Ulnar Nerve Morphology in Magnetic Resonance Imaging Predicts Nerve Recovery After Surgery for Cubital Tunnel Syndrome

Abstract Background: Magnetic resonance imaging (MRI) is helpful for the diagnosis of cubital tunnel syndrome (CuTS), but its prognostic value for surgical outcomes is unknown. We aimed to determine whether MRI parameters correlated with outcomes after surgery for CuTS. Methods: We reviewed 40 patients who had electrodiagnostic tests and MRIs for CuTS preoperatively and had 6-month evaluations postoperatively. The MRI parameters were ulnar nerve cross-sectional area (UNCSA) measured at 6 different levels around the medial epicondyle (ME), signal intensity changes of innervated muscles of the ulnar nerve, and the presence of ganglion around the ulnar nerve. Other factors assessed were age, symptom duration, symptom severity, presence of diabetes mellitus, and electrodiagnostic parameters including motor nerve conduction velocity (mNCV). We analyzed the factors associated with fair or poor outcomes graded by Wilson-Krout classification. Results: The UNCSA was the largest at ME level and smallest at 3cm distal to ME level. Increased ulnar nerve signal intensity changes were found in 34 subjects and increased forearm muscle signal intensity changes were found in two. Ten patients were found to have ganglia. Twelve patients (30%) had excellent results, 19 (48%) had good, 8 (20%) had fair, and 1 (4%) had a poor result. In univariate analysis, fair or poor outcomes were associated with increased UNCSA 1 cm proximal and 1 cm distal from the ME, the presence of ganglion, and decreased mNCV. In multivariate analysis, fair or poor outcomes were associated with either increased UNCSA 1 cm distal from the ME (OR 11.15; p = 0.019), or increased UNCSA 1 cm proximal from the ME (OR 16.01; p = 0.038) and decreased mNCV (OR 0.92; p = 0.044).Conclusions: This study demonstrated that increased ulnar nerve cross-sectional area on MRI correlated with suboptimal improvement after surgery for CuTS at 6 months follow up. MRI examination for morphologic changes of the ulnar nerve can be helpful for patient consultation on the prognosis of surgery for CuTS.