A calibrated paper clip is a reliable measure of two-point discrimination

The primary objective of this study was to compare two different instruments for assessing digital nerve function; a secondary aim was to determine interobserver agreement among emergency physicians by using static two-point testing of digital nerve function.

This was a prospective, blinded, observational study of static two-point discrimination involving healthy volunteers aged 18-59 years. The authors compared two instruments (paper clip set or Disk-Criminator) to assess two-point discrimination of the index and long fingers of the dominant hand. For each subject, the initial investigator and initial testing instrument were randomized. Two-point testing was conducted at 4, 5, and 6 mm by using six randomly selected stimuli (1 or 2 points) for each distal phalanx tested. The study was designed to detect a 25% difference in mean two-point distance with a power of 80%.

Seventy-five subjects were entered into the study, of which two were excluded. Interinstrument agreement for a given investigator ranged from 77% to 84% for absolute agreement and 98% to 100% within 2 mm. Weighted kappa values for interobserver differences of 2 mm or less was 0.79 to 1.00. There was no statistically significant difference between instruments.

Using a clinically relevant threshold of 2 mm, the authors found that a properly calibrated set of paper clips performed as well as the Disk-Criminator.