Meniscus

The menisci are C-shaped fibrocartilaginous structures located within the knee joint that play a crucial role in load distribution, shock absorption, and joint stability. They are essential for maintaining the congruity of the femorotibial articulation and protecting articular cartilage. Understanding their anatomy and physiology is fundamental for diagnosing and managing meniscal injuries.

Anatomy

Gross Anatomy

The knee contains two menisci: the medial and lateral meniscus. The medial meniscus is larger and more C-shaped, while the lateral meniscus is smaller and more circular. Both are attached to the tibial plateau at their anterior and posterior horns and are connected to the joint capsule and ligaments, providing stability and support.

Microscopic Anatomy

Menisci are composed of fibrocartilage, primarily type I collagen, organized in circumferential and radial patterns. The vascular supply varies across zones:

• Red-Red Zone: Peripheral area with good vascularity, capable of healing.
• Red-White Zone: Intermediate vascularity, partial healing potential.
• White-White Zone: Central avascular zone, limited healing capacity.

Biomechanical Role

Menisci function to distribute load across the knee joint, absorb shock during movement, and enhance joint congruity. They also contribute to rotational stability and assist in proprioceptive feedback, which is essential for coordinated knee function.

Physiology

Load Transmission

The menisci transfer axial loads from the femur to the tibia, reducing peak stress on articular cartilage. By increasing the contact area between joint surfaces, they prevent focal overload and cartilage degeneration.

Joint Lubrication

Menisci facilitate the distribution of synovial fluid within the joint, enhancing lubrication and reducing friction between the femoral and tibial surfaces. This supports smooth knee motion and protects cartilage.

Proprioception and Neuromuscular Feedback

Mechanoreceptors in the menisci provide sensory input to the central nervous system, aiding in the detection of joint position and movement. This proprioceptive function contributes to knee stability and coordinated muscular responses during dynamic activities.

Development and Embryology

Origin During Fetal Development

The menisci develop from mesenchymal tissue within the interzone of the knee joint during early fetal life. By the eighth week of gestation, the mesenchymal tissue differentiates into fibrocartilaginous structures forming the initial menisci.

Growth Patterns and Vascularization Changes

Initially, menisci are highly vascular throughout. As development progresses, vascularity diminishes from the inner to outer regions, leaving only the peripheral third (red-red zone) with significant blood supply in adulthood. This pattern is important for healing potential following injury.

Etiology of Meniscal Injuries

Traumatic Causes

Traumatic meniscal injuries often occur in young, active individuals, typically during sports or high-impact activities.

• Twisting or pivoting movements of the knee while the foot is planted
• Direct blows to the knee, especially with valgus or varus stress
• Sudden hyperflexion or hyperextension injuries

Degenerative Causes

Degenerative meniscal tears are common in older adults and are often associated with osteoarthritis. Chronic wear and reduced collagen integrity make the meniscus more susceptible to tears during routine activities.

Risk Factors

• Anatomical variations such as discoid meniscus
• History of previous knee injuries or ligamentous instability
• High levels of physical activity or repetitive stress

Clinical Features

Symptoms

Meniscal injuries commonly present with a combination of symptoms that reflect mechanical and inflammatory changes within the knee.

• Knee Pain: Localized along the joint line, often exacerbated by twisting or squatting movements.
• Swelling: Gradual or acute effusion depending on injury severity.
• Locking or Catching: Sensation of the knee getting stuck during movement.
• Clicking or Popping: Audible or palpable during knee motion.

Signs

Physical examination can reveal objective findings suggestive of meniscal injury.

• Joint line tenderness on palpation
• Reduced range of motion, especially in flexion and extension
• Presence of effusion or swelling
• Visible deformities or signs of associated ligamentous injury

Special Tests

• McMurray Test: Knee flexed and rotated to elicit pain or a click indicating a meniscal tear.
• Apley Grind Test: Compression and rotation of the tibia on the femur reproduces symptoms.
• Thessaly Test: Patient stands on one leg and rotates the knee to detect meniscal pathology.

Diagnosis

History and Physical Examination

Diagnosis begins with a detailed history of the mechanism of injury, symptom onset, and prior knee pathology. Physical examination includes inspection, palpation, range of motion assessment, and performance of special tests to identify meniscal tears.

Imaging Studies

Imaging is essential to confirm the diagnosis and evaluate the extent of injury.

• MRI: Gold standard for detecting meniscal tears, showing location, size, and type of tear.
• X-ray: Useful for identifying associated fractures, osteoarthritis, or joint space narrowing.

Arthroscopy

Knee arthroscopy can be used for both diagnostic and therapeutic purposes, allowing direct visualization of the meniscus and the option for immediate repair or partial meniscectomy.

Differential Diagnosis

• Anterior or posterior cruciate ligament injuries
• Osteoarthritis-related pain
• Patellofemoral pain syndrome
• Bursitis or synovial pathology

Management

Conservative Management

Non-surgical treatment is often effective for minor or stable meniscal injuries, particularly in older adults or degenerative tears.

• Rest, Ice, Compression, Elevation (RICE): Reduces pain and swelling in the acute phase.
• Physical Therapy: Strengthening and range-of-motion exercises improve knee stability and function.
• Activity Modification: Avoidance of activities that exacerbate symptoms, such as twisting or deep squatting.

Pharmacological Management

Medications may be used to alleviate pain and inflammation associated with meniscal injuries.

• Nonsteroidal anti-inflammatory drugs (NSAIDs) for pain relief and reduction of inflammation
• Analgesics as required for symptom control

Surgical Management

Surgical intervention is indicated for unstable, displaced, or complex tears that fail conservative management.

• Arthroscopic Meniscectomy: Removal of the torn meniscal fragment to relieve mechanical symptoms.
• Meniscal Repair: Suturing the tear, preferred for peripheral vascularized regions to preserve meniscus function.
• Meniscal Transplantation: Considered in cases of extensive meniscal loss to restore joint biomechanics.

Complications

Postoperative Stiffness or Pain

Following meniscal surgery, patients may experience temporary stiffness, pain, or swelling, which typically improves with rehabilitation and physiotherapy.

Recurrent Tears or Injury

Re-injury or incomplete healing can occur, particularly in active individuals or if the tear was repaired in the avascular zone with limited healing potential.

Osteoarthritis Development

Meniscectomy or extensive meniscal loss increases the risk of early osteoarthritis due to altered load distribution and decreased shock absorption in the knee joint.

Prognosis

Outcomes Based on Type and Location of Tear

The prognosis of meniscal injuries depends on the tear’s type, size, and location. Peripheral tears in the vascular red-red zone have a higher likelihood of healing, especially with surgical repair. Central tears in the avascular white-white zone have limited healing potential and may require partial meniscectomy.

Long-Term Joint Function

Successful management, whether conservative or surgical, can restore knee function and reduce symptoms. However, patients with large or complex tears, associated ligament injuries, or extensive meniscectomy may experience long-term functional limitations and an increased risk of osteoarthritis.

Prevention

Strengthening and Conditioning Exercises

Targeted exercises for the quadriceps, hamstrings, and hip muscles improve knee stability, reducing the risk of meniscal injuries during physical activity.

Injury Prevention Strategies in Sports

• Use of proper warm-up and stretching routines before activity
• Training in safe techniques for jumping, landing, and pivoting
• Utilization of supportive braces or taping when necessary

Proper Technique and Footwear

Correct movement patterns and appropriate footwear that provides support and shock absorption help minimize excessive stress on the menisci, reducing the likelihood of tears or degenerative changes.

References

1. Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020.
2. Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer; 2018.
3. Fox AJ, Bedi A, Rodeo SA. The basic science of human knee menisci: structure, composition, and function. Sports Health. 2012;4(4):340-351.
4. Beaufils P, Becker R, Kopf S, et al. Meniscus repair: indications and techniques. Orthop Traumatol Surg Res. 2017;103(1S):S1-S12.
5. Katz JN, et al. Treatment of meniscal tears: a systematic review. Arthritis Rheum. 2013;65(7):1717-1725.
6. McDermott ID, Amis AA. The consequences of meniscectomy. J Bone Joint Surg Br. 2006;88(12):1549-1556.
7. Makris EA, Hadidi P, Athanasiou KA. The knee meniscus: structure-function, pathophysiology, current repair techniques, and prospects for regeneration. Biomaterials. 2011;32(30):7411-7431.
8. van Trommel MF, et al. Meniscus injuries in the athlete. Clin Sports Med. 2002;21(3):381-400.