Effect of Phase Angle on Change in Quadriceps Muscle Strength 1 Year After Total Knee Arthroplasty: The Screening for People Suffering Sarcopenia in Orthopedic Cohort of Kobe Study.

Background: Phase angle (PhA) has been reported to be associated with quadriceps strength in patients who have knee osteoarthritis and were scheduled for total knee arthroplasty (TKA). The PhA can also be expected to predict the time course of quadriceps muscle strength loss and recovery. We aimed to investigate the relationship between the preoperative PhA and the time course of quadriceps muscle strength change in patients undergoing TKA.

Methods: A prospective cohort study was conducted on patients scheduled for primary unilateral TKA. A total of 855 patents were included in the analysis. The PhA and quadriceps muscle strength of the operated knee were measured preoperatively and at 3, 6, and 12 months postoperatively. To analyze the effect of the preoperative PhA on the change in postoperative quadriceps muscle strength, a linear mixed model with the quadriceps muscle strength as a dependent variable with the preoperative PhA, evaluation period (dummy variable), and their product terms as independent variables was conducted after adjusting for preoperative covariates.

Results: A statistically significant negative effect was present for a higher PhA, resulting in a greater decrease in quadriceps muscle strength between preoperative and 3 months postoperative (P = 0.012). In contrast, the effect was not statistically significant between 3 and 6 months postoperatively (P = 0.17). However, a statistically significant positive effect for a higher PhA resulting in a greater increase in quadriceps muscle strength was present between 6 and 12 months postoperatively (P = 0.027).

Conclusions: Preoperative PhA is a useful predictor of the quadriceps muscle strength change after TKA. These findings suggest that evaluating the preoperative PhA could aid in the development of targeted rehabilitation programs aimed at optimizing quadriceps muscle function in patients undergoing TKA.