Greater eccentric hamstrings to concentric quadriceps strength ratio at 6 months after anterior cruciate ligament reconstruction is associated with reduced odds of revision within 2 years

PURPOSE: To investigate the association between eccentric hamstrings-to-concentric quadriceps strength ratio (mixed hamstrings to quadriceps [HQ]-strength ratio) at 6 months postoperatively and revision anterior cruciate ligament reconstruction (ACL-R) within 2 years of primary surgery. The secondary purpose was to investigate the association between the mixed HQ-strength ratio and single-leg hop for distance limb symmetry index (LSI). METHODS: Data were collected from a local registry at Capio Artro Clinic, Stockholm, Sweden. Patients aged ≥15 years, without concomitant ligament injuries and meniscal resection or repair who underwent primary ACL-R with hamstring tendon autografts between 2005 and 2021 were included. Isokinetic eccentric hamstrings and concentric quadriceps strength were assessed using a Biodex dynamometer 6 months postoperatively. Associations between mixed HQ-strength ratio on the ACL-R leg and revision ACL-R were analysed using multivariable logistic regression analysis, presented with odds ratios (ORs), 95% confidence intervals (CIs) and area under the receiver operating characteristics curve (AUC). Associations between mixed HQ-strength ratio and single-leg hop for distance LSI were analysed with linear regression. RESULTS: Of the 3458 patients included, 49.5% were female and the mean age was 28.8 ± 10.4 years. Patients who underwent revision ACL-R within 2 years had lower mixed HQ-strength ratio on the ACL-R leg 6 months postoperatively. After adjustment for age at primary ACL-R and preinjury Tegner level, each 10-unit increase in the mixed HQ-strength ratio on the ACL-R leg was associated with lower odds of revision ACL-R (OR = 0.81, 95% CI [0.71;0.93], p = 0.003). However, the discriminatory ability was poor (AUC = 0.64). A greater mixed HQ-strength ratio was associated with poorer single-leg hop for distance LSI, adjusted for age at primary ACL-R and preinjury Tegner level (β = -1.30, 95% CI [-1.51;-1.09], p < 0.001). CONCLUSION: The mixed HQ-strength ratio may complement the evaluation of muscle strength recovery after ACL-R. However, its poor discriminatory ability limits its use to identify patients who will undergo revision ACL-R. LEVEL OF EVIDENCE: Level III.