Causes / typical injury mechanism: There are generally 2 mechanisms of meniscal injury, traumatic versus degenerative, which have unique presentation patterns. Traumatic tears typically occur in the context of athletics, therefore having a greater prevalence in younger populations, most frequently as a result of planting and twisting motions of the lower leg. The mechanism is not always clear and patients may not recall a specific incident. These injuries often present with intermittent pain along the joint line, sometimes with swelling and effusion. Patients may also complain of locking and catching, as well as popping sensations or the inability to reach full extension.
In contrast, degenerative meniscal tears occur predominantly in older individuals and have a more indolent course. These are not necessarily associated with trauma, often occurring concurrently with osteoarthritis (OA). Pain tends to be more generalized and mechanical symptoms may occur less frequently.
Classic history and presentation: Meniscal tears can generally be described by their location and pattern. The meniscus is classically divided into the anterior, middle, and posterior thirds, as well as the outer, middle, and inner thirds. The latter distribution is more closely associated with meniscal blood supply, with increased vascularity closer to the periphery, and is often stratified into the red-red (outer), red-white (middle), and white-white (inner) tears. Simple tear patterns include longitudinal, radial, horizontal, and oblique, with combinations of multiple patterns classified as complex tears.
Prevalence: Meniscal injuries are one of the most common soft tissue musculoskeletal injuries, thought to account for nearly 20% of those presenting to medical institutions for care. Injury to the medial meniscus is more common than the lateral meniscus.
- Age – The highest proportion of affected patients are between the ages of 20 and 29.
- Sex / gender – This disease primarily affects men over women.
Pathophysiology: The menisci are 2 semilunar fibrocartilaginous structures of the knee that support, stabilize, cushion, and lubricate the knee joint. They are wedge shaped in cross section, with the thickest portion located most externally and the thinnest portion internally. Both are anchored to the tibial plateau by attachments in their anterior and posterior horns. The medial meniscus has additional attachments to the medial collateral ligament (MCL), resulting in less freedom of movement relative to the lateral meniscus. The medial and lateral geniculate arteries supply blood to the menisci, but only the peripheral portion is vascularized, resulting in a poor healing capacity of the most internal sections. The menisci distribute and dissipate forces through the knee through hoop stresses, thereby reducing the amount of force placed upon the articular cartilage.
