A Cross-sectional Examination of Quadriceps Strength, Biomechanical Function, and Functional Performance From 9 to 24 Months After Anterior Cruciate Ligament Reconstruction

Background: Patients who undergo anterior cruciate ligament reconstruction (ACLR) have deficiencies in strength, functional performance, and biomechanical function at return to activity. Patients who have abnormal strength and function after ACLR may be at a greater risk for secondary injury and posttraumatic osteoarthritis. Purpose: To examine quadriceps strength, functional performance, and knee biomechanics in patients who are 9, 12, 18, and 24 months after ACLR. Study Design: Cross-sectional study; Level of evidence, 3. Methods: We recruited 82 participants (45 female) who underwent ACLR and were cleared to return to activity . Participants were assigned to 1 of 4 groups based on their time from ACLR: 9 months (285.26 +/- 8.16 days), 12 months (373.59 +/- 8.81 days), 18 months (557.50 +/- 11.96 days), and 24 months postoperative (741.05 +/- 11.86 days). Quadriceps strength was measured concentrically at 60 deg/s. Functional performance was assessed by measuring maximal hop distances or heights during dynamic hopping/jumping tests (single-leg hop, triple hop, crossover hop, and single-leg vertical hop). Biomechanical function was evaluated during the dynamic hop tests by using peak sagittal plane knee flexion angles recorded during landings. Strength, performance, and biomechanics data were collected for both limbs and reported as symmetry scores ([injured/uninjured] x 100). Self-perceived function was measured using the International Knee Documentation Committee subjective knee form. Results: Quadriceps strength in the 9-month (77.61 +/- 16.73) and 12-month (77.80 +/- 13.99) groups was significantly lower (P< .01) compared with the 24-month group (92.40 +/- 15.55). Self-perceived function for the 9-month group (79.33 +/- 10.40) was significantly lower (P< .01) when compared with 12-month (87.58 +/- 10.29), 18-month (89.81 +/- 8.36), and 24-month (91.59 +/- 5.70) groups. Single-leg hop distance symmetry was significantly lower (P< .01) for the 9-month group (90.01 +/- 9.46) when compared with the 18-month (96.24 +/- 6.47) and 24-month (96.30 +/- 6.46) groups; triple hop symmetry was significantly lower (P< .05) for the 9-month group (90.26 +/- 10.03) when compared with the 18-month (96.83 +/- 9.60) and 24-month (95.91 +/- 6.36) groups; and crossover hop was significantly lower (P< .05) for the 9-month group (88.35 +/- 13.53) when compared with the 18-month (95.85 +/- 8.63) and 24-month (97.10 +/- 4.12) groups. Conclusion: Quadriceps strength, self-perceived function, and functional performance improve 9 to 24 months after ACLR, indicating that recovery is ongoing after return to activity. Return-to-activity criteria after ACLR should objectively account for strength and function.