The nail matrix covers the bottom of the cul-de-sac and rises on the posterior quarter (or even less) of the ventral aspect of the proximal nail fold (PNF) (see chap. 1). The matrix rests on the base of the distal bony phalanx and forms a crescent with posteriorinferior concavity (Fig. 1A). One should bear in mind that on the great toes, both lateral ends of the crescent (also called the lateral horns of the matrix) expand much proximal on the lateral aspect of the phalanx than that of the fingers (Fig. 1B). This anatomical particularity explains why spicules are the most common complication of surgical treatment for ingrowing toenail and lateral longitudinal biopsies in unskilled hands. The lateral horns may reach to or even beyond the midline of the lateral aspect of the great toe. Two other important points should be kept in mind when performing nail matrix surgery.