Knee Disc (Meniscus): Anatomy, Functions, Injuries, and Treatments

What is knee disc?

The term "knee disc" is a common colloquialism that most accurately refers to the meniscus (plural: menisci), a crucial C-shaped or O-shaped fibrocartilaginous structure within the knee joint that serves vital roles in shock absorption, load distribution, and joint stability.

Understanding the Terminology: "Knee Disc" vs. Meniscus

While "knee disc" is a widely used term, particularly among the general public and fitness enthusiasts, it is not an anatomically precise descriptor. The structure being referred to is almost invariably the meniscus. The knee joint, unlike the spine, does not contain intervertebral discs. Instead, it houses two menisci, which are distinct from spinal discs in both their structure and function. Understanding this anatomical distinction is fundamental for accurate diagnosis, treatment, and communication regarding knee health.

Anatomy of the Meniscus

The knee joint, or tibiofemoral joint, is formed by the articulation of the thigh bone (femur) and the shin bone (tibia). Nestled between the condyles of the femur and the tibial plateau are two crescent-shaped pads of fibrocartilage:

• Medial Meniscus: Located on the inner (medial) side of the knee, it is C-shaped and less mobile than its lateral counterpart, making it more susceptible to injury.
• Lateral Meniscus: Positioned on the outer (lateral) side of the knee, it is more O-shaped (nearly circular) and more mobile, which helps it adapt to joint movements.

Both menisci are wedges of tough, rubbery fibrocartilage that are thicker on their outer edges and taper to a thin inner edge. They are attached to the tibial plateau by coronary ligaments and to the joint capsule, allowing them to move slightly during knee flexion and extension. The outer third of the meniscus, known as the "red zone," has a blood supply, while the inner two-thirds, the "white zone," is avascular, meaning it has a very limited blood supply. This difference in vascularity significantly impacts the healing potential of meniscal tears.

Primary Functions of the Meniscus

The menisci are far more than simple "spacers" within the knee. Their sophisticated design allows them to perform several critical biomechanical functions:

• Shock Absorption: The menisci act as primary shock absorbers, cushioning the impact between the femur and tibia during activities like walking, running, and jumping. They help dissipate forces that could otherwise damage the articular cartilage.
• Load Transmission and Distribution: By increasing the contact area between the rounded femoral condyles and the relatively flat tibial plateau, the menisci distribute compressive loads across the joint more evenly. This significantly reduces stress on the articular cartilage, preventing premature wear and tear. Without menisci, the contact area would be drastically reduced, leading to concentrated stress and accelerated degeneration.
• Joint Stability: The wedge shape of the menisci helps to deepen the tibial plateau, enhancing the congruence and stability of the knee joint, particularly during pivoting and rotational movements. They work in conjunction with the ligaments to prevent excessive anterior-posterior and rotational translation.
• Joint Lubrication and Nutrition: The menisci assist in the circulation and distribution of synovial fluid across the articular cartilage surfaces, which is essential for joint lubrication and the nourishment of chondrocytes (cartilage cells).
• Proprioception: The menisci contain mechanoreceptors and nerve endings that contribute to proprioception, the body's sense of joint position and movement. This feedback is crucial for coordinated movement and balance.

Common Meniscal Injuries

Meniscal injuries, commonly referred to as "meniscal tears," are among the most frequent knee problems, particularly in athletes and an aging population.

• Types of Tears:
  • Traumatic Tears: Often occur in younger, active individuals during sports or activities involving sudden twisting, pivoting, or deep squatting while the foot is planted. These tears can be acute and vary in pattern (e.g., radial, horizontal, longitudinal, bucket-handle).
  • Degenerative Tears: More common in older adults, these tears result from gradual wear and tear over time, often with minimal or no specific injury event. The cartilage becomes brittle and more prone to tearing with everyday activities.
• Mechanisms of Injury: Common mechanisms include forceful twisting of the knee, deep squatting, direct impact, or repetitive stress over time.
• Symptoms: Symptoms can vary depending on the size and location of the tear but commonly include:
  • Pain, often along the joint line.
  • Swelling and tenderness.
  • A popping or clicking sensation.
  • Catching or locking of the knee, where the knee gets stuck in a certain position.
  • Difficulty fully straightening or bending the knee.
  • Feeling of instability or the knee "giving way."
• Diagnosis: Diagnosis typically involves a thorough physical examination, including specific meniscal tests (e.g., McMurray's test), and imaging studies, with Magnetic Resonance Imaging (MRI) being the gold standard for visualizing meniscal tears.

Treatment and Management of Meniscal Injuries

The approach to treating a meniscal tear depends on several factors, including the type, size, and location of the tear, the patient's age, activity level, and symptoms.

• Non-Surgical Management: For smaller, stable tears (especially in the avascular zone) or degenerative tears with mild symptoms, conservative treatment is often the first line of defense:
  • RICE Protocol: Rest, Ice, Compression, Elevation.
  • NSAIDs: Non-steroidal anti-inflammatory drugs to reduce pain and swelling.
  • Physical Therapy: Focuses on restoring range of motion, strengthening the muscles around the knee (quadriceps, hamstrings, glutes), and improving proprioception and balance.
  • Activity Modification: Avoiding activities that exacerbate symptoms.
• Surgical Management: When conservative measures fail, or for larger, unstable tears (especially in the vascular zone), surgery may be recommended:
  • Partial Meniscectomy (Arthroscopic): The most common procedure, where the damaged or torn portion of the meniscus is trimmed and removed, leaving as much healthy meniscus as possible. This aims to alleviate symptoms by removing the unstable tissue.
  • Meniscus Repair (Arthroscopic): If the tear is in the "red zone" (outer third with blood supply) and suitable for repair, the torn edges are sutured together. This preserves the meniscus, which is highly beneficial for long-term knee health, but requires a longer and more cautious rehabilitation period.
  • Meniscus Transplant: A less common procedure considered for younger individuals who have had a meniscectomy and subsequently developed early-onset arthritis or persistent pain due to the absence of the meniscus. It involves transplanting a cadaveric meniscus.

Rehabilitation and Prevention

Regardless of the treatment approach, rehabilitation is crucial for optimal recovery and return to function.

• Rehabilitation Principles: A structured physical therapy program is essential to:
  • Restore full knee range of motion.
  • Strengthen the surrounding musculature to support the knee.
  • Improve balance and proprioception.
  • Gradually return to activity.
• Prevention Strategies: While not all meniscal tears are preventable, certain strategies can reduce risk:
  • Strength Training: Regularly strengthen the muscles supporting the knee, particularly the quadriceps, hamstrings, and glutes.
  • Flexibility: Maintain good flexibility in the hip, knee, and ankle joints.
  • Proper Technique: Learn and use correct form for exercises and sports-specific movements, especially those involving pivoting or deep squats.
  • Warm-up and Cool-down: Always perform dynamic warm-ups before activity and static stretches afterward.
  • Appropriate Footwear: Wear supportive shoes that fit well and are appropriate for the activity.
  • Avoid Sudden Twisting: Be mindful of movements that place excessive rotational stress on the knee.
  • Progressive Overload: Gradually increase intensity and volume in training to allow the body to adapt.

Conclusion

The "knee disc," correctly identified as the meniscus, is an indispensable component of the knee joint, critical for its long-term health and function. Its roles in shock absorption, load distribution, and stability are paramount. Understanding its anatomy, function, common injuries, and appropriate management strategies is key for fitness professionals, athletes, and individuals seeking to maintain optimal knee health and prevent future complications. Prioritizing proper training techniques, strength, and flexibility can significantly reduce the risk of meniscal injury and support a lifetime of active movement.