Body Composition, Not Body Mass Index, Is Associated with Clinical Outcomes Following ACL Reconstruction

Determine the associations of body mass index (BMI) and body composition (lean and fat mass) with i ) patient-reported outcomes, ii ) quadriceps strength, and iii ) physical performance in anterior cruciate ligament reconstruction (ACLR) patients.

Thirty-four individuals participated (56% female; 22 ± 4 yr; % body fat: 22.9% ± 6.7%). Dual-energy x-ray absorptiometry was used to measure percent lean (%LM) and fat (%FM) mass for the whole-body, and the whole-limb and thigh region of the ACLR limb. Knee Injury and Osteoarthritis Outcomes Score (KOOS) subscales were used to evaluate patient-reported outcomes. Isometric quadriceps strength (maximal voluntary isometric contraction (MVIC)) was measured using an isokinetic dynamometer with the knee flexed at 90°. Single-leg hop (SLH) distance was used to evaluate physical performance. Spearman rank correlations were used to separately evaluate the associations between BMI and body composition with KOOS, MVIC, and SLH.

BMI was not significantly associated with KOOS, MVIC, or SLH ( P > 0.05). Greater whole-body %LM was associated with greater MVIC and SLH, whereas greater whole-body %FM was associated with worse KOOS Activities of Daily Life, MVIC, and SLH ( P < 0.05). Greater whole-limb %LM was associated with greater MVIC, whereas greater whole-limb %FM was associated with worse KOOS Symptoms, Pain, Quality of Life, and MVIC ( P < 0.05). Greater thigh %LM was associated with better KOOS Symptoms and MVIC, and greater thigh %FM was associated with worse KOOS Symptoms, Pain, Quality of Life, and MVIC ( P < 0.05).

Body composition characteristics of higher %LM and lower %FM were associated with better clinical outcomes in ACLR patients of normal BMI status, thereby elucidating a potential modifiable target to mitigate poor ACLR-related outcomes. Future research should further evaluate mechanistic links between body composition and ACLR-related outcomes to inform clinical practice and rehabilitation frameworks.