Dynamic skin tension in the forearm: effects of pronation and supination.

Purpose: Longitudinal scars on the radial quadrant of the distal forearm skin envelope are typically observed to be wider than those on the ulnar quadrant and have an increased incidence of hypertrophic change. Forearm rotation movements may produce differential skin tensions within the forearm skin envelope, and this may lead to differential scarring patterns. This study was designed to measure skin tension changes in the forearm as a result of rotational position to see if these would be consistent with the hypothesis that greater tension changes are observed on the radial aspect of the forearm.

Methods: The effect of forearm position on the magnitude and direction of skin tension was measured on human volunteers. Standardized circles were marked in circumferential fashion at specified intervals on forearm skin, and the angular and dimensional distortion of these circles that occurred with forearm rotation was measured with caliper and goniometer. Data were analyzed for statistical significance using paired t-test.

Results: Pronation and supination resulted in marked angular rotation of the lines of maximal skin tension at all sites on the forearm. Supination resulted in a greater angular deviation of the lines of maximal skin tension from the longitudinal line of usual surgical incision, particularly on the radial aspect of the forearm. In supination, the magnitude of ellipsoid deformation at the distal forearm was greater on the radial aspect compared with that of the ulnar. Similar significant changes were also demonstrated at the mid-forearm and proximal forearm levels.

Conclusions: This study systematically maps the effects of pronation and supination on skin tension within the forearm skin envelope. The significant changes occurring in both the ellipsoid deformation and ellipsoid orientation support our hypothesis that the magnitude of skin tension changes significantly with forearm rotation. The radial aspect of the distal forearm experiences the greatest changes, particularly as the forearm supinates.