Bone Tunnel Enlargement after ACL Reconstruction with Hamstring Autograft Is Dependent on Original Bone Tunnel Diameter

Background Bone tunnel enlargement is a well-established phenomenon following anterior cruciate ligament (ACL) reconstruction, and is related to soft tissue grafts, suspension fixation devices, and absorbable implants. Severe tunnel enlargement can lead to reconstruction failure. The correlation between bone tunnel enlargement following ACL reconstruction and original bone tunnel diameter has not been elucidated. Purpose To determine whether bone tunnel enlargement after ACL reconstruction with hamstring autograft is dependent on original tunnel diameter established during primary ACL reconstruction. Materials and Methods A retrospective review was conducted on 56 patients scheduled for ACL revision surgery who had undergone computed tomography (CT) scanning as part of their preoperative evaluation. All patients had undergone previous hamstring ACL reconstruction. Original femoral and tibial bone tunnel diameters were extracted from operative reports, and femoral and tibial bone tunnel enlargement was assessed on CT serial sections. The correlation between original tunnel diameter and bone tunnel enlargement was investigated using regression analysis. Results Mean tibial bone tunnel enlargement was significantly and inversely dependent on the original tibial bone tunnel diameter with a correlation coefficient of −0.55 per unit (7 mm = +1.93 mm, 8 mm = +1.43 mm, 9 mm = 0.83 mm, p = 0.007). Thus, every additional increase (mm) in diameter of the original tibial bone tunnel reduces the extend of tunnel widening by 0.55 mm. Conclusions The results of this study indicate that tibial bone tunnel enlargement following ACL reconstruction is dependent on original tibial bone tunnel diameter with smaller diameter tunnels developing more tunnel enlargement than larger tunnels. The contributing factors remain unclear and need to be further investigated.