LONG-TERM FATE AND EFFECTS OF EXERCISE ON STERNAL CARTILAGE AUTOGRAFTS USED FOR REPAIR OF LARGE OSTEOCHONDRAL DEFECTS IN HORSES

Bilateral osteochondral defects (10 mm(2) x 3 mm deep) were created on the distal articular surface of the radial carpal bone of ten, 2- to 3-year-old horses. One defect of each horse was repaired, using a ster nal cartilage autograft (treated), and the other was left untreated (c ontrol). The horses were exercised on a high-speed treadmill at increm entally increased speed and duration over the course of 12 months. Hor ses were evaluated arthroscopically at 6 to 7 weeks, and clinical exam inations were conducted weekly at exercise. Twelve months after surger y, carpuses of each horse were radiographed and clinically examined pr ior to euthanasia. A gross pathologic evaluation of each joint was con ducted, and samples were collected for histologic, histochemical, hist omorphometric, and biochemical evaluation. Radiographically, the graft ed joints had more extensive evidence of arthropathy, and clinically, 8 of the 10 horses were more lame in the grafted limb. On the basis of histomorphometry, the repair tissue of the grafted defects contained a greater median percent age of hyaline cartilage (45%) than that of c ontrol defects (4.5%), and the control defects contained a greater per centage of fibrocartilage (82%) than did grafted defects (28.5%). A gr eater median percentage of repair tissue stained with safranin-O in th e grafted defects (24.5%) than in the control defects (3.5%). On gross pathologic and histologic evaluation, repair tissue of the control de fects had better continuity and was more firmly attached to the subcho ndral bone than was repair tissue of the grafted defects. Repair tissu e of the grafted defects had extensive fissure and flap formation. His tologically, subchondral bone reactivity and fibroplasia was extensive in grafted joints. Repair tissue of grafted defects had a greater per centage of type II collagen (mean +/- SEM, 83.5 +/- 2.95%) than did co ntrols (mean, 79.4 +/- 3.87%) that was not statistically significant. Hexosamine content was significantly higher (P < 0.05) in repair tissu e of the grafted defect (mean, 28.9 +/- 3.00 mg/g of dry weight) vs co ntrol (mean, 20.6 +/- 1.85 mg/g of dry weight). On the basis of this e xperimental model, sternal cartilage autografts cannot be recommended at this time for repair of osteochondral defects in athletic horses.