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Biomedical subjects

W Macdonald

Publications and source records attributed to W Macdonald.

12 recordsLinked to original sources
PubMed2003

Fatigue testing of a proximal femoral hip component.

The Gothenburg Osseointegrated Titanium (GOT) implant is a novel total hip replacement including a metaphyseal loading proximal femoral component fixed in the retained femoral neck. Endurance testing was performed under conditions analogous to ISO 7206-4: 1989. The cement-free implant is not fixed distally within the intramedullary canal, so distal embedding (as specified in the standard) would have been unrealistic. Instead glass-fibre-reinforced epoxy (GFRE) bushings were used to model reduced bone support mid-length at the medial cortex and distally at the lateral cortex. Such support simulated proximal bone loss, realistically reproducing the effect of osteolysis or fixation failure. Under such conditions the component survived unbroken for 10 million cycles at 3.0 kN peak load.

Compressive Strength↗
PubMed2003

A proximal femoral implant preserves physiological bone deformation: a biomechanical investigation in cadaveric bones.

The aim of this study was to compare the perturbances in bone deformation patterns of the proximal femur due to a conventional cemented femoral stem and a novel uncemented implant designed on the principles of osseointegration. Five matched pairs of fresh frozen human femora were mechanically tested. Bone deformation patterns, measured with a video digitizing system under 1.5 kN joint force, showed that the cemented Spectron femoral implant caused significant alterations to the proximal femoral deformation pattern, whereas the Gothenburg osseointegrated titanium femoral implant did not significantly alter the bone behaviour (p < 0.05). Vertical micromotions measured under 1 kN after 1000 cycles were within the threshold of movement tolerable for bone ingrowth (21 microm for the Gothenburg system and 26 microm for the cemented implant).

Biomechanical Phenomena↗
PubMed2000

Friction in orthopaedic zirconia taper assemblies.

The torque resistance of zirconia ceramic heads/titanium taper trunnion junctions was tested in accordance with ISO 7206-9:1994(E); using twelve modified heads of 32 mm diameter under representative physiological conditions. Test parameters studied included assembly force, vertical load during test (test load) and head length. Mean torque resistances measured were 8.9 N m for a 1 kN test load and 15 N m at 4 kN test load. Coefficients of friction calculated for the torsional stability ranged from 0.06 to greater than 1.0. Multiple regression analysis confirmed that the failure torques measured were significantly dependent on test load (beta = 0.77; P < 0.001) whereas assembly force and head length played a lesser, insignificant, part in the variation. Data from push-on/pull-off tests were used to calculate coefficients of friction under axial loading, which were significantly correlated with taper angle and material. Torque testing shows greater variability than push-on/pull-off tests for similar combinations, and for zirconia heads on other tapers. The coefficients of friction measured (0.16-0.31) are significantly different from values typically used in stress analyses.

Biocompatible Materials↗
PubMed1999

Inaccuracy of acetabular reaming under surgical conditions.

Press-fit uncemented acetabular components require accurate implant-bone cavity fit. Ten cavities produced during actual hip arthroplasty using debris-retaining reamers were replicated in dental alginate. An experimental reamer with better cutting prepared 12 acetabulae in mortuo under similar conditions. Positives in dental stone were measured on a coordinate measuring center. Spheres of best-fit and variation of each point from these spheres were calculated. Control cavities in polyurethane foam were measured to estimate casting errors. Diametral errors of conventionally reamed cavities averaged 2.1%, whereas experimental reamers' cavities varied by 0.5% (P < .005). Overall surface variation from hemispheric form in conventionally reamed cavities exceeded the experimental reamer's results (P < .005). Conventional acetabular reamers cut bone inaccurately. Reamers designed for improved bone cutting reduce cavity errors.

Acetabulum↗
PubMed1999

Press-fit acetabular cup fixation: principles and testing.

Pre-clinical testing of the fixation of press-fit acetabular components of total hip prostheses relies on cadaver or synthetic bone, but the properties and geometry of bone models differ from those of physiological bone. Cup designs use varied mechanisms for initial stability in bone; therefore, using different analogues and tests is appropriate. Press-fit cup stability was tested in the following: firstly, polyurethane (PU) foam modelling cancellous support; secondly, glass-fibre reinforced epoxide (GFRE) tubes modelling acetabular cortical support; thirdly, cadaveric acetabula. Three commercial cups [Harris-Galante II (H-G-II), Zimmer; Optifix, Smith & Nephew, Richards; porous coated anatomic (PCA), Howmedica] and an experimental cup with enhanced rim fixation were tested in three modes: direct pull-out, lever-out and axial torque. The fixation stabilities measured in the PU and the GFRE models showed trends consistent with those in cadaver bone, differing in the oversizing and cup geometry. The experimental cup was significantly more secure in most modes than other cups; the H-G II and Optifix cups showed similar stabilities, lower than that of the experimental cup but greater than that of the PCA cup (analysis of variance and Tukey's highly significant test; p < 0.001). The stabilities measured in cadaver bone more closely approximated those in GFRE. The use of several bone analogues enables separation of fixation mechanisms, allowing more accurate prediction of in vivo performance.

Analysis of Variance↗
PubMed1998

Gothenburg osseointegrated hip arthroplasty. Experience with a novel type of hip design.

The culmination of more than 10 years of laboratory and clinical research has been the clinical trial of a novel hip arthroplasty for osseointegration. The femoral component of this Gothenburg hip is a neck retaining, threaded fixture with rotational symmetry, produced in commercially pure titanium with a specific surface texture. Proximally, a standard orthopaedic taper trunnion mates with a 28-mm diameter zirconia head that articulates against the acetabular component. The latter is also of textured commercially pure titanium, encapsulating a thick ultra high molecular weight polyethylene liner. Dedicated alignment guides and cutting instruments ensure accurate bone preparation and implant placement. Limited clinical trials commenced in 1992 and expanded to multicenter clinical trials in 1997. Every hip has been monitored with radiostereometry to measure migration to an accuracy of 0.1 mm. All calcar implanted femoral components show excellent function at 4 to 5 years followup, with no migration revealed by radiostereometry.

Animals↗
PubMed1995

Dissociation in bulimic and non-eating-disordered women.

A relationship between dissociative experiences and the eating disorders has been reported. However the nature of that link is not clearly understood. This study investigates the links between dissociation (as measured by the Dissociative Experiences Scale-DES II) and eating psychopathology in a clinical group of bulimic women and a nonclinical group of undergraduates. In the nonclinical group, specific dissociative styles were found to be linked with bulimic attitudes on the Eating Attitudes Test. In the eating-disordered group, there was an association between the scales of the DES II and frequency of bringing. This association was primarily due to the effects of the dissociative style of absorption (e.g., daydreaming). Suggestions are made for further research, and the clinical implications of the findings are discussed.

Adult↗
PubMed1988

A device for producing experimental fractures.

A device is reported for the production of transverse fractures of canine tibiae by a three-point bending technique. With strain-gauged load arms, the device enables simultaneous measurement of the bend strength of the intact bone. Results from a series of 14 dogs confirm the reproducibility of this technique.

Animals↗
PubMed1987

Carbon fiber reinforced plastic (CFRP) plates versus stainless steel dynamic compression plates in the treatment of fractures of the tibiae in dogs.

In a series of 14 dogs, fractures of both tibiae were caused by a "bone-breaker" designed in the authors' department and observed to produce a consistent and realistic canine fracture. One tibia was plated with a carbon fiber reinforced plastic (CFRP) plate and the other with a dynamic compression (DC) plate. Roentgenographic examination demonstrated healing of the CFRP-plated tibiae with abundant callus, and almost total remodeling of the fracture callus between ten and 20 weeks. Biomechanical testing by three-point bending revealed little difference between the strength of union of the fractures at 12-16 weeks. At 20 weeks, although the numbers were too small for statistical confirmation, the CFRP-plated tibiae were consistently stronger than the DC-plated tibiae.

Animals↗
PubMed1986

Designing an implant by CT scanning and solid modelling. Arthrodesis of the shoulder after excision of the upper humerus.

Techniques are described by which metal implants can be designed and produced to fit precisely a bony site at a subsequent operation. CT scans and solid modelling were used to produce an accurate three-dimensional representation of the surface of the bone. These techniques were applied to the production of an internal fixation device for shoulder arthrodesis after the resection of a neoplasm of the proximal humerus. The reconstruction utilised a free vascularised fibular graft between the scapula and the distal humeral remnant, fixation being secured with the custom-made implant.

Adolescent↗