A 42 year old female ex-professional player presented with a four month history of recurring swelling, instability and mechanical symptoms in her right knee. This was on a background of more longstanding patellofemoral symptoms. On examination she was found to have a loss of terminal knee flexion as well as a moderate effusion.
The MRI sequences show that the patella is mildly subluxed laterally with extensive full-thickness chondral loss and subarticular reactive changes at the lateral patellar facet. There is further full-thickness chondral loss at the superolateral aspect of the femoral trochlea with mild spurring at the lateral joint margin. There is a moderate joint effusion and synovitis with frond-like depositions of fat signal intensity foci, consistent with lipoma arborescens.
This player was successfully treated with an arthroscopy and excision of the abnormal synovium. While this resolved the recurring swelling and mechanical symptoms, she continued to have anterior knee pain. This is likely due to the patellofemoral chondral disease. She has been managing this with a cycling programme, strengthening exercises and taping for football.
Lipoma arborescens occurs when the normal synovium becomes replaced by hypertrophied villi with deposition of mature fat cells in the sub-synovial connective tissue. It is generally thought to be a nonspecific reactive response to chronic synovial irritation, due to either mechanical or inflammatory pathology.
The typical presentation is of recurring unilateral joint swelling and pain, however instability and mechanical symptoms can also occur. While it usually involves the suprapatellar pouch of the knee joint it can occur at other sites. X-rays may show an effusion or soft tissue swelling however they are generally not helpful for establishing a diagnosis. In most cases the diagnosis is made on the basis of MRI findings. An effusion with an associated fat-containing frond-like synovial mass is typically seen on MRI.
The treatment of choice for this condition is generally a synovectomy. This can be done using either open or arthroscopic methods. Recurrence after surgery is uncommon. It is possible that a delay in treatment can lead to degenerative changes within the joint.
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