WO1996040028A1

WO1996040028A1 - Orthopedic cast

Info

Publication number: WO1996040028A1
Application number: PCT/US1996/008666
Authority: WO
Inventors: Lawrence C. Greene; Andrew W. Larson
Original assignee: Landec Corporation
Priority date: 1995-06-07
Filing date: 1996-06-04
Publication date: 1996-12-19
Also published as: AU6037996A

Abstract

The final shape of a heat-recoverable orthopedic cast (1) is changed by a shaping member (4) which modifies the forces exerted on selected parts of the cast. The cast (1) includes an elastically deformed support (11, 12, 13) and a solid casting composition which maintains the support in its elastically deformed condition. When the cast is heated, the casting composition softens, releasing the elastic recovery forces of the support. The shaping member modifies the elastic recovery forces and/or external forces which are applied to the softened cast to change its shape, for example to bend a generally tubular cast such as a short leg walking cast.

Description

ORTHOPEDIC CAST

This invention relates orthopedic casts..

It is well known to make orthopedic casts, splints, supports, braces, shields, wound covers, and like orthopedic devices (all of which are referred to herein simply as "casts") from calcined gypsum (Plaster of Paris), or from a polymer which is formed into shape while hot and hardens on cooling, or from a prepolymer which is formed into shape and then polymerized in situ, e.g. a polyurethane prepolymer which is hardened by water. The term "casting composition" is used herein to denote a polymeric composition which can be formed into shape around a substrate (often referred to herein simply as a limb) and then hardened by chemical reaction or by cooling. Known casting compositions can comprise a single polymer or a mixture of two or more polymers, and can contain additional ingredients such as inorganic fillers, and can be associated with a flexible support, which may be elastic, for example a fabric or a foam sheet. Reference may be made for example to US Patent Nos. 3,692,023 (Phillips), 3,728,206 (Buese), 3,809,600 (Larson), 4,019,505 (Wartman), 4,105,025 (Wang), 4,193,295 (Gruber), 4,231,356 (Usukura), 4,273,115 (Holland), 4,326,509 (Usukura), 4,404,333 (Watanabe), 4,433,680 (Yoon), 4,473,671 (Green), 4,483,333 (Wartman), 4,643,909 (Kammerer), 4,668,563 (Buese), 4,784,123 (Robeson), 4,912,174 (Grouiller), 4,937,145 (Dull), 4,946,726 (Sandvig), 4,951,656 (Gorka), and 5,027,804 (Forsyth), European Patent Publication Nos. 0086686, 0110860, 0169037, 0338815 and 0358451, and PCT Publication Nos. WO 90/14060 and 91/09909.

A new type of orthopedic cast has recently been introduced by Landec Corporation under the trade name QuickCast. In these new casts, a tubular elastically deformable support is held in an elastically deformed condition by means of a solid thermoplastic casting composition. The tubular cast is sufficiently oversize to allow it to be placed around the patient's limb (the term "limb" is used throughout this specification to refer to any part of a patient's body, including the torso). When the cast is in place, it is heated to soften the casting composition. This releases the elastic forces of the support and causes the cast to recover around the limb. For a detailed description of such heat-recoverable casts, reference should be made to published International Application Nos. PCT/US93/03962 and PCT/US94/04138. Although these new heat-recoverable casts are very satisfactory for many purposes, we have found that the elastic forces of the support, if satisfactory for one part of the cast, may be insufficient or excessive for another part of the cast. This is particularly apparent when the cast must be recovered over a very irregular substrate; when the cast must be recovered over a substrate having one or more areas where pressure is undesirable; and when the desired finished shape of the cast has a distinct angle in it, as for example a short leg walking cast. Thus, when making a short leg walking cast, the cast is usually placed over the foot and leg of the patient while the foot is in the relaxed plantar flexion (i.e. at an angle of about 120° to the leg), and, after the cast has been softened by heating, the cast is bent so that the foot is at an angle of about 90° to the leg. We have found that when the cast is bent in this way, it tends to crease or fold, creating a pressure point on the patient.

In some cases, the problems caused by insufficient or excessive elastic forces can be mitigated by skilful hand-shaping of the softened cast while it is around the patient's limb. However, not all problems can be solved in this way, especially when the desired final shape of the cast requires that the cast should be subjected to external forces which oppose some of the elastic recovery forces. Furthermore, it is in any case desirable to reduce the level of skill needed to apply a satisfactory cast.

We have now discovered that these disadvantages can be mitigated or overcome through the use of a shaping member which exerts appropriate forces on selected parts of the cast while the casting composition is in a softened state. The shaping member can for example be placed between the layers of a support having multiple layers, but it is preferably placed in a retaining member. The retaining member can be attached to the heat-recoverable cast or it can be separate from the heat-recoverable cast. When the retaining member is attached to the heat-recoverable cast, it is preferably attached to the interior of the cast; for example the retaining member can be a strip of foam whose edges are secured to the interior of the support to form a channel, as further described below. The retaining member can be permanently attached to the cast, or it can be attached in such a way that it can be removed from the cast, at least before the cast is recovered. When the retaining member is separate from the heat-recoverable cast, it is placed between the cast and the limb before recovery of the cast; for example, the retaining member can be a tubular liner, preferably a padded liner, which is placed around the limb before the heat-recoverable cast. Preferably, the shaping member and the retaining member are such that the shaping member can be removed after the cast has been recovered.

In a first preferred aspect, this invention provides a heat-recoverable orthopedic cast which comprises

(1 ) a heat-recoverable main member which comprises

(a) a support which is in an elastically deformed condition, and

(b) a solid casting composition which

(i) comprises a casting polymer having a transition point T_s, (ii) contacts the support and maintains it in its elastically deformed condition, and (iii) when the cast is heated to a temperature above T_s, softens and releases elastic recovery forces of the heat- recoverable support, thereby causing recovery of the cast; and

(2) a shaping member which

(a) is adjacent to the main member, and

(b) when the casting composition is softened, modifies forces exerted on selected parts of the support, said forces being selected from (i) the elastic recovery forces of the support, and (ii) the elastic recovery forces of the support in combination with external forces which oppose some of the elastic recovery forces, the shaping member thereby causing the cast to recover to a configuration which is different from the configuration which it would have adopted in the absence of the shaping member.

Thus, the shaping member produces a selective modification of the elastic recovery forces when the softened cast is subjected to external forces opposed to the elastic recovery forces, and/or when the cast is recovered without subjecting it to any such external forces.

In a second preferred aspect, this invention provides a process for forming an orthopedic cast around the limb of a patient which comprises

(A) placing around the limb a heat-recoverable orthopedic cast which comprises

(1 ) a heat-recoverable main member which comprises

(a) a support which is in an elastically deformed condition, and

(b) a solid casting composition which (i) comprises a casting polymer having a transition point T_s, (ii) contacts the support and maintains it in its elastically deformed condition, and (iii) when the cast is heated to a temperature above T_s, softens and releases elastic recovery forces of the heat-recoverable support, thereby causing recovery of the cast;

(B) providing a shaping member which is adjacent to the heat-recoverable main member; and (C) heating the cast to soften the casting composition and cause recovery of the heat-recoverable member towards the limb, and optionally subjecting the cast, while the casting composition is softened, to external forces; said shaping member, when the casting composition is softened, modifying forces exerted on selected parts of the support, and thereby causing the cast to recover to a configuration which is different from the configuration which it would have adopted in the absence of the shaping member.

The invention is particularly useful when the process includes subjecting the softened cast to external forces in a direction different from the elastic recovery forces, for example when the cast is bent axially through an angle of at least 45°.

In a third preferred aspect, the invention provides a heat-recoverable cast which is adapted to receive, and retain during recovery, a shaping member, in particular a heat-recoverable orthopedic cast which comprises

(1) a heat-recoverable main member which comprises

(a) a support which is in an elastically deformed condition, and

(b) a solid casting composition which

(i) comprises a casting polymer having a transition point T_s, (ii) contacts the support and maintains it in its elastically deformed condition, and (iii) when the cast is heated to a temperature above T_s, softens and releases elastic recovery forces of the heat- recoverable support; and

(2) a retaining member which can retain a shaping member adjacent to selected parts of the main member when the cast is heated to a temperature above T_s, and into which can be inserted a shaping member, said shaping member, when the casting composition is softened, modifying forces exerted on selected parts of the support, said forces being selected from (i) the elastic recovery forces of the support, and (ii) the elastic recovery forces of the support in combination with external forces which oppose some of the elastic recovery forces; the shaping member thereby causing the cast to recover to a configuration which is different from the configuration which it would have adopted in the absence of the shaping member.

In a fourth preferred aspect, this invention provides a liner, preferably a padded liner, for a heat-recoverable cast, the liner incorporating a shaping member, or being provided with a retaining member for a shaping member. In a preferred embodiment, the liner is a tubular elastically deformable fabric liner having a channel which runs axially of the liner and into which a shaping member can be inserted.

A particularly preferred embodiment of the first aspect of the invention is a tubular heat-recoverable orthopedic cast which comprises

(1) a tubular heat-recoverable main member which has a length x and an interior circumference y, and comprises

(a) a tubular knitted elastic fabric support which is in a radially elastically expanded condition, and (b) a solid casting composition which

(i) comprises a casting polymer having a transition point T_s of 45° to 85°C, preferably a crystalline polymer having a crystalline melting point of 45° to 60°C, (ii) impregnates the support and maintains it in its expanded condition, and

(iii) when the cast is heated to a temperature above T_s, softens and releases elastic recovery forces of the heat- recoverable member; and (2) an elongate shaping member which (a) is adjacent to the interior of the main member,

(b) runs axially of the member,

(c) has a length of at least 0.5x,

(d) has a width of 0.01 y to 0.06 y, and (e) is composed of a polymeric composition comprising a crystalline polymer having a melting point of at least (T_s + 25)°C.

Such a cast is particularly suitable for forming a short leg walking cast by

(A) placing the cast around a part of a foot and leg of a patient while the foot is in relaxed plantar flexion, with the shaping member on the part of the cast closest to the front of the patient's ankle;

(B) heating the cast to soften the casting composition and cause recovery of the heat-recoverable member towards the leg and foot;

(C) while the casting composition is softened, bending the axis of the cast so that the foot is at an angle of about 90° to the leg; and

(D) allowing the cast to cool while the foot is at an angle of about 90° to the leg.

The shaping member can be composed of any material and can be of any shape such that, in use, it produces a desirable modification in the configuration of the recovered cast. The shaping member produces this desirable modification by modifying the forces which act on the cast to produce its final shape. These forces can be solely the elastic recovery forces of the support, or solely a combination of these elastic recovery forces with external forces which reinforce those elastic recovery forces (typically those applied by the hands of the practitioner applying the cast).

Under such circumstances, the shaping member can resist the forces acting on a part of the cast, for example to prevent pressure on a swollen area on the patient, or can enhance the forces acting on a part of the cast. However, the invention is particularly useful when the application of the cast includes the use of external forces which oppose some of the elastic recovery forces. Such opposing external forces are typically used when a generally tubular heat-recoverable cast is used to produce a finished cast which has a bent axis. Typically such a bent cast is produced by the practitioner bending the cast, while the casting composition is softened. However, in the absence of a suitable shaping member, this is liable to cause the cast to buckle, crease or fold, so that undesirable pressure points are created on the patient.

The invention includes the possibility that the shaping member does not substantially modify the configuration of the cast when it is initially recovered, but does so when the cast is reheated to soften the casting composition and is reshaped to a different configuration. For example, a tubular cast containing an axial shaping member could be initially recovered in a straight configuration which was not influenced by the shaping member, and later (e.g. a few days later) reheated and shaped into a bent configuration.

The shaping member must retain substantial strength during recovery of the cast, so that it can modify the forces which shape one or more selected parts of the cast. Generally, the shaping member will undergo elastic deformation but not plastic deformation, while the softened cast is shaped into its final configuration. However, the invention includes the possibility that the shaping member undergoes both elastic and plastic deformation, or even plastic deformation with substantially no elastic deformation. The shaping member can also be a heat-recoverable member which also undergoes recovery during the recovery of the cast.

The shaping member is preferably composed of a polymeric material. The polymeric material can be a thermoplastic, elastomeric or thermoset material providing the shaping member has the necessary functional characteristics. Preferably the polymeric material comprises a crystalline polymer. The crystalline polymer preferably is not crosslinked and has a melting point substantially above T_s , particularly above (T_S+25)°C, especially above (T_S+35)°C, e.g. at least 120°C, particularly at least 140°C, so that it does not soften unduly when the cast is recovered. Polypropylene is a preferred polymer. Alternatively the crystalline polymer can be crosslinked, in which case its crystalline melting point can be above or below T_s. In one particular embodiment, the shaping member is a heat-recoverable member which (a) is composed of a crosslinked crystalline polymeric composition having a crystalline melting point T_x, and (b) has been rendered heat-recoverable by a process which comprises (i) deforming a shaped article composed of the crosslinked polymeric composition at a temperature above T_x from a first configuration to a second configuration, and (ii) cooling the article to a temperature below T_x while it is in the second configuration; and the cast is recovered by heating it to a temperature which is not only above T_s but also above T_x.

The shaping member can also be composed of another material, e.g. a metal such as stainless steel or a nickel-titanium alloy, or two or more materials, e.g. a polymer-coated metal.

The shape of the shaping member and its position adjacent the cast will be determined by the way in which it is to modify the final configuration of the cast. Two or more shaping members can be used together. The internal surface area of the cast prior to recovery is substantially greater than, for example 10 to 500 times, the area of the shaping member(s).

The shaping member will often run in the axial direction of a tubular cast. We have obtained particularly useful results when the cast is tubular and the shaping member is an elongate strip which runs axially therein, and which thus overcomes (or at least reduces) the tendency of the cast to buckle when it is bent. The term "tubular" is used herein to denote any cast which has a closed cross-section and recovers radially inwards. Such a cast may be, for example, substantially cylindrical and comprise two or three plys of an elastic fabric impregnated by the casting composition which maintains it in a radially extended condition. In a tubular cast in which the main member has an axial length x and an interior circumference y, the shaping member is preferably an elongate axial member which has a length of at least 0.25x, particularly at least 0.75x, especially at least x, and a width of 0.005 y to 0.15 y, particularly 0.01 to 0.06 y. There may be a single axial shaping member, or two or more such members. Tubular casts for different parts of the human anatomy and modified in this way may for example have the following dimensions x x for fingers 6 to 12 cm 6 to 13 cm for arms 27 to 36 cm 24 to 44 cm for legs 50 to 90 cm 48 to 80 cm for torsos 35 to 50 cm 150 to 300 cm

In another embodiment, the shaping member runs circumferentially around a tubular cast, generally around at least 50%, particularly at least 75%, especially 100%, of the circumference, so that recovery of the cast is reduced over a part of the length of the cast. For example, such members can be placed at each end of the cast to ensure that it does not rub against the patient's limb or torso.

In other embodiments, the shaping member is in the form of a patch which reduces the extent of recovery of the cast in the area which it covers.

The shaping member can be maintained adjacent the cast (and in a position which ensures the desired modification of the cast) in any convenient way. In most cases, the shaping member will be placed in the cast itself, or between the interior surface of the cast and the patient. The shaping member generally does not serve any useful purpose once the cast has reached its final configuration, and indeed its presence can create undesirable pressure points. Especially in the latter case, it is preferred that the shaping member be removed after the cast has reached its final configuration. It is preferred that the cast itself, or a liner placed between the cast and the patient, be provided with a retaining member into which the shaping member can be placed and from which the shaping member can preferably be removed after the cast has reached -l i¬

fts final configuration. The retaining member is preferably a channel comprising a fabric and/or a foam material. The channel may be for example on the interior of the cast, on the exterior of a padded liner placed between the cast and the patient. The padded liner may be attached to the cast and the ends of the liner optionally unfolded to cover the adjacent exposed portions of the patient's limb before the cast is recovered, or the padded liner can be placed on the patient before the cast. The channel can be formed by continuously or intermittently attaching a polymeric foam or a fabric, preferably a padded fabric, to the cast or to the liner.

When the shaping member is ultimately to be removed from the hardened cast, it should preferably extend beyond the cast and include an extending portion which is shaped so that it can be engaged (by the operator's hand or a suitable tool) to make its removal simple.

Preferred characteristics of the elastically deformed support include one or more of the following:

(1 ) It is a fabric support which

(a) is in an elastically stretched condition, and

(b) comprises elastic fibers which are (i) composed of an elastomeric material and

(ii) elastically stretched.

(2) It can be stretched elastically by at least 25%, based on the corresponding dimension of the support in its unstretched state.

(3) It is a knitted fabric in which at least one of the yarns is composed of an elastomeric material, preferably a fabric knitted from at least one elastomeric yarn and at least one glass fiber yarn.

(4) It is is a knitted fabric having a power of 0.1 to 2 lb/inch.

Preferred characteristics of the casting polymer include one or more of the following: (1) It comprises a crystalline polymer having a crystalline melting point of 45° to 85°C.

(2) It comprises polycaprolactone.

(3) It comprises a side chain crystalline polymer.

Preferred characteristics of the heat-recoverable main member include one or more of the following:

(1) When it is heated to a temperature above T_s and permitted to shrink in the absence of any restraint, it has at least one dimension which shrinks by at least 25%, preferably 25 to 62%, based on that dimension prior to heating.

(2) Its shrinkage, when it is heated, is provided substantially entirely by elastic recovery of elastically stretched fibers in the support.

(3) Its strength, after it has been heated to a temperature above T_s and permitted to shrink in the absence of any restraint, followed by cooling to 25°C, is at least 4.3 kg/cm (5 lb/inch).

(4) It has a plurality of apertures through its thickness, each of the apertures having an area of 0.01 to 0.12 cm^, and preferably such that it has an air flow permeability of 10 to 60%.

Preferably the cast includes a liner which comprises padding material and is secured to the inside of the main member. Preferred characteristics of the padded liner include one or more of the following:

(1) It comprises a tube of elastically deformed stockinette fabric. (2) It has an air flow permeability of less than 25%.

(3) It has an air flow permeability which is less than 0.75 times the air flow permeability of the heat-recoverable main member.

(4) It comprises a padding material which comprises a non-woven fabric of cellulosic or polyester fibers, or a foamed polymer. For further details of heat-recoverable casts which can be used in conjunction with shaping members in accordance with the present invention, and for further details of liners which can be used with the heat-recoverable casts (and which can act as carriers for the shaping members), reference should be made to the documents referred to above.

Referring now to the drawings, Figures 1 and 2 show a heat-recoverable short leg walking cast. In the cast, a heat-recoverable main member 1 is made up of three plies 11, 12, 13, each composed of an elastic fabric support maintained in a radially extended condition by a solid casting composition (not shown) impregnated therethrough. The three plies are made by wrapping a single length of impregnated stretched fabric around a mandrel and securing the plies together by a line 15 of hot melt adhesive along the line of the outer wrapped end. Between the inner and intermediate plies 11, 12, opposite the line of adhesive 15, are placed reinforcing patches 21, 22 of the same impregnated stretched fabric; the patches recover in the same direction as the plies 11, 12, 13. On the interior surface of the cast, the edges of a foam strip 3 are spot bonded at intervals to the inner ply 11 , to form a retaining member in the form of an axial channel. Removably positioned in the channel is a shaping member 4 which has a ring 41 formed in the extending portion thereof.

EXAMPLES

The invention is illustrated by the following examples. In each of the examples, the support was made from an elastically extensible fabric obtained from Caroline Narrow Fabrics (Winston Salem, North Carolina, USA). The fabric is a three bar knitted warp fabric with ECDE 37 1/0 Z glass fiber yarn in the first and second bars and a natural rubber yarn in the third bar. The third bar rubber yarn is a natural rubber monofϊlament which has a diameter of about .019 inch (0.05 cm) and is available from Globe Rubber Co., under the trade name GM9. It has a density (unstretched) of 1000 +/-100 g/m and will return to substantially its original length if stretched by up to about 3 times its original length. In each of the examples the fabric was stretched by about 200%, i.e. to about 3 times its original length and while stretched was melt coated with a polycaprolactone (PCL) composition which is available from Solvay Interox Chemicals (Warrington, Great Britain) under the trade name CAPA 640, and which has a T_m of about 57°C and a reported molecular weight of about 37,000. The stretched, coated fabric was maintained at a temperature of about 110°C for a time sufficient to ensure that the fabric was thoroughly impregnated by the PCL, and was then cooled in the stretched state. The coated fabric was about 61 cm wide.

Example 1

A tubular cast substantially as shown in Figures 1 and 2 was made by winding a length of about 170 cm of the coated fabric 3 times around a mandrel having a diameter of about 17 cm (circumference about 54 cm), and securing the outside end to the fabric by means of an ethylene/vinyl acetate copolymer hot melt adhesive. Reinforcing patches were placed between the first and second plies, as shown in Figures 1 and 2. To the interior of this tube, along the glue line, was attached a piece of high density polyethylene foam (3 x 24 x 0.125 inch, 7.6 x 61 x 0.32 cm) obtained from E. N. Murray Co., Denver, under the trade name Volara 2A, using the same hot melt adhesive. This formed a sleeve into which was inserted a plastic shaping member, 1 x 25 x 0.125 inch (2.5 x 63.5 x 0.32 cm), made of polypropylene (Laird Plastics, Santa Clara, CA. . The shaping member had been die cut to have a ring at one end to facilitate the removal of the shaping member after the cast had cooled.

Example 2

The cast made in Example 1 was applied to the lower leg and foot of an adult patient by the following procedure.

1. The leg and foot were covered by a padded stockinette liner (QuickCast All-In-One Liner available from Landec Corp., California, USA). 2. The cast was placed over the leg and the foot in the plantar flexion. The top of the cast was about 1 inch (2.5 cm) below the knee, and the shaping member ran along the top of the foot and the front of the leg, with the extending ring end at the toe end of the cast. 3. A hot air blower was used to soften the PCL casting composition, thus causing the cast to recover. While the PCL was still soft, the foot was rotated into the walking position (about 90° relative to the leg). Hand pressure was used to complete the shaping of the cast.

4. The cast was allowed to cool, keeping the foot in the walking position, and the shaping member was then removed.

Example 3

The procedure of Example 1 was followed except that (1) the coated fabric was about 16 x 64.5 inch (40.6 x 164 cm) and was wrapped three times around a mandrel of 44 cm circumference, (2) the foam member was about 3 x 16 x 0.125 inch (7.5 x 40.6 x 0.32 cm), and (3) the shaping member was 17 inch (43 cm) long. In this way, a short leg walking cast for a child was prepared.

Claims

1. A heat-recoverable orthopedic cast which comprises

(1) a heat-recoverable main member which comprises

(a) a support which is in an elastically deformed condition, and

(b) a solid casting composition which

(2) a shaping member which

(a) is adjacent to the main member, and

(b) when the casting composition is softened, modifies forces exerted on selected parts of the support, said forces being selected from (i) the elastic recovery forces^'of the support, and (ii) the elastic recovery forces of the support in combination with external forces which oppose some of the elastic recovery forces, the shaping member thereby causing the cast to recover to a configuration which is different from the configuration which it would have adopted in the absence of the shaping member.

2. A cast according to claim 1 wherein the cast includes a retaining member which is a channel attached to the interior of the heat-recoverable cast, and in which the shaping member is removably positioned.

3. A cast according to claim 1 or 2 wherein

(1) the main member is tubular and has a length x and an interior circumference y;

(2) the support is a knitted elastic fabric support which is in the form of a radially elastically expanded tube;

(3) the casting polymer is a crystalline polymer having a melting point T_p of 45° to 85°C; and

(4) the shaping member is elongate and

(a) is adjacent to the interior of the main member,

(b) runs axially of the main member,

(c) has a length of at least 0.5x,

(d) has a width of 0.01 y to 0.06 y, and

(e) is composed of a polymeric composition comprising a crystalline polymer having a melting point of at least (T_p + 25)°C.

4. A cast according to claim 3 wherein x and y are selected from

(1) x is 6 to 12 cm, and y is 6 to 13 cm;

(2) x is 27 to 36 cm, and y is 24 to 44 cm;

(3) x is 50 to 90 cm, and y is 48 to 80 cm; and

(4) x is 35 to 50 cm, and y is 150 to 300 cm.

5. A cast according to any one of the preceding claims wherein the cast includes a liner which comprises padding maerial and is secured to the inside of the main member.

6. A heat-recoverable orthopedic cast which comprises

(1) a heat-recoverable main member which comprises

(a) a support which is in an elastically deformed condition, and

(b) a solid casting composition which

(i) comprises a casting polymer having a transition point T_s, (ii) contacts the support and maintains it in its elastically deformed condition, and (iii) when the cast is heated to a temperature above T_s, softens and releases elastic recovery forces of the heat- recoverable support; and (2) a retaining member which can retain a shaping member adjacent to selected parts of the main member when the cast is heated to a temperature above T_s, and into which can be inserted a shaping member, said shaping member, when the casting composition is softened, modifying forces exerted on selected parts of the support, said forces being selected from (i) the elastic recovery forces of the support, and (ii) the elastic recovery forces of the support in combination with external forces which oppose some of the elastic recovery forces; the shaping member thereby causing the cast to recover to a configuration which is different from the configuration which it would have adopted in the absence of the shaping member.

7. A cast according to claim 6 which is tubular and is radially recoverable, and wherein the retaining member is a channel which runs axially of the tubular cast.

8. A cast according to claim 7 wherein the main member has a length x and an interior circumference y, and the channel has a length of at least 0.75 x and a width of 0.005 y to 0.15 y.

9. A process for forming an orthopedic cast around a limb of a patient, the process comprising

(A) placing around the limb a heat-recoverable orthopedic cast which comprises (1 ) a heat-recoverable main member which comprises (a) a support which is in an elastically deformed condition, and

(b) a solid casting composition which

(i) comprises a casting polymer having a transition point T_s, (ii) contacts the support and maintains it in its elastically deformed condition, and (iii) when the cast is heated to a temperature above T_s, softens and releases elastic recovery forces of the heat-recoverable support, thereby causing recovery of the cast;

(B) providing a shaping member which is adjacent to the heat-recoverable main member; and

(C) heating the cast to soften the casting composition and cause recovery of the heat-recoverable member towards the limb, and optionally subjecting the cast, while the casting composition is softened, to external forces; said shaping member, when the casting composition is softened, modifying forces exerted on selected parts of the support, and thereby causing the cast to recover to a configuration which is different from the configuration which it would have adopted in the absence of the shaping member.

10. A process according to claim 9 wherein

(1) a short leg walking cast is formed around a part of a foot and leg of a patient, the tubular heat-recoverable cast being positioned around a part of the foot and leg of the patient while the foot is in relaxed plantar flexion, with the shaping member on the part of the cast closest to the front of the patient's ankle; and

(2) while the casting composition is softened, the cast is bent axially so that the foot is at an angle of about 90° to the leg; and the casting composition rehardens while the foot is at an angle of about 90° to the leg.