Quantification of benefits in terms of fit and fill of a customized osseointegrated prosthesis for tranfemoral amputees

This study presents a localized imaging-based analysis comparing the performance of a customized osseointegrated transfemoral prosthesis, the OsteoCustom, to a standard commercial prosthesis. The primary focus was to evaluate the fit and fill characteristics by quantifying cortical bone removal and implant-host bone contact. These key factors may influence the biomechanical stability of osseointegrated implants. The study utilized pre- and post-implant CT images of femur specimens to analyze how much cortical bone was removed during implantation and to measure the contact area between the implant and the femur. Bone removal was quantified both in volume and cortical thickness across eight equidistant regions of the femoral cross-section. This approach allowed for a detailed, regional assessment of bone preservation and implant fit. The customized OsteoCustom stem demonstrated a clear advantage in preserving cortical bone, particularly in the distal regions of the femur. The customized design, tailored to match the natural ellipticity and anatomical variability of the femoral canal, resulted in less bone removal compared to commercial implants. This was especially evident in more elliptical regions, where commercial stems, designed in standardized, limited sizes, often caused more aggressive bone removal. A notable outcome was the reduction in the range of cortical thickness removal with the OsteoCustom stem. Unlike commercial implants that exhibited greater fluctuations in bone removal due to their standardized shapes, the customized design provided a more homogeneous and consistent removal pattern. Both the customized and commercial implants achieved good contact area values, which is essential for primary stability and osseointegration. However, the OsteoCustom stem achieved good contact while preserving more cortical bone. In contrast, commercial stems required extensive bone removal to achieve a similar level of contact, especially in regions with high anatomical variability. Additionally, at the resection site — where the femur is cut for implant insertion — the OsteoCustom stem showed a significantly higher contact area. This may suggesting better stability and initial fixation. The study highlighted that commercial stems may not be viable for certain femurs, particularly smaller specimens. In these cases, commercial designs led to excessive bone loss and extremely thin remaining cortical walls, which could compromise implant stability or even preclude implantation. The OsteoCustom stem, by adapting to individual femoral geometry, mitigated these issues, offering a feasible solution for more patients. The findings suggest that customized osseointegrated implants offer several advantages over commercial stems. The first advantages is the improved anatomical fit and fill. Additionally, it reduced bone loss, both globally (volume) and locally (cortical thickness).The customized OtsweoCustom stem allowed for better adaptation to anatomical variability, expanding the range of patients eligible for implantation. Lastly, it provided higher contact area at the resection site.