Abstract:
A bone splint manufactured in a polylactide copolymer, the splint comprising an elongate bridging member adapted to be secured to and across fractured bone ends and means to reduce the effective length of the bridging member so that, in use, the splint holds the bone ends together.

Description:
INTRODUCTION 
       [0001]    This invention relates to a bone splint particularly for use in open surgical fixation of fractured ribs. 
       BACKGROUND OF THE INVENTION 
       [0002]    Rib fractures are a painful and potentially disabling injury. When multiple ribs are fractured in more than one place, a flail segment of the chest wall can occur. This injury can lead to respiratory failure requiring mechanical ventilation. The mainstay of management in these patients has traditionally been analgesia and positive pressure ventilation to splint the chest wall and allow healing of the ribs to begin. However, this management option leads to prolonged intensive care unit stay with increasing complication rates as patients remain ventilated for prolonged periods. In particular, patients are at risk of pneumonia and sepsis and will often require tracheostomy formation to aid with bronchial suctioning and weaning. Long term disabilities which have been reported in these patients include ongoing pain syndromes, inability to return to work, particularly manual type labour and cosmetic chest wall deformities. 
         [0003]    Flail chest is a potentially life threatening injury whereby ribs which are broken in more than one place are no longer ‘fixed’ in the chest wall and become free floating. Thus during the respiratory cycle, the negative intrathoracic pressure generated during inspiration causes that segment of the chest wall to be sucked inwards rather than expanding the chest and sucking air into the lungs. This leads to paradoxical chest wall motion and impairs the mechanics of breathing which can lead to respiratory failure. 
         [0004]    Although flail chest is the most severe manifestation of fractured ribs less severe forms of fractured ribs can still lead to severe pain and disability. 
         [0005]    There have been proposals for operative fixation of rib fractures. Such methods include the use of anterior plates with wire cerclage, anterior plating with bicortical screws, judet struts, U-plates and absorbable plates. 
         [0006]    However, the use of any product for rib fixation is problematic because of the repetitive movement and load bearing of the bones being fixed. It is not possible to immobilise the affected area as would be routine management in most other bone fractures. Although the ribs do not carry a heavy load, they are affected by torque in multiple directions due to the layers of intercostal muscles inserting onto the ribs. The forces impacting on the ribs are therefore constant and in multiple directions. Any rib fixation strategy needs to take these factors into account. 
         [0007]    Most published studies of operative fixation use metal implants. Kirschner wires are prone to migration and provide no torsional stability. Pins and encircling wires have also not given reliable results in this application. Currently available metal plates are designed for other long bones and do not follow the complex curvatures of the ribs. Other drawbacks of metal plates are the need to return to theatre for removal if any complications such as infection or migration occur. Other post operative issues that can mandate removal are pain on palpation of the area particularly in thin patients, and thermal sensitivity. Further, the presence of metallic implants contradicts any future magnetic resonance imaging for the patient. 
         [0008]    More recently, it has been suggested to use polylactide copolymers as prostheses to avoid many of the potential complications caused by metal implants. 
         [0009]    It is these issues that have brought about the present invention. 
       SUMMARY OF THE INVENTION 
       [0010]    According to one aspect of the present invention there is provided a bone splint manufactured in a polylactide copolymer, the splint comprising an elongate bridging member adapted to be secured to and across fractured bone ends and means to reduce the effective length of the bridging member so that, in use, the splint holds the bone ends together. 
         [0011]    Preferably, the members are located within the medullary canals of the bone ends by cement. 
         [0012]    The means to control relative displacement may comprise serrations on the outside of the first member arranged to engage serrations on the inside of the second member, the interengagement of the serrations allowing relative displacement in one direction. 
         [0013]    In another embodiment the means to control the relative displacement comprises a threaded interrelationship between the outside of the first member and the inside of the second member. 
         [0014]    The first and second members are preferably hollow tubes. 
         [0015]    The cross section of the tubes may be circular or shaped to correspond to the cross-section of the medullary canals. 
         [0016]    In use, the splint is heated to be malleable when inserted into the bone ends. 
         [0017]    According to a further aspect of the present invention there is provided a method of fixing fractured ribs using a splint comprising an elongate bridging member, the member being manufactured in a polylactide copolymer, the method comprising the steps of:
       (a) heating the splint until malleable;   (b) securing the ends of the bridging member to end regions of adjacent bone pieces of the fractured ribs; and   (c) reducing the length of the bridging member to bring the ends together.       
 
         [0021]    According to a still further aspect of the present invention there is provided a method of fixing fractured ribs using a splint comprising a first hollow member in telescopic engagement within a second hollow member, the members being manufactured in a polylactide copolymer, the method comprising the steps of:
       (a) heating the splint until malleable;   (b) inserting the second member into the end of a first bone piece of the fractured rib;   (c) displacing the first member out of the second member and locating the projecting end of the first member into the bone end of a second bone piece;   (d) injecting cement into the medullary canals of the bone pieces; and (e) holding the bone ends in abutting contact until the cement sets.       
 
         [0026]    Preferably the cement is injected through a hole in the wall of the first and second members until cement flows past the ends of the members to contact the bone of the medullary canals. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0027]    Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0028]      FIG. 1  is a perspective side view of a splint, 
           [0029]      FIG. 2  is an end view of the splint, 
           [0030]      FIG. 3  is a perspective view illustrating the overlapping end of inner and outer members of the splint, 
           [0031]      FIG. 4  is an exploded side view illustrating the inner and outer members, 
           [0032]      FIG. 5  is a side elevational view showing two broken rib pieces secured together with the splint intramedullary located, 
           [0033]      FIG. 6  is a side elevational view of a splint in accordance with a second embodiment joining two bone ends together, 
           [0034]      FIG. 7  is a perspective view of a C-shaped connector forming part of the splint, 
           [0035]      FIG. 8  is a perspective view of a lateral connector for use with the splint, 
           [0036]      FIG. 9  is a cross sectional view showing a first form of thumb tack joining the splint to bone, 
           [0037]      FIG. 10  is a cross sectional view of the second form of thumb tack joining the splint to bone, 
           [0038]      FIG. 11  is a sectioned perspective view showing use of the splint to join bones together, 
           [0039]      FIG. 12  is a exploded perspective view illustrating the means of interfitting the components of the splint, 
           [0040]      FIGS. 13 to 15  are exploded perspective views illustrating installation of a splint in accordance with another embodiment, 
           [0041]      FIG. 16  is a cross sectional view of a plug forming part of the splint, 
           [0042]      FIG. 17  is a cross sectional view of the plug and peg secured to a bone end, and 
           [0043]      FIGS. 18 ,  19  and  20  are exploded perspective views showing installation of the splint in accordance with a further embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0044]    The bone splint  10  of a first embodiment is illustrated in  FIGS. 1 to 5  of the attached drawings and comprises two hollow tubes  11 ,  12  that are extruded in a polylactide copolymer. Polylactide copolymers are, over time, absorbed by the body and are biodegradable. Polylactide copolymers become malleable when heated and then become more rigid as they cool. These copolymers maintain at least 40% of their strength for three months after insertion. 
         [0045]    The tubes  11 ,  12  are hollow and comprise a first tube member  11  that is in a telescopic fit within a second tube member  12 . Each member  11 ,  12  is 30 mm in length with an elongate throughway  13 ,  14  on the interior. The inter relationship between the members  11 ,  12  allows the tubes to be displaceable from a first withdrawn position in which the inner member  11  is wholly within the outer member  12  to an extended position shown in  FIG. 1  in which the inner member extends out of the outer member  12  for 20 mm providing a splint  10  having a total length of 50 mm with a 10 mm overlap. 
         [0046]    The cross section of rib bones are quite complex varying from the anterior to posterior ends of the rib and the inner and outer sides. In some cases the cross section of the rib bone is elliptical and in other cases it becomes virtually circular or even triangular. The cross section of the medullary canal mirrors the cross section of the exterior of the rib. 
         [0047]    In this embodiment the splint  10  is to locate within the medullary canal of the bone pieces. The cross section of the splint is designed to mirror the cross section of the canal. This variation in cross section can be accommodated by the malleable nature of the heated polylactide copolymer or alternatively splints can be manufactured in a variety of cross sections to accommodate the varying cross sections of the rib canals. Alternatively, the splint  10  can have a simple circular cross section. This arrangement can be used when the elliptical correction proved to be a difficult fit within the medullary canals. 
         [0048]    As shown in  FIG. 2  the outer member  12  has an elliptical cross section, the longer side measuring 8.6 mm and the shorter side measuring 5.4 mm. The throughway along the length of the outer member  12  is similarly shaped with a longer dimension of 5.8 mm and a smaller dimension of 3.6 mm. The wall thickness of the outer member  12  is approximately 1.4 mm uniform around the circumference. 
         [0049]    The inner member  11  has its outer cross section mirroring the inner cross section of the throughway  14  of the outer member  12 . The longer dimension is 5.6 mm with the shorter dimension being 3.4 mm which allows the inner member  11  to be a sliding fit within the outer member  12 . The inner member  11  has a central elongate throughway  13  of circular cross section with a diameter of 1.6 mm. Due to the elliptical cross section of the inner member the wall thickness varies from a minimum of 0.9 mm to a maximum of 2 mm. 
         [0050]    A feature of the splint  10  described herein is the telescopic nature of the two members  11 ,  12  shown in  FIG. 1 . The inter relationship between the outer surface of the inner member  11  and the inner surface of the outer member  12  is such that the inner member is free to slide outwardly from a retracted position to the fully extended position, but is not free to return to the fully withdrawn position. The inter relationship is also designed to ensure that the inner member  11  cannot separate from the outer member  12 . 
         [0051]    There are a number of ways of effecting this relationship. In the embodiment shown in  FIG. 4  the outer wall of the inner member  11  is serrated and these serrations  20  mirror with serrations  21  on the inner wall of the outer member  12 . The inclination of the serrations  20 ,  21  is such that they facilitate a ratchet action whereby outward displacement is possible but inward or return displacement is prevented. The relationship at the end of the inner wall of the outer member  12  and the outer wall of the inner member  11  is such that the inner member  11  cannot be separated from the outer member  12 . In another embodiment (not shown) the cross section of the throughway is the outer member  12  and the cross section of the inner member  11  are circular and there is a threaded relationship between the inner and outer members  11 ,  12  whereby rotation of one member relative to the other causes the inner member to move from the fully withdrawn position within the outer member  12  to the fully extended position where it projects out of the outer member  12 . 
         [0052]    It is understood that in designing the serrations  21 ,  20  on the inner wall of the outer member  12  and outer wall of the inner member  11 , the serrations may be positioned on the poles of the oval cross section and not around the whole circumference. Alternatively the serrations may be placed around the circumference. Where serrations are used on circular members a detent may be required to prevent relative rotation of the members  11  and  12 . 
         [0053]    As shown in  FIG. 5  to use the splint described above, the larger or second member  12  is first inserted into the end of the larger bone piece P 1 , that is, into the medullary canal. This step is carried out with the first member  11  withdrawn within the second member  12 . Once the second member  12  is located in the larger bone piece the first inner member  11  is withdrawn from the outer member  12  to the fully extended position where it is slid into the medullary canal of the end of the adjacent bone piece P 2 . 
         [0054]    As shown in  FIG. 3  a preformed 1.6 mm hole  25  is drilled through the wall of the outer and inner members  11 ,  12  to communicate with the throughway  13  of the inner member  11 . When the holes  25  in the outer and inner members line up the inner member is in the fully extended position. The bone ends are kept distracted and cement is then injected through the hole  25  and into the throughways of both the inner and outer members  11 ,  12 . Sufficient cement is injected until the cement flows out of the throughways and into the medullary canals of both bone ends. When sufficient cement has been injected to ensure a significant blob at the end of each member  11 ,  12  the surgeon pushes the bone ends into abutting contact and hold the bone ends in place until the cement sets, which usually takes about one minute. Once the cement has set the surgeon can then release the bone ends which are then held in abutting contact by the splint  10  and its association with the cement, see  FIG. 5 . 
         [0055]    Instead of preforming the holes  25  the surgeon can insert the splint  10  and then drill a hole through the larger bone piece adjacent the fractured end and through the walls of the inner and outer members  11 ,  12 . The cement can then be injected into the splint via the drilled hole in the bone piece. 
         [0056]    There are a number of different tools that could be used to displace the inner member  11  from the outer member  12 . On the assumption that the inner member  11  is never totally within the outer member  12  a gripping tool can engage the projecting end to pull the projecting end out of the outer member  12  to the extended position. The force to pull the inner member relative to the outer member would have to resist the interengagement of the serrations. However, the malleable nature of the splint  10  when first inserted should render this displacement fairly easy. 
         [0057]    In the embodiment where screw threads replace the serrations a suitable tool will be used to rotate the inner member  11  relative to the outer member  12  thereby causing it to project outwardly to the extended position. Another possible means of displacing the inner member relative to the outer member would be to use the cement to force the inner member out of the outer member. It is understood that in this circumstance there would have to be an abutment within the throughway of the inner member against which the cement could bear to force the inner member to move out of the outer member. It is also envisaged that the inner member could be of solid construction in which case the cement would force the inner member out by engaging the end wall of the inner member. In this embodiment it is understood that a separate source of cement would have to placed in the medullary canal of the smaller bone piece. 
         [0058]    Another option is for the surgeon to scrape out some of the medullary cancellous bone from the ends of the fractured bone pieces and then inject a blob of cement directly into the bone ends. The splint is then inserted, placed in the extended position, and the bones held in abutting contact until the cement sets. 
         [0059]    It is understood that the bone cement would be a conventional bone cement used in the orthopaedic industry. The bone cement would have low viscosity and designed to be fast setting. 
         [0060]    In another embodiment shown in  FIGS. 6 to 12 , a bone splint  100  comprises a pair of C-shaped connectors  110 , that are located in a hole  105  in the bone ends drilled transversely of the bone. Each C-shaped connector has a curved arm  112  with a projecting end  113  with a serrated outer surface  114 . A locking strut  120  in the form of a hollow cylinder with a serrated inner surface  121  can be pushed onto the ends  113  of the C-shaped connectors  110 . The interrelationship of the serrated surfaces allows inward movement of the ends  113  of the C-shaped clips  110  into the locking strut  120  but prevents outward movement. 
         [0061]    In use, the hole  105  is drilled away from the fractured end of the bone pieces P 1 , P 2  transversely across the bone and the C-shaped connector  110  is located in the hole  105  by placing the arm  112  through the hole and manoeuvring the arm  112  through the hole  105  to engage one side of the bone with the serrated end  113  being located on the other side of the bone as shown in  FIG. 6 . A similar exercise is repeated for the other bone end and then the locating strut  120  is cut to length ( FIG. 11 ). The bone ends P 1 , P 2  are pushed together and the C-shaped connectors  110  are forced into the ends of the locating strut  120  thereby holding the bone ends in abutting contact. It is understood that the C-shaped connectors  110  and locating strut  120  are manufactured from polylactide copolymers. 
         [0062]    To further reinforce the bone splint  100  it is understood that additional holes can be drilled through the locating strut  120  transversely of the bone ends to accommodate a locking overplate  130  ( FIG. 8 ) comprising a U-shaped bracket  131  with internal male and female projections  132 ,  133 . The over plate  130  is positioned over the bone and the sides of the plate are pushed inwardly so that the male projection  132  is located firmly within the female projection  133 . The male projection  132  has an upstanding rib  134  that clips into a groove  135  in the female projection  133 . 
         [0063]    As shown in  FIG. 9  another option includes the use of a plastics thumb tack  140  with an enlarged tapered head  141  at one end and a location flange  142  at the other. The tack  140  is forced through the locking strut  120  and into the centre of the bone through an aperture  145  drilled on one side of the bone. In another alternative shown in  FIG. 10  the thumb tack  145  is longer so that the head  141  of the thumb tack extends across the bone through an aperture  146  drilled transverse to the bone to locate outside the opposite side of the bone. In this embodiment it is understood that the locking strut  120  will taper to a solid flange  128  to enable location of the thumb tacks  140 . The flange  128  is shown with particular reference to  FIG. 6 . 
         [0064]    It is understood that the use of thumb tacks  140  or a locking over plate  130  can be into one bone end P 1  or both bone ends P 1 , P 2  and it is further understood that in an extreme situation two location points can be positioned for the over plate  130  or thumb tacks  140  in both bone ends. The thumb tacks  140  or locking over plate  130  are only positioned in the bone ends after the bone ends have been brought into abutting contact and the locking strut  120  has been adjusted to the final position. 
         [0065]    In a still further embodiment shown in  FIGS. 13 to 17  the C-shaped connectors  110  are replaced by a hollow conical pin  150  with a serrated outer surface  151  which is located through a transverse hole  152  from one side of the bone P 1 , P 2 . A enlarged peg  155  can then be driven into the conical plug  150  to expand the serrated outer surface  151  against the wall of the hole  152  in the bone to improve the grip on the bone. 
         [0066]    As shown in  FIGS. 16 and 17  the plug  150  has a C-shaped upper flange  153 . The C-shaped flange  153  accommodates the head  158  of an arm  156  with serration  157  on its exterior. The head  158  fits into the top of the plug  150 . The underside of the head  158  is integrally formed with the peg  155 . 
         [0067]    In  FIGS. 13 to 17  the arms  156  which are rectangular are pushed into a rectangular internally serrated bridging member  180 . 
         [0068]    In an embodiment shown in  FIGS. 18 to 20 , an elongate hollow rectangular receptor  160  having a serrated inner surface  161  is moulded to have two downwardly projecting pegs  162 ,  163  with a ribbed exterior  164 . The two pegs  162 ,  163  can be forced into the conical pin  150  that is located in the bone to locate the receptor onto the bone end as shown in  FIG. 17 . This assembly is completed on both bone ends P 1 , P 2  and when a crossbar  170  with appropriate serrations  171  on its exterior can be forced into the receptors  160  to hold the bones together. The serrated edges  171  of the cross bar  170  and receptors only allows movement of the cross bar  170  into the receptors  160  and prevent outward movement thereby holding the bone ends together. 
         [0069]    To use the splint  100  of this embodiment the bones are first pushed together and the holes  152  drilled into the bone. The length of the receptors and crossbar is then adjusted to ensure the ends of the bone pieces remain in abutting contact. 
         [0070]    It is understood that the receptors  160  could be held to the bone end by a single peg/pin though two spaced pegs/pins is a preferred option. 
         [0071]    As shown in  FIGS. 16 and 17  the internal surface of the plug  150  and the exterior of the peg  155  are serrated to facilitate one way movement to ensure that the peg  155  cannot escape from the plug  150 . 
         [0072]    The use of a polylactide copolymer splint avoids many of the potential complications caused by metal implants. The fact that the polylactide copolymer is malleable when heated allows the splint to assume the complex profile of the rib. Copolymers of this type maintain at least 40% of their strength after 3 months at which time the fractures would have expected to be completely healed. The copolymer is completely absorbed without toxicity over between 1 and 3 years. Animal testing has shown faster and stronger healing with absorbable splints compared to traditional metal plates which may actually slow bone healing. This occurs because the metal plate protects the bone from any load but in doing so removes the stimulus for new bone growth. In contrast the absorbable splint allows gradual transfer stress loads to the bone, stimulating faster bone growth. 
         [0073]    An absorbable splint has the advantage that the material does not have to be removed. Furthermore, if there are complications such as migration or breakage a conservative approach can be adopted that does not warrant removal of the splint. 
         [0074]    When the splint is warmed in hot water it becomes malleable which allows the surgeon to bend the splint to match the curve of the rib at the point of breakage. The implant has sufficient strength over its first three months to allow the bone to take up the additional stress over time. The fact that the implant becomes totally absorbed over three years avoids the likelihood of stress shielding which can cause bone weakness. 
         [0075]    The splint described above has been specifically designed for its ease of use without the need for a second operation to later remove the splint. The simple method of fixation without screws is another significant feature of the splint. 
         [0076]    Whilst the splint is described primarily for use in the fixation of ribs it is understood that the splint can be used on other bones, especially where the bones are not subjected to high forces and stresses. It is also understood that splints of this kind could be used in the veterinary industry on animals. 
         [0077]    In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.