Description

• 2 menisci: Medial and lateral C-shaped fibrocartilagenous structures located intra-articularly between the femoral condyles and the tibal plateaus
• Each meniscus has a body, anterior horn, and posterior horn.
• The menisci play a role in load distribution, absorbing forces, and stabilizing the knee. Also contribute to joint lubrication and nutrition
• After the age of 10, the menisci begin to devascularize:
  • In adults, the outer 1/3 remains vascularized, whereas the inner 2/3 is avascular and heals poorly
• The medial meniscus is attached to the joint capsule and medial collateral ligament. It is less mobile, and concurrent medial collateral ligament (MCL)/anterior cruciate ligament (ACL) injuries are more common

Geriatric Considerations
Meniscal tears in older patients are more likely due to chronic degeneration of the meniscus that can result in a tear with minimal trauma.

• It is rare to sustain a meniscal injury <10 years old or prior to physial fusion.
• Meniscal tears in young children are often due to a discoid meniscus:
  • Discoid meniscus is an anatomic variant primarily involving the lateral meniscus (incidence of 3.5–5%) that can present with tears, locking, popping (1)[B].
• MRI is less sensitive and specific in diagnosing meniscal tears in children <12 (2)[B]:
  • On MRI, normal vascular meniscal tissue can be misinterpreted as a tear

Epidemiology

• Meniscal tears are more common in the 3rd–5th decades of life.
• More common in males: Male > Female (2.5:1–4:1)

• Injuries are more common in the medial meniscus because of its reduced mobility and role as the primary weight-bearing surface.
• Injuries can be acute or degenerative:
  • Degenerative tears more likely >40
  • Acute traumatic tears more likely in adolescents and adults <40; 80–90% occur during athletics

Prevalence
One of the most common musculoskeletal injuries; frequency of 23.8 per 100,000 per year (3)[B]

Risk Factors

• Increased age
• Obesity
• High degree of physical activity (especially pivot/cutting sports)
• Tibiofemoral arthritis
• ACL insufficiency
• Posterior cruciate ligament (PCL) insufficiency

Genetics
A congenital abnormality leading to discoid meniscus increases the risk of meniscal tear among children. No specific gene locus has been identified.

General Prevention

• Strengthening of quadriceps and hamstring muscles
• Conditioning while participating in sports
• Treatment and rehabilitation of previous knee injuries, particularly ACL injuries
• Improving core proprioception and hamstring flexibility may prevent knee injuries in female athletes.

Etiology

• Acute tears typically occur due to a twisting motion of the knee while the foot is planted. Also can occur due to a hyperflexion event:
  • Common mechanisms during sports: Cutting, decelerating, hyperflexing, or landing from a jump
• Degenerative tears occur secondary to minimal trauma

Commonly Associated Conditions

• ACL is concomitantly torn in 1/3 of cases.
• MCL and lateral collateral (LCL) ligament tears
• Tibial plateau fractures
• Femoral shaft fractures
• Tibiofemoral joint dislocation (seen occasionally)