WO2006111852A2

WO2006111852A2 - Fixation of bones after fracture

Info

Publication number: WO2006111852A2
Application number: PCT/IB2006/001083
Authority: WO
Inventors: Vagn-Erik Dall; Hans Hilmar Dall
Original assignee: Dalmatic Lystrup A/S
Priority date: 2005-04-20
Filing date: 2006-04-19
Publication date: 2006-10-26
Also published as: WO2006111852A3

Abstract

A bone fixation system comprises a plate member (4) having an upper face and a contact face, and is formed with at least one hole (10). The or each hole has one end length of a first cross-section extending from the upper face with the other end length tapering towards the contact face (11) to a cross-section less than the first cross- section. The system includes a bone screw (22) having a distal end and an enlarged proximal end (24) of cross-section complementing that of the other end length of the hole, and a locking element (26) to be received and locked in the one end length of the hole. The locking element can thus clamp the proximal end of the bone screw (22) against the other end length of the hole with the distal end projecting therefrom to secure the plate member to a bone part. The enlarged proximal end (24) of the bone screw can extend beyond the contact face (11) of the plate member when clamped against the other end length of the hole by the locking element. In this way the enlarged end prevents the contact face of the plate from actually engaging the bone surface (25).

Description

FIXATION OF BONES AFTER FRACTURE

This invention relates to plate systems for fixing bone fractures. Such systems have use in many surgical operations. The present invention relates particularly, but not exclusively, to plate systems for use in the internal fixation of bones.

In the surgical repair of broken bones, it is often required to fix a fracture in order to ensure that the bone parts are held in a correct mutual position, and stabilized during fusion. The fixing enables the respective body part to be used very shortly after fracture, which has the advantage that rehabilitation may be commenced at an early date. Rehabilitation of the injured body part also stimulates the blood supply to the broken area, whereby the healing process and the fusion are accelerated. There are basically two techniques for fixing fractures; external fixation and internal fixation. In external fixation the skin barrier is broken by long bone screws which are used to secure the fracture during the entire period of treatment or recovery. During that period there is a risk that the patient contracts infections. Bacterial infections are often very difficult and time consuming to overcome. There is also a risk of "pin track infection" which can result in wasting of the bone screws.

With internal fixation, it is only necessary to break the skin barrier during the fixing process, as it is carried out by surgical intervention. Thus, the skin barrier can recover after surgery, and does not remain broken in the treatment or recovery period itself. The risk of infection then, is only major as a consequence of the surgical intervention. Internal fixation is also preferred to external fixation, as it is less restrictive on the movements of the patient.

The present invention relates to the securement of a plate to a bone part in a bone fixation system. According to the invention such a system comprises a plate member having an upper face and a contact face, and is formed with at least one hole therethrough. The or each hole has one end length of a first cross-section extending from the upper face with the other end length tapering towards the contact face to a cross-section less than the first cross-section. The system includes a bone screw having a distal end and an enlarged proximal end of cross-section complementing that of the other end length of the hole, and a locking element to be received and locked in the one end length of the hole. The locking element can thus clamp the proximal end of the bone screw against the other end length of the hole with the distal end projecting therefrom to secure the plate member to a bone part. The enlarged proximal end of the bone screw can extend beyond the contact face of the plate member when clamped against the other end length of the hole by the locking element. In this way the enlarged end prevents the contact face of the plate from actually engaging the bone surface.

In a system according to the invention the tapering cross-section of the other end length of the hole in the plate is spherical. It is also preferred that the cross-section of the one end length of the hole is greater than the maximum cross-section of the other end length of the hole, forming an annular shoulder therebetween.

A plate system for the fixation of bones according to another aspect of the invention comprises a plurality of plate members, each for securement to a bone part. The plate members are coupled to each other by at least one connecting element, with the spacing between the plate members being adjustable by displacement of at least one of the plate members on the connecting element or elements. The or each connecting element can be a plain rod or tube, or can have a polygonal cross-section received in a complementary opening or socket in one or each plate member. The or each connecting element can also be flexible, to allow the system to fix bones by attachment to surfaces that are not substantially in a common plane. A connecting element can also be fastened to a stop for securement to a bone part. This enables the element or elements to be fixed relative to one bone part with the plate system being movable relative thereto.

In these plate systems the securement of each plate is preferably accomplished using the technique of the invention described above. In any event, each plate member is preferably formed with a surface for laying against the respective bone, which has a number of projections giving support for the respective plate member against the periosteum of a respective bone part. This reduces the influence of the respective plate member on the periosteum of the bone.

Plate members in systems according to the invention are normally secured to bone parts by means of screws, and the holes in the plate members can be adapted to accommodate such a screw in such a manner that it forms a projection on the contact surface of the plate member and in engagement with a respective bone part when the screw is installed in a respective hole. In a similar manner to that described above, this results in multiple contact areas between the projections and the periosteum of a respective bone, once again minimizing or at least reducing the influence of the fixing plate on the periosteum.

Plate systems according to the invention can also be adapted to receive bone screws at different angles. This can be of particular benefit when fixing multiple fractures, and it is not possible to secure the bond screw at a predetermined, normally perpendicular, angle to the contact surface of a respective plate member. This aspect of the invention, which is described in more detail hereinafter, can also be exploited in plate systems in which the spacing between the plate members is not adjustable. It is certainly possible that in some circumstances a non-adjustable plate system may be preferred, if the respective plate members can be secured by bone screws oriented at irregular angles (non-perpendicular) to the contact surface of the respective plate members.

Plate systems according to the invention will most simply consist of two plate members, with each member secured to the respective bone on either side of a fracture. However, the system can be extended to include additional plate members coupled in series to the original two, and adjacent plate members in such a series can be mounted on the same connecting elements. The option of using flexible connecting elements is of particular value in this variant of the invention as there is of course a greater likelihood of the respective bone surface or surfaces not being in a common plane. The system can also be expanded laterally; ie not in the direction of the connecting element or elements, but on one or both sides thereof. Additional plate members coupled to the system in this way can be attached to either a plate member, or to a connecting element extending between plate members. This lateral extension facility does enable fixation to be affected over a wide area of bone surface, and this can be valuable for multiple fractures of the larger bones.

Adjustable plate systems of the invention can use a number of plate members which are mutually connected by at least one connecting element, with at least one of the plate members being capable of displacement in relation to the connecting element in its longitudinal direction. The adjustable spacing between the plate members creates the possibility of a dynamic axial compression. It is well known to use dynamic axial compression to stimulate formation of hard calcium "callus" in the bone of the area of the fracture - also known as ad modum "pro-callus". According to existing clinical documentation, this means that the bone can become stronger after fusion.

Using dynamic axial compression, the individual plate members are fixed to individual bone parts, after which the spacing between individual plate members is adjusted to achieve optimal repositioning of the respective bone parts. This is a substantial departure from known internal fixation systems, in which the spacing between individual bone parts cannot be adjusted after the plate system is fitted without at least one plate member having to be loosened or detached from a bone part.

Of course, any fixation system must seek to secure individual bone parts relative to each other during fusion and recovery, so that the bone parts fuse as anatomically correctly as possible. It is important to prevent the plate members from twisting in relation to each other. This can be avoided by using two or more connecting elements side-by-side, or a single connecting element with a polygonal cross-section which prevents relative rotation. Any suitable polygonal cross-section may be selected, such as star-shaped, rectangular or triangular. Neither of course do the sides of the polygon have to be straight. Splined couplings can also be used. As noted above, the connecting elements upon which the plate members are mounted can themselves be fastened to stops in the respective bone parts. That in effect fixes the distance between the bone parts, with the plate members securing their relative juxtaposition. In an alternative, if it is desired to urge the respective bone parts continuously towards each other during a treatment and recovery period, then some form of resilient can be included. If the connecting members are attached to one but not both of the stops, then the resilient member or spring can be inserted between a stop and a plate member to urge the bone to which the plate member is attached, in a particular direction.

Any suitable mechanism may be used to lock the plate members and possibly the stops, relative to the connecting members. Typically, screws or pointed screws in the respective connecting member or stop can be urged against a connecting member installed therein. As indicate above, direct contact between a plate in a plate system for bone fixation can be a problem leading to damage to the periosteum, and/or having vital influence on the fusion of the bone parts due to reduced blood supply to the bone periosteum whence the nourishment for the fusion comes. The provision of projections on the contact surface of the respective plate members, either in the body of the plate member or as a feature of the means by which a bone screw is driven through the plate member and into the bone, maintains a spacing between the bone periosteum and the bulk of the contact surface.

The individual projections on the contact surface of the plate members as described above, may be formed by a screw that forms a projection on the contact surface when it is arranged in the respective screw hole. The effect is to lift the respective plate member as does a jack, as the screw is finally secured. Such screw units may advantageously be of the type described in US Patent Publication No: 2004/0144211 , incorporated herein by reference. A screw unit disclosed in that publication includes a nut which is screwed down into a screw hole in the plate member in order to secure the plate member to the bone. This is required as the screw diameter is less than the diameter of the screw hole, making it possible to mount the screws at an angle relative to the direction of the screw holes.

In particularly preferred embodiments of the invention, the plate members have holes each of which includes a seat adapted to interact with a screw unit. The screw has a nut or enlarged section at one end which is pressed against the periosteum when the respective plate member is finally secured. The enlarged end thus forms a projection on the contact side of the plate member, keeping it spaced from the periosteum of the bone. Thus, only the individual enlarged ends of the screws are in contact with the periosteum. Plate systems of the invention can be used in many surgical situations, and particularly when surgery is necessary on vertebra. The plate system can be used to immobilise the vertebra relative to each other. However, if there is a wish to maintain some mobility between the vertebra, the plate system of the invention may be adapted such that the connecting elements are replaced or provided with movable segments between the plate members.

Because plate systems of the invention are often needed for securement to a bone structure for long periods of time, it is of course important that suitable materials are used. Preferred materials which are biologically compatible are high vacuum melted steel, titanium, gold and graphite.

In addition to fixing bone fractures, the invention may be used in connection with extending tubular bones. The plate system may be expanded with a suitable form of motor which displaces the plate members from each other very slowly, so that the bone is stretched and thereby extended. In this way it is possible to extend tubular bones without using an external fixation system and the long bone screws that increase the risk of pin track infection as discussed above.

Embodiments of the invention will now be described by way of example and with reference to the accompanying schematic drawings wherein:

Figure 1 is a front perspective view of a plate system according of the invention;

Figure 2 is a cross-section of one of the plate members shown in Figure 1 ;

Figure 3 is a longitudinal cross-section through a plate member of Figure 1 ; Figure 4 shows a connecting element;

Figure 5 shows in cross-section how bone screws can be fixed in a plate member;

Figure 6 shows in more detail an opening in the plate member; a closure member and a locking screw;

Figure 7 shows how a plate system of the kind illustrated in Figures 1 to 6 can be fitted to a tubular bone;

Figure 8 shows a plate system according to a second embodiment of the invention;

Figure 9 shows a third embodiment of the invention in which a plate system is adapted to fixing a fracture between the neck of the femur and the head of the femur;

Figure 10 shows a fourth embodiment of the invention as it can be used for immobilising vertebra;

Figure 11 shows a fifth embodiment of the invention including multiple plate members;

Figure 12 shows how two plate systems of the kind illustrated in Figure 11 can be used simultaneously;

Figure 13 shows how a plate system of the invention can be extended laterally;

Figure 14 shows how a laterally extended plate system according to the invention can be used in the fixation of a complex bone fracture;

Figures 15 and 16 illustrate a sixth embodiment of the invention; Figure 17 shows the use of the plate system of Figure 11 for the fixation of a bone fracture of a tubular bone;

Figures 18 and 19 show how the invention can be used to orient bone screws at selected angles; and

Figures 2OA to H illustrate various stages in the securement of a plate member to a bone.

The plate system shown in Figures 1 to 4 has two plate members 4 mutually connected by connecting elements 8. Each plate member is formed with holes 10 which are prepared and shaped for receiving a screw element (not shown). A stop unit 12 with a screw hole 14 is disposed at either end of the system. Depending on the precise application for which the system is being used, the connecting elements 8 can be fixedly or movably received in the stop elements 12.

As shown in Figure 2, the contact side 11 of the respective plate member 4 is shaped, in this illustration concave, to substantially follow the outer shape of a bone. It will be noted also that the screw hole 10 is of reduced cross-section as it approaches the contact side 11 , the wall of this reduced cross-section portion is substantially spherical, for reasons which will be described hereafter.

Figures 5 and 6 illustrate in rather more detail how bone screws 22 are fitted to a bone, and held at their ends in a plate member 4. As shown in Figure 5, each bone screw 22 has an enlarged end 24 of substantially spherical shape complementing that of the reduced cross-section portion 23 in the plate member 4. One of the bone screws is shown installed at an approximate right angle to the general plane of the bone surface; the other at an angle thereto. The bone screws are installed with the enlarged section received in and projecting beyond the reduced cross-section 23 in the plate member. The enlarged end 24 sits on the periosteum 25 at the surface of the bone, but with the contact surface 11 of the plate member kept spaced therefrom. This arrangement is secured by a locking screw 26 which also has a spherically concave recess at its end, which engages the enlarged spherical end of the respective bone screw. When screwed into the hole 10, it closes around the enlarged spherical end of the bone screw and locks it in place with the contact surface 11 of the plate member spaced from the periosteum 25 of the bone. The spacing distance is preferably around one millimetre.

Figure 7 shows the application of a plate system broadly of the kind shown in Figure 1 , to form a dynamic compression plate system 30. Two plate members 4 are coupled by two connecting elements 8, and bone screws 22 are disposed in the respective screw holes 10, preferably in the manner described above with reference to Figures 5 and 6. The system shown is applied to a tubular bone 34, and the bone screws traverse the bone to engage opposing sides. This enables the best possible fixation to be achieved. It will be noted that the bone screws are oriented at different angles relative to the respective plate members. As noted above, this can be accomplished using the mechanism described with reference to Figures 5 and 6. Freedom with regard to the angle of the bone screws can also be maintained by the use of screws 22 having a diameter less than that of the screw holes 10. This freedom, however it is achieved, provides the surgeon with the option of selecting the orientation of the individual screws to achieve the best result, both with regard to the other screws and the location and nature of the fracture.

The plate system will use two connecting elements 8, and this will prevent twisting between the plate members and also therefore lateral displacement or rotation of one bone part 32 or 34, relative to the other. At the opposite ends of the plate system, the elements 8 in this embodiment of the invention are connected to stops 12 which retain the distance between the bone parts 32 and 34. However, a resilient member such as a spring or a curved or wavy plate spring, can be fitted between each stop and the adjacent plate member to put the respective bone part under stress, to encourage fusion at the point of fracture.

Figure 8 shows a plate system 40 in which the plate members 42 and 44 are coupled by a single connecting element 48, which is an integral part of the plate member 42 and has a cruciform cross-section. The opposition plate member 44 has a complementary recess for receiving the connecting element 48 and this matching cross-section of the element 48 and the recess 50 does of course prevent twisting between the respective plate members. Even so, if additional reinforcement is required, rods of the kind described with reference to Figures 1 to 4 can also be installed in holes 16 in the respective plate members shown.

Figure 9 illustrates an extended plate system 50 consisting of a series of plate members 52 and an end member 54, all coupled by connecting rods 56. The end member 54 is adapted to receive one or more relatively long bone screws 58 which extend from one side of a tubular bone; the neck of the femur 62 as shown through bushings 63 in the bone and further upwards into the head of the femur 64 under an obtuse angle relative to the end member 54 for fixing a fracture between the neck of the femur 62 and the head of the femur 64. The plate system shown may also include clamping and/or spring mechanisms for providing additional compression to the fracture, with the object of accelerating rehabilitation and stimulation of the blood supply to the fracture area and thereby the healing process and bone fusion. A similar plate system can be used for fixing fractures between the humerus and the bone head forming the joint between the humerus and the shoulder blade. Figure 12 shows another plate system in which two plate members 70 and 72 are secured on respective vertebra by screws 73. The purpose here is to immobilise the two adjacent vertebra 74, and for this purpose the plate members include pointed screws 76 which lock the respective plate members relative to the connecting elements 78 that extend through parallel holes in the two plate members 70 and 72.

It will be appreciated from the above description that plate systems of the invention can be used for fixing fractures in all types of bones.

Figure 11 shows another plate system in which multiple plate members or sledges 82 are coupled by connecting or track elements 84. Check blocks 86 and locking nuts 26 hide the heads of the bone screws (not shown).

Figure 12 shows how two systems of the kind shown in Figure 11 can be used for the immobilization of vertebra.

Figure 13 shows a modified version of the system of Figure 11 extended laterally by additional plate members or sledges attached on both sides thereof to the respective connecting or track elements 84. It will be appreciated that these lateral members or sledges can be inclined at an angle relative to the other elements mounted on both connecting elements 84. It should also be appreciated that the elements 84 may themselves be flexible to allow the lateral members to be inclined relative to the other members in two dimensions. Rather than a stop at the end of the connecting elements 84, there is a separate closure member 90. Figure 14 shows how a system of the kind illustrated in Figure 13, but with only one laterally extended plate member shown, can be used in the fixation of a complicated bone fracture.

Figures 15 and 16 show another variation of the invention in which plate members are coupled laterally rather than longitudinally. Adjacent members are coupled by links 99 which allow the system to bend in a single plane in the manner of a cycle chain. In the embodiment illustrated, rods 96 that couple the links 99 to the respective plate members 92 are splined such that the angle between any two adjacent links is locked. Thus, each system can be assembled individually from a particular application. Of course, if it is decided to retain some flexibility in the system, then the splined rods 96 can be replaced selectively by plain surfaced rods. In another alternative, rods which allow relative rotation can be used with separate locking mechanisms. However, the proper fixing of the plate members or sledges in relation to the bone or bone parts will primarily be resolved by means of the bone screws and the manner in which they are secured.

Figure 17 shows how a system of the kind illustrated in Figure 11 can be used for the fixing of a tubular bone fracture, and in order to obtain axial compression and traction on the fracture parts.

Figures 18 and 19 show how the angle of the bone screws may be selected to provide the best securement, longitudinally and transversely, along the length of the plate system. As can be seen, the angular positions of the screws can be adjusted within a mutual angle of up to 30°.

Figures 2OA to 2OH illustrate the steps in the mounting of bone screws 22 and fixing nuts 24 in a bone through the hole 10 of the plate member or sledge in any of the embodiments described above. Figure 2OA shows the fixing nut in the insertion holder 102 which is normally of plastics material. Figure 2OB shows the fixing nut as seen from the top as well as from one side. Figure 2OC shows how a screw insertion guide is mounted and fixed in the sledge by means of a threaded end part. Figure 2OD shows the insertion of the bone screw; 2OE the fixing nut mounted by means of the insertion holder 102. Figure 2OF illustrates the situation just before wringing off the bone screw in the fixing nut; and Figure 2OG illustrates the wringing off of the upper par of the bone screw using a special tool. Finally, Figure 2OH shows how the fixing nut and fixing screw together are tightened by means of a screwdriver 104.

Claims

1. A bone fixation system comprising a plate member having an upper face and a contact face, and formed with at least one hole therethrough, in which said at least one hole has one end length of a first cross-section extending from the upper face with the other end length tapering towards the contact face to a cross-section less than the first cross-section; a bone screw having a distal end and an enlarged proximal end of cross-section complementing that of the other end length of the hole; and a locking element to be received and locked in the one end length of the hole to clamp the proximal end of the bone screw against the other end length of the hole with the distal end projecting therefrom to secure the plate member to a bone part.

2. A system according to Claim 1 , wherein the enlarged proximal end of the bone screw extends beyond the contact face of the plate member when clamped against the other end length of the hole by the locking element.

3. A system according to Claim 1 or Claim 2, wherein the tapering cross-section of the other end length of the hole is spherical.

4. A system according to any preceding Claim, wherein the cross- section of the one end length of the hole is greater than the maximum cross- section of the other end length of the hole, forming an annular shoulder therebetween.

5. A system according to any preceding Claim, wherein the one end length of the hole is formed with an internal screw thread, and the locking screw is formed with a complementary external screw thread.

6. A plate system for the fixation of bones, comprising a plurality of plate members each for securement to a bone part, the plate members being coupled to each other by at least one connecting element, and wherein the spacing between the plate members is adjustable by displacement of at least one of the plate members on the said at least one connecting element.

7. A plate system according to Claim 6, wherein said at least one connecting element has a polygonal cross-section, received in a complementary opening in a said plate member.

8. A plate system according to Claim 6 or Claim 7, wherein a said connecting element is fastened to a stop for securement to a bone part.

9. A plate system according to any of Claims 6 to 8, wherein each plate member has a contact surface with ha number of projections forming support for the plate members against the periosteum of a respective bone part.

10. A plate system according to any of Claims 6 to 9, including screws for securing the plates to bone parts, each of which screws forms a projection on the contact surface of the plate member and in engagement with a respective bone part when the screw is installed.

11. A plate system according to any of Claim 6 to 10, including screws for securing the plates to bone parts, and wherein each plate is formed with holes, each of which is adapted for interacting with a part of a said screw.

12. A plate system according to any of Claims 6 to 10, wherein one of the plate members is a contact member adapted to be disposed at an angle relative to another plate member.

13. A plate system according to any of Claims 6 to 12, including at least two plate members coupled by at least one connecting element in a first direction, and at least one additional member coupled to the system laterally with respect to said first direction.

14. A plate system according to Claim 13, wherein at least one additional member is coupled to a plate member.

15. A plate system according to Claim 13 or Claim 14, wherein at least one additional member is coupled to a connecting element.