The stability of the LCP plays a major role in determining the healing process of complex fractures. Studies have shown that the main factors affecting LCP stability include plate length and thickness, number and distribution of screws, plate length, distance between the plate and the bone surface, and LCP placement [23, 24]. Kanchanomai et al. [23] suggested that the structural stability of the LCP for external fixators of the tibia in stable fractures (fracture gap of 1 mm) allows patients to undergo early partial weight-bearing after surgery, whereas in unstable fractures (fracture gap of 5–10 mm), the fixation stability is lower than the former, and the failure rate of early weight-bearing external fixators is higher.
In an experiment investigating the relationship between the distance between the LCP and fracture healing, it was shown that the distance between the LCP and the bone surface did not change much in the structural stability of the LCP for distances less than 2 mm; when the distance was greater than 5 mm, the axial compression strength of the LCP decreased by 63%, and its structural stability was greatly reduced [22]. Ching-Hou Ma et al. treated 52 open tibial fractures using the tibial LCP as an external fixator for 38 months of follow-up [25]. They performed both static axial compression and torsion tests to assess the strength of this fixation technique. The results indicated that the distal tibial LCP external fixator was not as strong as standard internal locking plate constructs, thus necessitating further biomechanical studies to improve structural strength. It has been found that LCP external fixator stability decreases with increasing distance and provides good biomechanical stability only when the limiting distance between the LCP and bone is less than 30 mm [20, 24]. Therefore, the farthest distance between the bone and LCP was selected as 30 mm in this study. The distance between the bone surface and the plate significantly affects the stiffness of the LCP, and in this paper, by studying the IT-44, ET-44 and EF-44 groups, the results showed that the stability of the LCP decreases with increasing distance, which is consistent with the results of related reports [24].
Liu et al. found that increasing the screw diameter and plate size significantly improved torsional stiffness but had little effect on compression stiffness. This confirms that the biomechanical stability of the distal femoral LCP is superior to that of the distal tibial LCP and is more suitable as an external fixator for the treatment of lower tibial fractures, which is consistent with the results of this study [24]. In this study, by changing the size of the plate and the diameter of the screw, it was found that the torsional and bending stability of group EF-44 was higher than that of group IT-44 and group ET-44, and group IT-44 was higher than that of group ET-44. In terms of compression resistance, group IT-44 had a higher compression stiffness than group EF-44 because it was attached to the bone surface, while group ET-44 was the worst. Although the axial compression stiffness of the distal femoral LCP external fixator was insufficient, the axial compression stiffness was higher than that of the distal tibial LCP external fixator, and the bending and torsional stiffness were higher than those of the distal tibial LCP external fixator and distal tibial LCP internal fixator. Bottlang [35] used a locking plate to fix femoral fractures 1 mm away from the bone surface to investigate the effect of its structural stiffness on fracture healing, and it was found that this fixation method made the axial micromotion of the fracture and could stimulate osteogenesis at the fracture site, thereby promoting fracture healing. According to the biomechanical properties of the structure in this study, the LCP of the distal femur can perform elastic fixation at the fracture site, and we speculate that this fixation method can produce axial micromotion at the fracture site and stimulate osteogenesis at the fracture site to promote fracture healing [20, 24, 34, 36,37,38].
Studies have found that the LCP can also achieve similar torsional and flexural stiffness with the selection of a smaller number of screws for fixation [39,40,41,42]. All three EF groups had higher flexural stiffness than group IT-44 and group ET-44, group EF-44 and group EF-33 had higher flexural stiffness than group IT-44 and group ET-44, and group EF-22 had a similar torsional resistance to group IT-44. The number of plate screw fixations had a significant effect on the stability of the plate [41, 42]. A study comparing the three EF groups showed that in terms of compression resistance and flexural stability, the stability decreased with the decrease in the number of screws, proving that the distal femoral LCP external fixator has good biomechanical stability and adjustability. However, there was no statistically significant difference in torsional stiffness between the two adjacent groups of the three EF groups, proving that a small increase in the number of screws would not significantly increase the torsional stiffness. The elastic fixation of the steel plate can produce axial micromovement at the fracture end, and the stress stimulation of axial micromovement can promote fracture healing [20, 24, 34,35,36,37]. LCP external fixation of the distal femur has biomechanical adjustability. During fracture healing, the LCP fixation strength is gradually reduced by gradually decreasing the number of screws, thereby reducing stress shading and generating axial micromotion at the fracture to stimulate osteogenesis, thereby promoting fracture healing and shortening the time to healing.
For the first time, in a biomechanical study of the stability of fixators for lower tibial fractures, this paper presents a comprehensive study of conventional external fixators, internal tibial LCP fixators, external tibial LCP fixators, and external distal femoral LCP fixators. Hoenig, Yang, and Liu et al. found that distal femoral LCP external fixators had approximately the same stiffness as standard plates or Ilizarov fixators, consistent with the experimental findings in this paper [24, 43, 44]. The biomechanical stability of the steel plate clearly influences the healing of the fracture, and fixator structures that are either too stiff or too flexible will hinder fracture healing and lead to delayed healing or bone nonunion [24, 45]. In this study, the CEF-22 group was found to have the best biomechanical stability, but most of the external fixators were unstable, and a few were fixed with too much strength and would produce stress masking. Both of these conditions can lead to bone nonunion and delayed healing, which are also common in clinical practice. Moreover, prolonged fixation of the external fixator across the joint can lead to functional stiffness of the joint. In addition, the large size of the external fixation frame can cause inconvenience and psychological problems for patients. The biomechanical results of this study showed that tibial LCP external fixation had the worst compressive, flexural and rotational stability, which is consistent with the reported results [24]. The stability against compression, bending and rotation of the distal femoral LCP external fixator was higher than that of the distal tibial LCP external fixator, but the axial compressive stability of the distal femoral LCP external fixator was lower than that of the distal tibial LCP internal fixator. This is because the closer the LCP distance, the more structural the splice plate is [24]. However, its moderate flexibility may promote fracture healing. Therefore, for the selection of an external fixator for the treatment of lower tibial fractures, the distal femoral LCP is superior to the distal tibial LCP.
Zhou et al. used a locking compression plate as an external fixator to treat closed distal tibial fractures with soft tissue injury [31]. This trial provided successful cases with high healing rates, comfortable clinical procedures, and good ankle motion; however, this medical treatment has limited indications. Therefore, to increase the clinical relevance of this study, a case of distal femoral LCP as an external fixator for lower tibial fractures is provided. LCP was originally designed for use as an internal fixator, as its use as an external fixator would be unethical and has limited indications [24, 31, 34]. Therefore, according to the purpose of this study, one patient selected for both conventional internal fixator and external fixator treatment was unsuitable. The hospital ethics committee and internal review board approved the study, and informed consent was obtained from this patient. Patient-related information was as follows: Male, 56 years old, crushed by a 2-ton weight of channel steel, closed lower tibial fracture with soft tissue injury (Fig. 5a, b).
According to the results of the above anatomical study, we treated this patient with external fixation with a 5 mm 10-hole LCP (Chuang Sheng Medical Equipment Co., Ltd., Jiangsu, China) of the distal femur, fixed with four and three 5 mm locking screws at the distal and proximal holes of the fracture, respectively. After the patient underwent closed reduction of the fracture with an external LCP fixator of the distal femur (Fig. 5c), functional ankle exercises were performed on the first day (Fig. 5d). Full weight-bearing was possible 2 weeks after surgery (Fig. 5e). Radiographs at 1.5 months postoperatively showed a small amount of bone scab formation at the fracture end (Fig. 5f). The reduction of 3 screws (1 proximal and 2 distal) at 2.5 months postoperatively was found to facilitate fracture healing after reducing the stress shading. Bony healing at 4.5 months postoperatively (Fig. 5g) allowed the removal of the external fixator plate. It can be hypothesized from this case that the external fixator of the femoral LCP has good biomechanical stability and adjustability for fracture healing when the technique is used in a standardized manner according to the anatomical study in this article.
This study concluded that distal femoral LCP promotes fracture healing with several advantages: (1) The soft tissue on the bone surface is the main source of blood supply to the fracture end, and a distal femoral LCP external fixator can reduce stripping and damage to the periosteum. (2) Because of the relatively thick distal femoral LCP plate, there are more screws at the distal end, and its locking screws are thick in diameter and long enough to fix both cortices, which has good stability. (3) As the fracture heals, the reduction in the number of screws not only provides good stability but also reduces stress shielding and allows early functional exercise to promote fracture healing. (4) The contour of the distal femoral LCP is similar to the curvature of the anteromedial tibial side, and the plate can be placed closer to the skin on the anteromedial side. The patient can wear socks and pants normally to cover the plate after surgery, which meets the patient’s aesthetic needs. (5) The distal femoral LCP is made of titanium alloy, which is lightweight, inexpensive, and histocompatible and has high patient acceptance. Moreover, it is easy to remove after surgery to avoid secondary surgical injury.
For lower tibial fractures, the distal femoral LCP is more suitable for use as an external fixator than the tibial LCP and conventional external fixators [24], and this trial confirms this view. Therefore, the distal femoral LCP deserves to be promoted as an external fixator. In this study, the distal femoral LCP was found to have higher axial compression stiffness, torsional stiffness, and flexural stiffness, making it a better choice for external fixator treatment of lower tibial fractures. Although this study showed that the distal femoral LCP external fixator for distal tibial fractures can provide adequate stability, it is important to recognize the limitations of this study: first, we used a composite tibial model and did not use real human bone, which cannot simulate real human weight-bearing. Second, the effect of muscle forces, etc., was not considered, and this experiment was a static test, which cannot simulate the stability of the plate during motion,. Third, there was no further study of the effect of the number and distribution of screws on the stability of the plate. Fourth, there was no assessment of the LCP stability when axial micromovement was produced at the fracture end. Our team will continue to enhance subsequent trials to provide a sufficient basis for the clinical use of distal femoral LCP external fixators for distal tibial fractures.
Despite the shortcomings of this trial, a distal femoral LCP is still recommended for use as an external fixator for the treatment of distal tibial fractures. Considering all the advantages and risks, the indications should be understood and used with caution [24, 31, 32, 34, 38]. However, it is still possible that a distal femoral LCP external fixator can be used as an external fixator for lower tibial fractures. Although this fixation method cannot replace conventional incisional internal fixators, the use of distal femoral LCP external fixators may yield unexpected clinical results in cases of severe soft tissue problems associated with lower tibial fractures, which can cause serious complications with the use of conventional internal fixators and common external fixator frames. This technique embodies both the minimally invasive and fast track surgery (FTS) concepts. It can be used as both temporary fixation and ultimate fixation and is a treatment modality worth promoting.