Relation of tunnel enlargement and tunnel placement after single-bundle anterior cruciate ligament reconstruction.

PURPOSE To determine the relation between tunnel placement and tunnel enlargement after single-bundle anterior cruciate ligament (ACL) reconstruction. METHODS Seventy-two subjects (mean age, 30.1 years; 17.5 months' follow-up) who underwent single-bundle ACL reconstruction with hamstring autograft were studied. EndoButton fixation (Ethicon, Somerville, NJ) was used on the femoral side, whereas staples were used on the tibial side. A transtibial femoral tunnel position technique was used in 53 subjects, whereas positioning through the medial portal was used in the other 19 cases. Tunnel enlargement was determined by comparing the diameter of the tunnel on the radiograph obtained after 12 months and the radiograph obtained instantly after the operation. The centers of the femoral and tibial tunnels and the angles between the graft and tibial plateau were also measured on standard radiographs. Clinical outcomes including KT-1000 assessment (MEDmetric, San Diego, CA) and International Knee Documentation Committee (IKDC) score were also collected in all patients. The relations between tunnel enlargement/tunnel position and knee joint laxity and IKDC score were analyzed. RESULTS The mean KT-1000 side-to-side difference significantly decreased, from 6.07 ± 2.75 mm to 1.57 ± 2.14 mm, after ACL reconstruction; the IKDC subjective score increased from 52.8 to 87.5. On lateral radiographs, the tunnel enlargement rates were 41% on the femoral side and 35% on the tibial side; on plain anteroposterior radiographs, the tunnel enlargement rates were 39% on the femoral side and 32% on the tibial side. Subjects with a higher femoral tunnel had a greater enlargement rate (P < .001). Subjects with a more vertical graft also had a larger femoral enlargement (P < .05). More anterior placement of the femoral tunnel was associated with larger tibial tunnel enlargement on anteroposterior plain radiographs (P < .05). A more vertical graft was also associated with larger tibial tunnel enlargement. Subjects in whom the transtibial femoral position technique was used had more femoral tunnel enlargements (P < .01). CONCLUSIONS Drilling the femoral tunnel through the medial portal created a lower, more posterior, and less vertical tunnel than drilling through the tibial tunnel. Femoral and tibial tunnel enlargements were greater with more anterior, more proximal, and more vertical femoral tunnels. Whereas no clinical differences were seen in the 2 groups, drilling the femoral tunnel from the medial portal will result in smaller postoperative tunnel enlargements. LEVEL OF EVIDENCE Level III, retrospective comparative study.