Working Diagnosis:
Osteoarthritis with Lipoma Arborescens

Treatment:
The patient was referred to Rheumatology given her joint fluid results and abnormal inflammatory markers. Additional labs were ordered to evaluate for rheumatoid arthritis and a synovial biopsy was recommended based on MRI results. The patient was then referred to Orthopedic Surgery. A right knee arthroscopy with extensive synovectomy and debridement with biopsy was recommended and performed. The patient's synovial biopsy showed synovium-lined mature adipose tissue consistent with lipoma arborescens as suspected. Photo 4 of note, the additional autoimmune work-up was unremarkable.

Outcome:
Approximately 1 week after her surgery, the patient started formal physical therapy, focused on range of motion and lower extremity strengthening and stabilization. She was discharged to a home exercise program 2 months later. At her 3 month post-operative visit, she had regained her range of motion and had no swelling. She had mild pain of the medial compartment that was thought to be due to her known osteoarthritis. She was advised to avoid all high impact activities in the future. She will follow-up on an as needed basis.

Author's Comments:
Lipoma arborescens (LA) is a rare, benign, intra-articular lesion that often presents as unilateral painless joint swelling. LA has a predilection for the knee, particularly the suprapatellar pouch. Men and women are equally affected, with presentation typically in the 4th-5th decades of life. LA is characterized by villous hypertrophy and fatty infiltration of the synovium. Appearance on MRI is diagnostic and demonstrates a mass with high-intensity signal and frond-like projections. There may be a correlation between LA and osteoarthritis. The treatment of choice is arthroscopic synovectomy.

Editor's Comments:
Lipoma arborescens is a rare cause of persistent joint swelling. In this case, the patient's symptoms failed to improve with standard initial therapy, a sign that should key a provider to broaden their differential and trigger a more extensive work-up. Here the MRI revealed the source of the patient's symptoms, and led to the appropriate treatment, though the blood work and synovial fluid analysis may have been keys to discovering other uncommon disorders.

References:
1) Davies AP, Blewitt N. Lipoma arborescens of the knee. Knee. 2005 Oct;12(5):394-6. PMID 16005236
2) Kim RS et al. Lipoma arborescens of the knee. Arthroscopy. 2004 Oct;20(8):e95-9. PMID 15483537.

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