Abstract: Objective  To evaluate the feasibility and accuracy of the guide needle inserted through the calcaneal sustentaculum tali by locating from inside, while putting the screw from the outside.  Methods  The L-shaped extended incision was simulated to expose the lateral calcaneal structure and subtalar joints on 10 adult cadaveric specimens (20 sides). The self-designed calcaneal sustentaculum tali director was adopted. First, placed the "positioning needle" from the inside into the subtalar joint, made the “positioning hole” of the “inner arm” entangled the positioning needle, then placed and adjusted the "inner arm of the director" so that the latter "guiding channel" was located in the center of the sustentaculum tali, installed  “the lateral arm” to fix “the handle”. Then, a "guide needle" was inserted to the calcaneal from inside to outside via the"guide channel", after C-arm fluoroscopy clarifiing the ideal position of the "guide needle", drilled with a hollow hole from the outside along the "guide needle", then screwed in the appropriate hollow pressure screw. Finally, the specimens were scanned under spiral CT and the accuracy of the insertion screw was evaluated using CT images. Collecting relevant data during the process to evaluate the function of the director.  Results  The guide needles of all the specimens were located in the sustentaculum tali, 65% of them were located in the center, 25% below and 10% behind. On the inside, 75% of the guide needles passed through the posterior tibia tendon, 15% lied between the posterior tibia tendon and the flexor digitorum longus tendon, and 10% passes through the upper 1/3 of the flexor digitorum longus tendon. On the outside, the distance between the needle outlet point of the guide needle and the calcaneocuboid joint was (38.03±5.60) mm, the distance from the posterior articular surface was (15.01±3.38) mm, the average length of screw was (44.80±3.59) mm. In the CT scan image, all the screws were located in the sustentaculum tali, two cases penetrated the upper bony cortex, no cases showed that screw pierced the inferior and anterior of the sustentaculum tali or lower bony cortex.  Conclusions  The guidance of the self-designed director which adopted the "medial-oriented method" can improve the accuracy of sustentaculum tali screw placement and reduce the complications such as screw entry into the joint and calcaneal medial cortex.

Key words: Calcaneal, 　Sustentaculum Tali, 　Director, 　Anatomical, 　Radiographic