Knee Meniscus – How to Treat Meniscus Injuries

Knee Meniscus Structure

The knee joint contains two menisci: medial and lateral. These are crescent-shaped fibrocartilaginous structures located between the cartilage-covered surfaces of the femur and tibia. The term "meniscus" derives from the Greek word meniskos, meaning "crescent," a diminutive of mene, meaning "moon." The meniscal crescents have a triangular cross-section and cover approximately half to two-thirds of the respective tibial condyle’s surface.

Medial Meniscus

The posterior root of the medial meniscus is attached to the tibia via the posterior root ligament, located anterior to the posterior cruciate ligament (PCL) attachment and posterior to the lateral meniscus’ posterior root. The anterior root ligament of the medial meniscus typically attaches to the tibia in front of the anterior cruciate ligament (ACL) or, less commonly, connects to nearby connective tissue. The medial meniscus has a C-shaped structure, and its horn attachments are far apart. It is further secured to the tibia by the meniscotibial ligament and to the joint capsule and medial collateral ligament (MCL) fibers. This stable attachment makes the medial meniscus less mobile and more prone to chronic, overload injuries even without significant trauma.

Lateral Meniscus

The posterior root of the lateral meniscus is attached to the tibia via the posterior root ligament, just behind the ACL. Additional reinforcement comes from the posterior meniscofemoral ligament (Wrisberg’s ligament) and the anterior meniscofemoral ligament (Humphrey’s ligament), which connect the posterior horn of the lateral meniscus to the femur and PCL. The anterior root ligament of the lateral meniscus attaches to the tibia near the ACL. The lateral meniscus has an O-shaped structure, with horn attachments closer together. Unlike the medial meniscus, it is not fully attached to the tibia and lacks a connection to the joint capsule. This makes the lateral meniscus more mobile and less prone to injuries. It covers 60-80% of the lateral tibial condyle's surface and plays a key role in accommodating the rounded femoral condyle. Lateral meniscus damage significantly increases stress on joint surfaces, accelerating degenerative changes.

Histological Structure, Vascularization, and Innervation of the Meniscus

The meniscus consists mainly of collagen fibers arranged circumferentially and radially, interwoven with elastic fibers. Embedded within the collagen fibers are chondrofibrocytes, characteristic of fibrocartilage. The outer third (near the joint capsule) of the meniscus is well-vascularized and innervated. Blood vessels and nerve endings gradually diminish toward the central portion, becoming absent at the free edge within the joint. This structure affects healing and regeneration processes, which are easier in the vascularized red zone but limited or absent in the poorly vascularized and avascular white zone, often requiring biological assistance.

Function of the Meniscus in the Knee Joint

The menisci adapt the tibial condyles’ surface to the moving femoral condyles, absorbing forces on the knee cartilage. They also contribute to joint stability, nutrient exchange, and metabolic waste removal by filtering synovial fluid. Meniscal nerve endings act as proprioceptive receptors, forming part of the body's posture and movement control system.

Causes of Meniscus Injuries

Meniscus injuries typically result from significant knee stress, often during physical activity. Forces damaging the meniscal tissue may act in various directions, such as twisting or tearing under compression (e.g., in deep squats). In younger individuals, the meniscus has high strength and elasticity, so injuries often occur due to significant trauma, such as sports activities (e.g., skiing, soccer, squash) or traffic accidents. In older individuals, repeated microtraumas and age-related degenerative changes reduce meniscal durability, causing injuries even during routine activities like deep squats. Degenerative meniscus injuries result from cumulative microtraumas superimposed on joint degeneration, with symptoms such as gradual pain and dysfunction without a specific traumatic event.

Symptoms and Diagnosis of Meniscus Injuries

Common symptoms include pain localized to the injured meniscus, knee swelling, joint locking, popping sensations, or restricted movement. Tenderness along the joint line and positive meniscal tests confirm the diagnosis. Additional imaging such as ultrasound (US) or magnetic resonance imaging (MRI) can further confirm meniscus injuries. MRI scans allow precise planning of treatment for meniscus and other knee structures.

Treatment of Meniscus Injuries

The success of meniscus treatment depends on biological healing potential and mechanical stability of the damaged meniscus parts. Most meniscus injuries require surgical treatment, typically through minimally invasive arthroscopy. Prompt consultation with an orthopedic clinic ensures the most appropriate treatment approach.

Surgical Treatment

During knee arthroscopy, the orthopedic surgeon evaluates the damaged meniscus and determines the best way to repair it. Several techniques are available for placing stable sutures to reapproximate and secure the damaged meniscus fragment. Sutures can be placed using all-inside techniques (no additional surgical access) or mixed techniques like outside-in or inside-out, which require small additional incisions.

Biological Augmentation

In cases where stable sutures can be placed but healing potential is uncertain, biological augmentation techniques may be employed, such as injecting bone marrow with stem cells, stem cell concentrates, or introducing an exogenous clot near the injury. Advanced techniques involve covering the meniscus with a collagen membrane and injecting bone marrow between the membrane and the meniscus. These methods preserve the meniscus in cases where meniscectomy (removal) would otherwise be necessary.

Postoperative Care and Rehabilitation

Following meniscus surgery, patients are advised to stay home for two weeks, elevate the operated leg, and ice the knee at least three times daily for 20 minutes. Depending on the surgical procedure, postoperative care may include using a knee brace or continuous passive motion (CPM) devices. Weight-bearing restrictions with crutches range from 2 to 8 weeks post-surgery.

Non-Surgical Treatment

Non-surgical treatment is reserved for stable, degenerative meniscal injuries, such as horizontal tears. Effective rehabilitation over 3-6 months may relieve symptoms without surgery. Supplements like collagen, glycosaminoglycans, vitamins C, D3, K, and injectable treatments like hyaluronic acid or platelet-rich plasma (PRP) are often used during rehabilitation.

Can You Walk with a Torn Meniscus?

A torn, unstable meniscus loses its protective function, accelerating knee degeneration. Meniscus removal significantly increases the risk of early degenerative changes, even in young individuals, within approximately five years after meniscectomy.

Summary

Meniscus injuries are a common cause of knee joint issues across all age groups. The primary principle in treating meniscus injuries is to preserve the meniscus. Advances in medical knowledge and technology provide realistic opportunities to save the meniscus, aligning with the motto: "Save the meniscus."

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Bibliography:

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• Beaufils P, Becker R, Kopf S, Englund M, Verdonk R, Ollivier M, Seil R. Surgical Management of Degenerative Meniscus Lesions: The 2016 ESSKA Meniscus Consensus. Joints. 2017;28,5(2):59-69
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