Discoid Meniscus

By admin On Jan 15, 2024

Ovid: 5-Minute Orthopaedic Consult

Editors: Frassica, Frank J.; Sponseller, Paul D.; Wilckens, John H.

Title: 5-Minute Orthopaedic Consult, 2nd Edition

> Table of Contents > Discoid Meniscus

Discoid Meniscus

Jason W. Hammond MD

Basics

Description

Discoid meniscus is a thickened, pancake-shaped lateral meniscus of developmental origin (Fig. 1).
It often causes clicking or locking of the knee in childhood or early adulthood.
It may be unilateral or bilateral.
Classification:
- General (1):
  - Complete: Meniscus covers entire lateral tibial plateau
  - Incomplete: Meniscus larger than normal but does not cover the entire lateral plateau
- Wrisberg (1):
  - Ligament type
  - Unstable
  - Lacks posterior attachment of meniscus to tibia
Synonym: Wrisberg meniscus

Epidemiology

Incidence

The approximate incidence is <1% in the United States and up to 26% in Japan (2).
Most cases present in late childhood or early adolescence.

Prevalence

The United States prevalence is ~4–5% (1).

Etiology

This condition is an anatomic or developmental abnormality.

Fig. 1. A diseased lateral meniscus lacks the normal semilunar shape and covers the entire lateral side of the tibia.

Diagnosis

Signs and Symptoms

Many patients are asymptomatic.
Presentation is highly variable, depending on the type of meniscus and the presence or absence of a tear.
The classic snapping-knee syndrome is characterized by a “clunk” at the terminal limits of flexion and extension.
May be associated with pain, clicking, swelling, locking, popping, and blocks to motion
The onset often is insidious, without a history of trauma.
If symptoms are acute or associated with trauma, an acute tear may be the cause.

Physical Exam

Usually, little to no effusion is present in the knee.
Mild tenderness may be present at the lateral joint line, but not as severe as that with an acute meniscus tear.
Often, a pop or click is noted with the McMurray test (rotating the knee while it is in a fully flexed position).
The examiner may note a block to full extension or the patient’s apprehension when the knee is straightened.

Tests

The McMurray test: Extension and rotation of a maximally flexed knee:
- A positive test is pain or popping at the lateral joint line.

Imaging

Plain radiography:
- Wide lateral joint space (3)
- Lateral joint lipping
- Cupping of the lateral tibial plateau
- Flattening of the lateral femoral condyle
MRI:
- 3 or more contiguous 5-mm sagittal sections showing continuity between the anterior and posterior horns
- Block “bow tie” appearance on the coronal view with increased width of the mid-AP diameter

Pathological Findings

Disc-shaped meniscus
Stable variant: Normal tibial ligaments
Unstable variant: Absence of the posterolateral tibial attachments

Differential Diagnosis

Acute meniscus tear
OATS or osteochondral fracture
Physeal fracture
Fracture of the tibial eminence
ACL tear

P.103

Treatment

General Measures

Asymptomatic patients should be observed.
Symptomatic patients often require
surgical treatment, which varies depending on whether a tear is present
and whether the meniscus is stable or unstable.
Nonoperative methods are rarely helpful
in the patient with symptomatic discoid meniscus, although a trial of
immobilization may be attempted in patients with acute-onset cases.
Patients may resume normal activity when symptoms resolve.

Surgery

Stable meniscus: Partial meniscectomy or saucerization (trimming) to form a more normal-appearing meniscus (4)
Unstable meniscus:
- Saucerization and reattachment to the posterolateral capsule in an attempt to preserve the meniscus
- Complete meniscectomy is indicated if the patient has degenerative changes or a large meniscal tear.

Follow-up

Prognosis

Patients with a stable discoid meniscus have good results with saucerization.

Complications

Degenerative joint disease is possible with complete meniscectomy.
Recurrent meniscal tears

Patient Monitoring

Patients should be followed until symptoms resolve.

References

1. Jordan MR. Lateral meniscal variants: evaluation and treatment. J Am Acad Orthop Surg 1996;4:191–200.

2. Miller RH, III. Knee injuries. In: Canale ST, ed. Campbell’s Operative Orthopaedics, 9th ed. St. Louis: Mosby-Year Book Inc., 1998:1113–1299.

3. Asik M, Sen C, Taser OF, et al. Discoid lateral meniscus: diagnosis and results of arthroscopic treatment. Knee Surg Sports Traumatol Arthrosc 2003;11:99–104.

4. Youm T, Chen AL. Discoid lateral meniscus: evaluation and treatment. Am J Orthop 2004;33:234–238.

Miscellaneous

Codes

ICD9-CM

717.5 Discoid meniscus

Patient Teaching

Observation, if the discoid meniscus is asymptomatic
Increased risk of degenerative changes after total meniscectomy

FAQ

Q: Do patients with discoid lateral meniscus require surgery?

A:
If the discoid lateral meniscus is truly asymptomatic or is noted
incidentally on MRI or at the time of arthroscopy, surgical repair is
not necessary. If the discoid meniscus is symptomatic (lateral knee
pain, locking, swelling), it should be saucerized to resemble a normal
lateral meniscus. Degenerative tears should be débrided, but unstable
peripheral tears should be repaired after saucerization.