Analysis of the stress and displacement distribution of inferior tibiofibular syndesmosis injuries repaired with screw fixation: a finite element study

Fracture Line Morphology and a Novel Classification of Pilon Fractures

OBJECTIVE

Currently, there is no research that includes a comprehensive three-dimensional fracture mapping encompassing all types of Pilon fractures. Moreover, the existing classification systems for Pilon fractures exhibit only moderate to fair consistency and reproducibility. Additionally, some of these classification systems fail to accurately depict the morphological characteristics of the fractures. This study aimed to create a fracture map encompassing all types of Pilon fractures by three-dimensional fracture mapping. In addition, this study conducted a finite element analysis of the normal ankle joint, and based on the distribution of fracture lines and the stress distribution at the distal tibia, proposed a new classification for Pilon fractures.

METHODS

A retrospective analysis of Pilon fractures in our hospital from January 2018 to January 2024 was performed. A total of two hundred forty-four Pilon fractures were included, and their fracture lines were transcribed onto the tibia and fibula templates, and fracture maps and heat maps were created. A nonhomogeneous model of the ankle joint was constructed and verified, and the stress distribution on the distal tibia articular surface was measured and analyzed in three models (neutral, dorsiflexed, and plantarflexed model). Based on the fracture map and stress distribution, a five-column classification system for Pilon fractures was proposed, and the intraobserver and interobserver reliability was calculated using Cohen and Fleiss k statistics.

RESULT

The fracture line on the distal tibia articular surface showed a V-shaped distribution. One branch extended from the junction of the medial malleolar articular surface and the inferior tibial articular surface toward the medial malleolus. The other branch extended from the middle of the fibular notch to the posterior part of the medial ankle, toward the tibial shaft. The fibula fracture line mainly extended from the anterior and lower part of the lateral malleolus to the posterior and upper part. As evidenced by the neutral, dorsiflexed, and plantar flexion models, the stress on the posterolateral articular surface (posterolateral column) was low, while the majority of the stress was concentrated in the center. Three-column fractures were the most common, followed by two-column fractures. Using the five-column classification, the K-weighted values of interobserver and intraobserver analysis were 0.653 (p < 0.001) and 0.708 (p < 0.001), respectively.

CONCLUSIONS

In this study, the fracture line and morphological characteristics of Pilon fractures were analyzed in detail by three-dimensional mapping. In addition, this study conducted a finite element analysis of the stress distribution on the distal tibial joint surface of the normal ankle joint. Moreover, a novel classification system was proposed to reflect these findings. The new classification not only exhibits greater consistency, facilitating accurate communication of fracture characteristics among surgeons, but also aids in understanding the mechanisms of injury and formulating surgical strategies.

Biomechanical Sequelae of Syndesmosis Injury and Repair

This review characterizes fibula mechanics in the context of syndesmosis injury and repair. Through detailed understanding of fibula kinematics (the study of motion) and kinetics (the study of forces that cause motion), the full complexity of fibula motion can be appreciated. Although the magnitudes of fibula rotation and translation are inherently small, even slight alterations of fibula position or movement can substantially impact force propagation through the ankle and hindfoot joints. Accordingly, implications for clinical care are discussed.

Disease-Specific Finite element Analysis of the Foot and Ankle

Finite-element analysis is a computational modeling technique that can be used to quantify parameters that are difficult or impossible to measure externally in a geometrically complex structure such as the foot and ankle. It has been used to improve our understanding of pathomechanics and to evaluate proposed treatments for several disorders, including progressive collapsing foot deformity, ankle arthritis, syndesmotic injury, ankle fracture, plantar fasciitis, diabetic foot ulceration, hallux valgus, and lesser toe deformities. Parameters calculated from finite-element models have been widely used to make predictions about their biomechanical correlates.

Personalised statistical modelling of soft tissue structures in the ankle

BACKGROUND AND OBJECTIVE

Revealing the complexity behind subject-specific ankle joint mechanics requires simultaneous analysis of three-dimensional bony and soft-tissue structures. 3D musculoskeletal models have become pivotal in orthopedic treatment planning and biomechanical research. Since manual segmentation of these models is time-consuming and subject to manual errors, (semi-) automatic methods could improve the accuracy and enlarge the sample size of personalised 'in silico' biomechanical experiments and computer-assisted treatment planning. Therefore, our aim was to automatically predict ligament paths, cartilage topography and thickness in the ankle joint based on statistical shape modelling.

METHODS

A personalised cartilage and ligamentous prediction algorithm was established using geometric morphometrics, based on an 'in-house' generated lower limb skeletal model (N = 542), tibiotalar cartilage (N = 60) and ankle ligament segmentations (N = 10). For cartilage, a population-averaged thickness map was determined by use of partial least-squares regression. Ligaments were wrapped around bony contours based on iterative shortest path calculation. Accuracy of ligament path and cartilage thickness prediction was quantified using leave-one-out experiments. The novel personalised thickness prediction was compared with a constant cartilage thickness of 1.50 mm by use of a paired sample T-test.

RESULTS

Mean distance error of cartilage and ligament prediction was 0.12 mm (SD 0.04 mm) and 0.54 mm (SD 0.05 mm), respectively. No significant differences were found between the personalised thickness cartilage and segmented cartilage of the tibia (p = 0.73, CI [-1.60 .10^-17, 1.13 .10^-17]) and talus (p = 0.95, CI[ -1.35 .10^-17, 1.28 .10^-17]). For the constant thickness cartilage, a statistically significant difference was found in 89% and 92% of the tibial (p < 0.001, CI [0.51, 0.58]) and talar (p < 0.001, CI [0.33, 0.40]) cartilage area.

CONCLUSIONS

In this study, we described a personalised prediction algorithm of cartilage and ligaments in the ankle joint. We were able to predict cartilage and main ankle ligaments with submillimeter accuracy. The proposed method has a high potential for generating large (virtual) sample sizes in biomechanical research and mitigates technological advances in computer-assisted orthopaedic surgery.

Predicting ankle joint syndesmotic screw lifetime using finite element and fatigue analysis

After recovery and loading on the patient’s leg, syndesmotic screws mounted on an injured ankle may fail. The main subject of this study is to estimate the lifetime of screws considering the patient’s weight and physical activity. Method: A 3D finite element model of the bone and implemented screws were provided assigning the mechanical properties of ligaments, bones, and screws. Considering axial and tangential physiological loads during the walking phase, the stress and fatigue analyses were performed. Results: The stress distribution had an identical pattern in the screws and all of them experienced the maximum stress during 60–70% of the walking phase. Conclusion: The results of analyses show that body weight has a significant effect on the mounted screw lifetime. Patients with a weight of more than [Formula: see text] kg should prevent applying body load on the operated leg. Conversely, no worry about a patient having less than [Formula: see text] kg body weight.

A Review of Finite Element Models of Ligaments in the Foot and Considerations for Practical Application

PURPOSE

Finite element (FE) modeling has been used as a research tool for investigating underlying ligaments biomechanics and orthopedic applications. However, FE models of the ligament in the foot have been developed with various configurations, mainly due to their complex 3D geometry, material properties, and boundary conditions. Therefore, the purpose of this review was to summarize the current state of finite element modeling approaches that have been used in the ?eld of ligament biomechanics, to discuss their applicability to foot ligament modeling in a practical setting, and also to acknowledge current limitations and challenges.

METHODS

A comprehensive literature search was performed. Each article was analyzed in terms of the methods used for: (a) ligament geometry, (b) material property, (c) boundary and loading condition related to its application, and (d) model verification and validation.

RESULTS

Of the reviewed studies, 80% of the studies used simplified representations of ligament geometry, the non-linear mechanical behavior of ligaments was taken into account in only 19.2% of the studies, 33% of included studies did not include any kind of validation of the FE model.

CONCLUSION

Further refinement in the functional modeling of ligaments, the micro-structure level characteristics, nonlinearity, and time-dependent response, may be warranted to ensure the predictive ability of the models.

Anatomical reconstruction of the anterior inferior tibiofibular ligament in elite athletes using InternalBrace suture tape

AIMS

The ideal management of acute syndesmotic injuries in elite athletes is controversial. Among several treatment methods used to stabilize the syndesmosis and facilitate healing of the ligaments, the use of suture tape (InternalBrace) has previously been described. The purpose of this study was to analyze the functional outcome, including American Orthopaedic Foot & Ankle Society (AOFAS) scores, knee-to-wall measurements, and the time to return to play in days, of unstable syndesmotic injuries treated with the use of the InternalBrace in elite athletes.

METHODS

Data on a consecutive group of elite athletes who underwent isolated reconstruction of the anterior inferior tibiofibular ligament using the InternalBrace were collected prospectively. Our patient group consisted of 19 elite male athletes with a mean age of 24.5 years (17 to 52). Isolated injuries were seen in 12 patients while associated injuries were found in seven patients (fibular fracture, medial malleolus fracture, anterior talofibular ligament rupture, and posterior malleolus fracture). All patients had a minimum follow-up period of 17 months (mean 27 months (17 to 35)).

RESULTS

All patients returned to their pre-injury level of sports activities. One patient developed a delayed union of the medial malleolus. The mean return to play was 62 days (49 to 84) for isolated injuries, while the patients with concomitant injuries returned to play in a mean of 104 days (56 to 196). The AOFAS score returned to 100 postoperatively in all patients. Knee-to-wall measurements were the same as the contralateral side in 18 patients, while one patient lacked 2 cm compared to the contralateral side.

CONCLUSION

This study suggests the use of the InternalBrace in the management of unstable syndesmotic injuries offers an alternative method of stabilization, with good short-term results, including early return to sports in elite athletes. Cite this article: Bone Joint J 2022;104-B(1):68-75.

Biomechanical comparison of screw, tightrope and novel double endobutton in the treatment of tibiofibular syndesmotic injuries

BACKGROUND

Adequate reduction and stabilization of the syndesmosis are significant to prevent early degeneration of the ankle joint and get better clinical outcomes. However, the routine surgical methods have diffierent limitations. The purpose of this study was to develop a novel double Endobutton fixation to treat the distal tibiofibular syndesmotic injuries, and determine whether the novel double Endobutton fixation demonstrates a better biomechanical property compare with the intact syndesmosis, the screw fixation and the Tightrope fixation.

METHODS

Twenty-four normal fresh-frozen ankle specimens with a mean age of 42 ± 8 (range, 28-62) years were randomly divided equally into four groups: (1) the intact group, (2) the screw group, (3) the Tightrope group, (4) the Endobutton group. 3D printer technology was used to establish the personalized distal tibiofibular syndesmotic navigation modules to determine the accurate bone tunnel. Axial loading was applied in five ankle positions: neutral position, dorsiflexion, plantar flexion, varus and valgus. Rotation torque was applied in two ankle rotation of the neutral position: internal and external.

RESULTS

In most situations, the displacements of the intact group were larger than the screw group, the Tightrope group and the Endobutton group (P < .05), and the displacements of the screw group were smaller than other three groups (P < .05). The displacements of the double Endobutton group were slightly larger than the Tightrope group but no significant differences were found between these two groups except in the dorsiflexion position of axial loading experiments (P < .05). The novel double Endobutton fixation was steadier than intact syndesmosis and more micromotional than screw fixation.

CONCLUSION

Our study demonstrated that the novel double Endobutton can be considered as the better fixation in treatment of distal tibiofibular syndesmotic injuries.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Biomechanical evaluation of syndesmotic fixation techniques via finite element analysis: Screw vs. suture button

BACKGROUND AND OBJECTIVE

Tibiofibular syndesmotic injuries may cause degenerative changes, reduction in ankle function and compromising ankle stability. Different fixation techniques try to restore its functionality. Screw-fixation is the gold-standard. Recently, suture-button fixation has aroused the attention because it allows for physiologic micromotion while maintaining an accurate reduction. The aim of this study is to compare the biomechanical behaviour of both fixation techniques using the finite element method.

METHODS

A three-dimensional finite element model of the tibiofibular joint was reconstructed simulating the intact ankle and the injured syndesmosis. Then, different methods of syndesmosis fixation were analysed: screws (number of cortices, number of screws and distance between screws) and suture buttons (single, double parallel and double divergent with a sensitivity analysis on the pretension forces) configuration. Ligaments and cartilages were included and simulated as spring elements. Physiological loads during stance phase were simulated.

RESULTS

Syndesmosis widening and von Mises stresses were computed. Syndesmosis widening in the injured configuration compromised joint stability (2.06 mm), whereas using a single quadricortical screw (0.18 mm) stiffened the joint. Syndesmosis widening using suture-buttons were closer to syndesmosis widening of the intact ankle configuration (0.97 mm). Von Mises stresses were higher for the titanium screws than for the suture buttons.

CONCLUSIONS

A detailed biomechanical comparison among different syndesmotic fixation was performed. Suture buttons have advantages with regard to syndesmosis widening in comparison to screw fixation. This fact supports the good long-term clinical results obtained with suture buttons fixation. The proposed methodology could be an efficient tool for preoperative planning.

An inconspicuous stabilizer of the subtalar joint: MR arthrographic anatomy of the posterior talocalcaneal ligament

OBJECTIVE

The main function of the posterior talocalcaneal ligament (PTL) is to stabilize the posterior subtalar joint in the ankle. PTL is a potential source of pain in chronic subtalar instability. Our knowledge of the anatomy and function of PTL is limited and there are not many studies regarding its morphology. The aim of this study is to provide detailed information about imaging anatomy and morphology of PTL.

MATERIALS AND METHODS

This retrospective study included 197 ankle images of 184 patients (13 bilateral) obtained from MR arthrography (MRA) and conventional MRI between 2012 and 2019. The incidence of PTL was evaluated using both methods. The location of the ligament to the calcaneus, shape, and intraarticular extension was determined by MRA. In addition, thickness and lengths were measured in millimeters, and the presence of os trigonum, contrast agent extravasation into adjacent anatomical structures, was evaluated. The upper surface of the calcaneus was divided into nine regions in the axial view and three regions in the sagittal view.

RESULTS

The incidence of PTL was 65.5% (n = 129). In axial view, the most common calcaneal attachment was in the 5th zone. The ligament was mostly fan-shaped (n = 104) and the extraarticular course was 87%. The average length was 15.9 mm and the average thickness was 1.1 mm. There were os trigonum in 18 cases.

CONCLUSION

Having knowledge of the morphology and variations of PTL and defining its relationship with adjacent anatomical structures can help evaluate subtalar instability.

Identification of Surgical Plan for Syndesmotic Fixation Procedure Based on Finite Element Method

Syndesmosis injuries account for approximately 20% of ankle fractures that require surgery. Although multiple surgical options are available, all of them are based on metal screws. Serious complications that arise when applying metal screws include screw loosening or breakage. To prevent such complications, we applied a simulation method using a finite element (FE) analysis. We created a 3D FE model of an ankle joint and conducted an FE analysis focusing on syndesmosis in terms of the level, material, and diameter of the syndesmotic screw and the number of penetrated cortical bones. The magnitude and direction of the force applied to the tibia in the midstance state were considered for simulating the model. The maximum von-Mises stress and syndesmosis widening were analyzed in terms of different biomechanical parameters. We identified the characteristics of the most biomechanically stable syndesmotic screw and its fixation point on the basis of the two parameters. We demonstrated that the ideal syndesmotic screw fixation should be fixed at a level 20 to 25 mm above the ankle using a 4.5 mm titanium screw.

Diagnosis and treatment of ankle syndesmosis injuries with associated interosseous membrane injury: a current concept review

BACKGROUND

Tibiofibular syndesmosis injury leads to ankle pain and dysfunction when ankle injuries are not treated properly. Despite several studies having been performed, many questions about diagnosis and treatment remain unanswered, especially in ankle syndesmosis injury with interosseous membrane injury. Therefore, the purpose of this study was to help guide best practice recommendations.

METHODS

This review explores the mechanism of injury, clinical features, diagnosis methods, and the treatment strategy for ankle syndesmosis injury with interosseous membrane injury to highlight the current evidence in terms of the controversies surrounding the management of these injuries.

RESULTS

Radiological and CT examination are an important basis for diagnosing ankle syndesmosis injury. Physical examination combined with MRI to determine the damage to the interosseous membrane is significant in guiding the treatment of ankle syndesmosis injury with interosseous membrane injury. In the past, inserting syndesmosis screws was the gold standard for treating ankle syndesmosis injury. However, there were increasingly more controversies regarding loss of reduction and broken nails, so elastic fixation has become more popular in recent years.

CONCLUSIONS

Anatomical reduction and effective fixation are the main aspects to be considered in the treatment of ankle syndesmosis injury with interosseous membrane injury and are the key to reducing postsurgery complications.

Effect of Complete Syndesmotic Disruption and Deltoid Injuries and Different Reduction Methods on Ankle Joint Contact Mechanics

BACKGROUND

Syndesmotic injuries can be associated with poor patient outcomes and posttraumatic ankle arthritis, particularly in the case of malreduction. However, ankle joint contact mechanics following a syndesmotic injury and reduction remains poorly understood. The purpose of this study was to characterize the effects of a syndesmotic injury and reduction techniques on ankle joint contact mechanics in a biomechanical model.

METHODS

Ten cadaveric whole lower leg specimens with undisturbed proximal tibiofibular joints were prepared and tested in this study. Contact area, contact force, and peak contact pressure were measured in the ankle joint during simulated standing in the intact, injured, and 3 reduction conditions: screw fixation with a clamp, screw fixation without a clamp (thumb technique), and a suture-button construct. Differences in these ankle contact parameters were detected between conditions using repeated-measures analysis of variance.

RESULTS

Syndesmotic disruption decreased tibial plafond contact area and force. Syndesmotic reduction did not restore ankle loading mechanics to values measured in the intact condition. Reduction with the thumb technique was able to restore significantly more joint contact area and force than the reduction clamp or suture-button construct.

CONCLUSION

Syndesmotic disruption decreased joint contact area and force. Although the thumb technique performed significantly better than the reduction clamp and suture-button construct, syndesmotic reduction did not restore contact mechanics to intact levels.

CLINICAL RELEVANCE

Decreased contact area and force with disruption imply that other structures are likely receiving more loads (eg, medial and lateral gutters), which may have clinical implications such as the development of posttraumatic arthritis.

Assessment of fracture risk in proximal tibia with tumorous bone defects by a finite element method

There has not been a satisfying method to predict the fracture risk in tumorous bone lesions. To tackle this challenge, we used a finite element method to assess the fracture risk in the proximal tibia (pT) when the size and location of the tumorous defects are varied in bone. Towards this end, the circular cortical defects, mimicking the tumorous lesions by forming cortical window defects, with a diameter (Ф) of 20, 30, 40, or 50 mm, are structured on the anteromedial, lateral, posterior wall of pT, which is located 5, 15, and 25 mm below articular margin, respectively. We found that under walking conditions, the Von Mises Stress of each defective tibia model was larger than that of the intact tibia model and also showed a positive linear correlation with the sizes of the defects. A notable fracture risk was not observed until the defect was Ф30 mm or larger. When the defect emerged, the anteromedial wall resisted fracture risk more than the rest of wall. Our results show that the size and location of the bone tumors are important factors affecting the fracture risk of pT. Our findings will be beneficial to clinicians when deciding what treatment to use for pT lesions.

Current trends in the diagnosis and management of syndesmotic injury

Ideal management of the various presentations of syndesmotic injury remains controversial to this day. High quality evidentiary science on this topic is rare, and numerous existing studies continue to contradict one another. The primary reasons for these discrepancies are that previous studies have failed to (1) properly distinguish between isolated (non-fractured) and non-isolated injuries, (2) accurately define stable from unstable injuries, and (3) sufficiently differentiate between acute and chronic injuries. The purpose of this review is to summarize today's body of literature regarding diagnosis and management of syndesmotic injury and discuss current trends and important future directions to optimize care of this very heterogeneous population.

Rotational Dynamics of the Normal Distal Tibiofibular Joint With Weight-Bearing Computed Tomography

BACKGROUND

The normal distal tibiofibular joint is strongly stabilized by the syndesmosis, where previous cadaveric, biomechanical studies demonstrated only minimal widening and posterior translation of the fibula in external rotation of the ankle. However, little is known about normal rotational dynamics of the distal tibiofibular joint in upright weight-bearing conditions. The purpose of this study was to investigate the normal anatomy and rotational dynamics of the distal tibiofibular joint under physiological conditions on weight-bearing cone beam computed tomography (WBCT).

METHODS

In a cross-sectional study of 32 subjects, low-dose WBCT scans of uninjured bilateral ankles were performed. Normal intersubject and intrasubject variation in neutral position and changes in maximal internal and external rotation of the ankle were studied. Sagittal translation of the fibula, anterior and posterior widths of the distal tibiofibular syndesmosis, tibiofibular clear space (TFCS), and rotation of the fibula were measured.

RESULTS

In the neutrally loaded ankle, the fibula was located anteriorly in the tibial incisura in 88% of the subjects. When the ankle was rotated, mean anteroposterior motion was 1.5 mm and mean rotation of the fibula was 3 degrees. There was no significant change in TFCS between internal and external rotation. Large intersubject variation was detected, but intrasubject variation between ankles was less than 1 mm and 1 degree.

CONCLUSIONS

This study provides reference values to evaluate the dynamics of the normal distal tibiofibular joint. The internal control of the contralateral ankle seemed to be a better reference than the population-based normal values.

CLINICAL RELEVANCE

The current study provides the reference values to evaluate the rotational dynamics of a normal distal tibiofibular joint.

Effects of inferior tibiofibular syndesmosis injury and screw stabilization on motion of the ankle: a finite element study

PURPOSE

Traditional studies of syndesmosis injury and screw stabilization have been conducted in cadaveric models, which cannot yield sufficient and exact biomechanical data about the interior of the ankle. The purpose of this study was to evaluate the effects of inferior tibiofibular syndesmosis injury (ITSI) and screw stabilization on the motion of the ankle with finite element analysis.

METHODS

Three-dimensional models of the ankle complex were created with CT images of a volunteer's right ankle in three states: normal, post-ITSI, and stabilization with a screw 2.5 cm above (parallel to) the ankle. Simulated loads were applied under three conditions: neutral position with single foot standing, internal rotation, and external rotation of the ankle.

RESULTS

Compared with the normal state, ITSI increased the relative displacement between the lower extremes of the tibia and fibula in the anteroposterior and mediolateral directions and the angular motion of the tibia, fibula, and talus at internal and external rotations (ERs). However, when stabilized with syndesmotic screws, the range of motion (ROM) and all these parameters significantly decreased.

CONCLUSION

ITSI can lead to internal and ER instability of the ankle joint. Screw stabilization is effective in controlling the instability, but may reduce markedly the ROM of the ankle joint. Through this study, it can be proposed that the screws should be removed once the healing is gained in order to restore normal function of the ankle joint as soon as possible.

Posterolateral ankle ligament injuries affect ankle stability: a finite element study

BACKGROUND

We have already discovered 23 patients during the work of the outpatient department and operations whose unstable signs on the posterolateral ankle. The anterior drawer test demonstrated normal during the physical examinations while the spaces of the posterior tibiotalar joints increased in stress X-ray plain films. ATFL intact and posterolateral ligaments lax were found during operations too. It is important to make existence claims and illuminate the mechanism of posterolateral ankle instability.

METHODS

A finite element model of the ankle was established for simulating to cut off posterolateral ligaments in turn. Ankle movements with tibia rotation under load on five forefoot positions were simulated as well.

RESULTS

The difference values with tibia external rotation were negative, and the positive results occurred with tibia internal rotation. The tibia-talus difference values in some forefoot positions were 2 ~ 3 mm after PTFL together with CFL or/and PITFL were cut off. The tibula-talus difference values were 2.21 ~ 2.76 mm after both PTFL and CFL were cut off. The tibia-fibula difference values were small. The difference values increased by 2 ~ 5 mm after cutting off the PITFL.

CONCLUSIONS

Posterolateral ankle ligaments, especially CFL and PITFL, play a significant role in maintaining ankle stability. The serious injuries of both CFL and PITFL would affect posterolateral ankle stabilities. PITFL was important to subtalar joint stability.

Effects of Ankle Arthrodesis on Biomechanical Performance of the Entire Foot

Background/Methodology

Ankle arthrodesis is one popular surgical treatment for ankle arthritis, chronic instability, and degenerative deformity. However, complications such as foot pain, joint arthritis, and bone fracture may cause patients to suffer other problems. Understanding the internal biomechanics of the foot is critical for assessing the effectiveness of ankle arthrodesis and provides a baseline for the surgical plan. This study aimed to understand the biomechanical effects of ankle arthrodesis on the entire foot and ankle using finite element analyses. A three-dimensional finite element model of the foot and ankle, involving 28 bones, 103 ligaments, the plantar fascia, major muscle groups, and encapsulated soft tissue, was developed and validated. The biomechanical performances of a normal foot and a foot with ankle arthrodesis were compared at three gait instants, first-peak, mid-stance, and second-peak.

Principal Findings/Conclusions

Changes in plantar pressure distribution, joint contact pressure and forces, von Mises stress on bone and foot deformation were predicted. Compared with those in the normal foot, the peak plantar pressure was increased and the center of pressure moved anteriorly in the foot with ankle arthrodesis. The talonavicular joint and joints of the first to third rays in the hind- and mid-foot bore the majority of the loading and sustained substantially increased loading after ankle arthrodesis. An average contact pressure of 2.14 MPa was predicted at the talonavicular joint after surgery and the maximum variation was shown to be 80% in joints of the first ray. The contact force and pressure of the subtalar joint decreased after surgery, indicating that arthritis at this joint was not necessarily a consequence of ankle arthrodesis but rather a progression of pre-existing degenerative changes. Von Mises stress in the second and third metatarsal bones at the second-peak instant increased to 52 MPa and 34 MPa, respectively, after surgery. These variations can provide indications for outcome assessment of ankle arthrodesis surgery.

Mid-term results of ankle fractures with and without syndesmotic rupture

BACKGROUNDS

This study investigated the effect of short term removal of syndesmotic screws on the ankle function after 6 years, as there still exists controversy on the duration of screw stabilization.

METHODS

Patients with an ankle fracture who received surgery between 1998 and 2004 were reviewed. One group was composed of patients with an ankle fracture needing a syndesmotic repair with screws. The second was composed of operated patients that did not need syndesmotic repair. The primary scoring used was the Olerud-Molander Ankle Score (OMAS).

RESULTS

A total of 59 patients were studied with comparable characteristics, with no significant difference on the OMAS after 6 years between the repair group (81.9) and the non-repair group (90.4). On additional clinical scoring groups remained the same. Joint degeneration was seen in both groups (86.7% vs. 55.5%).

CONCLUSIONS

Patients with ankle fractures using syndesmotic repair and screw removal after 8 weeks and operated patients without syndesmotic injury have comparable results after 6 years.