Graft healing after anterior cruciate ligament reconstruction in rabbits

Anterior cruciate ligament reconstruction with patellar tendon was performed in 50 rabbits (two groups of 25 animals) by the outside-in (Group I) and the inside-out (Group II) techniques. Five animals from each group were sacrificed at different times (2 weeks, 1, 3, 6, and 9 months). Histologic analysis showed that the intraarticular part of the graft was morphologically similar to a normal ligament in both groups at 9 months. In Group 1, a newly formed bone-graft junction along the tunnel walls was observed inside the femoral tunnel. At 6 months, this junction resembled a direct type junction. The old bone-tendon junction showed an early disappearance of the fibrocartilage and was differentiated as a direct junction only at 9 months. In Group 2, at the site of the old bone-tendon junction a fibrocartilaginous layer was present during the whole process of remodeling, and at 6 months this area resembled a direct junction. These observations would suggest that when the junction is placed inside the tunnel (outside-in technique) the process of remodeling is more dramatic and slower than when it is placed at the intraarticular exit of the tunnel (inside-out technique), probably because of the formation of a new bone-graft junction along the tunnel walls that partially unload the old junction.