Assessment of non-contacting optical methods to measure wear and surface roughness in ceramic total disc replacements

This study presents a method for measuring the low volumetric wear expected in ceramic total disc replacements, which can be used to replace intervertebral discs in the spine, using non-contacting optical methods. Alumina-on-alumina ball-on-disc tests were conducted with test conditions approximating those of cervical (neck region of the spine) total disc replacement wear tests. The samples were then scanned using a three-dimensional non-contacting optical profilometer and the data used to measure surface roughness and develop a method for measuring the wear volume. The results showed that the magnification of the optical lens affected the accuracy of both the surface roughness and wear volume measurements. The method was able to successfully measure wear volumes of 0.0001mm3, which corresponds to a mass of 0.0001 mg, which would have been undetectable using the gravimetric method. A further advantage of this method is that with one scan the user can measure changes in surface topography, volumetric wear and the location of the wear on the implant surface. This method could also be applied to more severe wear, other types of orthopaedic implants and different materials

Surface damage of bovine articular cartilage-off-bone::the effect of variations in underlying substrate and frequency

Abstract Background Changes in bone mineral density have been implicated with the onset of osteoarthritis, but its role in inducing failure of articular cartilage mechanically is unclear. This study aimed to determine the effect of substrate density, as the underlying bone, on the surface damage of cartilage-off-bone, at frequencies associated with gait, and above. Methods Bovine articular cartilage samples were tested off-bone to assess induced damage with an indenter under a compressive sinusoidal load range of 5–50 N at frequencies of 1, 10 and 50 Hz, corresponding to normal and above normal gait respectively, for up to 10,000 cycles. Cartilage samples were tested on four underlying substrates with densities of 0.1556, 0.3222, 0.5667 and 0.6000 g/cm3. India ink was applied to identify damage as cracks, measured across their length using ImageJ software. Linear regression was performed to identify if statistical significance existed between substrate density, and surface damage of articular cartilage-off-bone, at all three frequencies investigated (p  0.05) in surface damage with an increase in substrate density, at which the maximum mean crack length were 3.01 ± 3.41 mm and 5.65 ± 6.54 mm, respectively. Crack formation at all frequencies tended to form at the periphery of the cartilage specimen, with multiple straight-line cracking observed at 10 Hz, in comparison to single straight-line configurations produced at 1 and 50 Hz. Conclusions The effect of substrate density on the surface damage of articular cartilage-off-bone is multi-factorial, with an above-normal gait frequency. At 1 Hz cartilage damage is not associated with substrate density, however at 10 Hz, it is. This study has implications on the effects of the factors that contribute to the onset of osteoarthritis

Ergonomic t-handle for minimally invasive surgical instruments

A T-handle has been designed to be used for minimally invasive implantation of a dynamic hip screw to repair fractures of the proximal femur. It is capable of being used in two actions: (i) push and hold (while using an angle guide) and (ii) application of torque when using the insertion wrench and lag screw tap. The T-handle can be held in a power or precision grip. It is suitable for either single (sterilised by -irradiation) or multiple (sterilised by autoclaving) use. The principles developed here are applicable to handles for a wide range of surgical instruments

Investigation of techniques for the measurement of articular cartilage surface roughness

Articular cartilage is the bearing surface of synovial joints and plays a crucial role in the tribology to enable low friction joint movement. A detailed understanding of the surface roughness of articular cartilage is important to understand how natural joints behave and the parameters required for future joint replacement materials. Bovine articular cartilage on bone samples was prepared and the surface roughness was measured using scanning electron microscopy stereoscopic imaging at magnifications in the range 500× to 2000×. The surface roughness (two-dimensional, Ra, and three-dimensional, Sa) of each sample was then measured using atomic force microscopy (AFM). For stereoscopic imaging the surface roughness was found to linearly increase with increasing magnification. At a magnification of 500× the mean surface roughness, Ra, was in the range 165.4±5.2nm to 174±39.3 nm; total surface roughness Sa was in the range 183–261 nm. The surface roughness measurements made using AFM showed Ra in the range 82.6±4.6nm to 114.4±44.9nm and Sa in the range 86–136 nm. Values obtained using SEM stereo imaging were always larger than those obtained using AFM. Stereoscopic imaging can be used to investigate the surface roughness of articular cartilage. The variations seen between measurement techniques show that when making comparisons between the surface roughness of articular cartilage it is important that the same technique is used

Assessment of surface roughness and blood rheology on local coronary hemodynamics: a multi-scale computational fluid dynamics study

The surface roughness of the coronary artery is associated with the onset of atherosclerosis. The study applies, for the first time, the micro-scale variation of the artery surface to a 3D coronary model, investigating the impact on haemodynamic parameters which are indicators for atherosclerosis. The surface roughness of porcine coronary arteries have been detailed based on optical microscopy and implemented into a cylindrical section of coronary artery. Several approaches to rheology are compared to determine the benefits/limitations of both single and multiphase models for multi-scale geometry. Haemodynamic parameters averaged over the rough/smooth sections are similar; however, the rough surface experiences a much wider range, with maximum wall shear stress greater than 6 Pa compared to the approximately 3 Pa on the smooth segment. This suggests the smooth-walled assumption may neglect important near-wall haemodynamics. While rheological models lack sufficient definition to truly encompass the micro-scale effects occurring over the rough surface, single-phase models (Newtonian and non-Newtonian) provide numerically stable and comparable results to other coronary simulations. Multiphase models allow for phase interactions between plasma and red blood cells which is more suited to such multi-scale models. These models require additional physical laws to govern advection/aggregation of particulates in the near-wall region

Viscoelastic properties of bovine articular cartilage attached to subchondral bone at high frequencies

<p>Abstract</p> <p>Background</p> <p>Articular cartilage is a viscoelastic material, but its exact behaviour under the full range of physiological loading frequencies is unknown. The objective of this study was to measure the viscoelastic properties of bovine articular cartilage at loading frequencies of up to 92 Hz.</p> <p>Methods</p> <p>Intact tibial plateau cartilage, attached to subchondral bone, was investigated by dynamic mechanical analysis (DMA). A sinusoidally varying compressive force of between 16 N and 36 N, at frequencies from 1 Hz to 92 Hz, was applied to the cartilage surface by a flat indenter. The storage modulus, loss modulus and phase angle (between the applied force and the deformation induced) were determined.</p> <p>Results</p> <p>The storage modulus, <it>E'</it>, increased with increasing frequency, but at higher frequencies it tended towards a constant value. Its dependence on frequency, <it>f</it>, could be represented by, <it>E' </it>= <it>Alog</it>_{<it>e </it>}(<it>f</it>) + <it>B </it>where <it>A </it>= 2.5 ± 0.6 MPa and <it>B </it>= 50.1 ± 12.5 MPa (mean ± standard error). The values of the loss modulus (4.8 ± 1.0 MPa mean ± standard deviation) were much less than the values of storage modulus and showed no dependence on frequency. The phase angle was found to be non-zero for all frequencies tested (4.9 ± 0.6°).</p> <p>Conclusion</p> <p>Articular cartilage is viscoelastic throughout the full range of frequencies investigated. The behaviour has implications for mechanical damage to articular cartilage and the onset of osteoarthritis. Storage modulus increases with frequency, until the plateau region is reached, and has a higher value than loss modulus. Furthermore, loss modulus does not increase with loading frequency. This means that more energy is stored by the tissue than is dissipated and that this effect is greater at higher frequencies. The main mechanism for this excess energy to be dissipated is by the formation of cracks.</p