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), 5mg 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: 10mg/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.