Median and Ulnar Antidromic Sensory Studies to the Fourth Digit

The literature documents multiple reports of neurological injury resulting from both the implantation and the removal of orthopedic devices. These injuries can be easily and objectively evaluated with nerve conduction studies. This study was undertaken to derive a normative database for median and ulnar sensory conduction studies to the fourth digit. Testing was done utilizing a 14-cm antidromic technique on 192 asymptomatic subjects with no risk factors for neuropathy. The subjects were studied bilaterally. Onset latency, peak latency, onset-to-peak amplitude, peak-to-peak amplitude, rise time, and duration were recorded. Increasing age and body mass index were associated with decreasing amplitudes and area. No other demographic factors correlated with differences in waveform measurements. Mean onset latency was 2.7 +/- 0.3 ms for the median nerve and 2.6 +/- 0.2 for the ulnar nerve. Mean peak latency was 3.4 +/- 0.3 ms for the median nerve and 3.3 +/- 0.3 ms for the ulnar nerve. Mean onset-to-peak amplitude was 21 +/- 12 muV for the median nerve and 23 +/- 12muV for the ulnar nerve. Mean peak-to-peak amplitude was 34 +/- 20 muV for the median nerve and 36 +/- 23 muV for the ulnar nerve. Mean area was 25 +/- 17 nVs for the median nerve and 28 +/- 19 nVs for the ulnar nerve. Mean rise time was 0.7 +/- 0.1 ms for the median nerve and 0.7 +/- 0.2 ms for the ulnar nerve. Mean duration was 1.9 +/- 0.4 ms for the median nerve and 1.9 +/- 0.5 ms for the ulnar nerve. The mean difference in onset and peak latency between the median and ulnar nerves (median minus ulnar) was 0.1 +/- 0.2 ms. The upper limit of normal difference of median greater than ulnar onset and peak latency was 0.5 ms. The upper limit of normal difference of ulnar greater than median onset latency was 0.2 ms (0.3 ms for peak latency). The upper limit of normal drop in median peak-to-peak amplitude from one side to the other was 56%. For the ulnar nerve this value was 73%.