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Although total knee arthroplasty (TKA) has been studied extensively, objective muscle testing has not been reported. Isokinetic testing of 68 patients with degenerative joint disease scheduled for unilateral TKA revealed that marked muscular deficits in flexion and extension were present preoperatively in the involved knee. Postoperatively, hamstring peak-torque values were able to attain strength levels of the uninvolved knee within the period of seven to 12 months after surgery, whereas the quadriceps mechanism still showed a residual deficit at two years follow-up evaluation. In addition, the ratio of flexion to extension peak torques in the operated knee returned to normal values as the quadriceps mechanism was rehabilitated. A comprehensive evaluation system consisting of Cybex II isokinetic testing, gait mat analysis, and the Hospital for Special Surgery knee rating scale is also presented. Isokinetic testing correlated well with gait analysis. Patients with a nearly balanced quadriceps-to-hamstring ratio walked with a more symmetrical gait pattern. The knee rating scale was less reliable in assessing functional outcome. Functional testing and evaluation at the authors' institution has provided an important source of objective information that allows better planning and evaluation of TKAs. These isokinetic studies enable more critical planning of the rehabilitation program. Hamstring or quadricep exercises may be emphasized as required. The authors conclude that a balanced hamstring to quadriceps mechanism is needed for resumption of normal gait.

Using a gait mat, we characterized the functional results for thirty-five patients before and after a total knee replacement for the treatment of degenerative arthritis. Preoperatively, we studied three distinct populations of patients. Group I consisted of sixteen patients who were scheduled to have a unilateral total knee replacement and who had no signs or symptoms of arthritis in the contralateral knee. Group II consisted of twelve patients who were scheduled to have a unilateral total knee replacement but who had asymptomatic degenerative arthritis in the contralateral knee. Group III consisted of seven patients who had bilateral arthritis that was to be managed by total knee replacement. The gait mat allowed us to measure stance time, step length, double-support time, swing time, swing-to-stance ratio, and velocity. A knee-rating scale was used to measure pain. The data were compared with those obtained from an age-matched control group of ninety-one subjects. Postoperatively, the gait evaluation revealed marked improvement in all of the patients. However, the patients in Group II did not improve as much as those in Groups I and III did. We concluded that even asymptomatic arthritis can impair gait, that bilateral total knee replacement can yield excellent results, and that patients tend to use the lower limbs in as symmetrical a way as possible. Gait analysis can be an important source of objective information, and it is easily performed by using a gait mat.