The effect of COX-2 inhibitors on periprosthetic osteolysis

We aimed to test the hypothesis that COX(cyclooxygenase)-2 inhibitors suppress periprosthetic osteolysis in a rabbit model. Porous coated titanium bar was inserted into distal femur of 24 skeletally mature New Zealand white rabbits. The rabbits were randomized into 3 groups. Group I (8 rabbits) was the control group. In Group II (8 rabbits), 5 mg of ultrahigh molecular weight polyethylene particles was inserted along with prosthesis. In Group III (8 rabbits), the same procedure as in Group II was done and a COX-2 inhibitor (celecoxib, Pharmacia: 10 mg/day) was administered for 7 weeks. Rabbits were sacrificed after 8 weeks of implantation. Gross, radiological, histological, and immunohistochemical assessments were done. Gross examination showed that one implant in Group II was loose. In radiological evaluation, focal osteolysis was found in 2 rabbits of Group II and 1 rabbit of Group III. Linear osteolysis was found in 2 rabbits of Group II and 1 rabbit of Group III. On histological examination, focal area of granulation tissue laden with macrophages was observed in 6 rabbits of Group II and 6 rabbits of Group III. The mean number of osteoclasts as demonstrated by tartarate positive acid phosphatase staining was 0.5±0.5 in Group I, 6.5±2.7 in Group II, 3.6±2.6 in Group III (p<0.05). Immunohistochemical staining for inducible nitric acid synthase and COX-2 did not show significant difference between Groups II and III. The overall results of this study suggest that COX-2 inhibitors in the therapeutic dose may have a place in suppressing the process of periprosthetic osteolysis