Postoperative strength of knee flexor and extensor, and functional evaluation after arthroscopic menisectomy of the knee was evaluated objectively at the time of returning to daily life.

The 31 knees (29 patients) had meniscal injuries without associated ligament injury. The muscle strength was tested with Cybex 340 isokinetic dynamometer preoperatively and at 2, 4, 6, 10 weeks postoperatively. Clinical evaluation by Lysholm scoring system was also done simultaneously. The statistical analysis was evaluated by repeated measures of ANOVA.

Muscle strength of extensor (quadriceps) was abruptly decreased to about 45% torque of the preoperative level at postop 2 weeks, but slowly increased to about 90% torque at 10 weeks in 90 degree/sec and 180 degree/sec exercise. The flexor strength was also a little bit decreased at post-op 2 weeks, slowly increased to about 120%-150% torque of preoperative level in 90 degree/sec and 180 degree/sec exercise at post-op 10 weeks. The clinical evaluation by Lysholm scale showed 45 points at postop 2 weeks and slowly improved to 80 points at post-op 10 weeks.

Muscle weakness of knee extensor and flexor remained in isokinetic test at post-op 4-6 weeks. The recovery rate for weakness of hamstrings was faster than quadriceps. The rehabilitation of quadriceps should be accentuated in the prevention of knee injury due to muscle weakness.