Lateral meniscus root tear and meniscus extrusion with anterior cruciate ligament tear.

PURPOSE To retrospectively determine the prevalence of posterior lateral meniscus root tears (LMRTs), as depicted on magnetic resonance (MR) images, in patients with an anterior cruciate ligament (ACL) tear and to investigate the association of LMRTs with lateral meniscus extrusion and other ligament injuries. MATERIALS AND METHODS Institutional review board approval was obtained; informed consent was not required. This study was HIPAA compliant. MR images were obtained in 174 male and 119 female patients (mean age, 37 years; age range, 16-87 years) and retrospectively reviewed for LMRT, medial meniscus root tear (MMRT), nonroot meniscus tear, meniscus extrusion, and presence of meniscofemoral ligaments (MFLs). The chi2 and unpaired Student t tests were performed. RESULTS In 33 patients, 34 meniscus root tears were identified. An LMRT was present in 26 (9.8%) of 264 patients, and an MMRT was present in eight (3.0%) (P=.008). Lateral meniscus extrusion was present in six (23%) of 26 LMRTs and five (2.2%) of 231 patients with normal meniscus roots (P<.001). Complex or deep radial tears were found in three of five cases of lateral meniscus extrusion and normal root. The MFL was not observed in five (19%) of 26 studies of an LMRT. Among these 26 studies of an LMRT, lateral meniscus extrusion was identified in three (14%) of 21 cases in which the MFL was intact and in three (60%) of five cases in which the MFL was not identified (P<.03). Prevalence of an extruded meniscus was seven (88%) of eight for an MMRT and six (23%) of 26 for an LMRT (P=.001). CONCLUSION Prevalence of LMRTs is greater than that of MMRTs in patients with an ACL tear. LMRTs and complex and radial tears are associated with lateral meniscus extrusion; an absent MFL is more prevalent in patients with LMRTs and when the meniscus is extruded.