Title:
Comparison of tunnel locations of double bundle ACL reconstruction using the conventional transtibial technique with anatomic tunnel locations using a 3D CT model.

Abstract:
The purposes of this study were: (1) to compare tunnel locations using the conventional transtibial technique with reference data, and (2) to identify factors that make it difficult to position the femoral tunnel correctly or contribute to breakage of the bone bridge between the two tibial tunnels.
A prospective study was performed on 28 patients who underwent double bundle ACL reconstruction. Locations of each tunnel were determined using an anatomic coordinate axes method (ACAM). Measurements included: thickness of the bone bridge between tibial two tunnels (BB), height from the union (HU) point to expected joint surface, the ratio between the length of Blumensaat's line and the anterior-posterior length of the lateral femoral condyle (RBL), and the ratio between anterior-posterior and proximal-distal lengths of the medial wall of the lateral femoral condyle (RAPPD).
The posterior-anterior direction of femoral AM tunnel, the proximal-distal direction of femoral PL tunnel, and the posterior-anterior direction of femoral PL tunnel were statistically significantly different from the reference data. In correlation analyses between BB or HU and other variables, the AM tibial tunnel and RBL showed a moderate negative correlation. The cutoff point for tunnel breakage was an RLB of 1.14, meaning that the possibility of bone bridge breakage would increases for RBL values of >1.14.
It seems that conventional transtibial drilling technique used during double bundle ACL reconstruction does not reproduce correct tunnel locations compared with reference data. This problem was found to be related to the bony geometry of the medial wall of the lateral femoral condyle or the bone bridge between the two tibial tunnels. Our results indicate that RBL should be determined by pre-operative CT or plain lateral radiography, and that transtibial single bundle reconstruction or double bundle reconstruction using other methods should be attempted when the RBL exceeds 1.14.