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Biomedical subjects

A W Miles

Publications and source records attributed to A W Miles.

35 records · Page 2Linked to original sources
PubMed1994

An in vitro study of the effect of environment and storage time on the fracture properties of bone cement.

Changes either within the bone cement or at the cement-bone interface are known to contribute to loosening and hence failure of many cemented joint replacements. This study examines the in vitro changes in the fracture properties of bone cement as a result of storage, at both 21 and 37 degrees C, in air, water, Ringer's solution and lipid over a period of 2 years. Specimens stored in the fluid media were found to behave in a more ductile manner than those stored in air. Samples stored at 37 degrees C behaved in a more brittle manner than those stored at 21 degrees C. Although the work of fracture values measured for the samples stored in the water-based media increased during the first 18 months, this was followed by a decrease in the subsequent 6 months.

Bone Cements↗
PubMed1994

The effect of bleeding on the cement-bone interface. An experimental study.

A model was developed to simulate bleeding from cancellous bone at the physiologic pressures and flow rates that can occur during total hip arthroplasty. The consequences of simulated bleeding on the penetration of bone cement into cancellous bone, the shear strength of the cement-bone interface, and the shear strength of bone cement were investigated. In the presence of active bleeding, the shear strength of the cement-bone interface was reduced significantly in 50% of interfaces in which cements of lower viscosity were used. The simulated bleeding did not exert a detrimental effect on the depth of cement penetration.

Animals↗
PubMed1993

Load concentrations around crystal aggregates in articular cartilage under short-term loading.

The deposition of crystals in joints is a feature of a number of joint diseases. Crystals are frequently observed on the surface of articular cartilage and in the mid-zone. The purpose of this investigation was to model the stress concentrations in the mid-zone of the cartilage layer arising from the presence of large crystal aggregates. Scanning electron microscopy was used to determine the geometry and distribution of crystal aggregates within the cartilage layer. Finite element and photoelastic approaches were then used to predict the stress distribution around spherical aggregates 50 and 100 microns in diameter. The implication of the results is that very densely packed and tightly bound spherical aggregates will themselves carry a certain amount of load. However, less tightly packed aggregates, perhaps interspersed with fibrous tissue, are potentially much more damaging.

Cartilage, Articular↗
PubMed1993

Fracture and loosening of Charnley femoral stems. Comparison between first-generation and subsequent designs.

We report the results of a 4- to 17-year clinical and radiological follow-up of 264 Charnley first-generation stems in comparison with those of 402 second- and subsequent-generation stems. The incidence of fracture was 4.1% in first-generation stems and 0.5% in second- and subsequent-generation stems. The incidence of stem loosening requiring or likely to require revision was 3.1% in first-generation and 11.4% in second-generation stems. We believe that the increased loosening rate in second- and subsequent-generation stems is due to their larger cross-sectional area, which produces an increase in flexural stiffness.

Adolescent↗
PubMed1993

Bone surface preparation in cemented joint replacement.

We studied the effects of nine techniques of bone surface preparation on cement penetration and shear strength at the cement-bone interface in a standard model of bovine cancellous bone. In unprepared bone the mean penetration was 0.2 mm and the mean shear strength of the interface was 1.9 MPa, less than that of the underlying bone. Brushing with surface irrigation gave mean penetrations of 0.6 to 1.4 mm and mean shear strengths of 1.5 to 9.9 MPa. In 50% of specimens the interface was weaker than the underlying bone. The use of pressurised lavage resulted in mean penetrations of 4.8 to 7.9 mm and mean shear strengths of 26.5 to 36.1 MPa, which were greater than those of the cancellous bone in all specimens. Pressurised lavage was equally effective alone or in combination with brushing, and its efficacy was not altered by using pulsed or continuous jets, or by changing the temperature of the solution from 21 degrees C to 37 degrees C.

Animals↗
PubMed1990

The influence of curing time and environment on the fracture properties of bone cement.

Fracture of bone cement at the bone-cement interface is considered to be of significance in the aseptic loosening of orthopaedic implants. The characterisation of the fracture properties of bone cement is influenced by the time and environment in which it is cured. Cement samples stored in air and water at 21 and 37 degrees C for 7 and 21 days were tested using the 'Chevron' test to determine the work of fracture. It was found that the storage temperature and environment had important influences on the fracture resistance of bone cement. In a physiological environment cement appears to take longer to attain a fracture resistance equivalent to that of cement stored at room temperature.

Bone Cements↗
PubMed1989

Strain gauge and photoelastic evaluation of the load transfer in the pelvis in total hip replacement: the effect of the position of the axis of rotation.

Aseptic loosening of the acetabular component is the principal long-term complication in total hip replacement. Radiographic evidence suggests a higher incidence of loosening with medialization of the axis of rotation of the acetabular cup. A simplified two-dimensional photoelastic investigation of the load transfer in the pelvis demonstrates that the stress distribution is substantially changed when this axis of rotation is medialized. Strain gauge measurements on three dry hemi-pelvic bones confirm this effect. It is postulated that the redistribution of load resulting from medialization may result in inadequate skeletal support for the acetabular component predisposing to loosening.

Biomechanical Phenomena↗
PubMed1986

Accelerated polymerization of acrylic bone cement using preheated implants.

This article is an account of a procedure to accelerate polymerization of polymethylmethacrylate during total hip arthroplasty by preheating the stem of the femoral prosthesis. The increased temperature is shown to have a definite beneficial effect with regard to accelerated polymerization. Experimental investigations are presented to verify this supposition.

Bone Cements↗
PubMed1983

Re-attachment of the greater trochanter. The use of the trochanter cable-grip system.

In comparison with monofilament wire, multifilament cable was found to be a more suitable material for fixation of the greater trochanter. It is versatile, easy to work with and has superior mechanical properties. The "trochanter cable-grip system" was developed to exploit the use of multifilament cable as a means of reattaching the greater trochanter and experimental studies have yielded excellent results. This system was subjected to clinical trials for over four years in 321 hips and, at its present state of development, the incidence of detachment has been reduced to 1.5 per cent and that of cable breakage to 3.1 per cent.

Biomechanical Phenomena↗
PubMedDate not supplied

Failure of femoral head fixation: a cadaveric analysis of lag screw cut-out with the gamma locking nail and AO dynamic hip screw.

The most commonly reported failure mode of sliding hip screws in published literature is cut-out of the lag screw. This study investigates the resistance to failure of the femoral head, with lag screws used in two types of sliding hip screws, the gamma locking nail (Howmedica) and the dynamic hip screw (DHS) (Synthes). The investigation consisted of biomechanical tests under static loading conditions on 12 pairs of cadaveric femoral heads, to establish the failure loads due to screw cut-out for the two implant lag screws. The gamma nail appeared to reduce the tendency to cut-out in the osteoporotic bone (soft) associated with elderly patients in whom these devices are commonly used (p < 0.05). In high density bone (hard) the gamma lag screw also appeared to be stronger, because the DHS showed a tendency to bend. The larger diameter of the gamma nail lag screw resists bending and appears to reduce the risk of cut-out compared with the DHS.

Aged↗
PubMedDate not supplied

Bone loss during long term space flight is prevented by the application of a short term impulsive mechanical stimulus

In long term space flight, the mechanical forces applied to the skeleton are substantially reduced and are altered in character. This reduced skeletal loading results in a reduction in bone mass. Exercise techniques currently used in space can maintain muscle mass but the mechanical stimulus provided by this exercise does not prevent bone loss. By applying an external impulsive load for a short period each day, which is intended to mimic the heel strike transient, to the lower limb of an astronaut during a long term space flight (5 months), this study tests the hypothesis that the bone cells can be activated by an appropriate external mechanical stimulus to maintain bone mass throughout prolonged periods of weightlessness. A mechanical loading device was developed to produce a loading of the os-calcis similar to that observed during the heel strike transient. The device is activated by the astronaut to provide a transient load to the heel of one leg whilst providing an equivalent exercising load to the other leg. During the EUROMIR95 mission on the MIR space station, an astronaut used this device for a short period daily throughout the duration of the mission. Pre- and post-flight measurements of bone mineral density (BMD) of the os-calcis and femoral neck of the astronaut were made to determine the efficacy of the device in preventing loss of bone mineral during the mission. On the os-calcis which received the mechanical stimulus, BMD was maintained throughout the period of the flight, while it was reduced by up to 7% on the os-calcis which received no stimulus. Post-flight, BMD in both the stimulated and non-stimulated os-calcis reduces, the extent of this reduction however is less in the stimulated os-calcis. For the femoral neck, the mechanical stimulation does not produce a positive effect.

Aerospace Medicine↗
PubMedDate not supplied

Optimizing a hydroxyapatite/tricalcium-phosphate ceramic as a bone graft extender for impaction grafting.

The mechanical properties of morsellized bone allografts and synthetic hydroxapatite/tricalcium-phosphate (HA/TCP) ceramic extender materials for the use in impaction grafting revision hip surgery were investigated using two test methods: a basic compression test and an endurance test in an in-vitro model of an impaction grafted femur. Formalin fixed ovine bone graft was identified as mechanically similar to fresh human bone and thus suitable as an experimental material for in-vitro testing. For 1 : 1 volumetric mixes of bone allograft and synthetic extender, the granular ceramic's properties were varied in porosity, chemical composition, sintering temperature and particle size. Initial mechanical stability, a crucial prerequisite for clinical success in impaction grafting, was increased for all bone/extender mixes. A high porosity, tricalcium-phosphate rich ceramic of medium particle size and sintered at high temperatures was recognized as an optimized extender material for impaction grafting balancing the mechanical and biological demands. Using the extender without bone graft as a pure replacement is not recommended.

Journal Article↗