Discoid Meniscus: Diagnosis and Management

Key points

Anatomy and classification

The meniscus is completely vascular at birth with blood supply entering from the periphery of the meniscus. By the ninth month of life, the central third becomes avascular. Meniscal vascularity gradually diminishes to the peripheral 10% to 30% by age 10 years, at which time it resembles the adult meniscus.⁶ Increased blood supply and recent evidence suggesting regeneration of a discoid meniscus after saucerization suggests increased potential for repair and regeneration of the meniscal tissue

Clinical features

• •

  Asymptomatic: Children often have no symptoms from a discoid lateral meniscus.

• •

  Symptoms referable to a discoid meniscus typically stem from either a tear of the meniscus or from an unstable discoid variant.

• •

  The typical presentation in a young child with a symptomatic discoid meniscus is that of a popping or snapping of the knee that is heard and felt by the child or parent. The onset of the snapping or popping is usually insidious without any specific traumatic cause, classically between the ages

Investigations

Plain radiographs of the knee should be obtained in all children with an acute injury. These views include the anteroposterior, lateral, tunnel, and sunrise or Merchant views.

• •

  Tunnel views: to rule out osteochondritis dissecans (OCD) lesions as the source of knee pain. The typical anatomic location of an OCD lesion is the lateral aspect of the medial femoral condyle. However, lateral OCD lesions should raise the concern for a discoid meniscus as the underlying cause. Patellar dislocation may

MRI features of a lateral discoid

• •

  Ratio of the minimal meniscal width to maximal tibial width (on the coronal MRI slice) of more than 20%.¹¹

• •

  Three or more 5-mm thick consecutive sagittal sections demonstrate continuity of the meniscus between the anterior and posterior horns.¹³

• •

  An abnormal, thickened, bow-tie appearance of the meniscus may also be suggestive of a discoid meniscus (Fig. 5).

• •

  MRI can also show tears that are frequently associated with a discoid lateral meniscus. However, its ability to determine the type of tear is

Management

Many children with discoid meniscus remain asymptomatic and require no treatment according to most authors.16, 17, 18 Arthroscopic surgery is generally recommended if the discoid meniscus is associated with mechanical symptoms, such as pain, locking, swelling, giving way, or causing inability to participate in sports. Treatment recommendations for an asymptomatic, stable complete, or incomplete discoid lateral meniscus found during investigation or treatment of some other knee condition are

Surgical technique

• 1.

  In the supine position, lateral and then medial infrapatellar portals are established using a 4-mm 30° oblique arthroscope.

• 2.

  Routine diagnostic arthroscopic inspection of the knee joint is performed.

• 3.

  Surgical assistant applies constant varus stress to the knee with the leg in a leg holder or in the figure-of-four position for better maneuverability and visualization of the lateral compartment (Fig. 6).

• 4.

  After visualization, probing of the discoid meniscus is an important step to check the stability

Postoperative protocol

For saucerization only, usually no brace is required. Range of motion can be started as soon as comfortable with pain and weight bearing is as tolerated.

For meniscal repair and peripheral rim stabilization, the same rehabilitation protocol applies as any other meniscal repair, which is typically restricting the range of motion from 0° to 90° and toe touch weight bearing for about 4 to 6 weeks.

Surgical outcomes

There are few long-term outcome studies of discoid menisci treated with arthroscopy and saucerization. However, the few short-term studies that are available in the past decade that assess partial central meniscectomy, repair, and recontouring of the discoid meniscus are quite promising. In a study with a follow-up averaging 4.5 years, Ogut and colleagues²⁵ reviewed 10 knees with complete discoid lateral menisci that had undergone arthroscopic partial meniscectomy with excellent result in nine

Complications of surgery

• •

  Complications that are associated with knee arthroscopy for any meniscal surgery include premature osteoarthritis, incomplete resection of the torn unstable rim, injury to nerves/vessels, arthrofibrosis, persistent effusion, infection, and instrument breakage.

• •

  It is important to remember that following partial meniscectomy and/or repair of a discoid meniscus, the cartilage remains thickened because it is not a normal meniscus to begin with. Thus, a discoid meniscus is still more likely to

Summary

A discoid lateral meniscus is a common abnormal meniscal variant in children. A detailed history and physical examination, when combined with an MRI of the knee, can predictably diagnose a discoid meniscus. The discoid meniscus was typically classified as type I (complete), type II (incomplete), or type III (Wrisberg variant). It is now imperative to assess and determine the instability and the newer classification based on stability if the peripheral rim is more relevant clinically and from