High Yield Topics

Discoid Meniscus

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Ovid: 5-Minute Sports Medicine Consult, The


Discoid Meniscus
Melissa Nayak
Basics
Description
  • 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
Epidemiology
Incidence
  • 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)
Prevalence
0.4–20% in patients undergoing arthroscopy (2)
Risk Factors
Asian ancestry
Genetics
Genetic/familial transmission may play a role.
Etiology
  • 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
Diagnosis
History
  • 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)

P.125


Diagnostic Tests & Interpretation
Imaging
  • 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
Treatment
No treatment or surgical indications for asymptomatic patients
Additional Treatment
Referral
Orthopedic surgical consultation is indicated in patients still symptomatic after conservative measures.
Surgery/Other Procedures
  • Goal is meniscal preservation (2,3)[C].
  • Arthroscopic partial meniscectomy with saucerization (reshape meniscus) and repair of unstable or detached peripheral attachments to the capsule
  • Arthroscopic total meniscectomy not recommended owing to complication of osteoarthrosis; reserved for large or complex tears not amenable to saucerization or repair.
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.
Prognosis
  • Good prognosis when asymptomatic
  • Poorer prognosis when osteochondritis dissecans present
Complications
  • Osteochondritis dissecans of lateral femoral condyle
  • Postoperative complications:
    • Recurrence of meniscal instability
    • Cartilage remains thickened and more susceptible to developing tear.
    • Scuffing of articular surface
    • Osteoarthrosis
References
1. Hart ES, Kalra KP, Grottkau BE, et al. Discoid lateral meniscus in children. Orthop Nurs. 2008;27: 174–179.
2. Good CR, Green DW, Griffith MH, et al. Arthroscopic treatment of symptomatic discoid meniscus in children: classification, technique, and results. Arthroscopy. 2007;23:157–163.e1.
3. Yaniv M, Blumberg N. The discoid meniscus. J Child Orthop. 2007;1:89–96.
4. http://www.posna.org/education/StudyGuide/DiscoidMeniscus.asp
Codes
ICD9
717.5 Derangement of meniscus, not elsewhere classified


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