The authors measure the alignment of the nails in the hands of 100 normal adults with the interphalangeal joints extended and the metacarpophalangeal (MCP) joints at 0 and 90 degrees. When examining hands in MCP joint extension, only 17% of hands had all nails parallel (i.e., 5 degrees or less difference in rotation): this improved to 56% with the MCP joints flexed. When comparing matching fingers from the two hands, 76% of little, 83% of ring, 77% of middle, and 80% of index nails matched.
This study demonstrates that the inclination of the fingernails to the horizontal plane varies within a hand and between hands. The authors caution against examination of the injured hand alone when assessing finger rotation following fracture. Although matching fingers in the two hands may be a more reliable method of assessing for malrotation, variation in nail plate alignment is expected in approximately 20% of normal individuals. Rotational alignment may be better determined by active finger motion and/or passive wrist flexion and extension.
Nail, Rotation, Alignment, Finger, Flexion, Extension