Objective assessment of syndesmosis stability with an innovative Syndesmosis-Test-Tool - a biomechanical study

doi:10.21203/rs.3.rs-3612147/v1

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Objective assessment of syndesmosis stability with an innovative Syndesmosis-Test-Tool - a biomechanical study

https://doi.org/10.21203/rs.3.rs-3612147/v1

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published 18 Jan, 2024

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When treating ankle fractures, the question of syndesmosis complex involvement often arises. So far there is no standardized method to reliably detect syndesmosis injuries in the surgical treatment of ankle fractures. For this reason, an intraoperative Syndesmosis-Test-Tool (SST) was developed and compared to the recommended and established Hook-Test (HT).

Tests were performed on cadaveric lower legs (n=20) and the diastasis was visualized by 3D camera. Tests were performed at 50, 80, and 100 N in native condition and in four instability levels. Instability was induced from anterior to posterior and the reverse on the opposite side. The impact on diastasis regarding the direction, the force level, the instability level and the device used was checked using a general linear model for repeated measurement.

The direction of the induced instability showed no influence on the diastasis during the stability tests. The diastasis measured with the SST increased from 0.5 to 3.0 mm depending on the instability, while the range was lower with the HT (1.1 to 2.3 mm). The results showed that the differentiation between the instability levels was statistically significant better for the developed SST. The last level of maximum instability was significantly better differentiable with the STT compared to the HT. An average visualizable diastasis of more than 2 mm could only be achieved at maximum instability. In conclusion, to detect instability, the newly developed STT was superior to the commonly used HT.

Health sciences/Diseases/Trauma

Health sciences/Health care/Fracture repair

During stabilization of ankle fractures, the question usually arises as to whether syndesmosis stability is sufficient or whether additional stabilization is necessary [1]. To prevent long-term posttraumatic complications, relevant instability should not be overlooked and be adequately addressed, for example by suture and bracement of the syndesmosis, syndesmotic screws, or suture button stabilization [2–5]. However, there is a discussion whether an injury to the anterior inferior tibiofibular ligament (AITFL) alone requires syndesmosis stabilization [6]. To date, the question has not been conclusively answered as to when a syndesmosis injury becomes relevant to justify additive stabilization. Without doubt, stabilization should be performed if there is the slightest doubt about the stability of the syndesmotic complex [7].

To identify a syndesmosis injury related instability clinical signs of examination as well as imaging such as MRI, stress images or ultrasound are used [8]. The measurement of syndesmotic parameters such as medial or tibio-fibular clear space under stress recordings of the ankle is of limited value because of its dependence on ankle rotation [7, 9]. To avoid differences in the measured distances due to rotation, repeated exact adjustment of the mortise view would be necessary for all cases, but often cannot be achieved practically [9]. The sensitivity and specificity of radiographs can be further enhanced by stress imaging and provide important clues, but often cannot provide a definitive diagnosis [10–13]. An additional CT scan has a major role in surgical planning and can provide indirect evidence [7, 12, 14, 15]. However, numerous anatomic variants of the tibiofibular distance also make the diagnosis uncertain and necessitate comparison to the healthy opposite side in all cases [10, 16, 17]. MRI shows nearly perfect specificity and sensitivity close to 100% for syndesmotic injuries [10, 18, 19]. However, MRI is expensive and not ubiquitously and rapidly available preoperatively [20]. Both CT and MRI are static examinations that do not allow dynamic investigation of possible instability [7]. Intraoperative arthroscopy has a sensitivity and specificity of 100%, but is invasive, not ubiquitously available, and requires experience and appropriate skills [10, 19, 21].

Intraoperative lateral stress tests such as the Hook-Test (HT) or external rotation stress test (ERST) under X-ray inspection are common to detect instabilities [4, 22–24]. The morphology of the injury can also provide clues to the extent of damage to the syndesmotic complex. According to Lauge-Hansen, complete disruption of the syndesmotic ligaments is always expected in stadium 4 trimalleolar injuries for pronation or supination external rotation traumas [7, 25]. If there is any doubt about the decision to perform additional stabilization, the anterior syndesmosis can be visualized by lateral approach to the distal fibula or arthroscopically [4].

However, for intraoperative testing, some serious issues exist regarding the reliability and interpretation of the applications [26]. We showed in a recent study that the intraoperative HT has poor interrater-reliability and fails to achieve a relevant increase in diastasis [26]. It has also been shown that there is a high degree of individual laxity of the syndesmotic complex and thus a highly interindividual native diastasis of the ankle mortise [26]. Also, the external rotation stress test showed in studies poor, sometimes worse results than the HT [7, 27, 28]. The major problem of the stress tests are the large differences in the applied forces [26, 29]. A force between 50–100 N is recommended [7, 26]. Furthermore, Candal-Couto et al. found that fibular motion in the sagittal plane was consistently greater than motion in the coronary plane, so distal tibio-fibular instability may be more appropriate to assess in the sagittal plane using the HT [7, 30].

Currently there is no standardized recommendation for the force or direction in which the HT should be performed [26, 29]. This makes it clear that it is extremely difficult to compare results between different studies regarding syndesmotic instabilities.

For this purpose, an innovative Syndesmosis-Test-Tool (STT) was developed and compared to the established HT, which enables standardized intraoperative applied force (50-100N) to test the stability of ankle injuries. Both tests were examined by comparing the diastasis for native to maximum ankle instability in a biomechanical cadaver study.

General information

The stability of the syndesmosis was tested with ten human cadaveric lower leg pairs (n = 20) with increasing force (50, 80, and 100 N) at each level of instability (from intact to maximum instability). Instability of the syndesmosis was generated from two different directions. The stabilizing ligaments were serially cut in either a posterior-to-anterior or anterior-to-posterior order.

Validity of the Syndesmosis-Test-Tool

The validity of the STT for 50 N, 80 N and 100 N was checked in the series of 10 measurements each, resulting in 51 ± 1.4 N, 80 ± 1.7 N and 101 ± 2.0 N.

Direction of destabilization

The direction of generated instability by cutting the ankle ligaments stepwise from anterior to posterior or from posterior to anterior showed no significant impact on the diastasis (p = 0.853, Table 1). In Table 1 the p-values and effect sizes as p.Eta² of the general linear model (GLM) are given. Because the direction of the induced instability had no significant impact on the diastasis, it was not taken into account in the further analyses in order to increase the statistical power. The results of the GLM are given in Table 2 as p-values and the effect sizes for the main effects and interaction without consideration of the direction of the instability are listed.

Table 1

Statistical results of the GLM data to detect the impact of the direction (a-p or p-a) of induced instability on the diastasis.
	p-value	p.Eta²
Direction (a-p vs p-a)	0.853	0.002
Device * Direction	0.280^#	0.058
Force * Direction	0.473^#	0.032
Instability * Direction	0.676^#	0.018
Device * Force * Direction	0.681^#	0.013
Device * Instability * Direction	0.811^#	0.006
Force * Instability * Direction	0.139^#	0.085
Device * Force * Instability * Direction	0.570^#	0.035
# adjusted p-values by Greenhouse-Geisser. a: anterior, p: posterior

Table 2

Statistical results of the GLM without the consideration of the direction of induced instability.
	p-value	p.Eta²
Device	0.047	0.175
Force	< 0.001^#	0.392
Instability	< 0.001^#	0.750
Device * Force	0.002^#	0.310
Device * Instability	0.003^#	0.299
Force * Instability	0.721^#	0.023
Device * Force * Instability	0.025^#	0.123
# adjusted p-values by Greenhouse-Geisser.

Measurements of the diastasis generated by the Syndesmosis Test Tool and Hook Test

The HT showed overall larger mean diastasis with 1.5 ± 0.8 mm, compared to the STT with 1.2 ± 1.2 mm (p = 0.047), regardless of the applied force, the instability level or direction of the induced instability. The diastasis measured with the STT ranged from 0.5 ± 0.2 mm to 3.0 ± 1.6 mm depending on the instability level, while the range with the HT was 1.1 ± 0.4 mm to 2.3 ± 1.0 mm (Fig. 1, Table 3).

Table 3

Values of diastasis for both devices, Syndesmosis-Test-Tool (STT) and Hook-Test (HT) for each level of instability. The diastasis generated is given in mm as mean ± standard deviation (n = 20).
Level of instability	STT	HT	P
1	0.5 ± 0.2	1.1 ± 0.6	< 0.001
2	0.8 ± 0.8	1.3 ± 0.6	0.003
3	0.9 ± 0.4	1.4 ± 0.7	0.003
4	1.0 ± 0.6	1.6 ± 0.8	0.002
5	3.0 ± 1.6	2.3 ± 1.0	0.101

The diastasis measured with the HT (mean values of all instability levels: 50 N 1.3 ± 0.8 mm, 80 N 1.6 ± 0.9 mm, 100 N 1.7 ± 0.9 mm) depended on the applied forces (50 N vs. 80 N p < 0.001, 50 N vs. 100 N p < 0.001, 80 N vs 100 N p = 0.040), regardless the instability level (Fig. 1A). In contrast, the STT showed no force dependent diastases with p = 1.000 for each post hoc pairwise comparison (Fig. 1B).

By comparing both devices for each instability level, the HT showed significantly greater diastasis in each instability level (level 1 p < 0.001, level 2 p = 0.003, level 3 p = 0.003, level 4 p = 0.002, Table 3) compared to the STT, except at the maximal instability (instability level 5, p = 0.101, Table 3). The pairwise comparisons of the diastases between both devices for each instability level are given in Table 3.

Both devices showed different slopes depending on the instability level, which is statistically given as interaction between device and instability level with p = 0.003 in Table 2. This means, that HT and STT produced different diastases depending on the instability level. However, statistical analysis revealed very comparable frequency of reaching significance for both devices, except that the STT showed significance between native condition (level 1) and instability level 3 (p < 0.001), in contrast to the HT (p = 0.140, Table 4). With a moderate effect (Cohan's d greater 0.5) that distinguishes between different instability levels, the effect sizes for STT are larger compared to HT (Table 4). The greater the effect size, the greater the difference in diastasis between two instability level.

Table 4

Results of post hoc pairwise comparisons between the instability levels for each device, as p-values and the effect sizes (Cohens’d with d = 0.2 show small effect, d = 0.5 moderate effect and d = 0.8 large effect, n = 20).
Level of instability		STT		HT
		p	Cohens’d	p	Cohens’d
1	2	0.076	0.62	0.076	0.25
	3	< 0.001	1.04	0.140	0.32
	4	0.002	0.96	0.031	0.56
	5	< 0.001	1.50	< 0.001	1.11
2	3	1.000	0.09	1.000	0.11
	4	1.000	0.19	0.241	0.37
	5	< .001	1.33	< 0.001	1.02
3	4	1.000	0.15	0.903	0.26
	5	< 0.001	1.36	< 0.001	0.93
4	5	< 0.001	1.30	0.001	0.73

For visual comparison Fig. 1C displays the diastasis of both devices in dependency of the instability level. The apparently largest increase in diastases between adjacent instability levels produced the STT from instability level 4 to 5 with 2.0 ± 1.7 mm. For the HT, the increase from instability level 4 to 5 with 0.7 ± 0.7 mm was also the greatest between adjacent instability levels within the HT but was almost three times smaller compared to the STT. The difference between native condition (level 1) and maximal instability (level 5) was 2.5 ± 1.5 mm for the STT and 1.1 ± 0.8 mm for the Hook Test.

The effect sizes showed better discrimination between instability levels for the STT, than for the HT.

Visually discrimination in diastasis between the different instability levels is quite hard, despite significances.

Due to the heterogenous performance of the HT, regarding force applied by the surgeon and certain instability [26] the aim was to compare a developed device that will lead to improved testing of ankle instabilities. In this work, a newly developed STT was compared with a widely used and recommended intraoperative test, the HT [31]. For this purpose, the generated diastasis was measured in ankle joints with different instabilities (from native stability to maximum instability in terms of Lauge-Hansen) by applying different force levels.

Concluding our results, the instability showed the largest impact on diastasis. Using the HT, applied force (whether it was pulled with 50, 80 or 100 N) matters, but not for the STT. Since we know that surgeons perform the Hook-Test with very different forces [26, 29], the STT provides a clear advantage here with the reliable application between 50–100 N compared to a non-standardized intraoperative HT.

The direction of the generated instability, increasing instability from posterior to anterior versus anterior to posterior, did not affect the generated diastases. Statistically, the STT showed a better differentiation between the instability levels, compared to the HT. In addition, the increase in diastases at maximum instability was three times greater with the STT than with the HT and therefore the change in diastasis can be easily identified macroscopically.

The significant interaction between the applied force and the level of instability for the HT shows the dilemma of the HT. The induced diastasis depended on the force pulled with the HT and the instability level. This led to higher heterogeneity detecting instability. The STT did not show force dependent diastasis. Thus, the HT seems not that reliable to detect instability, compared to the STT.

Failing in the diagnosis of syndesmosis instability can have consequences such as early degenerative alterations of the upper ankle [10, 32]. Patients with instable syndesmosis injury benefit from surgical stabilization in the long term [33, 34]. Preoperatively, radiographic measures on native radiographic imaging may indicate syndesmosis instability [10]. The determination of instability, especially when maximum instability is present, is mandatory to initiate adequate therapy. Due to the larger effect sizes and the one more frequent significance (instability level 1 versus 3), the STT seems more suited to detect even partial injuries, compared to the established HT.

However, in absolute terms, except for level 5, the differences in diastases for instability levels 1 to 4 were less than 2 mm. These differences can hardly be detected visually under intraoperative X-ray. Unacceptable instability is usually assumed when the diastasis increases by at least 2 mm in the tibiofibular clear space [2, 24]. The HT showed force dependent diastasis and reached the commonly used sign of instability of 2 mm diastasis just in few cases, even for the maximum instability. Nevertheless, it is possible to detect maximum instability with the HT. However, this requires pulling with appropriate force, which can be different regarding to the surgeons [26]. At maximum instability, the diastasis between the three forces did not differ, both for the STT and for the HT. Here, the force does not seem to matter at this point. Even low forces of 50N are sufficient to detect the maximal instability for both devices.

For intraoperative testing the literature gives advantages in the Lateral stress test (= HT) [27, 28] others show that the ERST could be superior in the detection of instabilities [35, 36]. These tests detect only high-grade injuries of all syndesmosis ligaments (AITFL, PITFL, IOL, possibly deltoid ligament) in mortise view [26, 35]. The performance of the tests with the individually very different applied forces is subject to large interindividual variations, as is the correct radiographic setting of the mortise view [26, 29].

An important difference between the two test methods was the application of force to the syndesmosis. With the hook test, the force is usually applied at 90° to the shaft axis of the fibula [31]. However, whether the direction of the force applied laterally in the frontal plane is generally the appropriate direction for the HT is controversial [30]. With the STT, the force is built up by a spreading mechanism above the syndesmosis plane between the two bones. The oblique insertion of the STT (approx. 45 degrees compared to the HT, Fig. 3) between the fibula and tibia is due to both the anatomy and the design of the STT. The fibula lies dorsal to the tibia and the STT is therefore inserted at an oblique angle. Due to this methodical difference, not only the coronal but also the sagittal translation is taken into account for the STT. This may explain the advantage shown in comparison to the HT. Further studies should investigate the direction of the force vectors for the intraoperative test methods on the diastasis produced.

Due to the use of cadaver specimens, our results cannot be transferred one-to-one to the intraoperative situation, to the patient with muscles, ligament and soft tissue tension. Nevertheless, it is the closest simulation possible in the laboratory. Tests with newly developed tools must first prove their validity in biomechanical cadaveric studies before they can be tested in vivo. The availability of body donors and thus specimens is limited and thus the amount of specimen that can be tested biomechanically. Of course, larger numbers would be desirable here. Other biomechanical studies often use similar numbers of pairs. Between 8 to 12 pairs are regular sample sizes [37–41]. The tests performed here were standardized both with the HT and with the STT and were comprehensibly always performed with the same forces. For the HT, we know that it is used intraoperatively by surgeons with very different forces. However, to be able to compare the test methods, this standardization is necessary. The diastasis was monitored with a 3D camera that can detect movements with micrometer accuracy. This is not possible under fluoroscopic viewing of the ankle mortise at all. Therefore, the critical integration of the results for clinical practice must be done. Under X-ray control, even a few degrees deviation from the ideal setting of the mortise view can bias the results of the radiological parameters (tibio-fibular overlap/clear space, medial clear space).

Minor injuries with one or two ruptured ligaments are difficult to detect with the devices used in our study. The question of whether these one or two ligament injuries are stability-relevant and require surgical stabilization could not be answered until now. In a cadaver study, it was shown that direct visualization and measurement of diastasis in the syndesmosis appears to be more sensitive than radiographic imaging [42]. A combination of standardized applied force and direct visualization of the anterior syndesmosis with, if necessary, measurement of the syndesmosis at the ventral entrance of the incisura could be a good diagnostic tool in case of unclear findings in the pre- or intra-operative imaging.

In summary, a reliably visual detection of an incomplete syndesmosis injury is hardly possible, even with higher degrees of injury and even with a standardized procedure. Complete injury of the syndesmosis complex can be detected superior with the STT than with the HT. The STT shows significantly better differentiability in syndesmosis injury compared to the native condition. A macroscopically visible diastasis of 2 mm is not achieved in every case, even with higher-grade ligamentous injuries to the syndesmosis. Overall, the results show that the decision to stabilize the syndesmosis should not be based only on the intraoperative HT. Definitive evidence of instability seems often only possible in cases of maximum instability. The direction of the force application, which was technically different between both tools, seems to matter on the diastasis that should not be underestimated and should be investigated in more detail in the future.

Cadaveric specimens

This study was performed in accordance with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee (approval number: 2021-2431-Material). Ten pairs of fresh frozen intact lower legs were used (7 males, 3 females, mean age 87.1 years; range 74-94 years).

The specimens were lower legs from voluntary body donors from the Institute of Anatomy I of the University. Previous accidents or operations were not reported. Specimens were thawed at room temperature for 18 hours. Soft tissue in the malleolar region was removed, protecting the ligamentous portions. This included the ligamentous structures of the syndesmosis as well as the deltoid ligament in the medial malleolus region and lateral ligamentous structures in the lateral malleolus region.

Description of the developed STT

To be able to apply a standardized force and thus stress to the syndesmosis, a tool was developed in cooperation with the research workshop of the university (Figure 2). This consists of two metal plates which can be inserted in the space between the tibia and fibula. A spindle is built into the body of the tool, which in turn can be used to build up a defined force via a rotary wheel at the other end. A torque limiter can limit the maximum force to be applied via another wheel mounted at the end of the rotary wheel. Forces between 50-100 N can be set here. After the set force is reached, no further force is built up via the rotary wheel. The tool can thus be used to apply a force to be set between the fibula and the tibia. The metal plates and thus also the force vector are oriented slightly obliquely and thus in accordance with the orientation of the two bones to each other (about 45 degrees), with the fibula lying dorsal to the tibia (Figure 3).

Description of the intraoperative HT

A commercial portable digital scale was hooked to the fibula 2 cm proximal to the anterior syndesmosis. It was pulled horizontally (90 degrees to the fibula shaft axis) laterally on the fibula with the scale under constant control of the applied force.

Biomechanical evaluation of the syndesmotic diastasis

To record the induced diastasis between fibula and tibia by the forces applied in both tests, a 3D camera system of the Fraunhofer IOF was used (optical 3D measurement system »kolibri CORDLESS« with two stereo cameras of resolution 2048x1280 pixels, measurement uncertainty 20-100 µm, 30 frames per second for marker tracking). Two passive optical marker plates were applied to the distal fibula and tibia at the level of the syndesmosis. The marker plates consisted of three reflective spheres each and were labelled M1 (tibia) and M2 (fibula) (Figure 3). To perform the stress tests, the specimens were fixed proximally to the tibial plateau and distally to the foot. Initially, the stress tests were performed with the two tools on the intact lower legs, without destruction of the syndesmosis. Forces of 50, 80 and 100 N were applied in each test step. For this purpose, the STT was inserted 2 cm proximal to the level of the anterior syndesmosis between the fibula and the tibia and the rotary wheel was actuated until the torque sensor was triggered and the previously set force was reached. During this process, the change in diastasis or the movement of the two markers (M1 and M2) was recorded with the 3D camera system. The tests with the STT and the HT were performed one after the other. Which test was started with was randomized for the first sample and then alternated.

The right and left legs of each pair were randomly assigned to one of two groups (anterior to posterior or posterior to anterior). In the first step, all specimens were tested natively without injury to document the native diastasis of the syndesmosis as the initial condition. Steps 2.-5. follow as destabilization steps.

In the first group (anterior to posterior), stepwise instability of the syndesmosis was performed in the following protocol:

2. cutting of the anterior syndesmosis ligament (AITFL).

3. cutting of the intermediate syndesmotic ligament

4. osteotomy of the posterior tibial rim (bony fixation of the PIFTL)

5. cutting of the deltoid ligament.

The ligamentous structures were cut through a standard surgical scalpel. An oscillating saw was used to osteotomize the posterior malleolus.

In the second group (posterior to anterior), the protocol was performed in the reverse order as follows:

2. cutting of the deltoid ligament.

3. osteotomy of the posterior tibial rim (bony fixation of the PIFTL)

4. cutting of the intermediary syndesmotic ligament

5. cutting of the anterior syndesmotic ligament (AITFL)

After each of the four transection steps, a force was applied with the STT and the HT with 50, 80, and 100 N, respectively and one after the other. The change in diastasis was continuously monitored using a 3D camera. A relevant threshold value of relative motion between the two bones of > 2mm was determined. This value is based on a native physiological diastasis of about 1 mm in mediolateral direction, which is known from the literature [43-45].

The data bases regarding to the HT data, used in this work, has already been examined and published with regard to reliability [26].

Statistical methods

In a first step a general linear model (GLM) for repeated measures was used to detect the impact of the direction of stepwise induced instability. Therefore, as between subject factor the variable with the coded information of the direction of the stepwise performed instability (from anterior to posterior or from posterior to anterior) was used. The maximum diastasis, measured repeatedly provoked by the STT and the HT (device) during the applied force (3 level), the instability (5 level), was used as within subject factors (repeated measures). If the direction of stepwise induced instability showed no significance as a main effect and in the interaction effect, a second GLM was used, in which the direction is omitted to increase the power of the analysis.

If the Mauchly test for sphericity shows significance, the Greenhouse-Geisser p-value for the main and interaction effects (force and instability) is used. For the main effects (force, instability and device) additional to the p-value the effect sizes (ES) are given in partial eta square (p.Eta²). Values of 0.01, 0.06, or 0.14 indicate small, medium, or large effects, respectively [46]. Bonferroni corrected pairwise post hoc comparisons were used due to multiple testing and the resulting accumulation of alpha errors.

The post hoc pairwise comparisons between the levels of instability, separate for each device, are supplemented by Cohen's d [47] effect sizes in addition to the p-values for better differentiation and interpretation with d=0.2 small effects, d=0.5 moderate effect and d=0.8 large effect.

For visual comparison, the results are given as mean and 95% confidence intervals as error bars. This means that samples with non-overlapping error bars differ significantly, with p≤0.05.

The level of significance was set at p≤0.05. SPSS version 27 software (IBM Corp. Released 2020. IBM SPSS Statistics for Windows, Version 27.0. Armonk, NY: IBM Corp) was used for statistical analyses.

Data Availability

The datasets generated during and analysed during the current study are available from the corresponding author on reasonable request.

Conflict of interest

The work of Dr. F. Kohler was supported by the AO Trauma Germany as part of a scholarship for the promotion of young scientists with 15,000€. Dr. F. Kohler declares that there are no potential conflicts of interest.

Acknowledgments

We would like to thank AO Trauma Germany for the support in the context of the promotion of young scientists (F.C.K.).

We would also like to thank the colleagues of the research workshop of the University Hospital Jena for their help in developing the test tool.

Author contributions statement

Conceptualization, J.H., B.W.U., P.S., I.M. and F.C.K; methodology, F.C.K., J.H., and P.S.; software, P.S..; validation, F.C.K. and P.S.; formal analysis, G.O.H, P.S.; investigation, F.C.K, J.H., L.H., B.W.U; resources, J.H., U.B. L.H. F.C.K., B.W., I.M., G.O.H.; data curation, P.S..; writing—original draft preparation, F.C.K.; writing—review and editing, P.S., L.H., G.O.H, B.W., F.C.K., J.H., R.R., I.M:, M.L., U.B., B.W.U.; visualization, L.H., P.S.; supervision, P.S., J.H., B.W., G.O.H., B.W.U., F.C.K., I.M.; project administration, P.S. and F.C.K.; All authors have read and agreed to the published version of the manuscript.

Additional information

Informed consent was obtained from all subjects involved in the study.

The data presented in the study are stored on secure servers at University Hospital Jena. Donor consent forms are stored at the Anatomical Institute of the University Hospital in Jena. The data are available on request from the corresponding author.

The authors declare no conflict of interest.

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No competing interests reported.

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Objective assessment of syndesmosis stability with an innovative Syndesmosis-Test-Tool - a biomechanical study

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Validity of the Syndesmosis-Test-Tool

Direction of destabilization

Measurements of the diastasis generated by the Syndesmosis Test Tool and Hook Test

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