Associations Among Changes in Body Composition, Activity, Muscle Recovery, and Obesity Following Total Knee Arthroplasty: A Retrospective Study.

Purpose: Total knee arthroplasty (TKA) is expected to improve knee pain and enable patients to regain the ability to walk, but the associations between preoperative and postoperative changes in body composition, muscle strength, and activity remain unclear. In this study, we investigated the association between changes in body composition before and after TKA surgery, the recovery process of muscle strength, and changes in activity, as well as the effects of obesity on TKA.

Methods: A total of 124 patients with unilateral knee osteoarthritis (OA) who underwent TKA were retrospectively evaluated. Body weight (BW) and body composition (body fat percentage (BFP) and diseased limb muscle mass (DLMM)), measured by bioelectrical impedance analysis, quadriceps muscle strength (QMS), measured using the isometric muscle strength meter, number of steps (NOS), and Japanese Orthopaedic Association (JOA) OA knee diseases treatment outcome criteria (JOA score) before the operation, at postoperative six months (PO6M), and at postoperative one year (PO1Y) after the operation were investigated and compared between the non-obese (BMI < 25 kg/m²) group, including underweight (<18.5 kg/m²) and normal weight patients (18.5 to 24.9 kg/m²), and obese (BMI ≥ 25 kg/m²) group, including overweight (25.0 to 29.9 kg/m²) or obese patients (≥30.0 kg/m²).

Results: In all patients, JOA scores significantly improved from 59.7 preoperatively to 81.2 at PO6M, and 82.7 at PO1Y (both p < 0.01). QMS significantly increased from 112.4 N preoperatively to 144.0 N at PO6M, and 151.0 N at PO1Y (both p < 0.01). On the other hand, there was no significant change in BW, BFP, NOS, and DLMM. A comparison between the obese (n = 76) and non-obese (n = 48) groups demonstrated that there was no significant difference in JOA scores preoperatively, but scores at PO1Y were significantly higher in the non-obese group (p < 0.01), and QMS increased significantly postoperatively in both groups, but the enlargement rate at PO1Y was 1.4% in the obese group versus 10.4% in the non-obese group (p = 0.04).

Conclusion: In the body composition of TKA patients, BW, BFP, and DLMM/BW did not change significantly from preoperatively to PO1Y, but QMS and JOA scores showed significant improvement at PO6M and PO1Y compared to preoperatively. The obese patients showed less improvement in JOA scores than non-obese patients, and the rate of increase in QMS at PO1Y was smaller, suggesting that rehabilitation focusing on muscle-strengthening training is necessary even at PO6M, especially in obese patients.