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Biomedical subjects

J G Thacker

Publications and source records attributed to J G Thacker.

At least 73 records · Page 4Linked to original sources

Mechanical performance of a work hardened pointed surgical wire.

The design and material properties of a surgical wire have been enhanced to improve its performance in surgery. One blunt end of the wire has been honed to a point to decrease the axial compressive force required to penetrate tissue. In addition, its sharp end has been work hardened to increase its yield strength. The mechanical performance of this wire has been characterized by a series of in vitro experiments and a clinical trial.

Bone Wires↗

Heat welding for surgical sutures.

The purpose of this experimental study was to test the potential value of heat welding to cut the ends of knotted surgical sutures. This heat process resulted in knot security in a coated polyglactin suture with fewer throws than those needed for the same suture with knotted ends cut by scissors. Results of mechanical performance testing of the knotted sutures cut either by scissors or welding did not differ significantly. With refinements in the technical design of the heat source, suture welding may have important applications in surgery.

Hot Temperature↗

Evaluation of a new, improved surgical drainage system.

A new, improved drainage system has been specifically designed to provide either closed suction drainage for the ambulating patient or sump drainage for the patient confined to bed. This drainage system is made of silicone that has a hydrogel coating with a low coefficient of friction. This coating facilitates removal of the drain from the wound cavity and reduces the adherence of blood clots in the drainage system. A filter assembly is attached to the air vent lumen to remove particulate matter and bacteria from the air. Clinical evaluation of the filtered sump drainage system has confirmed its superiority over closed suction in its efficiency of removing fluids from the wound.

Drainage↗

Wheelchair tire rolling resistance and fatigue.

The hysteresis loss theory of rolling resistance is developed for solid rubber wheelchair tires. The analysis is used to correlate test data for a clay-filled natural rubber and a polyurethane tire material. A discussion of tire rolling work, hysteresis loss factor measurement, and rolling loss measurement is presented. An example calculation of rolling resistance for a polyurethane tire is given in detail. The subject of solid rubber tire design is developed on the basis of recommended fatigue life theory and practice. It is shown that polyurethane tires have a useful fatigue life due to a high shear modulus at useful values of hardness. This characteristic of polyurethane, if exploited, is predicted to lead to a tire with a lower rolling resistance than other wheelchair tires available. The effect of surface roughness on rolling resistance is briefly discussed and some experimental results are listed. The purpose of this paper is to give the rehabilitation engineer the means for wheelchair tire rolling resistance and fatigue life design and the methods to assess the tire characteristics when a tire design is modified or a new tire material is contemplated. Other important design factors, such as wear and chemical degradation, are not discussed, but references are suggested for information on these topics. As in most research and development projects, this study raises problems which need further work. For example, the fatigue properties of the rubber compounds employed in this application are not completely understood; this subject is planned for future investigation.

Equipment Design↗

Wheelchair caster shimmy and turning resistance.

The equations for wheelchair caster wheel shimmy are presented along with experimental data. The report includes the theory and performance of single wheel casters for a variety of tires, and a new design for wheelchair casters using a grooved dual-tread tire or co-rotating caster wheels. The dual-tread tire was found to significantly inhibit caster shimmy. The turning resistance due to a grooved caster wheel tire with a 1/2-inch groove was found to be 10 percent greater than for an ungrooved caster wheel tire. The analysis includes the methodology and the results of experiments developed to measure the sliding friction turning moment of the wheelchair caster wheel. A number of commercial wheelchair caster wheels were tested and the results for shimmy are presented.

Equipment Design↗

Knotting and handling characteristics of coated synthetic absorbable sutures.

The purpose of this study was to evaluate the knotting and handling characteristics of the new coated synthetic absorbable sutures. When compared to the coated polyglactin 910 sutures, the coated polyglycolic acid sutures displayed a lower coefficient of friction, encountered less tissue drag forces, and exhibited less flexural rigidity. In the case of sizes O, 2-O, and 3-O coated polyglycolic sutures, knot security was achieved with one less throw than with similar sizes of coated polyglactin 910 sutures. On the basis of these comprehensive mechanical performance tests, the knotting and handling characteristics of the coated polyglycolic acid sutures were judged to be superior to that of the coated polyglactin 910 sutures.

Absorption↗

Mechanical performance of polyglycolic acid and polyglactin 910 synthetic absorbable sutures.

The mechanical performance of polyglycolic acid and polyglactin 910 sutures has been assessed using standardized reproducible tests. The results of these studies demonstrated distinct differences in their performance that can be related, in part, to their structural configuration. The size of the 4-0 polyglactin suture was significantly larger than that of the 4-0 polyglycolic acid suture. Since the strength of any suture is proportional to its cross sectional area, the strength of unknotted and knotted polyglactin 910 sutures was signficantly greater than that of the polyglycolic acid sutures. The strength of both sutures was similarly diminished by the formation of the knot. When these sutures were added to tissue, the breaking strength was even further reduced. The rate of decline in breaking strength of the two absorbable sutures in healing skin wounds was comparable. These absorbable sutures displayed knot security with a two throw square knot, 1 = 1. The ability of these sutures to reach knot break with this knot configuration is characteristic of sutures in which the surface exhibits a high coefficient of friction. Their rough surface also caused them to drag through tissue, making difficult to adjust tension on a continuous running suture.

Absorption↗

Mechanical performance of sutures in surgery.

In this study, we have compared the recommended configuration of a knot with specified sutures as ascertained by mechanical performance tests to that employed by a group of board-certified surgeons. Agreement between the surgeon and the results of the test was encountered in only one fourth of the instances. In another one fourth of the cases the surgeon overestimated the number of throws required for a knot to reach knot break. This additional suture material further handicaps the host's defenses, thereby inviting infection. Surgeons employed knots that untied without reaching knot break in the remaining half of the cases. The holding power of many of the knots that untied was substantially less than that of knots reaching knot break. On the basis of the study, it is recommended that results of the mechanical performance tests be made readily available to the surgeon so that his patient can receive maximal benefits from the knotted suture with the least damage to the host's defenses.

Evaluation Studies as Topic↗

Management of soft tissue injury.

The fate of a surgical wound is held in a delicate balance between the host's resistance to infection and the causal factors of infection. Considerable insight into this relationship between the host and pathogen can be gained from the results of quantitative bacteriologic measurements. Newer rapid slide techniques have been developed which provide the surgeon with this information within 20 minutes. In most soft tissue injuries, the wound bacterial count gives an accurate prediction of subsequent infection. Wounds combining greater than 10(5) bacteria per gram of tissue are destined to develop infection. When the bacterial count is below that level, the wounds will usually heal per primam without infection. This large number of bacteria required to elicit infection reflects the remarkable ability of soft tissues to resist infection. This state of high resistance to infection can be reduced by several factors which include circulatory embarrassment, tissue injury, dead space, and the presence of foreign bodies (dirt, sutures, drains, etc.). When treating soft tissue injuries, the surgeon must employ specific therapeutic modalities that allow the wound to heal per primam without infection. On the basis of experimental studies supported by clinical experience, the following treatment protocol for soft tissue injuries is recommended. Using strict aseptic technique, the wound must be first anesthetized with 1 per cent Xylocaine to permit painless sound cleansing. All wounds should be subjected to high pressure syringe irrigation to remove bacteria, foreign bodies, and blood clots. When necessary, debridement of all devitalized tissue should be performed with a stainless steel scalpel. Many wounds caused by sharp wounding agents contain no foreign bodies and few bacteria and exhibit considerable resistance to infection. In these wounds, primary closure can be initiated after irrigation without the development of infection. Wounds resulting from impact forces have a diminished resistance to infection and are susceptible to infection by low level of bacterial contamination. Immediate antibiotic treatment of patients with impact injuries subjected to meticulous debridement and cleansing will permit a safe primary closure. In wounds contacted by pus or feces, open wound management followed by delayed primary closure is usually indicated. Antimicrobial prophylaxis is also recommended for patients with such wounds. Ideal postoperative care of all traumatic wounds includes a surgical dressing and immobilization and elevation of the site of injury.

Anesthesia, Local↗

Finite deformation theory for in vivo human skin.

A finite deformation mathematical model of in vivo human skin has been developed for the normal physiological load range. Uniaxial load-deformation measurements were carried out with a non-invasive extensometer and utilized in formulating the model. The in vivo strain energy function was found to be a linear function of the first two strain invariants and a quadratic function of the third strain invariant. Only three independent constants were necessary to specify the strain energy function completely for the upper extremities of human volunteers.

Adult↗

Practical applications of skin biomechanics.

The biomechanical properties of skin have an important influence on plastic surgical decisions. They aid the surgeon in planning elective incisions, excisions, or scar revisions. They provide insight into the most appropriate method of coverage of skin defects as well as the design of an artificial skin substitute. Skin biomechanics can, in part, be characterized in vivo by either a skin extensiometer or by studying the deformation of skin defects. These methods indicate the magnitude and directional orientation of skin tensions which are dependent partly on the mechanical characteristics of the dermal fibers and partly on the pattern in which they are woven. The tensions to which the skin are subjected can be classified as either static or dynamic in origin. Static skin tensions are the natural tensions existing in skin. The magnitude of static tensions varies between individuals, at different sites in the same person, and in different directions in many sites. The dynamic tensions are caused by a combination of forces which are associated with joint movement, mimetic and other voluntary muscle activity, and gravity. Knowledge of these tensions allows the surgeon to align the operative site in the direction of maximal tension and to approximate the wound with the least amount of tension. As a consequence of this, the scar healing between the cut edges of the wound should be narrow and inconspicuous.

Biomechanical Phenomena↗

Cleansing the traumatic wound by high pressure syringe irrigation.

The purpose of this study was to examine the influence of the fluid dynamics of syringe irrigation on the efficacy of wound cleansing and the infection rate of experimental wounds. The pressure experienced by a surface following wound irrigation was directly proportional to the pressure within the syringe and the size of the needle. High pressure syringe irrigation effectively removed bacteria from the surface of the wound. This reduction in the wound bacterial count resulted in a decrease in the infection rate of tissues. Low pressure irrigation with an asepto syringe did not significantly cleanse the wound of its bacterial contaminants and had no demonstrable clinical merit. On the basis of these studies, high pressure syringe irrigation is being employed routinely in our emergency department for the care of traumatic wounds.

Animals↗

Side-effects of high pressure irrigation.

This study was undertaken to identify side-effects of high pressure irrigation. Standardized surgical wounds made in Yorkshire pigs were subjected to high pressure syringe and pulsatile irrigation. As a result of these treatments, fluids were disseminated into the adjacent tissue of the wound, predominantly in a lateral direction. Bacteria did not accompany this disseminated fluid and apparently were filtered out by the surface tissues. This treatment results in a tissue injury which impairs its defenses, making the wound more susceptible to infection. However, the remarkable cleansing capacity of high pressure irrigation appears to outweigh this side-effect, since heavily contaminated wounds subjected to this treatment heal per primum without infection.

Animals↗

Mechanical cleansing of contaminated wounds with a surfactant.

Mechanical cleansing of a wound with a sponge soaked in a surfactant has prevented the development of experimental wound infection. The surfactant utilized for wound cleansing is Pluronic F-68, a member of a family of block copolymers called Pluronic polyols. Long-term toxicity studies and clinical trials suggest that this surfactant is safe for human use. Pluronic F-68 is a nonionic detergent that does not have any intrinsic antibacterial activity. Although mechanical cleansing with saline-soaked sponges effectively removes bacteria, it damages the wound and impairs its resistance to infection. The severity of the damage to the skin exerted by the sponge can be correlated with its porosity. Sponges with a low porosity are abrasive and exert more damage to skin than do sponges with a higher porosity. The addition of Pluronic F-68 to even the most abrasive sponges ensures that the bacterial removal efficiency of the sponge scrub is maintained, while tissue trauma is minimized. This dual effect of the surfactant results in a dramatic reduction in the infection rate of contaminated wounds. On the basis of these results, a clinical trial with surfactant-soaked sponges would appear to be indicated.

Animals↗