Evaluation of Two Techniques of Cancellous Bone Grafting of Experimental Subchondral Bone Cysts in the Medial Femoral Condyles of Horses

Cylindric (10 mm diameter X 15 mm deep) osteochondral defects were created in the medial femoral condyles of 5 horses to mimic clinical cases of subchondral bone cysts after debridement. The defects were created with either a standard square ended drill bit or a compaction drill bit. The compaction drill bit compresses bone laterally and distally creating a dense wall and floor. Twelve-mm sternal cancellous cylinders were compressed to 9.25 mm and inserted into the femoral defects where they were presumed to expand and tighten the fit. The end result was sternal cancellous bone that exactly fit the femoral defects. Fluorochrome bone labels were used to confirm the origin of bone present in the defects at necropsy, which was performed after 6 months. Successful graft incorporation occurred in 3 of the compacted and 2 of the noncompacted defects. The surfaces of the successful cancellous bone grafts contained predominately fibrocartilage. The unsuccessful noncompacted defects expanded laterally and deeply into the parent bone epiphysis while the unsuccessful compacted defects remained confined to the originally created size.