INTERRELATIONSHIPS OF CLINICAL OUTCOME, LENGTH OF RESECTION, AND ENERGY-COST OF WALKING AFTER PROSTHETIC KNEE REPLACEMENT FOLLOWING RESECTION OF A MALIGNANT-TUMOR OF THE DISTAL ASPECT OF THE FEMUR

The relationships between the functional scope according to the system of the International Society of Limb Salvage, the extent of resection , energy cost of walking, and gait characteristics were studied in thi rty-six patients who had had segmental knee replacement after resectio n of a malignant tumor of the distal aspect of the femur. The mean fre e-walking velocity was 62.3 meters per minute (79 per cent of normal), which was a result of decreases in both cadence and stride length. Th e mean nea energy cost during walking was 35 per cent greater than tha t of normal controls and correlated with the percentage of the femur t hat had been resected. All patients had decreased single-limb support time on the affected side compared with the unaffected side. There was a weak correlation between the asymmetry of the single-limb support t ime and the percentage of the femur that had been resected. The mean e xtensor torque of the affected knee was 30 per cent that of the unaffe cted knee when one head of the quadriceps muscle had been excised, 19 per cent when two heads had been excised, 4 per cent when three heads had been excised, and 1 per cent wheal four heads had been excised. Th e patients who had had an extra-articular resection had lower mean ext ensor and flexor torques at the knee compared with those who had had a n intra-articular resection. The asymmetry of the single-limb support time was inversely related to the residual extensor and flexor torques . The overall score according to the system of the International Socie ty of Limb Salvage ranged from 17 to 29 points (mean, 24.6 points; 82 per cent of normal). The net energy cost, percentage of maximum aerobi c capacity, and asymmetry of the single-limb support time had signific ant negative correlations with the overall functional score. Multivari ate analysis showed that the overall functional score anal the percent age of the femur that had been resected were the two most important fa ctors that predicted the net energy cost, pb our knowledge, this is th e first objective validation of the functional score according to the system of the International Society of Limb Salvage. As the wet energy cost can be predicted from universally available, inexpensive measure s, investigators can easily use it as a clinical and research tool to evaluate prosthetic performance and to assess operative outcome.