A 82 year old man presents with pain and swelling of his right knee for 1 year, resulting in difficulty in walking. He also noticed a mass in the same knee 6 months ago, which has gradually increased in size over time. He was diagnosed with type 2 diabetes mellitus 10 years ago, which is currently well controlled. An HbA1C last month was 5.5%. His surgical and family histories are unremarkable. He does not smoke or use recreational drugs, but drinks socially.
Radiography of right knee joint reveals a mass in close proximity to the joint, and abnormal calcification of the menisci. The joint space appears normal.
MRI imaging of the right knee joint reveals a 4 x 4 x 1.5 cm mass in the medial parapatellar joint space, with both marginal calcifications, and irregular calcifications throughout.
Arthrocentesis is attempted twice, but results in a dry tap on both occasions.
At the time of surgery, a 5 x 4.5 x 2 cm glossy white mass is seen, with partial apposition to the synovium; there are no palpable synovial masses. Geometric calcified deposits are observed on both the mass and joint synovium. Calcifications are also observed in the articular cartilage and meniscus, with no significant degeneration or destruction. Histology reveals massive calcified deposits on both the surface and interior of the mass. The interstitial matrix resembles fibrous cartilage, while the calcified deposits show positive birefringence under polarised light.