Mosaicplasty of the talus: a joint contact analysis in a cadaver model

Treating large osteochondral defects of the talar dome is a challenging problem for the foot and ankle surgeon. The purpose of this study was to determine if ankle joint surface mechanics can be restored by repairing large osteochondral defects with multiple osteochondral cylinder grafts. Pressure-sensitive film was used to measure total contact area and mean contact pressure of the ankle joint using a cadaver foot model. Specimens were sequentially tested evaluating the following conditions: 1) intact ankle, 2) with osteochondral defect, and 3) after mosaicplasty. An ovoid chondral defect measuring 8 x 12 mm for each specimen was consistently placed within the center of the contact zone. Multiple osteochondral grafts were harvested from donor tali and placed in the defect. Two graft arrays arranged in either a cluster of four 4 x 10 mm or two 6 x 10 mm plugs were inserted sequentially to fill the defect and were tested separately. Specimens were positioned in a neutral alignment on a custom load frame and axially loaded to 560 N with the pressure transducer in place. The transducers were then digitized and analyzed with an imaging software program. Data for total contact area and mean contact pressures for all conditions of each specimen were collected and statistically analyzed. Results demonstrated that the 6-mm grafts were less than optimal in fully restoring the defect in the contact zone of the talus. There was significant decrease in mean total contact area and increase in contact zone mean pressure compared to the intact condition (p < .05). Whereas, 4-mm plugs nearly restored joint contact area and pressure to normal levels. These findings suggest that focal talar dome defects can be repaired to restore normal ankle contact characteristics via the placement of small, osteochondral cylindrical grafts of talar origin.