Meniscus tears

Meniscal injuries (tears) are, like knee ligament injuries, also common sports injuries. Typically, these injuries cause “clicking” or “popping” and the sensation of the knee not moving properly during rotation of the knee joint. Injury of the medial meniscus is more common than the lateral, impairing external rotation.

The function of the menisci is to provide a deeper joint surface, equalise the weight load on the joints, reduce stress, and stabilise the joint. The blood supply of the menisci is best at the outer (lateral) edge (red zone) and poorest at the inner (medial) edge (white zone).

Etiology

Meniscal injuries occur due to sudden twisting of the knee with the lower leg in a fixed position with an axial load on the knee (usually the person's weight). In elderly it may also be due to degenerative disease.

Classification

Tears are classified according to their morphology:

• Localisation of tear
  • Medial meniscus
  • Lateral meniscus
  • White zone
    • The inner third
    • Avascular part of meniscus
  • Red-white zone
    • Middle third
    • Poorly vascularized
  • Red zone
    • Outer third
    • Well vascularized
• Dignity of tear
  • Simple
  • Complex (combination of multiple types)
• Type of tear
  • Vertical tear
  • Radial tear
  • Horizontal tear
  • Displaced tear
    • Bucket handle tear
    • Parrot beak tear

Clinical features

Symptoms include pain on the lateral or medial side, swelling, and joint lock-up or instability. Swelling may be due to hydrops or haemarthrosis due to a meniscal tear. Swelling develops over the subsequent 24 hours (and not immediately as in ligament injuries).

The sensation of something “slipping” or “tearing” is suspicious for meniscal injury. There may be pain upon palpation of the relevant joint space.

Diagnosis and evaluation

Many physical examination manoeuvres are used in the evaluation of meniscal injuries. The sensitivity of the McMurray and Apley tests are in the 50-60s percentages. The Thessaly test has much higher sensitivity (80-90%) but is not as widely used.

Apley test involves having the patient prone with the hip extended and knee flexed. Then, the patient’s upper leg is fixated (with the examiner’s leg), the knee is brought to 90° flexion. Then, the lower leg is internally and externally rotated both with and without applying downward pressure on the foot. External rotation tests the medial meniscus while internal rotation tests the lateral. Positive findings include increased pain during rotation when downward pressure is applied.

McMurray test involves having the patient supine with the hip and knee flexed. Then, varus stress and internal rotation is applied to the knee, after which the knee is extended. This tests the lateral meniscus, and positive findings include pain in the lateral joint space or “clicking” or “locking” in the knee. The test is then repeated while applying valgus stress and external rotation, which tests the medial meniscus.

Thessaly test involves having the patient and examiner facing each other (holding hands for support), and having the patient stand on one knee, flexing the knee to 20°, and rotating their body back and forth. Positive findings include pain or a locking or catching sensation.

MRI is the best modality to diagnose soft tissue injuries like ligament and meniscal injuries. Ultrasound may also be used.

Treatment

Treatment is almost always surgical and involves arthroscopy with suture, partial or total resection, or meniscus transplantation. Tears in the red zone of the meniscus have good prognosis due to good blood flow, while tears in the white zone rarely heal and instead require resection.