|Year : 2016 | Volume
| Issue : 1 | Page : 35-39
Ankle alignment after tibial lengthening and syndesmotic fixation: A comparison study
Oussama Abousamra1, Maria del Pilar Duque Orozco1, Kenneth J Rogers1, Christopher Iobst2, L Reid Nichols1, Mihir Thacker1
1 Department of Orthopaedics, Nemours Alfred I. duPont Hospital for Children, Wilmington, DE 19803, USA
2 Department of Orthopaedics, Nemours Children's Hospital, 13535 Nemours Pkwy, Orlando, FL 32827, USA
|Date of Submission||18-Mar-2016|
|Date of Acceptance||09-May-2016|
|Date of Web Publication||17-May-2016|
Department of Orthopaedics, Nemours Alfred I. duPont Hospital for Children, 1600 Rockland Road, Wilmington, DE 19803
Source of Support: None, Conflict of Interest: None
Background: This study aimed to compare two techniques of syndesmotic fixation in terms of preventing lateral malleolus migration and ankle malalignment during tibial lengthening.
Methods: Children who had tibial lengthening > 20 mm using Taylor Spatial Frame were included. Two techniques of syndesmotic fixation were evaluated: Transverse tricortical screws and oblique quadricortical screws. Radiographs, before frame application and at frame removal, were reviewed. Tibial length, angular deformity, distal tibiofibular index (DTFI), proximal tibiofibular index (PTFI), and lateral distal tibial angle (LDTA) were measured. Malhotra grades and duration of external fixation were also recorded. Eighteen patients (21 limbs) were identified (transverse screws in 15 limbs and oblique screws in 6 limbs). Age and gender were similar for both groups. There was no significant difference in lengthening amount (transverse: 40 mm and oblique: 35 mm), angular correction, lateral malleolar and fibular head migration, LDTA change, and frame duration.
Results: After lengthening, and only in the transverse group, DTFI and PTFI changed significantly (DTFI pre: 12 mm, post: 8 mm, P = 0.01; PTFI pre: 17 mm, post: 22 mm, P = 0.02). Two ankles in the transverse group moved from Malhotra 0 to 1; however, no grade change was noted in the oblique group. No screw-related complications were encountered in either group.
Conclusion: Although migration of lateral malleolus was encountered in the transverse group, the amount of DTFI change was similar to the oblique group and no LDTA change was noted in either group. No advantage of one syndesmotic fixation method over the other was found in this study.
Keywords: Ankle malalignment, syndesmotic fixation, tibial lengthening
|How to cite this article:|
Abousamra O, Duque Orozco Md, Rogers KJ, Iobst C, Nichols L R, Thacker M. Ankle alignment after tibial lengthening and syndesmotic fixation: A comparison study. J Limb Lengthen Reconstr 2016;2:35-9
|How to cite this URL:|
Abousamra O, Duque Orozco Md, Rogers KJ, Iobst C, Nichols L R, Thacker M. Ankle alignment after tibial lengthening and syndesmotic fixation: A comparison study. J Limb Lengthen Reconstr [serial online] 2016 [cited 2019 Jul 17];2:35-9. Available from: http://www.jlimblengthrecon.org/text.asp?2016/2/1/35/182574
| Introduction|| |
Malalignment of the ankle joint, especially valgus, has been reported in the context of surgical tibial lengthening since the procedure was described in the 1920s.  Vertical distortion of the distal tibiofibular anatomy, with the lateral malleolus migrating proximally, has been blamed for causing ankle valgus. ,, Different procedures were then described to prevent fibular migration. ,, Syndesmotic fixation, in order to preserve the tibiofibular relationship, has been recommended using wires or screws. ,, However, fibular migration has still been noted even when syndesmotic fixation was used. ,, The collapse of the fibular distraction gap, due to poor quality bone or nonunion, has been suggested as a cause of lateral malleolar migration and ankle valgus has been associated with migration of more than 5 mm. 
Although wire fixation reportedly had little damage to the joint, due to the small diameter,  it has been associated with fibular migration ,, and for higher risk situations, with longer lengthening, ankle protection with screws has been recommended.  More recently, ineffective syndesmosis, due to tricortical screws, has also been reported as a cause of fibular migration with quadricortical fixation found to be more effective in preserving the distal tibiofibular anatomy.  However, the small number of cases in addition to the variability of pathologies reported keep it challenging to define the factors leading to this migration, and therefore to find the procedures that might prevent it.
The aim of this study is to compare two techniques of syndesmotic fixation, used in our institution in the context of tibial lengthening: Transverse tricortical screws and oblique quadricortical screws. Migration of the lateral malleolus was evaluated as was the development of ankle valgus.
| Methods|| |
After obtaining the approval of our Institutional Review Board, records of all children with a tibial lengthening procedure, using a Taylor Spatial Frame  between 2004 and 2014, were reviewed. Two techniques of syndesmotic fixation were evaluated: Transverse tricortical screws and oblique quadricortical screws [Figure 1]a and b. Only patients with idiopathic tibial shortening or bowing, including Blount disease,  who had a normal ankle joint prior to lengthening, were included. Children with skeletal dysplasia were not included. Only limbs with lengthening of more than 20 mm were included in this study.
|Figure 1: (a) The transverse tricortical syndesmotic screw. (b) The oblique quadricortical syndesmotic screw|
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Preoperative radiographs, as well as initial radiographs after frame removal, were reviewed. The last radiographs reviewed in this study were the immediate radiographs postframe removal. Although further migration of the lateral malleolus may occur after screw removal, in this study the aim was to compare the role of two different fixation techniques in preventing the migration while the screws were in place. Syndesmotic screws were removed at the same time with the frame removal. All radiographs were performed in the standing position. Since parallax error might happen, all radiographs measured in this study were taken following the same standardized method and measurements were all performed by one reviewer following the same methods. In addition, EOS system (EOS Imaging, Paris, France) was used in almost all of our measurements, which minimizes the parallax effect. Tibial length, as measured on the mechanical axis of the tibia, was recorded in addition to the angular deformity. Distal tibiofibular index (DTFI) was identified as the distance between the tips of the medial and lateral malleoli , [Figure 2] and [Figure 3]. Fibular head migration was evaluated by the proximal tibiofibular index (PTFI) as identified by the distance between the fibular head and the tibial plateau.  Lateral distal tibial angle (LDTA) was identified as the angle formed by the anatomic axis of the tibia and the distal tibial articular surface.  Ankle deformity was assessed by the grade of lateral wedging of the distal tibial epiphysis, as described by Malhotra. 
|Figure 2: Distal tibiofemoral index. (a) Before lengthening with a transverse syndesmotic screw. (b) After frame removal. Distal tibiofemoral index decreased from 11 to 3 mm|
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|Figure 3: Distal tibiofibular index. (a) Before lengthening with an oblique syndesmotic screw. (b) After frame removal. Distal tibiofibular index changed from 9 to 8 mm|
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The amount of change of each measurement, preoperatively and postremoval, was compared between the two groups (the transverse screws group and the oblique screws group). Then, preoperative and postremoval measurements were compared within each group in order to assess immediate postlengthening changes. Independent and paired t-tests were used as well as Chi-square test. SPSS software (SPSS version 22, Chicago, IL, USA) was used. The level of significance was set as 0.05.
| Results|| |
A total of 18 patients (12 boys and 6 girls) with 21 limbs (11 right and 10 left) were identified. Transverse screws were used in 15 limbs and oblique screws in 6 limbs. The mean age at surgery was 11.9 years (4.4-18.3 years). Age and gender distributions were similar for the two groups [Table 1]. There was no significant difference between the two groups in the amount of lengthening (40 mm [13% of the preoperative length] in the transverse and 35 mm [11% of the preoperative length] in the oblique group), angular correction, lateral malleolar and fibular head migration, and LDTA change [Table 2]. External frame duration was similar (5 months for the transverse and 4 months for the oblique group) as was external fixator index (41.4 days/cm for the transverse and 42.2 days/cm for the oblique) [Table 2]. The average fibular lengthening was 32 mm in the transverse and 26 mm in the oblique group; however, the difference was not statistically significant between the amounts of fibular and tibial lengthening in either group (P = 0.1 in the transverse and P = 0.42 in the oblique group).
|Table 1: Age and gender distribution for the two groups of patients (with transverse screws and with oblique screws) |
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|Table 2: Preoperative and postframe removal (postoperative) measurements for the two groups |
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Comparing pre- and post-lengthening radiographs, a significant migration of lateral malleolus (DTFI pre: 12 mm; post: 8 mm) and fibular head (PTFI pre: 17 mm; post: 22 mm) was noted in the transverse screws group [Table 3] but not in the oblique screws group [Table 4]. However, the amount of change in DTFI (lateral malleolar migration) was similar for both groups [Table 2]. Preoperative Malhotra grades were higher in the oblique group (P = 0.03). Two ankles in the transverse group moved from Malhotra 0 to 1 after lengthening; however, no grade change was noted in the oblique group. It is important, however, to note that the number of cases in the oblique were small (6 limbs). There was no fibular nonunion in our patients and the fibulae, similar to the tibiae, had at least three cortices regenerated prior to frame removal. No screw-related complications were encountered in either group.
|Table 3: Preoperative and postframe removal (postoperative) measurements for the transverse group |
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|Table 4: Preoperative and postframe removal (postoperative) measurements for the oblique group |
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| Discussion|| |
The role of the fibula in the ankle biomechanics has been well described. , Alterations in the ankle alignment and stability might be caused by any change in the distal fibular length.  Ankle valgus has been reported as a result of lateral malleolar migration after tibial lengthening ,, with different measurements of the distal fibular length associated with the development of ankle valgus. A DTFI of 6 mm or less has been reported to be associated with some degree of ankle valgus.  Change of this index of more than 5 mm has also been found as a cutoff value between ankles with and without valgus.  In our study, the final DTFI in both groups was more than 6 mm, and the DTFI change was <5 mm. This finding, supported by data of the previous reports, , explains the minimal, not significant, change in LDTA found in our patients. Although DTFI change was statistically significant in the transverse group, it was <5 mm with a final mean value of more than 6 mm. Moreover, the amount of change in DTFI was similar for both methods. While the migration was noted in the radiographs with the frame on, for the purpose of consistency, the measurements were performed on the immediate radiographs postframe removal. Therefore, we believe that any migration noted had already occurred while the screw was in place and it was not a postframe removal migration.
Knee valgus was reported when fibular head migration was more than 10 mm.  However, no clinical signs or symptoms were noted even when the fibular head migrated distally as much as 3.3 cm.  No knee instability was found in our patients. PTFI change was similar for the two groups of screws and in both, it was <10 mm (5.1 mm in the transverse and 6.7 mm in the oblique group).
Malhotra grade progressed from 0 to 1 in two ankles of the transverse group. In both ankles, DTFI change was more than 5 mm (5.3 and 8.7 mm). However, LDTA change was 2° in both of them. No correlation between Malhotra Grade 1 and ankle valgus was previously found  and no definitive conclusion could be drawn based on these two cases.
In addition to the retrospective review, the small number of patients and the short-term follow-up were the main limitations of our study. None of our patients had any clinical issues with the change in ankle alignment, but longer follow-up is needed to further assess this. Premature consolidation of the fibula was not assessed. However, the aim of this study was to report the immediate outcomes after frame removal, comparing two techniques of syndesmotic fixation in terms of preventing lateral malleolar migration.
| Conclusion|| |
This study suggests that although migration of lateral malleolus was encountered in the transverse group, the amount of DTFI change was similar to the oblique group. Moreover, no significant LDTA change was noted in either group. No advantage of one syndesmotic fixation method over the other was found in this study. Longer follow-up is needed to detect any late changes.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4]