Summary
Isokinetic strength test results at 4 months after ACL reconstruction are important objective quantitative markers for predicting return to sport and assessing the risk of reinjury
Abstract
Background
Assessing Quantitative knee strength symmetry at 4 months post-anterior cruciate ligament reconstruction (ACLR) may help to predict functional long-term recovery outcomes. This study presents findings from two related investigations evaluating the association between early isokinetic strength deficits, return to sport (RTS), and reinjury risk.
Return-to-sport In a cohort of 113 ACLR patients (amateur and/or recreational athletes, mean age 25.2 ± 9.7 years, 42% female, 65% patellar tendon), quadriceps and hamstring limb symmetry indices (LSI) at 4 months were significantly associated with strength symmetry at 8 months and successful RTS rates within the first 2 years. A quadriceps LSI (Q-LSI) =60% at 4 months was predictive of achieving Q-LSI >80% at 8 months (p < 0.001) and increased the likelihood of RTS (60% vs. 31%, p = 0.003). Similarly, a hamstring LSI (H-LSI) =73% was associated with H-LSI >90% at 8 months (p < 0.001) and higher RTS rates (53% vs. 23%, p = 0.013). Additionally, factors such as extended tourniquet time, lower level of pre-injury sport, patellar tendon graft and older age were linked to reduced knee strength symmetry at 4 months.
Reinjury risk A secondary analysis in a cohort of 150 ACLR patients (mean age 25.8 ± 9.3 years, 46% female, 57% patellar tendon) investigated the relationship between early strength deficits (4 months) and reinjury risk at a minimum 2 years. Among participants, 24 (16%) sustained a reinjury, with 71% occurring within 36 months, and half of the reinjuries were secondary meniscus tears on the operated knee. Not achieving Q-LSI =60% at 4 months was associated with a 2.7-fold increased risk of reinjury (Z=2.243, p=0.025), reinforcing the relevance of early quadriceps strength assessment in reducing secondary knee injuries. Interestingly Q-LSI was correlated with the timing of reinjury (r=0.548, p=0.006), suggesting that strength asymmetry increases the risk of reinjury during the early postoperative years.
Conclusion
These findings highlight the clinical utility of isokinetic strength assessment at 4 months post-ACLR. Strength symmetry at this stage is predictive of both RTS success and reinjury risk, emphasizing its role in optimizing rehabilitation and return-to-sport decision-making.