Influence of the bone block position on the tunnel enlargement in ACL reconstruction

Tunnel enlargement can appear after anterior cruciate ligament reconstruction. We investigated the influence of the bone block position of a patellar tendon autograft on the tunnel enlargement in the femur and in the tibia from two aspects. On the one hand, we examined the influence of the tunnel position in respect to the ap-diameter. On the other hand, we examined the influence of the bone block depth in respect to the joint line. In a crossover study over three years, 103 knees with primary ACL reconstruction were included. The incidence of tunnel enlargement measured on X-rays after one year was 52% (n=103) in the femur and 81% (n=103) in the tibia. The average diameter of enlargement was 1.4 mm (14%) in the femur and 2.7 mm (27%) in the tibia. No correlation between the tunnel position and the tunnel enlargement in the sagital plane could be found. However, there is a significant positive correlation between the size of tunnel enlargement and the bone block depth in the femur and in the tibia. There is an average tunnel enlargement of about 0.6 mm (6%) per 10 mm deeper bone plug depth. The relative excess length of the patella tendon favors the development of tunnel enlargement. The effect of the bone block depth on the tunnel enlargement is equal in the femur and the tibia.