Safe zone for the placement of medial malleolar screws

BACKGROUND: Hardware placement for fracture fixation can put soft-tissue structures at risk for injury or abutment. The prominence of the hardware is a frequent cause of pain after the fixation of ankle fractures. This study was designed to assess the risk of injury or abutment of the posterior tibial tendon with the placement of medial malleolar screws. METHODS: Ten unmatched cadaveric limbs that had been disarticulated at the knee were used, and the medial malleolus was exposed by dissection of the skin. With use of fluoroscopy and direct visualization of the deep fascia, three Kirschner wires were placed through the tip of the medial malleolus and directed parallel to the medial articular surface. The first wire was placed in the center of the anterior colliculus. Two additional wires were placed parallel and posterior to the initial wire at 5-mm intervals. The wires were overdrilled, and 4.0-mm screws were inserted over the Kirschner wires. The specimens were dissected to inspect for trauma and the proximity of the screws to the posterior tibial tendon. The medial malleolus was divided into three zones on the basis of anatomic landmarks. Zone 1 is the anterior colliculus; Zone 2, the intercollicular groove; and Zone 3, the posterior colliculus. RESULTS: Screws placed in Zone 1 (the anterior colliculus) did not contact the posterior tibial tendon in any specimens. Screws placed in Zone 2 (the intercollicular groove) were, on the average, 2 mm from the posterior tibial tendon. Screws placed in Zone 3 (the posterior colliculus) resulted in tendon abutment in all ten specimens and in tendon injury in five of the ten specimens. CONCLUSIONS: Screws inserted posterior to the anterior colliculus place the posterior tibial tendon at significant risk for injury or abutment.