Time course of tissue asymmetry following anterior cruciate ligament reconstruction

Introduction: Anterior cruciate ligament (ACL) injuries significantly impact knee function and daily activity, with ACL reconstruction (ACLR) being the primary treatment. While functional deficits after ACLR are well understood, the musculoskeletal changes and factors remain unclear. Key factors such as sex, graft type, and time since surgery all contribute to recovery outcomes but are rarely assessed together. Purpose: To cross-sectionally map the time course of tissue asymmetry post-ACLR also known as the AI%, which was calculated as the interlimb difference divided by the mean multiplied by 100. Methods: This project compared tissue asymmetry and knee function (strength and power) between individuals with and without ACLR. Participants visited the MAAX Lab or Dr. Carr’s Lab at Texas Christian University once, where they provided consent, completed demographic questionnaires, underwent muscle performance testing on a Biodex dynamometer, and received tissue imaging via Dual-energy X-ray Absorptiometry (DXA). Aim 1 (ACLR n=33 vs CON n=30) and Aim 2 (ACLR Female n=22 vs ACLR Male n=11) were assessed using independent t-test with Cohen’s d effect sizes. Aim 3 (Time since Surgery <2 n=11, 2–5 n=13, or >5 years n=8) was assessed using One-Way ANOVA with eta2 effect sizes and LSD post-hocs with Cohen’s d effect sizes. Results: There were no significant differences between ACLR and Controls for age, height, weight, total body fat percent (BF%), or muscle power and strength measures (all p≥0.072, all d≤0.87). Significant lower-body LM, fat%, and BMD asymmetries showed that the ACLR limb (or non-dominant limb in controls) had less LM, lower BMD, and higher fat% (all p≤0.049, all d≥0.49). Both sexes were equivalent for all AI% measures (all p≥0.192, d≤0.49) within the ACLR group. For time since surgery, AI% was similar across groups for limb fat and muscle measures (all p≥0.077), but BMC reached symmetry only after 5+ years [ANOVA p=0.040, eta2=0.199 (large) & LSD post hoc p=0.014, Cohen’s d=0.65 (moderate)], with BMD showing similar trends (ANOVA p=0.051). Conclusion: Despite ACLR’s widespread use to restore knee function in active populations, our findings suggest long-term asymmetries in BMC and similar trends in BMD persist well beyond typical rehabilitation.