GB2130488A - Fracture cast-braces and casts incorporating them - Google Patents

Abstract

A hinge-brace for a fracture cast comprises a hinge portion 1 having secured to at least one end thereof a head-plate 2 for incorporation in a fracture cast. The head- plate has a thickened central region and upper and lower surfaces which are substantially coplanar with corresponding upper and lower surfaces at the adjacent end of the hinge portion, whereby, when the head-plate is embedded in casting material, the formation of dead spaces in the region where the hinge portion joins the head-plate is substantially eliminated. The hinge portion may be a plastics polycentric hinge portion or a monocentric metal hinge portion and the head- plates may be roughened or formed with teeth, splines or prongs to enhance and promote mechanical capture of the casting material. <IMAGE>

Description

SPECIFICATION Fracture cast-braces and casts incorporating them This invention relates to fracture cast-braces or hinge-braces and to casts incorporating such braces.

White Plaster of Paris casts, such as full leg casts, or casts which are applied to other areas, where immobilisation of fractured bone, or bone required to fixate by virtue of elective surgery, is required are well known for ensuring that fractured ends of bone, once "set" or re-aligned so that they approximate closely, do not undergo relative motion or displacement.

There are, however, therapeutic consequences to the use of plaster casts on long bones, not to mention certain inherent disadvantages of Plaster of Paris itself. Problems can be particularly pronounced when full leg casts are used on the long bones of the leg.

Commonly, orthopaedic surgeons and plaster technicians apply the cast not only to the affected part of the limb, but also to the adjacent (proximal or distal) part, e.g. the full leg or full arm cast. This is to ensure that most of the compressive load is transmitted from points beyond to points before the fracture. Perhaps even more important is the prevention of rotation which, if unchecked, could cause further damage at the fracture site, perhaps culminating in non-union of it.

Casts also provide general mechanical protection and their very nature encourages the patient to "guard" the injury.

When the whole leg is immobilised in a plaster cast for, say, a mid-shaft fracture of the femur, restriction of movement may continue for several months until healing is complete. Joint stiffness, together with considerable wastage of muscle under the plaster is common. In the wake of this, there is considerable need for physiotherapy and rehabilitative services which constitute a drain on health-care resources. Disturbances of gait and delayed return to work, school or other occupation are all additional sequels. To a lesser extent, some of these consequences occur when the long bones of the arm are immobilised for a long period and it is worth mentioning the delay in return to car driving which is often associated with the extended application of a rigid cast.

Recognition and awareness of these problems has made orthopaedic surgeons and plaster technicians receptive to methods which enable the benefits of plaster casting to be had, but with a reduction in the undesira ble side effects. A major contribution to this aim has been the concept of cast-bracing which is otherwise called hinge-bracing or fracture-bracing.

This concept involves the application of two casts to long bones either side of a joint, e.g.

above and below the knee or above and below the elbow. The two casts are jointed at the time they are formed by hinges, carefully applied so that the hinge axis lies along the condylar axis of the joint, the top and bottom of each hinge being embedded in the plaster cast.

Since the 1 960's, the gradual development of the concept of ambulatory care of lower extremity fractures has progressed to the point where cast-bracing is now almost universally approved and accepted. The hinged cast has the fundamental advantage of allowing early motion in a joint. Furthermore, in the case of distal femur and upper tibial fractures, there is the advantage of early ambulation in addition to maintaining motion at the knee. Rotation is controlled.

Cast-bracing allows partial weight bearing at the fracture itself which promotes healing and mobilises oedema fluid which would otherwise accumulate in the capsular and ligamentous structures of the joints. This is important since such accumulation leads to joint stiffness and temporary (sometimes permanent) loss of function.

The basic concept of cast-bracing or hingebracing is that immobilisation is unphysiologic while mobilisation is always physiologic. The solutions of the cast-brace are thus physiological solutions.

Cast-braces in common use fall into two main categories: a. Metal monocentric hinges: These are usually made of aluminium or aluminium alloy and the upper and lower components are hinged together in a conventional manner about a single axis, the form of the actual hinge being of the bar and disc type. At the top and bottom of each component is a plate which is secured to the bar.

This type of hinge allows no possibility of medial or lateral movement at the joint it is bracing. Elevation and depression of the distal part of the limb relative to the proximal part about a single axis is the only type of movement which this hinge allows for-hence the name 'monocentric". Clearly very accurate position of both medial and lateral hinge axes on the elevation/depression axis of the joint is very important, otherwise these movements will be very difficult and torsional forces may be brought to bear on the affected limb.

Fixation can only be correctly carried out by using a jig to ensure the centres of rotation of both hinges lie on the same axis and that they are in the same sagittal plane.

b. Polycentric plastic hinges: These provide hingeing by virtue of the property of maintained flexibility during repeated flexing and relaxing of modern polymer plastics including high molecular weight polyethylene. This is enhanced by the shaping of the single hinge component into broad convolutions parallel to the axis of elevation/ depression of the limb and at right angles to the axis of the limb itself. Flexure of the hinge component may occur at any of these convolutions-hence the hinge is termed polycentric.

It is a feature of this type of hinge that on flexure, reactive forces build up within it, so that the musculature of the limb derives benefit from isometric exercises against the hinge. During walking, this effect also manifests as a gentle "throwing forward" of the leg which assists the patient in assuming a more normal gait despite having to wear the plaster cast. Because repeated flexure of plastic will eventually lead to fatigue of the material, plastic cast-braces are intended to be discarded after single use. At the top and bottom of each hinge are head-plates very similar (sometimes identical) to those used on monocentric bracing hinges. They are usually pressed from thin plastic sheet into rectangular plates with rounded corners, typically they have four holes about 1 cm in diameter, pressed through them in a regular pattern.

These plates are usually rivetted to the inner aspect of the hinge which has a flattened end formed and drilled for the purpose.

It is accepted as axiomatic by the professions who use and fit hinge-braces that there must be good contact between the Plaster of Paris and the plates on the hinge.

The holes in the plates enable wet plaster bandage to be pushed into them, so making contact with the bandage previously applied and improving lamination and bonding-in of the hinge plate. Even so, it is not always possible to achieve good lamination because the hinge component rises signficantly from the plate and it is very difficult to eliminate dead space under the portion of the bandage adjacent to the hinge.

Plaster of Paris has a number of inherent disadvantages as a material for making casts and these disadvantages are well recognised.

The setting time can be as much as 36 hours and patients may have to be hospitalised during this period. These casts are heavy and uncomfortable for the patient to wear. The casts are opaque to X-rays, hence the progress towards healing cannot be monitored through the cast when Plaster of Paris is used.

These factors were probably the main motivation behind the development of the modern casting materials, including those marketed as "Baycast", "Orthoplast", "Hexcelite", "Zo roc", "Scotchcast" and "Litecast".

Most of these materials set quickly to loadbearing (in some cases as little as 20 minutes) and are radio-apparent as well as being very much lighter than Plaster of Paris.

"Baycast" for instance, is a polyurethane resin system impregnated onto a woven fabric with threads measured at 0.5 mm across and 0.25 mm down, enclosing interstices of 1.00 mm by 0.5 mm. The fabric usually has very little elasticity.

The resin curing period is accelerated by water, moisture in the air being usually sufficient to promote initial setting in a few minutes.

The cured bandage is thin but very strong in the same plane as the weave. Strength increases rapidly as successive layers are built up, but is is essential, as with all casting materials, that good lamination is achieved between layers. This means there must be continuous contact between them.

Unfortunately, the failure to achieve excellent lamination when using the new casting materials in conjunction with hinge-braces has limited acceptance of this combination. Despite instructions by the manufacturers to bind the braces into the cast well down onto the hinged component past the head-plate, delamination and loosening of the braces is quite common. This is a potentially disastrous situation if the fractured limb suddenly becomes loaded.

There are several reasons for this problem of hinge/bond failure. Firstly, the fabric or base material of the new casting materials is not generally amenable to the "push through" approach to the holes in the headplate of the brace which is used with the soft bandage of the Plaster of Paris casting technique. Consequently, the holes simply represent lost bonding area.

Pressing the bandage against the holes in the head-plate to form a 'dimple' which engages with the holes to some extent on setting, is probably acceptable on the lateral aspect of the limb but on the medial aspect, there is an associated risk of nerve compression. This leads many users to eschew the practice. In any case, there is always a risk of using too much pressure and and deforming the cast inwards. This could cause impingement on the limb and consequent skin abrasion.

Secondly, the significantly raised area of the head-plate at and adjacent to the portion thereof where the hinge part joins the headplate causes a dead space under the bandage.

The dead space significantly reduces the surface area over which the layers of casting material contact the head-plate.

The use of rivets to secure the head-plate to the brace intensifies the problem since the rivets form excrescences on both faces, which, though small, still "lift" the bandage slightly away from the faces.

The combined effect of the holes in the plate and the dead space close to the hinge and around the rivets probably represent together loss of over 40% of the bonding area on the outside face and about 20% on the inner face. It should be borne in mind that these bandage or bracing materials have little conformability to tight radius curves but this is precisely what current hinge/head-plate designs impose.

Finally, it must be mentioned that virtually no bonding occurs between head pieces made of smooth polyethylene and the modern polyester or polyurethane casting materials.

It is hardly surprising then that there have been less than totally satisfactory results with modern casting materials in hinge-bracing when the underlying design of current hingebraces is considered.

It is an object of the present invention to provide an improved hinge-brace for fracture casts, and one which is particularly suitable for use with modern resin casting materials.

According to one aspect of the present invention there is provided a hinge-brace for a fracture cast, wherein the brace comprises at least one head-plate for incorporation in a fracture cast, the head-plate having upper and lower surfaces and being thicker in its central region than in its edge regions, and comprises a hinge portion secured at at least one of its ends to the thicker central region of a headplate, and wherein the hinge portion and head-plate are so shaped and secured to one another that the upper surface of the headplate and a corresponding upper surface of the hinge portion, are substantially coplanar and that the lower surface of the head-plate and a corresponding lower surface of the hinge portion are likewise substantially coplanar, whereby, when the head-plate is embedded in casting material, the formation of dead spaces in the region where the hinge portion joins the head-plate is substantially eliminated.

The hinge portion may be a polycentric plastics hinge or a metal monocentric hinge as discussed above. The brace preferably has a head-plate at each end of the hinge portion and in the case where a head-plate is secured to a polycentric hinge portion by being moulded integrally therewith in one piece, the thickness of the central region of the headplate is equal to that of the end of the hinge portion. Alternatively, the central region of the head-plate is formed with a recess and the end of the hinge portion is shaped in a manner complementary to said recess and is a close fit therein. The recess may be a slot formed in the central region or an open recess in one of the surfaces with the end of the hinge portion rebated to fit closely in the recess and provide the substantially coplanar surfaces.As the head-plates have thicker central regions and thinner edge regions they are substantially crescent shaped in cross-section and are preferably of arcuate crescent shape.

At their thickest points, the central regions of the head-plates are preferably about 25% to 30% thinner than rivetted-hinge-to-head-plate thickness in conventional designs. At their thinnest points (along the edges) they have a thickness similar to existing braces. In one embodiment, the inner face of the head-plate has a moulded open recess exactly matching the end of the hinge portion except for two stakes which engage holes in the hinge portion. These stakes form spin-welds when pressed firmly with a suitable spinning glass or metal die. The excrescence on the inner hinge is minimal and less than a rivet.

Experiments on a "standard leg" and "standard arm" made from lengths of 6" and 4" heavy duty plastic soil-pipe respectively, show that the present brace provides much better laminating surfaces than previously proposed braces as measured by increased mechanical bond strength and by other tests.

Performance may be enhanced by the provision in the head-plates of short narrow-angle splines which may be incorporated to face various impressed or reactive force directions.

It is possible to use the present hinge brace with Plaster of Paris since with this material, too, lamination is improved.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example some embodiments thereof and in which Figure 1 is a plan view of a hinge-brace showing various modifications; Figure 2 is a cross-section along the line Il-Il in Fig. 1 before assembly of parts; Figure 3 is a cross-section along the line Il-Il in Fig. 1 after assembly of parts; Figure 4 is a view along the line V-V in Fig. 1; Figure 5 is a view similar to Fig. 3 of a further modification; Figure 6 is a view of a further hinge-brace shown partly in top plan view and partly in under plan view, and Figure 7 is a cross-section along the line VII-VII in Fig. 6.

Referring now to Fig. 1, there is shown a hinge-brace for a fracture cast. The brace comprises a polycentric hinge portion 1 which may for example be of plastics, such as ethylene or nylon, and which may be moulded or formed from polyethylene bar. At each end, the hinge portion 1 is secured to a head-plate 2 and various head-plate modifications and methods of securing are shown in the drawings.

The bottom half of Fig. 1 shows a headplate 2, integrally moulded with the hinge portion 1 while the upper half of Fig. 1 shows a separately made head-plate subsequently secured to the hinge portion.

The hinge portion 1 is of generally conventional shape and may have its major portion displaced out of the plane of the paper to prevent the brace, when in use, from rubbing against the condyles of a joint (c.f. Fig. 4).

The head-plate 2, however, differs consider ably from the head plates of previously used hinge braces. As clearly shown in Figs. 2, 3 and 5, the head-plate 2 is arcuate crescentshaped in cross-section being thicker in its central region and thinner at the edges. Furthermore, the head-plate and hinge portion are secured together in a substantially flush manner so as substantially to avoid the possibility of a dead space forming when the brace is used. That is to say, an upper surface of the head-plate and a corresponding upper surface of the hinge portion are substantially coplanar as are a lower surface of the head-plate and a corresponding lower surface of the hinge portion.

The head-plate shown in Figs. 2 to 4 is formed with a recess 3 in which are formed two upstanding stakes or stubs 4. The end 5 of the hinge portion 1 is formed with two holes 6 to receive the stakes 4 and has a thickness substantially equal to the depth of the recess so that, as shown in Figs. 3 and 4, the end 5 of the hinge portion can be received in a substantially flush manner in the recess 3. The free ends of the stakes 4 are then compressed in a press using a spinning die which both swages and welds them down onto and partly into the hinge portion as shown at 7, thereby securing the hinge portion to the head-plate.

In the modification shown in Fig. 5, the head-plate is formed with a central hole 8 to receive an appropriately shaped end of the hinge portion 1. If desired, adhesive or glue may be used to reinforce the connection between the headplate and the hinge portion.

Other forms of fixing the head-plate to the hinge portion are possible, including rivets, snap-on fixings, or adhesive fixings, provided that in each case the substantially flush fitting or the two parts is achieved.

The use of a hinge brace as just described is substantially the same as that of previously proposed braces. However, the arcuate crosssection of the head-plate provides close conformation with a limb and this conformation, together with the elimination of dead spaces due to the flush connection of the head-plates and hinge portion, ensure good lamination of the head-plates using modern resin casting materials.

In order to improve the lamination, the head-plates may be roughened or formed with teeth or splines 9 as shown at the bottom right hand side of Fig. 1 and in Fig. 1A. The teeth or splines 9 may be formed on one or both sides of the head-plate and may point in any direction, or, as shown, some may point in one direction and some in another.

The head plates may be formed with holes 10 as is conventional but in order to enhance bonding and to reinforce the benefits of using a curved and shaped head-plate, circular pieces of the casting material may be provided with the brace to fill the holes and link the underlying and overlying layers of casting fabric material.

Referring now to Figs. 6 and 7, there is shown another hinge-brace for a fracture cast, the top half of Fig. 6 being an under plan view and the lower half a top plan view of a head-plate 12 each of which is secured to a polycentric hinge portion 11 in a manner similar to that discussed with reference to Figs. 2 to 4. The outer or upper surface of each head-plate 12 is formed with upstanding prongs 13 which are shown arranged in groups and the inner or under surface of each head-plate is formed with upstanding prongs 1 4 which are shown also arranged in groups.

As seen in Fig. 7, the prongs 14 are shorter than the prongs 13. It will be seen that the polycentric hinge portion 11 is also formed at its ends with prongs 15 on the outer surface and 16 on the inner surface with the prongs 16 being shorter than the prongs 15. As shown in Fig. 7, each head-plate 12 is formed with two grooves 17 running parallel to the portion 11 and sub-dividing the head-plate into a central portion 18 and two wing portions 19.

The head-plates of the hinge brace shown in Figs. 6 and 7 are preferably made of polypropylene and because of this the wing portions 19 can be bent relative to the central portion 18 without breaking so that the headplate can be closely conformed to limbs of even small dimensions. The hinge portion is conveniently made of nylon.

Finally, the surfaces of the head-plates and the ends of the hinge portion 11 have been roughened as by spark erosion or the like so that the hinge-brace does not present a smooth surface to the casting material.

As indicated above, several factors are important in maintaining a close and immobile relationship between a hinge-brace and the cast in which it is incorporated. The first of these is to design and shape the hinge-brace in such a way as to reduce to a minimum the dead space which occurs with prior art braces.

The second is to ensure good contact between the brace and the casting material as by roughening the surface of those parts of the brace which are to be embedded in the casting material. This can be effected by the provision of the teeth and splines 9 or by the prongs 13, 14, 15 and 16 which can engage through the weave of the casting material and effect sound mechanical capture of the casting material on to the hinge brace. The third factor is to ensure that, so far as possible, relative motion and distortion between the components of the hinge brace within the cast is eliminated. This may be effected by making the head-plates and hinge portion integral as by moulding, or by ensuring that the hinge portion fits tightly into the head-plate without play.In this connection it can be shown that the presence of a dead space in the region where the hinge portion is joined to the headplate provides good conditions for leverage of the hinge portion relative to the head-plate leading to distortion of the connection, loosening of the connection and even failure.

It will thus be appreciated that the first and third factors listed above are to some extent interdependent.

It will be appreciated that with the embodiment of the present hinge-brace shown in Figs. 6 and 7, the grooves 17 represent dead spaces which, as indicated above, are to be avoided. However, these dead spaces are remote from the junction of the hinge portion and the head-plate and can, therefore, not contribute to relative motion and distortion between the hinge portion and the head-plate.

Furthermore, as there are prongs 14 on each side of a groove 17 there is good mechanical capture of the casting material across the groove so that the presence of the grooves has the minimum deleterious effect on the hinge-brace while at the same time providing the advantage that by bending along the grooves, the head-plate can be conformed to a limb to be braced so as to eliminate the dead space that would otherwise exist betwen the wing portions 19 of the head-plate and the limb.

As indicated above, a previously proposed hinge brace is in the form of a thin rectangular head-plate to which the end of a hinge portion is rivetted and thus stands up proud above the head-plate. In contradistinction, the head-plate of the present hinge brace has a central region which is at least as thick as the end of the hinge portion to enable a flush fitting arrangement of the head-plate and hinge portion to be achieved thereby eliminating dead spaces and considerably improving lamination, as well as reducing the possibility of relative motion occurring between the hinge portion and the head-plate.

The present invention makes it possible to design the head-plate so that it will be thinner at its thickest central portion than the thickness of a comparable previously proposed hinge brace.

Furthermore, due to the improved lamination which can be achieved with the present hinge brace, the bond strengths which can be obtained using modern resin casting materials may equal or surpass those which can be obtained using Plaster of Paris, which may, itself, of course, be used with the present hinge brace.

Claims (20)

1. A hinge-brace for a fracture cast, wherein the brace comprises at least one head-plate for incorporation in a fracture cast, the head-plate having upper and lower surfaces and being thicker in its central region than in its edge regions, and comprises a hinge portion secured at at least one of its ends to the thicker central region of a headplate, and wherein the hinge portion and head-plate are so shaped and secured to one another that the upper surface of the headplate and a corresponding upper surface of the hinge portion, are substantially coplanar and that the lower surface of the head-plate and a corresponding lower surface of the hinge portion are likewise substantially coplanar, whereby, when the head-plate is embedded in casting material, the formation of dead spaces in the region where the hinge portion joins the head-plate is substantially eliminated.

2. A hinge-brace as claimed in Claim 1, wherein the hinge portion is a plastics polycentric hinge portion.

3. A hinge-brace as claimed in Claim 1, wherein the hinge portion is a monocentric metal hinge portion.

4. A hinge-brace as claimed in any one of Claims 1 to 3, wherein a head-plate is secured at each end of the hinge portion.

5. A hinge-brace as claimed in Claim 2, wherein a head-plate is secured to the polycentric hinge portion by being moulded integrally therewith.

6. A hinge-brace as claimed in any one of Claims 1 to 4, wherein the central region of the head-plate is formed with a recess and the end of the hinge portion is shaped in a manner complementary to said recess and is a close fit therein.

7. A hinge-brace as claimed in Claim 6, wherein the head-plate has substantially continuous upper and lower surfaces and said recess is a slot formed within the central region.

8. A hinge-brace as claimed in Claim 6, wherein the head-plate has an open recess in one of said surfaces and the end of the hinge portion is rebated to fit closely in said recess and to provide the substantially coplanar surfaces.

9. A hinge-brace as claimed in any preceding claim, wherein the head-plate is arcuate crescent-shaped in cross section.

10. A hinge-brace as claimed in any preceding claim, wherein at least one of the surfaces of the head-plate is provided with means for promoting mechanical engagement or capture between the head-plate and the casting material.

11. A hinge-brace as claimed in any preceding claim, wherein the at least one of the corresponding upper and lower surfaces of the hinge portion is provided with means for promoting mechanical engagement or capture between the hinge portion and the casting material.

12. A hinge-brace as claimed in Claim 10 or 11, wherein said means comprises teeth or splines formed on one or both of said surfaces.

1 3. A hinge-brace as claimed in Claim 12, wherein said teeth or splines are arranged on the or each surface in two groups, and wherein the teeth or splines of one group extend in a different direction from those of another group.

14. A hinge-brace as claimed in Claim 10 or 11, wherein said means comprises prongs formed on one or both of said surfaces.

15. A hinge-brace as claimed in Claim 13, wherein the upper surface of the head-plate is formed with prongs and the lower surface is formed with prongs which are shorter than those formed in the upper surface.

16. A hinge-brace as claimed in any preceding claim, wherein the upper and lower surfaces of the head-plate and hinge portion are roughened.

17. A hinge-brace as claimed in any preceding claim, wherein the head-plate is formed with two parallel grooves on either side of said central region, and wherein the head-plate can be bent along said grooves to conform the head-plate more closely to a limb to be braced.

1 8. A hinge-brace as claimed in any preceding claim, wherein the or each head-plate is made of plastics material.

19. A hinge-brace as claimed in any preceding claim, wherein the or each head-plate is made of polypropylene and the hinge portion is a polycentric hinge portion made of nylon.

20. A hinge-brace substantially as hereinbefore described with reference to the top half of Fig. 1 and Figs. 2 to 4, the lower half of Fig. 1, Fig. 5 or Figs. 6 and 7 of the accompanying drawings.