Title:
ACL reconstruction with hamstrings: how different technique and fixation devices influence bone tunnel enlargement.

Abstract:
Bone tunnel enlargement after anterior cruciate ligament (ACL) reconstruction is well documented in the literature. The cause of this tunnel enlargement is unclear, but is thought to be multifactorial, with mechanical and biological factors playing a role.
The aim of this prospective study was to evaluate how the different techniques may affect the bone tunnel enlargement and clinical outcome.
Forty-five consecutive patients undergoing ACL reconstruction with autologous doubled semitendinosus and gracilis tendons entered this study. They were randomly assigned to enter group A (In-Out technique, with cortical fixation and Interference screw) and group B (Out-In technique, metal cortical fixation on the femour and tibia). At a mean follow-up of 10 months, all the patients underwent CT scan exam to evaluate the post-operative diameters of both femoral and they underwent tibial tunnels clinical examination after 24 months.
The mean femoral tunnel diameter increased significantly from 9.05±0.3 mm to 10.01±2.3 mm in group A and from 9.04±0.8 mm to 9.3±1.12 mm in group B. The mean increase in femoral tunnel diameters observed in group A was significantly higher than that observed in group B (p < 0.05) The mean tibial tunnel diameter increased significantly from 9.03±0.04 mm to 10.68±2.5 mm in group A and from 9.04±0.03 mm to 10.±0.78 mm in group B. The mean increase in tibial tunnel diameters observed in group A was significantly higher than that observed in group B (p < 0.05). No clinical differences were found between two groups and no correlations between clinical and radiological results were found in any patients of both groups.
Results of the study suggest that different mechanical fixation devices could influence tunnel widening. The lower stiffness of the fixation devices is probably responsible of the tunnel widening through the fixation devices's micromotions in the femoral and tibial tunnels.