Summary

The anterior tibial tunnel enlargement after anatomic triple-bundle ACL reconstruction was smaller than that of the posterior tunnel at the aperture site.

Abstract

Introduction

Tunnel enlargement after anterior cruciate ligament (ACL) reconstruction can influence the laxity of the knee joint postoperatively and make it difficult to create a new tunnel in revision surgery. Tibial tunnel enlargement at the aperture site after ACL reconstruction with a hamstring tendon graft was well documented, though there were few reports evaluating the enlargement inside the tunnel. Therefore, the aim of this study was to evaluate the tibial tunnel enlargement not only at the aperture but also inside the tunnel after anatomic triple-bundle ACL reconstruction using 3-dimensional (3D) computer models.

Materials And Methods

This study included 15 patients (6 males and 9 females) with unilateral ACL rupture. Their age was 24 years with a range of 14 to 48 at surgery. Anatomic triple-bundle ACL reconstruction with 2 femoral and 3 tibial (2 anterior and 1 posterior) tunnels was performed using 2 doubled semitendinosus tendon autografts. One graft was settled in the distal femoral and the posterior tibial tunnels. The loop end of the other graft was passed through the proximal femoral tunnel, while the free ends of the graft were inserted to two anterior tibial tunnels separately. Grafts were then fixed with 2 Endobutton-CLs at femur and 2 Double-Spike Plates: DSPs for tibia under a total initial tension of 20 N at 20 degree of knee flexion. After brace immobilization for 2 weeks postoperatively, range of motion exercise and partial weight-bearing were started. Return to sports was allowed 7-9 months after surgery. CT scans were taken 3 weeks and 1year after surgery, and 3D computer models of the tibia including each tunnels were created. The 3D models at the two periods were superimposed by surface registration technique. Then, we measured the cross sectional area (CSA) of the 2 anterior and 1 posterior tibial tunnels along the planes perpendicular to the long axes of each tunnels. The CSA measurement was performed at 0, 5, 10, and 15 mm from the aperture in the superimposed 3D models. Two anterior tunnels were assessed as one anterior tunnel in the CSA measurement, because the anterior tunnels were sometimes accompanied with each other. The tunnel enlargement rate of the anterior and posterior tunnels was also calculated.

Results

The CSAs of the anterior and posterior tunnels increased from 37.4 ± 7.4/20.2 ± 4.4 mm2 to 39.7 ± 12.4/28.5 ± 8.1 mm2 at the aperture, while those decreased inside the tunnels except for the CSA at 5 mm in the posterior tunnel. The tunnel enlargement rate at the aperture was 6.2 ± 26.2 % for the anterior tunnel and 40.6 ± 22.5 % for the posterior tunnel with a significant difference.

Discussion

and Conclusions: The enlargement of the anterior tibial tunnel was smaller than that of the posterior tunnel at the aperture. The anterior graft was passed through 2 tibial tunnels, while the posterior graft was located in 1 tunnel. Then the stress to the anterior tunnel wall could be smaller under anterior tibial load as the contact area to the graft was larger.