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Biomedical subjects

J R Field

Publications and source records attributed to J R Field.

14 recordsLinked to original sources
PubMed1999

The influence of screw omission on construction stiffness and bone surface strain in the application of bone plates to cadaveric bone.

Biological fracture repair is becoming an increasingly popular means of fracture fixation. This technique involves a reduction in the amount of surgical trauma thereby preserving vascular supply and soft-tissue integrity combined with the implantation of less hardware. The aim is the stimulation of callus formation as the means by which fracture union occurs. This paper describes the mechanical effect of the symmetrical omission of screws on construction stiffness and bone surface strain following the application of bone plates to cadaveric bone. The influence of the pattern of screw omission was evaluated in both intact and osteotomized bone specimens. The application of bone plates using certain patterns of screw omission did not significantly effect the stiffness of the final construction whilst inherent bone surface strain was increased. It was concluded that the omission of screws in certain defined patterns for a given plate-bone construction may meet the criteria for 'biological fixation'. There was no apparent deleterious effect on structural stiffness following the omission of 40% of the total screw complement from a plate-bone construction.

Animals↗
PubMed1999

Semi-quantitative assessment of tibial blood flow and distribution in response to surgical intervention using first pass radionuclide angiography and intravascular vital dye.

The acute vascular response in bone to surgical trauma was investigated utilizing a sheep model. Blood flow and distribution were determined using two methods; perfusion of the vasculature with an intravascular vital dye (Disulphine blue) prior to euthanasia and by radionuclide angiography (RNA) before and after each surgical intervention. The pattern of Disulphine blue distribution provided a good indication of local perfusion and response to surgical trauma (drilling holes). Radionuclide angiography provided a dynamic image of the vascular response to surgical trauma. The generation of time activity curves of the first pass of radionuclide bolus enabled calculation of the relative blood flow through selected regions. For both techniques areas of ischaemia were apparent which were directly related to the location of screw holes. We conclude that factors other than bone plate contact influence the ischaemia that develops in bone subsequent to the application of bone plates.

Animals↗
PubMed1998

The influence of screw torque, object radius of curvature, mode of bone plate application and bone plate design on bone-plate interface mechanics.

Using Fuji Prescale Pressure Sensitive Film we evaluated the influence of screw torque, object radius of curvature, mode of bone plate application (compression or neutral loading) and bone plate design on bone-plate interface mechanics. Testing was performed using 4.5 mm and 3.5 mm dynamic compression (DC) (stainless steel) and limited contact-dynamic compression (LC-DC) plates (titanium). Plexiglass tubing, having different radii of curvature, was used to simulate bone but having more uniform geometric and structural properties. With the film interposed between the bone plate and the plexiglass, bone plates were applied at predetermined levels of screw torque. The resultant image was digitized and then underwent computer-assisted analysis to yield the interface contact area (%) and the average force (in Newtons N) between the bone plate and the object to which it was applied. In any given object, screw torque had the most significant influence on both interface contact area (P = 0.0001) and average force (P = 0.0001) at the interface. The bone plates responded differently to dynamization. The DC plate, when applied in compression loading mode, was lifted off the object between the two central screws when compared to the same plate applied in neutral loading mode (P = 0.0001). Conversely, in the LC-DC plate, an increase in the overall interface contact area was observed when applied in compression loading mode (P = 0.0002). At a given level of applied screw torque, the object radius of curvature appeared to be a major determining factor for interface contact area and average force (P = 0.0001, P = 0.0001). We conclude that variables other than bone plate design also influence the interface contact area and average force between a bone plate and object to which it is applied.

Biomechanical Phenomena↗
PubMed1997

Bone plate fixation: an evaluation of interface contact area and force of the dynamic compression plate (DCP) and the limited contact-dynamic compression plate (LC-DCP) applied to cadaveric bone.

OBJECTIVES: To determine the effects of bone morphology on the interfacial mechanics of bone plate fixation. DESIGN: A comparison of two bone plate designs using measures of contact area and force in three conditions of bone type. INTERVENTION: The influence of bone plate design, bone type, and implant location on interfacial characteristics of contact area and average force were evaluated using pressure-sensitive film in cadaveric bone. Data were quantitated using computer-assisted image analysis. MAIN OUTCOME MEASUREMENTS: Means of the two dependent variables in each of the three conditions were compared using analysis of variance. RESULTS: In human femora and equine third metacarpi, there were no apparent differences in interface contact area attributed to bone plate design, although there were significant differences for interface contact force. In humeri, significant differences in both interface contact area and force were found between bone plate designs. CONCLUSIONS: Results show that bone surface topography and implant location are major determinants of the interfacial elements of contact area and average force between a plate and the bone to which it is applied.

Animals↗
PubMed1989

Equine laminitis--another hypothesis for pathogenesis.

Laminitis is an important condition in horses and ponies, not just because of the seriousness of the clinical signs and systemic changes involved, but because of the potentially poor prognosis and likelihood of recurrence. Laminitis is particularly prevalent in ponies and involves a multiplicity of aetiological factors. Fat ponies and those having previously suffered laminitis were found to be far more intolerant to oral glucose loading (1 g/kg bwt) than normal ponies or Standardbred horses. These ponies also exhibited a far greater response in plasma insulin levels after glucose loading. Insulin response tests (0.4 iu/kg bwt insulin intravenously) showed only a minimal and very protracted response in both the fat and laminitic ponies establishing the existence of an apparently innate insulin insensitivity in these animals. These findings are important in regulation of carbohydrate and lipid metabolism and play a role in the pathogenesis of laminitis. The reduction of insulin effectiveness leads to elevation in thromboxane A2 activity, predisposing the animal to peripheral vasoconstriction, compromisation of blood flow to the foot and the development of laminitis.

Animals↗
PubMed1986

Glucose tolerance and insulin sensitivity in ponies and Standardbred horses.

The existence of an innate insulin insensitivity in ponies was investigated and compared with the situation in larger breeds of horse. Ponies that were fat or had previously suffered laminitis were found to be far more intolerant to oral glucose loading (1 g/kg bodyweight [bwt]) than normal ponies or Standardbreds. These ponies also exhibited a far greater response in plasma insulin levels after glucose loading. Insulin response tests (0.4 iu/kg bwt insulin intravenously) showed only a minimal and very protracted response in both the fat and laminitic groups. The relevance of these findings in regulation of carbohydrate and lipid metabolism, and their role in the pathogenesis of hyperlipaemia, are discussed.

Animals↗
PubMed1985

Current concepts of hyperlipaemia in horses and ponies.

Hyperlipaemia is an important condition in ponies, not just because of the seriousness of the clinical signs and biochemical changes involved, but because of the distress it causes owners and breeders that have had animals suffer from it. Hyperlipaemia occurs most commonly in fat ponies in late pregnancy and is rarely seen in larger horses. The syndrome has similarities with conditions in other species but the definitive aetiologies are not yet known. The condition in ponies is undoubtedly related to stress. The biochemical mechanisms involved in equine hyperlipaemia are considered and an hypothesis of possible pathogenesis is put forward. This hypothesis is tested by presenting the results of a preliminary study to evaluate glucose and lipid metabolism in horses and ponies. It appears that the pony is markedly insensitive to insulin compared to larger horses which means that triglycerides are more readily mobilised and the animal is therefore susceptible to hyperlipaemia in a situation of negative energy balance. The effect of stress is to increase cortisol levels which only exacerbates the insulin insensitivity and so creates a vicious circle. The importance of an innate insulin insensitivity may also be important in the pathogenesis of such conditions as laminitis.

Animals↗
PubMed1980

Stress management: a multimodal approach.

This newly developed stress-management program evolved from study of the three major trends in stress research: psychological, physiological and sociological. Primarily geared to managers in an industrial setting, this program helps the individuals to reduce physiological tension via autohypnosis and alter stress-producing behaviors through a number of cognitive restructuring techniques. A variety of philosophical issues are raised that relate to 'type A' behavior focusing on 'the hurry syndrome', aggression and a general balance in 'life tasks'. In addition, there is an educational component and participants are acquainted with their 'health probabilities' in terms of life style, weight, smoking and other factors. This multimodal program follows participants over a 2-year period to reinforce psycho-behavioral changes.

Cognition↗
PubMed1970

Host resistance and survival in carcinoma of breast: a study of 104 cases of medullary carcinoma in a series of 1,411 cases of breast cancer followed for 20 years.

This paper deals with a special type of mammary carcinoma, generally of high-grade malignancy, which carries a remarkably good prognosis-the so-called "medullary carcinoma of the breast with lymphoid infiltrate." Probably the increased lymphoid tissue seen in these tumours is concerned with cell-mediated and humoral immunological reactions and reflects a strong host-defence mechanism which is responsible for the remarkably high survival rates following radical treatment. Since the evidence for host resistance to malignant disease is based largely on animal data, the opportunity to study a group of patients followed for 20 years, in whom this type of defence reaction appears to exist, is of considerable clinical interest.Among 1,411 cases of breast cancer there were 104 with medullary carcinoma (7.4%), for which the corrected 5- to 20-year survival rates have been calculated. After 20 years 74% of cases with operable medullary tumours were alive, compared with 14% of cases with similar stage non-medullary cancer. In the presence of histologically proved axillary metastases the 20-year survival rate was 61% for medullary cases, compared with only 13% for other types of breast cancer.In 30 cases of medullary cancer in which the axilla was free, the corrected 20-year survival rate was 95% following a combination of radical operation and radiotherapy. No evidence could be found that axillary dissection or postoperative irradiation is harmful to women with operable highly malignant breast cancer in whom a well-marked host resistance is thought to be present. A combination of radical mastectomy and postoperative irradiation appears to be the most effective treatment for such cases. The present grounds for rejecting a radical approach to treatment of breast cancer, based on current immunological considerations, are regarded as being quite inadequate.

Breast Neoplasms↗