The effect of metaphyseal holes and interposition material on the longitudinal growth stimulation of long bones in a rabbit model.

Aims: It remains unclear which factors influence overgrowth of the tibia, resulting from the metaphyseal hole created during anterior cruciate ligament (ACL) reconstruction in skeletally immature patients. This study aimed to investigate the effects of growth stimulation by creating a metaphyseal hole in a rabbit model, based on its distance from the physis and type of interposition material.

Methods: In Experiment 1, 38 skeletally immature male New Zealand white rabbits were randomized into one of four groups: a metaphyseal hole created at 5, 10, or 15 mm distal to the physis of the left proximal tibia with the hole filled with bone wax, or a sham control group. In Experiment 2, after establishing the distance associated with the most overgrowth, a defect was created at 10 mm distal to the physis in 20 additional rabbits, which were randomly assigned to have the defect filled with Tisseel, or be left unfilled. The rabbits were euthanized six weeks postoperatively.

Results: The length and rate of overgrowth were higher in the groups with holes drilled 5 and 10 mm distal to the physis compared to the sham group. A significant increase in new bone width was observed in the 10 mm distal hole group. Growth stimulation in both radiological and histological analyses was not significant in the unfilled and Tisseel groups. Valgus deformities were observed in all groups with metaphyseal holes compared to the sham group.

Conclusion: Creating a metaphyseal hole 10 mm distal to the physis of the proximal tibia can significantly stimulate longitudinal growth and induce tibia valga in rabbits; however, the effect varies depending on the type of interposition material. Notably, overgrowth was significant only in the group with holes filled with bone wax. Based on this study, the location of the metaphyseal hole during ACL reconstruction or physeal bar excision could be optimized.