| Objective: Fractures of calcaneus are the most common tarsal bone fractures (60%). Operation is the main treatment for it. Lateral approach is often adopted in operation. Anteriomedial fragments including sustentaculum tali (ST) have the smallest chance of movement for the constraint of surrounding articular capsule, ligments and musculotendon in fracture of calcaneus. In addition, maximum stability can be obtained only if the screw fixing posterior articular facet is implanted in ST because of sclerotic solidity of ST and calcaneal hillock under the posterior articular facet of calcaneus,but ST can not be exposed directly from lateral approach as it locates on the medial side of calcaneus. The purpose of our study was to determine the projection of ST on the lateral side of calcaneus and to provide screw's position, angle and length in internal fixation to enhance the preciseness and safety of operation. Errant screw placement into the subtalar joint is one of the serious complications in open reduction and internal fixation of calcaneal fractures. So the fluoroscopy is very important to be used in operation. The fluoroscopy which can demonstrate the articular surface of the posterior facet includes a lateral radiograph, a Harris axial radiograph and Broden's views. Each method has its own advantage and shortcoming. We designed another experiment to compare the sensitivity, specificity, and accuracy of the three methods in demonstrating joint penetration by screws in order to provide reference to clinical surgeons. Methods: 60 embalmed adult foot samples were collected for this study. The regional anatomy and bony measurement about ST were carried out. Four Kirschner-wires were drilled along the long axis of the ST from the four apexes of the ST to the lateral wall of calcaneus and formed into an approximate rectangle of projection. The width of rectangle is approximately parallel to the posterior joint facet. The height of projection was prolonged to the posterior joint facet. Two juncts would be obtained .The measurement were taken in relation the rectangle, which include: the average width and height of the projection, the average distance from these two junctions to apex of Gissane'angle, the average distance from superior base line to the posterior joint facet, the average distance from the center of the projection to ST. The internal fixation of calcaneus were simulated to implant the screw into ST from the lateral wall of calcaneus according to the experimental data. There were totally 60 screws being implanted into 30 feet with two screws in each foot. Screws were observed whether they penetrated the joint or ST after opening subtalar joint. The measurement results wereregistered and all of data were analyzed by SPSS10.0 statistical software. Another 30 feet were encoded and two screws were implanted into ST of each foot from lateral wall of calcaneus simulating clinical operation. The tips of 30 screws were penetrated subtalar joints and the others were not. And then the lateral view, axial view and Broden's views were projected respectively to judge if the tips of screws were in or out of the joint. Sensitivity, specificity and percent correct interpretations were then calculated for each method. Difference tested was used by binomial u test. Results: The contour of projection was similar to rectangle. Its width was parallel to the posterior joint facet. The average width and height of the projection were 12.88mm and 10.60mm. The average distance from these two junctions to apex of Gissane'angle were 4.86mm and 17.74mm, respectively. The average distance from superior base line to the posterior joint facet was 6.34mm. The average distance from the center of the projection to ST was 50.16mm. The experiment results showed that 97 percent of the placement had correct positions. The sensitivities of methods for observing the screw in joint were significantly different. The sensitivities of lateral view, axial view and Broden's view of calcaneus were 57%, 63%, 100%, respectively. There was no significant difference between the groups of lateral view and axial view (P>0.05), but significant difference existed in between lateralview and Broden's view and in between axial view and Broden's view (P<0.01). It showed that the projection of Broden's view had the maximum sensitivity in judging if the tips of screw penetrated the joint and minimum false negative value. Every method for judging the tip of screw being out of joint had very low specificity. The specificities of lateral view, axial view and Broden's view were 63%, 60% and 80% respectively. The three methods had no significant difference (P>0.05). The percent correct interpretations of the three methods were significantly different. The percent correct interpretations of lateral view, axial view and Broden's view were 60%, 62% and 90% respectively. There was no significant difference between the groups of lateral view and axial view (P>0.05), but significant difference existed in between lateral view and Broden's view and in between axial view and Broden's view (P<0.05). It showed that the projection of Broden's view had the maximum the percent correct interpretations in judging if the tips of screw were in joint. So Broden's view is the first choice to judge the position of screw in operation. There was no significant difference between the results which came from experienced and unexperienced groups (p>0.05). Conclusion: This study defined the projection of ST at the lateral side of calcaneus. It established a "safety tunnel"between ST and the projection to enhance the preciseness and safety of operation. It also showed that the projection of... |
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