In view of patient’s history of trauma, MRI features are in keeping with organised haematoma. The location of the lesion at the subcutaneous tissues just superficial to the muscle fascia makes Morel-Lavallée lesion the likely diagnosis. 

Although Morel Lavallée lesion is known for haematoma / degloving injury occurring over the greater trochanter, similar lesion can occur around the knee joint due to similar mechanism.

Case courtesy; Dr Rim Bastawy, Lecturer of radiodiagnosis, Alexandria University, Egypt.