Fluoroscopy-based tracking of femoral kinematics with statistical shape models

Precise knee kinematics assessment helps to diagnose knee pathologies and to improve the design of customized prosthetic components. The first step in identifying knee kinematics is to assess the femoral motion in the anatomical frame. However, no work has been done on pathological femurs, whose shape can be highly different from healthy ones

Treatment of the fixation surface improves glenoid prosthesis longevity in-vitro

Many commercial cemented glenoid components claim superior fixation designs and increased survivability. However, both research and clinical studies have shown conflicting results and it is unclear whether these design variations do improve loosening rates. Part of the difficulty in investigating fixation failure is the inability to directly observe the fixation interface, a problem addressed in this study by using a novel experimental set-up.Cyclic loading-displacement tests were carried out on 60 custom-made glenoid prostheses implanted into a bone substitute. Design parameters investigated included treatment of the fixation surface of the component resulting in different levels of back-surface roughness, flat-back versus curved-back, keel versus peg and more versus less conforming implants. Visually-observed failure and ASTM-recommended rim-displacements were recorded throughout testing to investigate fixation failure and if rim displacement is an appropriate measure of loosening. Roughening the implant back (Ra > 3 µm) improved resistance to failure (P < 0.005) by an order of magnitude with the rough and smooth groups failing at 8712 ± 5584 cycles (mean ± SD) and 1080 ± 1197 cycles, respectively. All other design parameters had no statistically significant effect on the number of cycles to failure. All implants failed inferiorly and 95 % (57/60) at the implant/cement interface. Rim-displacement correlated with visually observed failure. The most important effect was that of roughening the implant, which strengthened the polyethylene-cement interface. Rim-displacement can be used as an indicator of fixation failure, but the sensitivity was insufficient to capture subtle effects.Level of Evidence: Basic Science Study, Biomechanical Analysis

Failure mechanism of the all-polyethylene glenoid implant

Fixation failure of glenoid components is the main cause of unsuccessful total shoulder arthroplasties. The characteristics of these failures are still not well understood, hence, attempts at improving the implant fixation are somewhat blind and the failure rate remains high. This lack of understanding is largely due to the fundamental problem that direct observations of failure are impossible as the fixation is inherently embedded within the bone. Twenty custom made implants, reflecting various common fixation designs, and a specimen set-up was prepared to enable direct observation of failure when the specimens were exposed to cyclic superior loads during laboratory experiments. Finite element analyses of the laboratory tests were also carried out to explain the observed failure scenarios. All implants, irrespective of the particular fixation design, failed at the implant-cement interface and failure initiated at the inferior part of the component fixation. Finite element analyses indicated that this failure scenario was caused by a weak and brittle implant-cement interface and tensile stresses in the inferior region possibly worsened by a stress raiser effect at the inferior rim. The results of this study indicate that glenoid failure can be delayed or prevented by improving the implant/cement interface strength. Also any design features that reduce the geometrical stress raiser and the inferior tensile stresses in general should delay implant loosening

Good vs Poor Results After Total Hip Arthroplasty: An Analysis Method Using Implant and Anatomic Parameters With the EOS Imaging System

Background: Existing imaging techniques and single-parameter analyses, in nonfunctional positions, fail to detect the differences between patients with good vs poor results after total hip arthroplasty. Methods: The present study developed an analysis method using the EOS full-body, low-dose, biplanar, weightbearing imaging system to compare good vs poor patients after total hip arthroplasty and to report on our preliminary experiences (17 good, 18 poor). Results: All revision cases were found to have at least 4 high or low implant or anatomic parameters relative to the good group. These included acetabular cup orientation, sagittal pelvic tilt, sacral slope, femoral offset, and neckeshaft angle. Acetabular cup orientation differed significantly between groups. Conclusion: With the EOS system, a large cohort can be studied relatively quickly and at low dose, which could lead to patient-specific guidelines

Healthy vs. osteoarthritic hips: A comparison of hip, pelvis and femoral parameters and relationships using the EOS® system

Osteoarthritis is a debilitating disease, for which the development path is unknown. Hip, pelvis and femoral morphological and positional parameters relate either to individual differences or to changes in the disease state, both of which should be taken into account when diagnosing and treating patients. These have not yet been comprehensively quantified. Previous imaging studies have been limited by a number of factors: supine rather than standing measurements; high radiation dose; a limited field of view; and 2D rather than 3D measurements. EOS®, a new radiographic imaging modality that acquires simultaneous frontal and lateral (sagittal) X-ray images of the full body, allows 3D reconstruction of the hip, pelvis and lower limb. The aim of the study was to explore similarities and differences between healthy and osteoarthritis groups

Geology, structure and geochemistry of gold mineralization in the Geraldton Area, Northwestern Ontario

Gold mineralization in the Beardmore-Geraldton area occurs in a major, long-lived deformation zone, spatially coincident with the boundary between the Wabigoon subprovince to the north and the Quetico subprovince to the south. -- Regionally, the deposits are linearly distributed (east-west) parallel to the strata of the southern margin of the Wabigoon belt. Virtually all rock types host gold mineralization, except for the youngest intrusions, diabase and lamprophyre dykes. -- Gold mineralization in the Geraldton area occurs; 1) in quartz and quartz-carbonate veins in fractured greywacke, felsic and mafic intrusions and mafic volcanic rocks, 2) in disseminated sulphide-bearing, highly fractured, zones in greywacke and quartz-feldspar porphyry, and 3) in massive quartz-sulphide lenses in oxide iron formation. -- There is no primary sulphide or carbonate facies iron formation in the belt. All sulphide and carbonate minerals in iron formation are secondary alteration features associated with gold mineralization. The alteration is characterized by addition of CO₂, S, As, K, Ba and H₂O, and loss of Sr. There is no primary enrichment of gold in any of the rocks, background gold content of all rock types is less than 10 ppb. -- Gold-bearing veins occur in relatively young structures that crosscut all local Archean rock, and overprint several earlier phases of deformation. The major control on emplacement of veins is cleavage- and foliation-parallel fractures and dilations, and zones of intense deformation localized at the contacts of rocks of differing ductility. -- The U/Pb aircon age of felsic porphyry intrusions in the Geraldton area is 2691 +3/-2 Ma, significantly younger than volcanic rocks in the Onaman Lake area to the north, which are 2769 +6/-5 Ma. -- The age of gold mineralization is 2556 +72/-76 Ma as determined by a lead isochron on pyrite from mineralized felsic porphyries. This age is approximately 130 Ma younger than the age of the felsic porphyritic rocks and therefore there does not appear to be a direct magmatic- hydrothermal link between these intrusive rocks and the gold mineralization

A functional task analysis and motion simulation for the development of a powered upper-limb orthosis

The objective of this thesis is to determine an optimal configuration of a powered upper-limborthosis. The criterion is to minimize the complexity, defined as the number of degrees of freedom of the orthosis, while maintaining the ability to perform specific tasks. This goal was realized in three stages of research. In the first stage, potential users were interviewed to determine their task priorities. In the second stage, the natural arm motions of able-bodied individuals performing the tasks identified as high priority were profiled with a video trackingsystem. Finally, a kinematic simulation algorithm was developed to evaluate whether a given orthosis configuration is able to perform the identified high-priority tasks. It was found that the task functionality was overly compromised for any configuration with less than five degrees of freedom. Two different configurations with five degrees of freedom are recommended. The recommendations are: (1) to power all but the motions of elevation and wrist yaw, or (2) to power all but wrist flexion and wrist yaw.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat

Gaussian mixture models based 2D–3D registration of bone shapes for orthopedic surgery planning

In orthopedic surgery, precise kinematics assessment helps the diagnosis and the planning of the intervention. The correct placement of the prosthetic component in the case of knee replacement is necessary to ensure a correct load distribution and to avoid revision of the implant. 3D reconstruction of the knee kinematics under weight-bearing conditions becomes fundamental to understand existing in vivo loads and improve the joint motion tracking. Existing methods rely on the semiautomatic positioning of a shape previously segmented from a CT or MRI on a sequence of fluoroscopic images acquired during knee flexion. We propose a method based on statistical shape models (SSM) automatically superimposed on a sequence of fluoroscopic datasets. Our method is based on Gaussian mixture models, and the core of the algorithm is the maximization of the likelihood of the association between the projected silhouette and the extracted contour from the fluoroscopy image. We evaluated the algorithm using digitally reconstructed radiographies of both healthy and diseased subjects, with a CT-extracted shape and a SSM as the 3D model. In vivo tests were done with fluoroscopically acquired images and subject-specific CT shapes. The results obtained are in line with the literature, but the computational time is substantially reduced