Biomedical subjects
Publications and source records attributed to I K Ritchie.
We have assessed the current range of synthetic splinting bandages, using physical and mechanical tests and the subjective opinions of patients, volunteers and orthopaedic staff. Modern bandages have some better properties than standard plaster bandage but do not conform as well, are more expensive, and potentially more hazardous.
Fracture healing usually proceeds without difficulty. However, the diagnosis of delayed or non-union is not simple and can present difficulties in management. Normal fracture healing is briefly reviewed along with some methods of assessing the progress of union. The results of using the technique of impedence osteography in a preliminary study of fracture healing are presented. These indicate that the technique can clearly show a fracture and differentiate between normal bone, a united fracture and a non-union.
We used the Aberdeen impedance imaging system to drive a constant current of 1 mA on a 10 kHz sine wave into the upper arm encircled by an elastic belt of 16 equi-spaced strip electrodes. The system was used to examine a normal upper arm, an upper arm with a recent humeral fracture and an upper arm with a clinically united fracture. We approximated the human upper arm to a circular cylinder and assumed bilateral symmetry of normal human limbs. We measured transverse limb resistivity ratios and reconstructed static two-dimensional images of the spatial distribution of log(resistivity) by the equipotential back projection technique using a homogeneous muscle equivalent saline reference. Our results indicate that impedance osteography provides unique information about the changing electrical characteristics at the fracture site. This information could prove a useful adjunct to clinical and radiological tests for fracture union.
The occurrence of a fracture in a limb is accompanied by large changes in the electrical characteristics of the region. Resistivity of bone is more than a hundred times that of bone. The relative permittivities of the two are also different. The fracture site is also known to be electronegative. Electrical Impedance Imaging is capable of reconstructing a two dimensional (2D) representation of the average distribution of amplitude and phase in a three dimensional (3D) region. The spatial resolution in impedance imaging is low, yet the technique is sensitive to properties that are rapidly changing in growing tissues. Though the reconstructed image is an average of a thick slice, this may be of some advantage in impedance osteography precluding the need for imaging multiple planes to cover the extent of the fracture. We used the Aberdeen Impedance Imaging System which uses the 4 electrode technique in a split array, and a current of 1 milliampere on a carrier of 10 kHz to collect a number of data sets. The averaged data sets were used to reconstruct images by the Equipotential backprojection method. In this pilot study we concentrated on the real part of the complex impedance to produce images of log resistivity. The a-priori assumption of bilateral symmetry of human limbs allowed us to reconstruct equivalent regions of the normal and fractured limbs by inverting the electrode array. We obtained static images of the distribution of log resistivity when we used a homogeneous distribution as a reference, and a differential image comparing the fractured to the normal limb. The three patients in our study were at different clinical stages of fracture healing as confirmed by radiography. Our results show the feasibility of using the technique to study and monitor fractures during the healing process.
The potential fire hazard associated with polyurethane impregnated fibreglass bandages has been investigated. Tests have been carried out in accordance with the most appropriate British Standard (BS5438:1976). Results of these tests show that polyurethane impregnated fibreglass bandages do not represent a serious risk to a wearer as the rate of heat transfer through the casts is sufficiently rapid to alert the wearer of the proximity of a heat source before the cast ignites.
The airborne dust generated when cutting splinting bandages represents a potential respiratory hazard, particularly to those who regularly remove casts with a power saw. Plaster of Paris (POP) dust is already classified by the Health and Safety Executive as a nuisance dust. This paper reports on a study to determine the nature, size and concentration of dust produced when cutting polyurethane (PU) impregnated bandages using a power saw. It has been shown that, under severe conditions PU bandages produce lower airborne dust concentrations than POP bandage but that all of the bandages tested produced particles small enough to reach the final divisions of the lung. It is therefore recommended that a dust extraction unit be used when cutting all types of bandage.
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The introduction of polyurethane (PU) resin impregnated fibreglass bandages is likely to have a significant effect on modern orthopaedic practice. The manufacturers of these products claim many improved properties compared to plaster of Paris bandages, such as , high strength to weight ratio, rapid setting time and high radiolucency. This paper reports on a series of mechanical tests designed to assess the strength, flexibility, working time and wear properties of the current range of fibreglass bandages and to compare them with plaster of Paris bandages. The results have clearly demonstrated that the fibreglass bandages are mechanically superior and offer numerous advantages over plaster of Paris for use as the definitive casting material for both weight-bearing and non-weight-bearing casts.
Plaster of Paris (P.o.P.) bandage has been the pre-eminent external splinting material for over 150 years and from time to time synthetic alternatives have been tried. So far none has seriously challenged the dominance of P.o.P. as a primary or secondary material in the management of fractures. The recent introduction of Polyurethane coated fibreglass bandage appears to offer a more serious challenge than previous contenders. This technical note reviews bandage type splinting materials and explains some of the properties of the PU materials.
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