Objective: Full-thickness defects measuring 3 mm in diameter have been commonly used in studies of rabbits to evaluate new procedures designed to improve the quality of articular cartilage repair. These defects initially heal spontaneously. However, little information is available on the characteristics of repair of large defects. The aim of present study was to define the biomechanical characteristics of repair of 5x4 mm full- thickness osteochondral defects in the adolescent male rabbit.

Materials & Methods: In a Quasi - Experimental study 5 millimeter diameter and 4 mm deep osteochondral defects were drilled in femoral patellar groove of twenty-one rabbits , and examined at 4 ,8 and 16 weeks. The left knee was kept intact as the normal control. . The knee joints were removed, and both legs were examined biomechanically by in situ indentation method at three time- intervals (4, 8, 16 weeks). The instantaneous and equilibrium elastic- modulus (after 900 second) measured during the test.

Results: There were no differences in cartilage mechanical properties (instantaneous and equilibrium elastic- modulus) between weeks (4, 8, 16 weeks) in two groups (P > 0/05). Although Significant differences between experimental and control groups were seen in 16 weeks in instantaneous elastic- modulus (P < 0/05). New tissue supported high stiffness than normal control in 16 weeks.

Conclusion: Full-thickness osteochondral defects, measuring 5x4 mm in diameter and dept in patellar groove of adolescent rabbit knee heal spontaneously.