Plastic Molded Directly On Patient

CE. Browning, O.N.C., M.C.S.P.


This article, which originally appeared in the American Journal of Occupational Therapy, January-February 1966, adds to the growing literature on plastics that can be heated and molded directly on the patient's body. Prior articles on this subject by Colin A. McLaurin, B.A.Sc. (Polysar cast), and C. Corriveau, CP. & 0. (Vitrathene), were published in the November 1966 and January 1967 issues of the ICIB respectively.

Plastic splinting of polythene lined with polyurethane can be molded directly on to the patient. Polyurethane is a poor conductor of heat, so that most of the heat of the softened polythene does not reach the patient, who only experiences a pleasant warmth. The time-consuming and messy process of making a positive plaster cast is unnecessary, and simple splints can be made in under an hour.

Polythene (polyethylene) is a thermoplastic, moldable at a temperature of 120 C. It is physiologically inert and unaffected by body secretions. It does not cause skin reactions in patients with a history of sensitivity to other materials, but occasionally a slight rash may appear in patients who sweat profusely. It is unaffected by water, chemicals in common use in industry, and domestic cleansers. It is almost noninflammable, although it is softened by heat.

Polythene is supplied in sheet form in thicknesses of 1/16, inch, 1/8 inch, and 3/16 inch. Splints are usually made of 1/16 or 1/8 inch thickness, reinforced by additional strips of polythene where strain occurs. For most splints 1/16 inch is sufficient, as the flexibility ensures a good fit despite day-today variations in the amount of swelling of an arthritic joint.

The polythene can be natural or pink in color (flesh color), but like many plastics, yellowing occurs on exposure to daylight. This color change does not affect the durability of the splint.

Polyurethane is a foamlike plastic sold under many trade names in a variety of colors and thicknesses for sponges, bath toys, cushions, mattresses, draught excluders, etc.

It is physiologically inert and, like polythene, is not affected by other substances. It is extremely light and makes a soft lining for the splints. Unlike polythene, it is rather friable and can be damaged by vigorous scrubbing. It will wear away long before the polythene, but this does not usually affect the comfort of the splint. A thickness of 3/16 inch with a density of Sp. Ct. 0.006 is most satisfactory, and the color should be the same as the polythene .

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Even heating of the polythene is essential. The oven used should have a thermostat to maintain the temperature at 120 C (248 F). The most satisfactory type has overhead infrared elements, but it is possible to use a domestic gas or electric oven.

Other Requirements

  1. Stockinette to place on the sticky, softened polythene so that it can be handled. The same pieces can be used repeatedly because the stockinette is easily stripped off when it is cold. The roughened appearance of the polythene, produced by the ridges in the knitted stockinette, gives a more pleasing and unobtrusive finish than the shiny raw material.

  2. Crepe bandages in various widths. These are used to keep the splint in position while it is cooling and can be used repeatedly.

  3. Strong scissors or shears for cutting the polythene. The poly-urethane can be cut easily.

  4. Fastenings-buckles and straps are satisfactory. Velcro may be preferred.

  5. Rivets to secure the straps and buckles to the polythene; tool to insert rivets.

  6. Punch for making ventilation holes. A leather punch is sufficient if only a few splints are being made, but a foot-operated model is more satisfactory in a busy department and, with alternative attachments, can be used for inserting rivets

  7. Buffing wheel is not essential but useful for smoothing rough edges of the splint if it has been trimmed after molding.

The basic technique of application is the same for all splints made by this process.

The oven is preheated to 120 C (248 F).

The splint is discussed with the patient. This is essential for many reasons, both from the patient's point of view and from the therapist's. It is quite possible that the patient may have no idea why the doctor has ordered a splint and may be unwilling to wear one, either for cosmetic reasons or for fear of discomfort. If possible, the patient should be shown a sample of the type of splint that he is to wear and given the reasons for wearing it. If after this the patient is still reluctant, it may be advisable to make a trial splint in plaster of Paris. If the patient cannot tolerate a light plaster of Paris slab, he is unlikely to accept any more elaborate and expensive splint.

The measurements of the patient's limb are recorded.

The outline of the splint is drawn on the polythene, using a ball point pen. When measuring and cutting out splints, it is not desirable to have the margins of the splint meet, as a small gap will allow for adjustment according to variations in joint swelling.

The polyurethane lining should extend 1/2 inch beyond the polythene because polythene spreads when heated.

Reinforcing strips can be cut from off-cuts and should be 1/2 inch shorter than the splint and placed in the correct position (e.g. with a wrist splint, the strips should be in the middle of the flexor aspect of the forearm, parallel to the longitudinal aspect).

The materials should be carefully assembled because once they are fused together they cannot be separated. The result of a mistake is similar to the error made by a home dressmaker who cuts out two sleeves for the same arm.

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The splint is placed- in the oven with the polythene uppermost. If the polythene is placed in contact with the shelf it will adhere firmly to it when heated. The splint must remain in the oven until all the polythene, including the reinforcement, has been transparent for five minutes for complete blending of the separate layers. The total time in the oven will be 30-40 minutes according to the thickness of the reinforcement. If the splint is left in the oven longer, it will not be harmed but the polyurethane may become discolored.

A piece of stockinette of the same size, pillows to support the limb, and crepe bandages of a suitable width should be available.

When the splint is removed from the oven and placed on a flat surface with the polythene uppermost, it should be covered with the stockinette.

When the polyurethane side of the splint is cool enough, the splint is bandaged lightly in position. If it is applied too firmly, compression of the superficial capillaries will lead to local overheating of tissues, resulting in pain or even a burn. If the patient appears to have a sensitive skin, a piece or pieces of tubular stockinette can be placed on the limb, as it will not affect the fit of the splint.

When the splint is cold and firm (in about 20 minutes), it is unbandaged and removed. The stockinette is stripped off and the surplus polyurethane is cut away.

The splint is reapplied and checked for fit, with any portions to be trimmed and positions for fasteners marked.

After the splint is trimmed, the edges smoothed, the fasteners attached, and ventilation holes punched, the patient should be shown the correct way to apply and fasten the splint. A splint that is loose can cause as much discomfort as one that is too tight.

The patient should be told to wash the splint frequently and to dry it with a towel, not in the oven or near a fire. The polyurethane lining can be dried by pressing the water out with a towel. The lining must not be scrubbed.

It is advisable to ask the patient to come back after a week to check whether the splint is being worn correctly and whether any further trimming is needed. If the patient has never worn a splint before, it is essential to warn him that getting used to it will take several days.

The polyurethane will wear out first, but the splint will usually still be wearable and it is practically impossible to stick a new lining inside the polythene.

Splints may be remolded by softening them in the oven and reapplying them. This is never really satisfactory, and as the material is relatively inexpensive, it is better to make a new one.

These splints are not suitable in the following instances because of the danger of burns, the heat of nonabsorbent plastic, or the flexibility of polythene:

  1. Small and uncooperative children.

  2. Uncooperative patients.

  3. Flexor spasm of legs.

  4. Bed-ridden patients.

  5. Unstable fractures.

  6. Heavy patients with flail knees.

The flexibility of polythene, which allows the splints to yield slightly on movement of the limbs, makes them more comfortable to wear than those of more rigid materials.

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CE. Browning, O.N.C., M.C.S.P. is the Principal, The Prince of Wales's General Hospital School of Physiotherapy Tottenham, London