- 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;
-
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;
- 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;
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.
M.R. Jordan MD J. Am. Acad. Orthop. Surg. 1996; 4: 191-200.
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
