An experimental study on the digital precision of internal fixation via the sinus tarsi approach for calcaneal fractures

Objective: To investigate the effectiveness and accuracy of internal fixation of calcaneal fractures with a three-dimensional (3-D) printing navigation module via the sinus approach. Methods: Eleven lateral lower extremity specimens were used in the experiment and divided into the digital design (DD) group (n = 11) and the real surgery (RS) group (n = 11). For the DD group, thin-section computed tomography (CT) scans, virtual fracture modeling, virtual bone plate fixation, sinus occlusal module design, and navigation module design were performed for the cadaver specimens. A 3-D navigation module was printed using a 3-D printer. For the RS group, the sinus approach incision was made, and the navigation module was used to assist the placement of screw fixation and anatomically locked bone plate fixation. Thin-layer CT scans, 3-D reconstructions, and reconstruction of the nail paths were performed in the RS group and 3-D registered with the DD group. 3-D coordinate values for the screw entry and exit points in the RS and DD groups were recorded, and the corresponding offset values of the screw points were calculated. The number of qualified nails at different accuracy levels was counted. The chi(2) test was used to compare the data for the DD and RS groups to obtain the accuracy level for both groups when p > 0.05, which is the critical value for experimental accuracy. Results: A total of 11 bone plates were placed and 120 screws were locked. None of them protruded from the inferior articular surface. The screw entry and exit point offsets were 1.71 +/- 0.11 mm and 3.10 +/- 0.19 mm, respectively. When the accuracy requirement for the entry point was 3.8 mm, there was no statistically significant difference between the two groups (p > 0.05). Similarly, the accuracy of the exit point of the screw could only reach 6.6 mm. Conclusion: Internal fixation of calcaneal fractures via the sinus tarsi approach with an anatomical locking plate based on the 3-D printing navigation module can achieve accurate screw placement and good overall internal fixation.