Change in hamstring parameters by isokinetic analysis after arthroscopic ACL reconstruction using hamstring graft – A prospective study

Background and objectives: Anterior cruciate ligament (ACL) injuries are common among individuals who lead active lifestyles. A frequently used surgical approach to address this condition is ACL reconstruction (ACLR) utilizing autografts derived from the semitendinosus and gracilis (ST/G) tendons. The current study aimed to assess changes in isokinetic knee strength over a period of 18 months, while also comparing functional outcomes between patients who underwent ST/G ACLR and healthy individuals matched by age and activity level. Materials and methods: This prospective cohort study involved 102 participants—51 recreationally active individuals who underwent primary arthroscopic ST/G ACLR, and 51 healthy controls matched for age and activity. Isokinetic knee strength for both flexion and extension was evaluated at angular velocities of 60°/s, 90°/s, and 180°/s across three time points: 6, 12, and 18 months post-surgery. Functional outcomes were assessed using the Lysholm score, Tegner activity scale, and the International Knee Documentation Committee (IKDC) subjective knee form. Repeated measures analysis of variance (RM-ANOVA) with Bonferroni corrections was used for statistical comparison between groups and across time points. Results: Patients in the ACLR group demonstrated statistically significant improvements in quadriceps and hamstring strength at each follow-up compared to their baseline values (p < 0.001). By 18 months postoperatively, their strength approached that of the control group, particularly at higher movement speeds. Hamstring-to-quadriceps (H/Q) ratios progressively normalized throughout the follow-up period. Functional outcome scores revealed substantial recovery: Lysholm (mean: 98.4 ± 3.0), IKDC (mean: 86.6 ± 6.7). However, Tegner scores reached a plateau during the earlier recovery phases and showed limited progression afterward. Conclusion: Patients undergoing ACLR with ST/G autografts exhibited continuous improvements in muscle strength and knee function over an 18-month period. Comparisons with healthy counterparts suggest that muscular balance and full functional recovery, especially concerning return-to-sport potential, extend well beyond six months post-surgery. This underscores the importance of long-term rehabilitation programs to support complete recovery.