Novel anatomical reconstruction of distal tibiofibular ligaments restores syndesmotic biomechanics

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1 Novel anatomical reconstruction of distal tibiofibular ligaments restores syndesmotic biomechanics Jian Che 1,2,*,=, Chunbao Li 1,=, Zhipeng Gao 3, Wei Qi 1, Binping Ji 2, Yujie Liu 1,**, Ming Han Lincoln Liow 4 1 Department of Orthopedics, Chinese PLA General Hospital, Beijing, , China, * chejian301@163.com 2 Department of Orthopedics, Shanxi Huajin Orthopedic Hospital, Taiyuan, , China 3 Institute of Applied Mechanics and Biomedical Engineering, Taiyuan University of Technology, Taiyuan, , China 4 Department of Orthopaedic Surgery, Singapore General Hospital, 20 College Road, Academia, Level 4, Singapore, , Singapore ** liuyujie301@163.com Jian Che and Chunbao Li contributed equally to this paper. Abstract Purpose To date, there is a paucity of literature on syndesmostic reconstruction techniques that restore both anatomic stability and physiologic syndesmostic biomechanics. In this cadaveric study, (1) a novel syndesmotic reconstruction surgical technique using autogenous peroneus brevis tendon was described and (2) the biomechanical properties of the reconstruction was investigated. Methods Ten fresh-frozen lower extremities were used in this study. Reconstruction of the anterior and posterior, as well as the interosseous tibiofibular ligaments was performed with a halved peroneus brevis tendon. Biomechanics were assessed using foot external rotation torque and ankle dorsiflexion axial loading tests, which were performed in (a) intact, (b) cut, (c) anatomically reconstructed syndesmotic ligaments, and (d) 3.5 mm tricortical syndesmotic screw fixation. Medial lateral and anterior posterior displacements of the distal fibula were recorded during foot external rotation and fibular axial displacement was recorded during ankle axial loading. Results

2 The fibula was displaced posteriorly and proximally with respect to the tibia in all specimens during external rotation and axial loading tests, respectively. Significant differences (p < 0.05) were found in distal fibular displacements between anatomically reconstructed ligaments and screw fixation. Tricortical syndesmotic screw fixation resulted in 59% of posterior fibular displacement when compared to intact ligaments. No significant differences (n.s.) in distal fibular displacement was were demonstrated between intact ligaments and anatomically reconstructed ligaments. Conclusion Anatomical reconstruction of the distal tibiofibular ligaments with the peroneus brevis tendon provides stability and recreates the biomechanical properties of an intact syndesmosis. This new surgical technique may be a viable alternative for the treatment of syndesmotic injuries. Level of evidence Level 5 Keywords Anatomical reconstruction Surgical technique Distal tibiofibular ligaments Syndesmosis Biomechanical cadaveric study Introduction The syndesmosis is a dynamic stabilizer of the ankle and consists of the anteroinferior tibiofibular ligament (AITFL), posteroinferior tibiofibular ligament (PITFL), and interosseous tibiofibular ligament (ITFL) [<link rid="bib15">15</link>]. Syndesmotic injuries are most frequently caused by forced external rotation of the foot or high-impact, weight-bearing forces with the ankle in forced dorsiflexion. This adversely affects ankle joint biomechanics and significantly alter alters tibiotalar articulation contact pressures, which may result in the development of degenerative arthritis [<link rid="bib27">27</link>, <link rid="bib33">33</link>].

3 Several syndesmotic restorative surgical options have been described. Syndesmotic screw fixation, which provides rigid fixation to the distal tibiofibular syndesmosis, is recognized widely as the standard of care [<link rid="bib1">1</link>, <link rid="bib32">32</link>]. However, screw fixation limits physiologic syndesmotic motion, may result in screw breakage, and screw removal complications [<link rid="bib2">2</link>, <link rid="bib7">7</link>, <link rid="bib12">12</link>, <link rid="bib20">20</link>, <link rid="bib23">23</link>, <link rid="bib27">27</link>]. To address this, flexible syndesmotic fixation with suture button devices have has been developed which allow physiologic motion in the tibiofibular joint while maintaining the reduction of the syndesmosis [<link rid="bib6">6</link>, <link rid="bib17">17</link>]. Disadvantages of this technique include gradual relaxation under weight-bearing conditions, high cost, and the steep learning curve associated with this method [<link rid="bib9">9</link>]. Comment [01]: Author: Figure: Figure [1] was received; however, no citation was provided in the manuscript. Please check and confirm the inserted citation of Fig is correct. If not, please suggest an alternative citation. Distal syndesmotic ligament reconstruction aims to restore the original anatomy between the distal tibia and fibula to ensure stability of the talus within the ankle mortise. In the presence of an intact AITFL, bone block advancement has been demonstrated to be a viable reconstructive option [<link rid="bib4">4</link>]. When the AITFL is ruptured or attenuated, reconstructive surgery using local or free autograft tendon has been described. Moravek and Kadakia [<link rid="bib24">24</link>] described a technique utilizing a double-stranded hamstring allograft to primarily reconstruct the interosseous ligament with suture button augmentation, removing the need for hardware removal post-procedure. For complete syndesmotic injuries, two studies [<link rid="bib11">11</link>, <link rid="bib19">19</link>] have reported tri-ligamentous reconstruction methods with either peroneus longus or hamstring tendon autografts. These techniques have demonstrated satisfactory clinical results, ; however, the biomechanical parameters which may affect the development of post-traumatic arthritis has have not been elucidated. To date, there is a paucity of literature on syndesmostic reconstruction techniques that restore both anatomic stability and physiologic syndesmostic biomechanics. The aim of this cadaveric study is to (1) describe our syndesmotic reconstruction surgical technique using autogenous peroneus brevis tendon and (2) investigate the

4 biomechanical properties of the reconstruction. We hypothesized that this novel technique will provide stable syndesmotic fixation and restore physiologic syndesmostic biomechanics. Materials and methods Ten fresh-frozen lower extremities were used in this study. All specimens demonstrated ligamentous stability on manual testing and absence of prior surgical scars. All specimens were sectioned through the midshaft of the tibia and fibula and overlying soft tissues within 10 cm of the tibiotalar joint line were removed, preserving the anterior, posterior tibiofibular, and interosseous ligaments. The upper half of the tibia and fibula was not included in this experimental model, because whole leg specimens were not available. Test apparatus consist consists of three parts, respectively located in the proximal and middle tibial stem, and the foot. The proximal end of the tibia stem was securely attached to a Axial-Torsion Systems (Instron 8874; Instron Co, Canton, MA, USA). This system provides axial or torsion dynamic actuation to the specimen. The proximal end of the fibula was secured to the tibia to prevent excessive lateral motion. The anterior and posterior tibiofibular ligaments, along with the interosseous membrane, maintained the distal fibular in an anatomical position. Comment [02]: Author: Reference [3] is provided in the reference list but not cited inside the text. Please check and confirm. In the middle of the specimen, we utilized a dual-layer circular frame, which was firmly connected with the tibia. Two linear variable differential transformers (LVDT) were fixed to the frame and were used to measure medial lateral and anterior- posterior displacements of the distal fibula relative to the tibia in external foot torque test. The apex of LVDT was respectively contacted with the distal fibula posteriorly and laterally at the ankle joint level. A linear variable differential transformer was fixed to the frame and used to measure axial displacement of the distal fibula relative to the tibia in axial loading test [<link rid="bib21">21</link>]. The apex of LVDT was contacted with the proximal fibula. At the distal part of the specimen, the foot was strapped to a flat plate which allowed 90 degrees of ankle plantarflexion to maximum dorsiflexion. The talus and calcaneus

5 were fixed with two 5 mm threaded rods which secured the axis of tibia consistent with the axis of machine. Surgical procedure tunnel preparation The tendon of peroneus brevis was identified and harvested using a tendon stripper. A free tendon graft of cm in length was sufficient for the reconstruction procedure. Baseball-whip stitches were applied to each end of the graft. Four tunnels were required for graft passage, including transverse tunnels of the fibula and tibia, and longitudinal tunnels of the fibula and tibia. Entry point of the longitudinal tunnel of the tibia was located on the posterolateral (Volkmann) tibial tubercle. This tunnel was parallel to the articular surface of the ankle joint, which was about 15 degrees from the floor. The transverse tunnel of the tibia enters at the anterolateral tibial (Tillaux- Chaput) tubercle, transverses inward, and exits from the medial cortex of the tibia. The longitudinal tunnel of the fibula was located between the anterior (Wagstaffe) and posterior tubercles of the fibula, and parallel to the fibular articular surface. The transverse tunnel of the fibula was located 10 mm above the ankle joint gap and parallel to coronal axis of ankle joint (Fig. <link rid="fig1">1</link>). Surgical procedure graft passage and fixation The peroneus brevis graft was passed from the transverse tunnel of the fibula to the longitudinal tunnel of the tibia using an arthroscopic probe (Fig. <link rid="fig2">2</link>a, d), reconstructing the AITFL. Subsequently, the tendon was passed through the longitudinal tunnel of the fibula (Fig. <link rid="fig2">2</link>b, e), completing the reconstruction of the PITFL. LastlyFinally, the tendon ends met in the transverse tunnel of tibia, reconstructing a double-bundle AITFL (Fig. <link rid="fig2">2</link>c). A tension force of 40 N was applied on the graft prior to fixation. An interference screw that had a 1 mm larger diameter than the graft was inserted at the anterolateral tibial tubercle tunnel entry point to provide graft fixation (Fig. <link rid="fig2">2</link>c, f). <fig id="fig1"><number>fig. 1</number> Four tunnels for graft passage. a Anterolateral view of left ankle shows the entry of the tunnels. b Lateral view of left ankle (AITFL and ITFL had been excised, ; fibula was rotated externally). c Lateral view of left ankle (fibula was reduced). d Posterior view of left ankle. 1 transverse tunnel of fibula; 2 longitudinal tunnel of tibial; 3

6 longitudinal tunnel of fibula; 4 transverse tunnel of tibia; 5 tibia; 6 fibula; 7 talus; 8 calcaneus; 9 posterior talofibular ligament; 10 calcaneofibular ligament; 11 peroneal groove of the fibula</fig> <fig id="fig2"><number>fig. 2</number> Graft passage and fixation. a Posterior view of left ankle. b Posterior view of left ankle. c Anterolateral view of left ankle. d f Schematic diagrams showing axial-ct of syndesmosis. 1 transverse tunnel of fibula; 2 longitudinal tunnel of tibial; 3 longitudinal tunnel of fibula; 4 transverse tunnel of tibia; 5 tibia; 6 fibula; 7 talus; 8 calcaneus; 9 posterior talofibular ligament; 10 calcaneofibular ligament; 11 peroneal groove of the fibula; 12 PITFL; 13 AITFL; 14 interference screw</fig> Biomechanical testing External foot torque and axial loading tests were selected for the biomechanical testing based on common syndesmotic injury patterns [<link rid="bib21">21</link>]. For the external foot torque test, medial lateral and anterior- posterior displacements of the distal fibula were recorded when external foot torque was applied to the foot in 90 degrees of plantarflexion. The external foot torque was replaced with a maximum 10 Nm internal rotation moment to the tibia. For the axial loading test, proximal distal displacements of the distal fibula were recorded when axial load was applied to the ankle, which was at maximum dorsiflexion. The maximum axial load was 1000 N and was applied to the foot at 200 N/s. Both tests were performed in specimens with intact syndesmotic ligaments to establish a baseline of fibular displacement values. This was followed by performing the tests sequentially after excising the syndesmotic ligaments, anatomical reconstruction with peroneus brevis tendon grafts, and single 3.5 mm screw threecortex fixation. Test retest reliability was determined by the intra-class correlation coefficient (ICC). There was high test retest reliability, with ICC for ankle dorsiflexion loading test ranging from 0.92 to 0.96 and external foot torque test ranging from 0.80 to This study was approved by the Medical Ethics Committee of the Chinese PLA General Hospital. Statistical analysis The dependent variables measured in these experiments were related to the displacement of the distal fibula. The independent variables were applied axial force, applied external foot torque, and ankle status. Ankle status included foot position (90 or dorsiflexed) and syndesmotic ligament status (intact, excised, anatomically

7 reconstructed, and tricortical screw fixation). A one-way repeated repeatedmeasures ANOVA was performed to determine the significant differences in mean values of the dependent variable at different levels of the independent variable for a given condition of ankle status. Significant differences revealed by ANOVA were followed by post hoc Student- Newman- Keuls (SNK) test. The level of significance was p < Comment [03]: Author: As per journa instruction "funding" and "ethical approval" is mandatory. Please check and provide. Results External foot torque test The fibula was consistently displaced posteriorly with respect to the tibia for all specimens (Fig. <link rid="fig3">3</link>). Excising the tibiofibular ligaments significantly increased (p < 0.05) the posterior fibular displacement during applied external foot torque at applied moment levels greater than 1 Nm with the foot at 90 flexion. The mean posterior tibial displacement during application of 10 Nm external foot torque were was 2.6 mm with the intact tibiofibular ligaments, 4.4 mm with excised ligaments, 2.8 mm with the anatomically reconstructed ligaments, and 1.6 mm with tricortical screw fixation (Fig. <link rid="fig3">3</link>). No significant differences (n.s.) were observed in distal fibular displacements between intact ligaments and anatomically reconstructed ligaments, suggesting restoration of syndesmotic biomechanics. In addition, no significant differences (n.s.) were observed in distal fibular displacements between ligament reconstruction and screw fixation. However, tricortical syndesmotic screw fixation reduced posterior fibular displacement, resulting in 59% of posterior fibular displacement when compared to intact ligaments. No measurable lateral displacement of the fibula was recorded during any external foot torque test. <fig id="fig3"><number>fig. 3</number> Mean curves of distal fibular displacement versus applied external foot torque with the foot at 90 degree flexion. Mean values were shown with syndesmotic ligaments intact, excised, anatomically reconstructed, and tricortically fixed using a 3.5 mm screw. Posterior displacement of the fibula relative to the tibia was plotted as negative value. Sample standard deviations were shown with error bars. Indicated differences between mean values were significant at p < 0.05</fig> Ankle dorsiflexion loading test

8 The mean proximal fibular displacements recorded under 1000 N of applied axial weight weight-bearing force were 0.4 mm with the intact ligaments, 0.9 mm with excised ligaments, 0.5 mm with anatomically reconstructed ligaments, and 0.2 mm with screw fixation. Expectedly, excision of the distal tibiofibular ligaments significantly increased (p < 0.05) proximal fibular displacement. No significant differences (n.s.) were observed in proximal fibular displacements between intact ligaments and anatomically reconstructed ligaments, suggesting restoration of syndesmotic biomechanics. However, significant differences (p < 0.05) were observed in distal tibiofibular displacements between anatomically reconstructed ligaments and screw fixation. In addition, tricortical screw fixation reduced proximal fibula displacement to 40% of the intact ligaments. Figure <link rid="fig4">4</link> illustrates the biomechanical results of the different syndesmotic states, demonstrating convergence of data between intact and anatomically reconstructed ligaments. <fig id="fig4"><number>fig. 4</number> Mean curves of distal fibular displacement versus applied axial weight-bearing force with the foot at full dorsiflexion. Proximal displacement of the fibula relative to the tibia was plotted as positive value. Sample standard deviations were shown with error bars. Indicated differences between mean values were significant at p < 0.05</fig> Discussion The most important finding of the present study was that our novel anatomical reconstruction of distal tibiofibular ligaments with peroneus brevis tendon provides stability and recreates the biomechanical properties of an intact syndesmosis. The most common mechanisms for syndesmotic injuries, which may occur in combination or in isolation, are external rotation and hyperdorsiflexion [<link rid="bib26">26</link>]. In a biomechanical cadaver study, Markolf et al. [<link rid="bib21">21</link>] demonstrated that forced ankle dorsiflexion and external foot torque will result in syndesmotic injuries. They suggested that the most likely mechanism was pivoting on a neutrally planted, weight-bearing foot with an internally rotated tibia which results in an external rotation strain on the ankle ligaments. These findings were consistent with our study findings. Of note, tricortical screw fixation,

9 which is widely recognized as the standard of care, resulted in significant reduction of syndesmotic mobility. Syndesmotic screw fixation provides rigid fixation of the distal tibiofibular syndesmosis and is widely used as the standard of care; however, this technique has its drawbacks. Syndesmosis screws significantly limit tibiofibular relative motion to below physiologic values, requiring screw removal prior to full-weight-bearing [<link rid="bib15">15</link>]. Increased shear stresses can result in screw breakage for patients who attempt early weight-bearing [<link rid="bib8">8</link>]. Thus, some orthopedic surgeons will advise patients to maintain a non-weight-bearing status for up to 12 weeks postoperatively prior to screw removal. In addition, malreduction of the syndesmosis with screw fixation is not uncommon. The incidence has been reported to be as high as 52% [<link rid="bib10">10</link>]. Interestingly, screw removal or screw breakage can result in spontaneous reduction and improved symptoms in a high percentage of patients [<link rid="bib11">11</link>, <link rid="bib20">20</link>, <link rid="bib30">30</link>]. However, screw removal has also resulted in the loss of reduction of the syndesmosis [<link rid="bib14">14</link>, <link rid="bib16">16</link>, <link rid="bib29">29</link>]. To date, there is are insufficient data to support the retention or removal of syndesmotic screws. Dynamic syndesmotic fixation using suture-buttons have been suggested to result in better physiological fixation when compared to the rigid syndesmotic screw. A prospective, randomized control trial demonstrated better clinical and radiographic outcomes with a dynamic device, with improved maintenance of reduction and lower reoperation rate [<link rid="bib18">18</link>]. Recent systematic review showed that the TightRope system has a similar outcome compared with the syndesmotic screw or bolt fixation, but might lead to a quicker return to work [<link rid="bib28">28</link>]. Although removal of dynamic implants are is not required, DeGroot et al. [<link rid="bib5">5</link>] reported that 6 of 24 patients who were treated with suture button syndesmotic fixation required implant removal due to local irritation or reduced motion. Storey et al. [<link rid="bib31">31</link>] reported removal of the suture button in 8 of 102 cases for the following reasons: osteomyelitis, aseptic osteolysis, failure of stabilization, and unexplained pain over the implant. Moreover, a single suture button device has demonstrated lack of

10 sagittal stability compared with a screw. Two suture button devices must be used simultaneously to maintain sagittal reduction which adversely affects its overall costeffectiveness. Syndesmotic reconstructive techniques have the goal of restoring and maintaining stability between the distal tibia and fibula. Morris and colleagues [<link rid="bib25">25</link>] anatomically reconstructed the AITFL and the interosseous ligament using hamstring autograft using two parallel tunnels. The graft was secured medially and laterally with 15 mm interference screws. Grass and colleagues [<link rid="bib11">11</link>] reconstructed the three distal tibiofibular ligaments with a split peroneus longus tendon autograft. However, in this technique, the PITFL graft is passed through the tibiofibular interval, which would interfere with the anatomic reduction of the distal fibula into the tibial notch. Lui [<link rid="bib19">19</link>] described a minimally invasive tri-ligamentous reconstruction using three tunnels. The two ends of graft are sutured to each other and inserted into the anterior half of the tibial tunnel to reconstruct the AITFL. This technique was limited by the operator s ability to produce and maintain the proper tension on graft. Recent cadaveric and radiographic studies have described syndesmosis anatomy qualitatively and quantitatively [<link rid="bib13">13</link>, <link rid="bib33">33</link>, <link rid="bib34">34</link>]. Double-bundle AITFL fixed with interference screws result results in restoration of anatomy and can provide more anti-torque strength to the distal fibula. In comparison, reconstruction with a singlebundle AITFL has been reported to have less rotation stability, and can be vulnerable in high ankle sprains. By reconstructing the ITFL in our novel surgical technique, we can ensure anatomical fibula reduction and fixation into the tibia notch. Syndesmotic reconstruction should not be limited to chronic symptomatic insufficiency of the distal tibiofibular syndesmosis with widening of the mortise, but can also be performed to repair acute high ankle sprains. The intra-class correlation coefficient (ICC) of test retest reliability for the ankle dorsiflexion loading test was superior to the external foot torque test. The reason for these results could be that ankle stability are is enhanced at maximum dorsiflexion. The wider anterior portion of the talus wedges into the ankle mortise, enhancing

11 stability of the ankle joint [<link rid="bib13">13</link>, <link rid="bib15">15</link>, <link rid="bib22">22</link>, <link rid="bib26">26</link>]. The novel surgical technique in the present study was developed to recreate stable and physiologic syndesmostic biomechanics. On one hand, the anatomical reconstruction provides similar stability when compared with the intact syndesmosis; on the other hand, the anatomical reconstruction maintains syndesmotic physiologic biomechanics when compared to screw fixation. Our results demonstrated that screw fixation resulted in the lowest displacement values (during axial loading or external rotation torque tests) when compared to the other syndesmotic reconstructive techniques, suggesting over-tightening of the syndesmotic complex. In contrast, syndesmotic ligament reconstruction and intact syndesmotic complexes did not demonstrate any significant difference in biomechanics. When compared with other reconstruction studies [<link rid="bib19">19</link>, <link rid="bib24">24</link>, <link rid="bib25">25</link>], our technique has demonstrated the ability to accurately restore syndesmotic biomechanics, prevent over-tightening syndesmotic repair, and avoid the need for reoperation and screw removal. The results of this study needs to be interpreted in light of its potential limitations. Firstly, we demonstrated similar fibular displacements between intact and anatomically reconstructed syndesmotic ligaments. However, the physiologic movement of the syndesmosis is complex and six degree of freedom dynamic research is required to further define the biomechanics. Secondly, this novel operative technique is complex and has a steep learning curve for new surgeons. However, we are in the process of planning a clinical study to assess the efficacy of this technique. Conclusion Anatomical reconstruction of the distal tibiofibular ligaments with the peroneus brevis tendon provides stability, permits physiological syndesmotic movement, and recreates the biomechanical properties of an intact syndesmosis. This new surgical technique may be a viable alternative for the treatment of chronic syndesmotic instability or acute high ankle sprain injuries.

12 Acknowledgements We acknowledged Institute of Applied Mechanics and Biomedical Engineering of Taiyuan University of Technology for their assistance in biomechanical study. Compliance with ethical standards Conflict of interest The authors declare that they have no conflict of interest. References <bib id="bib1"><number>1.</number>bava E, Charlton T, Thordarson D (2010) Ankle fracture syndesmosis fixation and management: the current practice of orthopedic surgeons. Am J Orthop 39(5): </bib> <bib id="bib2"><number>2.</number>bell DP, Wong MK (2006) Syndesmotic screw fixation in Weber C ankle injuries should the screw be removed before weight bearing? Injury 37: </bib> <bib id="bib3"><number>3.</number>beumer A, Campo MM, Niesing R, Day J, Kleinrensink GJ, Swierstra BA (2005) Screw fixation of the syndesmosis: a cadaver model comparing stainless steel and titanium screws and three and four cortical fixation. Injury 36:60 64</bib> Comment [Comment4]: [3] is not cited in the text. Please insert a quote. <bib id="bib4"><number>4.</number>beumer A, Heijboer RP, Fontijne WP, Swierstra BA (2000) Late reconstruction of the anterior distal tibiofibular syndesmosis: good outcome in 9 patients. Acta Orthop Scand 71: </bib> <bib id="bib5"><number>5.</number>degroot H, Al-Omari AA, El Ghazaly SA (2011) Outcomes of suture button repair of the distal tibiofibular syndesmosis. Foot Ankle Int 32: </bib>

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