Knee Menisci: Anatomy, Functions, and Common Injuries

How many meniscus are in each leg?

Each leg contains two menisci within the knee joint: the medial meniscus and the lateral meniscus. These crescent-shaped cartilaginous structures play critical roles in the knee's function, stability, and health.

The Knee Joint: A Complex Structure

The knee is one of the largest and most complex joints in the human body, designed to provide both mobility and stability for activities ranging from walking to jumping. It is primarily a hinge joint, formed by the articulation of three bones: the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). Within this intricate joint, the menisci are essential components, acting as specialized shock absorbers and stabilizers.

Anatomy of the Menisci: Medial and Lateral

In each knee, there are two distinct menisci, each with unique characteristics and functions:

• Medial Meniscus:

  • Located on the inner (medial) side of the knee.
  • It is C-shaped, larger, and semilunar.
  • Its posterior horn is firmly attached to the tibia and the joint capsule, including the medial collateral ligament (MCL). This strong attachment makes the medial meniscus less mobile and, consequently, more susceptible to injury compared to the lateral meniscus.
  • It is broader posteriorly than anteriorly.

• Lateral Meniscus:

  • Located on the outer (lateral) side of the knee.
  • It is more O-shaped or circular, covering a larger portion of the tibial articular surface than the medial meniscus.
  • It is less firmly attached to the joint capsule and is not directly connected to the lateral collateral ligament (LCL), allowing it greater mobility. This increased mobility helps it to accommodate the dynamic movements of the knee joint and often makes it less prone to injury from direct forces compared to the medial meniscus, though it can still be injured.

Both menisci are composed of fibrocartilage, a tough, flexible tissue that is well-suited to withstand compressive and shear forces. They sit on the tibial plateau, between the condyles of the femur and the tibia.

Functions of the Menisci

The menisci are far more than simple pads; they are dynamic structures vital for optimal knee function:

• Shock Absorption: They act as cushions, absorbing and distributing compressive forces across the knee joint during weight-bearing activities. This protects the articular cartilage of the femur and tibia from excessive wear.
• Load Distribution: By increasing the contact area between the femoral and tibial condyles, the menisci help to distribute axial loads over a larger surface. This reduces stress on the articular cartilage, which is critical for long-term joint health. Without menisci, the load would be concentrated in a smaller area, leading to premature degeneration.
• Joint Stability: The wedge shape of the menisci helps to deepen the tibial plateau, improving the congruency between the rounded femoral condyles and the relatively flat tibial surface. This enhances the stability of the knee joint, particularly during rotational movements and weight-bearing.
• Lubrication and Nutrition: They assist in the circulation of synovial fluid, which lubricates the joint and provides nutrients to the articular cartilage.
• Proprioception: Recent research suggests that the menisci also contain mechanoreceptors, contributing to proprioception (the body's sense of position and movement), which is important for neuromuscular control and preventing injury.

Clinical Significance: Meniscus Injuries

Given their critical roles and location, the menisci are vulnerable to injury, particularly tears. Meniscus tears are common, especially in athletes and older adults.

• Causes: Tears often occur during activities involving twisting, pivoting, or deep squatting, especially when the knee is weight-bearing. Degenerative tears can also occur in older individuals due due to cumulative wear and tear.
• Symptoms: Common symptoms include pain, swelling, stiffness, a catching or locking sensation in the knee, and difficulty fully extending or bending the knee.
• Impact: An injured meniscus can significantly impair knee function, leading to pain and instability. Depending on the severity and location of the tear, treatment can range from conservative management (rest, physical therapy) to surgical repair or removal (meniscectomy).

Maintaining Meniscus Health

Understanding the structure and function of the menisci underscores the importance of proactive measures to maintain knee health:

• Proper Biomechanics: Focus on correct form during exercises and daily movements to avoid excessive twisting or sudden impacts on the knee.
• Strength Training: Strengthen the muscles surrounding the knee, particularly the quadriceps, hamstrings, and glutes. Strong muscles provide dynamic stability and help to absorb forces that would otherwise stress the menisci.
• Flexibility and Mobility: Maintain good range of motion in the knee and surrounding joints to prevent undue stress during movement.
• Weight Management: Carrying excess body weight significantly increases the load on the knee joints and menisci, accelerating wear and tear.
• Listen to Your Body: Pay attention to pain signals and avoid pushing through discomfort, especially during activities that involve twisting or deep knee flexion.

Conclusion

In summary, each leg is equipped with two vital menisci: the medial and lateral menisci. These fibrocartilaginous structures are indispensable for the knee's mechanical integrity, providing crucial shock absorption, load distribution, and stability. A thorough understanding of their anatomy and function is paramount for anyone invested in joint health, injury prevention, and optimizing physical performance. Prioritizing proper movement mechanics, strength, and overall joint care is essential for preserving the long-term health and functionality of these critical knee components.