Meniscus: Anatomy, Functions, Injuries, and Treatment

What is the meniscus in the lower limb?

The meniscus refers to two C-shaped pieces of tough, rubbery fibrocartilage located within the knee joint, acting as crucial shock absorbers and stabilizers between the thigh bone (femur) and shin bone (tibia).

Anatomy of the Meniscus

The knee joint, a complex hinge joint, houses two primary menisci: the medial meniscus and the lateral meniscus. Both are crescent-shaped, semi-circular discs composed of fibrocartilage, a type of connective tissue that is tougher and more resilient than hyaline cartilage found on the ends of bones.

• Medial Meniscus: This meniscus is located on the inner side of the knee. It is larger, more C-shaped, and less mobile than the lateral meniscus, primarily due to its firm attachment to the medial collateral ligament (MCL) and the joint capsule. This limited mobility makes it more susceptible to injury.
• Lateral Meniscus: Positioned on the outer side of the knee, the lateral meniscus is more O-shaped and smaller. It has looser attachments, particularly to the lateral collateral ligament (LCL), allowing it greater mobility within the joint. This increased movement can sometimes protect it from certain types of tears but also makes it vulnerable to others.

Both menisci have a thicker outer border that receives some blood supply (the "red zone") and a thinner inner border that is avascular (the "white zone"). This difference in blood supply significantly impacts the healing potential of meniscus tears.

Primary Functions of the Meniscus

The menisci are far more than just passive spacers; they are dynamic structures critical to the biomechanics and long-term health of the knee joint. Their primary functions include:

• Shock Absorption: During activities like walking, running, and jumping, the menisci act as crucial shock absorbers, distributing compressive forces across the knee joint. They can absorb up to 50% of the compressive load when the knee is extended and up to 85% when the knee is flexed, protecting the articular cartilage of the femur and tibia.
• Load Distribution: By increasing the contact area between the rounded femoral condyles and the relatively flat tibial plateau, the menisci help to evenly distribute the weight-bearing forces. Without them, stress would be concentrated on smaller areas, leading to premature wear and tear of the articular cartilage.
• Joint Stability: The C-shape of the menisci helps to deepen the shallow tibial plateau, creating a more congruent fit for the femoral condyles. This enhances the stability of the knee joint, particularly during rotational movements and when the knee is in motion. They work in conjunction with the knee ligaments to prevent excessive anterior-posterior translation and rotational movements.
• Lubrication and Nutrition: While not their primary role, the menisci also contribute to knee joint lubrication by helping to spread synovial fluid, which nourishes the articular cartilage and reduces friction during movement.

Common Meniscus Injuries

Meniscus injuries, often referred to as "torn cartilage," are common, especially in athletes and older adults. Tears can vary widely in type, location, and severity.

• Causes:
  • Acute Trauma: Sudden twisting or pivoting motions of the knee, often when the foot is planted, can cause an acute tear. This is common in sports like soccer, basketball, and skiing. A direct blow to the knee can also cause a tear.
  • Degenerative Changes: In older individuals, the meniscus can weaken and fray over time due to age-related degeneration, making it more susceptible to tears from relatively minor activities, such as squatting or getting up from a chair.
• Types of Tears: Tears are classified by their pattern (e.g., radial, longitudinal, horizontal, flap, bucket-handle) and location (e.g., red zone, white zone). The type and location dictate the severity and potential for healing.
• Symptoms: Common symptoms include:
  • Pain, often along the joint line.
  • Swelling and stiffness.
  • A popping or clicking sensation.
  • Catching or locking of the knee (where the knee temporarily gets stuck).
  • Difficulty fully straightening or bending the knee.

Diagnosis and Treatment Considerations

Accurate diagnosis is crucial for effective treatment of meniscus injuries.

• Diagnosis:
  • A thorough physical examination by a healthcare professional, including specific knee tests (e.g., McMurray's test), is usually the first step.
  • Imaging studies, particularly Magnetic Resonance Imaging (MRI), are often used to confirm the diagnosis, determine the type and location of the tear, and assess for other knee injuries. X-rays may be used to rule out fractures or assess for arthritis.
• Treatment: Treatment options depend on the tear's size, type, location, the patient's age, activity level, and symptoms.
  • Conservative Management: Many small, stable tears (especially in the vascular "red zone") or degenerative tears can be managed non-surgically with rest, ice, compression, elevation (RICE), pain medication, physical therapy, and activity modification.
  • Surgical Intervention: For larger, unstable, or symptomatic tears, particularly those causing locking or significant pain, surgical repair or removal may be recommended.
    • Meniscus Repair: The goal is to stitch the torn edges of the meniscus back together, preserving the tissue. This is often preferred for tears in the "red zone" with good healing potential.
    • Partial Meniscectomy: If repair is not possible, the damaged portion of the meniscus is surgically removed. While this can alleviate symptoms, it does reduce the knee's shock-absorbing capacity and may increase the risk of developing osteoarthritis over time.

Protecting Your Meniscus

Maintaining knee health and preventing meniscus injuries is paramount for long-term mobility and function.

• Proper Movement Mechanics: Focus on correct form during all physical activities, especially squats, lunges, and cutting movements. Avoid excessive twisting of the knee while weight-bearing.
• Strength Training: Develop strong muscles around the knee, particularly the quadriceps, hamstrings, and glutes. These muscles provide dynamic stability to the joint, reducing stress on the menisci.
• Flexibility and Mobility: Maintain adequate flexibility in the hip and ankle joints to ensure proper alignment and reduce compensatory stress on the knee.
• Gradual Progression: When increasing activity levels or starting new exercises, do so gradually to allow your body, including your menisci, to adapt.
• Weight Management: Maintaining a healthy body weight reduces the overall load and stress placed on the knee joints and menisci.
• Listen to Your Body: Pay attention to pain or discomfort in your knees. If you experience persistent pain, popping, or catching, seek professional medical advice promptly. Early intervention can often prevent minor issues from becoming major problems.