Studies of osteophyte pathogenesis in experimentally induced osteoarthritis.

Osteophyte formation in a partial meniscectomy model of osteoarthritis (OA) in rabbits was studied. Serial sacrifices were performed at 1 day, 3 days, and 1, 4, 6, 8, 12 weeks in partial meniscectomy (15), nonoperated (14) and sham-operated (7) animals. H and E, safranin-O/fast green and toluidine blue stains were performed on coronal sections and pathologic findings correlated with 3H-thymidine autoradiography. Sham-operated and nonoperated control animals (similar findings) revealed grade 1 synovial/periosteal proliferation. Sixty percent of control animals exhibited small nubbin-like spurs at the medial tibial plateau. In partial meniscectomy animals, osteophytes occurred as early as 1 week, and in 7/9 (78%) animals after 4 weeks. Grade 2-4 synovial, perichondrial/periosteal thickening, cell proliferation and vascularity were seen. Soft tissue and bone responded in parallel. Results demonstrated normally high cellular activity at the joint periphery; vascular responses did not precede osteophyte formation.