GB2429160A - Tensegrity osteotomy system comprising a threaded insert - Google Patents

Abstract

Apparatus for use in opening wedge osteotomy; the apparatus includes an insert 10 locatable in an opening in bone, the insert being elongate and converging to its distal end, the insert having an axial external thread 12. and a guide formation at its proximal end to facilitate its rotation. The guide formation may comprise a profiled opening or openings 14, 16 in the proximal end of the insert. Preferably, the insert is conical or frusto-conical in shape and made of an osteoconductive and/or bioabsorbable material. In use, a pair of inserts may be used. Preferably, the apparatus also includes gap closing means for applying a compressive force across a wedge gap 24. The gap closing means may comprise a screw (28. fig.6) extendable across the wedge gap or a plate (32, fig.7) or plates locatable across the opening of the wedge gap. Alternatively, the gap closing means may comprise tension bands (44, fig.10) extendable across the opening of the wedge gap with pins (42. fig.10) and/or screws mounted on either side of the wedge gap between which the tension bands may extend.

Description

Tensegrity Osteotomy System This invention concerns apparatus for use in

opening wedge osteotomy, and also a method of carrying out an opening wedge osteotomy.

An osteotomy is a surgical procedure whereby a bone is partially or completely cut through, then realigned or repositioned and held in its new position where it is allowed to fuse together or set. It is a technique that is used to correct skeletal deformity arising either through trauma, disease or congenital defects. The type of osteotomy performed depends upon the type of skeletal correction required.

For realignment of the angle of a bone, as opposed to a translation or axial or rotational realignment, the type of osteotomy can be either an opening or closing wedge. In a closing wedge procedure, two convergent cuts are made to form a bone wedge that is then removed. Bending one part of the bone relative to the other then closes the resultant gap and the angle of correction is equal to the taper angle of the bone wedge removed. In an opening wedge procedure, a single cut is made through the bone. Bending one part of the bone relative to the other opens up a gap that is maintained by some means while healing occurs. The bone is not cut completely through so that the far cortex can act as a hinge to the bending bone.

Unicompartmental arthritis of the knee with associated pain and instability is traditionally treated by total knee arthroplasty (TKA). This is a successful procedure with a survivorship of typically over 90% at 10 years.

Revision procedures are becoming increasingly common. For the younger and more active patient undergoing TKA however, further revisions may be required later in life.

High tibial or distal femoral opening wedge osteotomy procedures can be performed in cases of unicompartmental arthritis of the knee. They are far less invasive procedures than TKA and can be revised to a TKA later in life when the patient is older and generally less active. These procedures work by shifting the load axis from the damaged compartment to the healthy or less damaged side of the knee. To enable early weight bearing and to provide an environment conducive to healing, adequate post- operative stability is essential.

In an opening wedge procedure, maintenance of the gap between the cut ends of bone is generally undertaken by the use of a metallic plate that bridges the gap and is attached to the bones with surgical screws. A loadbearing device, such as a metallic block/chock, is often used within the cortical gap to prevent gap closure and help support the compressive forces involved in weight bearing. The use of a single block, however, to support compression is inherently unstable since the loads involved in weight bearing are then only supported at two points (the block and the apex of the cut i.e. the cortical hinge). Alternatively external fixators may be used but these are not well tolerated by the patient and pin-tract infection is often a serious complication. Some form of bone graft material is generally used within the gap to help the healing process.

Tensegrity is a system that confers mechanical stability to a structure by the combined use of the counteracting forces of compression and tension in different elements of the structure.

According to the present invention there is provided apparatus for use in opening wedge osteotomy, the apparatus including an insert locatable in an opening in bone, the insert being elongate and converging to its distal end, the insert having an axial external thread, and a guide formation at its proximal end to facilitate rotation thereof.

The insert may be conical or frusto conical.

The insert may be made of an osteoconductive and/or bioabsorbable material.

The guide formation may comprise a profiled opening or openings in the proximal end of the insert.

The apparatus preferably includes a pair of inserts.

The apparatus preferably also includes gap closing means for applying a compressive force across the wedge gap.

The gap closing means may include a plate or plates locatable across the opening of the wedge gap.

The gap closing means may include a screw extendable across the wedge gap.

The gap closing means may include tension bands extendable across the opening of the wedge gap. Pins and/or screws may be provided mountable on either side of the wedge gap, between which the tension bands may extend.

The invention also provides a method of carrying out an opening wedge osteotomy, the method including forming a cut in the bone, locating in the cut an insert as defined above, moving the insert into the cut to open same, and also applying a closing force to either side of the cut.

A pair of inserts are preferably located in the cut, spaced from each other.

Following forming of the cut, a guide hole or holes is preferably provided in the proximal end of the cut to locate an insert therein.

The closing force may be provided by locating a plate or plates across the opening of the cut.

The closing force may be provided by locating a screw extendible across the cut, which screw is preferably inclined relative to the cut.

The closing force may be provided by extending tension bands across the opening. Pins and/or screws may be mounted in the bone on either side of the opening, with the tension bands extending therebetween.

Once means have been put in place to apply a closing force across the cut, the insert is preferably moved a little further into the cut to ensure compressive and tension forces are applied to the cut.

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:Fig. I is a perspective view of an insert according to the invention; Figs. 2 and 3 are side views of a tibia upon which a method according to the invention is being carried out.

Fig. 4 is a horizontal sectional view through the tibia of Fig. 2; Fig. 5 is a similar view to Fig. 4 but with a slightly different method being carried out on a different tibia; Figs. 6 and 7 are similar views to Fig. 2 showing a method being carried out in a first version in Fig. 6 and a second version in Fig. 7 of the invention; and Figs. 8 - 10 are diagrammatic rear views of a tibia showing a method being carried out according to a third version of the invention.

Fig. 1 shows an insert 10 according to the invention usable in opening wedge osteotomy. The insert 10 is frusto conical and may of an osteo conductive and bioabsorbable material. An external thread is provided on the insert 10 by a helical rib 12. An engagement formation in the form of larger and smaller openings 14, 16 is provided in the larger proximal end of the insert 10.

The carrying out of an opening wedge osteotomy technique using the insert 10 of Fig. 1 will now be described. A medial opening wedge high tibial osteotomy procedure was undertaken to correct angular deformity associated with unicompartmental arthritis of the knee. The surgical procedure was performed according to the following steps: - Obtain full-length, standing A/P and lateral radiographs.

Geometrically determine the degree of correction required to shift the mechanical axis to the point of intersection on the lateral side.

Perform skin incision with care to avoid the saphenous vein and its branches.

Reflect back the anterior portion of the medial collateral ligament.

Drill two guide pins from the medial side to within 1cm of the lateral cortex (angled towards the fibular head 18).

Confirm position by radiology.

Dissect anteriorly behind the patellar tendon and posteriorly with decortication if possible to preserve a periosteal sleeve.

Pass curved elevators to protect the patellar tendon anteriorly and the major vessels posteriorly.

Position an oscillating saw inferior to the guide pins to cut medial to lateral taking great care not to penetrate the lateral cortex to cut a slot 20.

Drill two guide-holes 22 (see Fig. 8) in the cut plane extending 40mm (approximately two thirds) from the medial cortex angled towards the fibular head.

Two inserts 10 are located in the guide holes 22 and are rotated by an appropriate tool (not shown) and with gentle valgus stress, into the guide- holes 22 to open the osteotomy. Appropriate size inserts 10 are chosen relative to the degree of correction required. The proximal end of the inserts 10 should reside flush with the medial cortical surface when in their final position, taking care to maintain the lateral tibial cortex hinge. The degree of correction is then verified.

An appropriate system is then used to provide a closing force across the osteotomy to compress the size and provide stability to the reconstruction, details concerning this are provided below. The open wedge 24 produced is then filled with suitable bone graft. Preferred closure of wounds and post- operative management can then be followed.

The application of a compressive force e.g. by the use of a compression plate, across the osteotomy at the surface of the bone midway between the distraction elements will lever the lateral cortical hinge into tension. The preferred situation, in order to provide maximum stability to the reconstruction, is where compression is applied at all three points represented by the cortical hinge 26 and the two points of contact between the medial cortex and the proximal ends of the inserts 10. This is achieved when the tensile supporting elements of the system cross the central plane of the osteotomy within the triangle formed by these three points.

Fig. 6 shows one way of providing a compression force, with an inclined compression screw 28 extending across the wedge 24 to pass through said triangle. A countersink 30 is formed in the bone to receive the head of the screw 28.

Fig. 7 shows an alternative system for providing a compression force with a plate 32 one end of which is located in a slot 34 in the bone above the wedge 24. The plate 32 extends across the open end of the wedge 24 and is held in position therebelow by two screws 36.

Figs. 8 - 10 show a third system for providing a compression force. In this instance slightly different inserts 38 are used with a cruciform opening 40 to permit rotation thereof. Here four pins 42 are provided in the bone, two above and two below the open end of the wedge 24. Tension bands 44 extend between the pins 42 in a bow tie shaped configuration.

In practice when a compression force has been applied, for instance, in any of the above ways, the inserts 10, 34 will be rotated a little further into the wedge 24 to place the system in tension.

It is to be realised that the method and apparatus used can be modified as particular situations dictate. For instance the guide holes can be of different respective dimensions. The inserts may have different diameters, lengths and also degrees of convergence. Fig. 5 shows for instance an arrangement which differs from that in Fig. 4, with a shorter lower, as seen in the drawings, insert 46. Such variations can provide correction for anterior/posterior as well as lateral/medial angulation, or where the medial- lateral distance from the apex of the osteotomy varies due to the shape of the bone, as shown in Fig. 5.

There is thus described apparatus for, and also a method of, providing tensegrity in an opening wedge osteotomy system thereby conferring mechanical stability by the combined use of counteracting compression and tension. The apparatus used is such that it can be inexpensively produced by conventional methods.

Various other modifications may be made without departing from the scope of the invention. For instance the inserts may take a different form or shape. Different means for providing compression across the wedge may be used.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims (18)

1. Apparatus for use in opening wedge osteotomy, the apparatus including an insert locatable in an opening in bone, the insert being elongate and converging to its distal end, the insert having an axial external thread, and a guide formation at its proximal end to facilitate rotation thereof.

2. Apparatus according to claim 1, in which the insert is conical.

3. Apparatus according to claim 1, in which the insert is frusto conical.

4. Apparatus according to any of the preceding claims, in which the insert is made of an osteoconductive and/or bioabsorbable material.

5. Apparatus according to any of the preceding claims, in which the guide formation comprises a profiled opening or openings in the proximal end of the insert.

6. Apparatus according to any of the preceding claims, in which the apparatus includes a pair of inserts.

7. Apparatus according to any of the preceding claims, in which the apparatus also includes gap closing means for applying a compressive force across the wedge gap.

8. Apparatus according to claim 7, in which the gap closing means includes a plate or plates locatable across the opening of the wedge gap.

9. Apparatus according to claims 7 or 8, in which the gap closing means includes a screw extendable across the wedge gap.

10. Apparatus according to any of claims 7 to 9, in which the gap closing means includes tension bands extendable across the opening of the wedge gap.

11. Apparatus according to claim 10, in which pins and/or screws are provided mountable on either side of the wedge gap, between which the tension bands may extend.

12. Apparatus substantially as hereinbefore described and with reference to Figs. 1 -4 of the accompanying drawings.

13. Apparatus substantially as hereinbefore described and with reference to Fig. 5 of the accompanying drawings.

14. Apparatus substantially as hereinbefore described and with reference to Fig. 6 of the accompanying drawings.

15. Apparatus substantially as hereinbefore described and with reference to Fig. 7 of the accompanying drawings.

16. Apparatus substantially as hereinbefore described and with reference to Fig. 9 of the accompanying drawings.

17. Apparatus substantially as hereinbefore described and with reference to Fig. 10 of the accompanying drawings.

18. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.