Muscle function after endoprosthetic replacement of the proximal tibia:Different techniques for extensor reconstruction in 17 tumor patients

Abstract

We analyzed in 17 patients the outcome of various surgical techniques for reconstruction of the extension apparatus after resection of the proximal tibia and tumor prosthesis implantation. The mean follow-up period was 5 (1.5-11) years. Knee extension and flexion strength were measured isokinetically by dynamometer and muscle activities of the vastus medialis, the vastus lateralis and the rectus femoris muscles determined by means of EMG. Muscle function of the operated leg was compared to that of the contralateral extremity by using various surgical techniques: fibula transposition, transposition of the gastrocnemius muscle, and combination technique. The results concerning the operated leg were compared within the 3 groups and the activity and strength of both legs were compared to those of a control group of healthy subjects matched for age and weight. The strength of extensor muscles of the healthy leg was greater than that of the control group in flexion position (60°-90°); the hamstring strength values were within the normal range. The strength of extensor muscles of the operated leg differed between groups II and III at 90° in favor of group II (p < 0.01) and at 60° to 20° (p < 0.001) in favor of group III. Expressed in percentage ranges (nonoperated leg set at 100 percent) the flexor muscles averaged 30 percent, the extensor muscles represented on average 12 percent (9-17 percent) in group I, 9 percent (5-18 percent) in group II and 16 percent (6-26 percent) in group III, depending on the knee angle. In all 3 groups the EMG of the nonoperated leg indicated the highest activity in the vastus medialis or in the vastus lateralis muscle and the lowest activity in the rectus femoris muscle. In contrast, the highest EMG activity was registered in the rectus femoris muscle and the lowest in the vastus medialis muscle of the operated leg in all patients of all 3 groups.