Extra- and intra-articular distal tibia fractures account for 7% to 10% of all tibia fractures and present as a complex injury accompanying fibular fractures in 70% to 85% of cases.1) In addition, complications including delayed bone union, non-union, skin tissue necrosis, and joint stiffness commonly occur due to anatomical characteristics that are associated with increased vulnerability to accompanying injuries of the surrounding soft tissues, including severe comminution due to insufficient surrounding soft tissues, relatively poor blood supply, and thin periosteum.2) Open fractures due to high-energy flexion and rotational forces are also commonly involved.3)

The treatment of this subset of fractures remains controversial and challenging for most orthopedic surgeons. Some authors have suggested that bridging external fixation, with or without limited internal fixation, should be employed for high velocity injuries.4) Others suggest that primary open reduction and internal fixation (OR/IF) should be performed to avoid articular incongruence and the development of axial malalignment.5) However, a two-staged procedure involving primary external fixation and conversion to OR/IF is generally the treatment of choice when treating soft tissue swelling and comminuted fracture.6,7,8) This minimizes soft tissue complications and reduces problems caused by the external fixator itself.

During the conversion of conventional external fixation to definitive internal fixation, the external fixator must be removed prior to or during surgery. This facilitates surgical access to the fracture site and visualization of the fracture reduction and articular congruity using the C-arm. However, there is a high risk of loss of the previously achieved reduction, and articular incongruence may develop after removal of the external fixator, thereby prolonging the operative time and making it more difficult to perform definitive surgery.

To overcome such difficulties, we developed a novel box-frame type of external fixator that can offer parallel linkage between the posterior side of the tibial long axis and the calcaneus, correct the alignment of the fracture site using spanning and ligamentotaxis of the fracture site, maintain external fixators during definitive surgery, and aid in articular reduction and plate fixation. Herein, we report clinically satisfactory outcomes achieved using this box-frame type of external fixator.

In both groups, neither infection nor reduction loss around the pin-site was found while waiting for definitive surgery. The mean operative time of the definitive surgery was 62.4 minutes (range, 48–107 minutes) in Group A and 87.6 minutes (range, 53–123 minutes) in Group B (p=0.021). In addition, the mean radiation exposure time was 94.2 seconds (range, 45–132 seconds) in Group A and 152.6 seconds (range, 53–205 seconds) in Group B (p=0.030; Table 2). The mean time from the application of the temporary external fixator to the definitive surgery was 12 days (range, 10–17 days) in Group A and 13 days (range, 8–20 days) in Group B, showing no difference between the two groups.

Table 2
Outcomes of Box-Frame and Delta-Frame Groups

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Except for the 4 cases that presented with non-union, bone union occurred in 15.8 weeks in Group A and 17.2 weeks in Group B on mean, presenting no statistically significant difference (p=0.186). Although no statistically significant differences were found in angular deformity, ankle ROM, or the AOFAS score between the two groups, there were higher AOFAS scores in Group A than in Group B (Table 2).

Postsurgical complications of angular deformity ≥5° were observed in the final radiologic evaluation, with 2 cases of posterior angulation in Group A and 3 cases of valgus deformity in Group B. However, none of the cases in either group presented as malunion with an angular deformity ≥10°. Non-union was encountered in 2 cases from each of the two groups; all of the non-union cases resulted from open fractures, and bone union was achieved after conducting autogenous bone graft and plate augmentation. Superficial wound infection was encountered in 2 cases from Group A and 3 cases from Group B. Of the 5 wound infection cases, 4 improved with the use of antibiotics alone and 1 case (Group A, Gustilo grade II) recovered through debridement plus antibiotics.

In this study, compared to the conventional delta-frame external fixator, the box-frame external fixator provided better surgical visualization and sufficient space and allowed the surgery to be performed while maintaining ligamentotaxis (Fig. 1,2). This led to a reduction not only in the operative time but also in the radiation exposure as it can directly influence the health of both the operator and the patient. Furthermore, the use of a box-frame external fixator helps the easy anatomic reduction and eliminates the need to re-situate the external fixator on the tibia shaft and talus body to secure a better view of the joint (Fig. 3).

Fig. 2
(A) A simple ankle anteroposterior and lateral radiograph of a 71-year-old female patient presenting with an AO classification 43-B2 fracture and type II open fracture caused by a pedestrian traffic accident. (B, C) The alignment of the fracture site was corrected by conducting irrigation and debridement and applying the box-frame external fixator. (D, E) After allowing the soft tissue to rest for 10 days, tibia-fibular plating using a minimally invasive plate osteosynthesis technique was performed while maintaining the box-frame without other reduction. (F) Full bony union of the fracture site was achieved five months after surgery.

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Fig. 3
(A, B) A 54-year-old male patient who visited the hospital due to a traffic accident was diagnosed with ankle dislocation based on a physical examination and with a bilateral ankle fracture, posterior malleolar fracture, and medial gap widening based on simple ankle anteroposterior and lateral radiographs. (C, D) The valgus alignment of the ankle joint was corrected after performing traction by conducting irrigation and debridement and applying the box-frame external fixator. (E) Computed tomography performed afterward revealed the presence of a pilon fracture accompanying the anterior tibia intra-articular fracture. (F, G) Internal fixation was performed using the ligamentotaxis of the box-frame external fixator.

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Box frame external fixator is a square-shaped fixator that was designed from the idea of overcoming the inconvenience that temporary external fixator had to be removed when definitive surgery was performed to treat distal tibial fracture. This is the external fixator of the most optimal shape that satisfies all of complicated condition including maintaining the ligamentotaxis the same, providing good vision of surgical field during definitive surgery, and not disturbing the surgeon's procedure. These advantages can reduce radiation exposure and operative time and secure fixation strength with relatively simple method that is easy to follow by looking at pictures.

In terms of decreasing both infection rates and soft tissue complication rates with the use of an external fixator, many studies have reported good to excellent results for high velocity injuries.10,11,12) However, this cannot be regarded as a definitive treatment for these types of fractures, as secondary surgery with OR/IF is almost always essential. Depending on the location, the shape of the external fixator may vary by the severity and pattern of the fractures; in many studies, delta-frame external fixators have been positioned by placing half pins in a triangular shape on the anterior tibia shaft, the medial side of the foot, and the lateral side of the foot and aligned through the distraction of the fracture site.13,14,15) The advantage of the delta-frame external fixator is that it is stable as a bar is located on the shortest line linking the two pins regardless of the long axis. However, this also represents a disadvantage of the delta-frame external fixator, since it disrupts the view of the surgeons and the approach, reduction, and plate fixation processes, thereby necessitating removal of the external fixator to secure access for screw insertion. Moreover, the removal of the delta-frame breaks the ligamentotaxis and requires an additional procedure of ex-fix placement during the surgery in order to check the intra-articular lesion, thereby prolonging the operative time.

One study compared clinical outcomes between a unilateral ankle spanning external fixator and a hybrid ankle sparing external fixator that combined a unilateral frame with the Ilizarov system and reported a higher occurrence of malunion and traumatic osteoarthritis with the ankle spanning external fixator.16) This is thought to be because ligamentotaxis was not achieved by the traction of one axis alone with the unilateral external fixator. The Ilizarov external fixator has two or more wires that allow the alignment of the ankle joint to be maintained during the traction. However, the ability to maintain the Ilizarov fixator during OR/IF in definitive surgery is not expected due to the circular ring and wire of the Ilizarov. Good outcomes have been achieved through the use of the hybrid external fixator during definitive surgery depending on the condition of the soft tissue and the fracture pattern.17,18) However, anatomic reduction and stable fixation, which are the principle foundations of articular fracture treatment, are difficult to ensure with this type of external fixator, and long-term application may lead to increased risk of ankle joint stiffness and pin site infection.19)

Using another method of treatment, Tornetta et al.20) reported satisfactory outcomes after performing limited OR/IF in combination with the circular external fixator for the treatment of a pilon fracture, which is difficult to treat. However, this method also does not provide a direct view of the joint; hence, accurate reduction and fixation are still challenging and its use is limited in type C1 and C2 intra-articular simple fractures because the external fixator pins need to remain until bony consolidation is complete, which may inconvenience the patient. This highlights the difficulty of the treatment of pilon fractures despite the many treatment methods that have been proposed.21,22)

When proceeding with staged surgery keeping the external fixator intact, concerns of infection due to the external fixator may arise. Hak et al.23) reported that standard povidone-iodine alone was not sufficient to suppress the bacteria and that numerous bacterial colonies may exist on and be contacted through the crevices of the clamp while loosening it; in addition, a number of studies have argued that the infection rate must be reduced by performing many steps of pre-draping procedure.23,24,25) In the present study, every surgery was performed using a three-step disinfection procedure and the infection rates were not higher in the patients who underwent surgery after removal of the external fixator. When loosening of the clamp was needed, alcohol was sprayed around the clamp and the superficial glove was changed.

The box-frame external fixator configuration has some disadvantages. Structurally, it is not as rigid as the delta-frame or ankle spanning frames. Thus, it is recommended as a temporary fixation for distal tibia-fibula fractures prior to conversion to definitive internal fixation. We believe that its stability may be increased by using a single Denham pin instead of two half pins in the calcaneus, since this reduces the bending forces caused by the cantilever mechanism. In the cases of severe articular comminution and joint depression, ligamentotaxis may not provide adequate reduction and distraction of the spanning external fixator may interrupt the articular fracture reduction. However, because this is due to a fracture characteristic rather than a problem with the box-frame fixator, it can be resolved by loosening the distal clamps of the box-frame fixator during surgery.

This study was limited by the relatively small number of patients, as only patients who underwent fixation through staged operations, rather than all patients with distal tibia fractures, were included. Patient compliance was not considered in this study. A relatively short follow-up period limited the evaluation of clinical outcomes such as traumatic arthritis, which is a late-stage complication occurring in some intra-articular fracture patients. However, the effectiveness of this fixation method was still evident considering that the severe complications of general fractures usually occur at an early stage postoperatively. Lastly, this was a retrospective study to evaluate the effectiveness of the box-frame external fixator based on clinical and radiologic outcomes; further prospective research is required.

In staged operations for distal tibia fractures, application of the box-frame external fixator enabled reduction and fixation using ligamentotaxis through spanning without removal of the external fixators during definitive surgery. Therefore, box-frame fixation may be a useful method that reduces the operative time and radiation exposure, makes the surgery relatively easy, and provides both excellent surgical visualization and sufficient space for all stages of the procedure.