Anatomical parameters of sustentaculum Tali screw placement in the Asian population: A retrospective radio-anatomical study

3D simulation of percutaneous sustentaculum tali screw insertion in calcaneal fractures

BACKGROUND

In calcaneal fractures, the percutaneous screw fixation (PSF) is currently considered to be the better choice, but it is difficult to accurately place the screw into the sustentaculum tali (ST) during the operation. In this study, the ideal entry point, angle, diameter and length of the screw were calculated by simulating the operation process.

METHODS

We retrospectively collected the calcaneus computed tomography (CT) scans of 180 adults, DICOM-formatted CT-scan images of each patient were imported into Mimics software to establish calcaneus model. Virtual screws were placed on the lateral of the posterior talar articular surface (PTAS), the lateral edge of the anterior process of calcaneus (APC), and the calcaneal tuberosity, respectively, the trajectory and size of the screws were calculated.

RESULTS

The mean maximum diameter of the PTAS screw was 42.20 ± 3.71 mm. The vertical distance between the midpoint of the APC optimal screw trajectory and the lowest point of the tarsal sinus was 10.67 ± 1.84 mm, and the distance between the midpoint of the APC optimal screw trajectory and the calcaneocuboid joint was 5 mm ~ 19.81 ± 2.08 mm. The mean maximum lengths of APC screws was 44.69 ± 4.81 mm, and the Angle between the screw and the coronal plane of the calcaneus from proximal to distal was 4.72°±2.15° to 20.52°±3.77°. The optimal point of the maximum diameter of the calcaneal tuberosity screw was located at the lateral border of the achilles tendon endpoint. The mean maximum diameters of calcaneal tuberosity screws was 4.46 ± 0.85 mm, the mean maximum lengths of screws was 65.31 ± 4.76 mm. We found gender-dependent differences for the mean maximum diameter and the maximum length of the three screws.

CONCLUSIONS

The study provides effective positioning for percutaneous screw fixation of calcaneal fractures. For safer and more efficient screw placement, we suggest individualised preoperative 3D reconstruction simulations. Further biomechanical studies are needed to verify the function of the screw.

Modified Ni-Nail and C-Nail systems for intra-articular fractures of the calcaneus: A biomechancial study

OBJECTIVES

We have proposed a novel intramedullary nail (Ni-Nail) by incorporating a sustentaculum tali screw to improve the fixation stability of minimally invasive treatment for calcaneal fractures. This study aimed to evaluate the biomechanical characters of the Ni-Nail system and compare it with traditional C-Nail system.

METHODS

A finite element model of a Sanders type-IIIAB calcaneal fracture was reconstructed and fixed using two intramedullary nail systems, which was validated by a cadaver study. A vertical loading of 700 N was applied to the subtalar joint surfaces, and 525 N Achilles tendon tension was applied to the superior border of the Achilles tuberosity. The von Mises stresses and fracture displacements of both fixation models were evaluated.

RESULTS

The maximum von Mises stress of the screws of Ni-Nail and C-Nail were 27.92 MPa and 57.42 MPa, respectively, while that of the main nail were 67.44 MPa and 53.01 MPa. In addition, the maximum fracture displacement of the Ni-Nail was larger than that of C-Nail by 15.6% (0.37 mm vs.0.32 mm).

CONCLUSIONS

Our static simulation analysis showed that both Ni-Nail and C-Nail demonstrated similar biomechanical stability for calcaneal fixation. The Ni-Nail features a simple structure that is easier to operate and less traumatizing. Future studies may consider to further evaluate the clinical effectiveness by clinical trials and follow-ups.