Muscle strength in patients with unicompartmental arthroplasty

The aim of the current study was to evaluate the isokinetic strength of the knee in patients with unicondylar prostheses, to compare these results with healthy control subjects of the same age, and to correlate these results with clinical scores.

Seventeen patients were examined an average of 21.5 mos after surgery. Clinical examination was done using the Hospital for Special Surgery, Knee Society, and patellar scores and a visual analog scale for pain. Quality of life was assessed by the Short Form 36 Health Questionnaire. Isokinetic evaluation of knee extensor and flexor muscles was done using a Cybex 6000 dynamometer at angular velocities of 60 and 180 degrees/sec. Eleven healthy subjects of comparable age served as a control group.

Clinical results differed significantly in all categories. Quality of life differed only in the items of physical functioning, role limitation because of physical problems, and bodily pain. Isokinetic strength in patients showed a loss of torque of approximately 30% in extension and flexion at 60 and 180 degrees/sec compared with the control group. The flexion and extension ratio and the angles of maximum torque did not differ between the groups.

In comparison with healthy control subjects, persons with an implanted unilateral sledge prosthesis have strength deficits in extension and flexion. A deficit of the extensor muscles, as it has been described previously for patients with a total knee arthroplasty, could not be found.