Method for optimal digit alignment for the fitting of partial hand powered prostheses: A preliminary study

Current fitting procedures of powered partial hand prostheses heavily rely on manual “trial & error” approaches by skilled prosthetists without taking advantage of more modern engineering enabling technologies. Here we preliminary present an optimization method for the placement of the powered digits based on a biomechanical simplified model. The mathematical model is built taking into account the geometry of the residual limb, the functional conditions of the stump and the kinematics of the prosthesis. The optimization refers to the distance, on the palm plane, between the basements of two opposing digits. In particular it focused on the opposition capability of a prosthetic index digit with an unpaired thumb in a pinch grasp. The optimal posture is the one that allows the maximum control accuracy of the force along the direction of the grasp. We argue that the proposed method could be used to predict the quality of the fitting and to standardize the process.