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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 6  |  Issue : 1  |  Page : 33-39

The impact of radiographic parameters and bone grafting at the docking site on union following bone transport for segmental bone defects of the tibia and the femur: A retrospective cohort pilot study


1 Department of Surgery, Division of Orthopaedic Surgery, American University of Beirut Medical Center, Beirut, Lebanon
2 Department of Orthopedic Surgery, NYU Langone Health, New York, NY, USA
3 Department of Epidemiology, Faculty of Health Sciences, American University of Beirut, Beirut, Lebanon
4 Faculty of Medicine, American University of Beirut, Beirut, Lebanon

Date of Submission07-Mar-2020
Date of Decision13-Apr-2020
Date of Acceptance14-Apr-2020
Date of Web Publication30-Jun-2020

Correspondence Address:
Dr. Said Saghieh
Division of Orthopaedic Surgery, Department of Surgery, American University of Beirut Medical Center, Beirut
Lebanon
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jllr.jllr_8_20

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  Abstract 


Context: In patients with large bone defects, the method of bone transport remains one of the most adopted surgical techniques. Nonunion at the docking site is a critical complication of bone transport procedures. Aims: This study aimed to explore the impact of bone grafting at the docking site as well as radiographic parameters on union rates in patients who underwent bone transport for segmental bone defects of the tibia or femur. Settings and Design: This is a retrospective cohort of a consecutive series of adult patients treated with bone transport by a single surgeon at a single academic medical center. Subjects and Methods: Baseline characteristics of patients, bone transport procedure data, radiographic alignment data, and outcomes of those with bone grafting at the docking site were compared to those that did not. Statistical Analysis Used: Wilcoxon–Mann–Whitney U and Fisher's exact tests were used to analyze the study's data. Results: Thirty-two patients were included. Ten of 11 patients with bone graft at the docking site achieved union. Fifteen of 21 patients with no graft achieved union. Of the group that underwent bone transport without grafting, better alignment in the sagittal plane was significantly associated with achieving union (P = 0.026). The distraction gap of those that went on to unite (m = 9.33) was smaller than those that developed nonunion (m = 15.17) (P = 0.051). Conclusion: Although statistically insignificant, grafting of the docking site seemed to decrease the occurrence of nonunion at the clinical level. Higher distraction gap and translation in the sagittal plane may be the best predictors for nonunion of the docking site among nongrafted patients.

Keywords: Bone graft, bone transport, segmental bone defect, union


How to cite this article:
Nahouli H, Masrouha K, Abdul-Khalek R, Der-Boghossian A, Rteil A, Mourad W, Saghieh S. The impact of radiographic parameters and bone grafting at the docking site on union following bone transport for segmental bone defects of the tibia and the femur: A retrospective cohort pilot study. J Limb Lengthen Reconstr 2020;6:33-9

How to cite this URL:
Nahouli H, Masrouha K, Abdul-Khalek R, Der-Boghossian A, Rteil A, Mourad W, Saghieh S. The impact of radiographic parameters and bone grafting at the docking site on union following bone transport for segmental bone defects of the tibia and the femur: A retrospective cohort pilot study. J Limb Lengthen Reconstr [serial online] 2020 [cited 2020 Jul 2];6:33-9. Available from: http://www.jlimblengthrecon.org/text.asp?2020/6/1/33/288571




  Introduction Top


Segmental bone defects, often resulting from high-energy traumatic injuries or following the surgical treatment of tumors or infections,[1],[2] are a challenging clinical problem encountered in orthopedic practice.[3],[4] Many techniques have been described for defect closure, depending on the magnitude of bone loss; these include autogenous cancellous bone grafts, allografts, bone graft substitutes, vascularized or nonvascularized fibular bone grafts,[5] distraction osteogenesis, and the induced membrane technique.[6],[7],[8]

In patients with large bone defects, the method of bone transport[3] remains one of the most adopted surgical techniques.[9] This procedure can be performed using different approaches including the Ilizarov apparatus,[10] monolateral external fixation, or circular hexapod external fixation, as well as cable transport with external fixation,[11] which all allow for the formation of bone in the direction of distraction, with gradual and progressive closure of large bony defects.[10]

The bone transport method is reported to considerably maximize durability, strength, resistance against infection, biological affinity, as well as restored function.[12] Despite its many benefits, the bone transport technique is also related to a range of complications, with the most prevalent being nonunion at the docking site.[9],[13],[14] This can have several causes, including soft-tissue interposition, avascular soft-tissue envelope, relative avascularity of the leading edge of the transported bone segment,[10] infections,[15] high body mass index (BMI),[16] as well as cigarette smoking.[17] At the clinical level, nonunion poses a particular problem through prolongation of the consolidation phase of distraction osteogenesis and delayed removal of the external fixator.[18],[19],[20] It can also impose a significant economic burden on both the patients and the health-care system through increased pain, decreased quality of life, delayed return to work, as well as subsequent procedures and increased opioid use.[21]

Subsequently, research has focused on investigating the ideal approach to promote union at the docking site; however, no consensus has been reached among practitioners. Some studies reported complete union at the docking site without the use of bone graft.[22],[23] Others encourage the use of bone graft, particularly in cases of delayed maturation of the bone regeneration or delayed union at the docking site.[10],[24],[25],[26] The latter argue that grafting leads to earlier union, shorter external fixation time, and reduced risk of refracture.[10]

In light of this controversy, this study aimed to explore the impact of bone grafting at the docking site on union rates in patients who underwent bone transport for segmental bone defects of the tibia or femur. In addition, the study examined potential predictive factors for nonunion.


  Subjects and Methods Top


Study population

This is a retrospective cohort pilot of patients who were treated at our institution from January 1998 to January 2016. The institutional review board approval was obtained before the initiation of the study. Consecutive cases of patients aged 18 years and above and admitted for bone transport procedures for segmental bone defects of the tibia or the femur were identified and included in our study. Originally, a total of 118 medical records of patients who were admitted for surgical correction of segmental bone defect were reviewed for eligibility of inclusion. Patients who had missing data in their records (including missing X-rays) and patients who underwent acute shortening were excluded. Data from the medical records of 32 patients who underwent a bone transport procedure were finally included in the analysis. Among the included patients, 24 patients had a segmental bone defect in the tibia and 8 patients had a defect in the femur. Two types of external fixators were used in the performed bone transport procedure whereby the monolateral limb reconstruction system (LRS, Orthofix, Italy) was used on 13 patients and the Ilizarov apparatus (Ilizarov, Pitkar, India) was used in the remaining 19 patients. The majority of patients included (81.3%) were males, and the mean age was 32.6 years (standard deviation [SD]: 14.3). The mean distraction gap for patients who were grafted and those who were not grafted was relatively similar, with a mean of 78.0 mm (SD: 29.9) for the former and 75.0 mm (SD: 29.0) for the latter.

Outcome measures

The primary outcome of this study was union or consolidation at the docking site following a bone transport procedure for segmental bone defects of the tibia or femur. Union was defined as the appearance of three of four cortices on orthogonal radiographs.

Data collection

Baseline characteristics of patients including gender, age, and smoking status were recorded. Information on medication use, particularly the use of nonsteroidal anti-inflammatory drugs (NSAIDs), and the reason for admission for bone transport procedure (infection, nonunion, acute trauma, and tumor resection) were noted. Other data specific to the operative procedure performed including the defect location and length, osteotomy location (distal or proximal), bone reconstruction technique employed (simple bone transport or bone transport with active shortening), presence of preoperative tissue infection, the use of synthetic bone substitute or cement, the distraction gap, as well as the distraction–consolidation time were noted. Data on measurements made including the translation (percentage of displacement) as well as amount of angulation (in degrees) on both anteroposterior and lateral radiographs were noted.

Statistical analysis

Frequencies and percentages were used to describe categorical variables. Continuous variables were summarized using mean and SD; in the case of skewed data, we reported the median and interquartile range. Procedures in which grafting was performed were identified, and patients were stratified into two groups depending on whether grafting was performed. Group A included patients who underwent bone transport followed by grafting, and Group B included patients who underwent bone transport procedure without bone grafting. The primary outcome (union vs. nonunion) was examined in both groups. The Mann–Whitney U-test was used to compare continuous variables (mean rank [m]) between the groups, and the Fisher's exact test was used to compare categorical variables between the groups if expected cell count was below 5. Statistical tests were two-sided, and P < 0.05 was considered statistically significant. IBM Statistical Package for the Social Sciences (SPSS) version 25 was used for data analysis.

The surgery

The surgery consisted of a segmental resection either due to infection, tumor, or trauma with severe comminution and application of external fixator (circular or monolateral). The resection was planned to remove all devitalized bones or tumors. The bone cuts were designed to be parallel to assure smooth docking. In severely infected cases, the osteotomy for bone transport was delayed for 3–6 weeks while patients received antibiotherapy. A cement spacer or calcium sulfate mixed with antibiotics may have been used to fill the defect. The cement spacer would then be removed at the time of the osteotomy surgery.

Postoperatively, the patient was followed up biweekly and then on a monthly interval to monitor the progression of the distraction and the regeneration and subsequently the union [Figure 1].
Figure 1: (a) Anteroposterior view of an open and displaced tibia shaft fracture of an included patient upon presentation. (b) Lateral view of an open and displaced tibia shaft fracture of an included patient upon presentation. (c) Anteroposterior view of the application of the monorail fixator and proximal tibial osteotomy preparation for bone transport. (d) Lateral view of the application of the monorail fixator and proximal tibial osteotomy preparation for bone transport. (e) Imaging at 1 month postinitiation of bone transport (anteroposterior view). (f) Imaging at 1 month postinitiation of bone transport (lateral view). (g) Imaging at 6 months postinitiation of bone transport showing good healing (anteroposterior view). (h) Imaging at 6 months postinitiation of bone transport showing good healing (lateral view). (i) Imaging at 1 year postinitiation of bone transport, with fixator removed, and complete healing (anteroposterior view). (j) Imaging at 1 year postinitiation of bone transport, with fixator removed, and complete healing (lateral view)

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Once the bone edges became in contact, bone grafting option was discussed with the patient. There were no strict criteria for bone grafting, and no patient had major deformity at the docking site or at the regeneration that necessitated surgical correction.

The grafting technique

The grafting technique involved refreshing of the bone edges by decortication and debridement of any fibrous tissue. A mixture of synthetic calcium sulfate bone substitute (Stimulan Kit, Biocomposites Ltd., Staffordshire, England), antibiotics (1 g of vancomycin and 240 mg of gentamicin), and autogenous iliac bone graft was mixed and added to the docking site. Acute compression with the fixator was performed in the operating room.

Both the groups (A and B) were followed up on a monthly basis. Nonunion was diagnosed when there was a failure of progression of callus formation on two successive X-rays taken at 1-month interval.


  Results Top


Analyzed data from the medical records of 32 included patients who underwent a bone transport procedure are presented in [Table 1].
Table 1: Baseline characteristics of the patients in Group A (bone transport + grafting) and Group B (bone transport + no grafting)

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Of the patients included in our analysis, 11 had subsequent bone grafting (Group A), whereas 21 patients had no bone grafting (Group B). Ten of the 11 patients in Group A (90.9%) went on to unite at the docking site as compared to 15 of the 21 patients in Group B (71.4%). No statistical significance was detected with regard to the rate of union between these two groups (90.9% vs. 71.4%; P = 0.374).

Results of the Mann–Whitney U-test [Table 2] indicate that, among patients in Group B, bone characteristics such as alignment of the bone on lateral radiographs were significantly associated with union at the docking site (P = 0.026). Specifically, greater malalignment in the sagittal plane was significantly associated with nonunion (m = 15.75). In addition, among patients in Group B, the distraction gap of those that went on to unite (m = 9.33) was smaller than those that developed a nonunion (m = 15.17), with marginal statistical significance noted (P = 0.051). As for the patients in Group A, results showed no statistical difference between patients with union and those without union across the different variables studied.
Table 2: Association of clinical variables and union at docking site in Group A (grafting) and Group B (no grafting)

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Results of the Fisher's exact test [Table 3] reflected that none of the studied variables were associated with whether or not union at the docking site was achieved in both Groups A and B. These variables were as follows: smoking status of patient, NSAID use, defect location or osteotomy location being distal, reason for admission being tumor or trauma, presence of preoperative infection, or defect being in the tibia.
Table 3: Comparison of patients' characteristics and clinical variables associated with union and nonunion at docking site in Group A (grafting) and Group B (no grafting) patients

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  Discussion Top


This study explored the impact of bone grafting at the docking site on union rates in patients who underwent bone transport for segmental bone defects of the tibia or the femur, shedding light on predictive factors for nonunion in both the groups of patients. Despite reports advocating for the need to graft following bone transport,[20],[27],[28],[29],[30],[31],[32] our study showed no statistically significant difference with regard to achieving union between patients with and without grafting.

However, there are other predictive factors to consider. In their study on factors associated with failure of bone grafting of tibia nonunions and segmental bone defects, Maceroli et al. showed that gap size was significantly related to nonunion with a 6% increase in probability of revision surgery for every 10-mm increase in gap distance.[16] Similarly, our results highlighted an association between malalignment in the sagittal plane and higher distraction gap with nonunion among patients without grafting post-bone transport. While no other variables were shown to be statistically associated with nonunion in the present study, others have found that modifiable factors such as BMI are linked to nonunion.[16],[33] Our study was not able to test for this association due to the lack of BMI data in the medical records reviewed.

Despite some studies suggesting that cigarette smoking is associated with nonunion due to decreased healing rates noted among smokers,[34],[35] the findings of the present study are in agreement with several previous reports which found no association between smoking and nonunion.[16],[36],[37]

A number of limitations in this study are worth mentioning. First, the nature of the analyses could only support the establishment of associations. Specifically, the small sample size of the study may have underpowered the study's ability to detect the effect of grafting on union rates. In addition, if a larger sample size had been studied, other variables that are thought to clinically affect union such as translational malalignment in the coronal plane may have been detected to be significantly associated with nonunion. Nevertheless, this study can be considered as a pilot which other researchers can replicate with larger sample sizes to enhance the analytical power and increase the possibility of detecting potential associations. To increase the power given the rates of union and nonunion observed in our findings, a sample size of 139 patients (48 in Group A and 91 in Group B) is required to detect a statistically significant difference between Group A and Group B. This calculation is based on the 9.10% and 28.6% rates of nonunion in cases of grafting and no grafting, respectively, a ratio of 2 between patients in Group B versus Group A, and a power of 80%. This sample size estimation can help guide large-scale future studies on the sample size required to provide evidence on the improved outcomes with grafting in bone transport procedures.

Another limitation is the retrospective design of the study, which could have led to misclassification bias, especially given the missing data on some baseline characteristics. In addition, due to the rare type of procedure studied, this study covered data retrieved from patient records who visited the hospital over a span of 20 years, a period during which surgical technological advancements could have been introduced to the field, potentially affecting outcomes of interest.


  Conclusion Top


This study is retrospective with only a few patient cases and could be considered as a foundational base for prospective studies with the same research question yet larger sample sizes. Despite the statistical insignificance, more than 90% of patients in the grafting group achieved union compared to only 71.4% of patients with no grafting, a finding that may be considered as clinically significant. Factors such as a large distraction gap and translation in the sagittal plane may influence the surgeon to opt for grafting of the docking site.

Financial support and sponsorship

None.

Conflicts of interest

There are no conflicts of interest.



 
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