Development of a novel endoprosthesis for canine limb-sparing using a finite element approach

Abstract

Osteosarcoma is the most prevalent bone tumor in the canine population and the distal radius is the most commonly affected site. To date, amputation has been the preferred treatment option among veterinarians for distal radius osteosarcoma. However, with the advent of better chemotherapy protocols and the subsequent increasing survival rates, interest has now turned towards saving the legs of dogs with osteosarcoma. The current endoprosthesis used for limb-sparing is associated with a high failure rate, and hence, the design of a novel endoprosthesis is warranted. To aid in the development of a new endoprosthesis for canine limb-sparing a finite element model of the canine forelimb was generated. Accurate mechanical properties of soft tissues are essential to build a reliable finite element model. Since no data exists regarding the mechanical properties of canine carpal ligaments, six primary stabilizing ligaments of the canine carpus were identified and their mechanical properties were investigated by uniaxial testing in a materials testing machine. Convergence and validation are two crucial steps in the development of a finite element model. Convergence was investigated by generating three models with increasing mesh resolution. For the purposes of validation, eight intact canine forelimbs were tested in a materials testing machine. The limbs were instrumented to record bone strains and relative displacements. The acquired data were used to validate the canine forelimb model. The current endoprosthesis was evaluated to determine the mechanical underpinnings of clinical failures associated with these implants using the canine forelimb finite element model. The implant failure locations predicted by the model were similar to those observed clinically. The use of a locking plate in place of the current non-locking plate was also investigated. Several stress redistribution strategies were also examined. A novel modular design was developed in collaboration with the Colorado State University's Veterinary Teaching Hospital oncology surgeons. The design was extensively evaluated with the use of the validated and converged finite element of the canine antebrachium. The design was modified and improved based on the results. Significant stress reduction was achieved within the proximal radial screws and the distal metacarpal screws. Off-axis loading of the construct was also eliminated. The final design was approved for prototype development, biomechanical testing and cadaveric evaluation.