Conflicting evidence exists regarding the presence of aberrant gait biomechanics more than one-year following anterior cruciate ligament reconstruction (ACLR). Overground walking may not elucidate differences in those further removed from surgery due to the unexacting nature of the task. Quadriceps dysfunction is common post-ACLR and contributes to aberrant gait biomechanics, thus downhill walking may exacerbate differences as this task places greater demands on the quadriceps. Purpose: To compare gait biomechanics between individuals with ACLR and healthy controls during level and downhill walking conditions. Methods: 24 individuals more than 1-year removed from ACLR and 24 healthy controls completed both level and downhill (10 degree grade) gait biomechanics assessments on an instrumented split-belt treadmill at their preferred walking speed. Peak variables were evaluated over the first 50% of stance including the vertical ground reaction force, internal knee extension and abduction moments and knee flexion angle. Moments were normalized to %body weight*height (%BW*Ht) and vGRF was normalized to %body weight. Dependent variables were compared across groups and conditions via two-way repeated measures ANCOVAs controlling for gait speed. Results: There were no significant condition*group interaction effects nor group main effects for any outcomes. However, there were significant condition increases in knee extension moment (P=0.020) and knee flexion angle (P=0.018) from level to downhill. Conclusions: Downhill walking necessitates larger knee extension moments and knee flexion angle compared to level gait. Our results suggest that changes in gait biomechanics between level and downhill conditions do not differ between individuals with ACLR >1 year post-reconstruction and controls.
Listed In: Biomechanics, Gait, Orthopedic Research

The anterior cruciate ligament (ACL) stabilizes the lower limb against translational and rotational loads while the knee is is multiple postures. Surgical reconstruction, the most common treatment for ACL tears, is intended to replicate the biomechanical function of the native ACL in the postures and activities related to daily living and high-impact activities. In order to improve outcomes from ACL reconstructions in patients in pediatric and adolescent age groups, we need to improve our understanding of the knee posture dependent biomechanical function of the ACL. As such, the objective of this study was to quantify flexion angle dependent changes in the response of the ACL and the total knee to applied loads in the anterior-posterior and varus-valgus directions using a skeletally immature porcine model. To do this, we collected stifle (knee) joints from female Yorkshire-cross pigs at ages ranging from 1.5 to 18 months (n=30 total). The joints were tested using a 6 degree-of-freedom universal force sensing robotic system under applied anterior-posterior loads and varus-valgus moments at 40° and 60° of flexion. Studied parameters included anterior-posterior tibial translation (APTT), varus-valgus rotation (VVR), and anterior force carried by the ACL and its anteromedial and posterolateral bundles. We found increased knee laxity (APTT and VVR) was associated with both younger age and increased knee flexion. Greater anterior force carried in the ACL, and specifically in the anteromedial bundle, was associated with increased flexion, regardless of age. These findings have implications in intraoperative graft assessment and biomechanical models.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research, Sports Science

INTRODUCTION:Previous studies have reported that men and women demonstrate distinctly different biomechanics during running and that older runners use a variety of biomechanical adaptations compared with younger runners. It is hypothesized that excessive asymmetry due to biomechanical and anatomical abnormalities contributes to increased risk of injuries, however it is still unclear how age and gender might impact this.METHODS: A cross sectional study was employed and healthy recreational runners were categorized into four groups based on age and gender.Two-way multivariate analysis of variance was performed with age and gender as factors and Symmetry Angle values for peak hip adduction angle (HA), peak knee adduction moment (KAM), peak knee flexion angle (KF), and peak vertical ground reaction force (VGRF) were used as the dependent variables. RESULTS: Overall, gender had a significant effect on HA asymmetry (p=0.02) and both gender and age showed a significant interaction effect on KAM asymmetry (p=0.04).CONCLUSIONS:This study suggests that interlimb asymmetry in running gait for KAM and HA also differs with aging and gender.Understanding age and gender related adaptations in interlimb asymmetry will help improve running performance and develop programs aimed at reducing injury rates.
Listed In: Biomechanics, Gait, Orthopedic Research

Robotic testing was performed with a 6-degree of freedom load cell in order to analyze functional contributions of the soft tissues in the knee under physiologically relevant loading conditions. Age groups ranging from 1.5 months to 18 months, porcine equivalent to early youth through late adolescent human ages, were studied. Complete ACL transection resulted in increased APTT and VVR across all ages (p<0.05), while injury to the AM bundle did not affect APTT or VVR. Additionally, increasing age resulted in decreased APTT normalized to the tibial plateau (p<0.05) and an average 19° decrease in VVR across states from 0 to 18 months of age (p<0.05). The ACL was the primary restraint against anterior drawer in the intact knee state [75-111%]. Following AM bundle dissection, the PL bundle carried the vast majority of the anterior load regardless of age [66-112%]. Following complete ACL transection, the MCL and medial meniscus carried most of the force across ages under anterior drawer. The LCL contributed increasing resistance to varus torque across states with age, as did the MCL under valgus torque.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research, Sports Science

Residual stresses are known to exist in human intervertebral discs but have not been incorporated in finite element models. A multigeneration model was applied to the annulus fibrosus of the intervertebral disc to simulate residual stresses arising from growth and remodeling. The intervertebral disc shape and compressive creep were used to verify that the multigeneration approach generates realistic values of residual stress. The model was then validated by comparing its 6 degree-of-freedom mechanical response to experimental data. Human intervertebral discs were tested in a custom-built hexapod in all 6 degrees-of-freedom (lateral shear, anterior-posterior shear, torsion, bending, flexion, and compression). Incorporating residual stresses resulted in a finite element model which can predict 4 degrees-of-freedom while excluding residual stresses produces a finite element model that can only predict 2 degrees-of-freedom.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research