Finite element analysis of the effect of sagittal angle on ankle joint stability in posterior malleolus fracture: A cohort study

The effect of early weight-bearing on bone fusion after triple arthrodesis

Triple arthrodesis is an effective method for treating stiff horseshoe feet and severe osteoarthritis. However, it is still a challenge to improve postoperative bone fusion by changing early weight-bearing. This study improved the classical bone remodeling algorithm, established a mathematical relationship between density change rate and mechanical stimulation, and combined it with finite element theory. The proposed algorithm can not only predict the effect of early weight-bearing on triple arthrodesis but also visually demonstrate the change of bone mineral density with time. The analysis results indicated that 2.5% of the initial load was a potential factor leading to bone nonunion, and 50% of the initial load would result in bone resorption. Meanwhile, it was found that 25% of the external load was more conducive to postoperative rehabilitation. The study results have theoretical significance for enhancing the effect of postoperative bone fusion and formulating a more scientific rehabilitation program, thereby supporting patients' postoperative rehabilitation exercise.

Biomechanical insights into ankle instability: a finite element analysis of posterior malleolus fractures

BACKGROUND

Posterior malleolus fractures are known to be associated with ankle instability. The complexities involved in obtaining precise laboratory-based spatial pressure measurements of the ankle highlight the significance of exploring the biomechanical implications of these fractures.

METHODS

Finite element analysis was utilized to examine the stress distribution across the contact surface of the ankle joint, both in its natural state and under varied sagittal fracture line angles. The study aimed to identify stress concentration zones and understand the influence of sagittal angles on stress distribution.

RESULTS

Three distinct stress concentration zones were identified on the ankle's contact surface: the anterolateral tibia, the anteromedial tibia, and the fracture line. The most significant stress was observed at the fracture line when a fracture occurs. Stress at the fracture line notably spikes as the sagittal angle decreases, which can potentially compromise ankle stability. Larger sagittal angles exhibited only minor stress variations at the contact surface's three vertices. It was inferred that sagittal angles below 60° might pose risks to ankle stability.

CONCLUSIONS

The research underscores the potential implications of fractures on the stress profile of the ankle joint, emphasizing the role of the contact surface in ensuring stability. The identification of three zones of stress concentration and the influence of sagittal angles on stress distribution offers a valuable reference for therapeutic decision-making. Further, the study reinforces the importance of evaluating sagittal fracture angles, suggesting that angles below 60° may compromise ankle stability.

Clinically useful finite element models of the natural ankle - A review

BACKGROUND

Biomechanical simulation of the foot and ankle complex is a growing research area but compared to simulation of joints such as hip and knee, it has been under investigated and lacks consistency in research methodology. The methodology is variable, data is heterogenous and there are no clear output criteria. Therefore, it is very difficult to correlate clinically and draw meaningful inferences.

METHODS

The focus of this review is finite element simulation of the native ankle joint and we will explore: the different research questions asked, the model designs used, ways the model rigour has been ensured, the different output parameters of interest and the clinical impact and relevance of these studies.

FINDINGS

The 72 published studies explored in this review demonstrate wide variability in approach. Many studies demonstrated a preference for simplicity when representing different tissues, with the majority using linear isotropic material properties to represent the bone, cartilage and ligaments; this allows the models to be complex in another way such as to include more bones or complex loading. Most studies were validated against experimental or in vivo data, but a large proportion (40%) of studies were not validated at all, which is an area of concern.

INTERPRETATION

Finite element simulation of the ankle shows promise as a clinical tool for improving outcomes. Standardisation of model creation and standardisation of reporting would increase trust, and enable independent validation, through which successful clinical application of the research could be realised.

Methods for Biomechanical Testing of Posterior Malleolar Fractures in Ankle Fractures: A Scoping Review

BACKGROUND

The treatment of posterior malleolar fractures (PMFs) is debated, including the need for surgery and method of fixation. Recent literature has suggested that fracture pattern, rather than fragment size, may be an important predictor for ankle biomechanics and functional outcome. Biomechanical studies have been conducted to provide evidence-based treatment on the effects of fracture and fixation on contact pressure and stability. The objective of this scoping review is to summarize the methodologies used in biomechanical studies on PMFs and assess whether they are sufficient to test the need for surgery and method of fixation.

METHODS

A scoping review of publications before January 2022 was performed. PubMed/Medline and Embase Ovid were searched for cadaver or finite element analysis (FEA) studies that created and tested the effects of PMFs in ankle fractures. Both cadaver and FEA studies were included. Data about fragment characteristics, mode of testing, and outcomes were charted by 2 persons from the study group. The data were synthesized when possible and compared.

RESULTS

We included 25 biomechanical studies, including 19 cadaver studies, 5 FEA studies, and 1 cadaver and FEA study. Aside from the fragment size, few other fragment characteristics were reported. Mode of testing varied with different loads and foot positions. Strong conclusions on the effects of fracture and fixation on contact pressure and stability could not be made.

CONCLUSION

Biomechanical studies on PMFs demonstrate wide variability in fragment characteristics and mode of testing, which makes it difficult to compare studies and draw conclusions on the need for surgery and method of fixation. Additionally, limited reporting of fragment measurements questions the applicability to clinical practice. The biomechanical literature on PMFs would benefit from the use of a standard classification and universal fragment measurements to match clinical injuries in future biomechanical studies. Based on this review, we recommend the Mason classification, which addresses the pathomechanism, and use of the following fragment measurements in all 3 anatomic planes when creating and describing PMFs: fragment length ratio, axial angle, sagittal angle or fragment height, and interfragmentary angle. The testing protocol needs to reflect the purpose of the study.

CLINICAL RELEVANCE

This scoping review demonstrates wide methodological diversity of biomechanical studies. Consistency in methodology should enable comparison of study results, leading to stronger evidence-based recommendations to guide surgeons in decision making and offer PMF patients the best treatment.

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.

Suture button fixation method used in the treatment of syndesmosis injury: A biomechanical analysis of the effect of the placement of the button on the distal tibiofibular joint in the mid-stance phase with finite elements method

PURPOSE

The purpose of this study is to research the effect of suture button (SB) fixation, a method used at the treatment of ankle syndesmosis injury, which was applied in various angles, pretension force, and levels, on the distal tibiofibular joint (DTFJ) in the mid-stance phase, with the help of three-dimensional finite elements method (FEM) METHOD: The ankle of a healthy individual was digitally analyzed by a finite element method-based package computer program. Then, anterior inferior tibiofibular ligament (AITFL), interosseous ligament, posterior inferior tibiofibular ligament (PITFL) and deltoid ligament (DL) were cut and force and rotation has been applied to the proximal tibia, resulting in syndesmosis injury. Then, various suture button applications on the injured model have been analyzed. Three parameters have been changed; which were divergence in the axial plane (20°, 30°, 40°), distance from the ankle (2, 3, 4 cm), and pretension force (200, 300, 600 N) RESULTS: As the result of this study, the rotation, change in the gap between the distal tibia and distal fibula, and the displacements of the fibula in the x and y axes have been obtained, and numerical results were evaluated. As the force increased, rotation, change in the gap between the distal tibia and distal fibula, and the displacements of the fibula decreased. As suture button application rotation increased, change in the gap between the distal tibia and distal fibula, and displacements of the fibula increased. As the distance from the ankle increases and reaches a certain level, the results converge to those of the healthy model; in the proximal, it diverges from healthy results.

CONCLUSION

In the study, it has been shown that abnormal tibiofibular joint movements can be prevented with suture button application, and optimum application parameters (divergence in the axial plane, distance from the ankle, and pretension force) are given for proper reduction.

Quantitative initial safety range of early passive rehabilitation after ankle fracture surgery

BACKGROUND

Early rehabilitation training after ankle fracture surgery is critical to healing and avoiding complications. Inappropriate or excessive motion may impede healing or even lead to secondary injury. Currently, there is a lack of scientific quantitative postoperative rehabilitation methods after ankle fracture. Our purpose was to develop a universal method of quantifying early passive rehabilitation training after surgery by finite element (FE) analysis.

METHODS

A three-dimensional (3D) FE model of normal ankle was reconstructed from a computed tomography scan of a healthy male adult. Six types of ankle fractures were considered based on AO classification. We exerted joint motion load to explore the effect of movement on ankle joint mechanics after surgery. The corresponding relationship between the Inter-bone displacement and range of motion was measured to quantifying the ankle range of motion. The 44A3.3 fracture was used as an example to describe the implementation process in detail.

RESULTS

During ankle movement, most of the stress was sustained by the internal fixation devices, and the ratio of stress borne by the implants ranged from 67.9 to 94.9%. Flexion/extension exercise did not cause extra stress on the ankle contact surfaces. Ligament traction was the reason for ankle load during flexion/extension motion. The range of early passive postoperative rehabilitation training for six types of ankle fractures (AO classification) were provided.

CONCLUSION

A quantitative method of early passive rehabilitation training after ankle fracture surgery was developed using FE analysis. This modeling method has universality for any fracture that can be reconstructed.

Predicting ground reaction and tibiotalar contact forces after total ankle arthroplasty during walking

The motion capture and force plates data are essential inputs for musculoskeletal multibody dynamics models to predict in vivo tibiotalar contact forces. However, it could be almost impossible to obtain valid force plates data in old patients undergoing total ankle arthroplasty under some circumstances, such as smaller gait strides and inconsistent walking speeds during gait analysis. To remove the dependence of force plates, this study has established a patient-specific musculoskeletal multibody dynamics model with total ankle arthroplasty by combining a foot-ground contact model based on elastic contact elements. And the established model could predict ground reaction forces, ground reaction moments and tibiotalar contact forces simultaneously. Three patients' motion capture and force plates data during their normal walking were used to establish the patient-specific musculoskeletal models and evaluate the predicted ground reaction forces and ground reaction moments. Reasonable accuracies were achieved for the predicted and measured ground reaction forces and ground reaction moments. The predicted tibiotalar contact forces for all patients using the foot-ground contact model had good consistency with those using force plates data. These findings suggested that the foot-ground contact model could take the place of the force plates data for predicting the tibiotalar contact forces in other total ankle arthroplasty patients, thus providing a simplified and valid platform for further study of the patient-specific prosthetic designs and clinical problems of total ankle arthroplasty in the absence of force plates data.