PAPER 058: MUSCLE CO-ACTIVATION PATTERN DIFFERENCES PRE, ONE-YEAR AND TWO-YEAR POST TOTAL KNEE REPLACEMENT

Abstract

Purpose: To test for a decrease in knee musculature co-activation at one- and two-year post total knee replacement (TKR) compared to pre-TKR values.

Method Thirty men and 35 women with knee osteoarthritis (OA), after providing informed consent, participated in this study. Surface electromyograms (EMG) recorded the activation of seven muscle sites (rectus femoris, vastus lateralis and medialis, lateral and medial hamstrings, lateral and medial gastrocnemius) while subjects ambulated, at a self-selected velocity, along a six-meter walkway; one week prior to TKR surgery, and one- and two-years post-TKR. Linear enveloped EMG waveforms, amplitude normalized to 100%MVIC and time normalized to 100% of the gait cycle, were entered into a principal component analysis model [1]. A two-factor (pre-post, muscle) repeated measures ANOVA was applied to test statistically significant main effects (pre-post, muscle) and interactions (alpha = 0.05).

Results: The mean age, mass and height pre-TKR were 63.4 years, 91.4 kg and 1.69 m, respectively. Forty seven and 25 subjects completed the one- and two-year follow up, respectively. Walking velocity increased from 0.9 m/s pre-TKR to 1.1 m/s for both one- and two-year post TKR. Four principal components explained 89% of the variance in the waveform data. PC1 (60% of the variance), associated with co-activation throughout the entire stance phase, was found to be statistically significant (p< 0.05). The post hoc analysis revealed no significant differences between one- and two-year post-TKR PC1 scores, but the two vasti muscles and lateral hamstring had significantly lower PC1 scores post-TKR compared to pre-TKR values. There were significant differences among muscles with the two vasti muscles higher pre-TKR compared to all other muscles, and lateral hamstring higher pre-TKR than the remaining four muscles.

Conclusion: PC1 captured a co-activation pattern illustrating muscle activation during the majority of the stance phase of gait for the vasti and lateral hamstring muscles. This pattern, previously shown in severe OA gait [1], is considered an adapted response to the pain and joint instability associated with latter stages of OA progression. These findings support that the neuromuscular control strategies are altered within one year with no additional change for the two year post-TKR measures. These results support a more efficient neuromuscular control strategy post-TKR and perhaps an associated decrease in metabolic cost and an improvement in function.