WO2011075757A1

WO2011075757A1 - Fixation elements for fixation plates

Info

Publication number: WO2011075757A1
Application number: PCT/AU2009/001700
Authority: WO
Inventors: Ewen Laird
Original assignee: Austofix Group Pty Ltd
Priority date: 2008-12-23
Filing date: 2009-12-23
Publication date: 2011-06-30

Abstract

This invention describes a bone fracture fixation means (1) that comprises a plate (5) having first and second ends (2) and (3), fixation means (4) at the first end of the plate (5) for fixing the first end (2) of the plate (5) to the bone (50), aperture means (8) in the plate (5) towards the second end (3), and a plurality of elongate fixation elements (10) that locate into the bone (50) through aperture means (8) to fix the second end (3) of the plate (5) to the bone (50) wherein the longitudinal axis of at least one of the fixation elements (10) is at an angle with respect to a line normal to the plate (5). The angling of the elongate fixation elements (10) with respect to the plate (5) provide improved fixation of the plate (5) to the bone (50) in the case where forces would otherwise urge the plate (5) away from the bone (50).

Description

FIXATION ELEMENTS FOR FIXATION PLATES

TECHNICAL FIELD

This invention relates to a means of securing a fracture fixation plate to a bone. BACKGROUND OF THE INVENTION

Internal fracture fixation is often necessary when a fracture occurs in a load bearing region of the human body. A goal of the fixation is to provide immediate stabilization to the fracture. Another goal is to encourage rapid healing and return mobility to an individual thus preventing muscular atrophy. Metallic plates (CoCrMo alloy, stainless steel or titanium) can be used fixed to the outside of the bone using a number of screws, generally not less than four screws, selectively placed around a fracture site.

In one example of a fracture fixation plate, fractures to the femoral head and associated areas within the hip, require fixation through the femoral head and neck as well as additional support in the femoral shaft. This type of fracture uses a lag screw angled from a fixation plate across the fracture site to provide a compressive stress to the fracture, thus aiding healing. However, the lag screw needs support in the form of a fixation plate engaged with the femoral shaft.

There are a number of difficulties associated with the fixation of fractures. In the case of the femoral region, fractures extending to the neck and head regions of the femur are difficult to treat due mainly to the inaccessibility of the femoral head. Femoral fracture fixation plates and screws are subject to extremely high eccentric loading forces which create a bending movement which results in forces that place the screws in tension and that tend to urge the fixation plate away from the femoral shaft. As such, this bending movement can cause the implant to be rotated away from the femur. Under such forces, the screws are subject to shear and tensile loads and are susceptible to failure. One of the failure modes is due to the high 'pull out' stresses on the screws resulting from eccentric loads and resultant rotation forces. Such forces can pull both the screws and the plate away from the bone.

Screw and plate failure is attributed predominantly to implant loosening due to stress shielding, wear debris and micromotion, particularly in osteoporotic bone. If sufficient screw loosening occurs, screws, and in particular the lag screw in the femoral head, can cause significant bony damage and in some circumstances can pass through the femoral head. Any failure of the screw in the lifetime of the recipient will result in the need for revision surgery, placing further stress on both the patient and the fracture site. As such any method to increase the resilience, rigidity and strength of bone screws will be beneficial to the art. The length of the fracture fixation plate and the distribution of the screw holes along the plate determine the length of the incision required for internal plate fixation. As such, current fracture fixation plates using a plurality of screws will result in a lengthy incision by the surgeons. As such, it is desirable to minimise the number of screws required in conjunction with a fracture fixation plate.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a bone fracture fixation means comprises:

a plate having a first and second end,

fixation means at the first end of the plate for fixing the first end of the plate to the bone, aperture means in the plate towards the second end, and

a plurality of elongate fixation elements that locate into the bone through the aperture means to fix the second end of the plate to the bone wherein the longitudinal axis of at least one of the fixation elements is at an angle with respect to a line normal to the plate.

Preferably, the one fixation element is angled away from the first end of the fracture fixation means. Preferably, at least two fixation elements are at an angle with respect to the plate where they are each angled away from the first end of the plate.

This inclination of the fixation means provides more secure holding of the fixation elements with respect to the bone. When fixation elements, which may comprise screws, are screwed directly into the bone so that they are both normal to the bone and to the plate, they rely only on the strength of the threading engagement of the screws with respect to the bone. In other words, the pull out force is dependent only on the failure of the bone that engages the threads of the screw.

In many cases, fracture fixation means are placed under load conditions which result in the plate of the fracture fixation means being urged away from the surface of the bone. Such an example is a femoral fixation plate used to secure the fracture of the femoral head. Eccentric loads are applied to the fixation means which results in the plate being urged away from the bone surface.

In this invention, the inclination of the fixation elements with respect to the plate provides an improved degree of strength where the resistance to pull out of the fixation elements in this region of the plate is not solely dependent on the strength alone of threading engagement with bone.

Preferably, the plate is elongate and has a generally longitudinal axis and the aperture means may comprise any one or a combination of slots and apertures for location of elongate fixation elements within the apertures. The elongate fixation elements may comprise screws but may also comprise other fixation elements such as surgical nails, pegs or locking screws.

Preferably, where the aperture means comprises a plurality of apertures, they are generally or substantially aligned along the longitudinal axis of the elongate plate.

Preferably, the angle of the inclination of the fixation elements may be substantially within a plane that is normal to the plate and extends along the longitudinal axis of the elongate plate. In addition the fixation elements may be angled transversely either side to this longitudinal plane.

Further, where the aperture means comprises a plurality of apertures, these apertures may be located on either side of the longitudinal axis of the plate with one aperture located on one side of the axis and another aperture located on the other side of the axis with screws in these apertures angled laterally towards and across the longitudinal centre line of the elongate plate. This angling of the fixation elements results in improved strength for fixing the plate to bone and resists forces which might otherwise tend to pull fixation elements out of the bone if they were not at an angle and simply normal to the plate.

The bone fracture fixation means may be used to hold the fracture in the head of the femoral bone. In this case, the fixation means at the first end of the plate preferably comprises a lag screw for location within the femoral head and across the fracture site and the plate is fixed to the femoral bone.

Also, a jig is preferably used to assist in locating drill guides used to drill holes into the bone to receive threaded fixation elements. The jig may be a plastic moulding that clips onto the second end of the plate having apertures within which a drill sleeve can be threadably located. The apertures in the jig align the drill sleeve to the required angle with respect to the aperture. This is of particular assistance in drilling holes within the bone at the desired angle particularly when using fixation elements that comprise locking screws having a threaded head that threadably engages within the plate.

In this description, a bone fracture fixation means may be any plate used to position about or with respect to a fracture site for repair of that fracture. The bone fracture fixation means may be used in a variety of regions in the body such as but not limited to the extremities of the body such as arms and legs and also the mandibular and facial regions. The term "bone" is not limited to a single bone and may include a series of bones.

Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing both the process and apparatus of the present invention. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the present invention will now be described in more detail in relation to the following drawings in which:

Figure 1 is a side view of a first embodiment of a fracture fixation means;

Figure 2 is a side view of a second embodiment of a fracture fixation means;

Figure 3 is a frontal view of the second embodiment of the fracture fixation means illustrated in Fig.

2;

Figure 4 is an end view of Figure 3;

Figure 5 is a side view of a third embodiment of a fracture fixation means;

Figure 6 is a frontal view of the third embodiment of the fracture fixation means;

Figure 7 is a side view showing ajig coupled with a fracture fixation means; and

Figure 8 is a rear view of the jig coupled with a fracture fixation means.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 shows a side part cross-section view of a fracture fixation means 1 fixed to the femoral neck 51 and femoral head 52 on a femoral bone 50. The fracture fixation means 1 is used to fix a fracture 53 which is located in the femoral neck 51. The fixation means 1 shown in Figure 1 is used for the treatment of fractures of the femoral head 52 and femoral neck 51 such as intertrochanteric, intracapsular and basal neck fractures.

The fracture fixation means 1 uses a lag screw 4 that is located within the femoral head 52. The lag screw 4 is located at a first end 2 of a plate 5 and the plate 5 is secured to the femoral shaft 54. In this embodiment, the aperture means comprises a pair of apertures 8 that are located in the second end 3 of the plate 5. The lag screw 4 is angled at approximately 30 to 60 degrees from the vertical and it is located centrally within the femoral neck 51 and femoral head 52 of the bone 50. The lag screw 4 has a threaded region 4' and the shank portion 6 of the lag screw 4 is slidably engageable within an aperture (not shown) of a barrel 7 which is located at the first end 2 of the plate 5. The shank portion 6 slidably locates within the aperture of the barrel 7 and the shank 6 of the lag screw 4 has keying surfaces in the form of a flat on the lag screw 4 that engages a flat within the aperture of the barrel 7. This prevents rotation of the lag screw 4 after it is inserted within the femoral head 52, A barrel screw locates in the barrel 7 at an end opposite to the lag screw 4 and threadably engages within the lag screw 4 and acts to pull the first end 2 of the plate 5 onto the shank 6 of the lag screw 4. This in turn applies a compressive load across the fracture 53.

The second end 3 of the plate 5 has aperture means which in this embodiment comprises two apertures 8 vertically spaced and located towards the lower end or second end 3 of the plate 5. This second end 3 of the fixation plate 5 is fixed to the femoral shaft 54 by two fixation elements that comprise screws 10. The apertures 8 are angled so that the screws 10 threaded through the apertures 8 will be at an angle of 30 degrees from a line normal to the plate 5. The apertures 8 and screws 10 are angled to provide superior retention force of the plate 5 to the bone 50. The angle of the apertures 8 and screws 10 may be between 10 to 30 degrees from a line normal to the plate 5 with the screws angled away from the first end of the plate.

The screws 10 to be used in conjunction with the plate 5 are cortical locking screws that have a screw head 12 and a shank 13. The shank 13 is threaded and engages with the bone 50. The screw heads 12 are also threaded and locate within threaded apertures 8. This positively locks the screws 10 with respect to the plate 5 at the required angle.

As described above, the angled screws 10 improve the holding force when loads are applied to the femoral head 52. Eccentric loads are applied to plate 5 which then in turn causes it to be urged away from the femoral shaft 54. The angling of the screws 10 provides a superior degree of holding force which is not reliant alone on the strength of the thread engagement of the screws 10 with the bone 50.

A second embodiment is shown in Figures 2 to 4. The fracture fixation means 1 as shown in Figures 2 to 4 is similar to the first embodiment, in that it uses a lag screw 4 on the first end 2 of the plate 5 and has aperture means in a second end 3 of the plate 5.

The aperture means in this embodiment however comprises three apertures 106, 107 and 108 that are spaced along the longitudinal axis of the plate 5. The fixation elements comprise three screws 120, 130 and 140. As seen best in Figure 2, the longitudinal axis of the screws 130 and 140 are angled downwardly away from the first end 2 of the plate 5. In this embodiment, the angle of inclination of screw 130 is approximately 10 degrees and the angle of inclination of screw 140 is approximately 20 degrees.

The third screw 120 is not angled and is therefore substantially perpendicular to the plate 5. As it is closer to the first end 2 of the plate 5, there is less advantage to it being inclined with respect to the plate 5. Indeed, as an alternative, it may be angled towards the first end 2 of the plate 5.

The apertures 106, 107 and 108 are threaded and the heads 122, 132 and 142 of the screws 120, 130 and 140 respectively are also threaded so that the heads 122, 132 and 142 lockably engage with the plate 5. This holds the screws 120, 130 and 140 at the required angle with respect to the plate 5.

Further, as illustrated in Figure 4, the apertures 108 and 107 in the plate 5 are offset either side of the longitudinal axis of the plate 5 and in addition (referring to Figure 3) to the screws 130 and 140 being angled downwardly, they are also angled laterally so that each of the screws 130 and 140 is angled across a plane extending along the longitudinal axis of the plate 5 and also extending normally to the plate 5. With regard to Figure 3, screw 130 is angled to the right and screw 140 is angled to the left. This lateral angling of the screws 130 and 140 also aids in the retention force of the screws 130 and 140 with respect to the bone 50 when the plate 5 is urged away from the bone 50.

A third embodiment is shown in Figures 5 and 6. In this embodiment, only one of the screws 240 is angled away from the first end 2 of the plate 5. The remaining two screws 220 and 230 are both normal with respect to the plate 5. However, both screws 230 and 240 are angled in the transverse plane in a similar manner as described above. The two screws 230 and 240 may be divergent in the transverse plane at an angle of 5 to 10 degrees depending on surgical preference. Again, the apertures 230 and 240 are laterally offset either side of a centre line of the longitudinal axis of the plate 5. They are offset by a distance of 2-6mm. This offset combined with the downward angle of screw 240 as shown in Figure 5 produces the desired holding force for the second end 3 of plate 5.

Figures 7 and 8 illustrate a jig 500 that is used to locate drill guides at a correct angle with respect to the plate 5. The jig 500 is located on the second end 3 of the plate 5 and is located over the apertures 106 and 108 on the plate 5. The jig 500 is engaged with the plate 5 by fingers 530 that snap fit either side of the plate 5. In this embodiment, the jig 500 is located primarily with respect to the two apertures 106 and 108 but other designs of jig 500 may be aligned with either single apertures or more than two apertures. The jig 500 has two apertures 510 and 520 that align with the apertures 106 and 108. The apertures 510 and 520 in the jig are used to locate drill guides at the required angle with respect to the apertures 106 and 108. When a hole is drilled using the drill guides, the holes in the bone 50 are then at the required and correct angle. Upon drilling of the holes within the bone, the drill guides can be removed from the jig 500 and screws then inserted into the apertures 106 and 108 and the bone 50. The jig 500 can then be removed from the plate 5.

Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge.

It will be apparent by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that variations and modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications in its scope.

Claims

THE CLAIMS:

1. A bone fracture fixation means comprising:

a plate having a first and second end,

2. A bone fracture fixation means as claimed in claim 1 wherein the at least one fixation element is angled away from the first end.

3. A bone fracture fixation means as claimed in claim 2 wherein the angle is between 10 to 45 degrees.

4. A bone fracture fixation means as claimed in claim 2 wherein the angle is between 20 to 30 degrees.

5. A bone fracture fixation means according to claim 1 wherein two fixation elements are angled away from the first end.

6. A bone fracture fixation means as claimed in claim 5 wherein the angle of the two fixation elements is equal and between 10 to 45 degrees.

7. A bone fracture fixation means as claimed in claim 5 wherein the angle of one of the two fixation elements is less than the angle of the other.

8. A bone fracture fixation means as claimed in claim 5 wherein the angle of one of the fixation elements is between 10 to 20 degrees and the angle of the second fixation elements is between 20 to 30 degrees.

9. A bone fracture fixation means as claimed in any one of claims 5 to 8 wherein the plate is elongate and the two fixation elements are spaced along the longitudinal axis of the plate.

10. A bone fracture fixation means as claimed in claim 9 wherein the aperture means comprises at least two apertures through which said elongate fixation elements locate.

11. A bone fracture fixation means as claimed in claim 10 wherein the first aperture is spaced to one side of the longitudinal axis of the elongate plate and the second aperture is spaced to the other side of the longitudinal axis of the elongate plate.

12. A bone fracture fixation means as claimed in claim 11 wherein the two elongate fixation elements are also angled in a plane transverse to the longitudinal axis of the elongate plate.

13. A bone fracture fixation means according to any one of the preceding claims wherein the fixation means at the first end of the plate comprises a lag screw for location in a femoral head and across a fracture and wherein the plate is fixed to a femoral shaft.

14. A bone fracture fixation means according to any one of the preceding claims wherein the elongate fixation elements comprise screws.

15. A bone fracture fixation means according to claim 14 wherein the screws comprise locking screws.

16. A bone fracture fixation means according to claim 15 wherein the locking screws have threaded heads that locate in threaded apertures.

17. A bone fracture fixation means substantially as herein described and with reference to the accompanying drawings.