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The influence of partial union and spatial orientation on the mechanical strength of scaphoid fractures – a finite element study
We are looking for 2 engaged, dedicated students (mechanical engineering) to complete his/her master thesis, one from Sep/Oct 2020 onwards and the second starting in April 2021 for the project outlined below for the duration of 6 months each.
Background: CT scan is increasingly used not just to diagnose union, but also to deliver an estimation for how much of the fracture gap in percentage is bridged by healing bone. However, the issue is that the interpretation of the degree of union on the image remains rather descriptive as long as the clinical value of the percentage of healing is not known. In previous studies union was simply categorized along the cross section of the Scaphoid using arbitrary cut-off values in order to classify fractures as united or not.
It is essential for scientific purposes and for the treatment of patients with scaphoid fractures to diagnose union of the fracture on a CT scan with well-founded criteria. To our knowledge, no study has been published on how the degree of fracture union on a CT scan correlates to mechanical stability to avoid re-fracture under physiological loads.
Methods: A fresh frozen cadaveric human forearm is taken from a voluntary donor from the Anatomy Institute of the University of Zurich. HR-pQCT scanning at the Radiology Department of the University Hospital of Zurich is performed. Geometrical data is extracted using Matlab by MathWorks (Natick, Massachusetts, USA). On the basis of that a finite element (FE) model is built using ANSYS Academic Research Mechanical (Ansys Inc., Canonsburg, Pennsylvania, USA). Material properties can be assigned to each element (cortical, cancellous bone and cartilage) based on average Hounsfield Units (HU).
In the model physiologic loads are applied in different wrist positions. Different fracture patterns, will be incorporated as to analyse how much of the fracture requires to be united for mechanical stability.
Expected results:
- A cut-off value (%) of the required consolidation of the fracture to withstand physiological loads, which is quantified as a percentage of the whole fracture plane to determine union in a CT scan.
- A quantitative analysis of the stability of different fracture patterns under physiological loads with consolidation at the above cut-off value.
Clinical impact of the study: The criteria for scaphoid fracture union are currently not standardized. It seems sometimes difficult to decide whether the fracture has or has not united. Quantifying the proportion required in relation to the fracture geometry would be helpful in studying and treating scaphoid fractures, but most importantly lend itself to more rational clinical-decision making for both surgical and non-operative treatment.
A quantitative CT scan analysis in combination with a consistently applied clinical examination would be a desirable approach to develop guidelines as to whether scaphoid fractures can truly be considered united clinically and radiologically.
Background: CT scan is increasingly used not just to diagnose union, but also to deliver an estimation for how much of the fracture gap in percentage is bridged by healing bone. However, the issue is that the interpretation of the degree of union on the image remains rather descriptive as long as the clinical value of the percentage of healing is not known. In previous studies union was simply categorized along the cross section of the Scaphoid using arbitrary cut-off values in order to classify fractures as united or not. It is essential for scientific purposes and for the treatment of patients with scaphoid fractures to diagnose union of the fracture on a CT scan with well-founded criteria. To our knowledge, no study has been published on how the degree of fracture union on a CT scan correlates to mechanical stability to avoid re-fracture under physiological loads. Methods: A fresh frozen cadaveric human forearm is taken from a voluntary donor from the Anatomy Institute of the University of Zurich. HR-pQCT scanning at the Radiology Department of the University Hospital of Zurich is performed. Geometrical data is extracted using Matlab by MathWorks (Natick, Massachusetts, USA). On the basis of that a finite element (FE) model is built using ANSYS Academic Research Mechanical (Ansys Inc., Canonsburg, Pennsylvania, USA). Material properties can be assigned to each element (cortical, cancellous bone and cartilage) based on average Hounsfield Units (HU). In the model physiologic loads are applied in different wrist positions. Different fracture patterns, will be incorporated as to analyse how much of the fracture requires to be united for mechanical stability. Expected results: - A cut-off value (%) of the required consolidation of the fracture to withstand physiological loads, which is quantified as a percentage of the whole fracture plane to determine union in a CT scan. - A quantitative analysis of the stability of different fracture patterns under physiological loads with consolidation at the above cut-off value. Clinical impact of the study: The criteria for scaphoid fracture union are currently not standardized. It seems sometimes difficult to decide whether the fracture has or has not united. Quantifying the proportion required in relation to the fracture geometry would be helpful in studying and treating scaphoid fractures, but most importantly lend itself to more rational clinical-decision making for both surgical and non-operative treatment. A quantitative CT scan analysis in combination with a consistently applied clinical examination would be a desirable approach to develop guidelines as to whether scaphoid fractures can truly be considered united clinically and radiologically.
Aim of the study: Scaphoid fractures are among the most common upper extremity injuries. The aim of this biomechanical study is to investigate the extent of scaphoid fracture union that is required to withstand the forces applied to the wrist in daily life.
For solving this problem, a finite element model is established by extracting the geometrical features from a high resolution CT scan of a cadaveric forearm.
The model can simulate loads applied to the wrist, while fracture patterns in accordance with a commonly used classification are adopted. The physiological loads in different wrist positions including cartilage contact and ligament forces have been published previously and can be utilized for the computational calculations.
Aim of the study: Scaphoid fractures are among the most common upper extremity injuries. The aim of this biomechanical study is to investigate the extent of scaphoid fracture union that is required to withstand the forces applied to the wrist in daily life. For solving this problem, a finite element model is established by extracting the geometrical features from a high resolution CT scan of a cadaveric forearm. The model can simulate loads applied to the wrist, while fracture patterns in accordance with a commonly used classification are adopted. The physiological loads in different wrist positions including cartilage contact and ligament forces have been published previously and can be utilized for the computational calculations.
Prof. Dr. WR Taylor via bt@ethz.ch
Dr. E. Rothenfluh via Esin.Rothenfluh@usz.ch
Prof. Dr. WR Taylor via bt@ethz.ch Dr. E. Rothenfluh via Esin.Rothenfluh@usz.ch