Publications
40 results found
Macdonald W, Carlsson LV, Charnley GJ, et al., 1999, Press-fit acetabular cup fixation: principles and testing, Proc Inst Mech Eng [H], Vol: 213, Pages: 33-39, ISSN: 0954-4119
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.
Macdonald W, Carlsson LV, Charnley GJ, et al., 1999, Inaccuracy of acetabular reaming under surgical conditions, J Arthroplasty, Vol: 14, Pages: 730-737, ISSN: 0883-5403
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.
Albrektsson T, Carlsson LV, Jacobsson M, et al., 1998, Gothenburg osseointegrated hip arthroplasty. Experience with a novel type of hip design, Clin Orthop Relat Res, Vol: 352, Pages: 81-94, ISSN: 0009-921X
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.
Macdonald W, Swarts E, Beaver R, 1993, Penetration and shear strength of cement-bone interfaces in vivo, Clin Orthop Relat Res, Vol: 286, Pages: 283-288, ISSN: 0009-921X
Using sham replacement of the proximal femur in adult mongrel dogs, shear strength at the interface between polymethylmethacrylate bone cement and cancellous bone has been found to be linearly dependent on the depth of penetration of the cement into the bone. Shear strength at the interface was increased by 82% and penetration by 74% when distal bone plugging, pressure lavage, and pressurized insertion of cement were employed. Use of a lower-viscosity cement gave a further 18% increase in penetration and shear strength. There was no film of blood at the cement-bone interface with pressurized insertion of Simplex P and Palacos R cements.
Rosenstein A, Macdonald W, Iliadis A, et al., 1992, Revision of cemented fixation and cement-bone interface strength, Proc Inst Mech Eng [H], Vol: 206, Pages: 47-49
Interfacial shear strength between poly(methyl methacrylate) (PMMA) bone cement and cancellous bone was measured in bone samples from human proximal femora. Samples were prepared with fresh cement-bone, fresh cement inside a mantle of existing cement and with fresh cement-revised bone surfaces. Push-out tests to measure shear strength caused failure only at bone-cement interfaces; revised bone interfaces were 30 per cent weaker (P < 0.02) than primary interfaces. The clinical relevance is that revision of cemented joint arthroplasties may necessitate removal of components with sound cement-bone fixation. The practice of removing all traces of PMMA cement may not yield the optimal fixation; adhesion of fresh cement to freshly prepared surfaces of the existing cement might also be considered where circumstances are favourable.
Macdonald W, Atkins RM, 1990, An algometer for the automated measurement of pain threshold, Brit. J. Rheumatol, Vol: 29, Pages: 454-455
Macdonald W, Owen JW, 1988, The effect of total hip replacement on driving reactions, Journal of Bone and Joint Surgery, Vol: 70-B, Pages: 202-205
The driving reactions of 25 patients were assessed before and after operation for hip replacement. Driving reactions were tested by monitoring the delay and force of brake application after an emergency signal, using a simulated driving control system. Fifteen normal subjects were also tested. Statistical analysis demonstrated significant differences between patients with either left or right hip replacement and between pre- and postoperative testing. Most patients improved by the eighth week, but some had deteriorated and did not recover until re-tested eight months after operation. It is concluded that for most patients eight weeks' delay for return to driving is appropriate, but for a minority of patients with right hip replacement recovery of reaction speed requires longer rehabilitation.
Macdonald W, Skirving AP, Scull ER, 1988, A device for producing experimental fractures., Acta Orthop Scand, Vol: 59, Pages: 542-544
Skirving AP, Day R, Macdonald W, et al., 1987, Carbon fiber reinforced plastic (CFRP) plates versus stainless steel dynamic compression plates in the treatment of fractures of the tibiae in dogs, Clin Orthop Relat Res, Vol: 224, Pages: 117-124
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.
Macdonald W, Thrum CB, Hamilton SG, 1986, Designing an implant by CT scanning and solid modelling. Arthrodesis of the shoulder after excision of the upper humerus, Journal of Bone & Joint Surgery (British), Vol: 68-B, Pages: 208-212, ISSN: 0301-620X
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.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.