Continued Improvements in Quadriceps Strength and Biomechanical Symmetry of the Knee After Postoperative Anterior Cruciate Ligament Reconstruction Rehabilitation: Is It Time to Reconsider the 6-Month Return-to-Activity Criteria?

Context: Patients who undergo anterior cruciate ligament reconstruction (ACLR) present with strength and biomechanical deficits at return to activity (RTA). Deficits in strength and biomechanical symmetry impair function during activity and may predispose patients to subsequent injury. Objective: To compare strength and biomechanical function in patients with ACLR at RTA and more than 12 months post-ACLR. Design: Descriptive laboratory study. Setting: Research laboratory. Patients or Other Participants: A total of 20 participants (12 females, 8 males; age = 21.40 ± 5.60 years, height = 171.3 ± 10.2 cm, mass = 73.21 ± 19.41 kg) who had undergone ACLR and were cleared to RTA were recruited. Intervention(s): Strength was measured during knee extension and evaluated by the isometric and isokinetic quadriceps index. Biomechanical function was evaluated using symmetry values for sagittal-plane knee-joint rotations, changes in sagittal-plane knee-joint rotation, knee-extension moments, and changes in knee-extension moment that were recorded during a single-legged forward hop. Main Outcome Measure(s): Self-reported function was measured using the International Knee Documentation Committee Subjective Knee Evaluation Form. Participants were assessed at RTA (212.25 ± 28.11 days) and more than 12 months post-ACLR (556.25 ± 230.89 days). Results: At RTA, strength and biomechanical values were less than 80% symmetric. We observed improvements from RTA to more than 12 months post-ACLR for the isometric quadriceps index (F1,18 = 29.22, P .001), isokinetic quadriceps index (F1,18 = 10.88, P = .004), sagittal-plane knee-joint rotations (F1,19 = 9.58, P = .006), change in sagittal-plane knee-joint rotations (F1,19 = 7.83, P = .01), knee-extension moments (F1,19 = 5.73, P = .03), change in knee-extension moments (F1,19 = 21.10, P .001), and self-perceived function (F1,19 = 11.50, P = .003). Of the 7 variables that showed improvement at more than 12 months post-ACLR, only 3 met the recommended criteria (≥90%). Conclusions: Patients with ACLR showed asymmetry in strength and biomechanics at RTA. These asymmetries, along with self-perceived function, improved over time. However, despite improvements in strength and biomechanics at RTA, asymmetries of more than 10% were still present more than 12 months post-ACLR.