Bilaterally symmetrical ganglion and subchondral cysts of the knee: a case report

A 49-year-old patient, with a maternal history of arthritis, presented with an extra-capsular lump of the left knee. Following magnetic resonance imaging (MRI) scan and excision biopsy, the lump proved to be a benign ganglion cyst. The scan had also shown focal subchondral cyst formation and articular cartilage wear in the medial femoral condyle and patella, with no other abnormality. Four years later, she presented with identical symptoms and signs in the right knee. MRI scan confirmed a symmetrical pattern of ganglion and subchondral cyst location and size. Although both ganglion and subchondral cysts of the knee are common, their development is poorly understood and this combination of cyst formation and chondral wear has not been previously documented. Symmetry of end-stage knee osteoarthritis (OA) is recognized by clinicians. We speculate that OA of the knee begins asymptomatically with point-specific loss of articular cartilage, typically reflecting an inherent and bilateral vulnerability to degeneration.