Isometric muscle strength and endurance after knee arthroplasty with the modular knee in patients with osteoarthrosis and rheumatoid arthritis.

Maximum isometric muscle strength and endurance were used in an investigation of knee extension and knee flexion in patients with rheumatoid arthritis (RA) and osteoarthrosis (OA) with such severe changes of the joint that arthroplasty with the Modular prosthesis was performed. The measurements were done preoperatively and 3, 12, 24 and 36 months postoperatively. Muscle strength preoperatively was very weak compared with that of a group of healthy persons. The muscle strength 3 months postoperatively remained unchanged, which could mean a very slight trauma from the operation, very good pain relief and efficient physiotherapy. During the first 2 years the maximum isometric muscle strength was significantly increased both in patients with RA and in those with OA. Thereafter there was no increase in the RA patients, whereas in women with OA there was an improvement up to 3 years postoperatively. The improvement in the flexion strength was greater than that of the extension strength, thus indicating the importance of postoperative training of extension strength. Isometric muscle strength measurements show that there is an equalization between the non-diseased knee and the one operated with the Modular knee.