External fixation of the calcaneus and talus: an anatomical study for safe pin insertion

Fifteen fresh-frozen adult cadaver feet were dissected to investigate areas in the hindfoot where external fixation pins could be safely inserted with the least risk to underlying nerves, vessels, and tendons. Using palpable anatomic landmarks, four relative "safe zones" on the calcaneus and talus were delineated. These included an area on the medial calcaneus, the medial talus, the lateral calcaneus, and the lateral talus. The medial calcaneal safe zone was a large, easily definable rectangular area on the posterior aspect of the tuberosity, posterior to the neurovascular bundle and extrinsic tendons. The medial talar safe zone was located on the medial talar neck, anterior and superior to the tibialis posterior tendon. The lateral calcaneal safe zone consisted of a large area of the lateral calcaneal tuberosity, located posterior to the peroneal tendons and sural nerve trunk. The lateral talar safe zone included only a narrow, vaguely palpable, quadrangular area on the lateral neck of the talus. The medial safe zones could be easily delineated by palpation and appeared safe for routine unilateral external fixation across the medial hindfoot and ankle. The lateral safe zones appeared safe and useful if both medial and lateral frames were required. The structures most at risk for injury during pin insertion in the zones described were the medial and lateral calcaneal nerve branches, which inconsistently crossed the medial and lateral calcaneal safe zones, respectively. In these areas overlying the tuberosity, however, the subcutaneous tissues were thin, and iatrogenic nerve injury during pin insertion appeared avoidable if blunt dissection was used to reach the calcaneal cortex. The data presented here provide information to assist selection of pin sites that minimize risk to underlying soft tissues during external fixation of the talus and calcaneus.