Summary
Biomechanical cadaver study demonstrating the femoral tunnel should be shifted slightly proximally and the tibial tunnel slightly anteromedially to better center the tendinous portion of the BTB graft over the native footprint.
Abstract
Purpose
To assess the difference in position between the center of the drilled tunnel and center of the tendinous portion of the bone-patellar tendon-bone (BTB) graft on both the femoral and tibial sides following anterior cruciate ligament reconstruction (ACLR). It was hypothesized that the tendon center would be significantly more off center than the tunnel center from the native ACL footprint center.
Methods
Four cadaveric specimens with mean age of 43.0 years were included. The native ACL footprint on the femur and tibia were mapped with a MicroScribe 3D digitizer (CNC Services, Amherst, Virginia). This was used for subsequent analysis in a 3D visualizing software (Rhinoceros 3D, Seattle, WA).
The centroid of each femoral footprint was determined by creating a 3D surface patch using an area-weighted technique. A tunnel was drilled at this centroid. A BTB graft was then passed into the tunnel and secured with an interference screw at the 12 o’clock position. The size and location of the tunnel and tendinous portion of the graft were each mapped, and a centroid was derived for each. This was repeated for the tibial side. Surface areas of the native footprint, tunnel, and tendinous portion of the graft were calculated. Distances from the centroids of the tunnel to the footprint, tendon to footprint, and tendon to tunnel were calculated.
Results
On the femoral side, mean cross-sectional area of the ACL footprint, tunnel, and tendinous portion of the graft were 157.04 ± 55.10 mm2, 93.64 ± 12.65 mm2, and 52.57 ± 10.68 mm2, respectively. The tendinous portion provided mean 37.79% coverage of the native footprint. The tendon centroid was significantly further than the tunnel centroid from the native footprint centroid (2.41 ± 0.58 mm2 vs 0.54 ± 0.08 mm2, p=<0.001). The tendon centroid was mean 2.17 ± 0.19 mm2 (range 1.90-2.23) from the tunnel centroid, in the 6 o’clock direction (inferior).
On the tibial side, mean cross-sectional area of the ACL footprint, tunnel, and tendinous portion of the graft were 150.27 ± 37.96 mm2, 105.99 ± 5.73 mm2, 46.09 ± 5.15 mm2. The tendinous portion provided mean 32.13% coverage of the native footprint. The tendon centroid was significantly further that the tunnel centroid from the native footprint centroid (2.54 ± 0.33 mm2 vs 0.59 ± 0.06 mm2, p=<0.001). The tendon centroid was mean distance 2.45 ± 0.17 mm2 (range 2.30-2.48) from the tunnel centroid in the 11 o’clock direction (posterolateral).
Conclusion
On the femoral side, the tendon centroid was mean 2.17 mm inferior from tunnel centroid, and significantly further from the native footprint centroid. On the tibial side, the tendon centroid was mean 2.45 mm posterolateral from the tunnel centroid, and also significantly further from the native footprint.
Clinical Impact: To better position graft collagen over the native footprint, surgeons may consider shifting femoral tunnel placement 2.4 mm proximal and tibial tunnel placement 2.5 mm anteromedial relative to the native footprint to account for the difference between the center of the tunnel and center of the tendon when using BTB grafts.