Surgeons are always looking for ways to improve surgical technique in hopes of better outcomes for their patients. In the case of anterior cruciate ligament (ACL) reconstruction, there's been a slight shift in how the tunnels are drilled through the bone for the graft tendon. Along with that change comes the ability to place the graft in a more natural position. The net result is a more anatomic reconstruction.
It is always the case that ACL surgery is done with an eye toward restoring all the damaged structures to as normal as possible. That way, the patient has a fighting chance of returning to normal function with a stable knee. But it is also agreed that the anatomy of the anterior cruciate ligament is complex and difficult to mimic.
One of the more difficult aspects of ACL reconstructive surgery has always been drilling through the tibia (lower leg bone) in order to thread the tendon graft through the hole to the right spot for attachment. This type of tunnel is called a transtibial tunnel.
The tunnel drilling technique used until recently often placed the graft in a vertical (up and down) position. As a result of the slightly off-anatomic position, the knee could end up unstable even though the graft was intact.
Over the years surgeons have tried different ways to approach this problem. They have tried changing the way the second tunnel is constructed. This second tunnel is through the femur (thigh bone). They have tried making the tibial tunnel up higher and shorter. And they have used different starting points for the tibial tunnel along the medial side of the knee (side closest to the other knee).
None of these efforts has proved successful. Problems with joint instability, altered joint kinematics (movement), and early degenerative arthritis have occurred. The latest trend has been to drill the two tunnels separately from each other rather than using the entrance to one tunnel (tibial tunnel) to drill the second (femoral) tunnel. This approach is referred to as independent drilling of the tibial and femoral tunnels. The tunnels and subsequent graft line up in a more anatomic center.
Results of studies so far suggest that this more anatomic approach helps improve rotational stability of the knee. CT scans provide an accurate way to look at the bone tunnel position and compare the position to the results. In this way, researchers have systematically looked for the optimal tunnel (and graft) angle and position.
At first, these varying tunnel drilling techniques were tried on cadavers (bodies preserved after death for study). Using a robotic force sensor system, they were able to test for knee stability in all directions.
Now clinical studies of this independent drilling method have confirmed the improved results with shorter recovery time, earlier return to sports activity for athletes, and fewer failed ACL reconstructive surgeries.
In summary, the shift to independent drilling of femoral and tibial tunnels during ACL reconstructive surgery makes it possible to mimic the more natural or anatomic placement of the graft. The result is a more stable knee. Surgeons are advised to pay attention to optimal tunnel placement as well as graft position and go for the most anatomic alignment possible. Specific details of how to do this are included in this article for surgeons who may be interested in pursuing a more anatomic ACL graft placement.
Reference: Patrick A. Smith, MD. Update on New Techniques for Anatomic Anterior Cruciate Ligament Reconstruction. In Current Orthopaedic Practice. November/December 2011. Vol. 22. No. 6. Pp. 503-508.