Vertically growing ectopic nail. Nature's experiment on nail growth direction.

The cul-de-sac in which the nail is formed determines that it should grow outward instead of upward according to Kligman. This view was questioned by Baran based on clinical observations and review of the literature. A case of vertically growing ectopic nail of congenital origin indicated that the cul-de-sac was directed to the skin surface and the nail was growing vertically to the skin. The anatomy of the cul-de-sac, which may be influenced by local factors, appears to determine the direction of the nail.