Objective: To investigate the anatomical characters of the sustentaculum tali (ST), accurate entry point and direction for the placement of ST screw from posterior subtalar joint facet to the constant fragment (CF) in calcaneal fractures.
Methods: A total of 100 patients with calcaneal fractures performed ankle CT scans were enrolled between January 2016 and April 2016. According to the inclusion criteria, the clinical data of 33 patients were analyzed, including 18 males and 15 females, with a median age of 41.0 years (range, 18-60 years). There were 16 cases on left side and 17 cases on the right side. Three-dimensional (3D) calcaneal model was reconstructed by Mimics 17.0 software, and the ST anatomical references were measured, including the length of upper and lower edge, the length and height of the midline, the horizontal angle between the midline and foot plantar surface. The parameters of the optimal entry point position (P' point) and placement angle of the ST screw were determined. The length of ST screw was also measured. The differences between males and females or left and right sides were compared.
Results: The length of upper edge of the ST was (16.60±2.23) mm, lower edge (20.65±2.90) mm, midline (20.56±2.62) mm, and the height of midline was (9.61±1.36) mm. The horizontal angle between the midline and foot plantar surface was (23.43±3.36)°. The vertical distance from P' point to the lowest point of the tarsal sinus was (3.09±1.65) mm, while the horizontal distance was (14.29±2.75) mm. The distance from P' point to the apex of the lateral talus, subchondral bone of subtalar joint, calcaneocuboid joint was (11.41±3.22), (6.59±2.22), (34.58±3.75) mm, respectively. The horizontal angle between the ST screw and foot plantar surface was (-1.17±2.07)°. The anteversion angle of ST screw was (16.18±2.05)° and the length was (41.64 ± 3.09) mm. There were significant differences in the length of upper and lower edge, the length and height of the midline, the distance from P' point to the apex of the lateral talus, subchondral bone of subtalar joint, and calcaneocuboid joint, and the anteversion angle and length of the ST screw between males and females ( P<0.05). There was no significant difference in above all parameters between left and right sides ( P>0.05).
Conclusion: After appropriate reduction of the calcaneal fractures, the entry point of ST screw was recommended at about 14 mm posterior and about 3 mm upper related to the foot horizontal line through the lowest tarsal sinus point; and the direction of ST screw placement was about 17° anteversion for males and 15° anteversion for females.
目的: 探讨跟骨载距突（sustentaculum tali，ST）解剖特点及跟骨后距下关节面 ST 螺钉固定恒定骨折块（constant fragment，CF）的安全入口位置和植入方向。.
方法: 从 2016 年 1 月—4 月收治并行足踝 CT 扫描的 100 例跟骨骨折患者中，纳入 33 例符合选择标准的患者资料。男 18 例，女 15 例；年龄 18～60 岁，中位年龄 41.0 岁。骨折侧别：左侧 16 例，右侧 17 例。将 CT 扫描原始数据导入 Mimics 17.0 软件，建立跟骨三维模型；测量 ST 上缘长度、下缘长度、中线长度及高度、ST 中线与足底水平面成角，ST 螺钉入口（P’点）位置、植入角度相关参数以及 ST 螺钉长度。比较不同性别及侧别间各测量参数的差异。.
结果: 跟骨 ST 上缘长度为（16.60±2.23）mm、下缘长度（20.65±2.90）mm、中线长度（20.56±2.62）mm、中线高度（9.61±1.36）mm，ST 中线与足底水平面成角（23.43±3.36）°。P’点至跗骨窦最低点垂直距离为（3.09±1.65）mm、水平距离为（14.29±2.75）mm，P’点至距骨外侧突顶点距离、后距下关节面软骨下骨距离以及跟骰关节面水平距离分别为（11.41±3.22）、（6.59±2.22）、（34.58±3.75）mm。ST 螺钉与足底平面成角（–1.17±2.07）°、前倾角（16.18±2.05）°。ST 螺钉长度为（41.64±3.09）mm。其中，男性 ST 上缘长度、下缘长度、中线长度和高度，P’点至距骨外侧突顶点距离、后距下关节面软骨下骨距离、跟骰关节面水平距离，ST 螺钉前倾角及长度，均显著大于女性（ P<0.05）。以上测量参数左右侧比较，差异均无统计学意义（ P>0.05）。.
结论: 跟骨骨折复位后采用经跗骨窦最低点平行足底后方约 14 mm、上方约 3 mm 确定入口，男性前倾约 17°、女性前倾约 15° 植入 ST 螺钉。.
Keywords: Calcaneal fracture; constant fragment; entry point; screw placement; sustentaculum tali.