Meniscus: Anatomy, Divisions, Vascular Zones, and Clinical Significance

What are the different parts of the meniscus?

The meniscus, a crucial C-shaped fibrocartilaginous structure within the knee joint, is primarily composed of two distinct pads—the medial and lateral menisci—each further divided anatomically into an anterior horn, body, and posterior horn, and physiologically into vascular zones that dictate healing potential.

Introduction to the Meniscus

The knee joint, a complex marvel of human engineering, relies on several structures for its remarkable range of motion and stability. Among the most critical are the menisci. These two crescent-shaped wedges of fibrocartilage sit between the femoral condyles (thigh bone) and the tibial plateau (shin bone), acting as vital shock absorbers, load distributors, and stabilizers. Understanding their intricate anatomy is fundamental for anyone involved in exercise science, rehabilitation, or injury prevention.

The Two Primary Menisci: Medial and Lateral

Within each knee, there are two distinct menisci, each with unique characteristics and attachments:

• Medial Meniscus: Located on the inner (medial) side of the knee, this meniscus is larger and more C-shaped. It is more firmly attached to the joint capsule and the medial collateral ligament (MCL), making it less mobile than its lateral counterpart. This reduced mobility contributes to its higher susceptibility to injury, especially during twisting motions.

• Lateral Meniscus: Situated on the outer (lateral) side of the knee, the lateral meniscus is smaller and more O-shaped or circular. It is less firmly attached to the joint capsule and has a connection to the popliteus muscle tendon, which allows it greater mobility. This increased mobility helps it adapt to knee movements and makes it somewhat less prone to injury compared to the medial meniscus, though tears are still common.

Anatomical Divisions of Each Meniscus

Beyond the distinction between medial and lateral, each meniscus is further divided into three distinct anatomical regions:

• Anterior Horn: This is the front-most portion of the meniscus. Both the medial and lateral anterior horns are firmly anchored to the anterior aspect of the tibial plateau via strong meniscotibial ligaments, contributing to the stability of the knee. The anterior horns play a role in resisting anterior translation of the tibia.

• Body: The central and largest section of the meniscus, the body, lies beneath the femoral condyles. This is the primary load-bearing and shock-absorbing region. It is thickest at its periphery and tapers towards the inner edge, creating a concave surface that deepens the tibial plateau and enhances congruence with the femoral condyles.

• Posterior Horn: This is the rear-most portion of the meniscus. Similar to the anterior horn, both posterior horns are securely attached to the posterior aspect of the tibial plateau. The posterior horn, particularly of the medial meniscus, is a common site of injury due to the compressive and shear forces it experiences during deep knee flexion and twisting movements.

Vascularity and Healing Zones

The healing potential of a meniscal injury is highly dependent on its blood supply, which varies across different regions of the meniscus. These regions are often categorized into three distinct zones:

• Red Zone (Outer Third): This outermost 10-30% of the meniscus is well-vascularized, meaning it receives a direct blood supply from the capsular arteries. Injuries in this zone, often referred to as "red-on-red" tears, have the highest potential for healing with surgical repair due to the presence of blood-borne healing factors.

• Red-White Zone (Middle Third): This intermediate zone has a more limited blood supply, receiving some vascularity from the outer red zone but diminishing towards the center. Tears in this "red-on-white" zone have a moderate healing potential, often requiring careful consideration for repair versus debridement.

• White Zone (Inner Third): The innermost 60-70% of the meniscus is largely avascular, meaning it has no direct blood supply. Tears in this "white-on-white" zone typically have very poor healing potential. Consequently, injuries here are often treated with partial meniscectomy (removal of the damaged tissue) rather than repair, as the tissue lacks the necessary blood flow for regeneration.

Clinical Significance and Injury Considerations

Understanding these anatomical and vascular divisions is crucial for diagnosing and treating meniscal injuries. Tears can occur in any of these parts and zones, with implications for symptoms, treatment, and recovery:

• Location of Tears: Posterior horn tears are common, especially in the medial meniscus, often associated with squatting or twisting. Bucket-handle tears, where a large portion of the meniscus detaches, can involve the body and extend into the horns.
• Healing Potential: A tear in the vascular Red Zone has a much better prognosis for repair than one in the avascular White Zone, which typically requires removal of the damaged tissue.
• Surgical Approach: Surgeons consider the location and vascularity when deciding whether to repair a torn meniscus (suturing it back together) or perform a meniscectomy (removing the damaged portion).

Conclusion

The meniscus, far from being a simple cushion, is a sophisticated structure with distinct parts and functional zones. The medial and lateral menisci, each subdivided into anterior horn, body, and posterior horn, work synergistically to provide stability, absorb shock, and distribute loads within the knee. Furthermore, the varying vascularity across its red, red-white, and white zones profoundly influences its capacity for healing. A comprehensive understanding of these intricate components is paramount for fitness professionals and individuals alike to appreciate knee mechanics, prevent injury, and optimize rehabilitation strategies.