Introduction: By compromising bone structure, peri-prosthetic osteolysis may increase the risk of fracture and/or aseptic loosening of components leading to revision surgery. Our purpose was to develop a reproducible rabbit model of periprosthetic osteolysis and observe the effects of implant type and fixation on the latency to onset and size of the osteolytic lesions.

Methods: Thirty-seven New Zealand White rabbits (71 knees) underwent knee arthrotomy and placement of cylindrical intramedullary stainless steel or polymethylmethacrylate (PMMA) implants. Each knee contained both a metallic and PMMA implant in either the femur or tibia that communicated with a common synovial space. A suspension of polyethylene particles (size < 4.5 um and concentration of 1-5 x 106 particles/ul) was injected into each knee at two-week intervals for ten weeks to induce osteolysis. Serial radiographs were taken at 4, 8, 14, 18, and 22 weeks postoperatively to document the progression of osteolysis. Statistical analysis was performed utilizing a two-tailed, unpaired t-test and a Mantel-Cox test with the level of significance set a p < 0.05.

Results: Radiographic analysis revealed that 96.9% of the stainless steel implants had evidence of osteolysis by 22 weeks compared to 22.9% of the PMMA implants (p< 0.001). The earliest onset of lesions in the metal implant group occurred at four weeks compared to 14 weeks in the PMMA group. We also found the area and volume of the osteolytic lesions to be significantly larger in the metal implants when compared to the implants composed of PMMA (p < 0.01).

Conclusions: Onset of osteolysis around metal implants occurred in a significantly shorter period of time and more frequently when compared to implants composed of PMMA. Also, the area and volume of the osteolytic lesions around the metal implants was found to be significantly larger than those of the PMMA. We concluded that relative material effects on osteoclast induced bone resorption and differences in ease of transport of particulate debris along metallic compared to PMMA surfaces may account for observed differences in frequency and severity of osteolytic lesions.