Design of a corrective hip orthosis for patients with abnormal flexor pattern after transfemoral amputation

Transfemoral amputation is a surgical procedure performed to remove the lower limb above the knee joint when that part of the body has been severely damaged by trauma, disease, or congenital defect. The result is the loss of important anatomical structures such as the knee, tibia, fibula, ankle, and foot. Currently, the evolution of this medical procedure has highlighted the relevance of muscle stabilization and biomechanical principles. As a part of most relevant goals, after the amputation process, is to preserve the adductor magnus and perform a myodesis (the muscle is secured to the bone by suturing the distal tendon via pre-drilled holes to the bone) with the purpose to have a functional stump. If biomechanical principles are correctly applied in addition with an effective surgical technique, patients could have better prognosis, and more chances to have a prosthetic device. In addition to this, it’s important to mention that the shape of the residual limb is crucial for the prosthetic fitting and rehabilitation process. On the other hand, there is a lack of information about the relevance of the adductor magnus in preserving the anatomical femur axis after the amputation process. Actually, the loss of function of the adductor magnus, and other adductor muscles, leads to an abnormal abduction and flexion of the femoral stump; this condition modifies the posture, specially when patients are in sitting position or try to walk with crutches. In addition to this, their center of gravity is modified, affecting the possible suspension and handling of the prostheses, in case they have one. According to this, it’s important to correct the abnormal abductor and flexor pattern of the femoral stump before fitting a prosthetic device. Hence, this project aims to develop an orthosis that helps patients to keep the lower limb in a more anatomical position, after the amputation and during their rehabilitation treatment. For the development of this device it was necessary to design an anthropometric protocol taking as a reference the case of a patient with an appropriate transfemoral amputation. The design proposal highlights specific anthropometric measurements, such as residual limb length, circumferences, and shape, to ensure an optimal and fit of the orthosis. For the selection of materials, it was important that these were flexible, comfortable and they didn't cause any discomfort after several hours of use. Additionally, through a system of harnesses that were placed to provide traction, the flexor and abductor patterns were modified to keep the amputated stump in a completely vertical axis.