Ultrasound Evaluation and Treatment of Posterior Medial Antebrachial Cutaneous Nerve Injury Following Cubital Tunnel Release

This case highlights the diagnostic value of high-resolution ultrasonography in identifying postoperative injury of the posterior branch of the medial antebrachial cutaneous nerve (MABCN) following cubital tunnel surgery. A 45-year-old man developed localized pain, warmth, and paresthesia extending from the medial epicondyle to the proximal anterior forearm one month after ulnar nerve decompression and anterior transposition. Physical examination revealed focal allodynia and a positive Tinel sign. Because previous surgery may substantially alter the anatomical location of the surrounding nerves, electrodiagnostic localization can be technically challenging and less reliable. Ultrasonography therefore played a key diagnostic role. The images demonstrated the normal sonoanatomy of the MABCN and its anatomical relationship with the basilic vein and ulnar nerve, followed by pathologic findings of focal enlargement of the posterior branch adjacent to postoperative scar tissue. These imaging features, together with a positive sonographic Tinel sign, supported the diagnosis of localized nerve irritation. Ultrasound-guided hydrodissection using 5% dextrose and methylcobalamin resulted in marked clinical improvement, with the Visual Analog Scale pain score decreasing from 9 to 2. This case is particularly illustrative because postoperative injury of the MABCN may mimic recurrent cubital tunnel syndrome yet typically produces purely sensory symptoms confined to the medial elbow region. Targeted ultrasonographic evaluation can reveal subtle postoperative nerve pathology and guide effective ultrasound-guided intervention.