Discoid Meniscus Treatment & Management


Practice Essentials

One element in the differential diagnosis of knee pathology is a discoid meniscus. Discoid meniscus can manifest itself as an abnormal band, medial and lateral discoid menisci in the same knee, bilateral and medial discoid menisci, or, more commonly, a discoid lateral meniscus. [12345]

Discoid lateral menisci were first described in the late 1800s. The normal configuration of a meniscus is that of a matured crescent moon, whereas that of a discoid meniscus generally is a thickened, very early crescent moon. Variations of this general shape occur relatively rarely, and occasionally, the lunar appearance is also found in the medial meniscus. The discoid shape results in a membrane barrier that prevents normal contact between the articular surfaces of the knee and has a high incidence of mechanical deformation.

Patients present with any combination of pain, giving way, effusion, and clicking or snapping knee. [6]

The widened and thickened discoid meniscus may be demonstrated on routine radiography of the knee. Magnetic resonance imaging (MRI) is the modality of choice for evaluating a discoid meniscus before surgery. [78]

Abnormalities of knee function, pain, and effusion are indications for surgical treatment. Surgical treatment varies according to the type of lateral discoid meniscus present. An otherwise asymptomatic knee with the incidental finding of discoid meniscus is a contraindication for surgical treatment.

Pathophysiology

Two distinct types of discoid lateral meniscus exist:

  • Hypermobile, or Wrisberg, lateral meniscus
  • Misshapen or discoid form of an otherwise normal lateral meniscus

Each type presents its own unique pathophysiologic problems.

The Wrisberg type lacks an attachment to stabilize the posterior horn to the tibia. [9 It may also be of normal shape rather than discoid. The only attachment of the posterior horn is to the Wrisberg or meniscofemoral ligament. The general configuration produces an unstable or hypermobile lateral meniscus.

A discoid lateral meniscus results from a developmental anomaly before birth. [10 After birth, no sudden change occurs in meniscal development. [11]

Epidemiology

Discoid lateral menisci have been reported to occur at the rate of 1.5-3% in the general population, whereas discoid medial menisci have been reported to occur at the rate of 0.1-0.3%. [12 

The Asian population has a slightly higher rate of occurrence; Tokyo's Teishin Hospital reported that 16.6% of all knees examined arthroscopically had a discoid lateral meniscus. [13]

Symptomatic discoid lateral menisci appear to be most common in adolescent males. [14]

Prognosis

In a retrospective study of 40 children with symptomatic lateral discoid meniscus, miniarthrotomy and arthroscopy were compared. Miniarthrotomy was found to provide slightly better results than arthroscopic resection with regard to functional outcome. The authors recommended miniarthrotomy for the resection of lateral discoid meniscus, particularly in young children with narrow joint spaces and for surgeons who are not familiar with arthroscopy in small joints. [15]

Ahn et al evaluated the long-term clinical and radiographic results of arthroscopic reshaping, with or without peripheral meniscus repair, in 38 children (48 knees; mean age, 9.9 years) with symptomatic discoid lateral meniscus. [16 The surgical procedure performed was arthroscopic partial meniscectomy alone (22 knees), partial meniscectomy with repair (18 knees), or subtotal meniscectomy (8 knees). At a mean follow-up of 10.1 years, progression of degenerative changes was significantly greater in the group treated with subtotal meniscectomy than in either of the partial meniscectomy groups.

Lee et al carried out a systematic review of 11 studies with more than 5 years of follow-up in which the clinical and radiologic outcomes of surgical treatment of discoid lateral meniscus (open or arthroscopic partial central meniscectomy, subtotal meniscectomy, total meniscectomy, or partial meniscectomy with repair) were evaluated. [17Most of the studies showed good clinical results. There was minimal progression of degenerative change and no findings of moderate or advanced degenerative changes. Possible risk factors for degenerative changes included greater age at the time of surgery, longer follow-up period, and subtotal or total meniscectomy.

In a meta-analysis aimed at comparing clinical and radiographic results between partial and total meniscectomy in patients with symptomatic discoid lateral meniscus, Lee et al found that radiographic outcomes were better with partial meniscectomy with or without repair than with total meniscectomy but that clinical outcomes were comparable for the two procedures. [18These findings suggest that meniscal preservation may be a better option than total meniscectomy for symptomatic discoid lateral meniscus.


History and Physical Examination

Patients present with any combination of pain, giving way, effusion, and clicking or snapping knee. [6]

Children with discoid meniscus usually present with a snapping knee joint, especially those around 7 years old. The snap can be seen and heard. Translation of the femoral condyle over a thickened posterior rim of lateral meniscus occurs. If the child remains otherwise asymptomatic, only observation is necessary; however, snapping greatly increases the chance of tearing the lateral meniscus, either by continued microtrauma or by trauma that would not cause tearing otherwise. 


Radiography

The widened and thickened discoid meniscus may be demonstrated on routine radiography of the knee. Radiography may reveal any combination of widening of the lateral joint clear space and cupping (see the images below). Cupping is a reversal of the normally flat-to-convex bony shape of the lateral tibial plateau into a more concave shape.

Radiograph of 8-year-old child with bilateral discRadiograph of 8-year-old child with bilateral discoid menisci, diagnosis confirmed by MRI. Patient is only symptomatic on left side. Patient underwent arthroscopy and partial meniscectomy and is now asymptomatic. Image courtesy of Dennis P Grogan, MD.
Knee radiograph of 17-year-old athlete with a discKnee radiograph of 17-year-old athlete with a discoid lateral meniscus. Lateral joint space is widened, and tibial plateau has flattened appearance. Image courtesy of Robert D Bronstein, MD.

Magnetic Resonance Imaging

The positive predictive value (PPV) of magnetic resonance imaging (MRI) for demonstrating a discoid meniscus tear is approximately 57%, whereas the PPV for predicting a discoid meniscus is approximately 92%. [12 (See the images below.) The PPV is determined by creating a fraction in which the sum of the number of true- and false-positive results is the denominator and the number of true-positive results the numerator, then multiplying that fraction by 100%.

MRI scan of typical discoid meniscus. Image courteMRI scan of typical discoid meniscus. Image courtesy of William Morrison, MD.
MRI scan of typical discoid meniscus. Image courteMRI scan of typical discoid meniscus. Image courtesy of William Morrison, MD.
Coronal MRI scan demonstrating complete discoid meCoronal MRI scan demonstrating complete discoid meniscus (arrow). Image courtesy of Robert D Bronstein, MD.

Larger meniscal size may be one of the main risk factors predisposing to discoid meniscus tears. [21]

MRI is the modality of choice for evaluating a discoid meniscus before surgery. [78 The most common diagnostic finding is that of a "bow-tie" sign, a viewing of the anterior and the posterior meniscal sections connected together on more than two sagittal MRI serial images.

A discoid lateral meniscus commonly occurs bilaterally; in patients who are symptomatic, an intrameniscal signal is also commonly found.

Procedures

When the McMurray test is performed on a patient with a discoid meniscus, a loud click or snap is both felt and heard. For more information on the McMurray test, please see Meniscal Tears on MRI.


Approach Considerations

Abnormalities of knee function, pain, and effusion are indications for surgical treatment. Surgical treatment varies according to the type of lateral discoid meniscus present. Arthroscopic procedures are quite successful and are somewhat more technically demanding than are routine meniscal tear excisions because of the younger age, the tighter joints, and reduced room available to manipulate arthroscopic equipment. [2223]

An otherwise asymptomatic knee with the incidental finding of discoid meniscus is a contraindication for surgical treatment.

Surgical Therapy

Surgical techniques for treatment of discoid menisci range from sculpting and partial meniscectomy to complete removal, starting with removal of the anterior portion for better arthroscopic visualization. [2425 (See the images below.)

Arthroscopic appearance of complete discoid lateraArthroscopic appearance of complete discoid lateral meniscus. Probe is showing medial extent of lateral meniscus, which completely covers lateral tibial plateau. Image courtesy of Robert D Bronstein, MD.
Arthroscopic photograph following saucerization ofArthroscopic photograph following saucerization of discoid lateral meniscus. Edge of horizontal tear that traversed meniscus can be observed. Image courtesy of Robert D Bronstein, MD.

Arthroscopic removal of a torn, normally configured lateral meniscus, in its entirety, is accomplished by first releasing the anterior horn, then releasing the attachment to the popliteal tendon, and then partially releasing the posterior horn. Finally, the meniscus is displaced into the intercondylar notch to complete the posterior release and remove the entire meniscus. [26]

A discoid lateral meniscus often has a continuous attachment from the popliteal tendon to the posterior horn. Removal of the anterior horn is necessary; the remainder of the discoid meniscus is then removed in a piecemeal fashion. An arthroscopic Bovie or other type of coagulation system should be available to stop possible bleeding from a branch of the lateral geniculate artery.

Because of the hypermobility of the entire meniscus in the Wrisberg (type III) deformity, sculpting the meniscus is ineffective, and better results have been reported with a near-complete to complete meniscectomy. Some attempts have been made to avoid total meniscectomy by tying down the meniscus through drill holes in the tibia to correct the anatomic defect. [2728]

In terms of the Watanabe classification, the indicated treatment for tears of discoid meniscus type I (complete), type II (incomplete), and the central-holed or ring-shaped version is removal of the central discoid and ring portions, including any areas of tearing, followed by arthroscopic sculpting of the remaining meniscus. [29]

Complications

Possible complications include the following:

  • Bleeding from a branch of the lateral geniculate artery
  • Damage to the articular surface of the joint
  • Incomplete removal of the tear
  • Rigid high border in unsculpted removal, resulting in further tearing
  • Postoperative hemarthrosis
  • Phlebitis



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