Effect of isolated hip abductor fatigue on single-leg landing mechanics and simulated ACL loading.

BACKGROUND: Altered movement biomechanics are a risk factor for ACL injury. While hip abductor weakness has been shown to negatively impact landing biomechanics, the role of this musculature and injury risk is not clear. The aim of this musculoskeletal simulation study was to determine the effect of hip abductor fatigue-induced weakness on ACL loading, force production of lower extremity muscles, and lower extremity biomechanics during single-leg landing. METHODS: Biomechanical data from ten healthy adults were collected before and after a fatigue protocol and used to derive subject-specific estimates of muscle forces and ACL loading using a 5-degree of freedom (DOF) model. RESULTS: There were no significant differences in knee joint angles and ACL loading between pre and post-fatigue. However, there were significant differences, due to fatigue, in lateral trunk flexion angle, total excursion of trunk, muscle forces, and joint moments. CONCLUSION: Altered landing mechanics, due to hip abductor fatigue-induced weakness, may be associated with increased risk of ACL injury during single-leg landings. Clinical assessment or screening of ACL injury risk will benefit from subject-specific musculoskeletal models during dynamic movements. Future study considering the type of the fatigue protocols, cognitive loads, and various tasks is needed to further identify the effect of hip abductor weakness on lower extremity landing biomechanics.

The effects of pediatric obesity on patellofemoral joint contact force during walking.

BACKGROUND: Obesity increases a child's risk of developing knee pain across the lifespan, potentially through elevated patellofemoral joint loads that occur during habitual weight-bearing activities. RESEARCH QUESTION: Do obese children have greater absolute and patellar-area-normalized patellofemoral joint forces compared to healthy weight children during walking? METHODS: We utilized a cross-sectional design to address the aims of this study. Experimental biomechanics data were collected during treadmill walking in 10 healthy-weight and 10 obese 8-12 year-olds. We used radiographic images to develop subject-specific musculoskeletal models, generated walking simulations from the experimental data, and predicted patellofemoral joint contact force using established techniques. RESULTS: We found that the obese children had 1.98 times greater absolute (p = 0.002) and 1.81 times greater patellar-area-normalized (p = 0.008) patellofemoral joint contact forces compared to the healthy-weight children. We observed a stronger relationship between absolute patellofemoral joint contact force and BMI (r2=0.58) than between patellofemoral joint contact force and body fat percentage (r2=0.38). SIGNIFICANCE: Our results indicate that obese children walk with increased patellofemoral loads in absolute terms and also relative to the area of the articulating surfaces, which likely contributes to the increased risk of knee pain in this pediatric population. This information, which provides a baseline comparison for future longitudinal studies, also informs the type and frequency of physical activity prescription aimed at reducing the risk of knee injury and improving long-term outcomes.