A patient-matched prosthesis for thumb amputations: design, mechanical and functional evaluation

Thumb amputations strongly affect hand functionality in daily activities. The currently available solutions, such as microsurgical treatments and external vacuum prostheses present disadvantages, which can be successfully addressed through the osseointegration technique. However, despite its widespread use in oral applications, only a few osseointegrated solutions for the treatment of hand-finger amputations are available. Bone remaining limbs may have different lengths, diameters, and conditions and no patient-matched osseointegrated medical devices are available on the market. The manuscript presents the first patient-matched medical device for the treatment of thumb amputations. The prosthesis mainly consists of three components: an osseointegrated fixture which is implanted into the medullary canal of the bone remaining limb, an abutment, and an external digital prosthesis. The design phase is followed by computational and experimental analysis to optimize the design of each component attached to the osseointegrated fixture in order to preserve the implant fixture and bone. The maximum force generated during the pinch test in a healthy subject is approximately 80 N. The mechanical performance required during daily activities is achieved by the novel proposed device and the obtained results confirm that, in case of loads greater than daily ones, the failure may occur in the abutment component which is external to the body. A limitation of the current study consists in the lack of analysis on the bone-implant interface for which specific investigations would be required: currently, the contact between bone and fixture is assumed to be fixed, i.e. no micro motions are considered. Research is ongoing to test the entire device in a clinical study to collect quantitative and qualitative information from patients and surgeons.