Demystifying upper limb hybrid prostheses-a scoping review

Hybrid-power is a prosthesis class that combines body-power and external-power into a singular embodiment. The class is rarely discussed in literature and is ill-defined, with the term "hybrid" being used to describe a broad range of upper-limb prostheses. This is despite the increased use of hybrid-power prostheses in clinical practice for treating people with above-elbow amputations; there is also little literature assessing their performance relative to the functional benchmarks of body-power or external-power prostheses. This scoping review aims to identify the various subcategories of hybrid prosthesis that exist, with an explicit focus on hybrid-power devices, and to report on the designs and use-cases of hybrid-power devices presented in clinical and research contexts. Where possible, comparisons are made between the performance of hybrid-power devices and other active prostheses.

This study follows PRISMA 2020 systematic review reporting guidelines to identify, sort, and select relevant literature from databases. Searches were conducted on three research databases (Scopus, Web of Science, PubMed) and two patent databases (eSpacenet, Derwent Innovations Index) to identify relevant sources on the topic of hybrid-powered prostheses. 142 unique research papers were identified from the three identified research databases, which were screened by title and abstract and further filtered following a full text review, leaving 13 relevant studies and 2 patents which underwent full-text screenings by the lead-author.

Five prominent categories of "hybridisation" were identified: hybrid-power, hybrid-control, hybrid-strategy, hybrid-actuation, and hybrid-feedback. Within the hybrid-power class, two prominent use-cases were identified: increasing active control inputs and reducing the physical effort necessary to operate a prosthesis. Additional use-cases were found within research, including increasing the number of grasps available for a transradial prosthesis, and providing flexible control options in areas with limited resources.

Insufficient quantitative evidence was found to draw any conclusions about the performance of hybrid-power prostheses relative to body-power or external-power devices. Further research should be conducted into the testing of conventional hybrid-power devices using standard clinical means, to establish a meaningful benchmark performance that future developments in research can draw from.