Review Question - QID 216794

Re-rupture after ACL reconstruction is most commonly due to technical error, specifically tunnel malposition. A femoral tunnel centered on the lateral intercondylar ridge is too anterior, and would greatly increase the risk of graft failure, as seen in this patient.

ACL reconstruction is one of the most commonly performed orthopaedic procedures, with over 400,000 performed per year. When performed properly, ACL reconstruction is a durable and reliable procedure, which can predictably allow patients to return to sport and activity. That said, the procedure is not without complication, and a variety of errors can lead to an increased risk of re-rupture following reconstruction. The most common cause of failure following ACL reconstruction is technical error leading to re-rupture, with the most common technical error being tunnel misplacement. The most common error in tunnel positioning occurs on the femoral side: anterior tunnel placement causes the graft to be overly taut in flexion and lax in extension, while a vertical tunnel leads to residual rotational instability. In the coronal plane, the femoral tunnel should be located at the 10 o'clock position for the right knee and at the 2 o'clock position for the left knee.

Trojani et al. performed a retrospective multicenter study over a 12-year period across ten French orthopaedic centers. Their study population included 293 patients who failed primary ACL reconstruction. The most common cause of failure was technical error (147 patients), and an anteriorly placed femoral tunnel was the most common technical error (108 patients). They reported that patients who are revised for an anteriorly-placed femoral tunnel, fortunately, have good functional outcomes, especially when compared to other forms of failure.

Morgan and the Multicenter ACL Revision Study (MARS) group reported on 460 revision ACL reconstructions performed by 87 surgeons. Of the 460 revision procedures included in their study, failure of the index procedure was attributed to a specific identifiable technical error in 276 (60%) of cases. Of these cases, femoral malposition was the most common technical error. The authors found the most common error with femoral tunnel placement to be too vertical of in 42 (35.9%) cases, too anterior in 35 (20.0%) cases and both too vertical and anterior in 31 (26.5%) cases. 91 (82.1%) revision procedures required femoral tunnel redrilling. The authors concluded that femoral tunnel malposition was the leading cause of failure in their large, multicenter cohort.

Figures A and B are 3D representations of the lateral intercondylar notch and tibial plateau, respectively.

Incorrect Answers:
Answer 1: These findings may be suggestive of infection. Infection is a rare complication following ACL reconstruction and often presents within the first 10-14 days. In addition, it is a much less common cause of failure than tunnel malposition.
Answer 3: This is the appropriate femoral tunnel position for the right knee.
Answer 4: This is the appropriate tibial tunnel position.
Answer 5: A tunnel placed anterior to the posterior border of the anterior horn of the lateral meniscus is far too anterior, and will cause tightness in flexion with roof impingement during extension. Tibial tunnel malposition, however, is a less common error than femoral tunnel malposition.