Quadriceps Function Does Not Differ Between Subjects With ACL Reconstruction With Impulsive Vs. Normal Loading

Abstract

Individuals with anterior cruciate ligament reconstruction (ACLR) are at a significant greater risk of knee osteoarthritis (OA). The heelstrike transient (HST) during gait is indicative of impulsive/high-rate loading, which has been implicated in cartilage degradation and knee OA development. The quadriceps attenuates loading during gait, and quadriceps dysfunction following ACLR may contribute to impulsive loading and knee OA risk. PURPOSE: To determine the differences in quadriceps function between impulsive loaders and non-impulsive loaders during walking gait. METHODS: Forty-five volunteers with unilateral ACLR participated in this study (32F, 20±3 years old, 71±19 kg, 1.7±0.1 m, 23±15 [range 7-58] months post-ACLR). Quadriceps function in the ACLR limb was quantified during maximal isometric contraction at 90° of knee flexion via the peak torque, rate of torque development (RTD) from 20% to 80% of the interval from onset to peak torque, RTD from onset to 100 ms, and RTD from 100ms to 200ms. All values were normalized to body mass. Gait biomechanics were assessed during overground walking at a self-selected pace. A trial was classified as possessing a HST if the ratio of the vertical ground reaction force peak immediately following heelstrike to the impending local minimum exceeded 1.2. Subjects were classified as “Impulsive” loaders if a HST was identified in at least 3 of 5 of trials. Independent t-tests and correlations were utilized for the analysis. RESULTS: 31% of the subjects were identified as Impulsive loaders. However, there were no significant differences between Impulsive and Normal loaders for RTD20-80% (0.41±0.46 vs. 0.42±0.44, p=0.96), RTD0-100ms (2.9±1.9 vs. 3.5±2.6, p=0.41), RTD100-200ms (2.5±1.4 vs. 2.3±1.5, p=0.62), or peak torque (2.2±0.7vs. 2.3±0.7, p=0.45). There were no significant correlations between the %trials with HST and the quadriceps function indices (r=-0.043-0.172, p=0.258-0.952). CONCLUSION: Roughly 1/3 of our subjects were identified as Impulsive loaders. This statistic mirrors the risk of knee OA development (~30%) in the first decade following ACLR. Our data suggest that this relationship is not associated with quadriceps function. Future research is necessary to determine the role of the HST in knee OA development and the factors that contribute to its presence.