Pre-clinical assessment of an intuitive prosthetic elbow control strategy using residual limb motion with osseo-integrated patients

Abstract

Most transhumeral amputees deplore that their prosthesis lacks functionality due to control-related limitations. Externally powered prosthetic devices are commonly controlled via myoelectric control whereby biceps and triceps contractions drive sequentially the prosthetic joints. Because of a complex control scheme, transhumeral amputees are generally equipped with a 1-degree-of-freedom myoelectric hand, a myoelectric wrist rotator, and a manually locked elbow, despite the commercialization of more advanced devices. This results in the development of compensatory strategies to overcome the prosthesis’ lack of mobility. An alternative control strategy relates the residual limb motions to the prosthetic elbow motion using the natural coordination between shoulder and elbow observed in healthy movements. However, conventional external sockets tend to prevent the residual limb mobility, limiting the potentiality of this novel control strategy. Osseo-integration enables a stable attachment of the prosthetic device and frees the residual limb. This study focuses on the performance of three osseo-integrated patients using an automatically driven prosthesis. A prosthesis prototype including a myoelectric hand, a wrist rotator, and a motorized elbow was mounted on the participants’ abutment from the osseo-integrated implant system. The subjects were asked to point at targets while the motorized elbow was controlled by residual limb movements based on a model of healthy shoulder/elbow coordination. For comparison purposes, the task was also performed with conventional sequential myoelectric control. Body movements were assessed with the data recorded with a motion capture system. Large trunk compensatory movements were measured during pointing gesture with a myoelectrically driven elbow. Automatic control of the elbow enabled a more natural body behavior whereby the trunk displacements were small, and the shoulder and the prosthetic elbow were moving synchronously. The study shows that osseo-integration made possible residual limb movements of large amplitudes, allowing the participants to achieve the pointing task with a prosthetic elbow driven by the residual limb motions. Moreover, simultaneous control of elbow and end-effector was achieved by one subject. Hence, this work highlights the interest of combining osseo-integration with an automatic control strategy for intermediate joints in terms of compensatory movement reduction and control intuitiveness gain.