Strain in the nail at fingertip compression

Distribution of nail strain due to compressive force in the finger pulp was investigated.

Nail strain of the right index finger of 10 healthy men was measured using three strain gauges with two axes. Each nail strain was measured along the longitudinal and the transverse axis using sensor interface. Three CCD cameras recorded the compressive force and the fingertip deformation. Each subject pressed the right index finger with 30 degrees, 45 degrees and 60 degrees in the contact angle, with the compressive force increased from 0 to 14 N.

When the contact angle was 30 degrees, the strain along the transverse axis increased according to the compressive force increased. The proximal-radial-transverse strain at compressive force of 13 N was significantly (P<0.01) larger than the proximal-ulnar-transverse strain. At the same compressive force, the distal-central-transverse strain was significantly (P<0.05) larger than the proximal-ulnar-transverse strain. The proximal-radial-transverse strain was significantly (P<0.01) larger than the proximal-radial-longitudinal strain. In the contact angle of 45 degrees and 60 degrees, same results were gained.

Nail strain due to compressive force in the finger pulp was different between the rectangular axes, between the distal and the proximal parts of the nail, and between the radial and the ulnar sides.