Ultrasound as a Complementary Tool to Electrodiagnostics in the Evaluation of Compressive Neuropathy of the Common Fibular Nerve

Background: Compressive neuropathy of the common fibular nerve (CFN) is increasingly recognized as an etiology for foot drop and falls. Electrodiagnostic (EDX) studies are widely used to evaluate this condition, but such tests are invasive and costly. As with carpal and cubital tunnel syndromes, there may be patients with characteristic symptoms of CFN compressive neuropathy but normal EDX studies in which ultrasound may aid in decision-making. Purpose: We sought to examine the association between ultrasound and nerve conduction studies (NCS) and electromyography (EMG) in the diagnosis of compressive neuropathy of the CFN. Methods: We performed a retrospective review identifying 104 patients who underwent CFN decompression from January 1, 2015, to June 30, 2023. Patients were included if they had both ultrasound and NCS/EMG prior to CFN decompression for compressive neuropathy and if they were older than 18 years at time of surgery. Patients were excluded if they had entrapment secondary to trauma, iatrogenic injury, or if they had had superficial fibular decompression alone without CFN decompression. After applying exclusion criteria, 17 patients remained in the cohort. Results: Mean ultrasound cross-sectional area and side-to-side (STS) ratios were significantly higher in those with abnormal compound muscle action potential (CMAP) amplitudes versus those with normal CMAP amplitudes. The probability of having an abnormal CMAP amplitude when STS ratio was abnormal was 18 times greater compared with those with normal STS ratio. With each unit increase in STS ratio, CMAP amplitude was reduced by 2.79 mV. Conclusions: This retrospective review found that ultrasound may provide complementary diagnostic information to EMG/NCS for compressive neuropathy of the CFN. Further study is needed to examine the relationship between ultrasound findings for CFN compressive neuropathy and results of surgical decompression.