lateral meniscus

**Anatomy** - Fibrocartilage (mostly type I collagen) wedge-shaped in cross-section. It deepens the tibial plateau, which is relatively flat. - Shape: nearly circular (C-shaped), covering a larger share of the tibial plateau than the medial meniscus. - Attachments: it is NOT attached to the lateral collateral ligament (LCL) and has no firm peripheral attachment to the joint capsule at the popliteus hiatus. The popliteus tendon passes near it, and some popliteus fibers attach to it, so it retracts during knee flexion. The meniscofemoral ligaments (Humphrey, anterior, and Wrisberg, posterior) connect it to the PCL and medial femoral condyle. - Result: it is more mobile than the medial meniscus, so it tears less often. - Blood supply: the medial, lateral, and middle genicular arteries (branches of the popliteal artery) supply the peripheral 10–30%, the red zone. The inner portion is avascular and gets nutrients by diffusion from synovial fluid. A red-red or red-white tear near the periphery can heal or be repaired. A white-white tear in the inner zone generally cannot. - Innervation: free nerve endings and mechanoreceptors (proprioception) are mostly in the outer third.

**Function** - Shock absorption and load transmission. The lateral meniscus carries about 70% of the load in the lateral compartment. Removing the meniscus (meniscectomy) causes early osteoarthritis. - Joint stability, congruity, lubrication, and proprioception.

**Clinical significance** - The medial meniscus is injured more often, because it is less mobile and is attached to the MCL and capsule. Lateral meniscus tears are more common with acute ACL injuries (lateral tears with acute ACL rupture, medial tears with chronic ACL deficiency). - Mechanism: twisting or rotational force on a planted, flexed knee, as in sports. In older patients, degenerative tears occur with minimal trauma. - Presentation: joint line tenderness (lateral), catching or locking, giving way, and delayed effusion (hours to a day). Locking is classically from a bucket-handle tear. - Exam: McMurray test (flex the knee, apply valgus or varus stress, and rotate the tibia while extending; a palpable or audible click or pain suggests a tear. Lateral meniscus: internal rotation and varus stress). Apley grind test and Thessaly test are also used. - Imaging: MRI is the best test. Plain films exclude fracture and show arthritis. - Management: conservative care (RICE, NSAIDs, PT) for stable or degenerative tears. Arthroscopic repair for peripheral (red-zone) tears in young patients. Partial meniscectomy for irreparable tears. - Discoid lateral meniscus: a congenital variant in which the meniscus is thick and disc-shaped. It can cause a snapping knee in children. - Unhappy (O'Donoghue) triad: ACL + MCL + medial meniscus tear. The lateral meniscus is more often involved in non-contact ACL injuries. - Associated structures: the common peroneal (fibular) nerve wraps around the fibular neck laterally and can be injured with lateral knee trauma. Popliteus tendon and LCL injuries are part of posterolateral corner injuries.

**High-yield mnemonic** - Lateral meniscus = Larger coverage, Looser attachment, Less often torn.