Selective thigh muscle atrophy in trans-tibial amputees: an ultrasonographic study

In trans-tibial amputees, PTB (patellar tendon bearing) prostheses provide almost physiological mobility of the knee joint in the sagittal plane. Neve rtheless, there are characteristic adaptations of the knee joint muscles. M yosonography is a suitable method for depicting muscle atrophy and hypertro phy due to muscle dysfunction. The present study was intended to assess ana tomical alterations of thigh muscles in trans-tibial amputees wearing a PTB prothesis. Thicknesses and cross-sectional areas of the quadriceps femoris , sartorius, gracilis, semitendinosus and biceps femoris muscles were deter mined ultrasonographically on both limbs in 17 amputees with a PTB prothesi s. The gait was analysed using an optoelectronical system, force plates and surface electromyography of the vastus lateralis and biceps femoris muscle s. Quadriceps femoris and sartorius muscles of the amputated extremity exhi bited significant atrophy compared with the contralateral limb (reduction o f muscle thickness ranged between 11.7% and 30.4%), whereas the gracilis an d hamstring muscles were not significantly affected. Even the quadriceps fe moris muscle of the non-amputated limb showed a slight atrophy compared wit h a reference group. Increased echointensities were found predominantly in the quadriceps muscle on the amputated leg. During gait, electromyographica l activity within the amputated limb was reduced in the vastus lateralis an d increased in the biceps femoris muscle. Even long-term adaptation to PTB prostheses results in characteristic deviation from normal gait. Atrophy oc curs in the ventral thigh muscles, predominantly on the amputated leg, wher eas the dorsal thigh muscles are hardly affected, probably due to compensat ory hyperactivity.