Medical engineering & physics
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Minimally invasive surgery poses high demands on tool design. The goal was to measure the influence of drill bit geometry on maximum thrust forces required for drilling, and compare this relative to the known influence of feed rate and bone composition. Blind holes were drilled perpendicular to the iliac crest up to 10 mm depth in cadaveric pelvic bones of 20 pigs (adolescent) and 11 goats (full grown) with eight substantially different drill bits of ∅ 3-3.2 mm. ⋯ The results show that both drill bit geometry and feed rate have a significant influence on the maximum thrust forces, with a dominant influence of drill bit geometry in terms of shape of the flutes, sharpness of cutting edges and value of point angle. The differences in thrust forces between cortical and trabecular bone are substantial for all measured conditions. The measured values can be used for drill design.
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This paper analyses the suitability of a system comprising a Dynamic Compression Plate (DCP) and Screw Locking Elements (SLEs) to allow sufficient interfragmentary motion to promote secondary bone healing in osteoporotic fractures. Four fixation systems were mounted on bone-simulating reinforced epoxy bars filled with solid rigid polyurethane foam. Group 1, used for comparison purposes, represents a system comprised of a Locking Compression Plate (LCP) and eight locking screws. ⋯ For group 1 (the LCP construct) the mean stiffness at 10,000 cycles was 3144±446 N mm(-1), 3.25 times higher than that of groups 2 and 3 (there being significant differences: p=0.00002), and 1.6 times higher than that of the DCP+8SLEs construct (1944±408 N mm(-1), there being significant differences: p=0.007). It is concluded that using the DCP+2SLEs construct sufficient interfragmentary motion is ensured to promote secondary bone healing. However, if too many SLEs are used the result may be, as with the LCP, an excessively rigid system for callus formation.
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Flow diverters (FDs) are high density meshed stents designed to reduce blood flow into intra-cranial aneurysms. Though the FD is one of many intracranial aneurysm (IA) treatments, FD implantation may also result in the growth and rupture of residual aneurysms. The purpose of this research is to investigate the effect of FD implantation on IA hemodynamics. ⋯ The reason was that the flow resistance force at the aneurysm neck section was calculated to be lower than the flow driving force. In order to completely occlude the aneurysm, a higher resistance FD stent is to be required to suppress the dynamic forces. Patient-specific hemodynamic simulations offer means of quantitative estimation FD treatment outcomes.
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Obtaining access to blood vessels can be difficult, especially in children. Visualization of subsurface blood vessels might be a solution. Ultrasound and visible light have been used to this purpose, but have some drawbacks. ⋯ A phantom study showed that the maximum depth of visibility (5.5mm for a 3.6mm blood vessel) is sufficient to visualize blood vessels in typical locations for peripheral venous and arterial access. A quantitative comparison of the VascuLuminator and to two other vessel imaging devices, using reflection of near-infrared light instead of transillumination, was conducted. The VascuLuminator is able to decrease failure at first attempt in blood withdrawal in pediatric patients from 10/80 (13%) to 1/45 (2%; P=.05).
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Subluxation of the affected shoulder in post-stroke patients is associated with nerve disorders and muscle fatigue. Clinicians must be able to accurately and reliably measure inferior glenohumeral subluxation in patients to provide appropriate treatment. However, quantitative methods for evaluating the laxity and stiffness of the glenohumeral joint (GHJ) are still being developed. ⋯ Furthermore, subjects wearing a humerus brace with a belt, which creates the effect of lifting the humerus toward the acromion, had greater GHJ stiffness compared to subjects wearing a shoulder brace without a belt to lift the humerus under the proposed testing conditions. This study provides experimental evidence that shoulder braces may reduce GHJ laxity under an external load, implying that the use of a humeral brace can prevent subluxation in post-stroke patients. The resulting optimal testing conditions for measuring the laxity and stiffness of the GHJ is to constrain the unloaded shoulder and bend the loaded arm at the elbow with loading on the upper arm using a pulley system.