The hamstring/quadriceps ratio is an indicator of function in ACL-deficient, but not in ACL-reconstructed knees.

Purpose: The purpose of this study was to investigate the isokinetic, eccentric and isometric hamstring/quadriceps (HQ) ratios in patients before and after ACL reconstruction (ACLR) using bone-patellar tendon grafts and to establish the relationships between HQ ratio and knee function.
Methods: Forty-four patients (mean age of 26.6 years) underwent isokinetic testing of quadriceps and hamstring muscles before and after ACLR and HQ ratios were calculated. Lysholm, IKDC and Cincinnati Scores were used to assess function. Isokinetic concentric and eccentric peak torque (Nm/kg) was measured at three different speeds: 60, 120, and 180°/s. Isometric strength was tested at 30° and 60° of knee flexion.
Results: For the isometric tests, the HQ ratio between the involved and non-involved limb was not different for the ACLD knee (p = 0.28) at 30° knee flexion, but significant at the 60° flexion angle (p = 0.02) and for the ACLR knees at 30° and 60° (p = 0.02). For the isokinetic tests, the ratio between involved and non-involved limb was significant for ACL-deficient knees at both 60 (p = 0.039) and 120°/s (p = 0.05). There were significant differences between limbs for all speeds in ACLR knees (p = 0.0003-0.01). For the eccentric tests, the HQ ratio between the involved and non-involved limbs was not significant for both the ACLD (p = 0.19) and ACLR knees (p = 0.29) at the speed of 60°/s. At 120 and 180°/s, there were significant differences between limbs for both the ACLD (p = 0.02) and ACLR knees (p = 0.003). Linear regression did not reveal significant relationships between Cincinnati, Lysholm, and IKDC scores and HQ ratios in the ACLD (R ²  = 0.35, p = 0.58; R ²  = 0.34, p = 0.63; R ²  = 0.38, p = 0.49). In contrast, there were significant correlations between the Lysholm and IKDC scores and HQ ratios in the ACLR knees (R ²  = 0.84, p = 0.002; R ²  = 0.86, p = 0.001).
Conclusions: The findings of this study suggest that the HQ ratio in ACLD patients was not a predictor, but an indicator of patient-perceived knee function following ACLR.
Level of Evidence: Level IV, case series.