The Anteromedial Cortex of the Calcaneus: A Cadaveric Study

CATEGORY: Hindfoot INTRODUCTION/PURPOSE: The irregular morphology of the calcaneus obstructs its clear visualization on radiographic imaging. Particularly challenging is identifying the medial cortex given its concavity and bony overlap of the calcaneal body. Iatrogenic screw penetration of the medial wall of the calcaneus comes with increased risk of injuring the neurovascular bundle and the flexor hallucis longus tendon. Despite all intraoperative precautions, it is not infrequent to see misplaced screws in postoperative imaging. The objective of the present study is to evaluate the normal proportion of the calcaneus width to radiographically define the extent of the medial cortex on axial fluoroscopic imaging. METHODS: Eight left sided fresh-frozen below-the-knee amputated cadaveric specimens were utilized for this study. Each specimen was dissected on the medial side of the hindfoot to allow visualization of the medial cortex of the calcaneus. A partial cuboid ostectomy was performed to visualize the calcaneocuboid joint and to install radiopaque markers on the borders of the anterior calcaneal facet. Finally, Harris axial views were obtained. Two independent observers measured the widths of the calcaneus on digital fluoroscopic Harris views at two levels: the maximal width at the sustentaculum tali and the maximal width at the anterior process. A ratio was calculated between these measurements. RESULTS: The ratio between the maximal width at the anterior process and the sustentaculum ranged between 0.42 and 0.52 with an average ratio of 0.47 +/- 0.04. CONCLUSION: Calcaneal screw misplacement, particularly from lateral to medial, can lead to damage of the neurovascular bundle and the flexor hallucis long tendon ultimately affecting clinical outcomes. The measurements in the present study suggest a lower risk of violating the medial cortex when the length of the screw placed in the anterior process of the calcaneus is less than half of the maximal width of the calcaneus at the sustentaculum tali. As the medial cortex is difficult to visualize on intraoperative fluoroscopy, the clinical use of this normal ratio in axial views could help surgeons to avoid calcaneal screw misplacement.