E1570. Lateral Meniscocapsular Injury on MRI with Arthroscopic Correlation
  1. Jennifer Levy; University of Pennsylvania
  2. Sarah Thomas; University of Pennsylvania
  3. Robert Parisien; Harvard University
  4. Dhruv Goyal; Drexel University
  5. Stephanie Jo; University of Pennsylvania
The MR diagnosis of lateral meniscocapsular separation (LMCS) is challenging due to the complex anatomy in this region, the loose attachments of the posterolateral joint capsule, and the normal interruptions in the capsular attachments at the popliteal hiatus [1,2]. Furthermore, the normal mobility of the lateral meniscus makes the traditional MR sign of LMCS, meniscal displacement from the posterior tibial rim, relatively non-specific for the diagnosis [3]. Despite these challenges, diagnosing this entity on MR—and differentiating it from the more common lateral meniscal tear—remains critically important, as it can lead to meniscal hypermobility and explain symptoms of knee instability [4]. Fortunately, because the peripheral aspect of the meniscus is highly vascular and heals easily, isolated LMCS portends a favorable prognosis, usually requiring only conservative management [4].

Educational Goals / Teaching Points
The goals of this educational exhibit are to (1) review the normal anatomy of the posterior horn of the lateral meniscus and its surrounding structures, (2) define meniscocapsular separation and distinguish it from meniscal tears, and (3) demonstrate the MR imaging features of LMCS with arthroscopic correlation.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The important anatomic structures that will be covered in this exhibit are the lateral meniscal attachments: popliteomeniscal fascicles, meniscofemoral ligaments, meniscotibial ligament, and joint capsule. We present several appearances of LMCS, including blunting of the peripheral margin of the posterior horn of the lateral meniscus and high signal intensity in the periphery of the meniscus that does not extend to the articular surface. These findings are contrasted with the appearance of lateral meniscal tears.

LMCS has a distinct MR imaging appearance which can be used to distinguish it from lateral meniscal tears.