Fractures of the distal tibia are usually the result of combined compressive and shear forces and may involve metaphyseal instability, articular depression and soft tissue injury. Injury complexity, lack of muscle coverage and poor vascularity make these fractures difficult to treat. The ideal treatment modality for distal tibial fractures is controversial, and depends on fracture morphology, displacement and comminution. Surgical treatment of distal tibial fractures includes several options: external fixation, intramedullary (IM) nailing, ORIF and MIPO. However, none of these methods are ideal. External fixation is very useful as a temporary option for skeletal and soft tissue traction, but may result in malalignment, malunion, nonunion, pin tract infection and ankle stiffness if used as a definitive treatment method [15, 16]. IM nailing has been proposed as a good option due to the biologic concepts of fixation and load sharing. However, concerns about the routine use of IM nails for distal tibial fractures include instability, malunion and non-union . These risks are particularly concerning in the setting of an open fracture, where a higher incidence of complications was noted after IM nailing. IM nailing was also associated with greater post-operative malalignment than plating [18, 19]. Precise reduction of the articular fragments can be achieved with ORIF, and this methodis therefore used to restore the anatomic structures of the joint surface. However, ORIF requires widespread dissection of the soft tissues, which can lead to increased rates of infection and soft tissue complications. ORIF has also been found to alter the blood supply of the tibia, which may lead to delayed union or nonunion [2,3,4].
The MIPO technique permits indirect fracture reduction and stable fixation with minimal soft tissue dissection by maintaining the fracture hematoma. The fracture is primarily reduced by ligamentotaxis, and plating is performed percutaneously using a minimally invasive technique. The use of indirect reduction techniques has led to improved fracture-healing and reduced the need for bone-grafting compared with older direct reduction techniques .Consequently, MIPO has recently been recognized as an ideal choice for the treatment of distal tibial fractures [6,7,8,9, 21].
To maximize the advantages of MIPO osteosynthesis over other fracture reduction techniques, exposure of the metaphyseal and diaphyseal fragments should be avoided. This means that careful indirect reduction of the fracture is necessary prior to definitive fixation. Not only is indirect reduction a challenge for surgeons who are used to open techniques, but the maintenance of any achieved reduction can be difficult until it is held in place with the plate. Indirect fracture reduction often necessitates applying considerable force to displace one or both ends of the broken bone against the natural forces of the muscles and tendons.
Manual traction is an indirect reduction technique. Manual traction is performed by the surgeon and medical staff, occasionally with the help of an image intensifier to evaluate the reduction. There is always danger of over-distraction with this technique, which may result in unnecessary muscle, tissue and ligament strain during the manipulation process, and of excessive x-ray exposure that is undesirable for both the patient and the medical staff. Furthermore, due to the large holding forces that are necessary to reduce the fracture, exact ‘first time’ positioning is virtually impossible. What is needed is a mechanical system to permit the precise positioning of the fractured bone ends without the need for multiple docking attempts. Bony fragments need to be held in correct alignment as long as necessary while osteosynthesis is performed .
An AO distractor [8, 9] is a device-assisted indirect reduction technique. After Schanz screws are placed into the proximal and distal parts of the fracture, the fracture is distracted and reduced by manipulating the mobile elements of the device (Fig. 1B). Our study demonstrates that the use of an AO distractor results in a significantly shorter operative times, smaller incision lengths and lower blood loss compared with manual reduction alone. These differences indicate that an AO distractor is a satisfactory reduction device that can improve the efficiency of the operation. The reason for the benefits of the AO distractor may be that it helps to reduce the strain and fatigue that often accompanies manual traction. This percutaneous technique minimizes soft tissue insult and the disruption of fracture biology. Moed et al.  presented a series of 44 fractures of the tibia that required operative stabilization and were treated using an intra-operative external transfixion pin frame and IM nailing. For added reduction stability, the carbon fiber rod on the concave side of the angular deformity can be replaced with an AO/ASIF universal distractor. The authors’ technique shortens setup time, provides complete access to the distal tibia, and permits free manipulation of the limb, thereby facilitating nail insertion and placement of distal locking screws.
To the best of our knowledge, no clinical study has previously compared the outcomes of AO distractor-and manual traction-mediated MIPO for distal tibial fractures. The present work found no significant differences between the two techniques in terms of time until union, AOFAS score and range of motion. Kim et al. reported excellent AOFAS scores after MIPO and minimal ORIF (86.0 and 86.7, respectively) in patients with distal tibial fractures. Our study found that the mean AOFAS ankle scores were 90 in group A and 88 in group M, which were not significantly different. The satisfactory results following both treatment methods were probably because most of our cases were AO/OTA type A or type B distal tibia fractures (Table 1). Prior use of MIPO on AO/OTA type C distal tibia fractures was associated with worse functional outcomes compared with type A and B fractures. The complexity of AO/OTA type C fractures is mainly due to their commonly high-energy injury mechanisms, which have been shown to have higher complication rates and poorer long-term results than lower-energy partial articular type B or extra-articular type A fractures .
Complications associated with the use of MIPO in distal tibial fractures include skin impingement, malunion, delayed union and intra-operative saphenous nerve and vein injury [26, 27]. One patient (3.1%) in group A and three (11.5%) in group M that developed skin irritation, which was characterized by discomfort and pain around the medial malleolus. However, these symptoms were not severe and the plate was removed after bony union. No statistically significant differences in postoperative complications were observed between the two groups. Medial plates can cause skin irritation because they are located directly under the skin and the subcutaneous soft tissues on the medial side of the distal tibia are thin. Plate exposure can also occur when the medial plate is inserted . The skin incisions used in the present work were limited to one 2-cm-long anterior curved incision for plate entry and several 0.5-cm-long stab incisions for locking screws (Fig. 1C). Indirect reduction and subcutaneously applied plates respect the soft tissues and the periosteal blood supply. AO distractor and manual traction-mediated reduction of distal tibia fractures can not only improve operative efficiency, but also significantly reduce soft tissue injury.
Radiographic results were assessed at the final follow-up. There were no significant differences in mean varus deformity, valgus deformity, anterior angulation or posterior angulation between the groups. No patients had gross angular deformity. Mean tibial shortening was not significantly different between the groups, and no patient had tibial shortening of > 10 mm. Hasenboehler et al.  showed that varus or valgus angulation exceeding 5°, recurvatum or procurvatum exceeding 5° or rotation and shortening is beyond 5° represents significant malalignment. Sagittal plan deformity remains a common complication of MIPO. Malalignments of up to 20° are frequently observed. Vallier et al.  showed that 55% of patients who went onto malunion had open fractures, and that 85% of patients with malalignment after IM nailing did not require fibula fixation. The lack of adequate reduction aids explains the significant incidence of post-traumatic malalignment of the lower extremity. Our study demonstrates that the use of an AO distractor can significantly lower the rate of coronal plane malalignment compared with manual reduction alone, although there was no significant difference between the two groups. Malalignment may also be minimized by reducing the fracture via manual traction, maintaining that reduction with an AO reduction device and then fixing the fibula.
A limitation of this study was that no smoking and diabetes patients were included, although studies have shown that these conditions can lead to increased wound complications . There were also few subjects in each group.