Discoid Meniscus

Ovid: 5-Minute Sports Medicine Consult, The

Discoid Meniscus
Melissa Nayak
  • Menisci are fibrocartilaginous structures that are C-shaped (axial plane) and wedge-shaped (coronal plane).
  • Discoid meniscus lacks C-shaped configuration.
    • Completely filled in center or small void in center with thicker outer rim
    • Anatomic variation alters normal mechanics and predisposes to tearing.
  • Most common abnormal meniscal variant in children (1)
  • Predominantly lateral; may be medial or bilateral
  • May not be symptomatic until adolescence or adulthood
  • Watanabe classification (1,2,3)[C]:
    • Most widely accepted classification system
    • Type I (complete):
      • Most common
      • Disk-shaped thickened meniscus with thin center, complete tibial plateau coverage
    • Type II (incomplete): Semilunar-shaped meniscus with partial tibial plateau coverage
    • Type III (Wrisberg type):
      • Least common
      • Hypermobile meniscus resulting from deficient posterior tibial plateau attachments
      • Presence of ligament of Wrisberg (from posterior horn lateral meniscus to posterior aspect medial femoral condyle)
      • Unstable and may displace
  • 1–3% (pediatric population) (1)
  • Bilateral (lateral) in 10–20% of patients (1,3)
  • Increased incidence in Asian populations (1,3)
  • Up to 17% in Korean and Japanese populations (1)
0.4–20% in patients undergoing arthroscopy (2)
Risk Factors
Asian ancestry
Genetic/familial transmission may play a role.
  • Exact cause unknown
  • May be congenital anomaly or malformation
  • Discoid lateral menisci:
    • Thicker, poorer vascularity
    • Some have unstable peripheral attachments (Wrisberg type) and thus increased susceptibility to tearing.
Commonly Associated Conditions
  • Associated meniscal tears (70% of time; incidence increases with age) (4)
  • Osteochondritis dissecans, lateral femoral condyle
  • High fibular head
  • Hypoplasia of lateral femoral condyle
  • Hypoplasia of tibial spines
  • Abnormal shape of lateral malleolus
  • Enlarged inferior lateral geniculate artery
  • Patients may be asymptomatic.
  • Signs and symptoms (in absence of trauma) include:
    • Pain
    • Clunking
    • Giving way
    • Popping
    • Snapping
    • Swelling
    • Locking
    • Decreased knee extension
Physical Exam
  • Palpable click near complete extension
  • Quadriceps atrophy
  • Lack of full extension
  • Joint-line tenderness
  • Effusion less common
  • Positive McMurray test (with associated meniscal tears)


Diagnostic Tests & Interpretation
  • Radiographs (weight-bearing AP, lateral, tunnel, and Merchant views):
    • May be normal
    • Widened lateral joint space
    • Squared off appearance of lateral femoral condyle
    • Cupping of lateral tibial plateau
    • Flattening of tibial eminence
  • MRI:
    • Test of choice
    • May not show abnormal signal intensity
    • Lateral meniscal height greater than medial, with high intrameniscal signal
    • Abnormal thickened “bow tie” appearance of meniscus
Differential Diagnosis
  • Meniscal tear
  • Popliteus tendinitis
  • Osteochondritis dissecans
  • Loose body
  • Any condition that causes a “snapping” knee:
    • Subluxation or dislocation of patellofemoral joint
    • Snapping of tendons around knee
    • Congenital subluxation of tibiofemoral joint
    • Subluxation/dislocation of proximal tibiofemoral joint
    • Meniscal cyst
Ongoing Care
Postoperative physical therapy for knee range of motion, quadriceps strengthening, hamstring stretching, and gait training
Patient Education
  • Asymptomatic discoid meniscus needs no treatment.
  • Surgery is recommended if mechanical symptoms present: Pain, locking, swelling, giving way, functional limitations, inability to participate in sports.
  • Good prognosis when asymptomatic
  • Poorer prognosis when osteochondritis dissecans present
717.5 Derangement of meniscus, not elsewhere classified

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More