Treatment for tibia bone and soft tissue defects
Options for tibia bone and soft tissue defects are varied. At present, the acute shortening and re-lengthening technique (AST) and bone transport are two common methods to treat posttraumatic tibial bone and soft tissue defects using an external fixator. AST is a satisfactory management method for tibia defects less than or equal to 5cm, and has the advantage of a shortened healing time and easy control of axial deviation. However, vascular or nerve compromise frequently occurs when AST are performed on the patients of tibia defects > 5cm [1, 3, 16]. Fortunately, bone transport can avoid limb discrepancy, contracture, blood circulation obstacles, and soft tissue incarceration, which are often encountered with the AST technique.
Currently, large post-traumatic tibial bone defects can be managed with BFT or FTT. According to previous research, when treating bone defects sized >6 cm, the TFT technique may shorten the time of distraction, shorten the healing time of soft tissue defect, and reduce the rate of complications [17,18,19]. Paley et al stated that TFT achieved better results in cases of bone defect >10 cm as compared to the other Ilizarov technique . Chevardin et al.  showed that the risk of hypoplastic bone formation increased in case of BFT regeneration of >5 cm, and delayed osteogenesis occurred when the regeneration reached 8–10 cm. In our series, the mean bone defect size was 11.4 cm (range, 8–18.2). In our experience, for tibia defects ranging from 6–8 cm, the BFT technique is the most preferred approach because of the relatively simple manipulation. However, for tibia defects sized > 8 cm, the TFT technique is optimal.
Bone transport combined with soft-tissue transport (open bone transport)
Previously, the Ilizarov external fixation technique was the most commonly used technique for large bone defects without soft tissue defects [8, 22]. In recent years, an increasing number of studies have reported that bone transport with external fixation can be used to simultaneously treat massive bone and soft tissue defects [5, 9, 23, 24]. The technique of bone transport combined with soft-tissue transport (open bone transport) was first proposed by Suger . It is a process of the skin and subcutaneous tissue be stretched by pins and screws of Ilizarov ring along with the bone distraction. Then, the soft-tissue defect was covered by the new formed skin tissue before the bone ends contact at the docking site. In 2000, Paley et al  reported a retrospective trial of tibial bone defect treatment. Seven of the eight soft tissue defects were closed with soft-tissue transport and achieved healing. Then, several other scholars also reported this technique when treating tibial bone loss and soft-tissue defect [26-28]. This technique emphasises no flap transfer to cover the wound when performing bone transport to manage bone and soft-tissue defects which has no bone exposure after debridement. Regular dressing changes are needed for the wound, usually once a day (Fig. 6). The technique offers the advantage of simultaneously reconstructing both bone and soft-tissue defects with distraction, avoiding the procedure of flap. However, this technique also has the disadvantages of a long duration of regenerate consolidation and frame wearing, regenerated scarred soft tissues and frequent dressing change . Paley et al  stated that bone transport beneath the flap seemed to proceed more easily than in closed defects with scarred soft tissues and flap coverage may contribute to docking site union without grafting. The mean EFI in this series was 1.91 ± 0.3 months/cm, inferior to that reported by recent research studies on bone transport and flap technique [10, 11]. In addition, this technique is only suitable for the cases with both ends with good soft-tissue coverage and without bone exposure after debridement. In other cases, the bone ends will protrude through the wound during bone transport . Finally, this technique is a feasible method to simultaneously manage large bone and soft-tissue defects without flap graft; however, its safety and efficacy warrant further investigation.
Non-union, delayed union, re-fracture, recurrence of infection, infection of new forming bone, poor osteogenesis and axis deviation are common complications of bone transport [3, 5, 9, 10, 30]. Flat and wide bone ends may contribute to the stability of the docking site because of decreasing shear force. Therefore, it is easy to obtain union at the docking site without bone grafting. If the bone ends are sharp or contact narrowly, bone grafting may be required; otherwise, bone grafting should be performed only if there is no obvious callus formation after three months. In this study, delayed union and nonunion were defined as no obvious callus observed at the docking site at 3 and 6 months, respectively, after bone ends contact at the docking site. Six patients were identified with docking site delayed union and four cases with docking site nonunion. We treated four delayed union patients with bone ends trimming without bone graft and six delayed union or nonunion patients with autologous bone graft. Moreover, poor osteogenesis in the elongation area was observed in three cases. They were treated using the accordion maneuver  that involves repeatedly compressing and distracting the lengthening segments or were managed using autologous iliac cancellous bone. Notably, bone end trimming with an electric saw can cause mechanical and thermal damage to the bones, resulting in prolonged bone healing and complications. Therefore, osteotome could be a better alternative to an electric saw. Open bone grafting, which opens the soft-tissue defects, accompanied with an external fixator and vacuum-assisted wound closure (VAC), is also a feasible method that facilitates rich vascularization so encourages fast healing. If there is skin embedded between bone ends, relaxation surgery should be performed immediately [30, 31].
Previously, few studies have reported the technique of bone transport combined with soft-tissue transport because of the concern of increased risk of infection. In the series, 3 out of 31 (9.7%) subjects developed deep infection because the osteotomy was too close to the wound. Thus, the performance of osteotomy at a site that is far away from the wound increases the chances of success. In addition, the nursing quality of the osteotomy incision, such as dressing changes every 2 days and keeping it dry, plays a crucial role in avoiding contamination of the osteotomy sites. The presence of pus in the infectious bone area should be an indicator of delayed osteotomy in the metaphyseal. The two-step protocol implied in our series could significantly reduce the infection rate. First, complete debridement and VAC drainage were undertaken. Second, osteotomy and distraction were performed after fresh granulation tissue formation. Moreover, according our centre and other authors’ experience, placing vancomycin cement rods on the infectious site for one to two months can effectively control the infection [32, 33].
A total of four cases had the problem of axial deviation and the main reason was that the axial line is poor when placing the frame and the patients were not followed up in time. The prevention of axial deviation requires experienced surgeon to perform limb axial alignment under C-arm. Moreover, patients should be closely followed-up after the operation so that problems can be addressed in a timely fashion.
Time in frame
Owing to the prolonged time in frame, most patients always complain when large post-traumatic bone defects are treated using the bone transport technique. In the study, the mean external fixation time was 22.74 ± 6.82 months (range, 14-37 months). More and more studies report bone transport over an intramedullary nail for reconstruction of long bone defects in the tibia, which can reduce the total time in frame [5, 34-39]. Lin et al.  reported a study of infectious tibial bone defects, and osteotomy and bone transport were performed after debridement. When an obvious callus was visible in the elongation area, usually after four to five months, the frame was replaced by nail. A total of 16 patients were treated with this protocol, 15 cases were successful, and one case had recurrent osteomyelitis. Replacement of the intramedullary nail or plate may be considered for patients for whom it is inconvenient to carry a frame. However, this protocol may increase the total cost of treatment and the risk of infection. Therefore, further investigation is needed to prove its safety and efficacy.
Limitations of the study
This study was a single-centre retrospective case series report, rather than a case control study, which provides limited value. In addition, due to the limited number of cases, it was impossible to further analyse and investigate the TFT technique according to the subgroups of age, bone defects size and bone transport type. However, our series contribute successful reconstruction of both massive bone and soft-tissue defects by distraction.