Subchondral cyst of the tibia secondary to Wilson disease.

We present the case of a 40-year-old male patient who had been suffering from Wilson disease for over 20 years, whose knee was diagnosed as osteoarthritis combined with subchondral cyst of the tibia. Preoperative examinations (X-ray, CT and MRI) confirmed the diagnosis. The microscopic examination detected thickening of the synovial membrane, and histopathological findings revealed that lymphoid cells and plasma cells were infiltrated at the synovial membrane. On copper-specific staining, no copper pigmentation was identified. However, the energy-dispersive X-ray (EDX) microanalysis revealed copper pigmentation in high concentration. These findings may contribute to our better comprehension of the development process of the arthropathy in patients with Wilson disease. The combination of subchondral cyst with Wilson disease is extremely rare, as only about 16 such cases have been reported in the English literature.