Clinical Predictors of Knee Mechanics at Return to Sport after ACL Reconstruction

Purpose: Despite significant rehabilitation, many athletes experience protracted weakness and faulty mechanics after anterior cruciate ligament reconstruction (ACLR). Clinical tests performed early in rehabilitation, which predict knee mechanics at return-to-sport, are virtually unknown and critically needed to guide clinical decision making. The purpose of this study is to determine if quadriceps strength, Y balance anterior (YB-A) reach distance, and single-leg step-down test performance (SLSD) conducted 3 months post-ACLR are predictive of knee flexion excursion (KFLEX) and knee extensor moment (KEM) during running 6 months post-ACLR. Methods: Thirty (16 females) subjects were collected 3 and 6 months post-ACLR. Age, 21.3 7.6 yr; mass, 69.85 11.4 kg; height, 1.73 +/- 0.09 m. At 3 months post-ACLR, subjects performed isometric quadriceps strength testing, YB-A, and SLSD assessments. At 6 months post-ACLR, subjects underwent three-dimensional motion analysis while running on an instrumented treadmill. Pearson correlation coefficients and stepwise multiple regression were used to assess the relationships of 3-month and 6-month variables. Results: Quadriceps strength (r = 0.493, P < 0.01), YB-A (r = 0.394, P = 0.03), and SLSD (r = 0.648, P < 0.01) were significantly correlated to KFLEX. Quadriceps strength (0.505, P < 0.01) and SLSD (.541, P < 0.01) were significantly correlated with KEM, whereas YB-A (.276, P = 0.06) was not. SLSD and quadriceps strength were predictive of KEM (adj R-2, 0.36; P = 0.001) whereas only SLSD was predictive of KFLEX (adj R-2, 0.40; P < 0.001). Conclusions: After ACLR, better performance in SLSD and quadriceps strength 3 months postsurgery is predictive of improved sagittal plane knee mechanics during running 6 months postsurgery.