Search

Micro-extrusion-based 3D printing of complex geometrical and porous calcium phosphate (CaP) can improve treatment of bone defects through the production of personalized bone substitutes. However, achieving printing and post-printing shape stabilities for the efficient fabrication and application of rapid hardening protocol are still challenging. In this work, the coaxial printing of a self-setting CaP cement with water and ethanol mixtures aiming to increase the ink yield stress upon extrusion and the stability of fabricated structures was explored. Printing height of overhang structure was doubled when aqueous solvents were used and a 2 log increase of the stiffness was achieved post-printing. A standard and fast steam sterilization protocol applied as hardening step on the coaxial printed CaP cement (CPC) ink resulted in constructs with 4 to 5 times higher compressive moduli in comparison to extrusion process in the absence of solvent. This improved mechanical performance is likely due to rapid CPC setting, preventing cracks formation during hardening process. Thus, coaxial micro-extrusion-based 3D printing of a CPC ink with aqueous solvent enhances printability and allows the use of the widespread steam sterilization cycle as a standalone post-processing technique for production of 3D printed personalized CaP bone substitutes. Coaxial micro-extrusion-based 3D printing of a self-setting CaP cement with water:ethanol mixtures increased the ink yield stress upon extrusion and the stability of fabricated structures. Printing height of overhang structure was doubled when aqueous solvents were used, and a 2 orders of magnitude log increase of the stiffness was achieved post-printing. A fast hardening step consisting of a standard steam sterilization was applied. Four to 5 times higher compressive moduli was obtained for hardened coaxially printed constructs. This improved mechanical performance is likely due to rapid CPC setting in the coaxial printing, preventing cracks formation during hardening process. [Display omitted] [ABSTRACT FROM AUTHOR]

The number of elective refractive surgeries is constantly increasing due to the drastic increase in myopia prevalence. Since corneal biomechanics are critical to human vision, accurate modeling is essential to improve surgical planning and optimize the results of laser vision correction. In this study, we present a numerical model of the anterior cornea of young patients who are candidates for laser vision correction. Model parameters were determined from uniaxial tests performed on lenticules of patients undergoing refractive surgery by means of lenticule extraction, using patient-specific models of the lenticules. The models also took into account the known orientation of collagen fibers in the tissue, which have an isotropic distribution in the corneal plane, while they are aligned along the corneal curvature and have a low dispersion outside the corneal plane. The model was able to reproduce the experimental data well with only three parameters. These parameters, determined using a realistic fiber distribution, yielded lower values than those reported in the literature. Accurate characterization and modeling of the cornea of young patients is essential to study better refractive surgery for the population undergoing these treatments, to develop in silico models that take corneal biomechanics into account when planning refractive surgery, and to provide a basis for improving visual outcomes in the rapidly growing population undergoing these treatments. [ABSTRACT FROM AUTHOR]

Purpose: Establishing the symmetry of intraindividual orbital volumes is crucial for radiologic assessment, preoperative planning, and postoperative outcome evaluation. However, no reliable method exists to measure orbital volume because of problems in defining the bony boundaries of the orbit. Therefore, the purpose of this study was to propose a new approach to analyze human orbits and determine its application for quantifying bony symmetry in a cohort of patients.Patients and Methods: Computed tomography scans of 93 patients were retrospectively collected from our institutional database. The intraindividual volume difference was quantified using a surface model derived from manual segmentations. The average shape of the orbit was calculated iteratively and nonrigidly registered to both orbits of all patients. After registration, the surface reconstructions of all orbits had an identical mesh topology and vertices at corresponding anatomic locations. The volume difference was calculated locally based on the relative position of the vertices at equivalent locations in the left orbit and right orbit. This approach was used to quantify the volume difference between the left and right orbits for all patients. Interobserver sensitivity was assessed in 5 randomly chosen patients and was measured independently by 3 specialists.Results: An average difference of 600 ± 500 μL between the volumes of the left and right orbits was found, representing a difference of 2.1%. Although the difference in volume was small, the volumes were significantly different (P = .039). The largest asymmetries were found in the roof and floor area.Conclusions: The method proposed to measure the difference in volume between the left and right orbits is automated and does not rely on a closed orbital volume, which provides more objective volume measurements. With the help of modern computed tomography techniques and the coherent point drift method, it was possible to show that the intraindividual volume difference in the orbits is approximately 2%, not 7 to 8% as often cited in the literature. [ABSTRACT FROM AUTHOR]

Background This study proposes a method for inferring the premorbid glenoid shape and orientation of scapulae affected by glenohumeral osteoarthritis (OA) to inform restorative surgery. Methods A statistical shape model (SSM) built from 64 healthy scapulae was used to reconstruct the premorbid glenoid shape based on anatomic features that are considered unaffected by OA. First, the method was validated on healthy scapulae by quantifying the accuracy of the predicted shape in terms of surface distance, glenoid version, and inclination. The SSM-based reconstruction was then applied to 30 OA scapulae. Glenoid version and inclination were measured fully automatically and compared between the original OA glenoids, SSM-based glenoid reconstructions, and healthy scapulae. Results Validation on healthy scapulae showed a root-mean-square surface distance between original and predicted glenoids of 1.0 ± 0.2 mm. The prediction error was 2.3° ± 1.8° for glenoid version and 2.1° ± 2.0° for inclination. When applied to an OA dataset, SSM-based reconstruction restored average glenoid version and inclination to values similar to the healthy situation. No differences were observed between average orientation values measured on SSM-based reconstructed and healthy scapulae (P ≥.10). However, the average orientation of the reconstructed premorbid glenoid differed from the average orientation of OA glenoids for Walch classes A1 (version) and B2 (version, inclination, and medialization). Conclusion The proposed SSM can predict the premorbid glenoid cavity of healthy scapulae with millimeter accuracy. This technique has the potential to reconstruct the premorbid glenoid cavity shape, as it was prior to OA, and thus to guide the positioning of glenoid implants in total shoulder arthroplasty. [ABSTRACT FROM AUTHOR]

The objective of this work was to develop a system for three-dimensional (3D) reconstruction of the femoropopliteal artery from two angiographic views and to quantify the in vivo 3D deformations in 18 patients before balloon angioplasty and after primary stent implantation. The procedure had an insignificant effect on the bending behavior of the artery, as the average mean curvature change within the lesion remained constant before (0.04 cm-1 ± 0.03) and after stent implantation (0.03 cm-1 ± 0.04). A significant effect of stent implantation was measured in terms of a decrease in arterial shortening during leg flexion. [ABSTRACT FROM AUTHOR]

Purpose To compare the initial stability and stability after fatigue of three different locking systems (Synthes ® , Stryker ® and Medartis ® ) for mandibular fixation and reconstruction. Method Standard mandible locking plates with identical profile height (1,5 mm), comparable length and screws with identical diameter (2,0 mm) were used. Plates were fixed with six screws according a preparation protocol. Four point bending tests were then performed using artificial bone material to compare their initial stability and failure limit under realistic loading conditions. Loading of the plates was performed using of a servo hydraulic driven testing machine. The stiffness of the implant/bone construct was calculated using a linear regression on the experimental data included in a range of applied moment between 2 Nm and 6 Nm. Results No statistical difference in the elastic stiffness was visible between the three types of plate. However, differences were observed between the systems concerning the maximal load supported. The Stryker and Synthes systems were able to support a significantly higher moment. Conclusion For clinical application all systems show good and reliable results. Practical aspects such as handling, possible angulation of screw fixation, possibility of screw/plate removal, etc. may favour one or the other plating system. [ABSTRACT FROM AUTHOR]

Numerical models of the intervertebral disc, which address mechanical questions commonly make use of the difference in water content between annulus and nucleus, and thus fluid and solid parts are separated. Despite this simplification, models remain complex due to the anisotropy and nonlinearity of the annulus and regional variations of the collagen fibre density. Additionally, it has been shown that cross-links make a large contribution to the stiffness of the annulus. Because of this complex composite structure, it is difficult to reproduce several sets of experimental data with one single set of material parameters. This study addresses the question to which extent the ultrastructure of the intervertebral disc should be modelled so that its moment–angle behaviour can be adequately described. Therefore, a hyperelastic constitutive law, based on continuum mechanical principles was derived, which does not only consider the anisotropy from the collagen fibres, but also interactions among the fibres and between the fibres and the ground substance. Eight ovine lumbar intervertebral discs were tested on a custom made spinal loading simulator in flexion/extension, lateral bending and axial rotation. Specimen-specific geometrical models were generated using CT images and T2 maps to distinguish between annulus fibrosus and nucleus pulposus. For the identification of the material parameters the annulus fibrosus was described with two scenarios: with and without fibre–matrix and fibre–fibre interactions. Both scenarios showed a similar behaviour on a load displacement level. Comparing model predictions to the experimental data, the mean RMS of all specimens and all load cases was 0.54±0.15° without the interaction and 0.54±0.19° when the fibre–matrix and fibre–fibre interactions were included. However, due to the increased stiffness when cross-links effects were included, this scenario showed more physiological stress–strain relations in uniaxial and biaxial stress states. Thus, the present study suggests that fibre–matrix and fibre–fibre interactions should be considered in the constitutive law when the model addresses questions concerning the stress field of the annulus fibrosus. [ABSTRACT FROM AUTHOR]

Objectives: Despite its importance, implant removal torque can be assessed at present only after implantation. This paper presents a new technique to help clinicians preoperatively evaluate implant stability. Study design: Planning software has been combined with an in-house finite element solver. Once the clinician has chosen the implant position on the planner, a finite element analysis automatically calculates the primary stability. The process was designed to be as simple and fast as possible for clinical use. This paper describes application of the method to the prediction of removal torque. A preliminary validation has been performed in both polyurethane foam and sheep bone. Results: The predicted torque is quantitatively equivalent to experimental values with correlation coefficients of >0.7 in both materials. Conclusions: This preliminary study is a first step toward the introduction of finite element models in computer-assisted surgery. The fact that the process is fast and automatic makes it suitable for a clinical use. [Copyright &y& Elsevier]

Osteoarthritis of the shoulder is frequently associated with posterior glenoid wear, which may be difficult to correct during shoulder arthroplasty. This study was designed to evaluate the risks that a prosthetic glenoid implanted in retroversion will loosen. The scapula, the humerus, the rotator cuff, and a total shoulder prosthesis were reconstructed with a 3-dimensional finite element model. The glenoid was placed in 5 different angles of retroversion (0°, 5°, 10°, 15°, and 20°). Location of the glenohumeral contact point, articular pressure, bone and cement stress, and micromotion around the glenoid implant were calculated during internal and external rotation. Glenoid retroversion induced a posterior displacement of the glenohumeral contact point during internal and external rotation, inducing a significant increase of stress within the cement mantel (+326%) and within the glenoid bone (+162%). Furthermore, a major increase of micromotion was measured at the bone-cement interface (+706%). According to this study, glenoid retroversion exceeding 10° should be corrected during total shoulder arthroplasty. If the correction is impossible, not replacing the glenoid should be considered. [Copyright &y& Elsevier]

Glenohumeral conformity has been reported to be one of the most critical implant-related features that may affect the occurrence of glenoid loosening. This study evaluated the mechanical effects of this parameter with a 3-dimensional finite element model of a prosthetic shoulder, which included the scapula, the humerus, and the rotator cuff muscles. Aequalis humeral and glenoid components were implanted numerically according to manufacturer’s recommendations for 2 different orientations of the glenoid component (0° and 15° of retroversion). Different values of glenohumeral conformity (1–15 mm of radial mismatch) were tested by a progressive flattening of the glenoid surface. Free and countered rotation movements were simulated. Glenohumeral contact pressure, cement stress, shear stress, and micromotions at the bone-cement interface were calculated. At 0° of retroversion, conformity had only a slight effect, whereas at 15° of retroversion, all quantities increased by more than 200% and exceeded critical values above 10 mm of mismatch. [Copyright &y& Elsevier]

Background: Statistical shape models are widely used in biomedical research. They are routinely implemented for automatic image segmentation or object identification in medical images. In these fields, however, the acquisition of the large training datasets, required to develop these models, is usually a time-consuming process. Even after this effort, the collections of datasets are often lost or mishandled resulting in replication of work. Objective: To solve these problems, the Virtual Skeleton Database (VSD) is proposed as a centralized storage system where the data necessary to build statistical shape models can be stored and shared. Methods: The VSD provides an online repository system tailored to the needs of the medical research community. The processing of the most common image file types, a statistical shape model framework, and an ontology-based search provide the generic tools to store, exchange, and retrieve digital medical datasets. The hosted data are accessible to the community, and collaborative research catalyzes their productivity. Results: To illustrate the need for an online repository for medical research, three exemplary projects of the VSD are presented: (1) an international collaboration to achieve improvement in cochlear surgery and implant optimization, (2) a population-based analysis of femoral fracture risk between genders, and (3) an online application developed for the evaluation and comparison of the segmentation of brain tumors. Conclusions: The VSD is a novel system for scientific collaboration for the medical image community with a data-centric concept and semantically driven search option for anatomical structures. The repository has been proven to be a useful tool for collaborative model building, as a resource for biomechanical population studies, or to enhance segmentation algorithms. [ABSTRACT FROM AUTHOR]

Abstract: Craniosynostosis consists of a premature fusion of the sutures in an infant skull that restricts skull and brain growth. During the last decades, there has been a rapid increase of fundamentally diverse surgical treatment methods. At present, the surgical outcome has been assessed using global variables such as cephalic index, head circumference, and intracranial volume. However, these variables have failed in describing the local deformations and morphological changes that may have a role in the neurologic disorders observed in the patients. This report describes a rigid image registration–based method to evaluate outcomes of craniosynostosis surgical treatments, local quantification of head growth, and indirect intracranial volume change measurements. The developed semiautomatic analysis method was applied to computed tomography data sets of a 5-month-old boy with sagittal craniosynostosis who underwent expansion of the posterior skull with cranioplasty. Quantification of the local changes between pre- and postoperative images was quantified by mapping the minimum distance of individual points from the preoperative to the postoperative surface meshes, and indirect intracranial volume changes were estimated. The proposed methodology can provide the surgeon a tool for the quantitative evaluation of surgical procedures and detection of abnormalities of the infant skull and its development. [Copyright &y& Elsevier]