Meniscal flounce

Meniscal flounces refer to the "ruffled" appearance of the inner margin of knee menisci. They were initially thought to be only an arthroscopic finding, as a result of joint distension and anesthetic muscle relaxants but they are occasionally seen on MRI. 

Epidemiology

Meniscal flounces are uncommon with initial studies suggesting a frequency of around 0.2% on MRI scans, however more recently a frequency of up to 5% in relation to the medial meniscus has been reported.^1,4 It is far more common to be seen with the medial meniscus than the lateral meniscus.

Pathology

They are not associated with an increased incidence of meniscal tears, but can be mistaken for one. They reflect a degree of redundancy in the medial meniscus and are typically seen in the flexed knee. 

Radiographic features

MRI

In the sagittal plane the flounce is seen as a wave or kink in the inner margin of the meniscus. In the coronal plane, they may make the inner margin of the meniscus appear truncated or blurred and simulate a small radial tear.

Whenever a flounce is identified it is important to check that there are no ligamentous or capsular injuries that may be resulting in the laxity. This is particularly important if a lateral meniscal flounce is seen, as these are rare and may be a sign of popliteomeniscal fascicle injury/deficiency with hypermobile meniscus. 

History and etymology

Out of interest, a flounce is a ruffle placed around a garment (often undergarment) as a decoration.

Differential diagnosis

• radial-type meniscal tear