Plastic splints and appliances in orthopaedic surgery.

A wide range of plastic materials is now available in industry. It was thought that a number of these might be suitable for the construction of orthopaedic splints and they have been tried with varying degrees of success. Most have been found unsuitable for one reason or another, some because the technique of manipulation was too elaborate, and others because they were lacking in certain necessary qualities. The practical properties required of plastic materials for use in splint-making include : relative ease of manipulation ; durability; I esistance to fatigue strain ; light weight ; radiolucency and transparency ; inertness to chemical agents ; freedom from irritants causing dermatitis ; porosity ; cheapness. No plastic material satisfies all these requirements but several are available which satisfy most of them. The ideal plastic will be one which after direct application to the patient, or to a mould, will polymerise rapidly to form a rigid material (cf. gypsum) or alternatively one which is soluble in high concentration, about 80 per cent., in a cheap solvent such as water. The curing or setting time must not exceed fifteen to twenty minutes and should preferably be less. Such a plastic when cured or set should have the properties enumerated above. We hope that this goal may be achieved by experimental work now proceeding. Plastic materials may be divided into two main groups: 1) thermoplastic resins which can be resoftened and remoulded by the application of heat and pressure ; 2) thermosetting resins which become more or less permanently hard and insoluble on curing (Worner 1946)1. The materials which have been considered experimentally for the construction of splints include : Thermoplastic-methyl methacrylate, polyvinyl chloride (P.V.C.), polyvinyl acetate (P.V.A.), P.V.C. & A. copolymer, cellulose acetate, polythene, polystyrene; Thermosetting-high prcssure-phenolformaldehyde, casein formaldehyde, urea formaldehyde; Ther nosetting-low prcssure-allyl and polyester resins. It was hoped that new low-pressure thermosetting resins would eliminate some of the difficulties in processing which are found with high-pressure resins, and at the same time have the additional property of high tensile strength which non-laminated thermoplastic materials lack. To date, however, these materials have been found unsuitable for individual splint-making although experimental work in artificial limb production shows promise of success. Of thermoplastic materials, those nearest to our requirements have so far been methyl methacrylate, P.V.C. and P.V.C. & A. copolymer-each having their usefulness in different types of splints. It should be noted that if great strength is required a laminated plastic is essential. Laminating materials which can be used include glass fibre cloth, cotton, paper, and asbestos. Such lamination does, however, require modification of the usual technique. External splints using woven cellulose acetate and glass fibre in bandage form have been described (Anderson and Erickson 1945)2. The plastic bandage is wetted with a setting solution and applied directly to the patient. A trial of these bandages shows that they have many advantages as compared with plaster-of-Paris bandages, but certain disadvantages have still to be overcome. Their merits include: lightness of weight-not more than onequarter to one-sixth the weight of plaster of Paris; strength and durability when in complete cast form; coolness in wearing; admission of light and air; capability of sterilisation by autoclaving; the fact that they are waterproof, porous, and unaffected by body secretions; and the ease and cleanliness of application. Nevertheless there are disadvantages. 1) The process involves evaporation of acetone which is an expensive and inflammable solvent.