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Biomedical subjects

J R Atkinson

Publications and source records attributed to J R Atkinson.

At least 19 recordsLinked to original sources
PubMed1992

A tribological study of retrieved hip prostheses.

One hundred Charnley cemented acetabular cups, 78 of which had the associated femoral stems, were obtained after revision surgery. Patient characteristics, which were obtained from hospital records, and roentgenographs showed that component loosening was the most common cause of failure. Examination of the acetabular cups revealed six categories of damage: socket erosion, rim wear, cement ingress, cratering, discoloration, and articulating surface scoring. Damage to the femoral stems was characterized by stem fracture and roughening of the femoral head. The latter was predominantly caused by the roentgenographic contrast medium within the acrylic cement scratching the articulating surface. The amount of wear, in terms of the penetration of the femoral head into the acetabular cup, could be measured in 87 cases. The mean penetration was 1.69 mm and the mean penetration rate was 0.21 mm per year with a range from less than 0.005 mm to 0.6 mm per year. It was shown that within this group, a high penetration rate precludes a long service life. It is therefore likely that reducing the rate of wear would improve the performance of the artificial hip joint.

Acetabulum↗
PubMed1988

Neuropeptide Y is a vasoconstrictor of human coronary arteries.

Neuropeptide Y (NPY) is a 36-amino-acid polypeptide which coexists with catecholamines in many adrenergic and noradrenergic neurons. It has been demonstrated to exert pressor effects in the perfused guinea pig heart and to constrict large cerebral and coronary blood vessels in animal studies. To determine if NPY might be a human coronary vasoconstrictor, the authors studied its effect on postmortem human coronary arteries. Proximal epicardial coronary rings were studied in a superfusion apparatus in Krebs-Ringer bicarbonate buffer (37 degrees C, pH 7.4) presaturated with 95% O2-5% CO2. Concentration-response curves were obtained using NPY in 0.1% bovine serum albumin in buffer and the responses were compared to those obtained in the presence of alpha 1, beta, and cyclooxygenase antagonists. A dose-related constrictor effect was obtained with NPY, which was significantly more potent than noradrenaline, constriction often being seen at 10(-12) M concentration. A vasorelaxant effect was seen in nonatherosclerotic vessels at higher concentrations. The vasoconstriction produced by noradrenaline was potentiated by subthreshold concentrations of NPY. The vasoconstrictor effect of NPY was not inhibited by prazosin (10(-6) M), and the vasodilatory effect was not inhibited by propranolol (10(-5) M). Indomethacin (3 X 10(-6) M) did not alter either vasoconstriction or vasorelaxation. The authors conclude that NPY is a potent constrictor of the human coronary artery at concentrations that may be achievable in vivo; it may thus be a contributor to sympathetic enhancement of coronary artery tone.

Coronary Vessels↗
PubMed1987

External wear of the polyethylene socket in cemented total hip arthroplasty.

We examined 59 cemented high density polyethylene sockets removed at revision hip arthroplasty. Of these 19 showed areas of wear between the outside of the socket and the acetabular bone. This was associated with lack of acrylic cement in those areas and was also related to the depth of the wear on the articulating surface of the socket. It is suggested that, in some cases, changes at the bone-cement junction are secondary to socket loosening and abrasion against the bone of the acetabulum, rather than to particles migrating from the metal-polyethylene interface. It is therefore important that impingement of the neck of the femoral stem on the edge of the cup be avoided and that, when the socket is inserted, it is not in direct contact with the bone.

Acetabulum↗
PubMed1984

Silane crosslinked polyethylene for prosthetic applications. II. Creep and wear behaviour and a preliminary moulding test.

Creep and wear tests have been carried out on a high density polyethylene crosslinked using a silane. A comparison of the results with those obtained for ultra high molecular weight polyethylene (RCH 1000) indicates the superiority of the crosslinked material. It can be injection moulded without difficulty. It is our conclusion that silane crosslinked polyethylene is an exciting prospect in the field of prosthetic materials.

Biocompatible Materials↗
PubMed1983

Silane cross-linked polyethylene for prosthetic applications. Part I. Certain physical and mechanical properties related to the nature of the material.

Certain physical and mechanical tests have been conducted and scanning electron microscopy carried out in order to characterize a high density polyethylene cross-linked using vinyl trimethoxysilane. It is suggested that this cross-linked polyethylene could be an alternative to high molecular weight polyethylene for prosthetic applications.

Biomechanical Phenomena↗
PubMed1980

Materials for internal prostheses: the present position and possible future developments.

In this paper we consider solid phase forming as a method of manufacturing acetabular cups. Static and cyclic creep tests have been carried out on Charnley cups and indicate that creep, rather than wear, plays the major role in the penetration of the socket by the femoral ball, at least in the first few years. We have investigated a new type of cross-linked polyethylene and found it to be extremely good from both a wear and creep viewpoint, particularly under high loads and at high sliding velocities.

Alloys↗
PubMed1978

The characteristics of acetabular cups worn in the human body.

In laboratory tests, the ultra-high molecular weight polyethylene used for the acetabular cups of Charnley hip prostheses has a very low wear rate against steel. In the body radiographic measurements indicate that the polyethylene wears more rapidly. In order to investigate this higher wear rate, the sockets of acetabular cups removed at post-mortem have been examined using optical and electron microscopy. It has been shown that a socket wears predominantly on its superior part and that this is a direct consequence of the orientation of the cup in the body and the direction of loading of the hip. In the worn region the femoral head in effect bores out a new socket for itself, a process which is visible with the naked eye after approximately eight years. Electron microscopy shows that the predominant wear mechanism is adhesion, but after about eight years the appearance of surface cracks suggests that surface fatigue is taking place in addition to this. Laboratory wear tests have shown that pure surface fatigue is not sufficient to account for the high clinical wear rate. Other deformation processes are suggested and discussed with regard to the higher clinical wear rate.

Acetabulum↗
PubMed1973

Cortical blood flow in controlled hypotension as measured by thermal diffusion.

A thermal diffusion flow probe which gave a continuous, dynamic, quantitative record of cortical blood flow (CBF) was used to assess CBF in experimental animals with controlled hypotension. Acute hypotension was produced by trimethaphan camsylate, halothane, and sodium nitroprusside. Halothane produced less reduction in CBF per drop in blood pressure than the other two agents.

Anesthesia, Intravenous↗