Early Measures of Torque Development are Related to Peak Torque at Six Months Following ACL Reconstruction

Background and Purpose Individuals following anterior cruciate ligament reconstruction (ACLR) are at increased risk for subsequent anterior cruciate ligament (ACL) injury, with quadriceps strength deficits being a risk factor. While early measures of quadriceps strength can predict strength in the later stages of rehabilitation, it remains unclear whether isometric rate of torque development (RTD) is related to later outcomes. The purpose of this study was to examine the correlation between quadriceps RTD values at four months post-ACLR and quadriceps isokinetic peak torque values at six months post-ACLR. It was hypothesized that isometric RTD at four months would be significantly correlated with isokinetic peak torque at six months post-ACLR. A secondary hypothesis was that the involved limb RT would be significantly slower than the uninvolved limb at four months post-operative. Study Design Retrospective case series Methods Forty-seven patients (22 males and 25 females) who had undergone ACLR performed isometric testing at four months and isokinetic testing at six months post-operatively. Isometric testing was utilized to measure torque from 0-100ms (RTD₁₀₀) and from 100-200ms (RTD₂₀₀), and isometric peak torque. Isokinetic testing was utilized to measure peak torque at 60°/sec and 180°/sec. Correlations between isometric and isokinetic measures were evaluated using Spearman’s rho. RTD was compared between the involved and uninvolved limbs. Results The four-month measures of RTD₁₀₀ (r=.55, r=.45), RTD₂₀₀ (r=.63, r=.52), and peak isometric torque (r=.77, r=.64) were all significantly correlated with 60°/sec and 180°/sec isokinetic peak torque (p≤0.001), respectively. The involved limb rate of torque development was slower, and strength was lower than the uninvolved limb (p<0.001). Conclusions The hypotheses were supported as four-month isometric measures were moderately to strongly correlated to six-month isokinetic peak torque measures and the involved limb RTD was slower than the uninvolved limb. Incorporation of interventions focusing on development of force quickly is encouraged during rehabilitation.