Lateral Meniscal Oblique Radial Tears Are Common With ACL Injury: A Classification System Based on Arthroscopic Tear Patterns in 600 Consecutive Patients

Background: Meniscal root tears and ramp lesions have been rigorously characterized in recent literature. However, one of the most common lateral meniscal injuries identified with an acute anterior cruciate ligament (ACL) disruption, a posterior horn lateral meniscal oblique radial tear (LMORT), has not been thoroughly described. Purpose: To determine the incidence of all meniscal tears and, more specifically, the incidence of posterior horn LMORTs in a multicenter cohort of consecutive, acute ACL reconstructions. Additionally, the authors aimed to develop a new classification system to help guide treatment of posterior horn LMORTs. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A multicenter retrospective cohort design was used to analyze 200 consecutive cases of acute ACL reconstruction from each of 3 different surgeons, for a total of 600 patients. The operative notes and intraoperative photos were analyzed to determine the incidence and laterality of all meniscal tears. A classification system based on tear characterization was then used to categorize tear patterns into similar groups. Results: A total of 396 (66%) of the 600 patients with acute ACL disruption had concomitant meniscal tears. Specifically, 187 (31%) had a lateral meniscal injury, 89 (15%) had a medial meniscal injury, and 122 (20%) had both medial and lateral meniscal injuries. The most common lateral meniscal tear was an LMORT; 71 (18%) patients with meniscal tears had a posterior horn LMORT. Overall, the incidence of ACL injury with a concomitant posterior horn LMORT was 12%. A classification was developed, which included type 1 tear (partial thickness <10 mm from the root attachment), type 2 tear (complete radial oblique tear that extended <10 mm from root), type 3 tear (incomplete LMORT that extended >10 mm from root), and type 4 tear (complete LMORT >10 mm from root). Conclusion: In 600 consecutive acute ACL reconstructions, the incidence of concomitant ACL injury with meniscal injury was 66%, and posterior horn LMORTs represented a large proportion of all meniscal tears (12%). A classification scheme was developed for posterior horn LMORTs to aid reporting and clinical decision making for these common tears.