Principal component analysis as a tool for determining optimal tibial baseplate geometry in modern TKA design.

Optimal tibial component fixation in total knee arthroplasty (TKA) requires maximal tibial bone coverage, optimized mediolateral cortical fit as well as component rotation. Failure to achieve an optimal fit may result in component subsidence and loosening in case of undersizing, or overhang with subsequent soft tissue impingement in case of overhang. To date there is no consensus on optimal tibial component shape, and significant variability exists among different design manufacturers. In this study "principal component analysis" was used as a statistical tool in order to determine the ideal tibia baseplate shape, based upon anthropometric CT- scan data defining an average proximal tibial shape and variations. Gender specificity was evaluated and differences in geometry depending on anatomic constitution (varus, neutral, valgus) were analyzed. The results from our study indicate that in the arthritic knee differences in proximal tibial morphology at the resection level were mainly attributed to size and not shape. This is true for both Caucasian men and women, and is independent from the anatomical constitution.

Chronic exposure to haloperidol and olanzapine leads to common and divergent shape changes in the rat hippocampus in the absence of grey-matter volume loss.

BACKGROUND: One of the most consistently reported brain abnormalities in schizophrenia (SCZ) is decreased volume and shape deformation of the hippocampus. However, the potential contribution of chronic antipsychotic medication exposure to these phenomena remains unclear. METHOD: We examined the effect of chronic exposure (8 weeks) to clinically relevant doses of either haloperidol (HAL) or olanzapine (OLZ) on adult rat hippocampal volume and shape using ex vivo structural MRI with the brain retained inside the cranium to prevent distortions due to dissection, followed by tensor-based morphometry (TBM) and elastic surface-based shape deformation analysis. The volume of the hippocampus was also measured post-mortem from brain tissue sections in each group. RESULTS: Chronic exposure to either HAL or OLZ had no effect on the volume of the hippocampus, even at exploratory thresholds, which was confirmed post-mortem. In contrast, shape deformation analysis revealed that chronic HAL and OLZ exposure lead to both common and divergent shape deformations (q = 0.05, FDR-corrected) in the rat hippocampus. In particular, in the dorsal hippocampus, HAL exposure led to inward shape deformation, whereas OLZ exposure led to outward shape deformation. Interestingly, outward shape deformations that were common to both drugs occurred in the ventral hippocampus. These effects remained significant after controlling for hippocampal volume suggesting true shape changes. CONCLUSIONS: Chronic exposure to either HAL or OLZ leads to both common and divergent effects on rat hippocampal shape in the absence of volume change. The implications of these findings for the clinic are discussed.

Evaluation of prominence of straight plates and precontoured clavicle plates using automated plate-to-bone alignment.

Hardware prominence after plate fixation for clavicle fracture is a common complication. The aim of the study was to perform a 3D analysis of the prominence of different types of superior clavicle plates. An automated fitting of 3 straight and 10 precontoured plates was performed on 52 3D-CT-scan reconstructed cadaver clavicles. The mean and maximum bone-plate distance and maximum prominence was significant higher with the straight plates compared to the precontoured plates. The mean and maximum boneplate distance was significant higher with the precontoured DePuy-Synthes plates compared to the precontoured Acumed plates but when evaluating the maximum prominence there was no significant difference between the most commonly used 8-holes plates. To conclude, precontoured plates of the clavicula diminish significantly hardware prominence. There exists a difference in hardware prominence between different brands of precontoured plates but this difference is limited and in most cases not significant.

Dense 3D pressure discomfort threshold (PDT) map of the human head, face and neck: A new method for mapping human sensitivity.

When designing wearables that interface with the human head, face and neck, designers and engineers consider human senses, ergonomics and comfort. A dense 3D pressure discomfort threshold map could be helpful, but does not exist yet. Differences in pressure discomfort threshold for areas of the head, neck and face were recorded, to create a 3D pressure discomfort threshold map. Between 126 and 146 landmarks were placed on the left side of the head, face and neck of twenty-eight healthy participants (gender balanced). The positions of the landmarks were specified using an EEG 10-20 system-based landmark-grid on the head and a self-developed grid on the face and neck. A 3D scan was made to capture the head geometry and landmark coordinates. In a randomised order, pressure was applied on each landmark with a force gauge until the participant indicated experiencing discomfort. By interpolating all collected pressure discomfort thresholds based on their corresponding 3D coordinates, a dense 3D pressure discomfort threshold map was made. A relatively low-pressure discomfort threshold was found in areas around the nose, neck front, mouth, chin-jaw, cheek and cheekbone, possibly due to the proximate or direct location of nerves, blood veins and soft (muscular) tissue. Medium pressure discomfort was found in the neck back, forehead and temple regions. High pressure discomfort threshold was found in the back of the head and scalp, where skin is relatively thin and closely supported by bone, making these regions interesting for mounting or resting head, face and neck related equipment upon.

A 3D active shape model for the evaluation of the alignment of the spine during sleeping.

This paper explains how the shape of the spine can be evaluated from back surface measurements in a recumbent position, by using point distribution models (PDM) and typical shape variability of the spine in a lateral sleeping position. CT-scans of 12 volunteers were taken in this posture on a firm and a soft sleeping system to provide a training set for the PDM. Active shape models (ASM) were used to enhance the accuracy of the spinal reconstruction from measurements by limiting the shape of the spine to characteristic shapes from a biomechanical and/or clinical point of view. A comparison was made between calculated shapes, obtained from surface measurements, and those measured vertebral body centres (from CT-scans). An RMS accuracy of 2.6mm was obtained in 3D, and 1.8mm in frontal view, which was sufficient to compare spinal deformations of a subject on different sleeping systems.

An active shape model for the reconstruction of scoliotic deformities from back shape data.

OBJECTIVE: The objective of the present study is to improve the accuracy and reliability of the spinal midline reconstructions in scoliosis from back shape data. Design. An active shape model which covers the variety of scoliotic curves with a minimum of adjustable parameters is designed for the reconstruction of the spinal midline based on rasterstereographic back surface measurements. BACKGROUND: To reduce the number of X-rays needed for patients with a scoliosis, an automatic method was developed for the reconstruction of spinal deformities from back shape data. METHODS: 264 digital X-rays of 264 patients with scoliosis were used as a training set. By examining the statistics of the vertebral body centres a point distribution model was derived. The model is used as a basis to reconstruct the spinal midline from back shape data (active shape model). RESULTS: 478 rasterstereographs of 114 scoliotic patients have been evaluated with this new procedure and with an existing procedure. Both procedures deliver a three-dimensional curve of the spinal midline. The frontal projections of these spinal midlines are compared with the vertebral centres of the corresponding 478 X-rays. The active shape model improved the results as compared to the existing procedure from sigma(x)=3.4mm to sigma(x)=3.0mm. CONCLUSION: The use of the active shape model improves the overall accuracy of the spinal midline reconstructions in scoliosis from back shape data.RELEVANCE. Improvements to the accuracy and the reliability of the three-dimensional spinal reconstruction based on back shape data, can lead to an additional reduction of X-rays for patients with a scoliosis.

A three-dimensional active shape model for the detection of anatomical landmarks on the back surface.

In this study relations between anatomical landmarks on the dorsal surface of the human torso corresponding to underlying skeletal structures are established. By examining the statistics of the positions of the landmarks in a training set of subjects a point distribution model is derived. Rotations of the pelvis are simulated in order to show that the main mode shapes of variation are consistent with rotations of the pelvis relative to the trunk. The parameters of these mode shapes can therefore be used as independent measures of clinical parameters such as pelvic inclination, pelvic tilt, etc. The point distribution model is further applied to improve reliability and robustness for an automatic and objective detection of the anatomical landmarks on the back surface (active shape model). The results show that it is possible to replace radiographs by surface measurements in order to measure position and orientation of the pelvis, which is particularly valuable in the case of functional examinations that normally involve a large number of radiographs (e.g. to measure the position of the pelvis in a scoliosis).

Three-dimensional mathematical reconstruction of the spinal shape, based on active contours.

To reduce the amount of radiographs needed for patients with a scoliosis, a radiation-free method based on topographic images of the back was developed. An active contour model simulating spinal stiffness has been applied to video rasterstereographic (VRS) data. The aim of the present study is (a) to evaluate the applicability of active contours to improve the accuracy and the reliability of the three-dimensional (3D) spinal midline reconstruction from back surface data and (b) to design a more robust method to detect the spinal midline. To evaluate the reliability and accuracy, the active contour-based method is compared to a conventional procedure, which has been specifically developed for scoliosis; both methods produce a 3D curve of the spinal midline. The frontal projections and surface rotations of these spinal midlines are compared; r.m.s. deviations of 0.9 mm between the frontal curves and 0.4 degrees between the surface rotations were obtained. Applying the active contour-based method does therefore not result in a substantial difference in accuracy to the conventional procedure. As a conclusion the active contour method is a valuable mathematical method that can accurately reconstruct the spinal midline based on back surface data. In addition, the method can be applied to various postures.