An eleven-year-old female player presented complaining of recurring clunking in her left knee. This had been present for six months but had become worse in the month prior to her presentation. During this time, she had also developed some localised lateral knee pain and her parents had noticed that her knee appeared swollen.
On examination there was a small effusion. There was an audible clunking sensation as her knee was moved from full extension to full flexion. There was some modest lateral joint line tenderness as well as pain and clicking with McMurray’s test.
An x-ray series of the left knee is normal. MRI sequences showed that there is a complete discoid lateral meniscus. The meniscal tissue is thickened and hyperintense with a partial tear. Meniscal material is bulging posteriorly. There are normal chondral surfaces in the lateral compartment and a normal medial compartment
This young woman was treated with arthroscopic saucerization of the lateral meniscus followed by a five-month period of rest, physiotherapy and a progressive return to activity. At five months post-surgery she had a normal clinical examination and had returned to normal activities.
A discoid meniscus is a congenital abnormality of the knee found in approximately 3% of the population. The reported rates are higher in some ethnic groups. It most frequently affects the lateral meniscus and is bilateral in about 20% of patients. Instead of having the more ‘normal’ narrow crescent shape, a discoid meniscus is thickened, has a fuller crescent shape and does not taper towards the centre of the joint. These features make the meniscus larger and more prone to tearing. As a result, the most common presenting symptoms are pain, swelling or mechanical symptoms (including locking, catching and clunking).
X-rays are generally normal in patients with a discoid meniscus. There are however some x-ray findings that may raise the suspicion of this diagnosis. These include widening of the lateral joint space, a squared-off appearance of the lateral femoral condyle, cupping of the lateral tibial plateau, elevation of the fibular head, and flattening of the tibial eminence. MRI is the imaging modality of choice. Continuity of the meniscus between the anterior and posterior horns on three or more (5-mm thick) consecutive sagittal slices is generally considered to be abnormal.
Many patients with a discoid meniscus are completely asymptomatic. These patients do not require specific treatment. Operative treatment is generally necessary if there are symptoms. Partial meniscectomy, with saucerization, is generally the treatment of choice. This procedure aims to preserve a stable peripheral rim of tissue and can be combined with meniscal repair.
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