The fixation of calcaneal fractures aims to provide substantial stability, enabling early motion and weight-bearing without compromising the achieved reduction while minimizing soft tissue dissection4,13 The use of screws and minimally invasive LCP for fixation in calcaneal fractures has been proposed to minimize soft tissue dissection and yield favorable clinical results (Wilmsen et al. 2022; Ebrahimpour et al. 2021; Luo et al. 2022; Ivanov et al. 2022 and Song et al. 2023). Nevertheless, ongoing debates persist regarding the stability of this construct and its ability to maintain fixation until complete healing is achieved. Addressing this concern necessitates conducting biomechanical and clinical studies to comprehensively understand the construct's stability and effectiveness in sustaining fixation throughout the healing process.
The minimally invasive LCP fixation in this study employs double-point fixation, which can be performed with less soft tissue dissection compared to triple-point fixation but still involves more dissection compared to the screw fixation technique. The double-point fixation technique was demonstrated in a biomechanical study to maintain reduction after fixation (Lv et al., 2022). The biomechanical study shows that EQV stress distribution occurred on the implants, which can verify that the material will fail. However, it did not exceed the material yield strength. EQV stress distribution between the three devices is directly incomparable. So, the safety factor is the best choice in the discussion and comparison. If EQV stress is lower, the significance is that the safety factor is high. Figure 6 displayed the results of EQV stress in the TP with tuberosity device displayed a higher level than the SF and TP without tuberosity, respectively. Therefore, the factor of safety was arranged from highest to lowest; those are TP with tuberosity (7.98),
The SF (2.99) and TP without tuberosity (2.04) are, respectively, in type II. Conversely, in the case of type III, the factor of safety was arranged from highest to lowest: TP with tuberosity (3.76), TP without tuberosity (2.12), and SF (1.86), respectively. For the comparison between the same device and fracture type differently, the typical magnitude of safety factor on type II exhibited a higher than type III for these fixation devices except for TP without tuberosity. Therefore, lower failure is TP with tuberosity in type II, type III, SF type II, TP without tuberosity type III, type II, and SF type III, respectively. However, to compare with the device's stability, we considered the strain on the fracture site standard gold. A high fracture site strain value means low fixation stability, while low strain values indicate high fixation stability. In this previous study for effective bone remodeling connection, we used the standard gold in the strain distribution, which should be recommended to less than 2% of the fracture site gap. If the strain of the fracture site level is between 2% and 10%, the fibrocartilaginous callus formation may take up to 4–6 weeks. Hematoma formation will have poor performance and may take more than six weeks to recover the bone for the strain on fracture sites above 10%. Therefore, the results found that the magnitude of strain on the fracture site occurred near the region of the joint facet due to the axial force direction to the joint facet. Comparatively, the strain on the fracture site in the case of SF fixation was highest, with TP without tuberosity and TP with tuberosity, respectively, under the same fracture type. Therefore, TP with tuberosity fixation has more stability than TP without tuberosity and SF fixation devices. In the clinical study, this research demonstrates a comparable immediate postoperative quality of reduction for both screw fixation and minimally invasive LCP fixation. However, during follow-up, a more significant loss of reduction is observed in the screw fixation group, indicating that this group provides less stability than minimally invasive LCP fixation in joint depression-type calcaneal fractures. The functional outcome of calcaneal fractures is correlated with Bohler’s angle (Loucks and Buckley 1999; Su et al. 2013; Mallya et al. 2024). This study also reveals a better functional outcome in the minimally invasive LCP fixation group, which exhibits a superior Bohler angle compared to the screw fixation group.