Muscle Strength And Loading Patterns During Sport-related Tasks In Persons With Acetabular Dysplasia

Abstract

PURPOSE: Acetabular dysplasia (AD) is described as insufficient bony coverage of the femoral head by the acetabulum that leads to joint instability, pain, and decreased function. Little is known regarding the effects of AD on muscle strength and loading patterns during sport-related tasks. We compared muscle strength and loading patterns during squat and countermovement jump (CMJ) tasks between limbs and examined associations among these variables in persons with AD. METHOD: We enrolled 12 persons with AD (11 females) and evaluated isometric strength of the knee flexors and extensors and the hip flexors, extensors, and abductors using an electromechanical dynamometer (Biodex 3). We used peak torque values (Nm/kg) for the involved and uninvolved limbs to calculate limb symmetry indices (LSI) for each muscle group. Loading patterns during a squat and CMJ takeoff and landing were evaluated using two portable force plates (ForceDecks). Average peak ground-reaction force (GRF) for the involved and uninvolved limbs (N/N) and LSI for each task were calculated. We used Wilcoxon signed-rank test to evaluate differences in muscle strength and loading patterns between limbs. We examined associations between involved limb muscle strength and loading patterns using Spearman’s rho test. RESULT: The involved limb exhibited lower knee extensor strength compared to the uninvolved limb (involved = 1.75 Nm/Kg; uninvolved = 2.11 Nm/Kg; p = 0.005). There were no other differences between limbs for the remaining muscle strength variables or for squat and CMJ loading patterns variables (all p > 0.05). Per muscle group, the following proportions exhibited ≥90% LSI: 41.7% for knee extensors and flexors and hip flexors; 66.7% for hip extensors; 90% for hip abductors. Per movement task, the following proportions exhibited ≥90% LSI: 72.7% for the squat; 90% for CMJ takeoff; 54.5% for CMJ landing. Higher hip extensor strength was associated with higher GRF during CMJ landing for involved limb (r = 0.70; p = 0.016). CONCLUSION: Persons with AD exhibited decreased involved limb knee extensor strength and asymmetric strength and loading patterns. Higher hip strength was associated with higher involved limb landing during CMJ. Further study of the associations among strength and joint loading patterns is needed in larger samples of persons with AD.