Tunnel expansion following anterior cruciate ligament reconstruction: A comparison of hamstring and patellar tendon autografts

Thirty patients having had anterior cruciate ligament (ACL) reconstruction with bone-patellar tendon-bone (BPTB) autograft and thirty patients having had ACL reconstruction with hamstring (HS) autograft were enrolled. All procedures were performed using an endoscopic technique with identical postoperative rehabilitation, such that the only variable was the type of graft and its fixation. Lateral and 45° posteroanterior (PA) weightbearing radiographs were performed in each patient at 6-12 (mean 9) months postoperatively in the HS group and 9-22 (mean 13) months postoperatively in the PT group. The sclerotic margins of the tunnel were measured at the widest dimension of the tunnel by a single observer and were compared with the initially drilled tunnel size after correction for radiographic magnification. For the BPTB group, all bone plugs appeared to be incorporated radiographically. On the femoral side, the bone plug was incorporated at the roof of the intercondylar notch, such that no tunnel measurement could be made. Well-defined sclerotic margins were always present at the tibial and femoral tunnels for the HS group and at the tibial tunnel for the BPTB group. The mean percentage increase in tunnel size in the PA view was 9.7% ± 14.7% for the BPTB tibial tunnel, 20.9% ± 13.4% for the HS tibial tunnel, and 30.2% ± 17.2% for the HS femoral tunnel. The mean percentage increase in tunnel size in the lateral view was 14.4% ± 16.1% for the BPTB tibial tunnel, 25.5% ± 16.7% for the HS tibial tunnel, and 28.1% ± 14.7% for the HS femoral tunnel. The difference in HS and BPTB tibial tunnel expansion on both the PA and lateral views was statistically significant (P = 0.003 and P = 0.01, respectively). Inter-observer variability was excellent with an intra-class correlation coefficient of 0.92. Tunnel expansion was significantly greater following ACL reconstruction using HS autografts than in those using BPTB autografts. The points of fixation for the HS grafts are at a greater distance from the normal insertion site and biomechanical point of action of the ACL than the points of fixation for BPTB grafts. We believe that this greater distance creates a potentially larger force moment during graft cycling which may lead to greater expansion of bone tunnels.