| Description |
Socket suspensions that fit over the residual limb of an amputee are the standard of care in prosthetic limb attachment. Unfortunately, complications related to pain, inconvenience, and lack of functionality lead to rejection rates as high as 65% in upper extremity amputees. Percutaneous Osseointegrated Docking Systems (PODS) for direct skeletal attachment of prosthetic limbs represent an alternative for those underserved by the current standard of care. PODS have been used in Europe for prosthetic attachment in above knee amputees since 1990 with limited surgeries occurring in the United States in recent years. Use in above elbow amputees has been less common, and it is troubled with poor implant fit leading to high rates of complication, including aseptic loosening and adverse cortical remodeling. Such complications highlight the challenges of designing an implant system capable of stable fixation at multiple amputation levels in the humerus. Detailed morphologic evaluation of the humeral diaphysis revealed that proximal stabilization of an implanted stem is made difficult by the diverging canal of the humerus and progressive thinning of cortical bone proximally. Therefore, we propose a novel implant design that leverages our recent experience with a press-fit porous coated implant for transfemoral use, and it incorporates proximal interlocking screws for enhanced fixation. This design underwent preclinical mechanical testing of initial stability in cadaver humeri to evaluate construct stiffness, yield strength, and ultimate fracture strength. The contribution of interlocking screws to initial stability was also compared against press-fit fixation without proximal stabilization. Ensuring the safety and effectiveness of this design required improved understanding of the loads experienced by the humerus during daily motion. Therefore, the last aim of this dissertation characterized the dynamic mechanical forces experienced by the humerus during advanced activities of daily living (AADLs) representative of an active amputee population. Tensile, torsional, and bending loads were estimated from inverse dynamic analysis in healthy volunteers. Results indicated that noncontact AADLs were capable of producing forces and moments at or above fracture loads reported in the humerus, motivating the development of overload protection devices that isolate the implant from damaging forces. |
