Reconstruction of massive tibial bone and soft-tissue defects by trifocal bone transport combined with soft-tissue transport: experience from 31 cases

Background The study was designed to investigate the safety and ecacy of trifocal bone transport (TFT) and soft-tissue transport with the Ilizarov technique for large posttraumatic tibial bone and soft tissue defects. Methods We retrospectively reviewed 31 patients with massive posttraumatic tibial bone and soft tissue defects from May 2009 to May 2016. All of the eligible patients were managed by TFT and soft-tissue transport. The median age was 33.4 years (range, 2-58 years). The mean defect of bone was 11.87cm ± 2.78cm (range, 8.2-18.2cm) after radical resection performed by TFT. The soft tissue defects ranged from 7cm x 8cm to 24cm x 12cm. The observed results included bone union time, wound close time and true complications. The Association for the Study and Application of the Method of Ilizarov (ASAMI) scoring system was used to assess bone and functional results and postoperative complications were evaluated by Paley classication. Results The mean duration of follow-up after frame removal was 32 months (range, 12-96 months). All cases achieved complete union in both the elongation sites and the docking sites, and eradication of infection. The mean bone transport time was 94.04 ± 23.33 days (range, 63.7-147 days). The mean external xation time was 22.74 ± 6.82 months (range, 14-37 months), and the mean external xation index (EFI) was 1.91 ± 0.3 months/cm (range, 1.2–2.5 months/cm). The bone results were excellent in 6 patients, good in 14 patients, fair in 8 patients and poor in 3 patients. The functional results were excellent in 8 patients, good in 15 patients, fair in 5 patients and poor in 3 patients. Conclusion The TFT in concert with soft-tissue transport technique can be used successfully to manage large tibial bone and soft-tissue defects. Soft-tissue transport can offer a feasible method for the defects with good soft tissue coverage on the bone ends. However, imprecision in the series results precludes a denitive conclusion, and comparative study is needed to assess whether soft-tissue transport is more effective than ap transfer for

long-term complications are still unclear. Previously, the studies of applying distraction to simultaneously manage posttraumatic long tibial defects composited with massive soft tissue defects are really rare. In addition, the argument of whether it is important to restore soft-tissue envelop before bone transport is always there.
In this series, we assess the results of TFT in concert with soft-tissue transport in management of posttraumatic large tibial bone loss composited with soft tissue defects.

Inclusion and exclusion criteria
Inclusion: i) The bone defect of the tibia caused by trauma was ≥ 8 cm after debridement, and combined with large soft tissue defects; ii) All of the tibial bone, including bilateral ends of the bone defects and osteotomy sites, were covered with soft tissue after debridement; iii) The soft tissue wound, which has no exposed bone, was managed by soft-tissue transport; ) Patients were aged 18-65; ) Follow-up was longer than two years.
Exclusion: i) Bilateral tibial bone defect; ii) Soft tissue wound was managed by ap graft; iii) diabetic/corticosteriod treated patients, who are susceptible to infection and non-union.
Demographic data A total of 31 cases were eligible, including 27 males and 4 females, with a mean age of 33.4 years (range, 18 to 58). There were 20 affected limbs on the right and 11 on the left. Fifteen cases were injured by tra c accident, 12 were machine injuries and 4 were crushed by stones. The fracture classi cation of all the patients was identi ed as Gustilo B. The mean length of tibia defects was 11.4 cm (range, 8 to 18.2).
The mean soft tissue defect was 56 to 288 cm 2 . The mean time from injury to surgery was 101.7 days (range, 20 to 450). Radiographs, blood test and bacterial culture were performed on each patient. The blood test included white blood cell level, C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) and these data were reported in table 1.

Surgical technique
In order to avoid cross-infection, the operation was performed according to the principle of "the clean area rst, then the polluted area". For the 31 cases, two osteotomies were undertaken on the proximal and distal tibia. Then, the osteotomy sites were wrapped with iodic gauze. All internal xation, necrotic bone and infectious soft tissue were completely removed, and meticulous debridement was performed until fresh blood appearance on the surface of the bone and soft tissue. Repeated irrigation with hydrogen peroxide solution, 0.9% normal saline, and iodophor were undertaken. Both bone ends were trimmed with electric saw to keep smooth and enough healthy soft tissue coverage. Restoration of limb length and axis was achieved when installing a half ring external xator or Ilizarov external xator. The gap of the osteotomy site was immediately extended by 0.3 cm to 0.5 cm. Finally, it was ensured that the soft tissue wound was open and wrapped with iodic gauze. The soft tissue wound was repaired by soft-tissue transport along with bone transport. The modes of TFT are shown in the diagrams (Fig. 1). More detailed manipulation and process are illustrated in Figures (Fig. 2-5).

Postoperative management
It was necessary to keep the pin-tract and surrounding skin clean and sterilise them with 75% ethanol, usually once a day. Frequent assessments of blood circulation, sensation and movement of the affected limbs and toes were also important. In the series, we lled the wound with iodophor gauze and changed the dressing regularly. On the rst postoperative day, if no vascular or nerve crisis appeared at the distal of the affected limbs, the proximal bone segment was transported at the rate of 1 mm/d, while the distal segment was transported at the speed of 0.6 mm/d, by operating once in the morning and once in the evening. Two weeks later, the transport speed was slowed to 0.5 mm/d to 0.6 mm/d. Six weeks later, the speed was adjusted according to the osteogenesis condition. During the process of distraction, if patients felt intense pain, the distraction was stopped for one week. When bone ends reaches docking sites, autologous bone grafts were performed if the ends were sharp or touched narrowly. However, if the bone ends touched widely, the protocol of dynamising the frames for three months is performed rstly. If no obvious callus was then seen at the docking site, an autologous bone graft was performed immediately. When X-rays showed new bone formation and ne consolidation, bone union was achieved and the affected limb could fully bear load without a frame. The bone and functional results were assessed according to ASAMI classi cation [12] and complications were classi ed according to Paley classi cation [13].

General Results
The details of all patients are shown in Table 1.The mean follow-up was 32 months (range, 12 to 96 months). All cases achieved complete union both in soft tissue and bone defects. The limb length of 28 patients was completely restored, while a discrepancy of 1 cm to 2 cm was observed in 3 patients. The mean healing time of soft tissue wounds was 2.86 ± 1.22 months (range, 1.0-5.8 months). The mean bone union time was 20.98 ± 6.59 months (range, 14 to 35). Four patients showed delayed bone union in the docking site and the problem was solved by bone grafting. The mean bone transport time was 94.04 ± 23.33 days (range, 63.7-147 days). The mean soft tissue defects was 42.72 cm 2 (ranged, 56-288 cm 2 ). Nine patients were addressed with skin grafting and 22 patients healed by soft-tissue transport. The mean external xation time was 22.74 ± 6.82 months (range, 14-37 months), and the mean external xation index was 1.91 ± 0.3 months/cm (range, 1.2-2.5 months/cm).

ASAMI Score
The bone and functional results were assessed according to ASAMI classi cation at last visit (mean of 32 months) and was summarized in Table 2. The bone results were excellent in 6 patients, good in 14 patients, fair in 8 patients and poor in 3 patients. The functional results were excellent in 8 patients, good in 15 patients, fair in 5 patients and poor in 3 patients.

Complications
Complications were classi ed according to Paley classi cation and detailed data were reported in Table 3. Muscle contraction was encountered in nine cases and resolved by physiotherapy, or Achilles tendon lengthening or applying apparatus. Three patients showed infection and poor osteogenesis in the distraction area, and this was treated with a vancomycin cement rod for two months and accordion maneuver. Four patients showed axial deviation, which disappeared after adjusting the frame. Two patients suffered severe pin-tract infection, which was addressed by dressing changes and oral antibiotic treatment. Ten cases showed delayed docking union and were managed by autologous bone graft. One case suffered re-fracture on the docking site after removal of the frame and was treated by plate internal xation and autologous bone graft. One showed K-wire cut out and healed after medical treatment and weight bearing. Joint stiffness either in knee or ankle occurred in 12 cases (38.70%) in our study and most of the cases was successfully improved by positive physiotherapy or extending apparatus. The details of complications are shown in Table 3.

Discussion Treatment for tibia bone and soft tissue defects
Options for tibia bone and soft tissue defects are varied. At present, the acute shortening and relengthening technique (AST) and bone transport are two common methods to treat posttraumatic tibial bone and soft tissue defects using an external xator. AST is a satisfactory management method for tibia defects less than or equal to 5 cm, 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 > 5 cm [1,3,14]. 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 [15,16,17]. Paley et al stated that TFT achieved better results in cases of bone defect > 10 cm as compared to the other Ilizarov technique [18]. Chevardin et al. [19] 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 xation technique was the most commonly used technique for large bone defects without soft tissue defects [8,20]. In recent years, an increasing number of studies have reported that bone transport with external xation can be used to simultaneously treat massive bone and soft tissue defects [5,9,21,22]. The technique of bone transport combined with soft-tissue transport (open bone transport) was rst proposed by Suger [23]. In 2000, Paley et al [19] 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 [24][25][26]. This technique emphasises no ap transfer to cover the wound when performing bone transport to manage bone and soft-tissue defects which has no bone exposure after debridement. The bone segment and soft tissue are simultaneously distracted during distraction osteogenesis, and the soft-tissue defect gradually heals before the bone ends touch at the docking site. 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 ap. 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 [27]. Paley et al [19] stated that bone transport beneath the ap seemed to proceed more easily than in closed defects with scarred soft tissues and ap 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 ap technique [10,11]. In addition, this technique is only suitable for the cases with bilateral ends of the bone defects 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 [22].
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. Moreover, timely replacement of wet dressings was an effective method of avoiding contamination of the osteotomy sites. Finally, this technique is a feasible method to simultaneously manage large bone and soft-tissue defects without ap graft; however, its safety and e cacy warrant further investigation.

Complications
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 [3,5,9,10,28]. 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 touch narrowly, bone grafting may be required; otherwise, bone grafting should be performed only if there is no obvious callus formation after three months. Open bone grafting, which opens the soft-tissue defects, accompanied with an external xator 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 [29,30].
In this study, there were three cases with infection of the elongation area and poor osteogenesis. The reason may be that the infectious area was too close to the osteotomy site. Although osteotomy is performed rst and then the infectious area is debrided, both are within the same surgical operation area. The presence of pus in the infectious bone area should be an indicator of delayed osteotomy in the metaphyseal. The protocol of two steps can signi cantly reduce the rate of infection. 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 [31,32].
Poor osteogenesis in the elongation area can be treated with accordion maneuver [33], which involves repeatedly compressing and distracting the lengthening segments, or managed with autologous iliac cancellous bone. 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.
It takes a long time to manage posttraumatic large bone defects with the bone transport technique. More and more studies report bone transport over an intramedullary nail for reconstruction of long bone defects in the tibia [5,[34][35][36][37][38][39]. Lin et al.
[39] 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 ve 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 e cacy.
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.

Conclusion
The TFT in concert with soft-tissue transport technique can be used successfully to manage large tibial bone loss composited with soft-tissue defects. Soft-tissue transport can offer a feasible method for the defects with good soft tissue coverage on the bone ends. However, imprecision in the series results precludes a de nitive conclusion, and comparative study is needed to assess whether soft-tissue transport is more effective than ap transfer for such soft-tissue defect.
Abbreviations TFT: trifocal bone transport technique; ASAMI: association for the study and application of the method of Ilizarov; EFI: external xation index; AST: acute shortening and re-lengthening technique; VSD: vacuum sealing drainage.

Declarations
Ethics approval and consent to participate This study was reviewed and approved by the Medical Ethics Committee of 920th Hospital of Joint Logistics Support Force.
Authors' contributions YQX initiated the idea and wrote the manuscript. HJW supervised and reviewed the manuscript. XYF and XQH gathered the data and did the data analysis. All authors read and approved the nal manuscript.

Funding
The design, data collection and data analysis of the study and interpretation of data and writing of the manuscript were supported by National Natural Science Foundation of China: (H0607).

Availability of data and materials
All data generated or analyzed during this study are included in this published article.

Ethics approval and consent to participate
The study protocol was approved by the institutional review board of The 920th Hospital of Joint Logistics Support Force and complied with the Good Clinical Practice guidelines and applicable laws and regulations.

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