An improved approach to the evaluation of the deep motor branch of the ulnar nerve

The detection of ulnar nerve lesions at Guyon's canal requires evaluation of the distal ulnar sensory and distal motor latency to the abductor digiti minimi (ADM). In addition precision in the measurement of distal motor latencies (DL) to the first dorsal interosseous (1DI) muscle and response amplitude is necessary. This study examines a standardized technique assessing distal ulnar nerve conduction aimed to provide a more sensitive evaluation of these lesions. Fifty normals and eighteen subjects with hand symptoms were assessed to determine DL to the ADM and 1DI and response amplitudes. These standard values were then compared to values obtained from clinically proven cases of distal ulnar lesions over the previous 2 years. The main outcome measures were elimination of premotor potentials and prolongation of 1DI DL. The results revealed that the standardized technique consistently eliminates premotor potentials (PMP) and provides a significantly narrowed range of normal DL values. This enhanced precision allows for more accurate normative values, making recognition of more subtle lesions possible. Normative data compared to values from a 2 year chart review of distal ulnar lesions shows predictive trends toward prolonged 1DI DL and diminution of 1DI amplitudes (AMP).