Compression neuropathy of the common peroneal nerve by the fabella.

The fabella is a normal anatomical variant and has been found in up to 30% of the general population. We present the case of a 67-year-old man with pain down the lateral aspect of the left lower limb of 18 months duration. A clinical examination revealed a palpable fabella and nerve conduction studies confirmed a common peroneal nerve neuropathy at its level. Dynamic ultrasound scan and MRI of the knee showed the fabella to be impinging on the common peroneal nerve. Operative excision of the fabella was performed with significant improvement at 3 months and full recovery at 1 year. A literature review has shown that the last reported case of a compression neuropathy of the common peroneal nerve was in 1976. Anatomical considerations need to be taken into account and operative treatment has been recommended due to the favourable outcome in this case.