Year : 2008 | Volume
: 18 | Issue : 2 | Page : 130--131
Posterior subluxation of bilateral discoid lateral menisci in a child
Alexis Lacout, Dominique Mompoint, Christian Alfred Vallee, Robert Yves Carlier
Department of Radiology, Raymond Poincare Hospital (Assistance Public-Paris Hospitals) 104 Boulevard Raymond Poincare, 92380 Garches, France
71 rue Gutenberg, 75015 Paris
|How to cite this article:|
Lacout A, Mompoint D, Vallee CA, Carlier RY. Posterior subluxation of bilateral discoid lateral menisci in a child.Indian J Radiol Imaging 2008;18:130-131
|How to cite this URL:|
Lacout A, Mompoint D, Vallee CA, Carlier RY. Posterior subluxation of bilateral discoid lateral menisci in a child. Indian J Radiol Imaging [serial online] 2008 [cited 2020 Feb 22 ];18:130-131
Available from: http://www.ijri.org/text.asp?2008/18/2/130/40295
The discoid meniscus of the knee is an anatomic variant in which the meniscus is thickened, disc-shaped, and covers a larger area of the tibial plateau than the normal meniscus.  Discoid menisci are often asymptomatic, but can be associated with knee pain, a snapping or popping knee,  and episodes of locking of the knee.  They may be bilateral in about 6% of patients.  An association of discoid meniscus with meniscal degeneration and tears has been reported. , Furthermore, discoid menisci are prone to peripheral detachment and disruption. ,,, We recently saw a child with bilateral posterior subluxation of the anterior horns of discoid lateral menisci, suggesting detachment and instability of the anterior horns. To the best of our knowledge, such an occurrence has not previously been reported.
A 14-year-old girl, who practiced classical dance, came with a history of multiple episodes of locking of the right knee. At 8 years of age, she had complained of a snapping left knee, which was confirmed at physical examination, with the knee in valgus. At that time, the right knee was clinically normal, with normal standard radiographs. An MRI of both knees, performed on a 0.5T scanner, showed bilateral discoid lateral menisci, without meniscal tears. The girl was treated symptomatically only.
Two years later, in 2002, she came with bilateral painful snapping knees, associated with multiple episodes of right knee locking. An MRI of the knees, performed on a 0.5T scanner, showed increased intrameniscal signal on the T2W images in the discoid lateral menisci, consistent with mucoid degeneration [Figure 1]. The patient was not treated. She came back 3 years later, in 2005, for repeated locking of the right knee. Another MRI of both knees, now performed on a 1.5T scanner, showed that the anterior horns of both lateral menisci were dislocated and luxated, posteriorly and medially, toward the posterior horns. The MRI showed increased signal within the menisci on the T2W weighted images, consistent with mucoid degeneration [Figure 2]. As the menisci were luxated, it was difficult to evaluate whether a true meniscal tear was present or absent. A subsequent arthroscopy confirmed the diagnosis of bilateral discoid lateral menisci with dislocation and tear. The patient underwent right lateral meniscoplasty and was asymptomatic 2 weeks later; she refused surgery on the left.
Discoid meniscus of the knee is an anatomic variant in which the meniscus is thickened and disc shaped.  Discoid menisci occur almost exclusively on the lateral side; medial discoid menisci are exceedingly rare. They have a reported incidence of 0-7% on cadaveric studies and 0.4-16.6% on arthroscopic studies,  with a 20% incidence of bilateral occurrence. 
Discoid lateral menisci may be classified into three types.  Type 1 is complete and covers the entire tibial plateau; type 2 is incomplete and does not cover the entire tibial plateau; and type 3 (Wrisberg ligament type) results from a lack of posterior tibial attachment, which causes posterior rim instability. Type 3 may either be complete or incomplete. 
Discoid lateral menisci are associated with an increased incidence (71%) of tears,  as compared to nondiscoid menisci (54%). The presence of a Wrisberg variant (type 3) can result in instability of the posterior horns and is associated with a higher incidence of symptomatic meniscal tears. ,, Peripheral rim instability (28.1%) has also been reported on arthroscopy,  47.2% being unstable at the anterior-third peripheral attachment, 11.1% at the middle-third peripheral attachment, and 38.9% at the posterior-third peripheral attachment.  This instability leads to degeneration and tears, which are associated with pain, snapping or popping, and locked knees. Physical examination may show effusion and audible or palpable clicks, snaps, or clunks at terminal extension.  Treatment usually consists of partial or complete arthroscopic meniscectomy, which provide good results. ,, However, the long-term prognosis is related to the volume of the meniscus removed. ,
MRI is required to confirm a clinical suspicion of discoid meniscus. On MRI, a discoid meniscus is diagnosed when sagittal views show continuity between the anterior and the posterior horns on three or more consecutive 5-mm sections.  Coronal views will show a complete meniscus in all sections.  Associated changes of meniscal degeneration, tears, and subluxation can be diagnosed if present. ,
This report, to the best of our knowledge, is the first to describe bilateral posterior subluxation of the anterior horns of discoid lateral menisci. This posterior subluxation was probably a consequence of peripheral anterior instability which, in turn, was probably due to micro-traumatic meniscocapsular separation induced by the stress of classical dance. However, this posterior subluxation could also suggest the presence of a variant other than the Wrisberg type, with congenital detachment and hypermobility of the anterior horn. In either situation though, the intense practice of dance may have played a key role in the posterior displacement of the anterior horn of the meniscus.
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