POST-FRACTURE BONE FIXATOR

Abstract: A post-fracture fixator comprises an elongate support (1) and at least two pin clamps (8, 9) mounted on the support, at least one of the pin clamps (8, 9), being lockably mounted on the support by means of a lockable ball and socket joint (10, 11), the ball (21) being formed from a rigid material and the material of the socket (19, 20) comprising an elastomeric material.

Description: POST-FRACTURE BONE FIXATOR This invention relates to a post-fracture bone fixator. There have been a number of proposals described in the literature relating to post-fracture bone fixators or ^ stabilisers. For example reference may be made to British Patent Specifications Nos. 567715, 1480167, and 2029702A. A device known as the Oxford fixator is described in a paper in "Engineering in Medicine", I.Mech.E. (1979), by J. Kenwright et al at pages 138 to 142, and in another paper by M. Evans et al, loc. cit. , at pages 133 to 137. Many types of device are at present being used to hold bone ends in correct relationship to each other while a fracture mends. All do reasonable jobs, at the time, but many are bulky and difficult to apply and adjust; whilst others may even require partial dismantling to allow access for other techniques such as skin or bone grafting. Others incorporate in their construction various parts which are moulded from polymers and, in particular, there are reports in the literature that nylon pin sleeves wear rapidly, or else distort under load, to allow movement between the pins and the clamp. The present invention seeks to provide a post-fracture bone fixator or stabiliser combining strength, lightness, and low bulk with ease of adjustment, in practice, so as to allow the patient to use the broken limb as quickly as possible. According to the present invention there is provided a post-fracture bone fixator comprising an elongate support and at least two pin clamps mounted on the support characterised in that at least one of the pin clamps is lockably mounted on the support by means OMPI of a lockable ball and socket joint, the ball being formed from a rigid material and the material of the socket comprising an elastomeric material. Preferably the fixator comprises two pin clamps, each lockably mounted on the support by means of a lockable ball and socket joint, the ball being formed from a rigid material and the material of the socket comprising an elastomeric material. Preferably the ball of the or each ball and socket joint is carried by the pin clamp and is provided with surface indentations, for example crevices which extend in both latitudinal and longitudinal directions around the ball. Each pin clamp is preferably adapted to receive a plurality of skeletal or Steinman pins, for example three skeletal pins, in spaced, substantially parallel relationship to one another. In a particularly preferred form of the invention each pin clamp comprises a block of elastomeric material, which has a rigid plate embedded therein, a clamping plate for clamping the skeletal pins against the block of elastomeric material, and means adapted to co-operate with the rigid plate to urge the clamping plate into clamping engagement with the block. In such a construction the ball of the lockable ball and socket joint is preferably located in the pin clamp by means of the rigid plate and the means adapted to co-operate with the rigid plate comprises a pair of bolts adapted to engage screw threadedly in the rigid plate. The socket is preferably formed in a block of elastomeric material which comprises a pair of jaws, each of which is formed with a surface that .is complementary to that of the ball, and means for drawing the jaws one towards the other to lock the ball therebetween; such complementary surfaces may each be substantially part-spherical. In such a construction the means for drawing the jaws one towards the other may comprise a rigid plate embedded in one of the jaws and bolt means adapted to bear against the other jaw and to engage screw threadedly in said rigid plate in said one jaw. The other jaw may also be provided with a rigid plate embedded therein. In one construction the elongate support comprises a rigid rod having a connector device corresponding to each pin clamp detachably mounted thereon, the lockable ball and socket joint being arranged to connect the respective pin clamp to the corresponding connector device. Each such pin clamp may be provided with the ball of the corresponding ball and socket joint, the socket of which is formed in the connector device. Preferably at least one of the connector devices is adjustable in position on the rod. In a particularly preferred construction the rod is threaded over at least a portion of its length and carries a pair of nuts for releasably securing the connector device to the rod in a selected position. The connector device preferably has a bore therethrough for snugly receiving the rod. The rod may be keyed in the bore through the connector device so as to restrict rotational movement of the connector device about the axis of the rod. For example, the bore through the connector device may be non-circular (e.g. of D-section) and the rod is of corresponding cross-section (e.g. of D-section) over at least a portion of its length. To , provide such a bore the connector device may comprise a block of elastomeric material having a cylindrical sleeve embedded therein for receipt of the rod, which sleeve is partly filled with elastomeric material forming part of the block so as to render the bore non-circular. The bore in the connector device may be formed in a portion which is offset longitudinally of the connector device with respect to the ball and socket joint. In this way reversal of one or both of the connector devices upon the rod can be used to obtain adjustment of the positions of the pin clamps relative to one another. In a particularly preferred construction the pin clamp is adapted to clamp a plurality of skeletal pins extending transversely of the- in clamp and the ball and socket joint is .arranged offset longitudinally of the pin clamp. By rotating one or both of the pin clamps through 180° about its respective ball and socket joint the distance between the pin clamps can be quickly adjusted. In an alternative preferred embodiment the elongate support comprises a pair of connector devices each having a screw threaded rod extending therefrom and a turnbuckle device for adjusting the distance between the connector devices. Preferably the threads on the two rods are of opposite hand one to another. Preferably also lock nuts are provided to secure the turnbuckle device and the connector devices one to another. In such a construction each connector device has the ball of the .ball and socket joint integrally formed therewith and the socket joint is formed in an end of a corresponding pin clamp. In order that' the invention may be clearly understood and readily carried into effect some preferred embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings,in which: Figure 1 is a side view of a post-fracture • * bone fixator constructed in accordance with the present invention; υ RE A OMPI Figure 2 is a plan view of the fixator of Figure 1; Figure 3 is an end view of the fixator of Figures 1 and 2; Figure 4 is a detail view of the ball of the lockable ball and socket joint of a modified form of fixator; Figure 5 is a side view of a drilling guide for use with the fixator of Figures 1 to 4; Figure 6 is a top plan view of the drilling guide of Figure 6; and Figure 7 is a side view of a second form of fixator. Referring to Figures 1 to 3 of the drawings, a post-fracture bone fixator comprises an elongate stainless steel rod 1, each end of which is threaded, as indicated at 2 and 3. Each of the threaded ends 2 and 3 of the rod 1 is machined to provide a corresponding flat running surface 4 and 5 respectively; thus the threaded portions 2 and 3 of the rod l ' are of D-section. Slidably mounted on the threaded portions 2 and 3 are a pair of corresponding connector devices 6 and 7, each of which supports a corresponding pin clamp 8,9 which is mounted in the respective connector device 6,7 by means of a corresponding lockable ball and socket joint indicated generally at 10 and 11 respectively. The two connector devices 6 and 7 are of similar construction but of opposite hand. Each of the connector devices 6 and 7 comprises a block moulded from a suitable elastomeric material. Preferably such elastomeric material comprises a synthetic rubbery polymeric material, for example one of the commercially available twin-pack synthetic rubbers which polymerise exother ally upon mixing the polymer component and cross linking agent prior to pouring the mixture in the mould. The elastomeric material should be a hard elastomeric material, preferably a material having a Shore hardness of at least 50, and even more preferably at least about 60. Particularly preferred materials have a Shore hardness in the range of from about 68 (Shore A) to about 78 (Shore D). In addition the elastomeric material should be capable of being autoclaved without deformation or significant detrimental effect upon its properties upon recooling to room temperature. A suitable material is that sold under the trade mark "Vulkollan", more particularly a "Vulkollan" material which is formulated to produce a cured polymer having a Shore hardness of about 70 (Shore A). If desired, the material may contain a pigment, such as carbon black; this has the advantage that any discolouration of the polymer in use due to the influence of light or heat is masked by the presence of the pigment. As can be seen in particular from Figure 3 of the drawings, connector device 6 is formed with a longitudinal slit in it so as to form a pair of jaws 12 and 13. Each jaw 12,13 has a corresponding stainless steel plate 14,15 embedded therein. A pair of bolts 16,17 are threadably engaged in the plate 14 and pass freely through corresponding apertures in the plate 15. Reference numeral 18. indicates washers on each of bolts 16,17. Each of jaws 12,13 has a hollowed out portion, as indicated at 19,20 in Figure 3, each having a part- spherical surface, so as to form together the socket of the lockable ball and socket joint. This joint allows considerable azimuthal adjustment of the corresponding pin clamp 8,9. The ball 21 of the ball and socket joint is - • carried by the pin clamp 8. Ball 21 is made of stainless steel and is formed with a series of surface grooves which extend both latitudinally and longitudinally with respect to the polar axis of the ball. Ball 21 is formed integrally with a flange 22 an with a shank 23 which carries a flange 40, having chamfered sides 41 (see Figure 2), and has at its end a screw threaded portion 24, the axis of which coincides with the polar axis of ball 21. By means of the threaded portion 24 ball 21 is secured in a stainless steel plate 25 which is embedded in the block of polymeric material (e.g. Vulkollan 70) from which the body of pin clamp 8 is formed. ' By tightening bolts 16 and 17 the jaws 12 and 13 can be drawn together thereby locking the ball and socket joint in the .desired position. The surface grooves on ball 21 enhance the locking action since the polymeric material can deform into these grooves and thereby grip the ball tightly. As bolts 16,17 are positioned close to the ends of the diameter of the ball 21 the clamping action is effective in locking the ball and socket joint. Pin clamp 8 has three transverse grooves 26,27,28 formed in the upper surface thereof. These are adapted to receive each a corresponding skeletal or Steinman pin (not shown). Grooves 26,27 and 28 are aligned parallel one to another. Clamping of the skeletal or Steinman pins is achieved by means of a clamping plate 29 and clamping bolts 30,31 which pass through corresponding holes in clamping plate 29 into the pin clamp 8 and are threadably received in corresponding threaded bores in plate 25. Reference numeral 32 indicates washers on bolts 30,31. Connector device 6 has a cylindrical sleeve 33 embedded therein, the internal diameter of which corresponds to the diameter of rod 1. Sleeve 33 has a *• • -8- number of holes 34 (only one of which is shown in Figure 1) drilled in the side wall thereof. In moulding connector device 6 a D-section rod is inserted, in place of the threaded portion 2 of rod 1, in the bore of 5 sleeve 33. When the moulding operation occurs, the elastomeric material .penetrates hole 34 and fills the space 35 above the flat surface of the inserted rod. In this way a D-section bore is created within sleeve 33, the polymeric material filling space 35 being keyed to 10 the remainder of the connector block through the holes 4. In view of the keying action provided by the D-section of the threaded portion 2 and by the D-section of the bore within the sleeve 33, although connector 15 device 6 can slide on to the threaded portion 2, rotation of the connector device 6 relative to the rod 1 is restricted to at most a small angle. Reference numeral 36 indicates washers embedded one at each end of sleeve 33 in the elastomeric material from which 20 connector block 6 is ' formed. Two nuts 37,38 are threaded upon threaded portion 2, being arranged one on each side of connector device 6 to lock the same upon threaded portion 2. The construction of connector device 7 is 25 similar to that of connector device 6, except that the bolts 16,17 are passed through from the opposite side of the device 7 to that used in device 6, the metal plates 14,15 being appropriately reversed. In this way the surgeon can tighten the bolts 16,17 on both connector 30 devices 6 and 7 working from the same side of the fixator. Pin clamp 9 is essentially similar to pin clamp 8 and the construction, of ball and socket joint 11 • • is similar to that of ball and socket joint 10. 35 As illustrated, the position of pin clamp 9 has been reversed by rotation through 180° about the polar axis of the ball of ball and socket joint 11, compared with pin clamp 8. As will be described below, this rotational movement provides a convenient means of adjusting the fixator for the surgeon during the course of a surgical operation. Figure 4 shows the ball 101 of a modified for of fixator. The longitudinal grooves 102 and the latitudinal grooves 103 are clearly visible. Figure 5 shows a drilling guide for use in conjunction with the fixator of Figures 1 to 3. This comprises a generally rectangular yoke piece 110, conveniently formed of carbon black-filled Vulkollan 70, having six metal sleeves 111 moulded therein. As can be seen from Figure 5 in particular, the sleeves 111 are arranged in pairs so as to provide three accurately parallel passages each for guiding a skeletal or Steinman pin during drilling and insertion of the pin through the corresponding part of the bone fracture. The spacing between sleeves 111 corresponds exactly to the spacing between the slots 26,27,28 and the space 112 within yoke piece 110 is designed to receive snugly either of the pin clamps 8,9. It is a particular advantage of the fixator illustrated in Figures 1 to 3 that the connector devices 6,7 and the pin clamps 8,9 can be assembled on the rod 1 and secured loosely in place by means of the nuts 37,38 before the start of a surgical operation. It is not necessary for the surgeon to assemble the parts in the course of the operation. Moreover adjustment of the fixator and locking of the ball and socket joints is rapidly accomplished and requires merely the use of a spanner. If all the bolts and nuts are of the same size, -then a single size of spanner only is required. However, it may be preferred to use a smaller size for bolts 16,17,30,31 from the size of the nuts 37,38; in this case two sizes of spanner or a double-ended spanner will be required. Once the nuts and bolts are tightened the fixing arrangement is generally so firm that it is seldom necessary to re-tighten any piece because the bolts put the elastomeric material into compression and are hence effectively "self-locking". In use the surgeon will use the drill guide 110 for insertion of the skeletal or Steinman pins into the parts of the bone fracture concerned. Most commonly this will be a tibia. However the fixator of Figures 1 to 3 can also be used in connection with fractures of the ulna, radius or humerus. Usually it will be convenient to insert first the middle pin, i.e. the one to occupy the groove 27, in the first set of three pins. Having inserted one set of three pins, one of the pin clamps 8 or 9 can be fixed to the first set of three pins and the other set of pins inserted in the other part of the bone fracture, using the guide 110 as before, having possibly first positioned this by fitting it over the other pin clamp 9 or 8 as the case may be. In order to bring the grooves 26,27,28 on the two pin clamps 8,9 to an appropriate position, either or both of the pin clamps 8,9 can be rotated about the corresponding ball and socket joint from the position shown in Figure 1 to compensate for differences in length of the bone in which the fracture has occurred. For example if the clamps 8,9 are both in a position similar to that of clamp 9 in Figure 1 and are then both rotated about the corresponding ball and socket joint 10,11 through 180° so that each ends up in a position corresponding to that of clamp 8 in Figure 1, then it -will be found that the positions of the outermost skeletal pins can differ by about 3 cm. This is a very easy way to obtain extra distance, either positive or OMPI negative, when constructing a scaffold around a bone fracture. Further adjustment can be obtained by moving connector devices 6 and 7 along the threaded portions 2 and 3. The use of nuts 37,38 on the rod 1 allows easy and precise movement of the connector devices 6,7, after the fixator has been attached to the patient, and the distance between the pin clamps 8,9 on the separate parts of the bone fracture can be reduced or lengthened by a fraction, or by a multiple, of the screw pitch. Further adjustment still is provided by reversing connector device 6 and/or 7 on the rod 1 from the positions shown in Figure 1 as the surgeon may require. Although the fixator illustrated in Figures 1 to 3 is suitable for use in cases of fracture in bones of varying length, it may be expedient to use a longer or shorter rod 1 than that illustrated. Each surgical case involving bone breakage or fracture is to a varying extent unique and each time the * fixator of Figures 1 to 3 is used it will be employed in a slightly- different way. In some cases it will be useful to store the fixator with two sizes of threaded stainless steel rod 1, one of normal length and one longer. The surgeon can then select the appropriate length of rod, depending upon the length of the bone in which fracture has occurred. In use it will normally be preferred to use two of the illustrated fixators arranged one on each side of the limb in which the fracture has occurred so that a scaffold is formed by the two fixators which are bridged by the skeletal or Steinman pins which themselves pass through the parts of the fracture to be stabilised. When the fixator of Figures 1 to 3 is in use the metal skeletal or Steinman pins are firmly, but not "hard" fixed to the pin clamps 8 and 9 and this metal/polymer contact, together with the metal/polymer contact between the portion 35 and the rod 1 gives the whole scaffolding a shock-resisting or anti-vibration characteristic. Instead of stainless steel any other suitable corrosion-resistant metal or alloy may be used for construction of any of the metal parts mentioned. If greater freedom of azimuthal movement is required the distance between flange 22 and ball 21 can be increased somewhat. Figure 7 illustrates a further embodiment according to the invention. This comprises two pin clamps 201, the construction of which is similar to that of pin clamps 8,9 of the embodiment of Figures 1 to 3. Grooves 202,203,204 are provided to receive the skeletal or Steinman pins which are held in place by means of clamping plate 205 and bolts 206,207. At one of its ends each pin clamp 201 has a pair of jaws 208; in ' Figures 7 only one jaw 208 of each pair is visible. The construction of jaws 208 is similar to that of the jaws 12,13 of the fixator of Figures 1 to 3. Jaws 208 each have a metal plate (not shown) embedded therein, similar to plates 14,15 and are formed with part-spherical recesses to form a socket of a lockable ball and socket joint, the ball of which is illustrated at 209. Jaws 208 can be drawn towards one another to clamp the ball 209 by means of bolts, the shanks of which are indicated at 210. Balls 209 are formed each at one end of a respective one of a pair of threaded rods 211 and 212. The thread on rod 211 has an opposite hand to that of the thread on rod 212. A turnbuckle device 213 is engaged with the free ends of the rods 211 and 212. Reference numerals 214 and 215 indicate lock nuts. Preferably balls 209 are formed with longitudinal and latitudinal crevices similar to those illustrated in Figure 4. The method of use of the fixator of Figure 7 is similar to that described in relation to the fixator of Figures 1 to 3. In this case, however, adjustment of the length of the elongate member formed by the rods 211 and 212 and the turnbuckle 213 can be adjusted by means of the turnbuckle 213 and this latter can be fixed in place by means of lock nuts 214,215.

Claims: CLAIMS 1. A post-fracture bone fixator comprising an elongate support and at least two pin clamps mounted on the support characterised in that at least one of the pin clamps is lockably mounted on the support by means of a lockable ball and socket joint, the ball being formed from a rigid material and the material of the socket comprising an elastomeric material. 2. A fixator according to claim 1, characterised in that it comprises two pin clamps, each lockably mounted on the support by means of a lockable ball and socket joint, the ball being formed from a rigid material and the material of the socket comprising an elastomeric material. 3. A fixator according to claim 1 or claim 2, characterised in that the ball of the or each ball and socket joint is carried by the pin clamp. 4. A fixator according to any one of claims 1 to 3, characterised in that the ball of the or each ball and socket joint is ' provided with surface indentations. 5. A fixator according to claim 4, characterised in that the surface indentations comprise crevices that extend in both latitudinal and longitudinal directions around the ball. 6. A fixator according to any one of claims 1 to - " 5, characterised in that each pin clamp is adapted to receive a plurality of skeletal pins in spaced, substantially parallel relationship to one another. 7. A fixator according to claim 6, characterised in that each pin clamp is adapted to receive three skeletal pins. 8. A fixator according to any one of claims 1 to 7, characterised in that each pin clamp comprises a block of elastomeric material, which has a rigid plate embedded therein, a clamping plate for clamping the skeletal pins against the block of elastomeric material, and means adapted to co-operate with the rigid plate to urge the clamping plate into clamping engagement with the block. 9. A fixator according to claim 8, characterised in that the ball of the lockable ball and socket joint is located in the pin clamp by means of the rigid plate. 10. A fixator according to claim 8 or claim 9, characterised in that the means adapted to co-operate with the rigid plate comprises a pair of bolts adapted to engage screw threadedly in the rigid plate. 11. A fixator according to any one of claims 1 to 10, characterised in that the socket is formed in a block of elastomeric material which comprises a pair of jaws, each of which is formed with a surface that is complementary to that of the ball, and means for drawing the jaws one towards the other to lock the ball therebetween. 12. A fixator according to claim 11, characterised in that the complementary surfaces are each substantially part spherical. -^JRE OMPI 13. A fixator according to claim 11 or claim 12, characterised in that the means for drawing the jaws one towards the other comprises a rigid plate embedded in one of the jaws and bolt means adapted to bear against the other jaw and to engage screw threadedly in said rigid plate in said one jaw. 14. A fixator according to claim 13, characterised in that the other jaw is also provided with a rigid plate embedded therein. 15. A fixator according to any one of claims 1 to 14, characterised in that the elastomeric material comprises a polyurethane,, 16. A fixator according to any one of claims 1 to 15, characterised in that the elastomeric material has a Shore hardness of at least about 50. 17. A fixator according to claim 16, characterised in that the elastomeric material has a Shore hardness lying in the range of from about 68 to about 78. 18. A fixator according to any one of claims 1 to 17, characterised in that the elongate support comprises a rigid rod having a connector device corresponding to each pin clamp detachably mounted thereon, the lockable ball and socket joint being arranged to connect the respective pin clamp to the corresponding connector device. 19. A fixator according to claim 18, characterised in that each pin clamp is provided with the ball of the corresponding ball and socket joint, the socket of which is formed in the connector device. 20. A fixator according to claim 18 or claim 19, characterised in that at least one of the connector devices is adjustable in position on the rod. 21. A fixator according to claim 20, characterise in that the rod is threaded over at least a portion of its length and carries a pair of nuts for releasably securing the connector device to the rod in a selected position. 22. A fixator according to any one of claims 18 to 21, characterised in that the connector device has a bore therethrough for snugly receiving the rod. 23. A fixator according to claim 22, characterised in that the rod is keyed in the bore through the connector device so as to restrict rotational movement of the connector device about the axis of the rod. 24. A fixator according to claim 23, characterised in that the bore through the connector device is non-circular and the rod is of corresponding cross section over at least a portion of its length. 25. A fixator according to claim 24, characterised in that the bore is of D-section and the rod is of D-section over at least a portion of its length. 26. A fixator according to claim 24 or claim 25, characterised in that the connector device comprises a block of elastomeric material having a cylindrical sleeve embedded therein for receipt of the rod, which • sleeve is partly filled with elastomeric material forming part of the block so as to render the bore non-circular. 27. - A fixator according to any one of claims 22 to 26, characterised in that the bore is formed in a portion of the connector device which is offset longitudinally of • the connector device with respect to the ball and socket joint. 28. A fixator according to any one of claims 18 to 27, characterised in that the pin clamp is adapted to clamp a plurality of skeletal pins extending transverse to the pin clamp and the ball and socket joint is arranged offset longitudinally of the pin clamp. 29. A fixator according to any one of claims 1 to 17, characterised in that the elongate support comprises a pair of connector devices each having a screw threaded rod extending therefrom, and a turnbuckle device for adjusting the distance between the connector devices. 30. A fixator according to claim 29, characterised in that the threads on the two rods are of opposite hand one to another. 31. A fixator according to claim 29 or claim 30, characterised in that lock nuts are provided to secure the turnbuckle device and the connector devices one to another. 32. A fixator according to any one of claims 29 to 31, characterised in that each connector device has the ball of the ball and socket joint integrally formed therewith and the socket of the joint is formed in an end of a corresponding pin clamp.

Inventors: LUNEY WILLIAM, TEMPLETON HOHN, LUNEY, WILLIAM, TEMPLETON, HOHN
Applicants: LUNEY WILLIAM, TEMPLETON HOHN, LUNEY, WILLIAM, TEMPLETON, HOHN
Application year: 1983
Main classification: A61B17
IPC codes: A61B17