Pain at the knee: the Morel-Lavallée lesion, a case series.

Post-traumatic pain at the knee is a common clinical presentation with a wide and varied differential diagnosis. The Morel-Lavallée lesion (MLL) is a rare cause of pain at the knee, caused by post-traumatic shearing of the hypodermis from the underlying fascia. The space created can fill with blood, lymph and necrotic fat giving specific findings on ultrasound and magnetic resonance (MR) evaluation. Three different cases of patients diagnosed with the MLL surrounding the knee are presented, with clinical and radiological findings. The different treatment options will be evaluated. The MLL is a rare but important cause of post-traumatic pain at the knee. Clinical exam and history are mandatory in diagnosing an MLL. Ultrasound and MR examination are very helpful in assessing the diagnosis. Various treatment options, nonsurgical as well as surgical, seem to be effective and should be considered depending on presentation and duration.