PROCEDURE 31

Discoid Lateral Meniscus

Hua Ming Siow and Theodore J. Ganley

Indications

 The presence of a discoid lateral meniscus on magnetic resonance imaging (MRI) associated with symptoms or a tear.

 Symptoms include pain, swelling, locking, instability, and extension block.

Pitfalls

• Nonoperative treatment for clicks and asymptomatic discoid meniscus discovered incidentally on MRI or arthroscopy

Controversies

• Clunking meniscus is thought to be an indication of instability and hence is operated on by some authors.

Examination/Imaging

 Examination may show joint line tenderness, effusion, decreased range of motion, quadriceps atrophy, bulge at the anterolateral joint line in full flexion, click and shift of the meniscus on extension, and a positive McMurray’s sign.

 Radiographs may show widening of the lateral joint space, cupping of the lateral tibial plateau, flattening of the lateral femoral condyle, tibial spine hypoplasia, and elevation of the fibular head.

 MRI should show continuity of the meniscus between the anterior and posterior horns on ≥ 3 consecutive sagittal sections that are 5 mm thick (Fig. 1).

 MRI should also show increased width of the meniscus at the midpoint of the anterior and posterior horns on a coronal view.

 MRI will help visualize tears and intrasubstance degeneration.

Treatment Options

• Nonoperative

• Partial meniscectomy

• Total meniscectomy

Surgical Anatomy

 Watanabe classification

• Type I: complete (Fig. 2A)

• Type II: incomplete (Fig. 2B)

• Type III: Wrisberg variant (Fig. 2C)

Positioning

 The patient is placed in the supine position.

 The hip is flexed and abducted, with external rotation when applying varus stress in the figure-of-4 position.

 A bolster is placed behind the knee to allow for 70–90° of flexion at rest.

 A tourniquet is applied and inflated after Esmarch bandaging.

Pearls

• Allow free and unrestricted movement of the knee for easier access and visualization of the knee.

Portals/Exposures

 Standard anterior medial and lateral portals are used (Fig. 3).

 Midpatellar medial and lateral portals are added as required (see Fig. 3).

 A posterolateral incision is made as necessary for inside-out meniscal repairs.

 An anterolateral incision is made as necessary for outside-in meniscal repairs.

Pearls

• Midpatellar portals are essential for visualization and access to thick discoid menisci.

Pitfalls

• Access to the joint through standard anterior portals may be difficult due to thick discoid menisci.

Procedure

Step 1: Arthroscopic Assessment

 The surgeon must visualize the discoid meniscus and determine its extent. Figure 4 shows an incomplete discoid meniscus.

 An assessment is made for tears and instability of the discoid meniscus.

 The surgeon should assess for chondral damage, osteochondritis dissecans lesions, and loose bodies.

Pitfalls

• Osteochondritis dissecans lesions and intrasubstance tears may not be visible and are better visualized on MRI.

Instrumentation/Implantation

• Standard 30° oblique 4-mm arthroscope

• Probe

Step 2: Partial Meniscectomy

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