Consequences of reaming with flat and convex reamers for bone volume and surface area of the glenoid : a basic science study

Background: The effect of reaming on bone volume and surface area of the glenoid is not precisely known. We hypothesize that (1) convex reamers create a larger surface area than flat reamers, (2) flat reamers cause less bone loss than convex reamers, and (3) the amount of bone loss increases with the amount of version correction. Methods: Reaming procedures with different types of reamers are performed on similar-sized uniconcave and biconcave glenoids created from Sawbones foam blocks. The loss of bone volume, the size of the remaining surface area, and the reaming depth are measured and evaluated. Results: Reaming with convex reamers results in a significantly larger surface area than with flat reamers for both uniconcave and biconcave glenoids (p = 0.013 and p = 0.001). Convex reamers cause more bone loss than flat reamers, but the difference is only significant for uniconcave glenoids (p = 0.007). Conclusions: In biconcave glenoids, convex reamers remove a similar amount of bone as flat reamers, but offer a larger surface area while maximizing the correction of the retroversion. In pathological uniconcave glenoids, convex reamers are preferred because of the conforming shape

Peri-implant bone tissue strains in cases of dehiscence: a finite element study

When patients with a narrow alveolar bone ridge are treated with oral implants, a dehiscence can occur. The lack of bony support at the buccal or lingual side of the implant may present an unfavourable situation from a biomechanical point of view. The hypothesis as to whether the presence of dehiscence leads to an increased risk of marginal bone overload was tested by means of the finite element method. Three different situations for a cylindrical oral implant, which was placed in a mandible, were modelled: i) no dehiscence, ii) a dehiscence at the buccal side and iii) dehiscences at the buccal and lingual sides. It was found that the presence of buccal and/or lingual dehiscences led to a marked increase in marginal bone strains at the mesial and distal sides of the implant, thus increasing the risk of bone tissue overload at these locations. Marginal bone strains at the buccal and/or lingual sides, however, did not increase.status: publishe

Assessment of relative brain-skull motion in quasistatic circumstances by Magnetic Resonance Imaging

Brain-skull relative motion plays a pivotal role in the etiology of traumatic brain injury (TBI). The present study aims to assess brain-skull relative motion in quasistatic circumstances, and to correlate cortical regions with high motion amplitudes with sites prone to cerebral contusions. The study includes 30 healthy volunteers scanned using a clinical 3-T MR scanner in four different head positions. Through image processing and 3D model registration, pairwise comparisons were performed to calculate the brain shift between sagittal and coronal head positional change. Next, local brain deformation was evaluated by comparison between cortical and ventricular amplitudes. Finally, the influence of age, sex, and skull geometry on the cortical and ventricular motion was investigated. The results describe complex brain shift patterns, with high regional and inter-individual variations, outweighing age and sex patterns. Regions with maximum motion amplitudes were identified at the inferolateral aspects of the frontal and temporal lobes, congruent with predilection sites for contusions. No significant influences of age and sex on the cortical shift amplitudes were detected. The 3D cortical deviations varied from -7.86 mm to +5.71 mm for the sagittal head movement, and from -11.46 mm to +7.30 mm for head movement in the coronal plane, for a 95% confidence interval. The present study contributes to a better understanding of the mechanopathogenesis of frontotemporal contusions, and is useful for the optimization of finite-element head models and neurosurgical navigation procedures. Moreover, our results prove that in vivo MRI allows for accurate assessment of brain-skull relative motion in quasistatic conditions.status: publishe

Subject-specific musculoskeletal models are needed to predict the influence of hip replacement on hip contact force

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Feasibility of monitoring bone remodelling around loaded percutaneous tibial implants in guinea pigs by in vivo microfocus computed tomography (µCT)

Guinea pigs were selected as an animal model for studying bone remodelling around loaded percutaneous implants. The feasibility of monitoring bone remodelling in vivo by microfocus computed tomography was assessed experimentally. A microfocus computed tomography (mCT) protocol was developed to minimise the side effects (i.e. radionecrosis) while maintaining sufficient image quality to allow segmentation of the mCT slices for subsequent processing into finite element models. (c) 2001 Elsevier Science B.V. All rights reserved.status: publishe

Feasibility of monitoring bone remodelling around loaded percutaneous tibial implants in guinea pigs by in vivo microfocus computed tomography

Guinea pigs were selected as an animal model for studying bone remodelling around loaded percutaneous implants. The feasibility of monitoring bone remodelling in vivo by microfocus computed tomography was assessed experimentally. A microfocus computed tomography (μCT) protocol was developed to minimise the side effects (i.e. radionecrosis) while maintaining sufficient image quality to allow segmentation of the μCT slices for subsequent processing into finite element models. © 2001 Elsevier Science B.V.status: publishe

The use of microfocus computerized tomography as a new technique for characterizing bone tissue around oral implants

Qualitative and quantitative analysis of peri-implant tissues around retrieved oral implants is typically done by means of light microscopy on thin histological sections containing the metal surface and the undecalcified bone. It remains, however, a labor-intensive and thus time-consuming job. Moreover, it is a destructive technique that allows tissue quantification in only a limited number of two-dimensional sections. As an alternative, we evaluated the bone structure around screw-shaped titanium implants by means of microfocus computerized tomography (micro-CT) because it presents a number of advantages compared to conventional sectioning techniques: micro-CT is nondestructive, fast, and allows a fully three-dimensional characterization of the bone structure around the implant. Images can be reconstructed in an arbitrary plane, and three-dimensional reconstructions are also possible. Because of its high resolution, individual trabeculae can be visualized. The accuracy of micro-CT was qualitatively evaluated by comparing histological sections with the corresponding CT slices for the same specimen. The overall trabecular structure is very similar according to both techniques. Even very close to the interface, the titanium implant does not seem to produce significant artifacts. Furthermore, because the complete digital data on the trabecular bone structure around the implant is available, it is possible to create finite-element models of the bone-implant system that model the trabeculae in detail so that mechanical stress transfer at the interface can be studied at the level of individual trabeculae. Therefore, micro-CT seems to be very promising for the in vitro assessment of the three-dimensional bone structure around oral implants. Further research will be needed to evaluate its accuracy in a more quantitative way.CD-romstatus: publishe

Combination shear-compression testing of foam materials for their application in bicycle helmets or other complexly loaded structures

The shear properties of the foam cushioning material in a bicycle helmet can be correlated to the resulting rotational acceleration of the head during impact. This rotational acceleration is known to cause significant brain injuries, and should be minimized. It is therefore important to study the shear behavior of helmet foams. Bicycle helmet foam, however, never experiences purely shear or compression deformation. Impacts are generally oriented at oblique angles and result in foam deformation with both a shear and a compressive component. A test method to apply a combination of shear and compressive displacements to a foam sample has been developed. Furthermore, it is possible to analyze the shear and compressive components of deformation separately so that the coupling between shear and compressive behavior in cellular materials can be observed.status: publishe