Establishing a New Bony Landmark for Safe Screw Insertion in Medial Displacement Calcaneal Osteotomy: A Simulation-Based Approach

CATEGORY: Hindfoot; Other INTRODUCTION/PURPOSE: Medial displacement calcaneal osteotomy (MDCO) is a commonly performed procedure in flatfoot reconstruction. Fixation is often achieved with screws due to its ability to compress across the osteotomy site. Screws are placed via a free-handed technique without direct fluoroscopic visualization, due to difficulty attaining a simultaneous axial calcaneal view. In addition, the posterior calcaneal tuber translates medially after displacement, resulting in altered anatomical geometry. It is therefore important to establish a reliable external bony landmark when performing free-handed interfragmentary fixation in order to avoid potential screw-related complications and to provide better surgical technique and fixation. The purposes of this study are to validate a new external bony landmark and to establish the appropriate trajectory and screw length for free-hand screw fixation in MDCO. METHODS: A total of 84 postoperative computed tomography (CT) scans of MDCO in 70 patients were analyzed. The images were reconstructed using a 3-dimensional simulation program (Vworks 4.0, Cybermed). Virtual screw insertion was simulated by aiming towards two bony landmarks: the base of the 5th metatarsal in the axial plane, and the sinus tarsi in the sagittal plane (Figure 1). A grading system was also utilized to classify scenarios in which the screw breached the distal cortical wall: Grade 1 was defined as contact between the virtual screw and the cortex, Grade 2 as the screw approaching the outer margin of the cortex, and Grade 3 as the screw penetrating the outer cortex. The trajectory angle between the screw and the osteotomy, as well as the screw size, were also measured. RESULTS: The average age of patients was 24.5 (range, 19 to 53), and 100% were males. The average displacement of the posterior calcaneal fragment was 7.3+-1.5 mm (range, 3.9 to 13.8). Among the 84 virtual screws, only five (6.0%) breached the medial cortical wall of the osteotomized calcaneus. All medial breaches were Grade 1. None of the virtual screws breached the lateral cortical wall. Mean trajectory angle between the virtual screw and the osteotomy site was 74.9+-6.7˚ (range, 60.0 to 89.8˚). In the perioperative data, estimated maximum screw length by simulation was 55.6+-4.4 mm (range, 50 to 65). CONCLUSION: Our results suggest that the optimal trajectory of free-handed screw placement can be determined through simulation of calcaneal interfragmentary screw insertion using postoperative CT imaging. Using this simulation technology, we determined a trajectory towards the sinus tarsi on the sagittal plane and the base of the 5th metatarsal on the axial plane to be a reliable external bony landmark for placement of screws in MDCO. These promising results have potential implications in achieving better fixation as well as improving union rates and operative outcomes.