To determine the anatomical parameters concerning the length, width and height of the sustentaculum fragment of the calcaneus using CT imaging data and their clinical significance.

A retrospective study was conducted to analyze the CT imaging data of normal calcaneus in 96 patients (100 feet) which had been collected by Department of Orthopedics, Shanghai Tongji Hospital from January 2019 to September 2020. There were 45 males (48 feet) and 51 females (52 feet) with an age of (42.1±13.6) years, and 56 left feet and 44 right feet. After 3D models were reconstructed with the CT data using software Mimics 22.0, the calcaneus was viewed layer by layer at each level of the scan. After the first continuous bone trabecula on the medial side of the calcaneal central triangle was taken as the boundary, the model of the sustentaculum fragment was segmented. The length, width, and height of the sustentaculum fragment were measured. The outer contour of the sustentaculum fragment was projected onto the lateral wall of the calcaneus to draw the contour line using software Materialise 3-Matic 22.0. By overlaying projection line diagrams, a summary of projection line diagrams of 100 sustentaculum fragments was obtained. Seven screw insertion points were selected in the summary region of the projection line diagrams of the lateral wall of the calcaneus, and the distance from each point to the medial side of the calcaneus were measureed. The length, width, and height of the sustentaculum fragment, as well as the distance from the 7 insertion points to the medial side of the calcaneus, were compared between different feet and genders.

The length, width, and height of the sustentaculum fragment were (45.19±4.60) mm, (38.57±4.59) mm and (40.76±5.48) mm, respectively. There were no significant differences in the length, width or height of the sustentaculum fragment between different feet or in the height of the sustentaculum fragment between different genders (P>0.05), but the length and width of the sustentaculum fragment in females were significantly smaller than those in the males (P<0.05). The projection of the sustentaculum fragment was approximately ellipse on the summary region of the projection line diagrams on the lateral wall of the calcaneus, with the long axis approximately parallel to the midpoint tangent of the lateral edge of the calcaneal posterior articular surface, ranging from 2 to 20 mm from the posterior articular surface. The distances from the 7 insertion points to the medial surface of the calcaneus were (39.91±3.77) mm at point A, (40.89±3.55) mm at point B, (36.42±5.98) mm at point C, (39.12±5.52) mm at point D, (40.04±4.84) mm at point E, (33.00±3.96) mm at point F, and (33.04±3.82) mm at point H. There was no significant difference in the distances from the 7 insertion points to the medial surface of the calcaneus between different feet (P>0.05), but the distances from the 7 insertion points to the medial surface of the calcaneus in the females were significantly smaller than those in the males (P<0.05).

Anatomical measurements of the sustentaculum fragment can provide a theoretical basis for the range of fixation of the sustentaculum screws. A summary of projection line diagrams of the sustentaculum fragment on the lateral surface of the calcaneus can serve as a reference for placement of sustentaculum screws. Measurement of the distances from 7 insertion points to the medial surface of the calcaneus can facilitate determination of the lengths of sustentaculum screws.

Calcaneus; Fractures, bone; Anatomy; Sustentaculum tali; 3D reconstruction