Discoid Meniscus

By admin On Dec 12, 2023

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