Water impermeable, water vapor permeable orthopedic cast

An immobilizing orthopedic cast is provided made of an inner liquid water-impermeable, water vapor-permeable protective sleeve next to the skin, a resilient padding layer, and a plaster or resin/glass fiber outer immobilizing layer. A microporous expanded polytetrafluoroethylene membrane protective sleeve material provides the above properties for a cast which will dry itself inside and the skin it covers, is bacteria proof, and is not a host for bacteria. This application is a continuation of U.S. patent application Ser. No. 07/180,650, filed Apr. 4, 1988, abandoned, which is a continuation-in-part of application U.S. patent application Ser. No. 07/043,201, filed Apr. 27, 1987. now abandoned.

BACKGROUND OF THE INVENTION 
The present invention relates to an orthopedic cast which is immobilizing, 
but allows the skin to function in a normal way. It is characterized by a 
protective sleeve, adapted to be positioned about a portion of the body of 
the wearer, that makes the skin under the cast impervious to liquid water 
and wetness, because it transmits water or perspiration or urine in the 
form of water vapor away from the skin of the wearer. This provides for 
increasing comfort and cleanliness of that wearer. 
In applying a conventional plaster-of-paris cast, it is standard practice 
to first cover the body member being treated with a protective cloth 
bandage or wrap, such as cotton or polyester knit fabric. The protective 
cloth-covered body member is then covered with cotton or polyester padding 
to provide a soft resilient padded protective liner. This padding is then 
overwrapped with wetted plaster-of-paris, in woven cloth wrapping of 
sufficient length and to such a thickness, so as to provide an 
immobilizing structure of adequate strength and durability for the 
intended length of its stay in place on the body member being treated. 
It is also known to make casts from glass fiber materials, which consist of 
heat-softened or curable organic polymeric resins coated on glass fibers 
which have been woven into fabrics or are formed into unwoven open fibrous 
mats. Such flexible coated glass fabrics are wrapped while warm about a 
body member to be immobilized in much the same manner as 
plaster-containing cloth and allowed to cool and harden after the cast is 
formed. Woodall, U.S. Pat. No. 3,882,827, describes a resin/glass fiber 
composite method as do U.S. Pat. Nos. 4,273,115 and 4,238,522. 
While the conventional plaster-of-paris casting system and the glass fiber 
casting system are in widespread use, they have several disadvantages. 
Both types of cast are considered in the art to be non-breathable and both 
must be kept dry inside the cast since they cannot breathe. 
It is also true that while the casts themselves are impervious to water and 
not affected by immersion in water, the skin is wet under the cast. A lack 
of air to dry the skin could permit maceration of the skin under the cast, 
thus opening it to attack by bacteria. 
An additional problem with many casts is that odor develops owing to 
retention of perspiration and body oils in the cast. As the body 
secretions or wound drainage are absorbed into the cast padding and 
ultimately into the cast itself, it may generate a very foul odor. This 
may become so objectionable as to require a complete change of cast. 
Deodorants are available for incorporation into the cast material or 
padding at the time of application, but these have generally proven to be 
ineffective and most are no longer in use. 
Skin erosion and subsequently formed pustules that eminate from blocked 
hair follicles may cause extreme itching and discomfort for a patient 
wearing a conventional cast. Additionally, urine soaked casts, 
particularly in the case of Spica casts worn by infants for several months 
at a time, have wet padding in constant touch with the skin and therefore 
unable to dry, resulting often in ulcerated areas on the skin.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The present invention is an immobilizing orthopedic cast which is 
characterized by impermeability to liquid water, which also includes 
perspiration, urine, or any other largely aqueous-based solution or 
mixture which is ordinarily encountered in daily life by a person wearing 
an immobilizing cast. 
The cast of this invention is comprised of an inner protective, preferably 
heat sealed, sleeve of approximately cylindrical configuration to be worn 
against the skin, followed by a layer of soft, resilient cotton or 
polyester padding wound, folded, or otherwise formed into a protective 
layer about the protective sleeve, and formed about both of these layers 
an immobilizing plaster-of-paris or organic polymer resin/glass fiber 
composite splinting material. 
This preferred form of protective wrapper is a heat-sealed sleeve of a 
porous liquid water impenetrable, water vapor permeable organic polymeric 
membrane, preferably of porous expanded polytetrafluoroethylene. This is 
characterized by properties which permit water, perspiration, or urine to 
vaporize away from the skin through the membrane by moisture vapor 
transmission so that the skin remains dry. Moisture vapor transmission of 
the membrane is the operative mechanism here, not air permeability. The 
wrapper of the invention is made from a composite membrane which has a 
continuous hydrophilic layer that transports water by an 
absorption-evaporation mechanism. The hydrophilic layer is attached to a 
microporous hydrophobic polymer layer which permits no detectable passage 
of liquid water to 100 pounds per square inch (psi). Any known membrane 
having the requisite properties may be used for this layer of the cast of 
this invention, although the preferred materials are the microporous 
expanded polytetrafluoroethylene membranes described in U.S. Pat. Nos. 
4,194,041 and 4,443,511. Also utilizable are microporous polypropylene 
films and polyurethane films and tightly woven fabrics of polyolefin 
fibers and polytetrafluoroethylene and other fluorinated polymer fibers. 
Breathability is achieved by evaporation of water inside the inner surface 
of the membrane, followed by gaseous diffusion of water vapor through the 
membrane to the outside. This ensures that the surface of the skin remains 
dry, thus guarding against immersion skin and skin irritation. Because of 
the intrinsic pore size of the membrane (9 billion per square inch), the 
membrane also serves to deter bacterial development, since it is a natural 
barrier to bacteria which cannot pass through pores of such small size. 
Also, the membrane has no nutritive substance for bacteria to feed upon. 
Thus, odor caused by rampant bacterial growth on moist skin unable to dry 
will not occur. Body secretions or wound drainage cannot seep into padding 
or ultimately into the cast itself. Therefore, odor is greatly reduced. 
A heat-sealed tube 2 of the membrane is placed over the area to be 
immobilized and overwrapped, such as the arm shown in FIG. 1. The membrane 
tube 2 is then covered or wrapped with a layer of, for instance, soft 
cotton or polyester padding 3, leaving small ends of membrane 2 uncovered. 
These may later be trimmed off after the cast has been completely formed 
and cured or may be folded up over a first layer of the wetted cloth 
plaster-of-paris web composite wrapping 1 which is now wrapped around the 
padded, membrane-covered area to be immobilized and anchored or buried 
inside layers of the wrapping. The cast is completed when an immobilizing 
thickness of material has been added and it has hardened sufficiently. 
Such liquid water that might enter the plaster layer of the cast during 
wear cannot of course penetrate the protective membrane sleeve 2 to harm 
the wearer and will evaporate through the padding or the outer surface of 
the cast. Most plaster casts are also air impermeable as well. 
Alternatively to the water-wet cloth/plaster-of-paris immobilizing layer, 
an organic polymer resin-impregnated or coated glass fiber cloth, roving. 
non-woven mesh, mat, or other glass or plastic fiber material in 
appropriately sized strips may be wound around the padding layer and the 
protective sleeve to form an immobilizing orthopedic cast. Many of these 
materials are warmed to levels above room temperature but to heat levels 
well tolerable by the body, and while soft, are wound, formed or shaped 
into a cast which then hardens fairly rapidly to an immobilizing 
stiffness. These resin/glass fiber casts are usually waterproof in 
practice, transmit little water vapor, and are not air breathable. 
Alternatively to a heat-sealed tube of membrane an overlapped wrap of the 
same or similar membrane material shown above may be used. Enough of the 
membrane must be used to overlap about itself on the area to be 
immobilized by a plaster or polymer/fiber cast so as to achieve good 
contact between the layers of member to insure waterproofness of the 
membrane protective warp. This way of using membrane requires more 
membrane to cover a given area than a heat-sealed tube of the same 
membrane on the same area and is consequently expensive, but is functional 
in this invention and may be useful for covering irregular or non-tubular 
type areas or used under emergency or other circumstances where no 
heat-sealed tube is available. Membrane formed into a tube by sealing 
pieces of it together with adhesives which will adhere sufficiently to 
polytetrafluoroethylene or other polymer membranes useful in this 
invention can also be used in place of the preferred heat-sealed membrane. 
Such adhesives may include epoxy, polyurethane, or thermoplastic 
fluoropolymers. 
It will be apparent to those skilled in the art that various modifications 
and variations could be made in materials and methods for making the casts 
without departing from the scope or spirit of the invention and the scope 
of the invention is delineated only by the appended claims.