THE RAT AS AN ANIMAL-MODEL FOR TOTAL HIP-REPLACEMENT ARTHROPLASTY

Dogs, goats, and sheep are the most commonly used animals in studies o f total hip replacement (THR) arthroplasty. However, the development o f a small, laboratory animal model could have significant economic and housing advantages over these models when studying the long-term syst emic effects of chronic mechanically functional implants. A THR was de signed and fabricated with a cobalt-alloy (F-75) femoral and UHMWPE ac etabular component for PMMA-cemented implantation in the rat. Mature S prague-Dawley rats (n = 18) were maintained at a constant weight (450 g) and were trained to walk on a low-speed (6 m/min), horizontal tread mill, 15 min/day, 5 days/week. Each animal was randomly assigned to on e of three surgical groups: functional, nonfunctional, and sham. The f unctional and nonfunctional groups underwent identical procedures, exc ept that in the nonfunctional group the femoral head was placed so as to prevent articulation with the socket in the acetabular component. T he sham procedure consisted of exposing and opening the joint capsule and the iliac wing without luxating the femoral head or severing the l igamentum teres. In addition, half of the animals in each group resume d exercising on the treadmill at 1 week after surgery. The implants we re recovered at 2 months after surgery. The results show that the surg ical procedure is feasible in the rat, the postoperative recovery was typical of that for THR, and the rats were able to resume their exerci sing regimens. Radiographic evaluation revealed that the majority of t he sham and the nonfunctional animals had luxated hips, while the majo rity of the functional animals had reduced hips. Histological results were typical of THR in other species. The success of the surgical mode l suggests that the rat may be a feasible, reduced-cast alternative to other lab species in systemic, long-term THR studies.