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The objectives of this study were to determine symmetry and sex differences in knee kinematics and ACL elongation waveforms in healthy athletes without history of knee injury during fast running, drop jump, and 180° internal/external rotation hops. It was hypothesized that knee abduction angle and ACL relative elongation would be greater in women than in men during all activities. Bilateral knee kinematics and ACL relative elongation were determined in 19 collegiate athletes using dynamic biplane radiography. Sex differences in kinematics and ACL relative elongation waveforms were identified using statistical parametric mapping. Average absolute side-to-side differences (SSDA ) in kinematics and ACL relative elongation waveforms were determined for each activity. Women had up to 2.3° (all p < 0.05) less knee adduction angle and had greater ACL relative elongation (max. 4.8% to 9.2%; all p

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

Arthrodesis is the standard of care for numerous pathologic conditions of the cervical spine and is performed over 150,000 times annually in the United States. The primary long-term concern after this surgery is adjacent segment disease (ASD), defined as new clinical symptoms adjacent to a previous fusion. The incidence of adjacent segment disease is approximately 3% per year, meaning that within 10 years of the initial surgery, approximately 25% of cervical arthrodesis patients require a second procedure to address symptomatic adjacent segment degeneration. Despite the high incidence of ASD, until recently, there was little data available to characterize in vivo adjacent segment mechanics during dynamic motion. This manuscript reviews recent advances in our knowledge of adjacent segment mechanics after cervical arthrodesis that have been facilitated by the use of dynamic biplane radiography. The primary observations from these studies are that current in vitro test paradigms often fail to replicate in vivo spine mechanics before and after arthrodesis, that intervertebral mechanics vary among cervical motion segments, and that joint arthrokinematics (i.e., the interactions between adjacent vertebrae) are superior to traditional kinematics measurements for identifying altered adjacent segment mechanics after arthrodesis. Future research challenges are identified, including improving the biofidelity of in vitro tests, determining the natural history of in vivo spine mechanics, conducting prospective longitudinal studies on adjacent segment kinematics and arthrokinematics after single and multiple-level arthrodesis, and creating subject-specific computational models to accurately estimate muscle forces and tissue loading in the spine during dynamic activities.

The aim of this study was to characterize cervical disc deformation in asymptomatic subjects and single-level arthrodesis patients during in vivo functional motion. A validated model-based tracking technique determined vertebral motion from biplane radiographs collected during dynamic flexion-extension. Level-dependent differences in disc compression-distraction and shear deformation were identified within the anterior and posterior annulus (PA) and the nucleus of 20 asymptomatic subjects and 15 arthrodesis patients using a mixed-model statistical analysis. In asymptomatic subjects, disc compression and shear deformation per degree of flexion-extension progressively decreased from C23 to C67. The anterior and PA experienced compression-distraction deformation of up to 20%, while the nucleus region was compressed between 0% (C67) and 12% (C23). Peak shear deformation ranged from 16% (at C67) to 33% (at C45). In the C5-C6 arthrodesis group, C45 discs were significantly less compressed than in the control group in all disc regions (all p ≤ 0.026). In the C6-C7 arthrodesis group, C56 discs were significantly less compressed than the control group in the nucleus (p = 0.023) and PA (p = 0.014), but not the anterior annulus (AA; p = 0.137). These results indicate in vivo disc deformation is level-dependent, and single-level anterior arthrodesis alters the compression-distraction deformation in the disc immediately superior to the arthrodesis.

Altered surface interactions following joint instability may apply novel, damaging loads to articular cartilage. This study measured the velocity of the centers of closest proximity on subchondral bone surfaces on the femur and tibia during running in normal and unstable canine stifle (knee) joints. The purpose was to explore the relationship between the velocity of the centers of closest proximity on subchondral bones and the severity of cartilage damage. Dynamic biplane radiography was used to acquire serial knee kinematics [5 control, 18 cranial cruciate ligament (CCL) deficient] during treadmill running over 2 years. Custom software calculated the difference between the rate at which the center of closest proximity on the femur translated relative to the femur bone surface and the rate at which the center of closest proximity on the tibia translated relative to the tibia bone surface. Comparisons were made between dogs that developed minor versus major medial compartment cartilage damage over 2 years. Major damage dogs showed a significantly greater increase in the difference between femur and tibia medial compartment closest proximity point velocity from the instant of paw strike to peak velocity difference at 2, 4, and 6 months after CCL transaction. This implies increased tangential forces associated with the velocity of the compressed cartilage region during joint movement (plowing) may be a mechanism that initiates osteoarthritis (OA) development and drives OA progression. In the future, articulating surface velocity measurements may be useful to identify patients at risk for long-term OA due to joint instability.