Bandages

Abstract: A knitted substrate suitable for use in a resin-coated, water-hardenable orthopaedic splinting bandage is described. The substrate comprises inelastic fibres being incorporated in the substrate in the length direction. In a preferred substrate the low modulus fibre is a multifilament polypropylene and the elastic fibre is a polyurethane yarn. Conformable orthopaedic bandages employing the substrate are also described.

Description: The present invention relates to water hardenable orthopaedic splinting bandages comprising a fabric substrate impregnated with a water-curable resin for example a resin containing isocyanate groups. More particularly the present invention relates to an orthopaedic bandage comprising a resin-coated fabric substrate which is stretchable in the lengthwise direction and to the substrate itself. Conventionally orthopaedic splinting bandages for use in the treatment of bone fractures or other conditions requiring immobilization of part of the body are formed from a substrate impregnated with a substance which hardens to a rigid structure after wrapping the bandage around the body. Traditionally Plaster of Paris was used but more recently certain plastics have gained acceptance as replacements for Plaster of Paris. Such new bandages are lighter, waterproof and permeable to X-rays. One way in which strength is added to such casts is to use a glass fibre substrate which it is believed not only acts as a carrier for the resin but also reinforces the final cured bandage. This substrate is preferably a glass fibre fabric such as that described in United States Patents Nos. 4502479, 4609578, 4668563 or 4323061. One disadvantage of glass fibre casts is that they can become brittle and break down during wear and hence need to be replaced. A second disadvantage is that during cast removal irritating glass dust or fibres may be generated. These disadvantages would be mitigated by using a substrate which gave a durable cast and did not give rise to irritating fibres on cast removal. However, heretofore such substrates have lacked the conformability and cast strength found when using glass fibre substrates. US-A-4668563 discloses a casting tape having a knitted substrate which comprises a combination of high modulus inelastic fibres such as glass fibres and elastic fibres. Surprisingly it has been found that by using as a substrate a knitted fabric which comprises low modulus, inelastic fibres and elastic fibres incorporated in the lengthwise direction, a bandage is achieved which has good conformability compared to those employing existing glass fabric substrates. Even more surprisingly the cast formed using this novel substrate has sufficient rigidity and can show no loss of strength compared to a cast which employs a glass fibre substrate. In addition it yields casts which are less brittle and can be more durable than some glass fibre based casts. In one aspect therefore the present invention provides a knitted substrate suitable for use in a resin-coated water hardenable orthopaedic splinting bandage which substrate comprises inelastic fibres and elastic fibres, said elastic fibres being incorporated in the substrate in the length direction characterised in that the inelastic fibres have a low modulus of elasticity, that is, a fibre in which individual filaments have a modulus of less than 1.38 x 10 8 Pa. Most suitably the resin is a water curable resin so that the bandage is one which hardens after being exposed to water. In another aspect the present invention provides a conformable water hardenable orthopaedic splinting bandage comprising a knitted substrate coated with a curable resin which substrate comprises inelastic fibres and elastic fibres, said elastic fibres being incorporated in the substrate in the length direction characterised in that the inelastic fibres have a low modulus of elasticity, that is, a fibre in which individual filaments have a modulus of less than 1.39 x 10 8 Pa. As is apparent herein, the term "fibre" relates to the yarn material which is knitted whether that yarn is comprised of mono or multifilaments. The orthopaedic splinting bandages of the present invention possess lengthwise extensibility by virtue of the presence in the substrate of elastic fibres incorporated in the lengthwise direction of the bandage. Suitable elastic fibres may be formed from rubber or elastomeric polymers which have high extensibility together with substantiably complete and rapid elastic recovery. Suitable fibres may have an elongation at break in excess of 100% and more suitably in excess of 300%, for example 500 to 800%. Suitable elastic yarn (fibres) include those formed from natural rubber or a synthetic elastomer such as polyisoprene, polybutadiene, copolymers of a diene and styrene or acrylonitrile, polychloroprene or copolymers thereof, elastomeric ethylene-propylene copolymers and polyurethane yarn. A preferred elastic fibre is a natural rubber fibre. A particularly preferred elastic fibre is a spandex fibre, that is a polyurethane fibre for example Lycra fibre (Trade mark). The successful use of such yarns as polyurethane yarns is surprising since the anticipated plasticisation by polyurethane prepolymer resins does not occur to an extent which results in unacceptable weakening of the product. The elastic fibre is present in the knitted substrate in the warp that is the machine direction. Suitably about 0.5 to 20% of the volume of the substrate may be made up from elastic fibres and more suitably 1 to 8% of the volume of the substrate is made up from elastic fibres. Suitably the lengthwise extension of the substrate may be such as to give the resin coated substrate an extension of from 15% to 80% and more suitably may be from 20% to 30% for example 25% when measured at a load of 640gm per inch (2.5cm). Suitably the widthwise extension of the substrate may be from 20 to 100%, more suitably 25 to 60% and preferably 30 to 50% for example 45% (when similarly measured). Suitably the substrate may be heat treated using steam to improve the stretch of the substrate and to provide a more consistent bandage after coating. The elastic fibres in the substrate appear to cause the substrate to return to its original length after stretching and so facilitates conformability of the substrate to the patient's body. The bandages were observed to conform easily to various shaped formers made to represent parts of the body. Suitably the knitted substrate has a low power, that is the force required to stretch the substrate for a given percentage extension. If this power is low then this will help to prevent constriction of the patient's limb after the bandage has been applied. Suitably the power can be less than 20g cm -1 width at 10% extension, more suitably less than 15g cm -1 width and preferably less than 10g cm -1 width at 10% extension. The lengthwise extension may be measured using an Instron Tensile Testing Machine. A 10cm length of substrate may be clamped in the jaws of the machine and the jaws separated at constant speed. A conventional stress-strain curve for the substrate may be recorded. The extension at a given load and the load required to give a given extension can be calculated from the curve for the substrate under test. The remainder of the knitted substrate may be formed from a fibre (yarn) which is a low modulus fibre that is a fibre in which individual filaments have a modulus of less than 2.07 x 10 10 Pa (3 x 10 6 psi), more suitably less than 1.38 x 10 10 (2 x 10 6 psi) and preferably less than 6.90 x 10 9 Pa (10 6 psi) which include polymer fibres such as polypropylene, polyester, polyamide and polyethylene. The low modulus fibre may have a modulus of elasticity of less than 6.90 x 10 7 Pa (10 4 psi). A preferred fibre is formed from polypropylene and may be employed as a multifilament or monofilament fibre. A second preferred fibre is polyester including multifilament or monofilament polyethylene terephthalate fibre. The use of such yarns leads to particularly durable casts. Suitably the substrate may have a thickness of from 0.375mm to 1.25mm, more suitably will be 0.45mm to 1.0mm thick and preferably 0.50mm to 0.875mm thick, for example 0.825mm. Suitably the knitted substrate may have a weight per unit area of from 50 to 500gm -2 , more suitably may have a weight of from 100 to 350gm -2 and preferably a weight of between 170 and 270gm -2 for example 250gm -2 Suitably the substrate will be in the form of a flexible fabric which has been knitted. Suitable knit-types for the substrate are described in for example United States Patents Nos. 4427002, 4502479, 4609578 and 4668563. Suitable fabrics may be employed as a Raschel knit, a crochet knit or a tricot knit. A preferred substrate will be in the form of a warp knitted fabric having a chain stitch along its length. A knitted fabric may be formed on a 3-bar knitting machine in which the first bar usually carries a low modulus fibre and is arranged to knit open lap stitches or closed lap stitches. The second bar usually carries the elastic fibre which can be knitted in with the fibre on the first bar or can be laid in. The third bar usually carries a low modulus fibre which is laid in in a zig-zag pattern across the fabric. The number of wales crossed by the fibre on the third bar can be used to control the width wise stretch, substrate weight and substrate dimensional stability. One suitable knit pattern is described in United States Patent No. 4427002 at column 3 line 33 to column 5 line 4. Unfortunately this earlier fabric was only poorly conformable). The knit is aptly of a type which can mitigate against formation of frayed ends when the substrate is cut. The use here of low modulus fibres instead of glass fibre also helps prevent the generation of stiff fibre ends which stick out from the set cast which may irritate the wearer and cast technician and give rise to a rough appearance to the cast. The use of low modulus fibres which bend easily allows smooth casts to be achieved especially at the edges. This is a considerable advantage as special treatments of fibres or the knitted substrate can be avoided. Suitably the substrate may be a mesh, that is it should have openings through it to enable the curing agent to penetrate into the rolled bandage to contact all parts of the resin. The openings of the substrate will also permit circulation of air to and evaporation of moisture from the skin beneath the cured bandage. The mesh may be defined by counting the number of repeating patterns of the knit on a square inch of the fabric. This may be accomplished by taking a photograph of a section of the substrate when relaxed at known magnification and counting the recurring units across and along the section for a distance equivalent to an inch in each direction and multiplying the two figures together. Suitably the fabric may have a mesh of from about 200 to 300 per sq. inch more suitably from 220 to 270 per sq. inch and preferably 240 to 260 per sq. inch, for example 240, 250 or 260 per sq. inch. In one favoured embodiment of the present invention the knitted substrate comprises elastic fibres in an amount of from 1 to 8% by volume of the substrate, said substrate having a lengthwise extension of from 15 to 80%. In a second favoured embodiment of the present invention the knitted substrate comprises inelastic fibres of modulus less than 1.38 x 10 8 Pa (2 x 10 4 psi) and elastic fibres in an amount of from 1 to 8% by volume of the substrate, said substrate when resin coated having a lengthwise extension of from 20 to 30%. In a preferred embodiment of the present invention the knitted substrate comprises inelastic polypropylene fibres of modulus less than 1.38 x 10 8 Pa (2 x 10 4 psi) and elastic polyurethane fibres in an amount of from 1 to 8% by volume of the substrate, said substrate when resin coated having a lengthwise extension of from 20 to 30%. The resins used in the orthopaedic bandage of the invention may be any curable resin which will satisfy the functional requirements of an orthopaedic cast. The preferred resins are those cured with water or moisture and include the resins described in United States Patent Nos. 4667661, 4502479, 4574793, 44336780, 4427002, 4411262, 39392526, 3908644, 3630194, in German Offenlegungsschrift No. 2651089 and in European Patent Application Nos. 35517, 57988, 86621 and 94222. Aptly the resin used to coat the fibre substrate may be a water curable isocyanate terminated prepolymer system. Among suitable prepolymer systems are those identified in United States Patent Nos. 4411262, 4427002, 4433680 and 4574793. Particularly preferred are those systems disclosed and claimed in United States Patents Nos. 4427002 and 4574793 the disclosures of which are incorporated herein by cross-reference. Suitably the bandage may be formed by coating or impregnating the substrate with the resin in the manner described in those patents, particularly in United States Patent No. 4427002. Suitably the weight of resin on the substrate may be from 150 to 500gm -2 , more suitably a weight of 200 to 450gm -2 and preferably between 250 to 400gm -2 . The weight of resin may be chosen so that suitably 40 to 60% of the total weight of bandage is resin and more suitably 50 to 55% of the total weight. Thus if the fabric weight is 250gm -2 and the resin coating is 55-60% of the bandage then the weight of resin taken is 305-375g. For the best shelf life of resin coated substrates, the elastic fibre used in the substrate must be compatible with the resin with which it is coated. Suitable compatible elastic fibres may be identified by forming a bandage incorporating the elastic fibre and coating with the desired resin and ageing in a sealed container for 12 weeks at 55°C. If at the end of this time the bandage may be used to form a satisfactory cast, then the elastic fibre is particularly suitable for use in conjunction with the resin. Difficulties with elastic fibres may be overcome by means of coating or wrapping the fibre with inert materials such as cotton or nylon yarn. The formed bandages may be packaged by heat sealing in waterproof pouches such as those formed from metal foil polyethylene laminates or polyethylene pouches. In use the bandages may be brought into contact with water and wrapped around the injured part of the body. The setting bandage has a working time which is sufficient to allow the bandage to be positioned on the limb and a set time which is the time taken for the cast to become rigid. Apt working times are 1 to 6 minutes and apt set times are 5 to 30 minutes. The cast incorporating the substrate of the invention is readily removable by conventional means such as by cutting with a conventional circular saw. Large casts may be removed using a single cut along the length of the cast which is not always achievable with fibre glass substrate casts. The use of polypropylene or polyester in the substrate makes cast removal easier and does not generate glass dust or fibres. The build-up of strength in the cast was assessed by wrapping the resin-coated substrate round a former to make a cylinder. The former is removed and the cylinder wall clamped in an Instron Tensile Testing Machine so as to measure diametral compression and extension forces. The machine is adapted so that the moving clamp would oscillate between positions 2.5mm from the rest position. The force required to deform the cast as it set over a period of time is measured. The results were recorded on a chart recorder. A bandage formed according to Example 2 was tested in comparison with a conventional glass fibre based bandage using cylinders formed of 5 layers of bandage. The bandage according to the invention was comparable in strength to the glass fibre bandage both on initial setting and after 24 hours. Rigidity (kg/cm width) Time after initiation of set 15 mins 30 mins 24 hr Bandage of Example 2 2.0 2.7 4.7 Glass fibre-based bandage 2.1 2.65 4.5 The durability of casts formed from bandages of the invention are tested by applying leg casts to volunteers which they wore for 48 hours during which they walked between 6 and 40km. No break down in the casts were observed. In a comparative trial using a conventional glass fibre cast 30% of the casts were obseved to have broken down at the end of the trial period. In one favoured embodiment of a splinting bandage of the present invention the knitted substrate comprises elastic fibres in an amount which comprises from 1 to 8% by volume of the substrate and the resin coated substrate has an extension in the lengthwise direction of 15 to 80%. In a particular preferred embodiment of a splinting bandage of the present invention the knitted substrate comprises inelastic polypropylene fibres of modulus less than 1.38 x 10 8 Pa (2 x 10 4 psi) and elastic polyurethane fibres fibres in an amount which comprises from 1 to 8% by volume of the substrate, said resin coated substrate having a lengthwise extension of from 20 to 30%. EXAMPLE 1 Preparation of Substrate A substrate is prepared by knitting together elastic polyurethane fibres and a low modulus fibre of polypropylene. The elastic polyurethane fibres are formed from a segmented polyurethane and are commercially available as Lycra spandex fibres. The polyurethane fibre is wrapped in nylon or cotton yarn. The polypropylene is a 70 filament yarn of weight per unit length of 470d Tex. The knit-type is a Raschel 3-bar warp knit in which the first bar is full set at 0-1/1-0 and carries polypropylene fibre,the middle bar is full set at 0-0/1-1 and carries polyurethane fibre and the third bar is full set at 0-0/3-3 and carries polypropylene fibre. The substrate is knitted as a long strip with a width of 10cm, when relaxed there are approximately 6.0 to 7.9 courses/cm and 4 to 6 wales/cm and a weight per unit area of 200gm -2 . The knitted fabric when coated with resin has an extension in the widthwise direction of 80% and extension in the lengthwise direction of 25%. EXAMPLE 2 Preparation of Bandages A water curable polyurethane resin system comprising a polyurethane prepolymer described in United States Patent No. 4574793 as prepolymer A and containing methane sulphonic acid as stabiliser and bis(2,6 dimethylmorpholino)diethyl ether as catalyst is coated onto a knitted substrate described in Example 1 using the process described in United States Patent No. 4427002. The weight of the resin applied is 240gm -2 which means that the resin forms 55% of the weight of the bandage. The bandage strip is cut into 3 metre lengths and spooled onto rolls. The bandage rolls are then placed in pouches which are heat sealed to prevent exposure of the contents to moisture. A bandage is made into a cast by dipping the bandage roll in water and wrapping around a body member. EXAMPLE 3 Preparation of Bandages A viscous prepolymer comprising a purified polyethylene glycol isocyanate terminated prepolymer prepared in the same manner as that described in Example 22 of European Patent Application No. 57988. A slurry is prepared by mixing a solution of the prepolymer in dry methylene chloride with potassium carbonate, alumina, Sylosiv A3 and Desmodur M44. A slurry is coated by means of a doctor blade onto a 10cm wide strip of a warp knit substrate comprising an elastic polyurethane fibre and a low modulus polypropylene fibre. The substrate may be stretched by up to 25% when subjected to tension. The coating is formed at a weight per unit area of 250g/m 2 . The bandage strip is cut into 1 metre lengths and spooled onto rolls. The bandage rolls are then heat sealed into pouches of low density polyethylene. EXAMPLE 4 Preparation of Substrate A substrate is prepared by knitting together elastic polyurethane fibres and a polyester fibre. The elastic polyurethane fibres are formed from a segmented polyurethane and are commercially available as Lycra spandex fibres. The polyurethane fibre is wrapped in nylon or cotton yarn. The polyester is a 1000 denier multifilament polyethyleneterephthalate. The knit-type is a Raschel knit using approximately 2 to 3 wales/cm width and 5 to 6 courses/cm length. The knitted fabric has an extension in the widthwise direction of 60% and extension in the lengthwise direction of 25%. The substrate may be coated with a moisture curable resin as described in Example 2 to form a bandage which is thereafter packaged in a waterproof pouch and used by removing the bandage from the pouch, dipping in water and wrapping around a body member. EXAMPLE 5 Preparation of Substrate A substrate is prepared by knitting together elastic polyurethane fibres and a low modulus fibre of polypropylene. The elastic polyurethane fibres are formed from a segmented polyurethane. The polyurethane is wrapped in nylon or cotton yarn. The polypropylene fibre is a 70 filament yarn with a weight per unit length of 470dTex. The warp knitted fabric is of a Raschel 3-bar knit-type in which the first bar is full set at 0-1/1-0 and carries polypropylene fibre, the middle bar is full set at 0-0/1-1 and carries polyurethane fibre and the third bar is half set at 0-0/3-3 and carries polypropylene fibre. The substrate is knitted as a long strip at a width of 10cm. With the fabric in a relaxed state there are approximately 6.0 to 7.9 courses/cm and 4 to 6 wales/cm. The fabric has a weight per unit area of 160gm -2 . The fabric therefore has a more open appearance that the substrates of Examples 1 and 4 and thereby slightly improved moisture vapour permeablility properties. The knitted fabric when coated with resin has an extension in the widthwise direction of 60% and an extension in the lengthwise direction of 25%. The substrate may be coated with a moisture curable resin as described in Example 2 to form a bandage which is thereafter packaged in a waterproof pouch and used by removing the bandage from the pouch, dipping in water and wrapping round a body member. If the weight of resin applied is 240gm -2 then this forms 60% of the weight of the bandage. EXAMPLE 6 Preparation of Substrate A substrate was prepared by knitting together an elastic Lycra fibre comprising a polyurethane yarn wrapped in crimped nylon yarn, in which the fibre has a weight per unit length of 78dTex and a polypropylene fibre comprising a 70 filament yarn with a weight per unit length of 470dTex. The substrate was knitted on a 3-bar machine in which bar 1 is full set at 0-1/1-0 and carries polypropylene fibre, bar 2 is full set at 0-0/1-1 and carries the Lycra fibre and bar 3 is full set at 0-0/3-3 and carries polypropylene fibre which is laid in across 3 wales. The fabric has 6.4 to 7.2 courses per cm and 5.4 to 5.7 wales per cm. This results in a fabric having a weight of approximately 220gm -2 and 244 openings per sq in. The fabric has a lengthwise stretch at 640gm -1 width of 48% and 25% when coated with resin. A sample of the substrate prepared above was coated with the resin described in Example 2. The resin coating was applied at a weight of 248gm -2 (approximately) which means that the resin forms 53% by weight of the bandage. A bandage strip was prepared by cutting the coated substrate into strips 10cm wide and 3 metres long. The strip may be spooled onto rolls and placed in moisture pouches which are heat sealed. A bandage strip was removed from a pouch, dipped in water and wrapped around a body member. The bandage had a working time of 3½ minutes and formed a rigid durable cast. EXAMPLE 7 Preparation of Substrate A substrate was prepared in a similar way to that described in Example 6 except that the elastic yarn was laid into the wale and that bar 3 was not half set. The fabric has 6.4 to 7.2 courses per cm and from 5.8 to 6.1 wales per cm. The resulting fabric had a weight per unit area of 240gm -2 and 261 openings per sq in. The fabric has lengthwise stretch at 640gcm -1 of 60% and of 30% when coated with resin. A sample of the substrate was coated with the resin described in Example 2. The resin coating was applied at a weight per unit area of 283gcm -2 which means that the resin forms 54% by weight of the bandage. The bandage formed from the coated substrate when dipped in water and wrapped around a body member formed a rigid, durable cast. The bandage was observed to have a working time of 3.5 - 4 minutes.

Claims: A knitted substrate suitable for use in a resin-coated, water hardenable orthopaedic splinting bandage which substrate comprises inelastic fibres and elastic fibres, said elastic fibres being incorporated in the substrate in the length direction characterised in that the inelastic fibres have a low modulus of elasticity, that is, a fibre in which individual filaments have a modulus of less than 1.38 x 10 8 Pa. A substrate as claimed in claim 1 in which the substrate has a lengthwise extension of from 15% to 80% and a widthwise extension of from 20% to 100%. A substrate as claimed in claim 1 in which the substrate has a weight per unit area of from 50 to 500 g m -2 and from 200 to 300 openings per sq. in. A substrate as claimed in claim 1 in which the substrate is a warp knitted fabric having a chain stitch along its length. A substrate as claimed in claim 1 in which the elastic fibre is a natural rubber or polyurethane fibre. A substrate as claimed in claim 1 in which the inelastic fibre of low modulus of elasticity is a polypropylene fibre. A substrate as claimed in claim 1 in which the inelastic fibre of low modulus of elasticity is a polyethylene terephthalate fibre. A conformable water hardenable orthopaedic splinting bandage comprising a knitted substrate coated with a curable resin which substrate comprises inelastic fibres and elastic fibres, said elastic fibres being incorporated in the substrate in the length direction characterised in that the inelastic fibres have a low modulus of elasticity, that is, a fibre in which individual filaments have a modulus of less than 1.38 x 10 8 Pa. A bandage as claimed in claim 8 in which the resin is a water curable isocyanate terminated prepolymer system. A bandage as claimed in claim 8 in which the resin coated substrate has a lengthwise extension of 15 to 80% and a widthwise extension of from 20 to 100%. A bandage as claimed in claim 8 in which the substrate has a weight per unit area of from 50 to 500 g m -2 and the weight of the resin is 40 to 60% of the total weight of the bandage. A bandage as claimed in claim 8 in which the elastic fibre is a natural rubber or polyurethane fibre. A bandage as claimed in claim 8 in which the inelastic fibre of low modulus of elasticity is a polypropylene fibre. A bandage as claimed in claim 8 in which the inelastic fibre of low modulus of elasticity is a polyethylene terephthalate fibre. A bandage as claimed in claim 8 in which the weight of the resin on the substrate is from 150 to 500 g m -2 .

Inventors: HULME RODERICK JOHN, PEARCE RICHARD HUGH, HULME, RODERICK JOHN, PEARCE, RICHARD HUGH
Applicants: SMITH & NEPHEW, SMITH & NEPHEW P.L.C.
Application year: 1989
Main classification: A61F13
IPC codes: A61F13, A61L15, D04B21