Recommended site and depth of newborn heel skin punctures based on anatomical measurements and histopathology

The heels of 40 children (0.56--13.15 kg), 35 of whom were newborn infants and 28 of whom had 2--20 visible skin punctures, were examined at necropsy, and the thickness of the tissue layers was measured with a metric vernier caliper. Histological examination showed that uncomplicated skin-puncture wounds heal with minimum scarring and no neuroma formation. 1 infant had an infected puncture track extending into the calcaneus and resulting in cellulitis and focal calcaneal necrotising chondritis. The skin's primary blood-supply is located at the junction of the dermis and subcutaneous tissue, and the distance from the surface of the heel to this junction was quite constant (0.35--1.6 mm). However, the distance from the skin surface to the calcaneus increased with infant weight (in the smallest infant it was 2.4 mm), and at the posterior curvature of the heel it was half that from the plantar surface to the calcaneus. The calcaneus rarely extended lateral to a line drawn posteriorly from a point midway between the 4th and 5th toes and running parallel to the lateral aspect of the heel or medial to a line extending posteriorly from the middle of the great toe and running parallel to the medial surface of the heel. Therefore, in order to avoid calcaneal puncture and the risk of osteochondritis, heel puncture in the newborn should be done: (1) on the most medial or lateral portions of the plantar surface of the heel; (2) no deeper than 2.4 mm; (3) not on the posterior curvature of the heel; and (4) not through previous puncture sites that may be infected.