Are Root Avulsions of the Lateral Meniscus Associated With Extrusion at the Time of Acute Anterior Cruciate Ligament Injury? A Case Control Study

Background: Lateral meniscal avulsions left in situ at the time of anterior cruciate ligament (ACL) reconstruction do well subjectively. Limited published results measure meniscal extrusion of the lateral compartment in this setting. Purpose: To determine whether an avulsion of the posterior root of the lateral meniscus is associated with meniscal extrusion on magnetic resonance imaging (MRI). Study Design: Cohort study (prevalence); Level of evidence, 2. Methods: A prospective database of surgically treated ACL tears from 2007 to 2012 was reviewed. Isolated ACL tears without a concomitant injury were identified along with ACL tears in combination with lateral meniscal tears of the posterior root (PRLMTs). Thirty-five patients had ACL tears and PRLMTs verified arthroscopically, of which 23 patients had preoperative MRI scans available for review. From the same database, 25 isolated ACL tears with no meniscal injury were randomly chosen for comparison. Plain radiographs were reviewed for degenerative joint disease using the Kellgren-Lawrence scale. A board-certified radiologist blinded to arthroscopic findings reviewed each MRI scan using midcoronal sections to measure extrusion of the lateral meniscus. The average extrusion was calculated for each group and compared using a Student t test. Results: In the 48 patients reviewed, 1 patient was excluded because of a complex lateral meniscal tear that could not be measured on MRI. The remaining 47 consisted of 22 with root tears and 25 with intact menisci. None of these patients were noted to have degenerative joint disease greater than Kellgren-Lawrence grade 1. All of the patients with PRLMTs were noted to have intact meniscofemoral ligaments at the time of arthroscopic surgery. In the patients with ACL tears and PRLMTs, the average extrusion was 0.8 mm, and in the ACL tear group with an intact meniscus, the average extrusion measured 0.5 mm. No significant difference in the amount of extrusion was observed (P = .22). Conclusion: At the time of acute ACL injuries, PRLMTs do not appear to result in meniscal extrusion on MRI.