A 52-year-old male labourer from Delhi presents with a 3-month history of progressive weakness and wasting of the intrinsic hand muscles, with sparing of forearm flexors. He reports a history of recurrent elbow trauma from his occupation. On examination, he has a positive Froment's sign and Wartenberg's sign. Sensory loss is noted over the medial 1.5 fingers. What is the most appropriate next step in management?