Successful Double-Bundle ACL Reconstruction Requires Precise Posterolateral Tunnel Position
Key findings
- Massachusetts General Hospital researchers used a 3D model to examine whether changes in femoral tunnel position affect graft forces
- As the posterolateral tunnel is placed more distally in a double-bundle ACL reconstruction, posterolateral graft forces increase during extension of the knee
- Meanwhile, load is shifted to the anteromedial graft during flexion
- The importance of posterolateral tunnel location suggests the need for improved surgical technologies or techniques for successful double-bundle ACL reconstruction
In double-bundle reconstruction of the anterior cruciate ligament, the limited arthroscopic view and irreversibility of guidewire placement make tunnel placement technically challenging. If the posterolateral tunnel is placed too proximally, it may not be possible to place the anteromedial tunnel accurately, and surgeons may have to err on the side of distal posterolateral tunnel placement.
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In a simulation of double-bundle ACL reconstruction, a research team including Peter Asnis, MD, chief, Sports Medicine Center at Massachusetts General Hospital, has determined that the location of the femoral posterolateral tunnel is as critical as the anteromedial tunnel location. Small changes in femoral tunnel position did not substantially affect postoperative kinematics but greatly affected graft mechanics, which may be more challenging to detect postoperatively. The findings were reported in The International Journal of Medical Robotics and Computer Assisted Surgery.
The research team made use of a 3D computational model that was created at Mass General and has been rigorously validated. The model includes tibial and femoral bones, cartilage layers, ligaments and meniscus elements.
The researchers used the model to simulate double-bundle ACL reconstruction with various femoral posterolateral tunnel locations (8–11 mm center–center tunnel spacing). They simulated graft fixation at both 0° and 30°. Knee biomechanics were examined with the knee under a 134-N anterior load and 400-N quadriceps load at 0°, 30°, 60° and 90° of flexion.
The team found that distal movement of the posterolateral tunnel resulted in large increases in posterolateral graft forces at 0° of flexion. Specifically, taking 8 mm as the anatomic center–center spacing, an increase of only 2 mm resulted in a 21.8% increase in posterolateral graft forces at 0° of flexion. The unloading of the posterolateral bundle at 30° to 90° of flexion appeared to shift the load to the anteromedial bundle, resulting in much larger anteromedial graft forces compared with the intact ACL.
Regardless of graft conditions, only minimal changes in knee kinematics were observed.
Excessive posterolateral strains at low flexion angles may decrease the functionality of a posterolateral graft or even cause it to rupture over time. In light of the low graft forces through the posterolateral bundle at higher flexion angles, the anteromedial bundle seems to acts like a high single-bundle repair at higher flexion angles.
Having identified the importance of the posterolateral tunnel location, the authors conclude that surgeons need improved tools for placing it. These might include better navigational techniques, planning systems and virtual imaging systems for arthroscopic viewing. The authors also affirm the importance of the current trend toward individualized approaches to ACL reconstruction.
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