Development of a fail-safe protective adapter for osseointegrated prosthetic limbs: Experimental and numerical investigation

• A novel fail-safe protective adapter was designed for osseointegrated prosthetic limb use. • The adapter utilized a strategically notched Co-Cr-Mo pin as a sacrificial component to prevent implant damage. • Experimental fatigue testing showed survival beyond 1.3 million gait-mimicking cycles. • Finite Element Analysis (FEA) predicted failure localization and validated the safe stress distribution. • The system enables noninvasive pin replacement, enhancing clinical safety and reducing the need for revision surgeries. Compared with traditional socket-based systems, osseointegrated prosthetic limbs provide greater comfort and mobility; however, the risks of implant fracture, bone failure, and fatigue damage from repeated loading compromise their long-term dependability. This study aimed to design and validate a fail-safe protective adapter with a Ti-6Al-4V sleeve and Co-Cr-Mo sacrificial pin that is strategically notched to function as a mechanical fuse in the event of an overload. The lack of clinically feasible methods to stop catastrophic failure at the bone–implant interface, which prevents osseointegration from being widely used, was the research problem addressed. Both numerical modeling and experimental testing were performed. Standardized specimens were subjected to tensile and fatigue tests in accordance with ASTM E8/E8M and ASTM E466, respectively, to determine the essential mechanical characteristics and endurance limits of the two alloys. A 168-cm, 63-kg male transfemoral amputee walked at a self-selected pace to obtain ground reaction force (GRF) data, which were used as boundary conditions in the finite element analysis (FEA). The titanium sleeve and implant structure remained intact, but the protective adapter failed only at the notched area of the sacrificial pin after withstanding more than 1.3 million simulated gait cycles. The validity of the design was confirmed by the FEA results, which closely matched the experimental fracture sites (von Mises stress of 16.6 MPa and a minimum safety factor of 2.4). The primary conclusion is that implant integrity can be maintained while controlled and replaceable failure is accomplished. This study presents a novel and clinically significant safety mechanism for osseointegrated prostheses, with the potential to be extended to load-bearing orthopedic implants. The contributions of this study include lowering the need for revision surgery, increasing implant longevity, and improving patient safety.