Can MR neurography of the common peroneal nerve predict a residual motor deficit in patients with foot drop?

Abstract

To determine if MR neurography of the common peroneal nerve (CPN) predicts a residual motor deficit at 12-month clinical follow-up in patients presenting with foot drop. A retrospective search for MR neurography cases evaluating the CPN at the knee was performed. Patients were included if they had electrodiagnostic testing (EDX) within 3months of imaging, ankle and/or forefoot dorsiflexion weakness at presentation, and at least 12-month follow-up. Two radiologists individually evaluated nerve size (enlarged/normal), nerve signal (T2 hyperintense/normal), muscle signal (T2 hyperintense/normal), muscle bulk (normal/Goutallier 1/Goutallier > 1), and nerve and muscle enhancement. Discrepancies were resolved via consensus review. Multivariable logistical regression was used to evaluate for association between each imaging finding and a residual motor deficit at 12-month follow-up. Twenty-three 3T MRIs in 22 patients (1 bilateral, mean age 52years, 16 male) met inclusion criteria. Eighteen cases demonstrated common peroneal neuropathy on EDX, and median duration of symptoms was 5months. Six cases demonstrated a residual motor deficit at 12-month follow-up. Fourteen cases underwent CPN decompression (1 bilateral) within 1year of presentation. Three cases demonstrated Goutallier > 1 anterior compartment muscle bulk. Multivariable logistical regression did not show a statistically significant association between any of the imaging findings and a residual motor deficit at 12-month follow-up. MR neurography did not predict a residual motor deficit at 12-month follow-up in patients presenting with foot drop, though few patients demonstrated muscle atrophy in this study.