A Clinically Representative Rat Model of Hip Hemiarthroplasty
Abstract
Joint replacement is an increasingly common surgery with over 130,000 procedures performed annually in Canada. Although joint replacement surgery is highly successful, implants do not last a lifetime, and often have to be replaced via costly revision surgeries. Before innovations aimed at extending the life of implants are applied to the clinic, testing must be performed in animal models. Clinically representative small-animal models of joint replacement would be ideal in the initial stages of research and development, due to ease of handling and low costs, but few such models have been established in the literature. Thus, we describe the development of a clinically representative rat model of hip hemiarthroplasty.
A database of micro-computed tomography volumes of skeletally mature male Sprague-Dawley rats was analyzed to quantify the dimensions of the proximal rat femur. This was done in order to guide the creation of a parameterized rat-hip implant in computer-aided design software. Sets of rat-specific femoral implants were then produced in medical-grade alloys using additive manufacturing. Implants were then installed into cadaveric, and then live rats. Micro-computed tomography imaging was used to evaluate the position of the implant within the proximal femur longitudinally. Animals also underwent a gait analysis protocol using a commercially available CatWalk XT system, in parallel with an X-ray fluoroscopy protocol, whereby animals were imaged while running on a custom made radiolucent treadmill.
Surgeries were successful in live animals; rats were able to tolerate the procedure and were observed ambulating on their affected limbs immediately following recovery from anaesthesia. Micro-CT imaging revealed clinically representative complications (implant subsidence) in some animals that mimic complications found in larger models. Functionally loaded implants were observed in the remaining animals at twelve weeks, postoperative. Rats were successful in completing gait analysis protocols on both the Catwalk and fluoroscopic treadmill systems. Animal gait was restored following hemiarthroplasty.
We report the first clinically representative rat hip hemiarthroplasty surgeries using custom 3D-printed metal implants. This thesis supports the feasibility of this model as a preclinical platform for basic scientists to study osseointegration, metal-on-cartilage interactions, and joint infection around a functional implant.