Background
Calcaneal fractures comprise approximately 60% of tarsal bone fractures and approximately 2% of all fractures [
1,
2]. These fractures can be intra-articular or extra-articular; intra-articular fractures comprise approximately 75% of all calcaneus fractures. The primary fracture line is oriented from plantar-medial to dorso-lateral and therefore creates the sustentacular fragment that varies in size based on the fracture line [
1,
3‐
5].
The current surgery options for calcaneal fractures are closed reduction, percutaneous fixation, or open reduction with internal fixation (ORIF) [
4]. The best method in achieving calcaneal anatomic reduction and morphology restoration of articular surface is believed to be ORIF [
6].
Correct placement of the sustentacular screw is one of the critical procedures during the ORIF of calcaneal fractures [
7,
8]. The functions of the screw have been demonstrated both biomechanically and clinically. Pang QJ [
8] proved that sustentacular screw placement was essential for the stability of the posterior facet based on the finite element model. A clinical study [
6] showed that the absence of a sustentacular screw in calcaneal fractures would cause the decrease of Bohler’s angle in long-term follow-up.
However, because of the lateral position during operation and the limited surgical exposure, accurate insertion of the sustentacular screw is technically difficult. Misplacement of the sustentacular screw jeopardizes many important structures around the sustentaculum, such as the subtalar joint, flexor digitorum longus, flexor hallucis longus, and neurovascular bundle, and may result in poor outcomes [
6,
7,
9].
Previous studies have proposed some techniques to improve the success rate of sustentacular screw insertion. Bussewitz BW [
9] determined the starting point and the inclined angle of the sustentacular screw in their anatomical study. He noted the screw should be inserted approximately 16 mm posterior to the ST reference point with an angle of approximately 30 ° from posterior and lateral to anterior and medial. However, this approach still greatly depends on the experience of the surgeons. Recently, the navigation system and the 3D fluoroscopic technique have been introduced to facilitate the screw placement; however, these techniques are relatively difficult to popularize because of the equipment limitations [
10].
Therefore, the goals of this study are (1) to design an assistant guidance device that can be easily operated and can effectively improve the accuracy of sustentacular screw placement and (2) to compare the accuracy of guidance-assisted technique with traditional screw placement performed by an experienced foot and ankle surgeon. Our hypothesis is that with the help of the guidance device, the success rate of sustentacular screw placements will be improved.
Discussion
Calcaneal fractures are commonly seen injuries in the foot and ankle, comprise approximately 2% of all fractures and account for approximately 65% of all tarsal bone fractures. When the calcaneal fracture occurs, the calcaneus can be compressed and the posterior articular surface be comminuted because of the vertical pressure from the talus. However, as a result of the strong stabilized structures of the tendons and ligaments around the sustentaculum tali, the displacement of the sustentaculum tali rarely occurred in the calcaneal fractures [
12]. Therefore, the sustentacular fragment is frequently the foundation for calcaneal fracture reduction because of its limited displacement [
6,
7].
Although no consensus has been achieved regarding the treatment of calcaneal fractures, ORIF is still the primary method in most conditions [
1,
4,
5]. Previous clinical and biomechanical research has demonstrated that anatomical reconstructions of displaced intra-articular calcaneal fractures contributed to providing better long-term outcomes compared with other therapies. Buckley R [
13] conducted a multicenter RCT of 471 displaced intra-articular calcaneal fractures and found that ORIF reduced the risk of arthrodesis by 83% compared with non-operative treatment. Marcel Csizy [
14] analyzed the clinical outcome of patients who failed after primary conservative or ORIF treatment of a displaced intra-articular calcaneal fracture. They discovered that the ORIF treatment had one-sixth the likelihood of secondary subtalar fusion.
Recent studies have also confirmed that sustentacular screw placement is essential to restore the stability of subtalar posterior facet [
2,
8,
9]. Incorrect placement of the sustentacular screw usually injures surrounding important structures and might result in severe complications such as arthritis of the subtalar joint, persistent pain and swelling of the medial hindfoot, chronic impingement of the FHL tendon, paraesthesia of the medial planta pedis, and tarsal tunnel syndrome [
15‐
17].
However, the success rate of accurate screw placement was not high enough when only relying on the anatomical experience of the surgeons [
10,
18,
19]. Geerling J [
10] found that during operations, sustentacular screws were intra-articular in 24% of the cases and penetrate the medial calcaneal cortex in 16% patients as documented by 3D scans.
Some previous studies contributed to improving the accuracy of screw placement. Phisitkul P [
11] determined the best trajectory for sustentacular screw insertion based on computational 3D bone model research. They found that the sustentacular screw should be approximately 40 mm in length and should start 15 mm below the posterior facet of subtalar joints. Bradly W [
9] described the anatomical morphology and anatomic landmarks of sustentaculum tali that can help target the “constant fragment” screw placement for calcaneal fractures. However, these studies were based anatomically on the structure and morphology of sustentaculum tali that still greatly rely on the surgeons’ experience.
A recent study reported using navigation techniques to reduce errors when placing sustentacular screws. Gras F [
20] evaluated the accuracy of sustentacular screw placement using different navigation procedures including 2D navigation, 3D navigation, and fluoro-free navigation compared to the traditional procedure. Although they discovered that the 3D navigation procedure provides the best orientation, there was no significant improvement observed in the accuracy of screw placement compared with the traditional method. Furthermore, these techniques require complicated equipment and infrastructure in addition to experience in the surgical team.
In the current study, the success rate of traditional screw placement was 65% and was consistent with a previous study that reported 61% [
10]. With the assistance of the guidance technique, significantly higher accuracy could be achieved even when undergoing the procedure by a less experienced surgeon.
However, we noticed that, in the guidance group, there were still 5 out of 40 screw placements in which the screws were misplaced primarily, these were inferior placements. We considered that these failures were caused by one specific defect of the current guidance design. The anchor was relatively short, and there was an enlarged ball structure behind the anchor. Therefore, the anchor could not firmly fix to the sustentaculum and tended to move inferiorly with the skin when tightening up the guidance.
The present study demonstrated that in the four insertion entry points, the 30% entry point was associated with the highest accuracy while the 90% entry point had the lowest successful rate in both the guidance-assisted group and the traditional group (Fig.
5).
There were several limitations in the present study. First, the sample size was relatively small in both tested groups. Even with 40 screw placements, the guidance-assisted approach showed its obvious advantages over the traditional experience-based approach. Second, some defects still existed in the current design of the customized guidance as explained above and may result in inferior misplacement of the sustentacular screw. However, after certain modifications, the success rate of sustentacular screw placement may be further improved. Third, this study was in vitro and has not been proven in clinical trials.
Acknowledgements
The authors gratefully acknowledge the financial support by the National Natural Science Foundation of China under Grant numbers 81472037 and 81601862.