Biomechanical Analysis of the Individual Ligament Contributions to Syndesmotic Stability

Kinematic Analysis of Combined Suture-Button and Suture Anchor Augment Constructs for Ankle Syndesmosis Injuries

BACKGROUND

Syndesmosis injuries are common, with up to 25% of all ankle injuries being reported to involve an associated syndesmosis injury. These injuries are typically treated with cortical screw fixation or suture-button implants when indicated, but the addition of a suture anchor augment implant has yet to be evaluated. The purpose of this study was to evaluate the ability of a suture anchor augment to add sagittal plane translational and transverse plane rotational constraint to suture-button constructs with syndesmosis injuries. We hypothesized that the suture anchor augment oriented in parallel with the fibers of an injured anterior-inferior tibiofibular ligament (AITFL) in addition to a suture-button construct would achieve physiological motion and stability at the syndesmosis through increased rotational and translational constraint of the fibula.

METHODS

Eleven fresh-frozen cadaver ankles were stressed in external rotation using a custom-made ankle rig. Each ankle had simultaneous recording of ultrasound video, 6 degrees-of-freedom kinematics of the fibula and tibia, and torque as the ankle was stressed by an examiner. The ankles were tested in 6 different states: native uninjured; injured with interosseous ligament and AITFL sectioned; 1× suture button; 2× suture buttons, divergent; 1× suture anchor augment with 2× suture buttons, divergent; and 1× suture anchor augment with 1× suture buttons.

RESULTS

Only the suture anchor augment + 2× suture buttons and suture anchor augment + 1× suture-button constructs were found to be significantly different from the injured state (P = .0003, P = .002) with mean external rotation of the fibula.

CONCLUSION

Overall, the most important finding of this study was that the addition of a suture anchor augment to suture-button constructs provided a mechanism to increase external rotational constraint of the fibula.

CLINICAL RELEVANCE

This study provides a mechanistic understanding of how the combined suture-button and suture anchor augment construct provides an anatomically similar reconstruction of constraints found in the native ankle. However, none of the constructs examined in this study were able to fully restore physiologic motion.

Sagittal instability with inversion is important to evaluate after syndesmosis injury and repair: a cadaveric robotic study

PURPOSE

Disruption of the syndesmosis, the anterior-inferior tibiofibular ligament (AITFL), the posterior-inferior tibiofibular ligament (PITFL), and the interosseous membrane (IOM), leads to residual symptoms after an ankle injury. The objective of this study was to quantify tibiofibular joint motion with isolated AITFL- and complete syndesmotic injury and with syndesmotic screw vs. suture button repair compared to the intact ankle.

METHODS

Nine fresh-frozen human cadaveric specimens (mean age 60 yrs.; range 38-73 yrs.) were tested using a six degree-of-freedom robotic testing system and three-dimensional tibiofibular motion was quantified using an optical tracking system. A 5 Nm inversion moment was applied to the ankle at 0°, 15°, and 30° plantarflexion, and 10° dorsiflexion. Outcome measures included fibular medial-lateral translation, anterior-posterior translation, and external rotation in each ankle state: 1) intact ankle, 2) AITFL transected (isolated AITFL injury), 3) AITFL, PITFL, and IOM transected (complete injury), 4) tricortical screw fixation, and 5) suture button repair.

RESULTS

Both isolated AITFL and complete injury caused significant increases in fibular posterior translation at 15° and 30° plantarflexion compared to the intact ankle (p < 0.05). Tricortical screw fixation restored the intact ankle tibiofibular kinematics in all planes. Suture button repair resulted in 3.7 mm, 3.8 mm, and 2.9 mm more posterior translation of the fibula compared to the intact ankle at 30° and 15° plantarflexion and 0° flexion, respectively (p < 0.05).

CONCLUSION

Ankle instability is similar after both isolated AITFL and complete syndesmosis injury and persists after suture button fixation in the sagittal plane in response an inversion stress. Sagittal instability with ankle inversion should be considered when treating patients with isolated AITFL syndesmosis injuries and after suture button fixation.

LEVEL OF EVIDENCE

Controlled laboratory study, Level V.

Ankle stability in ankle fracture

Restoration of normal ankle kinematics should be the all-encompassing ethos in the approach to management of ankle fractures. To do this, the ligamentous stabilisers must also form part of its assessment and definitive management and be considered during index fracture fixation surgery. This article is a review of the anatomy, mechanics and clinical testing of instability in ankle fractures.

MRI of the distal tibiofibular joint

The distal tibiofibular joint is a fibrous joint that plays a crucial role in the stability of the ankle joint. It is stabilized by three main ligaments: the anterior inferior tibiofibular ligament, the posterior inferior tibiofibular ligament, and the interosseous tibiofibular ligament, which are well delineated on magnetic resonance imaging. Pathology of the distal tibiofibular joint is mostly related to trauma and the longer-term complications of trauma, such as soft tissue impingement, heterotopic ossification, and synostosis. This review article outlines the MRI anatomy and pathology of this joint.

Anatomy, Classification, and Management of Ankle Fractures Involving the Posterior Malleolar Fragment: A Literature Review

The posterior malleolar fragment is frequently involved in rotational ankle fractures, but diagnosis and definitive management remains controversial. Ankle fractures with a posterior malleolar component that are not identified and treated in a timely manner may contribute significantly to future comorbidities, including continued pain, instability, and the development of arthritis. This article highlights the anatomic features of posterior malleolar ankle fractures, the classification schemes used, and discusses the various nonsurgical and surgical methods currently used.

Assessing mechanical ankle instability via functional 3D stress-MRI - A pilot study

BACKGROUND

Quantitative measurement of the mechanical deficit in chronic ankle instability (CAI) is difficult. Therefore, the distinction between functional (FAI) and mechanical ankle instability (MAI) as well as the evaluation of surgical techniques is difficult. This pilot study uses a novel method of functional 3-dimensional stress ankle-MRI to test its applicability for assessing mechanical ankle instability.

METHODS

We used a custom-built ankle arthrometer that allows a stepless positioning of the foot and an axial in situ loading with up to 500 N combined with a 3-dimensional MRI protocol. We assessed four parameters (3D cartilage contact area (CCA) fibulotalar, tibiotalar horizontal and vertical and intermalleolar distance) under six different conditions (neutral-null, plantarflexion-supination and dorsiflexion-pronation each with and without loading) in n = 10 individuals (7 suffering from MAI and 3 healthy controls).

FINDINGS

The MAI group showed a substantially increased reduction of lateral osseous constraint compared to healthy controls when the foot was positioned in plantarflexion-supination (CCA fibulotalar 69% vs. 30% in controls). The reduction of the weight bearing surface in plantarflexion-supination was also more pronounced (CCA tibiotalar horizontal -49% in MAI vs. -28% in controls).

INTERPRETATION

This novel technique is valuable for assessing mechanical ankle instability in the target population and has a potential clinical benefit for assessing the mechanical deficit of individual patients. Further studies are needed to provide evidence for a possible prognostic value of this novel technique.

Anatomy of the Insertion of the Posterior Inferior Tibiofibular Ligament and the Posterior Malleolar Fracture

BACKGROUND

Our aim in this study was to identify the extent of the posterior inferior tibiofibular ligament (PITFL) insertion on the posterior tibia and its relation to intra-articular posterior malleolar fractures.

METHODS

Careful dissection was undertaken on 10 cadaveric lower limbs to identify the ligamentous structures on the posterior aspect of the ankle. The ligamentous anatomy was further compared with our ankle fracture database, specifically posterior malleolar fracture patterns, demonstrating a rotational pilon etiology (Mason and Molloy type 2A and B). Computed tomography imaging was used to measure the dimensions of the fracture fragments.

RESULTS

The superficial PITFL was found to have a transverse component and an oblique component. The average size of the tibial insertion was 54.9 mm (95% CI, 51.8, 58.0) from joint line and 47.1 mm (95% CI, 43.0, 51.2) transverse. From our database of ankle fractures involving the posterior malleolus, 80 Mason and Molloy type 2 fractures were identified for analysis. Of these, 33 were type 2A and 47 were type 2B. The posterolateral fragments had an average size of 26.3 mm (95% CI, 25.0, 27.7) height and 22.1 mm (95% CI, 21.1, 23.1) width. The posteromedial fragments had an average size of 22.0 (95% CI, 18.9, 25.1) height and 19.8 (95% CI, 17.5, 22.0) width.

CONCLUSION

The superficial PITFL insertion on the tibia is broad. In comparison with the average size of the posterior malleolar fragments, the PITFL insertion is significantly larger. Therefore, for a posterior malleolar fracture to cause posterior syndesmotic instability, a ligamentous injury must also occur.

CLINICAL RELEVANCE

Posterior syndesmotic instability results from injury to the PITFL. It has been widely reported that a posterior malleolar fracture will also give rise to posterior syndesmotic instability due to the insertion of the deep PITFL on the posterior tibia. On the contrary, in this paper, we have shown that the superficial PITFL insertion on the tibia is very large, much greater than the average size of the posterior malleolar fragments. Therefore, for a posterior malleolar fracture to cause posterior syndesmotic instability, a ligamentous injury will also have to occur.

Can Weightbearing Computed Tomography Scans Be Used to Diagnose Subtalar Joint Instability? A Cadaver Study

Chronic hindfoot instability is a frequent problem that includes the ankle and/or the subtalar joint. While ankle joint instability can be diagnosed clinically, accurate assessment of the subtalar joint remains elusive. This study's purpose was to assess the ability of weightbearing computed tomography (CT) scans to detect subtalar joint instability. Seven pairs of fresh frozen male cadavers (tibial plateau to toe-tip) were tested. A radiolucent frame held specimens in a plantigrade position while non-weightbearing and weightbearing CT scans (with and without torque application) were taken. First, intact ankles (Native) were scanned. Second, one specimen from each pair underwent interosseous talo-calcaneal ligament (ITCL) transection, while the contralateral underwent calcaneo-fibular ligament (CFL) transection. Third, the remaining intact ITCL or CFL was transected. Finally, the deltoid ligament was transected in all ankles. Eight radiographic measurements were performed to assess the congruency of the subtalar joint on digitally reconstructed radiographs and single CT images. Axial loading did not impact most measurements, whereas torque did impact most measurements. Radiographic measurements performed at the subtalar joint level were more reliable and better predictors for subtalar joint instability compared with measurements performed at the ankle joint level. While torque application is crucial to identify subtalar joint instability, axial load application should be avoided. Measurements to assess the subtalar joint stability should primarily be performed at the subtalar joint level rather than at the ankle joint level when using weightbearing CT scans. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2457-2465, 2019.

Diagnostic capability of dynamic ultrasound evaluation of supination-external rotation ankle injuries: a cadaveric study

BACKGROUND

Ankle syndesmosis injuries are common and range in severity from subclinical to grossly unstable. Definitive diagnosis of these injuries can be made with plain film radiographs, but are often missed when severity or image quality is low. Computed tomography (CT) and magnetic resonance imaging (MRI) can provide definitive diagnosis, but are costly and introduce the patient to radiation when CT is used. Ultrasonography may circumvent many of these disadvantages by being inexpensive, efficient, and able to detect injuries without radiation exposure. The purpose of this study was to evaluate the ability of ultrasonography to detect early stage supination-external rotation (SER) ankle syndesmosis injuries with a dynamic external rotational stress test.

METHODS

Nine, all male, fresh frozen specimens were secured to an ankle rig and stress tested to 10 Nm of external rotational torque with ultrasonography at the tibiofibular clear space. The ankles were subjected to syndesmosis ligament sectioning and repeat stress measurements of the tibiofibular clear space at peak torque. Stress tests and measurements were repeated three times and averaged and analyzed using a repeated one-way analysis of variance (ANOVA). There were six ankle injury states examined including: Intact State, 75% of AITFL Cut, 100% of AITFL Cut, Fibula FX - Cut 8 cm proximal, 75% PITFL Cut, and 100% PITFL Cut.

RESULTS

Dynamic external rotation stress evaluation using ultrasonography was able to detect a significant difference between the uninjured ankle with a tibiofibular clear space of 4.5 mm and the stage 1 complete injured ankle with a clear space of 6.0 mm (P < .02). Additionally, this method was able to detect significant differences between the uninjured ankle and the stage 2-4 injury states.

CONCLUSION

Dynamic external rotational stress evaluation using ultrasonography was able to detect stage 1 Lauge-Hansen SER injuries with statistical significance and corroborates criteria for diagnosing a syndesmosis injury at ≥6.0 mm of tibiofibular clear space widening.

Alterations in tibiotalar joint reaction force following syndesmotic injury are restored with static syndesmotic fixation

INTRODUCTION

Syndesmotic injury alters joint mechanics, which may fail to be restored unless an anatomic reduction is obtained.

METHODS

A minimally invasive method of measuring joint forces was utilized that does not require significant dissection or intraarticular placement of sensory instruments. Steinmann pins were placed in the tibia and talus of eight fresh-frozen human cadaveric lower extremities and a baseline joint reaction force was determined. A syndesmotic injury was created and reduction (anatomic and anterior malreduction) performed with one or two quadricortical screws and joint reaction forces were measured after the injury and subsequent repairs.

FINDINGS

Baseline mean tibiotalar joint reaction force was 31.4 (SD 7.3 N) and syndesmotic injury resulted in a 35% decrease (mean 20.3, SD 8.4 N, p < 0.01). Fixation of the injury using one or two syndesmotic screws resulted in significant increase compared to the injury state (mean 28.7, SD3.9 N, and mean 28.3, SD 6.4 N, p < 0.05), however there was no significant difference between the two methods of fixation. Malreduction of the fibula also increased joint reaction force compared to the injury state (mean 31.5, SD 5.2 N, p < 0.01), however a significant difference was not detected between malreduction and anatomic reduction.

INTERPRETATION

The present study demonstrates that syndesmotic injury decreases joint reaction force within the tibiotalar joint, suggesting ankle joint instability. Tibiotalar force was restored with anatomic reduction with either a 1 or 2 quadricortical syndesmotic screws. Furthermore, anterior malreduction restored joint reaction force to levels similar to those observed at baseline and with anatomic reduction.

LEVEL OF EVIDENCE

Level V: biomechanical/cadaver study.

MRI for high ankle sprains with an unstable syndesmosis: posterior malleolus bone oedema is common and time to scan matters

PURPOSE

Early clinical examination combined with MRI allows accurate diagnosis of syndesmosis instability after a high ankle sprain. However, patients often present late. The aims of the current study were to describe MRI characteristics associated with syndesmosis instability and to test the hypothesis that MRI patterns would differ according to time from injury.

METHODS

Over a 5-year period, 164 consecutive patients who had arthroscopically proven syndesmosis instability requiring fixation were retrospectively studied. Patients with distal fibula fractures were not included. Injuries were classified as acute in 108 patients (< 6 weeks), intermediate in 32 (6-12 weeks) and chronic in 24 patients (> 12 weeks).

RESULTS

Posterior malleolus bone oedema was noted in 65 (60.2%), and posterior malleolus fracture in 17 (15.7%) of acute patients, respectively, which did not significantly differ over time. According to MRI, reported rates of posterior syndesmosis disruption significantly differed over time, observed in 101 (93.5%), 28 (87.5%) and 13 (54.2%) of acute, intermediate and chronic patients, respectively (p < 0.001). Apparent rates of PITFL injury significantly reduced with time (p < 0.001).

CONCLUSIONS

MRI detected a posterior syndesmosis injury in 93.5% of patients acutely but became less reliable with time. The clinical relevance of this study is that posterior malleolus bone oedema may be the only marker of a complete syndesmosis injury and can help clinically identify those injuries which require arthroscopic assessment for instability. If suspicious of a high ankle sprain, we advocate early MRI assessment to help determine stable versus unstable injuries as MRI becomes less reliable after 12 weeks.

LEVEL OF EVIDENCE

III.

Defining the three most responsive and specific CT measurements of ankle syndesmotic malreduction

PURPOSE

The purpose of this study was to compare the reliability and accuracy of existing computed tomography (CT) methods for measuring the distal tibiofibular syndesmosis in uninjured, paired cadaveric specimens and in simulated malreduction models. It was hypothesized that a repeatable set of measurements exists to accurately and quantitatively describe the typical forms of syndesmotic malreduction using contralateral ankle comparison.

METHODS

Twelve cadaveric lower-leg specimen pairs were imaged with CT to generate models for this study. Thirty-five measurements were performed on each native model. Next, four distinct fibular malreductions were produced via digital simulation and all measurements were repeated for each state: (1) 2-mm lateral translation; (2) 2-mm posterior translation; (3) 7-degree external rotation; (4) the previous three states combined. The modified standardized response mean (mSRM) was calculated for each measurement. To assess rater reliability and side-to-side agreements of the native state measurements, intraclass correlation coefficients (ICC) and Pearson correlation coefficients (PCC) were calculated, respectively.

RESULTS

The most responsive measurements for detecting isolated malreduction were the Leporjärvi clear space for lateral translation, the Nault anterior tibiofibular distance for posterior translation, and the Nault talar dome angle for external rotation of the fibula. These measurements demonstrated fair to excellent inter-rater ICCs (0.64-0.76) and variable side-to-side PCCs (0.14-0.47).

CONCLUSIONS

The most reliable method to assess the syndesmosis on CT was to compare side-to-side differences using three distinct measurements, one for each type of fibular malreduction, allowing assessment of the magnitude and directionality of syndesmosis malreduction. Reliable evaluation is essential for assessing subtle syndesmosis injuries, malreduction and surgical planning.

Torque application helps to diagnose incomplete syndesmotic injuries using weight-bearing computed tomography images

OBJECTIVE

Accurate identification of distal tibio-fibular syndesmotic injuries is essential to limit potential deleterious post-traumatic effects. To date, conventional radiographs, computed tomography (CT), and magnetic resonance imaging (MRI) have shown limited utilization. This cadaver study evaluates the utility of weight-bearing CT scans on the assessment of incomplete and more complete syndesmotic injuries.

MATERIALS AND METHODS

Ten male cadavers (tibial plateau to toe-tip) were included. Weight-bearing CTs were taken under four test conditions, with and without torque on the tibia (corresponding to external rotation of the foot and ankle). First, intact ankles (native) underwent imaging. Second, the anterior-inferior tibio-fibular ligament (AITFL) was transected (condition 1). Then, the deltoid ligament (condition 2) was transected, followed by the interosseous membrane (IOM, condition 3). Finally, the posterior-inferior tibio-fibular ligament (PITFL) was transected (condition 4). The medial clear space (MCS), the tibio-fibular clear space (TFCS), and the tibio-fibular overlap (TFO) were assessed on digitally reconstructed radiographs (DRRs), and on axial CT images.

RESULTS

The TFO differentiated isolated AITFL transection from native ankles when torque was applied. Also under torque conditions, the MCS was a useful predictor of an additional deltoid ligament transection, whereas the TFCS identified cadavers in which the PITFL was also transected.

CONCLUSION

Torque application helps to diagnose incomplete syndesmotic injuries when using weight-bearing CT. The TFO may be useful for identifying incomplete syndesmotic injuries, whereas the MCS and TFCS predict more complete injuries.

Anatomic Ligament Repairs of Syndesmotic Injuries

Poor clinical results are seen with syndesmotic injuries in the setting of ankle sprains and ankle fractures. The goal of syndesmosis repair is to restore the normal anatomic relationship of the distal tibiofibular joint and prevent ankle arthritis. Indications for surgical intervention for isolated syndesmotic injuries include frank syndesmosis diastasis, medial clear space widening on plain radiographs, significant radiographic syndesmosis diastasis during stress examination, or subtle syndesmotic diastasis detected by arthroscopic evaluation. Complications after syndesmosis repair include symptomatic hardware, malreduction, and arthritis. Anatomic reduction of the syndesmosis leads to better outcomes following surgery.

In Vivo CT Analysis of Physiological Fibular Motion at the Level of the Ankle Syndesmosis During Plantigrade Weightbearing

Background. It is clear that motion at the syndesmosis occurs due to ranging of the ankle joint, but the influence of weightbearing with the foot in the plantigrade position is unclear. In vivo computed tomographic (CT) evaluation of the syndesmosis has not been previously described. The purpose of this study is to quantify physiological fibular motion at the level of the ankle syndesmosis in both weightbearing and nonweightbearing conditions with the foot in the plantigrade position. Methods. CT images were obtained from 9 normal healthy subjects using a weightbearing CT imaging system. The subjects were positioned in a nonweightbearing and weightbearing state with their foot in the plantigrade position. Fibular translation and rotation were measured from the axial CT images using previously validated techniques. Results. Both the average lateral and anteroposterior translation of the fibula between weightbearing and nonweightbearing states was minimal (0.3 mm and 0.2 mm, respectively). The largest difference in translation observed in either direction was 0.9 mm. An average of 0.5° was found for rotational differences of the fibula between weightbearing and nonweightbearing. Neither of the translational and rotational parameters reached statistical significance. Conclusion. In vivo CT analysis of the distal tibiofibular joint with an intact syndesmosis did not reveal statistically significant physiological motion between weightbearing and nonweightbearing conditions with the foot in plantigrade position. Our findings suggest that weightbearing accounts for little motion at the syndesmosis and supports further investigation into the role of early protected weightbearing after syndesmosis fixation. Levels of Evidence: Level III: Case-control study.

Impact of Torque on Assessment of Syndesmotic Injuries Using Weightbearing Computed Tomography Scans

BACKGROUND

The diagnosis of subtle injuries to the distal tibiofibular syndesmosis remains elusive. Conventional radiographs miss a large subset of injuries that present without frank diastasis. This study evaluated the impact of torque application on the assessment of syndesmotic injuries when using weightbearing computed tomography (CT) scans.

METHODS

Seven pairs of male cadavers (tibia plateau to toe-tip) were included. CT scans with axial load application (85 kg) and with (10 Nm) or without torque to the tibia (corresponding to external rotation of the foot and ankle) were taken during 4 test conditions. First, intact ankles (native) were scanned. Second, 1 specimen from each pair underwent anterior inferior tibiofibular ligament (AITFL) transection (condition 1A), while the contralateral underwent deltoid transection (condition 1B). Third, the lesions were reversed on the same specimens and the remaining intact deltoid or AITFL was transected (condition 2). Finally, the distal tibiofibular interosseous membrane (IOM) was transected in all ankles (condition 3). Measurements were performed to assess the integrity of the distal tibiofibular syndesmosis on digitally reconstructed radiographs (DRRs) and on axial CT scans.

RESULTS

Torque impacted DRR and axial CT scan measurements in almost all conditions. The ability to diagnose syndesmotic injuries using axial CT measurements improved when torque was applied. No significant syndesmotic morphological change was observed with or without torque for either isolated AITFL or deltoid ligament transection.

DISCUSSION

Torque application had a notable impact on two-dimensional (2-D) measurements used to diagnose syndesmotic injuries for both DRRs and axial CT scans. Because weightbearing conditions allow for standardized positioning of the foot while radiographs or CT scans are taken, the combination of axial load and torque application may be desirable.

CLINICAL RELEVANCE

Application of torque to the tibia impacts 2-D measurements and may be useful when diagnosing syndesmotic injuries by DRRs or axial CT images.

Biomechanical Comparison of Syndesmotic Repair Techniques During External Rotation Stress

BACKGROUND

The purpose of this study was to compare mechanical behavior of conventional syndesmosis fixation devices with new anatomic repair techniques incorporating various repair augmentations to determine which approach would return rotational ankle mechanics closer to those of an intact ankle.

METHODS

Ten pairs of fresh-frozen through-the-knee cadaveric lower limbs were subjected to 7.5 Nm of external rotation torque while under 750 N of axial compression. After testing specimens intact and with the deltoid and syndesmotic ligament complexes completely destabilized, specimens underwent syndesmotic fixation using a screw, a suture button construct, a prototype structurally augmented flexible trans-syndesmotic fixation device, or the prototype device plus suture repairs of the anterior-inferior tibiofibular ligament and deep deltoid ligament. Syndesmotic repair devices were exchanged between tests so that each specimen was tested with 2 different fixation techniques. Whole-foot rotation angles at 7.5 Nm of applied torque were measured for comparison of the different repair strategies, and reflective markers mounted on the tibia, fibula, and talus were used to track translations and rotations of the talus and the fibula relative to the tibia during testing.

RESULTS

Syndesmotic destabilization significantly ( P < .001) increased whole-foot, talus, and fibula rotation in an axial plane and posterior fibula translation under 7.5 Nm of torque. Neither the suture button nor the augmented flexible trans-syndesmotic fixation device reduced those increases. Screw fixation or addition of anatomic ligament repairs to the augmented flexible fixation device successfully reduced axial plane rotations and sagittal plane translations to near intact levels.

CONCLUSION

Flexible trans-syndesmotic fixation alone was found to be insufficient for restoring rotational stability to the ankle/talus or preventing sagittal plane displacement of the fibula.

CLINICAL RELEVANCE

Repairs to simulate anatomic structures disrupted during a syndesmosis injury were required to restore rotational stability to the foot when using flexible trans-syndesmotic fixation that may have clinical applicability.

Development and validation of a robotic system for ankle joint testing

Ankle sprains are the most common sports injury. Gaining a better understanding of ankle mechanics will help improve current treatments, enabling a better quality of life for patients following surgery. In this paper, the development of a robotic system for ankle joint testing is presented. It is composed of an industrial robot, a universal force/torque sensor and bespoke holders allowing high repositioning of specimens. A specimen preparation protocol that uses optical tracking to register the ankle specimens is used. A registration technique is applied to define and calibrate the task related coordinate system needed to control the joint's degrees of freedom and to simulate standardised, clinical ankle laxity tests. Experiments were carried out at different flexion angles using the robotic platform. Optical tracking was used to record the resulting motion of the tibia for every simulated test. The measurements from the optical tracker and the robot were compared and used to validate the system. These findings showed that the optical tracking measurements validate those from the robot for ankle joint testing with interclass coefficients equal to 0.991, 0.996 and 0.999 for the anterior-posterior translations, internal-external and inversion-eversion rotations.

Imaging in syndesmotic injury: a systematic literature review

OBJECTIVES

To give a systematic overview of current diagnostic imaging options for assessment of the distal tibio-fibular syndesmosis.

MATERIALS AND METHODS

A systematic literature search across the following sources was performed: PubMed, ScienceDirect, Google Scholar, and SpringerLink. Forty-two articles were included and subdivided into three groups: group one consists of studies using conventional radiographs (22 articles), group two includes studies using computed tomography (CT) scans (15 articles), and group three comprises studies using magnet resonance imaging (MRI, 9 articles).The following data were extracted: imaging modality, measurement method, number of participants and ankles included, average age of participants, sensitivity, specificity, and accuracy of the measurement technique. The Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool was used to assess the methodological quality.

RESULTS

The three most common techniques used for assessment of the syndesmosis in conventional radiographs are the tibio-fibular clear space (TFCS), the tibio-fibular overlap (TFO), and the medial clear space (MCS). Regarding CT scans, the tibio-fibular width (axial images) was most commonly used. Most of the MRI studies used direct assessment of syndesmotic integrity. Overall, the included studies show low probability of bias and are applicable in daily practice.

CONCLUSIONS

Conventional radiographs cannot predict syndesmotic injuries reliably. CT scans outperform plain radiographs in detecting syndesmotic mal-reduction. Additionally, the syndesmotic interval can be assessed in greater detail by CT. MRI measurements achieve a sensitivity and specificity of nearly 100%; however, correlating MRI findings with patients' complaints is difficult, and utility with subtle syndesmotic instability needs further investigation. Overall, the methodological quality of these studies was satisfactory.

A Radiographic Dye Method for Intraoperative Evaluation of Syndesmotic Injuries

BACKGROUND

The Chertsey test has been recently defined as an intraoperative test for the detection of the syndesmotic injuries by the application of intra-articular contrast. However, no study has investigated the reliability and comparative analysis of the Chertsey test. The purpose of this study was to explore the diagnostic accuracy of the Chertsey test in predicting syndesmosis instability of the injured ankle, with correlation to preoperative computed tomography (CT) findings.

METHODS

A total of 39 patients who were operated on due to the unilateral ankle fracture and had no complaint on the contralateral ankle joint were included in the study. An intraoperative Chertsey test was performed on all ankle fractures and bilateral ankle CT was obtained preoperatively. Ankles were classified as Chertsey +, Chertsey -, and contralateral control group. The morphology categorization, width, and volume of the syndesmotic region were measured on axial images of the CT. Mann-Whitney U test was used to compare the data. Intraobserver and interobserver agreements were accessed by calculating the intraclass correlation coefficient (ICC) for radiologic parameters and the Chertsey test.

RESULTS

The Chertsey test was positive in 13 (33.3%) of 39 ankle fractures. Patients with a positive Chertsey test showed a significant increase in syndesmotic width and volume compared with Chertsey - and control group. However, there was no significant difference between Chertsey - and the control group. All the ICC values were excellent for both radiologic measurements and test.

CONCLUSION

The Chertsey test is a reliable and useful test that can be used intraoperatively in the diagnosis of syndesmotic injuries.

LEVEL OF EVIDENCE

III, comparative series.

Effect of Sequential Sectioning of Ligaments on Syndesmotic Instability in the Coronal Plane Evaluated Arthroscopically

BACKGROUND

Arthroscopic evaluation of the syndesmosis allows direct visualization of syndesmotic instability. The purpose of this study was to determine the minimum degree of ligamentous injury necessary to destabilize the syndesmosis in the coronal plane when assessed arthroscopically and pinpoint where such instability should be measured within the incisura.

METHODS

Fourteen cadaveric specimens were divided into 2 groups and arthroscopically assessed first with the syndesmosis intact and then following serial differential ligamentous transection. Group 1 (n = 7): anterior-inferior tibiofibular (AITFL), interosseous (IOL), posterior-inferior tibiofibular (PITFL), and deltoid (DL) ligament. Group 2 (n = 7): PITFL-IOL-AITFL-DL. At each step, a standard 100-N lateral hook test was applied and tibiofibular coronal plane diastasis measured arthroscopically at both the anterior and posterior third of the incisura. These measurements were in turn compared with those of the stressed intact ligamentous state.

RESULTS

There was no significant syndesmotic instability measured at either the anterior or posterior margin of the incisura after transection of a singular ligament (AITFL or PITFL) or after the IOL was additionally transected. Diastasis at the posterior margin was significantly increased when all syndesmotic ligaments were sectioned (group 1: P = .018; group 2: P = .008), but this was not noted along the anterior margin. Diastasis at the anterior margin reached significance only with complete transection of syndesmosis and DL (group 1: P < .001; group 2: P = .044).

CONCLUSION

Under arthroscopic evaluation, the syndesmosis becomes unstable in the coronal plane only when all syndesmotic ligaments are transected, which should preferentially be measured at the posterior margin of the incisura. Anteriorly, diastasis becomes apparent only with addition of DL disruption, although this added finding may aid in diagnosis of occult deltoid injury.

CLINICAL RELEVANCE

AITFL, IOL, and PITFL need to be injured to produce coronal plane syndesmotic instability. Arthroscopic assessment of such instability should occur along the posterior margin of the incisura. When they exist, similar findings anteriorly suggest concomitant deltoid injury.

3D Model Analysis of Ankle Flexion on Anatomic Reduction of a Syndesmotic Injury

BACKGROUND

The effect of ankle positioning during suture-button fixation for syndesmosis repair on range of motion (ROM) and anatomic reduction has yet to be investigated. The purpose of this cadaveric study was to compare the effects of 3 different ankle positions during suture-button repair on volumetric reduction of the syndesmosis, fibular displacement, and ROM of the ankle using 3-dimensional computed tomography (CT) analysis. The null hypothesis was that ankle position during fixation would not affect syndesmotic volume restoration, fibular displacement, or ROM.

METHODS

Twelve matched pair (n = 24) human cadaveric specimens were used for this study. Prior to syndesmotic sectioning, ROM assessment and CT scans were performed. Following sectioning of the syndesmosis, specimens were repaired in plantarflexion, dorsiflexion, or neutral, and simulated postrepair ROM evaluations and CT scans were repeated. Least squares mean differences between repair groups and the preinjury state were compared by analysis of variance and Tukey's method.

RESULTS

There were no significant differences between repair groups for volumetric reduction ( P = .917), fibular displacement (anterior-posterior, P = .805; medial-lateral, P = .949), or dorsiflexion capacity ( P = .249). Among all specimens, compared with the preinjury state, there was a significant mean ± SD volume reduction of 337 ± 400 mm³ and medial displacement of 1.9 ± 1.5 mm.

CONCLUSION

This study failed to reject the null hypothesis and demonstrated that ankle flexion at the time of syndesmotic fixation with a suture-button construct had no significant in vitro effect on volume changes, fibular displacement, or dorsiflexion capacity. However, in comparison to the preinjured state, suture-button repair resulted in significant overcompression with respect to syndesmosis volume and medial displacement of the fibula.

CLINICAL RELEVANCE

Ankle position at the time of syndesmotic fixation did not affect overall ankle ROM when using a suture-button construct; however, overcompression was observed in all positions. The clinical impact of syndesmotic overcompression remains largely unknown.

Biomechanical Comparison of 3 Current Ankle Syndesmosis Repair Techniques

BACKGROUND

Significant debate exists regarding optimal repair for unstable syndesmosis injuries. Techniques range from screw fixation, suture-button fixation, or a combination of the two. In this study, 3 common repairs were compared using a simulated weightbearing protocol with internal and external rotation of the foot.

METHODS

Twenty-four lower leg specimens with mean age 54 years (range, 38-68 years) were used for testing. Following creation of a complete syndesmotic injury (AITFL, ITFL, PITFL, interosseous membrane), specimens were repaired using 1 of 3 randomly assigned techniques: (1) one 3.5-mm syndesmotic screw, (2) 1 suture-button construct, and (3) 2 divergent suture-button constructs. Repairs were cycled for 500 cycles between 7.5 Nm of internal/external rotation torque under a constant 750 N axial compressive load in a neutral dorsiflexion position. At 0, 10, 100, and 500 cycles, torsional cyclic loading was interrupted to assess torsional resistance to rotation within a physiologic range of motion (15 degrees external rotation to 10 degrees internal rotation). Torque (Nm), rotational position (degrees), and 3-dimensional data were collected throughout the testing to characterize relative spatial relationships of the tibiofibular articulation.

RESULTS

There were no significant differences between repair techniques in resistance to internal and external rotation with respect to the intact syndesmosis. Three-dimensional analysis revealed significant differences between repair techniques for sagittal fibular translation with external rotation of the foot. Screw fixation had the smallest magnitude of posterior sagittal translation (2.5 mm), and a single suture-button construct demonstrated the largest magnitude of posterior sagittal translation (4.6 mm). Screw fixation also allowed for significantly less anterior sagittal translation with internal rotation of the foot (0.1 mm) when compared to both 1 (2.7 mm) and 2 (2.9 mm) suture-button constructs.

CONCLUSION

All repairs provided comparable rotational stability to the syndesmosis; however, no repair technique completely restored rotational stability and tibiofibular anatomic relationships of the preinjury state.

CLINICAL RELEVANCE

Constructs were comparable across most conditions; however, when repairing injuries with a suture-button construct, a single suture-button construct may not provide sufficient resistance to sagittal translation of the fibula.