Quadriceps Strength Loss Following Total Knee Arthroplasty as a Predictor of Three-Month Strength Recovery: A Secondary Analysis of a Randomized Controlled Trial

Background and objectives Patients often experience significant quadriceps muscle weakness immediately after total knee arthroplasty (TKA), which can persist and lead to reduced physical function, increased risk of falls, and reduced patient satisfaction. Immediate postoperative quadriceps weakness is commonly caused by several factors, such as preoperative quadriceps weakness related to knee osteoarthritis (OA) and TKA-induced quadriceps weakness. Although many interventions have focused on addressing knee OA-related quadriceps weakness, there may be fewer studies specifically investigating TKA-induced quadriceps weakness. This study aimed to clarify whether TKA-induced quadriceps weakness is a significant predictor of quadriceps strength at three months postoperatively, highlighting the clinical importance of preoperative interventions targeting this specific weakness. Methods This secondary analysis of a randomized controlled trial included patients aged 60-79 years with advanced knee OA who underwent unilateral TKA. The study used pooled data from two groups of 11 participants each: those receiving preoperative low-intensity resistance training with blood flow restriction and those performing low-intensity resistance training with slow movement and tonic force generation. Quadriceps strength was assessed using a pull-type handheld dynamometer preoperatively at six weeks and one week as well as postoperatively at four days, one month, and three months. TKA-induced quadriceps weakness was defined as a change in strength from one week preoperatively to four days postoperatively. Postoperative quadriceps strength gain, reflecting postoperative recovery, was defined as the strength change from four days to three months postoperatively. Correlation and multiple regression analyses were used to identify the predictors of postoperative quadriceps strength at three months. Statistical significance was set at p < 0.05. Results The analysis included 22 participants. The median preoperative quadriceps strength was 1.1 Nm/kg (IQR: 0.9-1.4) at six weeks and 1.3 Nm/kg (IQR: 1.1-1.4) at one week. Quadriceps strength significantly decreased immediately after TKA (median quadriceps strength dropped to 0.4 Nm/kg (IQR: 0.3-0.4) at four days postoperatively) and gradually improved over three months (median three-month postoperative quadriceps strength was 0.9 Nm/kg (IQR: 0.8-1.0)). TKA-induced quadriceps weakness was -72% (SD: 11%), and postoperative quadriceps strength gain was 210% (IQR: 98-324%). TKA-induced quadriceps weakness was strongly correlated with quadriceps strength at four days (r = 0.84, p < 0.01). The postoperative quadriceps strength at four days was significantly correlated with the quadriceps strength at three months (r = 0.51, p = 0.02). Regression analysis showed that one-week preoperative quadriceps strength, TKA-induced quadriceps weakness, and postoperative quadriceps strength gain significantly predicted quadriceps strength at three months (R² = 0.77, p < 0.001). Conclusions This study highlights TKA-induced quadriceps weakness as a key predictor of postoperative quadriceps strength at three months. Preoperative interventions targeting TKA-induced weakness may improve postoperative recovery of quadriceps strength and functional outcomes.