Development of a patient-specific anatomical foot model from structured light scan data

Custom orthotic design by integrating 3D scanning and subject-specific FE modelling workflow

The finite element (FE) foot model can help estimate pathomechanics and improve the customized foot orthoses design. However, the procedure of developing FE models can be time-consuming and costly. This study aimed to develop a subject-specific scaled foot modelling workflow for the foot orthoses design based on the scanned foot surface data. Six participants (twelve feet) were collected for the foot finite element modelling. The subject-specific surface-based finite element model (SFEM) was established by incorporating the scanned foot surface and scaled foot bone geometries. The geometric deviations between the scaled and the scanned foot surfaces were calculated. The SFEM model was adopted to predict barefoot and foot-orthosis interface pressures. The averaged distances between the scaled and scanned foot surfaces were 0.23 ± 0.09 mm. There was no significant difference for the hallux, medial forefoot, middle forefoot, midfoot, medial hindfoot, and lateral hindfoot, except for the lateral forefoot region (p = 0.045). The SFEM model evaluated slightly higher foot-orthoses interface pressure values than measured, with a maximum deviation of 7.1%. These results indicated that the SFEM technique could predict the barefoot and foot-orthoses interface pressure, which has the potential to expedite the process of orthotic design and optimization.

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.

Ankle-foot orthosis design between the tradition and the computerized perspectives

This study focuses on the drop foot case related to hyperthyroidism of the ankle joint resulting in the relaxation of the toes during walking. This condition requires treatment using an ankle-foot orthosis. Traditional orthosis techniques lack precision and depend on the skill of the fabricator. This research aims to make a bias in ankle-foot orthosis design and analysis methods, where a complete methodology of numerical design and testing has been proposed using advanced engineering software. A numerical model of the patient's foot was generated and used to design an ankle-foot orthosis model using SolidWorks. The designed model was mechanically analyzed by the finite element method using ANSYS Workbench 16.1 under different static and dynamic loading conditions. The ankle-foot orthosis model was numerically designed and analyzed before the manufacturing process. This is believed to reduce time and material loss and foster the use of numerical models in biomedical applications. This study suggests focusing on the design and analysis of orthoses according to the patient's measurements. This is expected to increase the comfort and raise the level of treatment. Numerical design methods also enable precise manufacturing using computerized devices such as three-dimensional printers.

Multiple Laser Stripe Scanning Profilometry Based on Microelectromechanical Systems Scanning Mirror Projection

In traditional laser-based 3D measurement technology, the width of the laser stripe is uncontrollable and uneven. In addition, speckle noise in the image and the noise caused by mechanical movement may reduce the accuracy of the scanning results. This work proposes a new multiple laser stripe scanning profilometry (MLSSP) based on microelectromechanical systems (MEMS) scanning mirror which can project high quality movable laser stripe. It can implement full-field scanning in a short time and does not need to move the measured object or camera. Compared with the traditional laser stripe, the brightness, width and position of the new multiple laser stripes projected by MEMS scanning mirror can be controlled by programming. In addition, the new laser strip can generate high-quality images and the noise caused by mechanical movement is completely eliminated. The experimental results show that the speckle noise is less and the light intensity distribution is more even. Furthermore, the number of pictures needed to be captured is significantly reduced to 1 / N ( N is the number of multiple laser stripes projected by MEMS scanning mirror) and the measurement efficiency is increased by N times, improving the efficiency and accuracy of 3D measurement.

Do volar locking plates fit the volar cortex of the distal radius?

The purpose of this study was to measure the volar cortical angles of the commercially available volar locking plates and evaluate how well they fit the distal radius. We measured the volar cortical angles of the radial and intermediate columns of eight volar locking plates and compared them with the volar cortical angles of 90 cadaver distal radii. The mean radial and intermediate column volar cortical angles of the wider plates were significantly larger than those of narrower plates. The mean radial and intermediate column volar cortical angles were significantly larger in wider radii than narrower radii. The width of the distal radius did not correlate well with the mean volar cortical angles of the radial and intermediate columns.

LEVEL OF EVIDENCE

IV.

Robust laser stripe extraction for three-dimensional reconstruction based on a cross-structured light sensor

Cross-structured light sensor architecture for 3D reconstruction was established. An improved center of mass method was proposed for laser stripe extraction. For each initial laser stripe center point, the center of mass method was performed along the normal direction that was calculated using the Hessian matrix. The normal directions can be used to divide the laser stripe center points into two categories. Laser stripe extraction experiments showed that the proposed method is fast and robust. 3D reconstruction of a cylinder was used to analyze reconstruction accuracy, with relative accuracy of less than 0.15 mm. 3D reconstruction of a shoe last showed that cross-structured light sensors can obtain more abundant information than single-structured light sensors.