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Discoid Meniscus

- Dicussion:
    - a thickened and wafer shaped lateral meniscus varient;
    - discoid meniscus may range from complete disc to a ring shaped meniscus;
    - occurs in upto 5% of population (but only a % of these are symptomatic) (prevalence may be higher in orientals (15%));
    - usually involves lateral meniscus and is frequently bilateral (20% of pts);
    - although a congenital etiology for discoid menisci has been proposed, the discoid variant is not normally  found in the fetus;
    - clinically patients may complain of pain, swelling, and snapping;
          - the classic discoid snapping knee is usually caused by a discoid meniscus w/ a deficient menisco-tibial ligament;
    - classification:
             - based on the degree of peripheral attachments to the tibia plateau;
             - complete vs. incomplete
                    - the terms complete and incomplete are sometimes used to describe the shape of the discoid meniscus (incomplete having
                              a more semilunar shape);
                    - the same terms (complete and incomplete have also been used to describe whether the meniscus is stable vs unstable;
             - stable
                    - complete type has normal peripheral attachments & normal mobility.
                    - these meniscal varients tend to be stable due to the presence of a posterior menisco-femoral ligament;
                    - when symptomatic, either a tear or a posterior menisco-femoral detachment is usualy present;
                    - treatment: arthroscopic partial menisectomy and meniscoplasty
             - unstable (wrisberg)
                    - these are unstable and hypermobile to due lack of posterior tibio-meniscal ligaments;
                    - has only one attachment posperiorly, posterior meniscofemoral ligament,
                    - on knee extension, abnormal meniscus is pulled posteromedially into the intercondylar notch (instead of gliding forward)
                            due to the action of the meniscofemoral ligaments;
                            - probably responsible for the true "snapping knee;"
                    - total menisectomy is recommended for Wrisberg type deformity since lacks posterior meniscal tibial attachments & has
                            unstable posterior horn;
                    - ref: Does discoid lateral meniscus have inborn peripheral rim instability? Comparison between intact discoid lateral
                                     meniscus and normal lateral meniscus
             - varients:
                    - anterior or posterior megahorn;

- Radiographs:
    - x-rays:
             - lateral joint space widening and cupping of lateral tibial plateau;
             - hypoplasia of the lateral tibial spine;
    - MRI:
             - suggestive finding include meniscal tissue on 3 or more contiguous saggital cuts;
             - note: a classic false negative can occur w/ an unstable (Wrisberg) type of discoid meniscus which maintains a relative
                      semilunar shape;

- Non Operative Treatment:
    - an asymptomapic discoid meniscus does not require treatment and prognosis is generally good;
    - symptoms of popping by itself is not harmful unless it is accompanied by pain or swelling of the knee;
    - knee arthroscopy for medial sided pain, current recommendation is to leave the asymptomatic discoid meniscus alone;
    - ref: Cautious surgery for discoid menisci.

- Operative Treatment:
    - all forms of operative treatment are controversial;
    - pain, swelling, & a history of trauma are relative indications for arthroscopy;
    - tears of a stable meniscus may require resection of the discoid lateral meniscus, leaving peripheral rim intact (meniscoplasty);
          - rescetion is often difficult because of increased meniscal thickness
    - w/ a unstable discoid meniscus, a complete menisectomy is required

Long-Term Results of Arthroscopic Reshaping for Symptomatic Discoid Lateral Meniscus in Children

Congenital discoid lateral meniscus in children. A follow-up study and evolution of management.

The discoid lateral-meniscus syndrome.

Discoid lateral meniscus in children. Long-term follow-up after excision.

Lateral Meniscal Variants: Evaluation and Treatment.

Management of discoid lateral meniscus tears: observations in 34 knees

Discoid lateral meniscus: prevalence of peripheral rim instability.

Torn discoid lateral meniscus treated using partial central meniscectomy and suture of the peripheral tear 

Symptomatic Bilateral Discoid Menisci in Children: A Comparison With Unilaterally Symptomatic Patients

Clinical Outcomes as a Function of Meniscal Stability in the Discoid Meniscus: A Preliminary Report