Knee Meniscus: Anatomy, Function, and Importance

The menisci of the knee are two crescent-shaped fibrocartilaginous structures interposed between the femur and the tibia, playing a fundamental role in joint biomechanics. Although they were long considered “vestigial remnants” without function, it is now known that the menisci perform indispensable tasks: they absorb loads, distribute forces, stabilize the knee, facilitate lubrication, and contribute to proprioception.

Meniscal injuries are among the most frequent knee pathologies, both in young athletes (traumatic mechanism) and in the adult population (degenerative mechanism). Understanding the anatomy and vascularization of the meniscus is now fundamental for guiding therapeutic decisions: to repair, treat conservatively, or, as a last resort, partially remove the damaged tissue.

Scientific research in recent decades has shown that meniscus preservation is a priority objective: its removal, even partial, profoundly alters knee biomechanics and accelerates cartilage degeneration.

Meniscus Anatomy

General Structure

The menisci are two pads of fibrocartilage shaped like a “C” (medial meniscus) and an almost complete “O” (lateral meniscus), positioned on the tibial plateau. In cross-section, each meniscus has a triangular (wedge) shape, with:

• A peripheral margin (outer): thick, vascularized, adherent to the joint capsule
• A free margin (inner): thin, avascular, facing the center of the joint
• A superior surface: concave, in contact with the femoral condyles
• An inferior surface: flat, resting on the tibial plateau

Medial Meniscus

The medial meniscus (inner) is “C”-shaped, larger, and less mobile than the lateral meniscus.

The adherence of the medial meniscus to the medial collateral ligament reduces its mobility, making it more vulnerable to trauma. The posterior horn of the medial meniscus is the most frequently injured portion.

Lateral Meniscus

The lateral meniscus (outer) has an almost circular, “O” shape, and covers a larger portion of the lateral tibial plateau.

The greater mobility of the lateral meniscus makes it less vulnerable to trauma compared to the medial. The presence of the popliteus muscle tendon, which interposes between the lateral meniscus and the lateral collateral ligament, creates an area devoid of capsular insertions (popliteal hiatus), which is a point of relative anatomical weakness.

Meniscal Attachments

Each meniscus is anchored to the tibia via the roots (attachments) of the anterior and posterior horns. These attachments are fundamental from a biomechanical perspective: they convert axial (compressive) load into circumferential tension in the meniscus body (hoop stress). A meniscal root tear is functionally equivalent to a total meniscectomy, because the meniscus loses its ability to distribute load.

Other important connections:

• Transverse ligament (anterior intermeniscal ligament): connects the anterior horns of the two menisci
• Meniscofemoral ligaments of Humphry and Wrisberg: connect the posterior horn of the lateral meniscus to the medial femoral condyle

Composition and Structure

The meniscus is fibrocartilage padding consisting of two crescent-shaped structures on the tibial plateau that absorb shock and distribute load between the femur and tibia. Meniscal tissue is composed of:

• Water: approximately 70-75% of total weight
• Collagen: approximately 75% of dry weight, predominantly type I (unlike hyaline cartilage, which contains type II)
• Proteoglycans: approximately 3-5% of dry weight, important for water retention and compression resistance
• Cells (fibrochondrocytes): produce and maintain the extracellular matrix

Collagen fibers are arranged with a predominantly circumferential orientation (parallel to the peripheral margin), which is fundamental for resisting tensile stresses generated by load. Radial fibers (“tie fibers”) connect the circumferential fibers, preventing longitudinal separation.

Meniscus Vascularization

Meniscus vascularization is an aspect of fundamental clinical importance because it determines the healing capacity of injuries.

The Three Vascular Zones

The vascularization of the menisci comes from the genicular arteries (superior and inferior, medial and lateral), which form a pericapsular vascular plexus in the periphery of the meniscus. From this plexus, vessels penetrate the meniscal tissue only in the peripheral third.

At birth, the meniscus is almost completely vascularized. With growth and loading, vascularization progressively reduces, and in adults, only the peripheral 10-30% of the meniscus is vascularized. In the elderly, the vascularized zone further diminishes.

Clinical Implications of Vascularization

The distinction into vascular zones is the main factor guiding the treatment of meniscal injuries:

• Injuries in the red zone: ideal candidate for meniscal repair (suture), with a healing rate of 70-90%
• Injuries in the pink zone: repair possible, with intermediate healing rates (50-70%)
• Injuries in the white zone: repair has low chances of success; selective partial meniscectomy is preferred or, in young patients, innovative techniques (scaffolds, biological augmentation)

Meniscus Functions

The menisci perform at least six fundamental functions for knee health.

1. Load Distribution

The most important function. Without the menisci, contact between the femur and tibia occurs over a very small (concentrated) surface, with very high pressures on the cartilage. The menisci increase the contact surface by 200-300%, proportionally reducing the pressure per unit area.

• With intact menisci: the load is distributed over approximately 70% of the tibial surface
• After total meniscectomy: the contact surface is reduced by 50-75% and the pressure on the cartilage increases by 200-300%

2. Shock Absorption

The menisci absorb approximately 20% of impact forces on the knee during walking and up to 50% during running and jumping. This function is linked to the viscoelastic structure of the meniscal tissue and its ability to deform under load and return to its original shape.

3. Joint Stability

The menisci contribute to knee stability, in particular:

• The medial meniscus is an important secondary stabilizer against anterior tibial translation (especially in cases of ACL deficiency). After ACL rupture, the posterior horn of the medial meniscus undergoes increased loads and is frequently injured.
• The menisci as a whole contribute to rotational and varus-valgus stability

4. Lubrication

The menisci facilitate lubrication of the knee joint. During loading, water contained in the meniscal tissue is extruded towards the articular surfaces, creating a liquid film that reduces friction. The menisci also contribute to the uniform distribution of synovial fluid over the articular cartilage.

5. Proprioception

The menisci contain mechanoreceptors (Ruffini corpuscles, Pacinian corpuscles, Golgi tendon organs, free nerve endings), especially in the peripheral portion and roots. These receptors provide information on joint position, movement speed, and applied forces, contributing to neuromuscular control of the knee.

6. Cartilage Nutrition

The menisci facilitate the nutrition of articular cartilage, promoting the circulation of synovial fluid over the cartilaginous surface through a “pump” mechanism during loading and unloading.

Mechanisms of Injury

Traumatic Injuries

Traumatic injuries are typical in young athletes and occur due to:

• Knee rotation under load: the most classic mechanism — the foot is fixed to the ground, the knee is flexed, and the body rotates. This mechanism traps the meniscus between the femoral condyle and the tibial plateau.
• Forced hyperflexion: deep squatting with load
• Hyperextension: trauma in forced extension
• Combination with ligamentous injuries: the “unhappy triad” (ACL injury + medial meniscus + medial collateral ligament) represents one of the most severe knee traumas.

Degenerative Injuries

Degenerative injuries are typical in the adult and elderly population (>40-50 years old) and occur in already deteriorated meniscal tissue. They can arise even without significant trauma, with simple squatting or twisting movements.

Types of Meniscal Injury

Healing Capacity by Zone

The meniscus’s ability to heal after an injury primarily depends on the vascular zone where the injury is located.

At birth, the meniscus is almost completely vascularized. With growth and loading, vascularization progressively reduces, and in adults, only the peripheral 10-30% of the meniscus is vascularized. In the elderly, the vascularized zone further diminishes.

Factors Influencing Healing

In addition to the vascular zone, other factors influence the prognosis:

• Type of injury: longitudinal tears heal better than radial and complex tears
• Patient age: younger patients have greater healing potential
• Knee stability: a knee with an ACL deficiency has lower meniscal healing rates (associated ACL reconstruction improves results)
• Time since injury: acute injuries (< 8 weeks) heal better than chronic ones
• Size of injury: injuries < 2 cm have a better prognosis

Consequences of Meniscectomy

The removal of the meniscus, even partial, has documented long-term consequences for knee health:

• Partial meniscectomy: reduces the contact surface by 10-25% for every 10% of tissue removed
• Total meniscectomy: increases pressure on the cartilage by 200-300% and significantly accelerates the development of osteoarthritis
• Post-meniscectomy osteoarthritis: after total meniscectomy, the prevalence of radiographic osteoarthritis at 10-20 years is 50-70%

For these reasons, the modern surgical approach prioritizes:

• Conservative treatment (physiotherapy) for stable degenerative injuries
• Meniscal repair (suture) whenever technically possible
• Selective partial meniscectomy only when necessary, preserving as much healthy tissue as possible
• Meniscus transplantation (allograft) in selected cases of total meniscectomy in young patients

Treatment of Meniscal Injuries

Conservative Treatment

Indicated for:

• Stable degenerative injuries, without joint locking
• Small (<10 mm), stable injuries in the red zone
• Patients with osteoarthritic knees (meniscectomy does not improve outcomes)

Conservative treatment includes:

• Physiotherapy: quadriceps and hamstring strengthening, recovery of mobility and proprioception
• Modified activity: avoid deep squatting and twisting in the first few weeks
• Pain and swelling management: ice, NSAIDs, possible initial partial weight-bearing

Surgical Treatment

• Meniscal repair (suture): indicated for traumatic injuries in the red-pink zone, especially in young patients. Requires longer rehabilitation (4-6 months) but preserves meniscal tissue.
• Arthroscopic partial meniscectomy: selective removal of damaged tissue. Rapid recovery (4-6 weeks) but possible long-term consequences.
• Meniscal transplantation: indicated in young patients (<50 years old) with previous total meniscectomy and pain in the corresponding compartment, without advanced osteoarthritis.

Recovery Times

Frequently Asked Questions (FAQ)

Frequently Asked Questions

What are the primary functions of the knee menisci?

The menisci are crucial fibrocartilaginous structures in the knee, primarily responsible for load distribution, shock absorption, and joint stabilization. They also contribute to joint lubrication, proprioception, and cartilage nutrition.

Why is meniscus preservation considered a priority in treatment decisions?

Meniscus preservation is prioritized due to its critical role in long-term knee health. Removal of meniscal tissue can significantly accelerate cartilage degeneration and increase the risk of developing osteoarthritis.

What are the common mechanisms leading to meniscal injuries?

Meniscal injuries commonly arise from two main mechanisms: traumatic events, often seen in athletes due to sudden twists or impacts, and degenerative processes, which are more prevalent in the adult population due to age-related wear and tear.

How does the vascularization of the meniscus influence its healing capacity?

The healing capacity of a meniscal injury is significantly influenced by its vascularization. Tears located in the well-vascularized ‘red zone’ near the capsule generally have a better potential for healing compared to those in the avascular ‘white zone’.

For a broader overview of related conditions, see our knee pain guide.

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Sources and Scientific References

1. Chirichella PS et al. (2019). Treatment of Knee Meniscus Pathology: Rehabilitation, Surgery, and Orthobiologics. PM R. 11:292-308. DOI | PubMed
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4. Noorduyn JCA et al. (2022). Effect of Physical Therapy vs Arthroscopic Partial Meniscectomy in People With Degenerative Meniscal Tears: Five-Year Follow-up of the ESCAPE Randomized Clinical Trial. JAMA Netw Open. 5:e2220394. DOI | PubMed
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