Currently, numerous studies have confirmed the priority of bridging plate fixation by MIPO [6–20–21]. However, the stiffness and stress shielding resulting from the locking plate may inhibit callus formation and lead to delayed union or nonunion. Some studies noted that the stiff construct did not facilitate adequate callus formation because of inadequate motion [9]. Moreover, some other reports revealed that bridging fixation by a locking plate for simple tibia fracture can lead to delayed union and suggested fixation of absolute stability [5–6]. Wenger and his colleagues [22] compared absolute stability with relative stability for simple distal tibia fracture by MIPO, and found that the median time to radiological was 19 weeks in the absolute fixation group and 27 weeks in the bridge plating group. However, whether the satisfactory reduction was achieved was not reported, which may be an interference factor for fracture healing. In this research, all of the fractures were fixed by relative stability, but we did not note prolonged healing time, with 4.06 ± 1.20 months in LCP group and 4.43 ± 1.66 months in the FCL group for radiological union. This may be attributed to the overall satisfactory reduction, as excellent reduction can accelerate fracture healing. Moreover, Plecko and his colleagues [23] also did not encounter prolonged healing when bridge plating was applied for simple fracture with satisfactory reduction.
Between the two groups, the patients’ demographics were comparable. The similar operative times demonstrated that the use of FCL screws did not increase the difficulty of fixation. The time to radiological fracture union, time to full weight bearing, and complications between the two groups did not show a significant difference, which may be due to the protection of the blood supply that promoted fracture healing and principles of fixation was adhered in both groups The data resembled the research of Wenger and his colleague, who compared absolute fixation with bridging fixation of simple tibia fractures and found that the median time to full weight bearing was 10 weeks [22]. A previous study reported the rate of malalignment and infection after plating for distal tibia by MIPO was low [24]. The anatomical reduction was achieved during operation and no high-grade open fracture was included in the trial; thus, there was no malalignment and the rate of infection was also very low.
The callus formation and RUST in the FCL group was significantly higher than those of the control group, which may imply that the FCL construct promoted fracture healing. The FCL construct possessed some important features shown to enhance fixation and fracture healing, which are as follows: flexible fixation, progressive stiffening, and parallel interfragmentary motion. Compared with the locked plating construct, biomechanical testing confirmed that the FCL constructs reduced the stiffness by 60–88%, similar to that of an external fixator, which significantly increases the axial interfragmentary motion but not shear motion [13–14–25]. The interfragmentary motion was also controlled in the proper range from 0.2 to 1 mm, which is known to promote callus formation. As callus formation represents the micromotion at the fracture site, the interfragmentary motion in the FCL group was inferred in the proper range for fracture healing. In fracture-healing mode, the FCL group exhibited a symmetric callus formation and had a greater callus volume and stronger fracture healing compared to the locked plating specimens [26]. Conversely, the callus in the control group was insignificant, which may refer to the lack of micromotion and callus formation at the fracture site. Given that this research was a retrospective analysis and CT was not routinely carried out to assess fracture healing, symmetrical callus formation in the FCL group cannot be revealed directly.
Clinical studies concerning FCL screws are limited, and only a few studies have assessed the clinical effect of the screws on lower limb fracture. Adams et al. reported that the FCL screw construct decreased the nonunion rate and complications for distal femoral fracture, showing that it may be a promising construct for fracture [27]. Galal created the FCL screw construct by near-cortical overdrilling for fixation of distal femur fracture, and the result demonstrated that all patients achieved an average union time of 13.4 weeks and a callus score of 1.8 [28]. Ries and his colleagues followed 18 patients with periprosthetic distal femur fractures who were treated by FCL constructs, and they discovered a high healing rate and that the callus was more robust and uniform compared to their previous experience with locking plate periprosthetic distal fracture [29]. However, Rice and his colleagues retrospectively reviewed 22 tibia fractures treated with the FCL construct or standard plating and found that the FCL implants were not superior [30]. This result may be due to the small cohort size and the diversity of the fracture types included, which decreased the difference between the two groups. Kidiyoor and his colleagues [31] discovered uniform callus formation and minimal complication rates for periarticular fracture treated with FCL screw constructs, and the average time for complete union was 20 weeks in tibial fracture, which was comparable to the results of the present study. Wang and colleagues retrospectively analyzed 76 patients treated with FCL screw constructs and 68 patients treated with plating techniques, and the results revealed that the average union time in the FCL group (2.8 ± 0.9 months) and RUST were superior to those of the standard plating techniques [32]. The majority of those researches demonstrated the advantage of the FCL construct for fracture healing, which coincides with our study.
However, there are still a few limitations in our study. First, this was a retrospective analysis, which reduced the level of evidence, and potential confounders could influence the outcome. Second, although there was a comparative control group, the cohort size was small, which decreases the statistical power. Third, CT was not routinely performed to assess healing, and callus formation at the fracture site could not be assessed accurately, especially the callus at the near cortex.