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.