The theoretical basis of Ilizarov's technology is the tensionstress law, in which the living tissue is subjected to sustained, slow, and stable traction to produce tension that stimulates the regeneration and growth of the tissue[15]. Currently, it has emerged as the gold standard for the treatment of massive tibial bone defects, eradicating infection and solving bone and soft tissue defects at the same time. Bone transport tecnique include distraction and consolidation period. The distraction period is generally 7 to 10 days after osteotomy, the bone segment is transported at a rate of 1 mm/d to reach the expected extended length and then enters the consolidation period, and the external fixator is removed after the newly formed bone is completely consolidation[16]. As a result, large bone defects tend to require longer EFT and increases the frame-related complications such as pin-tract infection, pin loosening, joint stiffness and psychological symptoms[17].
Several authors have addressed different treatment options in order to shorten treatment period and reduce the incidence of complications. Apivatthakakul[18] successfully cured 2 cases of distal femoral bone defects using MIPO technique combined with external fixator, and although the alignment of the docking end was maintained, it has also been found that the built-in plate affects the generation of callus at the bone end[19]. Liodakis[20] found that external fixation combined with intramedullary nail technique not only shortens the EFT. Moreover, combined external and internal fixation was found to have a greater risk of infection recurrence in the treatment of infected tibial nonunion and chronic osteomyelitis. Some more options of a combined technique have been reported, such as a lengthening nail for transport and a locking plate for docking and a carbon-fiber IMN[21]. However, besides its high cost, it was found clinically that the nail performs poorly in long-bone surgery and cannot be added to external fixation instead of a titanium nail even for combination.
Because accelerated lengthening at one osteotomy site is not possible due to biological and neurovascular considerations, the solution was to add one osteotomy while lengthening, ideally doubles the rate of lengthening effectively. Borzunov[22] first used double-level bone transport using the Ilizarov technique to treat large tibial bone defects, with a 2.5 times shorter docking time and a 1.3–1.9 times lower EFT compared with the single-level bone transport. Similarly Paley and Maar et al[23] recommended double-level bone transport for bone defects greater than 10 cm in order to shorten the EFT. It has also been suggested that trifocal bone transport should be considered when the defect length is over 6 cm[24]. However, the above studies did not describe complications, and bone or functional outcomes in the two groups.
We also compared the above two methods in this study, the mean bone defect length was greater in the TF group than in the BF group (P < 0.05). Although there were no statistically significant differences in DT, CT, and EFT between the two bone transport modes, the means of these data were smaller in the TF group than in the BF group, and the mean EFI was shorter in the TF group (P < 0.05). This finding suggests that despite the increased complexity of the TF group, it may provide a rapid recovery pathway.
Trifocal bone transport equates to faster docking contacts, which leads to early docking healing[25]. we anticipated that the addition of an osteotomy to the TFT would increase complications associated with the wires and distraction sites. In the study, the complication rate was 1.6 per patient in BF group and 1.7 per patient in TF group, the results showed no statistically significant complication rate between the two groups (P = 0.956). Possibly due to the relatively early frame removal in the two-level group. Therefore, we believe that the occurrence of complications may is associated with longer EFT. According to our experience and study, we recommend trifocal bone transport was performed when if the bone defect is more than 8.0 cm.
Some authors found that hypoplastic bone formation may occur during defect filling when single-level distraction regeneration growth exceeds 5 cm or 40% of the original segment length[26]. Chaddha[27] applied trifocal bone transport to treat tibial bone defects and had a higher incidence of delayed consolidation, which was caused by the the more distal osteotom and there was a high incidence of trauma to the nutrient artery in trifocal bone transport. The consolidation time of the distraction gap is also affected by blood supply, such that the closer the regeneration zone is to the metaphysis, the shorter the consolidation time[28]. No patient developed delayed consolidation in this study. This was done with both proximal-to-distal bone transport technique all cases in our study. In addition, the use of low-energy osteotomy techniques and adjustment of the lengthening rate may reduce the occurrence of such complications.
Although bone transport is widely used to treat large bone defects, some unavoidable complications have also been reported[29][30]. In our study, pin tract infection is the most common complication in 32 patients (66.7%), including 12 case in the double level group and 20 cases in the single-level group. Dahl[31] classified pin tract infection into Grade V according to severity. According to the above classification, twenty-eight patients were Grade I, three patients were Grade III and 1 patients were Grade IV. Most pin tract infections are treatable with improved wound care and a short course of oral antibiotics. One patients(Grade IV) suffered from a deep pin tract infection, which was successfully treated by pin replacement and intravenous antibiotics.
Our experience is that frequency of needle track cleaning did not reduce the rate of pin track infection, but rather increased allergic reactions around the needle track. In addition, dry sterile gauze is wrapped around each pin site to maintain dryness around the pins sites significantly reduced the incidence of pin tract infection.
Relevant literature suggests that nonunion is the rate-limiting step in bone transport for the treatment of bone defects[32]. Most scholars suggest that early revision and bone grafting can significantly reduce the incidence of nonunion when the transported segment had reached the target site[33]. In this study, 9 patients showed delayed union or nonunion at the docking site, which healed completely after freshening of the fracture ends with removal of any interposed soft tissue at the docking end.
In this study, 15 patients developed joint stiffness, and the incidences of muscle contracture, axial deviation, soft tissue incarceration, limb shortening, and fracture were 31.3% (15/48), 3.6% (16.7/48), 2.1% (1/48), 8.3% (4/48) and 2.1% (1/48), respectively. but all of them were finally solved by various means. No serious complications such as nerve and blood vessel injury occurred.
Our present study showed that both bifocal and trifocal bone transport achieved satisfactory bone and functional results in the treatment of tibial bone defects, and there was no significant differences in the incidence of complications between the two groups. All patients achieved complete healing at the docking site and consolidation in the regenerate bone.
The present study had several limitations. First, the sample is small and the data has a certain limitations. Second, it is difficult to exclude the influence of subjective factors of doctors in operation and results. Further investigations, especially muti-centered trails with a larger sample size should be conducted to overcome the limitations of our study.
Both trifocal and bifocal bone transport can yield satisfactory results for treament of complex segmental tibial defects. Trifocal bone transport significantly reduced the EFI without increasing the associated complications. According to our experience, there are many factors that can influence the success of distraction osteogenesis, such as a comprehensive understanding of the application of external fixators, careful selection of patients, timely follow-up and early detection of predicted complications throughout the treatment. They are specialized surgical techniques that require significant expertise to master. Bone transport is a specialized technique with a long learning curve. No attempt should be made unless performed by an experienced Ilizarov surgeon.