Morel-Lavallée lesion of the knee

Case
A 24-year-old female player presents after an innocuous twisting injury to her left knee. This was sustained whilst attempting a slide tackle. She reports that her knee became swollen (over a few hours) and was painful. She did attempt to play the following day, albeit with pain. On examination there was localised swelling about the medial aspect of her knee, tenderness around the medial patellar retinaculum and limited knee flexion. There were no other significant findings.

Findings
X-ray images of the left knee were normal. On MRI there is soft tissue swelling over the anterior and medial aspect of the knee. There is complex fluid signal intensity of the prepatellar and prepatellar tendon bursae. There is mixed signal intensity (likely to represent haemorrhagic material) within the medial aspect of the bursal fluid/haemorrhagic effusion.

Discussion
This player was diagnosed with a Morel-Lavallée Lesion (MLL) of the knee. She was managed with a short period of rest followed by a progressive re-introduction to training. She was initially more comfortable playing and training with a compressive knee sleeve. She did not require any other formal treatment. She was back to playing comfortably, albeit with some residual swelling, approximately one month after her injury.
MLL are a closed de-gloving injury that occur as a result of a shearing injury that separates the skin and subcutaneous tissue from the underlying fascia. This condition was first described by a French physician, Maurice Morel-Lavallée, in the 1853. The most common site for this pathology is the hip or lateral thigh. MRI is the preferred imaging modality of choice in the evaluation of MLLs. The signal characteristics of the lesions depend on their chronicity and their contents (fluid, methemoglobin or fat are common). Knee MLLs are relatively uncommon. When they do occur they more frequently affect the medial, rather than lateral, side of the knee. Based on a cadaveric study this may be due to the lower resistance in this location. In most cases time and observation are effective treatments. When there is a defined ‘capsule’, non-surgical treatment is less likely to be successful and surgical management should be considered.

Important notice
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