Analysis of rising from a chair after total knee arthroplasty.

The relationship between the range of motion following total knee arthroplasty (TKA) and the height of chairs when rising from a seated position was analyzed. Forty-six TKA subjects were evaluated; 16 had osteoarthritis, 30 had rheumatoid arthritis. Subjects were divided into two groups based on their degree of knee flexion (average: 96.0 degrees; range: 75 degrees to 135 degrees; group 1 contained 24 subjects with < 100 degrees of flexion and group 2 contained 22 subjects with > 100 degrees of flexion) in order to evaluate the acceptable knee flexion angle required for comfortably rising from a chair. To evaluate the flexion-extension angle of the knee and hip joints, three goniometers, a large reaction force plate, and a switch sensor on the chair surface to detect the initiation of rising were used. One chair had a height equal to the subjects' lower leg length, while the height of the second chair was 120% of the subjects' lower leg length. Analysis showed that TKA patients with less knee flexion (< 100 degrees) required a high angular velocity of the hip and excessive swing velocity to lift the trunk forward than did those with a larger degree of knee flexion (> 100 degrees). We concluded that a minimum of 100 degrees of postoperative flexion is desired and that a higher chair is more suitable for TKA patients.