that include internal loading conditions (kinetics), synchronized with advanced kinematic analyses in multiple subjects have been available. Our goal was to provide such datasets and thereby foster a new understanding of how in vivo knee joint movement and contact forces are interlinked – and thereby impact biomechanical interpretation of any new knee replacement design. In this collaborative study, we have created unique kinematic and kinetic datasets of the lower limb musculoskeletal system for worldwide dissemination by assessing a unique cohort of 6 subjects with instrumented knee implants (Charité – Universitätsmedizin Berlin) synchronized with a moving fluoroscope (ETH Zürich) and other measurement techniques (including whole body kinematics, ground reaction forces, video data, and electromyography data) for multiple complete cycles of 5 activities of daily living. Maximal tibio-femoral joint contact forces during walking (mean peak 2.74 BW), sit-to-stand (2.73 BW), stand-to-sit (2.57 BW), squats (2.64 BW), stair descent (3.38 BW), and ramp descent (3.39 BW) were observed. Internal rotation of the tibia ranged from 3° external to 9.3° internal. The greatest range of anterio-posterior translation was measured during stair descent (medial 9.3 ± 1.0 mm, lateral 7.5 ± 1.6 mm), and the lowest during stand-to-sit (medial 4.5 ± 1.1 mm, lateral 3.7 ± 1.4 mm). The complete and comprehensive datasets will soon be made available online for public use in biomechanical and orthopaedic research and development.

A trend within the orthopedic community is rejection of the belief that “one size fits all.” Freddie Fu, among others, strived to individualize the treatment of anterior cruciate ligament (ACL) injuries based on the patient’s anatomy. Further, during the last two decades, greater emphasis has been placed on improving the outcomes of ACL reconstruction (ACL-R). Accordingly, anatomic tunnel placement is paramount in preventing graft impingement and restoring knee kinematics. Additionally, identification and management of concomitant knee injuries help to re-establish knee kinematics and prevent lower outcomes and registry studies continue to determine which graft yields the best outcomes. The utilization of registry studies has provided several large-scale epidemiologic studies that have bolstered outcomes data, such as avoiding allografts in pediatric populations and incorporating extra-articular stabilizing procedures in younger athletes to prevent re-rupture. In describing the anatomic and biomechanical understanding of the ACL and the resulting improvements in terms of surgical reconstruction, the purpose of this article is to illustrate how basic science advancements have directly led to improvements in clinical outcomes for ACL-injured patients. Level of evidence V.

Normal biomechanics of the upper cervical spine, particularly at the atlantooccipital joint, remain poorly characterized. The purpose of this study was to determine the intervertebral kinematics of the atlantooccipital joint (occiput-C1) during three-dimensional in vivo physiologic movements. Twenty healthy young adults performed dynamic flexion/extension, axial rotation, and lateral bending while biplane radiographs were collected at 30 images per second. Motion at occiput-C1 was tracked using a validated volumetric model-based tracking process that matched subject-specific CT-based bone models to the radiographs. The occiput-C1 total range of motion (ROM) and helical axis of motion (HAM) was calculated for each movement. During flexion/extension, the occiput-C1 moved almost exclusively in-plane (ROM: 17.9 ± 6.9°) with high variability in kinematic waveforms (6.3°) compared to the in-plane variability during axial rotation (1.4°) and lateral bending (0.9°) movements. During axial rotation, there was small in-plane motion (ROM: 4.2 ± 2.5°) compared to out-of-plane flexion/extension (ROM: 12.7 ± 5.4°). During lateral bending, motion occurred in-plane (ROM: 9.0 ± 3.1°) and in the plane of flexion/extension (ROM: 7.3 ± 2.7°). The average occiput-C1 axis of rotation intersected the sagittal and coronal planes 7 mm to 18 mm superior to the occipital condyles. The occiput-C1 axis of rotation pointed 60° from the sagittal plane during axial rotation but only 10° from the sagittal plane during head lateral bending. These novel results are foundational for future work on upper cervical spine kinematics.

Wrist pathology is often diagnosed by using the contralateral wrist as a comparison of baseline motion and strength. However, recent range of motion studies suggest that females have different carpal motion patterns compared to males and that the dominant carpal bones have different motion patterns. The purpose of this study is to evaluate the effect of sex and hand dominance on in vivo kinematics of the scaphoid, lunate and capitate using four-dimensional computed tomography (4D-CT) analysis in healthy uninjured volunteers. In this prospective study, both wrist of 20 uninjured Caucasian volunteers (11 men and 9 women) were assessed using 4D-CT during active flexion–extension and radial-ulnar deviation. A linear mixed model was used to compare the carpal motion patterns. Sex had no influence on carpal kinematics. Hand-dominance in males did have a significant effect on carpal kinematics. During flexion–extension of the male wrist, more radial-ulnar deviation of the lunate, scaphoid and capitate of the non-dominant hand was seen. During radial-ulnar deviation of the male wrist, radial-ulnar deviation and pro-supination of the lunate was more in the dominant hand. This study provides a better understanding of carpal kinematics and the effect of sex and hand-dominance on the scaphoid, lunate and capitate in uninjured wrists.

This study aimed to develop and validate a novel flexion axis concept by calculating the points on femoral condyles that could maintain constant heights during knee flexion. Twenty-two knees of 22 healthy subjects were investigated when performing a weightbearing single leg lunge. The knee positions were captured using a validated dual fluoroscopic image system. The points on sagittal planes of the femoral condyles that had minimal changes in heights from the tibial plane along the flexion path were calculated. It was found that the points do formulate a medial-lateral flexion axis that was defined as the iso-height axis (IHA). The six degrees of freedom (6DOF) kinematics data calculated using the IHA were compared with those calculated using the conventional transepicondylar axis and geometrical center axis. The IHA measured minimal changes in proximal–distal translations and varus–valgus rotations along the flexion path, indicating that the IHA may have interesting clinical implications. Therefore, identifying the IHA could provide an alternative physiological reference for improvement of contemporary knee surgeries, such as ligament reconstruction and knee replacement surgeries that are aimed to reproduce normal knee kinematics and medial/lateral soft tissue tensions during knee flexion.

ObjectiveWe aimed to establish a quantitative description of motion patterns and establish test-retest reliability of the four-dimensional CT when quantifying in vivo kinematics of the scaphoid, lunate, and capitate.Materials and methodsWe assessed in vivo kinematics of both wrists of 20 healthy volunteers (11 men and 9 women) between the ages of 20 and 40 years. All volunteers performed active flexion-extension and radial-ulnar deviation with both wrists. To test for reliability, one motion cycle was rescanned for both wrists approximately 15 min after the first scan. The coefficient of multiple correlation was used to analyze reliability. When two motion patterns are similar, the coefficient of multiple correlation tends towards 1, whereas in dissimilar motion patterns, it tends towards 0. The root mean square deviation was used to analyze the total motion patterns variability between the two scans.ResultsOverall, mean or median coefficient of multiple correlations were higher than 0.86. The root mean square deviations were low and ranged from 1.17° to 4.29°.ConclusionThis innovative non-invasive imaging technique can reliably describe in vivo carpal kinematics of uninjured wrists in healthy individuals. It provides us with a better understanding and reference values of carpal kinematics of the scaphoid, lunate, and capitate.

Purpose The aim of the present study was to trace knee position at the time of bone bruise (BB) and investigate how much this position departed from the knee biomechanics of an in vivo flexion–extension. Methods From an original cohort of 62 patients, seven (11%) presented bicompartmental edemas and were included in the study. 3D models of bones and BB were obtained from MRI. Matching bone edemas, a reconstruction of the knee at the moment of BB was obtained. For the same patients, knee kinematics of a squat was calculated using dynamic Roentgen sterephotogrammetric analysis (RSA). Data describing knee position at the moment of BB were compared to kinematics of the same knee extrapolated from RSA system. Results Knee positions at the moment of BB was significantly different from the kinematics of the squat. In particular, all the patients’ positions were out of squat range for both anterior and proximal tibial translation, varus–valgus rotation (five in valgus and two in varus), tibial internal–external rotation (all but one, five externally and one internally). A direct comparison at same flexion angle between knee at the moment of BB (average 46.1° ± 3.8°) and knee during squat confirmed that tibia in the former was significantly more anterior ( p  < 0.0001), more externally rotated (6.1 ± 3.7°, p  = 0.04), and valgus (4.1 ± 2.4°, p  = 0.03). Conclusion Knee position at the moment of Bone bruise position was out of physiological in-vivo knee range of motion and could reflect a locked anterior subluxation occurring in the late phase of ACL injury rather than the mechanism leading to ligament failure. Level of evidence Level IV

PurposeDegenerative 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.MethodsSeven 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.ResultsStatic 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.ConclusionContinuous in vivo dynamic imaging in DS reveals a spectrum of aberrant motion with significantly greater kinematic heterogeneity than previously realized that is not readily seen on current clinical imaging.Level of evidenceLevel V dataGraphical abstractThese slides can be retrieved under Electronic Supplementary Material.

Background Dual fluoroscopic imaging system (DFIS) was employed to identify the Center of Rotation(COR) in the lower lumbar spine and determine its relationship with weight bearing. Methods In this study, twenty participants were recruited. A 3D model of each participant’s lumbar spine was created using CT images, and their relative positions were determined through DFIS. By integrating CT imaging with DFIS, the kinematic data of the participants’ spines during movement were captured. The lower lumbar spine’s COR was calculated using the method of perpendicular bisectors. Results While flexing and extending, the Center of Rotation (COR) initially moved downward with increasing load, followed by upward movement as the load further increased. During flexion and extension, the COR coordinates of L3-4 at 0 kg, 5 kg and 10 kg are(0.3549 ± 0.2176,0.0177 ± 0.1317),(0.0598 ± 0.2095,-0.1806 ± 0.1719),(0.1427 ± 0.1440,-0.0911 ± 0.2722); The center of rotation coordinates of L4-5 at 0 kg, 5 kg and 10 kg are(0.0566 ± 0.2693,-0.0727 ± 0.2132),(0.0964 ± 0.2671,-0.2037 ± 0.2299),(0.1648 ± 0.1520,-0.0049 ± 0.1641). The anterior-posterior position of the COR shifted posteriorly with increasing weight-bearing. During lateral bending, the center of rotation coordinates of L3-4 at 0 kg, 5 kg and 10 kg are(0.0745 ± 0.1229,0.0966 ± 0.3403) (-0.0438 ± 0.1281,0.1161 ± 0.1584), (-0.0464 ± 0.1517,0.1320 ± 0.2730); The center of rotation coordinates of L4-5 at 0 kg, 5 kg and 10 kg are(-0.0314 ± 0.1411,-0.0355 ± 0.2088), (-0.0764 ± 0.3135,0.0105 ± 0.3230),(-0.0376 ± 0.1701,0.0285 ± 0.2395). Throughout the lateral bending exercises, the upper and lower COR positions increased as the load increased, while the left and right COR positions remained unaffected by the load increment. The COR height differed between flexion and lateral bending. We observed variations in the COR position of the lumbar spine during lateral bending and flexion-extension movements. This enhanced our comprehension of coupled motion patterns within the lumbar spine. Conclusions Position of the lumbar spine COR changes with variations in the load. During different movements, the COR location of the lower lumbar spine varied. This finding suggests the presence of distinct motion patterns in the lower lumbar spine. As the load increases, the lumbar COR position changes significantly. Abnormal movement patterns of the lower lumbar spine under different loads may be one of the factors that accelerate lumbar disc degeneration.

Purpose Unicompartmental knee arthroplasty (UKA), resulting in similar kinematics to native knees, is functionally superior to total knee arthroplasty (TKA). However, ACL deficiency is generally considered to be a contraindication. The main purpose of this study was to investigate if UKA in ACL-deficient knees would result in similar kinematics to conventional UKA with an intact ACL. Methods Ten conventional UKA patients were compared to eight ACL-deficient patients with a reduced tibial slope to compensate for instability, resulting from the deficient ACL. Knee kinematics was evaluated with a moving fluoroscope, tracking the knee joint during daily activities. In a standing position (baseline), posterior shift of the femur was observed for ACL-deficient UKA patients, compared to conventional UKA patients. Results A significant posterior femoral shift in the ACL-deficient group was observed during the first 25% (near extension) of deep knee bend, while there was no difference in kinematic waveforms for all other activities. No significant range of motion differences across different activities between the two UKA groups were detected, except for an increase of medial AP translation in the ACL-deficient group, during deep knee bend and stair descent. Conclusion Despite the posterior femoral shift due to ACL deficiency, both UKA groups showed similar kinematic waveforms, indicating that posterior tibial slope reduction can partially compensate for ACL function. This supported our hypothesis that fixed bearing UKA can be a viable treatment option for selected ACL-deficient patients, allowing patient-specific kinematics. While anteroposterior laxity can be compensated, rotational stability was a prerequisite for this approach. Level of evidence III.