Review Question - QID 211172

If the tibial tunnel is placed too anteriorly, both knee extension and flexion will be limited, as the graft will impinge on the intercondylar notch in knee extension and be overly tight in knee flexion.

Tunnel malposition is the most common technical error resulting in an increased risk of graft failure in the postoperative period. Non-anatomic tunnel placement results in an anisometric graft. Tibial tunnel malposition occurs most often in the sagittal plane. The center of the tibial tunnel should be roughly 10mm anterior to the PCL and in line with the poster aspect of the anterior horn of the lateral meniscus. An anteriorly placed tibial tunnel leads to flexion tightness and inability to achieve full knee extension secondary to notch impingement. Conversely, a posteriorly placed tibial tunnel leads to impingement on the PCL in knee flexion (Illustrations A and B).

Battaglia et al. explains that more than 75% of all cases of failed ACL reconstruction are secondary to technical error, most commonly attributed to malpositioned tunnels. The authors discuss that revision ACL reconstruction following failure secondary to malpositioned tunnels is often complicated by bony defects and tunnel osteolysis.

Chhabra et al. reviewed the anatomy and biomechanics of the anteromedial (AM) and posterolateral (PL) bundles of the ACL. The authors discuss that the PL bundle is tight chiefly in extension and contributes to rotational stability, while the AM bundle becomes tight with flexion and contributes significantly to anteroposterior stability. As a result, the AM bundle may be assessed with the anterior drawer, while the PL bundle is assessed with the pivot shift.

Illustration A is a chart demonstrating expected clinical findings with ACL femoral and tibial malposition.


Incorrect Answers:
Answer 1: A vertical femoral tunnel will lead to persistent rotational instability. Rotational stability is assessed with the pivot shift. Anteroposterior stability is assessed with an anterior drawer or Lachman and is unaffected by vertical femoral tunnel malposition.
Answer 2: An anterior femoral tunnel will lead to a graft that is tight in knee flexion and loose in extension. As a result, knee flexion may be limited, and increased anterior tibial translation may be appreciable in knee extension.
Answer 4: Anterior tibial tunnel placement will lead to limited knee flexion AND extension due to excessive graft tightness in flexion and graft impingement on the intercondylar notch in extension. The pivot shift assesses for rotational instability, which may be seen with a vertical femoral tunnel.
Answer 5: A posterior femoral tunnel will result in limited knee extension and increased anterior tibial translation with the knee in flexion.