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Morphology of the Incisura Fibularis at the Distal Tibiofibular Syndesmosis in the Japanese Population
The Journal of Foot & Ankle Surgery xxx (2017) 1–4
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Original Research
Morphology of the Incisura Fibularis at the Distal Tibiofibular Syndesmosis in the Japanese Population Ichiro Tonogai, MD, PhD 1, Daisuke Hamada, MD, PhD 1, Koichi Sairyo, MD, PhD 2 1 2
Associate Professor, Department of Orthopedics, Institute of Biomedical Science, Tokushima University Graduate School, Tokushima, Japan Professor and Chairman, Department of Orthopedics, Institute of Biomedical Science, Tokushima University Graduate School, Tokushima, Japan
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 3
The morphology of the distal tibiofibular syndesmosis can determine the pathology and mechanism of syndesmotic injury. The present study assessed measurements obtained from computed tomography (CT) images of the normal distal tibiofibular syndesmosis in Japanese subjects. CT scans of 120 right feet with a normal distal tibiofibular syndesmosis obtained from January 2009 to December 2016 were retrospectively assessed at the level 10 mm proximal to the tibial plafond. The incisura fibularis was considered concave when its depth was 4 mm and shallow when its depth was <4 mm. The depth of the incisura fibularis, anterior tibiofibular distance (TFD), posterior TFD, and longitudinal/transverse length of the distal fibula were measured. The incisura fibularis was concave in 64.2% of the feet and shallow in 35.8%. The mean anterior TFD was 2.2 0.8 mm (2.4 0.8 mm in males; 2.1 0.8 mm in females; 2.1 0.8 mm for concave; 2.2 0.9 mm for shallow). The mean posterior TFD was 5.9 1.6 mm (6.7 2.1 in males; 5.7 1.3 mm in females; 5.5 1.3 mm for concave; 6.5 1.9 mm for shallow). The mean longitudinal/transverse length of the distal fibula at the level of the syndesmosis was 1.2 mm (1.3 mm in males; 1.2 mm in females; 1.1 mm for concave; 1.3 mm for shallow). The mean posterior TFD was significantly greater than the mean anterior TFD and was also significantly greater in males than in females. Significant differences were found in the body mass index, posterior TFD, and longitudinal/transverse length of the distal fibula according to whether the incisura fibularis was concave or shallow. The present study has provided measurements of the normal tibiofibular syndesmosis in the Japanese population. These data suggest that the morphology of the syndesmosis varies, especially with respect to whether the incisura fibularis is concave or shallow. Ó 2017 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: distal tibiofibular incisura fibularis syndesmosis
Distal tibiofibular syndesmotic injury occurs in 13% of all ankle fractures (1) and in 20% of patients requiring internal fixation of the ankle joint (2). Closed reduction of the distal tibiofibular joint results in malreduction in 16% to 52% of patients (3,4). The clinical outcomes of patients with malreduction are reported to be inferior to those of patients with an anatomic reduction (5). The need for anatomic reduction and stabilization of the injured syndesmosis is well established (6). Small changes in the congruity of the ankle joint, including the distal tibiofibular syndesmosis, have marked effects on joint contact stresses (7,8). Widening of the ankle mortise by 1 mm decreases the contact area at the tibiotalar joint by 42% (9) and can lead to chronic instability, arthrosis, and further injury if not diagnosed and treated Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Koichi Sairyo, MD, PhD, Department of Orthopedics, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15 Kuramoto, Tokushima 770-8503, Japan. E-mail address: [email protected] (K. Sairyo).
appropriately (10). Plain radiographs have limited sensitivity in detecting subtle displacement of the syndesmosis, and malalignment of the ankle joint is highly sensitive to positional changes (11,12). Computed tomography (CT) has been more widely used in the evaluation of ankle injury in recent years. The advantages of CT-based evaluation of the distal tibiofibular syndesmosis are that, unlike plain radiographs, CT provides axial views of the syndesmosis and is substantially less dependent on ankle positioning at the time of imaging (13). Ankle injury can be difficult to diagnose using radiographic criteria; thus, it is important to be aware of the wide anatomic variability in the depth of the fibular incisura, width of the syndesmosis, and shape of the distal fibula at the distal tibiofibular syndesmosis. However, syndesmotic morphology has not been investigated in the Japanese population. The present study assessed measurements taken from CT images of the normal distal tibiofibular syndesmosis in the Japanese population with the aim of identifying features that can help in the diagnosis of syndesmotic injury.
1067-2516/$ - see front matter Ó 2017 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2017.05.020
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Fig. 1. (A) Distance from the deepest point at the fibular incisura to the nearest point on the tangent between the tip of the anterior tibial tubercle and the tip of the posterior tibial tubercle. (B) A fibular incisura with a depth of 4 mm indicates the syndesmosis has a deep (i.e., concave) shape and a depth of <4 mm indicates a shallow shape. Patients and Methods The present retrospective study was conducted with approval from the ethics board of Tokushima University Hospital. CT images taken of 120 right feet of 120 patients (31 males, 89 females) who had undergone total knee arthroplasty from January 2009 to December 2016 at our institution were subjected to analysis. Whole leg CT had been performed for evaluation of the knee alignment and surgical planning before total knee arthroplasty. Patients with a history of previous ankle trauma or surgery, those with a congenital or developmental deformity, and those with inflammatory arthritis were excluded. The whole leg CT images were obtained in 1.0-mm-thick axial slices. The images were reviewed using the bone window setting (window 2200 HU; level 200 HU). CT scan data were imported into AquariusNET, version 1.6, software (TeraRecon Inc., San Mateo, CA) for analysis. The assessment was performed using axial CT images to assess the depth of the incisura fibularis, width of the distal tibiofibular syndesmosis, and shape of the distal fibula. The distal tibiofibular syndesmosis is generally measured at the level 10 mm proximal to the tibial plafond (14–19). Given that measurements of the distal tibiofibular syndesmosis taken from a position 1 cm above the ankle joint line are routinely accepted, we used measurements taken at this line. The morphology of the incisura fibularis was categorized as concave (a crescent-shaped syndesmosis) or shallow (a rectangular-shaped syndesmosis). The depth of the incisura fibularis was measured from its deepest point to the line between the tips of the anterior and posterior tubercles (Fig. 1A). The incisura fibularis was considered concave when its depth was 4 mm and shallow when its depth was <4 mm (Fig. 1B) (20). The following parameters were measured across the syndesmosis: 1. Anterior tibiofibular distance (TFD), from point A at the anterior border of the fibula to point B at the nearest perpendicular point from point A on the anterior tibial tubercle (Fig. 2A)
2. Posterior TFD, from point C at the medial border of the fibula to point D at the nearest perpendicular point from point C on the lateral border of the posterior tibial tubercle (Fig. 2A) 3. Longitudinal length of the distal fibula (Fig. 2B) 4. Transverse length of the distal fibula (Fig. 2B) The longitudinal/transverse length of the distal fibula was calculated by dividing the longitudinal length of the distal fibula (no. 3) by its transverse length (no. 4). An orthopedic surgeon who was not one of the study investigators and who was unaware of the purpose of the research recorded 3 sets of measurements for each parameter from which the average value was calculated. Statistical Analysis All data are reported as the mean standard deviation. Differences in the values obtained for each parameter were compared between groups using the unpaired t test, Mann-Whitney U test, or c2 test, as appropriate. All statistical analysis was performed using SPSS software, version 24.0 (IBM Corp., Armonk, NY). A p value < .05 was considered statistically significant.
Results The mean patient age was 74.3 7.8 years (73.3 7.5 years for males; 74.5 7.7 years for females). The mean body mass index (BMI) was 26.1 3.8 kg/m2 (25.5 2.8 kg/m2 for males; 26.4 4.0 kg/m2 for females). The morphology of the incisura fibularis was concave in
Fig. 2. (A) (1) indicates the anterior tibiofibular distance (TFD), which is the distance between point A (anterior border of the fibula) and point B (nearest perpendicular point from point A on anterior tibial tubercle); and (2) indicates the posterior tibiofibular distance, which is the distance between points C and D. Point C is the medial border of the fibula, and point D is the nearest point from point C on the lateral border of the posterior tibial tubercle. (B) (3) indicates the longitudinal length of the fibula on the distal tibiofibular syndesmosis, and (4) indicates the transverse length of the fibula on the distal tibiofibular syndesmosis.
I. Tonogai et al. / The Journal of Foot & Ankle Surgery xxx (2017) 1–4
Table 1 Comparison of measurements between males and females Overall Subjects (n) Age (y) BMI (kg/m2) Incisura fibularis type Concave Shallow Incisura fibularis depth (mm) Anterior TFD* (mm) Posterior TFD* (mm) Longitudinal length of fibula (mm) Transverse length of fibula (mm) Longitudinal/transverse length of fibula
Table 3 Reported occurrence of concave and shallow incisura fibularis types
Male
Female
p Value
120 31 (25.8) 89 (74.2) 74.3 7.8 73.6 7.5 74.5 7.7 NS 26.1 3.8 25.5 2.8 26.4 4.0 NS 77 (64.2) 43 (35.8) 4.1 1.7 2.2 0.8 5.9 1.6 16.3 1.9 13.5 1.6 1.2
18 13 4.1 2.4 6.7 17.6 13.7 1.3
1.8 0.8 2.1 2.0 1.9
59 30 4.5 2.1 5.7 15.8 13.4 1.2
1.6 0.8 1.3 1.6 1.5
NS NS NS NS NS NS NS NS
Abbreviations: BMI, body mass index; NS, not significant; TFD, tibiofibular distance. Data in parentheses are percentages. * The posterior TFD was significantly greater than the anterior TFD (p < .05).
64.2% of cases and shallow in 35.8% (Table 1). The mean anterior TFD was 2.2 0.8 mm (2.4 0.8 mm in males; 2.1 0.8 mm in females; Table 1) and was 2.1 0.8 mm for the concave type and 2.2 0.9 mm for the shallow type (Table 2). The mean posterior TFD was 5.9 1.6 mm (6.7 2.1 mm in males; 5.7 1.3 mm in females; Table 1) and was 5.51 1.38 mm for the concave type and 6.55 1.90 mm for the shallow type (Table 2). Overall, the posterior TFD was significantly greater than the anterior TFD (p < .05; Table 1). The mean longitudinal length of the distal fibula at the level of the distal tibiofibular syndesmosis was 16.3 1.9 mm (17.6 2.0 mm in males; 15.8 1.6 mm in females; Table 1) and was 15.7 1.7 mm for the concave type and 17.2 1.9 mm for the shallow type (Table 2). The mean transverse length of the distal fibula at the level of the syndesmosis was 13.5 1.9 mm (13.7 1.9 mm in males; 13.4 1.5 mm in females; Table 1) and was 14.0 1.5 mm for the concave type and 12.6 1.5 mm for the shallow type (Table 2). The mean ratio of the longitudinal length of the distal fibula to the transverse length of the distal fibula at the level of the syndesmosis was 1.2 (1.3 in males; 1.2 in females; Table 1) and was 1.1 for the concave type and 1.3 for the shallow type (Table 2). Overall, no significant differences were found between males and females in the depth of the incisura fibularis, anterior TFD, longitudinal or transverse length of the distal fibula, or longitudinal/transverse length of the distal fibula (Table 1). However, the posterior TFD was significantly greater in males than in females (p < .05; Table 1). No significant differences were found between patients with a concave incisura fibularis and those with a shallow one in gender, age, or anterior TFD (Table 2). However, significant differences were found in the BMI, posterior TFD, longitudinal and transverse lengths of the distal Table 2 Comparison of measurements between concave and shallow incisura fibularis types at distal tibiofibular syndesmosis Concave Type (n ¼ 77) Gender Male Female Age (y) BMI (kg/m2) Incisura fibularis depth (mm) Anterior TFD (mm) Posterior TFD (mm) Longitudinal length of fibula (mm) Transverse length of fibula (mm) Longitudinal/transverse length of fibula
18 59 74.0 27.0 5.3 2.1 5.5 15.7 14.0 1.1
7.9 3.0 1.0 0.8 1.3 1.7 1.5
3
Shallow Type (n ¼ 43) 13 30 74.7 24.6 2.4 2.2 6.5 17.2 12.6 1.3
7.6 3.0 1.0 0.9 1.9 1.9 1.5
p Value
NS <.05* NS NS <.05* <.05* <.05* <.05*
Abbreviations: BMI, body mass index; NS, not significant; TFD, tibiofibular distance. * Statistically significant difference.
Investigator Hocker et al (21), 1989 Ebraheim et al (22), 1998 Mavi et al (23), 2002 Yildirm et al (24), 2003 Taser et al (20), 2009 Elgafy et al (25), 2010 Yeung et al (26), 2015 Present study
Subjects (n) 25 12 18 150 35 100 123 120
Concave Type (%)
Shallow Type (%)
75
25 (convex and irregular forms) 40 65 45.4 65 33 46 35.8
60 35 54.6 35 67 45.2 64.2
fibula, and longitudinal/transverse length of the distal fibula according to incisura fibularis type (concave or shallow; p < .05; Table 2).
Discussion In the present study, the incisura fibularis was concave in 77 subjects (64.2%) and shallow in 43 (35.8%). The posterior TFD was be significantly greater in males than in females. We also found significant differences in the BMI, posterior TFD, longitudinal and transverse lengths of the distal fibula, and longitudinal/transverse length of the distal fibula according to whether the incisura fibularis was concave or shallow. The percentages of concave and shallow types of incisura fibularis at the distal tibiofibular syndesmosis as reported in published studies (21–26) are listed in Table 3. Taser et al (20) and Mavi et al (23) reported that 35% of patients presented with a concave shape and 65% had shallow concave fibular incisura. However, Hocker and Pachucki (21) reported the concave type in 75% of their subjects, convex in 16%, and irregular in 8%. Similarly, Ebraheim et al (22) reported the concave type in 60% and the shallow type in 40% of their cases. Similar to the latter 2 groups, most of our subjects had a concave incisura fibularis. The posterior TFD was longer than the anterior TFD at the distal tibiofibular syndesmosis in the present study, as reported previously (25–32). It has been demonstrated that the anterior tubercle is more prominent than the posterior tubercle (33,34), and it is likely that this prominence contributed to our finding of a difference between the anterior and posterior TFD. However, Pelton et al (35) found the anterior and posterior widths of the joint to be equal and suggested that the syndesmosis ratio is 1 in normal individuals. Gardner et al (4) considered a difference of 2 mm in the anterior and posterior measurements to indicate malreduction; however, we found the difference between the anterior and posterior TFD to be >2 mm, which was also reported by other investigators (Table 4) (25–32). A difference of Table 4 Reported measurements of anterior and posterior tibiofibular distances Investigator
Subjects (n)
TFD (mm) Anterior
Posterior
Elgafy et al (25), 2010 Mukhopadhyay et al (27), 2011 Nault et al (28), 2013 Lepojarvi et al (29), 2014 Mendelsohn et al (30), 2014 Chen et al (31), 2015
100 19 100 64 35 484
Yeung et al (26), 2015 Warner et al (32), 2015 Present study
123 155 120
2 2.25 4 2.8 1.7* Male, 2.8; female, 1.8 1.8 4.46 2.2
4 5.20 8 5.1 2.3y Male, 3.6–3.7; female, 2.8–2.9 4.1 8.80 5.9
Abbreviation: TFD, tibiofibular distance. * Anterior syndesmosis joint space. y Posterior syndesmosis joint space.
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>2 mm likely represents the normal anatomic variation in the general population. Elgafy et al (25) reported the mean anterior and posterior widths of the distal tibiofibular syndesmosis were, respectively, 2 mm and 5 mm in adult males and 2 mm and 4 mm in adult females. They suggested that the posterior TFD was slightly greater in males than in females and that the anterior TFD was similar between the genders. Our finding that the posterior TFD was influenced by gender is consistent with that of Elgafy et al (25). Moreover, the BMI was significantly greater in subjects with a concave incisura fibularis in our study. During normal ambulation, the force across the ankle joint can reach almost 4 times that of the body weight (36), and it is possible that the depth of the incisura fibularis is influenced by body weight. To the best of our knowledge, this is the first report showing that the posterior TFD is significantly greater in subjects with a concave incisura fibularis than in their counterparts with a shallow incisura fibularis. The risk of traumatic injury at the syndesmosis is thought to be related to the shape of the incisura fibularis. Taser et al (20) reported that an ankle mortise with a more posteriorly positioned fibula has less structural stability and is more susceptible to sprains. Mavi et al (23) reported that the anterior and posterior tubercles were longer, the fibular incisura depth was greater, and the fibula was more anterior in a group of patients with a history of recurrent ankle sprains than in a control group. Moreover, Hoefnagels et al (37) reported the mean load at which the anterior tibiofibular ligament failed was 625 255 N, and Beumer et al (38) reported that the strength of the anterior syndesmotic tibiofibular ligament was 499 N and the strength of the posterior syndesmotic tibiofibular ligament was 708 N. Further biomechanical studies are necessary to confirm whether a shallow or concave fibular incisura is a predisposing factor for displacement of the fibula associated with fracture dislocation. To the best of our knowledge, this is the first study to report that the longitudinal length of the distal fibula is greater than its transverse length when the incisura fibularis is concave and that the distal fibula is longer longitudinally in a concave incisura fibularis than in a shallow one. A relationship might also exist between the shape of the distal fibula and recurrent ankle instability. A strength of our study was its large sample size compared with that of other studies. Our data provide important information about the morphology of the distal tibiofibular syndesmosis. The main limitation of the present study was the level at which the syndesmosis was evaluated, given a recent report suggesting gender-related differences in the level of the distal tibiofibular syndesmosis (31). In conclusion, axial CT measurements of the depth of the incisura fibularis, TFD, and variability in the shape of the distal fibula might be useful for achieving accurate reduction of the syndesmosis when treating ankle fractures with a concomitant syndesmosis injury in the Japanese population.
References 1. Lindsjo U. Operative treatment of ankle fractures. Acta Orthop Scand Suppl 189:1– 131, 1981. 2. Pettrone FA, Gail M, Pee D, Fitzpatrick T, Van Herpe LB. Quantitative criteria for prediction of the results after displaced fracture of the ankle. J Bone Joint Surg Am 6:667–677, 1983. 3. Weening B, Bhandari M. Predictors of functional outcome following transsyndesmotic screw fixation of ankle fractures. J Orthop Trauma 19:102–108, 2005. 4. Gardner MJ, Demetrakopoulos D, Briggs SM, Helfet DL, Lorich DG. Malreduction of the tibiofibular syndesmosis in ankle fractures. Foot Ankle Int 27:788–792, 2006. 5. Sagi HC, Shah AR, Sanders RW. The functional consequence of syndesmotic joint malreduction at a minimum 2-year follow-up. J Orthop Trauma 26:439–443, 2012. 6. Chissell HR, Jones J. The influence of a diastasis screw on the outcome of Weber type-C ankle fractures. J Bone Joint Surg Br 77:435–438, 1995.
7. McKinley TO, Rudert MJ, Tochigi Y, Pedersen DR, Koos DC, Baer TE, Brown TD. Incongruity-dependent changes of contact stress rates in human cadaveric ankles. J Orthop Trauma 20:732–738, 2006. 8. Tochigi Y, Rudert MJ, McKinley TO, Pedersen DR, Brown TD. Correlation of dynamic cartilage contact stress aberrations with severity of instability in ankle incongruity. J Orthop Res 26:1186–1193, 2008. 9. Harris J, Fallat L. Effects of isolated Weber B fibular fractures on the tibiotalar contact area. J Foot Ankle Surg 43:3–9, 2004. 10. van den Bekerom MP, de Leeuw PA, van Dijk CN. Delayed operative treatment of syndesmotic instability: current concepts review. Injury 40:1137–1142, 2009. 11. Brage ME, Bennett CR, Whitehurst JB, Getty PJ, Toledano A. Observer reliability in ankle radiographic measurements. Foot Ankle Int 18:324–329, 1997. 12. Beumer A, van Hemert WL, Niesing R, Entius CA, Ginai AZ, Mulder PG, Swierstra BA. Radiographic measurement of the distal tibiofibular syndesmosis has limited use. Clin Orthop Relat Res 423:227–234, 2004. 13. Saldua NS, Harris JF, LeClere LE, Girard PJ, Carney JR. Plantar flexion influences radiographic measurements of the ankle mortise. J Bone Joint Surg Am 92:911– 915, 2010. 14. Leeds HC, Ehrlich MG. Instability of the distal tibiofibular syndesmosis after bimalleolar and trimalleolar ankle fractures. J Bone Joint Surg Am 66:490–503, 1984. 15. Harper MC, Keller TS. A radiographic evaluation of the tibiofibular syndesmosis. Foot Ankle 10:156–160, 1989. 16. Ostrum RF, De Meo P, Subramanian R. A critical analysis of the anterior-posterior radiographic anatomy of the ankle syndesmosis. Foot Ankle Int 16:128–131, 1995. 17. Ebraheim NA, Lu J, Yang H, Mekhail AO, Yeating RA. Radiographic and CT evaluation of tibiofibular syndesmotic diastasis: a cadaver study. Foot Ankle Int 8:693– 698, 1997. 18. Wuest TK. Injuries to the distal lower extremity syndesmosis. J Am Acad Orthop Surg 5:172–181, 1997. 19. Shah AS, Kadakia AR, Tan GJ, Karadsheh MS, Wolter TD, Sabb B. Radiographic evaluation of the normal distal tibiofibular syndesmosis. Foot Ankle Int 33:870– 876, 2012. lu V. Evaluation of morphometric characteristics of the 20. Tas¸er F, Toker S, Kilinc¸og fibular incisura on dry bones. Eklem Hastalik Cerrahisi 20:52–58, 2009. 21. Hocker K, Pachucki A. The fibular incisure[sic] of the tibia: the cross-sectional position of the fibula in distal syndesmosis [in German]. Unfallchirurg 92:401– 406, 1989. 22. Ebraheim NA, Lu J, Yang H, Rollins J. The fibular incisure[sic] of the tibia on CT scan: a cadaver study. Foot Ankle Int 19:318–321, 1998. 23. Mavi A, Yildirim H, Gunes H, Pestamalci T, Gumusburun E. The fibular incisura of the tibia with recurrent sprained ankle on magnetic resonance imaging. Saudi Med J 23:845–849, 2002. 24. Yildirim H, Mavi A, Buyukbebeci O, Gumuflburun E. Evaluation of the fibular incisura of the tibia with magnetic resonance imaging. Foot Ankle Int 24:387–391, 2003. 25. Elgafy H, Semaan HB, Blessinger B, Wassef A, Ebraheim NA. Computed tomography of normal distal tibiofibular syndesmosis. Skeletal Radiol 39:559– 564, 2010. 26. Yeung TW, Chan CY, Chan WC, Yeung YN, Yuen MK. Can pre-operative axial CT imaging predict syndesmosis instability in patients sustaining ankle fractures? Seven years’ experience in a tertiary trauma center. Skeletal Radiol 44:823–829, 2015. 27. Mukhopadhyay S, Metcalfe A, Guha AR, Mohanty K, Hemmadi S, Lyons K, O’Doherty D. Malreduction of syndesmosisdare we considering the anatomical variation? Injury 42:1073–1076, 2011. bert-Davies J, Laflamme GY, Leduc S. CT scan assessment of the 28. Nault ML, He syndesmosis: a new reproducible method. J Orthop Trauma 27:638–641, 2013. 29. Lepojarvi S, Pakarinen H, Savola O, Haapea M, Sequeiros RB, Niinimaki J. Posterior translation of the fibula may indicate malreduction: CT study of normal variation in uninjured ankles. J Orthop Trauma 28:205–209, 2014. 30. Mendelsohn ES, Hoshino CM, Harris TG, Zinar DM. CT characterizing the anatomy of uninjured ankle syndesmosis. Orthopedics 37:e157–e160, 2014. 31. Chen Y, Qiang M, Zhang K, Li H, Dai H. A reliable radiographic measurement for evaluation of normal distal tibiofibular syndesmosis: a multi-detector computed tomography study in adults. J Foot Ankle Res 8:32, 2015. 32. Warner SJ, Fabricant PD, Garner MR, Schottel PC, Helfet DL, Lorich DG. The measurement and clinical importance of syndesmotic reduction after operative fixation of rotational ankle fractures. J Bone Joint Surg Am 97:1935–1944, 2015. 33. Sclafani SJ. Ligamentous injury of the lower tibiofibular syndesmosis: radiographic evidence. Radiology 156:21–27, 1985. 34. Stiehl JB. Complex ankle fracture dislocations with syndesmotic diastasis. Orthop Rev 19:499–507, 1990. 35. Pelton K, Thordarson DB, Barnwell J. Open versus closed treatment of the fibula in Maisonneuve injuries. Foot Ankle Int 31:604–608, 2010. 36. Procter P, Paul JP. Ankle joint biomechanics. J Biomech 15:627–634, 1982. 37. Hoefnagels EM, Waites MD, Wing ID, Belkoff SM, Swierstra BA. Biomechanical comparison of the interosseous tibiofibular ligament and the anterior tibiofibular ligament. Foot Ankle Int 28:602–604, 2007. 38. Beumer A, van Hemert WL, Swierstra BA, Jasper LE, Belkoff SM. A biomechanical evaluation of the tibiofibular and tibiotalar ligaments of the ankle. Foot Ankle Int 24:426–429, 2003.
Contents lists available at ScienceDirect
The Journal of Foot & Ankle Surgery journal homepage: www.jfas.org
Original Research
Morphology of the Incisura Fibularis at the Distal Tibiofibular Syndesmosis in the Japanese Population Ichiro Tonogai, MD, PhD 1, Daisuke Hamada, MD, PhD 1, Koichi Sairyo, MD, PhD 2 1 2
Associate Professor, Department of Orthopedics, Institute of Biomedical Science, Tokushima University Graduate School, Tokushima, Japan Professor and Chairman, Department of Orthopedics, Institute of Biomedical Science, Tokushima University Graduate School, Tokushima, Japan
a r t i c l e i n f o
a b s t r a c t
Level of Clinical Evidence: 3
The morphology of the distal tibiofibular syndesmosis can determine the pathology and mechanism of syndesmotic injury. The present study assessed measurements obtained from computed tomography (CT) images of the normal distal tibiofibular syndesmosis in Japanese subjects. CT scans of 120 right feet with a normal distal tibiofibular syndesmosis obtained from January 2009 to December 2016 were retrospectively assessed at the level 10 mm proximal to the tibial plafond. The incisura fibularis was considered concave when its depth was 4 mm and shallow when its depth was <4 mm. The depth of the incisura fibularis, anterior tibiofibular distance (TFD), posterior TFD, and longitudinal/transverse length of the distal fibula were measured. The incisura fibularis was concave in 64.2% of the feet and shallow in 35.8%. The mean anterior TFD was 2.2 0.8 mm (2.4 0.8 mm in males; 2.1 0.8 mm in females; 2.1 0.8 mm for concave; 2.2 0.9 mm for shallow). The mean posterior TFD was 5.9 1.6 mm (6.7 2.1 in males; 5.7 1.3 mm in females; 5.5 1.3 mm for concave; 6.5 1.9 mm for shallow). The mean longitudinal/transverse length of the distal fibula at the level of the syndesmosis was 1.2 mm (1.3 mm in males; 1.2 mm in females; 1.1 mm for concave; 1.3 mm for shallow). The mean posterior TFD was significantly greater than the mean anterior TFD and was also significantly greater in males than in females. Significant differences were found in the body mass index, posterior TFD, and longitudinal/transverse length of the distal fibula according to whether the incisura fibularis was concave or shallow. The present study has provided measurements of the normal tibiofibular syndesmosis in the Japanese population. These data suggest that the morphology of the syndesmosis varies, especially with respect to whether the incisura fibularis is concave or shallow. Ó 2017 by the American College of Foot and Ankle Surgeons. All rights reserved.
Keywords: distal tibiofibular incisura fibularis syndesmosis
Distal tibiofibular syndesmotic injury occurs in 13% of all ankle fractures (1) and in 20% of patients requiring internal fixation of the ankle joint (2). Closed reduction of the distal tibiofibular joint results in malreduction in 16% to 52% of patients (3,4). The clinical outcomes of patients with malreduction are reported to be inferior to those of patients with an anatomic reduction (5). The need for anatomic reduction and stabilization of the injured syndesmosis is well established (6). Small changes in the congruity of the ankle joint, including the distal tibiofibular syndesmosis, have marked effects on joint contact stresses (7,8). Widening of the ankle mortise by 1 mm decreases the contact area at the tibiotalar joint by 42% (9) and can lead to chronic instability, arthrosis, and further injury if not diagnosed and treated Financial Disclosure: None reported. Conflict of Interest: None reported. Address correspondence to: Koichi Sairyo, MD, PhD, Department of Orthopedics, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15 Kuramoto, Tokushima 770-8503, Japan. E-mail address: [email protected] (K. Sairyo).
appropriately (10). Plain radiographs have limited sensitivity in detecting subtle displacement of the syndesmosis, and malalignment of the ankle joint is highly sensitive to positional changes (11,12). Computed tomography (CT) has been more widely used in the evaluation of ankle injury in recent years. The advantages of CT-based evaluation of the distal tibiofibular syndesmosis are that, unlike plain radiographs, CT provides axial views of the syndesmosis and is substantially less dependent on ankle positioning at the time of imaging (13). Ankle injury can be difficult to diagnose using radiographic criteria; thus, it is important to be aware of the wide anatomic variability in the depth of the fibular incisura, width of the syndesmosis, and shape of the distal fibula at the distal tibiofibular syndesmosis. However, syndesmotic morphology has not been investigated in the Japanese population. The present study assessed measurements taken from CT images of the normal distal tibiofibular syndesmosis in the Japanese population with the aim of identifying features that can help in the diagnosis of syndesmotic injury.
1067-2516/$ - see front matter Ó 2017 by the American College of Foot and Ankle Surgeons. All rights reserved. http://dx.doi.org/10.1053/j.jfas.2017.05.020
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Fig. 1. (A) Distance from the deepest point at the fibular incisura to the nearest point on the tangent between the tip of the anterior tibial tubercle and the tip of the posterior tibial tubercle. (B) A fibular incisura with a depth of 4 mm indicates the syndesmosis has a deep (i.e., concave) shape and a depth of <4 mm indicates a shallow shape. Patients and Methods The present retrospective study was conducted with approval from the ethics board of Tokushima University Hospital. CT images taken of 120 right feet of 120 patients (31 males, 89 females) who had undergone total knee arthroplasty from January 2009 to December 2016 at our institution were subjected to analysis. Whole leg CT had been performed for evaluation of the knee alignment and surgical planning before total knee arthroplasty. Patients with a history of previous ankle trauma or surgery, those with a congenital or developmental deformity, and those with inflammatory arthritis were excluded. The whole leg CT images were obtained in 1.0-mm-thick axial slices. The images were reviewed using the bone window setting (window 2200 HU; level 200 HU). CT scan data were imported into AquariusNET, version 1.6, software (TeraRecon Inc., San Mateo, CA) for analysis. The assessment was performed using axial CT images to assess the depth of the incisura fibularis, width of the distal tibiofibular syndesmosis, and shape of the distal fibula. The distal tibiofibular syndesmosis is generally measured at the level 10 mm proximal to the tibial plafond (14–19). Given that measurements of the distal tibiofibular syndesmosis taken from a position 1 cm above the ankle joint line are routinely accepted, we used measurements taken at this line. The morphology of the incisura fibularis was categorized as concave (a crescent-shaped syndesmosis) or shallow (a rectangular-shaped syndesmosis). The depth of the incisura fibularis was measured from its deepest point to the line between the tips of the anterior and posterior tubercles (Fig. 1A). The incisura fibularis was considered concave when its depth was 4 mm and shallow when its depth was <4 mm (Fig. 1B) (20). The following parameters were measured across the syndesmosis: 1. Anterior tibiofibular distance (TFD), from point A at the anterior border of the fibula to point B at the nearest perpendicular point from point A on the anterior tibial tubercle (Fig. 2A)
2. Posterior TFD, from point C at the medial border of the fibula to point D at the nearest perpendicular point from point C on the lateral border of the posterior tibial tubercle (Fig. 2A) 3. Longitudinal length of the distal fibula (Fig. 2B) 4. Transverse length of the distal fibula (Fig. 2B) The longitudinal/transverse length of the distal fibula was calculated by dividing the longitudinal length of the distal fibula (no. 3) by its transverse length (no. 4). An orthopedic surgeon who was not one of the study investigators and who was unaware of the purpose of the research recorded 3 sets of measurements for each parameter from which the average value was calculated. Statistical Analysis All data are reported as the mean standard deviation. Differences in the values obtained for each parameter were compared between groups using the unpaired t test, Mann-Whitney U test, or c2 test, as appropriate. All statistical analysis was performed using SPSS software, version 24.0 (IBM Corp., Armonk, NY). A p value < .05 was considered statistically significant.
Results The mean patient age was 74.3 7.8 years (73.3 7.5 years for males; 74.5 7.7 years for females). The mean body mass index (BMI) was 26.1 3.8 kg/m2 (25.5 2.8 kg/m2 for males; 26.4 4.0 kg/m2 for females). The morphology of the incisura fibularis was concave in
Fig. 2. (A) (1) indicates the anterior tibiofibular distance (TFD), which is the distance between point A (anterior border of the fibula) and point B (nearest perpendicular point from point A on anterior tibial tubercle); and (2) indicates the posterior tibiofibular distance, which is the distance between points C and D. Point C is the medial border of the fibula, and point D is the nearest point from point C on the lateral border of the posterior tibial tubercle. (B) (3) indicates the longitudinal length of the fibula on the distal tibiofibular syndesmosis, and (4) indicates the transverse length of the fibula on the distal tibiofibular syndesmosis.
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Table 1 Comparison of measurements between males and females Overall Subjects (n) Age (y) BMI (kg/m2) Incisura fibularis type Concave Shallow Incisura fibularis depth (mm) Anterior TFD* (mm) Posterior TFD* (mm) Longitudinal length of fibula (mm) Transverse length of fibula (mm) Longitudinal/transverse length of fibula
Table 3 Reported occurrence of concave and shallow incisura fibularis types
Male
Female
p Value
120 31 (25.8) 89 (74.2) 74.3 7.8 73.6 7.5 74.5 7.7 NS 26.1 3.8 25.5 2.8 26.4 4.0 NS 77 (64.2) 43 (35.8) 4.1 1.7 2.2 0.8 5.9 1.6 16.3 1.9 13.5 1.6 1.2
18 13 4.1 2.4 6.7 17.6 13.7 1.3
1.8 0.8 2.1 2.0 1.9
59 30 4.5 2.1 5.7 15.8 13.4 1.2
1.6 0.8 1.3 1.6 1.5
NS NS NS NS NS NS NS NS
Abbreviations: BMI, body mass index; NS, not significant; TFD, tibiofibular distance. Data in parentheses are percentages. * The posterior TFD was significantly greater than the anterior TFD (p < .05).
64.2% of cases and shallow in 35.8% (Table 1). The mean anterior TFD was 2.2 0.8 mm (2.4 0.8 mm in males; 2.1 0.8 mm in females; Table 1) and was 2.1 0.8 mm for the concave type and 2.2 0.9 mm for the shallow type (Table 2). The mean posterior TFD was 5.9 1.6 mm (6.7 2.1 mm in males; 5.7 1.3 mm in females; Table 1) and was 5.51 1.38 mm for the concave type and 6.55 1.90 mm for the shallow type (Table 2). Overall, the posterior TFD was significantly greater than the anterior TFD (p < .05; Table 1). The mean longitudinal length of the distal fibula at the level of the distal tibiofibular syndesmosis was 16.3 1.9 mm (17.6 2.0 mm in males; 15.8 1.6 mm in females; Table 1) and was 15.7 1.7 mm for the concave type and 17.2 1.9 mm for the shallow type (Table 2). The mean transverse length of the distal fibula at the level of the syndesmosis was 13.5 1.9 mm (13.7 1.9 mm in males; 13.4 1.5 mm in females; Table 1) and was 14.0 1.5 mm for the concave type and 12.6 1.5 mm for the shallow type (Table 2). The mean ratio of the longitudinal length of the distal fibula to the transverse length of the distal fibula at the level of the syndesmosis was 1.2 (1.3 in males; 1.2 in females; Table 1) and was 1.1 for the concave type and 1.3 for the shallow type (Table 2). Overall, no significant differences were found between males and females in the depth of the incisura fibularis, anterior TFD, longitudinal or transverse length of the distal fibula, or longitudinal/transverse length of the distal fibula (Table 1). However, the posterior TFD was significantly greater in males than in females (p < .05; Table 1). No significant differences were found between patients with a concave incisura fibularis and those with a shallow one in gender, age, or anterior TFD (Table 2). However, significant differences were found in the BMI, posterior TFD, longitudinal and transverse lengths of the distal Table 2 Comparison of measurements between concave and shallow incisura fibularis types at distal tibiofibular syndesmosis Concave Type (n ¼ 77) Gender Male Female Age (y) BMI (kg/m2) Incisura fibularis depth (mm) Anterior TFD (mm) Posterior TFD (mm) Longitudinal length of fibula (mm) Transverse length of fibula (mm) Longitudinal/transverse length of fibula
18 59 74.0 27.0 5.3 2.1 5.5 15.7 14.0 1.1
7.9 3.0 1.0 0.8 1.3 1.7 1.5
3
Shallow Type (n ¼ 43) 13 30 74.7 24.6 2.4 2.2 6.5 17.2 12.6 1.3
7.6 3.0 1.0 0.9 1.9 1.9 1.5
p Value
NS <.05* NS NS <.05* <.05* <.05* <.05*
Abbreviations: BMI, body mass index; NS, not significant; TFD, tibiofibular distance. * Statistically significant difference.
Investigator Hocker et al (21), 1989 Ebraheim et al (22), 1998 Mavi et al (23), 2002 Yildirm et al (24), 2003 Taser et al (20), 2009 Elgafy et al (25), 2010 Yeung et al (26), 2015 Present study
Subjects (n) 25 12 18 150 35 100 123 120
Concave Type (%)
Shallow Type (%)
75
25 (convex and irregular forms) 40 65 45.4 65 33 46 35.8
60 35 54.6 35 67 45.2 64.2
fibula, and longitudinal/transverse length of the distal fibula according to incisura fibularis type (concave or shallow; p < .05; Table 2).
Discussion In the present study, the incisura fibularis was concave in 77 subjects (64.2%) and shallow in 43 (35.8%). The posterior TFD was be significantly greater in males than in females. We also found significant differences in the BMI, posterior TFD, longitudinal and transverse lengths of the distal fibula, and longitudinal/transverse length of the distal fibula according to whether the incisura fibularis was concave or shallow. The percentages of concave and shallow types of incisura fibularis at the distal tibiofibular syndesmosis as reported in published studies (21–26) are listed in Table 3. Taser et al (20) and Mavi et al (23) reported that 35% of patients presented with a concave shape and 65% had shallow concave fibular incisura. However, Hocker and Pachucki (21) reported the concave type in 75% of their subjects, convex in 16%, and irregular in 8%. Similarly, Ebraheim et al (22) reported the concave type in 60% and the shallow type in 40% of their cases. Similar to the latter 2 groups, most of our subjects had a concave incisura fibularis. The posterior TFD was longer than the anterior TFD at the distal tibiofibular syndesmosis in the present study, as reported previously (25–32). It has been demonstrated that the anterior tubercle is more prominent than the posterior tubercle (33,34), and it is likely that this prominence contributed to our finding of a difference between the anterior and posterior TFD. However, Pelton et al (35) found the anterior and posterior widths of the joint to be equal and suggested that the syndesmosis ratio is 1 in normal individuals. Gardner et al (4) considered a difference of 2 mm in the anterior and posterior measurements to indicate malreduction; however, we found the difference between the anterior and posterior TFD to be >2 mm, which was also reported by other investigators (Table 4) (25–32). A difference of Table 4 Reported measurements of anterior and posterior tibiofibular distances Investigator
Subjects (n)
TFD (mm) Anterior
Posterior
Elgafy et al (25), 2010 Mukhopadhyay et al (27), 2011 Nault et al (28), 2013 Lepojarvi et al (29), 2014 Mendelsohn et al (30), 2014 Chen et al (31), 2015
100 19 100 64 35 484
Yeung et al (26), 2015 Warner et al (32), 2015 Present study
123 155 120
2 2.25 4 2.8 1.7* Male, 2.8; female, 1.8 1.8 4.46 2.2
4 5.20 8 5.1 2.3y Male, 3.6–3.7; female, 2.8–2.9 4.1 8.80 5.9
Abbreviation: TFD, tibiofibular distance. * Anterior syndesmosis joint space. y Posterior syndesmosis joint space.
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>2 mm likely represents the normal anatomic variation in the general population. Elgafy et al (25) reported the mean anterior and posterior widths of the distal tibiofibular syndesmosis were, respectively, 2 mm and 5 mm in adult males and 2 mm and 4 mm in adult females. They suggested that the posterior TFD was slightly greater in males than in females and that the anterior TFD was similar between the genders. Our finding that the posterior TFD was influenced by gender is consistent with that of Elgafy et al (25). Moreover, the BMI was significantly greater in subjects with a concave incisura fibularis in our study. During normal ambulation, the force across the ankle joint can reach almost 4 times that of the body weight (36), and it is possible that the depth of the incisura fibularis is influenced by body weight. To the best of our knowledge, this is the first report showing that the posterior TFD is significantly greater in subjects with a concave incisura fibularis than in their counterparts with a shallow incisura fibularis. The risk of traumatic injury at the syndesmosis is thought to be related to the shape of the incisura fibularis. Taser et al (20) reported that an ankle mortise with a more posteriorly positioned fibula has less structural stability and is more susceptible to sprains. Mavi et al (23) reported that the anterior and posterior tubercles were longer, the fibular incisura depth was greater, and the fibula was more anterior in a group of patients with a history of recurrent ankle sprains than in a control group. Moreover, Hoefnagels et al (37) reported the mean load at which the anterior tibiofibular ligament failed was 625 255 N, and Beumer et al (38) reported that the strength of the anterior syndesmotic tibiofibular ligament was 499 N and the strength of the posterior syndesmotic tibiofibular ligament was 708 N. Further biomechanical studies are necessary to confirm whether a shallow or concave fibular incisura is a predisposing factor for displacement of the fibula associated with fracture dislocation. To the best of our knowledge, this is the first study to report that the longitudinal length of the distal fibula is greater than its transverse length when the incisura fibularis is concave and that the distal fibula is longer longitudinally in a concave incisura fibularis than in a shallow one. A relationship might also exist between the shape of the distal fibula and recurrent ankle instability. A strength of our study was its large sample size compared with that of other studies. Our data provide important information about the morphology of the distal tibiofibular syndesmosis. The main limitation of the present study was the level at which the syndesmosis was evaluated, given a recent report suggesting gender-related differences in the level of the distal tibiofibular syndesmosis (31). In conclusion, axial CT measurements of the depth of the incisura fibularis, TFD, and variability in the shape of the distal fibula might be useful for achieving accurate reduction of the syndesmosis when treating ankle fractures with a concomitant syndesmosis injury in the Japanese population.
References 1. Lindsjo U. Operative treatment of ankle fractures. Acta Orthop Scand Suppl 189:1– 131, 1981. 2. Pettrone FA, Gail M, Pee D, Fitzpatrick T, Van Herpe LB. Quantitative criteria for prediction of the results after displaced fracture of the ankle. J Bone Joint Surg Am 6:667–677, 1983. 3. Weening B, Bhandari M. Predictors of functional outcome following transsyndesmotic screw fixation of ankle fractures. J Orthop Trauma 19:102–108, 2005. 4. Gardner MJ, Demetrakopoulos D, Briggs SM, Helfet DL, Lorich DG. Malreduction of the tibiofibular syndesmosis in ankle fractures. Foot Ankle Int 27:788–792, 2006. 5. Sagi HC, Shah AR, Sanders RW. The functional consequence of syndesmotic joint malreduction at a minimum 2-year follow-up. J Orthop Trauma 26:439–443, 2012. 6. Chissell HR, Jones J. The influence of a diastasis screw on the outcome of Weber type-C ankle fractures. J Bone Joint Surg Br 77:435–438, 1995.
7. McKinley TO, Rudert MJ, Tochigi Y, Pedersen DR, Koos DC, Baer TE, Brown TD. Incongruity-dependent changes of contact stress rates in human cadaveric ankles. J Orthop Trauma 20:732–738, 2006. 8. Tochigi Y, Rudert MJ, McKinley TO, Pedersen DR, Brown TD. Correlation of dynamic cartilage contact stress aberrations with severity of instability in ankle incongruity. J Orthop Res 26:1186–1193, 2008. 9. Harris J, Fallat L. Effects of isolated Weber B fibular fractures on the tibiotalar contact area. J Foot Ankle Surg 43:3–9, 2004. 10. van den Bekerom MP, de Leeuw PA, van Dijk CN. Delayed operative treatment of syndesmotic instability: current concepts review. Injury 40:1137–1142, 2009. 11. Brage ME, Bennett CR, Whitehurst JB, Getty PJ, Toledano A. Observer reliability in ankle radiographic measurements. Foot Ankle Int 18:324–329, 1997. 12. Beumer A, van Hemert WL, Niesing R, Entius CA, Ginai AZ, Mulder PG, Swierstra BA. Radiographic measurement of the distal tibiofibular syndesmosis has limited use. Clin Orthop Relat Res 423:227–234, 2004. 13. Saldua NS, Harris JF, LeClere LE, Girard PJ, Carney JR. Plantar flexion influences radiographic measurements of the ankle mortise. J Bone Joint Surg Am 92:911– 915, 2010. 14. Leeds HC, Ehrlich MG. Instability of the distal tibiofibular syndesmosis after bimalleolar and trimalleolar ankle fractures. J Bone Joint Surg Am 66:490–503, 1984. 15. Harper MC, Keller TS. A radiographic evaluation of the tibiofibular syndesmosis. Foot Ankle 10:156–160, 1989. 16. Ostrum RF, De Meo P, Subramanian R. A critical analysis of the anterior-posterior radiographic anatomy of the ankle syndesmosis. Foot Ankle Int 16:128–131, 1995. 17. Ebraheim NA, Lu J, Yang H, Mekhail AO, Yeating RA. Radiographic and CT evaluation of tibiofibular syndesmotic diastasis: a cadaver study. Foot Ankle Int 8:693– 698, 1997. 18. Wuest TK. Injuries to the distal lower extremity syndesmosis. J Am Acad Orthop Surg 5:172–181, 1997. 19. Shah AS, Kadakia AR, Tan GJ, Karadsheh MS, Wolter TD, Sabb B. Radiographic evaluation of the normal distal tibiofibular syndesmosis. Foot Ankle Int 33:870– 876, 2012. lu V. Evaluation of morphometric characteristics of the 20. Tas¸er F, Toker S, Kilinc¸og fibular incisura on dry bones. Eklem Hastalik Cerrahisi 20:52–58, 2009. 21. Hocker K, Pachucki A. The fibular incisure[sic] of the tibia: the cross-sectional position of the fibula in distal syndesmosis [in German]. Unfallchirurg 92:401– 406, 1989. 22. Ebraheim NA, Lu J, Yang H, Rollins J. The fibular incisure[sic] of the tibia on CT scan: a cadaver study. Foot Ankle Int 19:318–321, 1998. 23. Mavi A, Yildirim H, Gunes H, Pestamalci T, Gumusburun E. The fibular incisura of the tibia with recurrent sprained ankle on magnetic resonance imaging. Saudi Med J 23:845–849, 2002. 24. Yildirim H, Mavi A, Buyukbebeci O, Gumuflburun E. Evaluation of the fibular incisura of the tibia with magnetic resonance imaging. Foot Ankle Int 24:387–391, 2003. 25. Elgafy H, Semaan HB, Blessinger B, Wassef A, Ebraheim NA. Computed tomography of normal distal tibiofibular syndesmosis. Skeletal Radiol 39:559– 564, 2010. 26. Yeung TW, Chan CY, Chan WC, Yeung YN, Yuen MK. Can pre-operative axial CT imaging predict syndesmosis instability in patients sustaining ankle fractures? Seven years’ experience in a tertiary trauma center. Skeletal Radiol 44:823–829, 2015. 27. Mukhopadhyay S, Metcalfe A, Guha AR, Mohanty K, Hemmadi S, Lyons K, O’Doherty D. Malreduction of syndesmosisdare we considering the anatomical variation? Injury 42:1073–1076, 2011. bert-Davies J, Laflamme GY, Leduc S. CT scan assessment of the 28. Nault ML, He syndesmosis: a new reproducible method. J Orthop Trauma 27:638–641, 2013. 29. Lepojarvi S, Pakarinen H, Savola O, Haapea M, Sequeiros RB, Niinimaki J. Posterior translation of the fibula may indicate malreduction: CT study of normal variation in uninjured ankles. J Orthop Trauma 28:205–209, 2014. 30. Mendelsohn ES, Hoshino CM, Harris TG, Zinar DM. CT characterizing the anatomy of uninjured ankle syndesmosis. Orthopedics 37:e157–e160, 2014. 31. Chen Y, Qiang M, Zhang K, Li H, Dai H. A reliable radiographic measurement for evaluation of normal distal tibiofibular syndesmosis: a multi-detector computed tomography study in adults. J Foot Ankle Res 8:32, 2015. 32. Warner SJ, Fabricant PD, Garner MR, Schottel PC, Helfet DL, Lorich DG. The measurement and clinical importance of syndesmotic reduction after operative fixation of rotational ankle fractures. J Bone Joint Surg Am 97:1935–1944, 2015. 33. Sclafani SJ. Ligamentous injury of the lower tibiofibular syndesmosis: radiographic evidence. Radiology 156:21–27, 1985. 34. Stiehl JB. Complex ankle fracture dislocations with syndesmotic diastasis. Orthop Rev 19:499–507, 1990. 35. Pelton K, Thordarson DB, Barnwell J. Open versus closed treatment of the fibula in Maisonneuve injuries. Foot Ankle Int 31:604–608, 2010. 36. Procter P, Paul JP. Ankle joint biomechanics. J Biomech 15:627–634, 1982. 37. Hoefnagels EM, Waites MD, Wing ID, Belkoff SM, Swierstra BA. Biomechanical comparison of the interosseous tibiofibular ligament and the anterior tibiofibular ligament. Foot Ankle Int 28:602–604, 2007. 38. Beumer A, van Hemert WL, Swierstra BA, Jasper LE, Belkoff SM. A biomechanical evaluation of the tibiofibular and tibiotalar ligaments of the ankle. Foot Ankle Int 24:426–429, 2003.