To learn about the changes appearing in hip muscles after an above-knee amputation, 3-dimensional reconstructions of the hip and thigh region of 12 patients with above-knee amputations were made based on transverse magnetic resonance images. In all patients, the amputations were done at least 2 years before the study and were necessitated by trauma or osteosarcoma. The results show that, at higher amputation levels, the geometry of the once-biarticular muscles was changed. The cleaved muscles (40%-60%) and the intact muscles (0-30%) at the amputated side were atrophied. The amount of atrophy of the intact muscles at the amputated side was related to stump length. To avoid an abduction contracture in 8 patients with amputations, the iliotibial tract was not fixed. In 4 of these 8 patients, a flexion contracture was visible. If the tract was not fixed, the hip extension torque of the gluteus maximus, which inserts into the tract, decreased. As a result, the risk of appearance of a flexion contracture increased because the strongest hip flexor (iliopsoas muscle) was not involved in the amputation. Abduction contracture could be avoided only if the hip adductors were fixed accurately, especially at higher amputation levels.