Preliminary design of an active hip prosthesis for disarticulated amputees

Lower limb amputations are events that affect human mobility and health at different levels, causing the person to partially or totally lose his/her independence and quality of life. When amputations are performed at lower levels, like the ankle joint, although traumatic, there are several technological advances that can fairly reestablish the patient's healthy biomechanics. However, as the amputation is done at higher levels, like the hip, the challenges to successfully replace the healthy system increase exponentially. Hip disarticulation and hemipelvectomy are amputations at the level of the hip joint. Individuals who suffer this loss, present reduced levels of motor function compared to other amputees and their mobility is limited by the lack of available prostheses that can efficiently replicate biologically accurate movements. To be able to use a prosthesis, they require a great deal of rehabilitation training and even if they can walk using it, their walking speed and metabolic cost are out of the normal ranges of healthy individuals. Given the low incidence rates compared to other types of amputations, few studies and technological improvements have been done to help these patients recover their mobility. Evidence in prosthetics have shown that active actuation during gait improves the biomechanics and metabolic costs of amputees, and yet for hip disarticulation no active joints have been released. In this thesis, the concept of active prosthetics is explored with the purpose of designing a prosthetic hip joint. By studying the mechanical advantages of the best passive prosthetic hip joint, together with the supporting evidence of the need of hip actuation, the preliminary design of a prosthetic hip joint was done. A polycentric and compliant electromechanical prosthetic hip joint, fixed anterior to the socket was chosen. The design proposed is based on (i) a timing belt with the proximal pulley fixed, (ii) a four-bar mechanism and (iii) a parallel spring, that reduces the torque and power demands of the joint; thus, increasing energy-efficiency and reducing the size of the motors. The selection of the main components in the catalog, the estimation of the stiffness for the parallel elastic actuator (PEA) and their optimal assembly in the virtual volume of the prosthetic joint were achieved.