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Treatment of segmental tibial defects by bone transport with circular external fixation and a locking plate.

Objective To evaluate the effectiveness of bone transport involving circular external fixation and locking plate application for the treatment of segmental tibial defects. Methods A retrospective review of 12 patients with segmental tibial defects who underwent bone transport with circular external fixation and locking plate application. We evaluated external fixation time, external fixation index, time to achieve union, and complications. Clinical results were assessed using the Association for the Study and Application of the Methods of Ilizarov (ASAMI) score. Generic health-related outcome was assessed using the 36-Item Short-Form Health Survey questionnaire (SF-36). Results The mean follow-up was 25.8 months, and the mean defect size was 6.7 cm. All of the patients achieved union at the distraction callus and docking site. The average external fixation time was 299.5 days. The mean external fixation index was 16.5 days/cm, and the mean healing index was 44.9 days/cm. The functional outcomes were excellent in eight cases and good in four. The average SF-36 score was 92. Conclusion Bone transport with external fixation and locking plate application may be a promising method for the treatment of segmental tibial defects.


Introduction
Segmental defects of the tibia can be caused by trauma, nonunion, infection, and malignancy, and can cause significant disability in patients. Segmental tibial defects are a difficult problem for the orthopedic surgeon. 1 Many treatment strategies have been described to treat segmental tibial defects, including autogenous iliac bone graft, vascularized fibula transfers, bone transport, and the Masquelet technique. Autogenous iliac bone graft is the standard for the treatment of bone defects <5 cm in size. However, a high failure rate of graft absorption has been reported in segmental defects >5 cm. 2 The Masquelet technique is a reliable method for the management of segmental defects, but it requires adequate autogenous bone graft. 2,3 The technique of vascularized fibula transfers is difficult, and this treatment option is associated with nonunion and stress fractures. 4,5 Bone transport using both circular external fixation and monolateral external fixation has been described in the literature. 6,7 The advantages of using bone transport for the management of segmental bone defects include reliability, early load-bearing, and no limit on the size of the defect. 1 However, a high rate of complications (such as pin-tract infections, joint stiffness, discomfort, deformity, and re-fracture) secondary to the long duration of external fixation has been reported by multiple authors. 6,8,9 Bone transport with external fixation and locking plate application has been shown to successfully treat segmental defects in the femur. 10 There are relatively few reports that describe the outcomes of segmental tibial defects treated with plateguided bone transport. Therefore, in this paper we report the treatment of segmental tibial defects using bone transport with circular external fixation and locking plate application.

Materials and methods
This study was a retrospective review of the medical records of 12 patients with segmental tibial defects who underwent bone transport with medial tibial fixation and locking plate application between January 2013 and January 2017 in HongHui Hospital, Xi'an Jiaotong University. Demographic data are summarized in Table 1.

Surgical technique
Bone transport with external fixation and locking plate application involves three stages, two operations, and an intervening transport period.
Stage one -preparation for bone transport. All patients underwent continuous debridement (an average of 2.5 times) before bone grafting with a locking plate until the infection was controlled. At the time of debridement, all necrotic bones were radically resected until bleeding occurred at the proximal and distal bones of the bone defect. The specimens were taken for culture, and the bones were temporarily fixed using double needles and double nails (Figure 1a). The bone defect was filled with antibiotic bone cement containing 3 g vancomycin. The skin was closed, and soft tissue reconstruction was needed since the skin could not be closed under poor soft tissue conditions (two cases of free vascular flap and three cases of myocutaneous flap). The erythrocyte sedimentation rate, C-reactive protein, and procalcitonin were reviewed for the elimination of chronic low-toxicity infections in the first month after surgery. The final reconstruction was performed once there was no clinical or laboratory evidence of infection.
Stage two -plate fixation, external fixation and osteotomy. The temporary external fixation was removed 7 days before the reconstruction,  and the bone cement was removed from the original incision. Internal plate fixation was expected to performed before external fixation. Locking plates of different types were used depending on the location of the bone defect. A bone plate was inserted to span the defect using minimally invasive or transdermal techniques, and the proximal and distal ends were secured with three or four screws. All 12 patients were treated with a circular external fixator, which was fixed with two flat rings at the distal and proximal ends, and the transport section was fixed with a flat ring (Figure 1b). Corticotomy was performed at the appropriate level (at the metaphysis). The level of osteotomy was located between the distal and proximal segments of the bone plate, and the osteotomy end was pressurized. Distraction was started on the 10th day after surgery at a rate of 1 mm (0.25 mm/time, four times a day) per day to regenerate periosteal blood supply at the site of the corticotomy (Figure 1c). Patients were encouraged to perform functional exercises on the knee, ankle, and foot from the first day after surgery, and receive orthotopic and lateral radiographs every 2 weeks to assess the formation of the callus. All patients received 2 to 4 weeks of antibiotic therapy after the first surgery (plate implantation) according to microbiological culture and serological results.
Stage three -transport bone fixation with screws and external fixator removal. After the transport section was aligned and pressurized, the cortical bone screw was placed through the bone plate by the principle of the compression screw, and the broken end of the transport section was further pressurized. Then the external fixator was removed ( Figure 1d). All patients were encouraged to perform some weight-bearing functional exercise from the second day after surgery, and receive clinical and radiological examinations every month. The load was gradually increased as the comfort level increases.
Patients were allowed to fully load when there were three layers of cortical callus in the transport segment (Figure 1e and 1f).

Outcome measures
Outcomes included bone union, complications, Association for the Study and Application of the Methods of Ilizarov (ASAMI) bone and functional scores, and SF-36 scores. 11

Statistical analysis
The discrete categorical data were represented as numbers or percentages. The normality of the quantitative data was examined using the Kolmogorov-Smirnov test. Continuous data were assumed to be normally distributed (age, defect size, number of previous operations, external fixation time, removal time, healing time, external fixation index, healing index, and SF-36 score) as mean and standard deviation. All statistical analyses were performed using GraphPad Prism 7.0 software (La Jolla, CA, USA).

Results
The average age of the 12 included patients was 45 years (range, 20-65 years); 10 patients were men, and 2 were women. The bone defects were caused by open fracture in nine cases and nonunion in three cases. The defects were located in the middle of the tibia in four cases and the distal part of the tibia in eight cases. The original injuries were traffic injuries in seven cases, falls in three cases, and heavy pound injuries in two cases. The time from injury to operation was 1 to 14 months, with an average of 5.2 months. The number of operations in previously injured limbs ranged from one to five, with an average of 2.5 operations. All patients had bone defects of varying degrees with defect lengths ranging from 4 to 9.2 cm, with an average of 6.7 cm. In this study, acceptable bone transport with circular external fixation and locking plate application was accomplished in all patients. The mean duration of revision follow-up was 25.8 months (range, 12-48 months) after frame removal. After employing our protocol, all of the patients achieved union at the distraction callus and docking site. The mean distance of transported bone was 6.7 cm. All patients had clinical and radiographic evidence of union, and the average union time was 299.5 days. The average external fixation time (EFT) was 112.1 days. The mean external fixation index (EFI) was 16.5 days/cm, and the mean healing index (HI) was 44.5 days/cm ( Table 2).
The bony outcomes were excellent in all patients. The functional outcomes were excellent in eight cases and good in four. In 50% of the patients, the transport segment was slightly backward and downward during the transport process, but no malunion more than 5 was observed in the coronal or sagittal plane and no fractures, dislocations, or plate fractures were found after the fixator was removed. The most common complication was chronic pain (occurred in seven cases) caused by limb distraction during bone transport, and the symptoms were relieved after the administration of oral painkillers. Four patients developed needle infections, all of which were Dahl grade 1 infections that healed with topical dressing and the administration of oral antibiotics. 12 No distraction fractures, malunion, docking fractures, internal fixation failure, iatrogenic neurological paralysis, increased knee or ankle stiffness, new or recurrent deep infections, or voluntary amputation were observed at the final follow-up.

Discussion
Tibial defects remain a difficult problem for orthopedic surgeons. Distraction osteogenesis, external fixation with or without autogenous iliac bone graft, vascularized fibula transfers, and the Masquelet technique are all described techniques for dealing with these difficult problems. The purpose is to achieve tibial healing, correct the deformity, cover the soft tissue, adjust the limbs, make up for differences in angulation, and restore rotation and leg length, thereby enabling patients to achieve early return activities and normal everyday life. However, infection and malunion are still commonly seen. Distraction osteogenesis, a classical therapy for segmental tibial defects, is a dynamic process involving cutting, slowly separating bone by external fixation, allowing the bone healing process to fill in the gap, and finally promoting cartilage calcification. Related basic research has shown that the blood vessels of bone tissue and cell division increase, and local metabolism is strong under tension-stress stimulation. 13 In 1951, Soviet surgeon Ilizarov used a circular external fixator for bone transport and achieved satisfactory results. However, circular external fixation requires a long fixation time and prevents patients from being able to move well. Additionally, patients do not tolerate the persistent chronic pain well, and some patients develop different psychological problems. Some scholars have achieved similar effects with circular external fixation by using a uniplanar external fixator. Compared with the circular external fixator, the uniplanar external fixator is smaller in size and allows for more patient mobility, but does not shorten the fixation time or decrease incidence of needle infection. 14 The main complication of bone transport is related to the time to place the fixed needle on the external fixator. Therefore, the longer the fixation is, the more complications occur. 3 At the present, the EFI of adult external fixation is used to measure the fixation time. The EFI of the classic tibia Ilizarov reconstruction is 48 days/cm to 75 days/cm. 15,16 To shorten the fixation time and reduce complications, many researchers have performed bone transport using unilateral external fixation combined with intramedullary nailing. 17,18 Because the locking of the transported bone segment can protect the new callus, the external fixator can be removed early once the anchor point is in contact. Thus, the fixation time can be greatly reduced and the EFI can be reduced to less than 30 days/cm. However, since the intramedullary nail occupies the entire medullary cavity, it is difficult to prevent the fixation needle of the external fixation from intersecting the intramedullary nail, thus increasing the incidence of deep infection. An increasing number of researchers believe that the use of an external fixator for more than 28 days before intramedullary nail fixation can significantly increase the infection rate, and the infection rate in the tibial bone defect can be as high as 8.8%. Moreover, the smooth placement of the intramedullary nail will be affected if there is bone end hardening or stenosis of the medullary cavity. 19,20 In recent years, the use of locking plates combined with external fixators for bone transport has achieved good results. [21][22][23] Compared with intramedullary nails, locking steel plates can allow for screwing in the transported segment, increasing its stability, and eliminating the time required to heal the anchor point. In this way, the locking plates not only move the disassembly time earlier, but also allow a large space for the insertion of the external fixation needle, which does not frequently contact the locking steel plates, thereby reducing the occurrence of deep infection. 22,24 We treated segmental tibial bone defects using locking plates combined with external fixation with an average EFI of 15.1 days/1 cm. A similar observation was made by Gupta et al. 21 We attributed the reduced EFI to the locking plate's ability to provide sufficient stability, such that the external fixator was able to be removed after the distraction was completed.
Results were evaluated using the ASAMI bone and functional scores. All 12 patients had excellent bone evaluation results. The functional outcomes were excellent in eight cases and good in four. All patients in the study returned back to their pre-injury work. This is similar to that reported by Oh et al. 22 in 10 patients with segmental tibial defects, using a combination technique including an Ilizarov and a locking plate. Using the classical Ilizarov technique, Papakostidis et al. 25 described a sub-group analysis of 11 studies with a total of 261 patients with infected tibial nonunions. The poor outcomes have been reported in between 0% and 48% of patients. The reason for poor functional scores may be because they did not combine external fixation with a plate, and patients spent a longer time in a less bulky fixator.
Early removal of the external fixator can reduce the risk of needle infection and allow the patient to recover quickly. Using a combination technique including an Ilizarov and an intramedullary nail, Deniz et al. 26 reported a complication rate of 2.6 per patient in a study of five patients with tibial nonunions with bone loss. Sen et al. 27 found a rate of 2.08 complications per patient in a study of 24 patients. In the current study, seven patients developed distraction pain and four patients developed needle infection. Our complication rate was 0.9 per patient, significantly lower than in previous studies. Most of the complications were mild and can be treated without additional surgery. Alignment was recorded as a bone transport complication. In our study, maximum angular deformity in either the coronal or the sagittal plane was < 5 resulting from the Ilizarov external fixator. Internal fixation failure usually occurs during the fracture healing period after removal of the external fixator. 28 When the distraction callus is long and the normal segment is short, the risk of fracture callus is increased. In our study, we observed no fractures at the distraction site, malunion, fractures at the docking site or internal fixation failure, iatrogenic neurological paralysis, increased knee or ankle stiffness, or new or recurrent deep infections. This study had several weaknesses. Our study was a single-center retrospective study and the number of patients included was small. Retrospective studies depend on the memory of patients and medical records, which may lead to deviation of the results due to changes in the physical and mental state of patients or inaccurate records.
In conclusion, the use of external fixation combined with a long locking plate for the treatment of segmental tibial bone defects may effectively decrease the fixation time, reduce the pain of patients, and have relatively few complications. Therefore, treatment of segmental tibial bone defects with external fixation and locking plate application may be appropriate, though further studies with a greater number of patients are needed to confirm this.

Abbreviations
ASAMI ¼ Association for the Study and Application of Methods of Ilizarov EFI ¼ external fixation index HI ¼ healing index EFT ¼ external fixation time.