Role of Sonography in the Diagnosis and Treatment of Common Peroneal Neuropathy Secondary to Fabellae.

The fabella is a sesamoid bone situated in the posterolateral knee, which may contribute to posterolateral knee pain by impinging on the adjacent common peroneal nerve (CPN). Although anatomic studies have established an relationship between the fabella and CPN, we present 4 cases of posterolateral knee pain radiating into the anterolateral leg in which sonography was able to determine the source of the pain as CPN compression by an adjacent fabella. In 2 of these cases, resolution of symptoms was achieved with ultrasound-guided CPN blocks, whereas 1 case was surgically treated, and another was managed with oral analgesics. These cases illustrate the utility of diagnostic and interventional sonography in the evaluation and treatment of posterolateral knee pain secondary to fabellar impingement of the CPN.