Feasibility study for an osseointegrated prosthesis for transhumeral amputees

Osseointegrated prostheses for patients with transhumeral amputation provide a direct connection between the external prosthesis and the patient’s bone. However, there are some problems that are still to be solved. One of the main problems is that not all patients are eligible for the osseointegrated implantation. Commercially available prostheses are produced in a restricted range of sizes. Therefore, they do not account for the high anatomical variability of the medullary canal. A possible solution could be to consider the anatomic variability of the medullary canal in developing a new prosthesis design. The aim was to assess the feasibility of a transhumeral osseointegrated prosthesis that would better match the variability of the humeral medullary canal. To this aim a patent research was conducted. Moreover, an experimental assessment of humeral anatomical variability was carried out. This was followed by the application of SSM to identify the principal modes of variation and to determine the sample size required for convergence in shape analysis. The medullary canals of 64 humeri were segmented from CT images and the resulting 3D meshes were registered to align the structures. Each mesh was then sliced at 19 lengths to simulate different amputation levels. The resulting meshes were subsequently analysed through SSM and PCA to identify and quantify the shape variations of the canals. Finally, the number of instances necessary to obtain accurate results was evaluated through a convergence analysis. Results showed how at most 4 PCs are necessary to explain 90% of the shape variance of each canal segment. The 64 instances available resulted sufficient for all the PCs and canal segment evaluated, with the only exception of the first PC of the segment of 80% of residual canal length. The results highlight relevant shape variation within humeral medullary canal. This supports the idea of adapting the geometry of osseointegrated prostheses to these shape variations.