Exothermic properties of plaster–synthetic composite casts

Purpose

Plaster casts can cause burns. Synthetic casts do not. Composite plaster–synthetic casts have not been thoroughly evaluated. This study analyzed the temperature from plaster casts compared with composite casts in a variety of in vitro conditions that would simulate clinical practice.

Methods

A Pyrex cylinder filled with constant body temperature circulating water simulated a human extremity. Circumferential casts, of either plaster or composite construction (plaster inner layer with outer synthetic layer), were applied to the model. Peak temperatures generated by the exothermic reactions were studied relative to the following variables: dip water temperature (24 °C versus 40 °C), cast thickness (16, 30, and 34 ply), and delayed (5-min) versus immediate application of the synthetic outer layers. Peak temperatures from the all-plaster casts were compared with the composite casts of the same thickness. Finally, the relative cast strength was determined.

Results

Potentially dangerous high temperatures were measured only when 40 °C dip water was used or when thick (30- or 34-ply) casts were made. Cast strength increased with increasing cast thickness. However, the presence of synthetics in the composite casts layers did not increase cast strength in every case.

Conclusion

When applying composite casts, the outer synthetic layers should be applied several minutes after the plaster to minimize temperature rise. Composite casts do not routinely generate peak temperatures higher than plaster casts of similar thickness. Because the skin of children and the elderly is more temperature-sensitive than average adult skin, extra care should be taken to limit the exothermic reaction when casting children and the elderly: clean, room temperature dip water, minimal required cast thickness, avoidance of insulating pillows/blankets while the cast is drying.     

Diagnosis of periprosthetic infection following total hip arthroplasty – evaluation of the diagnostic values of pre- and intraoperative parameters and the associated strategy to preoperatively select patients with a high probability of joint infection

Background

Most cast materials mature and harden via an exothermic reaction. Although rare, thermal injuries secondary to casting can occur. The purpose of this study was to evaluate factors that contribute to the elevated temperature beneath a cast and, more specifically, evaluate the differences of modern casting materials including fiberglass and prefabricated splints.

Methods

The temperature beneath various types (plaster, fiberglass, and fiberglass splints), brands, and thickness of cast material were measured after they were applied over thermometer which was on the surface of a single diameter and thickness PVC tube. A single layer of cotton stockinette with variable layers and types of cast padding were placed prior to application of the cast. Serial temperature measurements were made as the cast matured and reached peak temperature. Time to peak, duration of peak, and peak temperature were noted. Additional tests included varying the dip water temperature and assessing external insulating factors. Ambient temperature, ambient humidity and dip water freshness were controlled.

Results

Outcomes revealed that material type, cast thickness, and dip water temperature played key roles regarding the temperature beneath the cast. Faster setting plasters achieved peak temperature quicker and at a higher level than slower setting plasters. Thicker fiberglass and plaster casts led to greater peak temperature levels. Likewise increasing dip-water temperature led to elevated temperatures. The thickness and type of cast padding had less of an effect for all materials. With a definition of thermal injury risk of skin injury being greater than 49 degrees Celsius, we found that thick casts of extra fast setting plaster consistently approached dangerous levels (greater than 49 degrees for an extended period). Indeed a cast of extra-fast setting plaster, 20 layers thick, placed on a pillow during maturation maintained temperatures over 50 degrees of Celsius for over 20 minutes.

Conclusion

Clinicians should be cautious when applying thick casts with warm dip water. Fast setting plasters have increased risk of thermal injury while brand does not appear to play a significant role. Prefabricated fiberglass splints appear to be safer than circumferential casts. The greatest risk of thermal injury occurs when thick casts are allowed to mature while resting on pillow.     

Strong and light plaster casts?

Three geometries of volar slab plaster cast for the stabilisation of wrist fractures were investigated. It was found that by moulding reinforcement ridges on the inferior surface of the slab the strength and stiffness could be doubled with only a 20% increase in weight. It was discovered that to provide the same increase in strength with a traditional cast the entire thickness of the cast would have to be doubled, with a 100% increase in weight that would be cumbersome to most users. Bending theory is presented in a simple manner to allow clinicians to understand how reinforcement mouldings can improve the strength and stiffness of plaster casts without adversely influencing weight, or cost.     

Properties of a hybrid plaster-fibreglass cast.

OBJECTIVE: To examine the suitability of a plaster-fibreglass hybrid cast for orthopedic applications, comparing them to plaster of Paris (POP) and fibreglass constructs. METHOD: Groups of 10 standardized hybrid, POP and fibreglass casts were studied. An Instron servohydraulic system was used to test the casts in 3-point bending and shear. OUTCOME MEASURES: Strength, stiffness, weight, thickness and cost of the 3 types of cast, and shear strength at the interface between the POP and fibreglass in the hybrid casts. RESULTS: The hybrid casts were twice as strong as the POP constructs, were stiffer and weighed 14% less but were thicker and cost 2.5 times more. They were almost as strong as and less than half the cost of the fibreglass constructs but were thicker, not as stiff, and weighed 42% more. The shear strength of the POP-fibreglass interface in the hybrid casts was higher than the 3-point bending strength of this construct by a factor of 3. CONCLUSIONS: Plaster-fibreglass hybrid casts should be considered for orthopedic use on the basis of their strength, stiffness, weight and cost, combined with their acknowledged advantages of good moulding ability and water resistance.     

Three experimental designs testing orthopedic casting material strength

Three methods for testing the comparative strength of orthopedic casts have been considered. Two of the tests, three-point-beam-bending and diametral compression, were expected to yield information about "material" strength, and a third simulated an actual cast yielding information about "structural" strength. In one study using these three methods, differences in strength were detected in the material tests, but not in the structural test. Thus, the authors believe that tests of material strength alone are insufficient to establish clinically relevant differences between the strength of orthopedic casts. Adequate testing must include structural tests like the cast-cylinder test described in this article if meaningful and clinically relevant conclusions are to be drawn regarding the comparative strength of the actual cast. Since both the three-point-beam-bending and diametral compression tests produced essentially the same results, both tests are probably not necessary. However, each of these two tests does serve to substantiate the results of the other.     

A systematic review of the treatment of acute fractures of the scaphoid

A systematic review of the literature identified eight trials comparing surgery with cast treatment and found no significant difference in pain, tenderness, cost, functional outcome or patient satisfaction. In the group treated surgically, the rate of non-union was three times less, there was a quicker return to function and grip strength and range of movement was also transiently better. There were, however, more complications among those treated surgically. No significant differences were reported in the two trials that compared above and below elbow casts or the trial that compared scaphoid and Colles' casts.     

Biomechanical assessment of gait in below-knee walking casts.

The introduction of modern synthetic casting bandages for splinting of fractures and soft tissue injuries has allowed the development of new casting techniques. Casts can be constructed with a greater degree of function so that controlled motion and stabilisation can be provided within the same cast. This study has shown that a very efficient gait can be achieved with modern synthetic bandages, if they are correctly applied. The authors have compared the gait of volunteer subjects fitted respectively with below-knee walking casts constructed from a rigid glass fibre bandage and a flexible glass fibre bandage which is reinforced. These casts were wrapped so that minimal amounts of bandage were used whilst appropriate strength and stiffness was provided. The temporal and spatial factors of cast gait were not statistically different from normal gait. The cast gait was found to be slightly more asymmetrical (dominant versus non-dominant leg) when a cast was worn and there was also a greater Physiological Cost Index (PCI). The flexible bandage has some advantages compared with the rigid bandage as normal footwear can be worn, the casts are more comfortable and they could be removed with shears, obviating the need for a power saw.     

Buoyancy of synthetic cast and its implications to young patients

One of the authors' young patients suffered near-drowning while being treated with a synthetic below-knee cast, and this intrigued them into examining the buoyancy of waterproof casts and their use in small children. Synthetic and fiberglass casts were fabricated and subjected to immersion testing using lead pellets. Fiberglass casts sank immediately, while synthetic casts stayed afloat. With the addition of weights averaging 221 g, the synthetic casts finally sank. When supine, the casts stayed afloat with more weights. This study shows that synthetic liners are buoyant. Although the weight necessary to sink the casts was small, the weights were lead pellets, which is different from a human limb. Enhanced buoyancy of synthetic casts may pose a potential danger to a small child when not properly supervised in water. The initial buoyant force may be too startling and may place them at a higher risk for near-drowning.     

Early mobilization in the treatment of Colles'' fracture: a 3 year prospective study

Ninety consecutive women with unilateral Colles' fractures were randomized into two different treatment groups. The control group was treated for 5 weeks in conventional short-arm, below the elbow plaster of Paris casts. The other group (N = 45) was treated similarly in plaster casts for 3 weeks and then had flexible casting applied for the remaining 2 weeks which allowed for early joint mobilization. Functional recovery was assessed by measuring grip strength and joint mobility at intervals over the 3 years. Radiographic and overall assessments were also made during 3 year course of study. Virtually all patients reported greater comfort after switching to the flexible casting. Mean grip scores and joint mobilities were higher at all time points with early mobilization, reaching levels of statistical significance at 6 months for grip score and at 3 months for joint mobility. By 3 years most differences between treatment groups had resolved. We found no evidence that early mobilization was detrimental to recovery. We conclude that early mobilization is a satisfactory treatment option for Colles' fracture, and may, in fact, hasten functional recovery.     

The influence of diabetes on free flap transfer: I. Flap survival and microvascular healing.

Although recent clinical case presentations suggest that diabetes does not predispose free tissue transfers to increased risk of failure, this remains an open question. The present study used a syngeneic rat strain (Lewis) for free groin flap transplantations between normal rats and streptozotocin-induced diabetic rats (2 months' duration of symptoms), to investigate the influence of diabetes on flap transfer. Flap survival at 1 week, vascular patency, flap histology and ultrastructure, and scanning electron microscopy of anastomotic sites and of corrosion casts of flap vasculature were used as bases for comparison. No differences were found in comparisons of flap survival between any groups of transfer combinations (normal flap onto normal recipient, diabetic flap onto normal recipient, normal flap onto diabetic recipient, and diabetic flap onto diabetic recipient); 100% success was achieved in each group. No differences were found in histology or corrosion casts. Transmission electron microscopy revealed a thickening of the capillary basement membrane in rat diabetic skin after only 8 weeks of symptoms. This ultrastructural finding is consistent with similar capillary basement membrane thickening seen in many other tissues of short- and long-term diabetic animals and humans. Re-endothelialization across the arterial anastomosis at 2 weeks postoperatively was significantly faster in normal versus diabetic animals (p less than 0.05). The predominantly negative findings of this study support the application of free flap transfers in diabetic patients. It is concluded that reconstructive efforts involving free tissue transfer may not be contraindicated in diabetic patients.     

The farsighted studies of the Italian Carlo L. Rovida (1844-1877) on the nature of urinary casts

Carlo L. Rovida (1844-1877) was an Italian physician who graduated in Pavia (1866) and worked in Milan (1868) and Turin (1874), where he ran the Institute of Clinical Medicine at the university. Between 1870 and 1876 Rovida published several studies on the nature of urinary casts, which can still be considered valid today. He distinguished two main types of casts, i.e., "colorless" (hyaline) and "yellowish" (waxy). By painstaking microscopic observation of the urine, performed mainly by microchemical techniques, and histological examination of the kidneys, he came to the conclusion that both types of casts were produced by tubular cells. In addition, he found that the colorless casts were composed of a unique protein, which was different from any other protein known at the time, and which he called "cilindrina" (cylindrine). Instead, Rovida found that the yellowish casts contain a different, ill-defined protein, which was also present in the lateral and basal membrane of the tubular cells. Rovida should be remembered today because his views were much ahead of the prevailing theories of the time, which considered the casts as coagulated fibrin (a view sustained mainly in Germany) or as elements derived from either tubular degeneration or tubular production (a view sustained mainly in the United Kingdom and Sweden); his results concerning the site of production of hyaline casts and their unique nature were confirmed 90 years later, in the early 1960s, when it was demonstrated that these casts are made of Tamm-Horsfall glycoprotein, a protein which is produced by the cells of Henle's loop; and his conclusions about the special nature of waxy casts were also correct. In fact, even though the true composition of these casts is still not yet totally clear, there is now evidence that they contain a substance different from Tamm-Horsfall protein. Rovida is also a paradigm of how the progress of science is strictly dependent on the development of technology. In fact, it was only when appropriate techniques (e.g., electrophoresis, immunoelectrophoresis, and immunofluorescent microscopy) became available that the nature of casts could be defined with certainty.     

Effect of cotton padding on the setting properties of plaster slabs

Introduction

Plaster of Paris (PoP) impregnated bandages have been used to maintain the position of bones and joints for over a century. Classically, wool dressing is applied to the limb before the PoP, which can then be moulded to the desired shape. A modification of this practice is to wrap the PoP bandages circumferentially in cotton before wetting and applying to the patient in an attempt to reduce inhalation of plaster dust and reduce mess. However, this may affect the water content of the cast and therefore also its setting properties and strength. This study compared the setting properties of PoP casts when used with and without cotton wrapping.

Methods

Sixty specimens, compliant with the American Society for Testing and Materials standards for three-point bending tests, were prepared, with thirty wrapped in cotton. All were weighed before and after water immersion, and wrapped around a plastic cylinder to mimic limb application. Bending stiffness and yield strength was measured on a servohydraulic materials testing machine at 2, 6, 12, 24, 48 and 72 hours.

Results

The water content of cotton-wrapped plaster was significantly higher (50%) than that of standard plaster. It had significantly lower strength up to 24 hours and significantly lower stiffness up to 72 hours.

Conclusions

The initial decrease in strength and stiffness of the cast wrapped in cotton may comprise the ability of the backslab to hold the joint or bone in an optimal position. Any modification of the standard plaster slab application technique should allow for the potential adverse effects on the plaster setting properties.     

New fracture immobilization materials—a fire hazard?

The inflammability of various new materials for the immobilization of fractures was tested. All synthetic substances ignited when tested as block specimens, but were far less inflammable when casts were used. It is felt, however, that patients should be warned to keep such casts away from flames.     

Effect of mixing technique on the properties of acrylic bone-cement: a comparison of syringe and bowl mixing systems

Syringe mixing systems have been introduced, but few data exist regarding the mechanical performance of cement they produce. We compared the properties of polymethyl methacrylate cement produced by these systems with that produced by a multiaxial bowl. Mixtures of cement were prepared using the Optivac, Cemvac, and Summit syringes and the Summit bowl. The mixtures were cured in molds to create casts that were radiographed and analyzed for void content, then cut into strips, weighed, measured, and tested to failure in 4-point bending. Syringe-mixed cement was of greater density, bending modulus, and bending strength than bowl-mixed cement (Mann-Whitney, P < .01) and contained fewer microvoids and macrovoids (Mann-Whitney, P < .01). No significant differences between the syringes were found for these variables (Kruskall-Wallis, P > .05).     

Driving plastered: who does it, is it safe and what to tell patients

BACKGROUND: The number and safety of patients who drive in an upper limb fracture cast has been largely untested. This study investigates the proportion of persons who drive in their casts and the capability of a casted persons driving is also assessed. The stance of government and insurance bodies is reviewed. The aim is to provide a guide for when a doctor should advise a patient not to drive while wearing an upper limb fracture cast. METHODS: Patients attending fracture clinic in upper limb casts were anonymously surveyed and asked (along with demographics) if they drove while in a cast and if they believed it illegal or covered by insurance to drive. Driving tests of the author wearing upper limb fracture casts were undertaken. The Queensland police traffic branch, the Queensland Department of Transport and the RACQ insurance company were contacted to review the legal and insurance issues involved. RESULTS: Two-thirds of male and one-third of female patients (half overall) were found to drive while in an upper limb cast. The author failed driving instructor tests in all casts and occupational therapist driving assessments while wearing long arm casts. The author passed occupational therapy driving assessments in left and right short arm casts. CONCLUSIONS: According to these results, a doctor's advice should be to patients not to drive in a long arm upper limb fracture cast and to consider concomitant patient factors when advising patients in short arm casts. Although we do not suggest that patients drive while wearing any cast, we have found a large proportion do. Our limited study has found that a young, fit and pain-free person may be able to drive well enough to pass a driving test while wearing a short arm cast.     

The Effect of Drinking Water Fluoridation on the Fluoride Content,Strength and Mineral Density of Human Bone

The effect of drinking water fluoridation on the fluoride content of human bone, on cancellous bone strength and on the mineral density of bone was studied by analysing 158 autopsy samples of the anterior iliac crest from persons from two different areas. in the samples from the town of Kuopio, where drinking water has been fluoridated since 1959, the fluoride concentrations were considerably higher than in samples from the surrounding area where low—fluoride drinking water is used. the fluoride content of bones from Kuopio increased significantly with age, while considerably less change with age was found in samples from outside Kuopio. the highest fluoride content in bone ash was observed in women with severe osteoporosis.

Cancellous bone strength measured by a strain transducer was statistically significantly higher in women with chronic immobilizing disease from Kuopio, compared with the corresponding group from outside Kuopio. No statistically significant differences in bone strength were found in men. There were no statistically significant differences in bone mineral density, as measured by gamma ray attenuation, between the samples from the fluoridated and non—fluoridated areas.     

Delayed primary closure: Collagen synthesis and content in healing rat skin incisions

The rate of collagen synthesis was determined by measuring the specific activity of [³H]hydroxyproline 10, 20, and 60 days postoperatively in order to elucidate differences previously found in the mechanical strength of delayed primary closure (DPC) and primary closure (PC) wounds in rat skin. The rate of collagen synthesis was significantly higher in the DPC wounds than in the PC wounds during the time period studied. At the same time, the collagen content was lower in the DPC wounds on the 10th postoperative day. There were no differences in collagen content on the 20th or on the 60th postoperative day. These data suggest that there is more degradation of collagen in DPC wounds, starting at the 20th postoperative day. Differences in the rates of collagen synthesis in DPC and PC wounds are compatible with previously found differences in the gains of mechanical strength. It is suggested that the superior mechanical strength of DPC wounds is a result of a higher remodeling activity of collagen in DPC wounds.     

Factors causing differences in voiding parameters between conventional and ambulatory urodynamics

Voiding parameter values measured with ambulatory urodynamic monitoring (AM) are generally found to be different from those measured with conventional cystometry (CMG). The reason for this is unclear, but might be related to differences in the voided volume. To verify this hypothesis, we compared voidings from female patients at an initial bladder volume that was close to the modal volume (that is, the volume most often voided by the patient as derived from frequency/volume charts) with voidings at maximum cystometric capacity during a routine video urodynamic examination. A first group of 35 patients voided at the modal volume before they did at capacity. The order was reversed in a second group of 12 patients. The dependence of the voiding parameters on the voided volume and the order of the measurements were examined. It was found that the maximum flow rate depended significantly on the voided volume, but the associated detrusor pressure did not. Urethral resistance and bladder contraction strength were not volume dependent either. It was concluded that the differences between AM and CMG cannot be explained from possible differences in the voided volume. Received: 23 August 1999 / Accepted: 16 December 1999     

Study on the strength and microcleanliness of the stem of the total hip prostheses

Using 8 types of total hip prosthetic stems that are presently the most commonly used in clinical applications, we conducted a mechanical and metallurgical study based on measurements of strength and microcleanliness. The Müller, Kyocera Bioceram 4M type and the Thackray Charnley proved to be excellent in terms of strength, whereas the Müller and Kyocera Bioceram 4M type yielded superior results for microcleanliness. The strength and microcleanliness of the casts were of a lower grades, allowing the wroughts to be superior to the former. Vacuum-melted stems gave particularly favorable results. Even those stems which had been made with the same mold or of the same metallic material varied in terms of strength and microcleanliness depending upon the manufacturing processes. There were notable correlations among microcleanliness, O2 content and strength, and improvements in metallic materials and manufacturing processes will enable us to minimize nonmetallic inclusions and O2 contents and thus increase the strength and microcleanliness as well.     

When should a synthetic casting material be used in preference to plaster-of-Paris? A cost analysis and guidance for casting departments

An accurate cost analysis of the use of one of the new synthetic casting materials (Cellacast) compared with plaster-of-Paris (Gypsona) was undertaken over a 3-month period in the fracture clinic of Cardiff Royal Infirmary. The mean duration of usage before failure for synthetic forearm, scaphoid and below-knee casts was found to be approximately twice that of plaster casts. The use of synthetic casting materials was found to be cost-effective in situations where there was thought to be a high probability that structural failure of the cast would occur. Guidelines for the use of plaster-of-Paris and synthetic casting materials are presented.