IS THERE A STRONG AND SUFFICIENT BONE BRIDGE BETWEEN THE BONE TUNNELS AFTER DOUBLE BUNDLE ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION? A COMPUTED TOMOGRAPHY STUDY

Abstract

Aim: To determine the quantity and the quality of the bone bridge between the bone tunnels, in both the femoral and tibial side, after double-bundle anterior cruciate ligament (ACL) reconstruction.

Material and methods: Twenty-seven patients undergoing primary double-bundle ACL reconstruction with hamstring tendon autograft were included in this prospective study. Computed tomography (CT) was performed in all patients at a mean of 13 months postoperatively. The amount of the bone bridge between the bone tunnels was measured, in both the femoral and tibial side, on an axial plane at three locations:

1. at the level of the joint line

2. at the mid-portion of the bone bridge and

3. at the base of the bone bridge.

In addition, the bone density of the bone bridge was measured in Hounsfield units (HU) in the same locations. Bone density of the anterior tibial cortex lateral femoral condyle, and adjacent cancellous area, and were measured for comparisons.

Results: CT confirmed that the bone bridge was triangular in shape in all cases in both the femoral and tibial side. On the femoral side, at the level of joint line (apex of the bone bridge) the mean thickness of the bone bridge was 1.7 mm, at the mid-portion the mean thickness of the bone bridge was 3.7 mm and at the base of the bone bridge the mean thickness was 7.1 mm. On the tibal side, at the level of joint line (apex of the bone bridge) the mean thickness of the bone bridge was 1.5 mm, at the mid-portion the mean thickness of the bone bridge was 3.2 mm and at the base of the bone bridge the mean thickness was 6.5 mm. Bone density at the mid-portion and at the base of the bone bridge was similar to the cancellous bone for both the femoral and tibial side. However, the bone density of the bone bridge, at the level of the joint line, for the femoral side was 860 HU and this was not statistically significant in comparison to the density of the lateral femoral cortex (960 HU). Similarly, the bone density of the bone bridge, at the level of the joint line, for the tibial side was 885 HU and this was not statistically significant in comparison to the density of the anterior tibial cortex (970 HU).

Conclusions: Our study demonstrated one year after double-bundle ACL reconstruction the thickness of the triangular bone bridge between the bone tunnels is sufficient at the mid-portion and at the base of the triangle but is thin at the level of the joint line. However, the bone bridge at the apex of the triangle is very strong since its density is similar to that of cortical bone. We believe that the “corticalization” of the bone bridge at the level of the joint line on both the femoral and tibial side is important and contributes significantly to avoid communication of the bone tunnels.