The ultimate destination of treating bone defects is to reconstruct a fully functional extremity without any unacceptable deformities or limb length discrepancy24. There is no doubt that the treatment of a long segmental bone defect is a challenge for orthopedic surgeons, especially combined with deep infection. For most treating surgeons, simultaneously managing bone defects as necessary as infection. Options for the treatment of bone defects are varied6-13, while the subsequent outcomes are not completely satisfactory. The concept of distraction osteogenesis (DO) given by Ilizarov, in which bone regeneration occurs when subjected to tensile stress, contributes to manage this complex problem27.
At present, the two common techniques for long bone defects are acute shortening followed by re-lengthening (AST) and bone transport using an external fixator. However, neurovascular injury, limb discrepancy, and blood circulation obstacles are worth considering problems when the AST is conducted on cases with bone defects > 5cm9, 14, 28. The bone transport technique has been widely applied to manage bone defects for decades14, 15, 17-20, and problems including infection, deformity, joint stiffness, or limb discrepancy can be resolved simultaneously. The main drawback of the bone transport technique is the long procedure in a cumbersome frame, resulting in inconvenient daily life and increasing numerous complications, including pin tract problems, joint stiffness, pain, and psychological symptoms. These problems have been the obstacles to the extended application of bone transport. In addition, many patients with bone defects caused by an infection usually underwent several previous operations that fail and developed compromised surrounding soft tissues. Therefore, a shorter duration and fewer complications treatment is really a goal worth striving for.
Several methods have been developed to decrease the external fixation index, reduce the potential complications, and accomplish satisfactory clinical results. S.Gupta et al.29 performed a three-stage treatment in 14 consecutive patients with tibial infected nonunion using a long lateral locked plate and a six-pin monorail fixator. In this group of patients, the mean defect size was 6.4 cm and the mean external fixator index was 21.2 days/cm, while the complication rate was 0.5 per patient. They declared that composite fixation reduces the fixator time and the associated complications for patients with a segmental tibial defect due to infected nonunion, and provides high emotional acceptance of final clinical outcomes. Gulabi.D et al.30 developed a technique to reduce complications by using a circular external fixator combined with an intramedullary nail to achieve union, limb lengthening, and regenerate stability. In their treatment of five tibial nonunion patients with bone defect, all cases acquired satisfactory outcomes. Similarly, Kocaoglu.M et al.31 also summarized their experience with distraction osteogenesis in the management of bone defects and limb-shortening due to radical debridement of chronic osteomyelitis using an external fixator combined with an intramedullary nail. Although the mentioned techniques above enable less duration in the external fixator, the combination can not accelerate the regenerate consolidation and has difficulty in resolving the chronic infection simultaneously. Furthermore, the external combined with internal fixation treatment requires several additional surgical interventions. It is difficult to accept for most patients due to their unpleasant experience in numerous previous operations.
The trifocal bone transport technique was proposed to accelerate the defect closure and shorten the treatment duration. Considering the biological characteristic of incapable speed up lengthening at just one osteotomy site, the TFT was derived from the theoretical basis of distraction simultaneously using two osteotomy leads to effectively double lengthening speed. In this procedure, the regeneration time is theoretically decreased to 50%, and the total treating time is reduced accordingly24. Additionally, the regenerate consolidation time is inversely proportional to the bone defect length, two shorter fragments are therefore capable of rapid consolidation compared with only one fragment.
Borzunov23 conducted an experimental comparison in the treatment of tibial defects using BFT and multilevel technique firstly, subsequently extend to clinical application. For the management of patients with large tibial defects that ranged from 12 to 14 cm using the multilevel techniques, distraction duration can be reduced 2.5 times, and fixation period can be reduced between 1.3 to 1.9 times. Sala et al.32 compared the clinical outcomes of TFT and BFT in the treatment of postinfectious segmental tibial bone defects with a combined Ilizarov and Taylor spatial frame method. In their retrospective study of 12 patients with atrophic tibial nonunions, although the average lengthening size was increased (9.7cm in TFT, 5.5cm in BFT) in the TFT group, there was a shorter mean period in the frame (379 days in TFT, 457 in BFT). In addition, the TFT technique reduced the mean lengthening index (1.31 months/cm in TFT, 2.63 months/cm in BFT).
In the present study, the clinical results of 53 patients with long segmental tibial bone defects treated by bifocal or trifocal bone transport technique were retrospectively analyzed and compared. The mean defect size was significantly increased in the TFT group (9.4±1.5 cm in TFT, 7.8±1.8 cm in BFT). In contrast, the mean docking time (65.9±10.8 days in TFT, 96.8±22.6 days in BFT), mean external fixation time (328.0±57.2 days in TFT, 474.5±103.2 days in BFT), and mean external fixation index (34.8±2.1 days/cm in TFT, 60.8±1.9 days/cm in BFT) were significantly reduced. The results were comparable to the previous studies23, 32.
A previous study reported that hypoplastic bone formation was a common complication when the bone defects exceed 5cm or 40 % of the injured bone and treated by BFT33. The regenerate consolidation will be affected by the osteotomy technique and location, distraction length, and blood supply of transported fragment. In our study, there were 4 patients who suffer delayed consolidation in BFT, and none was observed in the TFT group. According to our experience, low energy osteotomy technique, timely lengthening speed adjustment, and application of TFT technique in massive bone defects were recommended for avoiding this problem.
Although additional surgical procedures of one transport sliding block and an osteotomy site in TFT may increase the complications correspond to Schanz screws and distraction zone, the faster regeneration and early frame removal have counteracted this negative effect. In this study, the BFT group had a statistically significant increase in mean rate of difficulty (2.9 difficulties/patient in BFT, 1.7 difficulties/patient in TFT) and complication (1.0 complications per patient in BFT, 0.5 complications per patient in TFT), this can be explained by the longer frame duration in these patients. The only shortcoming of the TFT group is the significantly increasing operation time (161.9±8.9 minutes in TFT, 122.5±11.2 minutes in BFT).
Furthermore, compare with previous studies15, 28, 32, the Ilizarov circular external fixator is relatively cumbersome, complex, difficult-learning, time-consuming, and fraught with lots of potential complications. The monolateral rail external fixator used in this study, working on the same principles as Ilizarov circular external fixator, is portable, easy to construct, and has a short learning curve. It is also easy to adjust the sliding clamps adapt to the transporting bone fragments without altering the nut bolts over the threaded rods, unlike in the Ilizarov circular external fixator.
The clinical results of the present study manifest that both BFT and TFT in the reconstruction of long segmental tibial bone defects caused by infection using a monolateral rail external fixator achieve satisfactory outcomes. Although there were no significant differences between BFT and TFT in the final bone and functional results, the external fixation index, difficulties, and complications were significantly decreased in the TFT group. According to our experience, the most vital step is radical debridement of the infectious tissues in the reconstruction of bone defects caused by infection. In addition, comprehensive frame understanding, prudent patient selection, appropriate pins insertion, meticulous care, early complications detection, and proper intervention or psychological counseling ensure satisfactory results.
The present study may be limited by the retrospective nature with a single-center small sample size, a conservative attitude therefore should be adopted regarding the interpretations of our results. Multi-centered trials with larger sample size, life quality assessments, and mental evaluations should be adopted in further investigations.