Review Question - QID 2

A tibial tunnel drilled too anteriorly will limit full extension and causes tightness in flexion.

The majority of early ACL reconstruction failures are felt to be due to errors in surgical technique. The most common error in ACL reconstruction is aberrant tunnel placement. Placing the tibial tunnel too far anterior may cause notch impingement of the graft limiting full extension. It also causes tightness in flexion. Loss of full extension of the knee prevents appropriate heel-strike and alters the normal gait cycle.

Markolf et al used cadaveric knees to evaluate the effects of different femoral tunnel placements on the stability of an ACL reconstruction. They found that anterior and posterior errors resulted in greater laxity than errors medial or lateral around the notch clockface.

Chabra et al and Zantop et al review the anatomy and biomechanics of the two bundles of the ACL. The posterolateral (PL) bundle is tight in extension, while the anteromedial (AM) bundle becomes tight with flexion. The PL bundle appears to be more prevalent in providing rotatory stability.

Illustration A is a table demonstrating how aberrant tunnel placement affects knee range of motion. Illustration B shows an example of tunnel placement with label A being correct placement, label B being anterior tibial and femoral tunnel malposition.

Incorrect Answers:
1. Femoral tunnel drilled too anterior will lead to tightness in flexion and laxity in extension.
2. Failure to cycle the knee may lead to stretching out of the ACL and residual laxity in flexion and extension.
3. Femoral tunnel drilled to vertically is associated with transtibial drilling and will result in rotational instability.
4. Tibia tunnel drilled to vertically is not typically a problem with ACL reconstruction.