Introduction: Large cysts of the proximal tibial metaphysis are an uncommon radiological finding amongst the elderly presenting to an arthroplasty clinic. We present two cases of such pathology in elderly patients. These were both associated with advanced degenerate disease in the knee.

In view of the size of the lesions these were both fully investigated with pre-operative radiology and an image guided biopsy. The first case was found to be a large degenerate myxoid cyst involving the majority of the tibial plateau. The second case appeared similar radiologically yet was a large metastasis from a bladder cancer. The only history offered by the after this had been established was that she had had a benign polyp removed some years previously.

Management: When dealing with unusual features of disease a cautious approach should be recommended. Both patients underwent staging investigations and biopsy prior to knee replacement surgery. In each case it was possible to graft the defect and using revision prostheses a good outcome has been achieved.

Conclusion: Large cysts appearing in association with degenerate disease of the knee are uncommon. Whilst these will often be related to the underlying arthritis this is not always the case and appropriate care should be taken to establish a diagnosis prior to surgery.