Abstract
Objectives:
Much literature has been devoted to determining the proper tunnel positioning during arthroscopic anterior cruciate ligament (ACL) reconstruction (ACLR). However, to date, no literature has assessed whether the tunnel centroid closely approximates the final bone-patellar tendon-bone (BTB) graft positioning following interference screw fixation. Thus, the purpose of this human cadaveric study was to assess the difference in position between the native ACL footprint, drilled tunnel, and tendinous portion of a BTB graft following ACLR. It was hypothesized that the tendon position would be significantly more offset than the tunnel position from the native ACL footprint, given that the patellar tendon is not centered on the bone plugs of the BTB graft.
Methods:
Ten cadaveric specimens were included. A standard BTB graft was harvested from each specimen using an oscillating saw and scalpel and bone plugs were sized to a diameter of 10 mm for graft passage. The native ACL footprint (femur and tibia) of each specimen was mapped with a MicroScribe 3-dimensional (3D) coordinate digitizer. The centroid of each femoral footprint was determined by creating a 3D surface patch using an area-weighted technique. A guidewire was placed at the centroid of the native footprint and a 10 mm tunnel was overreamed to best approximate the centroid of the native footprint. The borders of the tunnel were then subsequently mapped out using the digitizer. A BTB graft was passed and secured in hyperextension with an 8 x 20 mm interference screw. Following fixation, the tendinous portion of the graft was mapped and a centroid was derived. This was repeated for the tibial side.
Results:
On the femur, mean cross-sectional area of the ACL footprint, tunnel, and tendinous portion of the graft were 154.89 ± 55.10 mm2, 86.45 ± 12.65 mm2, and 40.14 ± 10.68 mm2, respectively. The tendinous portion provided 26.7% coverage of the native footprint. The tendon centroid was significantly further than the tunnel centroid from the native footprint (2.90 ± 0.98 mm2 vs 0.38 ± 0.15 mm2, p ≤ 0.001). The tendon was mean 2.84 ± 0.83 mm2 from the tunnel, in the 6 o’clock direction (inferior). On the tibia, mean cross-sectional area of the ACL footprint, tunnel, and tendinous portion of the graft were 143.60 ± 19.00 mm2, 86.48 ± 8.76 mm2, 42.84 ± 6.70 mm2. The tendinous portion provided 30.01% coverage of the native footprint. The tendon centroid was significantly further that the tunnel centroid from the native footprint centroid (3.13 ± 0.23 mm2 vs 0.28 ± 0.07 mm2, p ≤ 0.001). The tendon centroid was mean 3.02 ± 0.16 mm2 from the tunnel centroid in the 11 o’clock direction (posterolateral).
Conclusions:
The findings of this study suggest that the soft tissue portion of BTB grafts is significantly offset from the tunnel centroid following ACLR fixation. While previous studies have emphasized tunnel placement from an isometry and biomechanical standpoint, future studies should study tunnel position in the context of where the soft tissue of the BTB graft ends up relative to the tunnel centroid. Future avenues of study would include determining whether a tunnel "cheat distance and direction" can be determined to routinely center the soft tissue of the ACLR graft appropriately within the anteromedial bundle of the native ACLR footprint for an optimal anatomic reconstruction.
