Discoid Meniscus

The discoid meniscus is an abnormal variation of the knee meniscus, typically affecting the lateral meniscus, and is most commonly found in children and adolescents. Often referred to as “popping knee syndrome,” this condition can lead to mechanical knee symptoms such as snapping, clicking, or locking, especially during movement.

 

Anatomy & Function

The meniscus is a crescent-shaped fibrocartilage structure located between the femur (thigh bone) and tibia (shin bone). There are two menisci in each knee:

• Medial meniscus is located on the inner side of the knee.
• Lateral meniscus is located on the outer side of the knee.

Key Functions:

• Acts as a shock absorber.
• Aids in joint stability (secondary to ligaments).
• Enhances load distribution across the joint.
• Supports joint lubrication and nutrition.

In a discoid meniscus, especially the lateral type, the shape deviates from the normal crescent, becoming more disc-shaped, which can interfere with normal knee biomechanics.

 

Epidemiology and Prevalence

The discoid meniscus is a congenital condition, present at birth and remains unchanged over time. It can be asymptomatic, making it difficult to determine its exact incidence.

Prevalence:

• Lateral discoid meniscus is more prevalent.
• Medial discoid meniscus is much rarer.
• More common in Asian populations.

 

Classification Systems

Incomplete Type

• The meniscus is thicker and wider than normal but does not completely cover the tibial surface.

Complete Type

• The meniscus fully covers the tibial plateau.

Wrisberg Variant (Hypermobile Meniscus)

• Appears normal in shape.
• Lacks posterior ligament attachment (Wrisberg ligament), making it hypermobile.
• Very rare (~0.2% prevalence).
• Leads to instability symptoms without an obvious tear.

 

Biomechanics & Kinematics

Although no direct biomechanical studies exist for DLM but it alters normal knee loading mechanics

• Reduced lateral tibial translation and internal rotation in torn DLM knees is seen
• 3D gait analysis shows reduced sagittal and axial plane motion in symptomatic knees
• Total meniscectomy drastically alters biomechanics:

         > Reduces contact area by 40–50%
         >Increases load by 200–300%

Clinical Presentation

Common Symptoms

• Vague lateral knee pain
• Clicking or snapping (especially at 10–20° of terminal extension)
• Locking, swelling, instability
• Loss of range of motion (flexion/extension)
• Quadriceps wasting

Age-Specific Differences

• Young children - snapping or clunking during movement
• Older children - more likely to present with tears

 

Risk Factors for Tear or Cartilage Damage

• Higher BMI
• Female gender
• High activity level
• Symptoms > 6 months

 

Diagnosing Discoid Meniscus 

Complications of Untreated DLM

• Recurrent snapping/catching
• Instability
• Increased risk of meniscal tears
• Early onset osteoarthritis

  

Differential Diagnosis

• Meniscal tear (non-discoid)
• Lateral collateral ligament (LCL) injury
• Osteochondritis dissecans
• Synovial plica syndrome
• Patellofemoral pain syndrome
• Iliotibial band syndrome
• Juvenile idiopathic arthritis
• Osgood-Schlatter disease
• Loose bodies in the joint
• Popliteal cyst (Baker's cyst)

Management and Rehabilitation of Discoid Meniscus

Conservative Management

• Most asymptomatic cases of discoid meniscus do not require any treatment.
• The knee adapts to the altered meniscal shape, maintaining function.
• Even in patients with mild bulging or abnormal MRI findings, no intervention is necessary unless symptoms arise.
• Routine monitoring and patient education are essential.
• There is no evidence to support prophylactic surgery for asymptomatic contralateral knees.
• Patients should be advised to report symptoms like pain, swelling, or locking if they develop.

 

Surgical Indications and Philosophy

When Is Surgery Indicated?

Surgical treatment is recommended in the presence of:

• Persistent pain
• Mechanical symptoms - locking, catching, restricted motion
• Recurrent swelling
• Limitation in daily or sports activity

The goal of surgery is meniscal preservation to:

• Reduce the risk of early joint degeneration
• Maintain load distribution (as the lateral meniscus carries ~70% of the lateral compartment load)

Historically total meniscectomy was the norm but led to rapid cartilage degeneration and early-onset osteoarthritis. Currently total meniscectomy is avoided, especially in children and young adults. The preferred modern technique is arthroscopic partial meniscectomy (also known as saucerization).

Saucerization and Repair

Saucerization is the removal of the central thickened portion of the discoid meniscus to recreate a normal “C” shape. It aims to preserve 5–8 mm of the peripheral rim. In cases of instability, peripheral repair is performed using:

• All-inside
• Inside-out
• Outside-in techniques, based on tear location.

Tear repair decision making is based on:

• Tear location (peripheral tears have better healing)
• Extent and pattern (radial or complex tears may be irreparable)

Rehabilitation Phases

1. Pain and Inflammation Control

• Cryotherapy, NSAIDs, analgesics
• Continue throughout rehab as needed

2. Restore Range of Motion (ROM)

• Begin gentle ROM under guidance
• Avoid deep flexion and rotation for 8-12 weeks post-repair

3. Muscle Strengthening

• Quadriceps - mini squats, isometrics
• Hamstrings - resistance curls
• Hips & Glutes - clamshells, bridges

4. Proprioception & Neuromuscular Control

• Balance board training
• Single-leg stance
• Progressive agility drills

5. Gradual Weight-Bearing

• Follow surgeon’s loading protocol
• Promote controlled loading to stimulate healing