Surgical deepening of the groove in the femoral trochlea is a technique commonly employed in the correction of patellar dislocation in dogs. In order to discover how this deep articular defect repairs the operation was studied experimentally in young goats. Observations were made on the appearance of the trochlea and the histologic changes that had taken place after approximately six, 12, and 40 weeks. The abraded groove became filled with fibrocartilage with a relatively smooth surface and it articulated freely with the patella. The majority of the replacement tissues arose by differentiation of the granulation tissue which initially filled the groove, but there appeared to have been some contribution made by the hyaline cartilage at the margins of the groove.