WO2012072111A1

WO2012072111A1 - Orthopaedic implant

Info

Publication number: WO2012072111A1
Application number: PCT/EP2010/068514
Authority: WO
Inventors: Stephanie Regula Margrethe Grassmann; Andreas Klockow
Original assignee: Smith & Nephew Orthopaedics Ag
Priority date: 2010-11-30
Filing date: 2010-11-30
Publication date: 2012-06-07

Abstract

An orthopaedic implant (1) comprises first and second components (9, 10). The first component (9) has an outer surface defining a self-tapping thread (11) that is adapted for implantation of the component (9) directly into a bone by screwing. The second component (10) is adapted for connection to die first component (9) intta-operatively and defines an external geometry adapted to resist axial rotation. Preferably, the second component (10) defines an external geometry adapted to resist axial rotation of both the fust and the second components (9, 10) after connection to die first component (9). The first component (9) may also define external features adapted to resist axial rotation. Such an implant (1) is intended to prevent or to mitigate post-operative displacement and rotation of the implant (1) and, therefore, post-operative loosening. The implant (1) is primarily intended for use in long bones in die human or animal body.

Description

ORTHOPAEDIC IMPLANT

The present invention relates to an orthopaedic implant in particular, but not exclusively, for long bones in a human or animal body.

The loosening of orthopaedic implants in situ is one of the primary causes of their postoperative failure. This problem can be caused by axial rotation of the implant and/or by translation, which is movement of the implant longitudinally, typically caused by subsidence within the long bone. The problem has been addressed in several ways. Some long-bone implants have longitudinal ridges while others have saw-tooth shaped teeth which limit or prevent axial rotation. To limit translation, some implants have a stepped profile or an external geometry similar to tlie anatomical bone cavity. However, the inherent geometrical design of no orthopaedic implant systems have been devised to limit post-operative displacement by both axial rotation and translation of the implant. Thereby, some long-bone implants comprising of stems have holes into which transverse screws or lag screws are located to hold the stem of the implant in place to prevent displacement, translation or axial rotation. These additional implants are not bone conserving, increase surgical time and may significantly decrease the bone rigidity. it is an object of the present invention to provide an ordiopaedic implant diat obviates or substantially mitigates post-operative displacement of the implant and that thereby obviates or substantially mitigates post-operative loosening of the implant.

According to the present invention there is provided a modular ordiopaedic implant comprising a first component having an outer surface defining a self-tapping diread adapted for implantation of the component directiy into a bone by screwing, and a second component adapted for connection to the first component intra-operatively and defining an external geometry adapted to resist axial rotation.

The first component is therefore adapted to limit translation of the implant, diat is the longitudinally movement of the implant within the bone whereas the second component is adapted to resist axial rotation of the implant within the bone. Preferably, the second component defines an exteinal geometiy adapted to resist axial rotation of bodi the first and the second components after connection to the first component.

Preferably also, the first component also defines external features adapted to resist axial rotation.

Preferably also, the second component has an external geometry that comprises external characteristics in the form of one or more radial projections and/or a non- rotational transverse profile. Advantageously, the second component has one of a rectangular profile, a square profile, a trapezoidal profile, a rhombic profile, an oval profile or a circular/ oval profile with ribs.

Preferably also, the second component comprises one or more radial projections in the form of any or a. combination of fins, pins and tines.

Preferably also, the first and second components form a joint. In some embodiments, the joint is in the form of a mortise and tenon joint or a tongue and groove joint wherein the first component defines the mortise or groove and the second component defines the tenon or tongue or vice versa.

Preferably also, the first and second components are adapted to be secured together by means of one or more fasteners, for example one or more screw fasteners.

Preferably also, the first component comprises a geometry diat enables bone chip breaking and/or tissue collection when screwing the first component during implantation. In some embodiments, the first component preferably comprises a geometiy defining one or more grooves, columns and/or recesses diat enables bone chip breaking and/or tissue collection when screwing the first component during implantation. Preferably also, the implant is modular whereby the first and second components thereof are connectable to a range of differently shaped and/or sized second and first components respectively.

Preferably also, the first component is a distal component and the second component is a proximal component.

Preferably, the implant comprises or forms a part of an implant adapted for implantation in a long bone.

Other preferred but non-essential features of the various aspects of the present invention are described in the dependent claims appended hereto.

An embodiment of the present invention will now be described by way of example widi reference to tlie accompanying drawing in which:

Fig. 1 is schematic front view of a first embodiment of the invention in tlie form of a femoral stem of a hip joint prosthesis;

Fig. 2 is a side view of tlie femoral stem shown in Fig. 1;

Fig. 3 is a plan view of the femoral stem shown in Figs. 1 and 2;

Figs. 4 and 5 are views similar to Fig. 2 and 3 respectively but of a second embodiment of femoral stem.

Throughout this description, similar components or parts in the various embodiments and modifications are given the same reference numeral.

A femoral stem 1 as shown in the drawings comprises a neck 2 and an anchoring blade 3 diat tapers towards a distal end 4. The blade 3 widens conically from the distal end 4 in the direction of the proximal end. The neck 2 is terminated by a conically tapering pin 5 on which a spherical joint head (not shown) can be located. On the side of the blade 3 opposite the neck 2 the cone widens out and then defines a trochanter wing 6 before merging, via a shoulder 7, into the neck 2. As in conventional femoral stems, the two through holes 8 are formed dirough the trochanter wing 6 for the purposes of x- ray identification.

In accordance widi the present invention, a first embodiment of stem 1 as shown in Figs. 1 to 3 comprises first and second components 9 and 10 respectively diat are adapted to be connected together. The first component 9 is a distal component and forms the blade 3. The conical outer surface of the component 9 defines a self-tapping thread 11 so that it can be implanted direcdy into a bone by screwing. The design of the diread 11 is such that it enables a surgeon to implant the component 9 by screwing the component 9 direcdy into a bone either manually or by using power tools. The component 9 may therefore drill dirough corticalis and cancellous bone and thence into the medullary cavity of the bone. The thread 11 therefore engages the inner bone surface of the cavity, which may be cancellous or corticalis or botii, following implantation. The diread 11 does not necessarily need to cover the full length of the component 9 from its distal to its proximal ends and may cover only part of the lengdi of the component 9.

The profile of the thread 1 1 may be customized dependent on the type of bone diat the component 9 will come into contact widi during implantation and post-operatively. Hence, different components 9 may be provided for use widi the same component 10, at the choice of a surgeon, and have different diread profiles and lengdis to match different patients¹ requirements of bone type and condition, for example osteoporotic bone, and different surgical techniques.

In addition to the diread 1 1, component 9 also defines a geometry diat enables bone chip breaking and/or tissue collection when screwing the component 9 during implantation. In the illustrated embodiment, this geometry defines a longitudinal channel 12 for the collection of tissue or bone chips. In other embodiments, the geometry may define one or more grooves, columns and/ or recesses. The second component 10 comprises a proximal part of the stem 1 including the neck 2 and the trochanter wing 6. As shown in Figs. 2 and 3, the distal part of the component 10 locates within a slot 13 formed at the proximal end of the component 9. The first and second components 9 and 10 therefore form a joint which in diis embodiment is in the form of a tongue and groove joint. The distal part of the component 9 defines a tongue which fits into the slot 13 of the component 10 that defines the groove. It will be appreciated diat in other embodiments diis arrangement may be reversed so that the component 9 defines the groove and the component 10 defines the tongue. In a slight variation, the joint could comprise a mortise and tenon joint. In addition, the components 9 and 10 when joined define a co-axial tapped bore 14 so diat tiiey can be secured together by means of a fastener such as a screw fastener (not shown). The shoulder 7 of the component 9 is provided widi a countersinking 15 to accommodate the head of the screw. It will also be appreciated, however, diat other forms of joint between the components 9, 10 are possible.

The component 10 defines an external geometry diat resists axial rotation and in particular resists rotation of bodi itself arid the component 9 after it has been implanted and connected thereto.

In a second embodiment of femoral stem 1 as shown in Figs. 4 and 5, the first component 9 is as described above but the second component 10 has a circular cross- sectional profile and is secured to the component 9 by means of one or mole fasteners (not shown) in addition to the fastener diat is located in the a co-axial tapped bore 14, similar to that described above. Hence, rotation of the components 9 and 10 relative to one another is prevented. The component 10 is adapted to resist rotation relative to the cavity in which it is implanted by the provision of a plurality of external ribs or fins 16 which extend radially outwards and extend longitudinally down substantially the whole length of the component 10. A series of such ribs 16 is spaced around the circumference of the component 10, as shown in Fig. 4.

In the embodiment shown in Figs. 1 to 3 the component 10 has a rectangular transverse profile whereas in the embodiment shown in Figs. 4 and 5, the component 10 has a circular transverse profile. However, in other embodiments the component 10 may have any of a rectangular profile, a square profile, a trapezoidal profile, a rhombic profile, an oval profile or a circular /oval profile with projecting ribs. Such an external geometry resists rotation.

In otiier embodiments, rotation of either one or both of the component 9 and 10 may be resisted by the provision of features such as slots, apertures or channels into which fasteners, pins or tines may be located diat engage the osseous walls of the bone cavity.

In a modification, the component 10 may define a neck 2 widi a pin 5 defining a Morse taper (not shown) for connection to other components, for example a femoral neck of a hip prosthesis, or a may define a connecting mechanism to which a modular neck or bearing component can be fitted.

It will be appreciated diat after implantation of the component 9, the component 10 is fitted and attached thereto intra-operatively. After implantation, the component 9 will resist translational movement of the stem 1 longitudinally within the bone as the threads 11 firmly engage the inner bone surface. Similarly, the component 10 will resist rotational movement of the implant 1 owing to its non-rotational rectangular shape. As the two components 9, 10 are connected togetiier the implant as a whole will therefore resist bodi forms of movement to reduce the likelihood of post-operative loosening of the implant.

It will be appreciated diat an implant in accordance with the present invention is not limited only to the form of a femoral stem and the principles described above can be adapted for use in implants designed for implantation in any long bone such as leg, arm finger and toe bones. It may also be possible to adapt the implants for use in other bones in the same way. It is also expected that components 9 and 10 which respectively resist translational and rotational movement after implantation may form a part of implants along with other components. These other components may also assist the implant to resist translational and/or rotational movement after implantation and may, for example, take the form of screws and the like diat are connected to the components 9 and 10 after implantation. Either or both of the components 9, 10 may, therefore, be provided with slots and/ or apertures to connect to these other components. In addition, the implant 1 itself is modular whereby the first and second components 9, 10 are connectable to a range of differently shaped and/or sized second and first components 10, 9 respectively as determined by the surgeon to suit a particular patient.

In some embodiments the components 9, 10 may, at least in part, have a spiral or tubular design and/or be hollow or partially hollow. In particular, the components 9, 10 may be adapted for the intra-operative or post-operative drainage of collected materials or the introduction of fluent materials, for example fluent materials that can be pumped through the implant 1 for therapeutic purposes. In diis case either or both of the components together may define at least one channel communicating with apertures or pores defined in therir surface for tills purpose.

The implant 1 may also be designed for use in combination with cement or other implant fixation materials adapted to limit translational and/or rotational movement in addition to the action of the components 9 and 10.

The components 9 and 10 are manufactured from bio-compatible materials, which may include any or a mixture of any of the following, namely titanium, titanium alloy, stainless steel, stainless steel alloy, cobalt chrome alloy; a polymer or a polymer composite, a ceramic or a ceramic composite, and a metal composite.. The thread 11 may comprise or have a cutting tip made from the same or a different material from the rest of the component 9. In particular, the diread 1 1 may have a cutting tip made from any of the following, namely a ceramic material, a ceramic composite material, a metal, a metal composite, and a polymer composite. The implant may also comprise natural or artificial bone graft or bioabsorbable material.

Either or both of the components 9 and 10 may also comprise biocompatible pliable, flexible or viscoelastic materials. Such materials would impart flexibility to the implant and enable it to fit the geometiy of an inner bone cavity by allowing the implant or part of it to change its diameter, external profile or geometiy to adapt to the internal geometry of the bone cavity. Viscoelastic materials would mimic the surrounding osseous environment. The components 9 and 10, as modular components may be made available in different lengdis and geometries including diickncss and cross-sectional shape, according to the characteristics of the patient, the patient bone or the requirements of the surgical procedure. Their surfaces and diose of the implant as a whole may be surface treated or surface roughened to assist the osteointegradon of the implant. This treatment may include, for example, adding surface layer(s) of titanium, hydroxyapatite, biocompatible phase- trans forming material or other, pressure or grit blasting with zirconium oxide or other grit material(s). Alternatively, the surfaces of the components 9 and 10 may be produced with rapid prototype manufacturing procedures, i.e. laser sintering.

In some embodiments, the implant 1 may comprise or be at least partially comprised of a radiograpliic material or comprise a radiographic marker. in another embodiment, the implant may comprise the distal components of an ardirodesis (fixed joint).

The implant may comprise a short-term implant, a long-term implant or a trauma implant. More generally, the design and geometry of the modular implant may be such as to enable the implant to be attached to instrumentation during surgery, for example to retrieve or move components of the implant intra-operatively, for example during revision surgery, or to remove the implant, for example for replacement. In order to facilitate the removal or movement of the components 1, 2 during revision surgery, the components 1, 2 may be provided widi an external contour on their proximal end to allow their removal widi currently available instrumentation, For example, the proximal end external geometry may define a proximal end recess with radial cut-outs into which an end of a tool is engageable. Typically, the tool will comprise a clutch widi a cross- brace that fits into the recess and cut-outs.

The implant may comprise or form a part of an implant adapted for implantation in one of a hip joint, a knee joint, an ankle joint, a toe joint, a shoulder joint, an elbow joint, a wrist joint, a hand joint, a finger joint, and the spine. Hence, an orthopaedic implant in accordance with the invention obviates or substantially mitigates post-operative displacement and rotation of the implant and thereby obviates or substantially mitigates post-operative loosening of the implant. In addition, the self-tapping thread 1 1 of the component 9 has the further advantage that it enables bone to be conserved during the surgical implantation procedure.

Claims

1. An orthopaedic implant (1) comprising a first component (9) having an outer surface defining a self-tapping thread (11) adapted for implantation of the component (9) direcdy into a bone by screwing, and a second component (10) adapted for connection to the first component (9) intra- opera tively and defining an external geometry adapted to resist axial rotation.

2. An implant as claimed in Claim 1, wherein tire second component (10) defines an external geomctiy adapted to resist axial rotation of both the first and the second components (9, 10) after connection to the first component (9).

3. An implant as claimed in Claim 1 or Claim 2, wherein the first component (9) defines external features adapted to resist axial rotation.

4. An implant as claimed in any of Claims 1 to 3, wherein the outer surface of the first component (9) diat defines the self-tapping diread (1 1) is conical.

5. An implant as claimed in any of Claim 1 to 4, wherein the second component (10) has an external geometry that comprises external characteristics in the form of one or more radial projections and/or longitudinal ribs and/or a non- rotational transverse profile.

6. An implant as claimed in any of Claims 1 to 5, wherein the second component (10) has one of a rectangular profile, a square profile, a trapezoidal profile, a rhombic profile, an oval profile or a circular/oval profile witii ribs.

7. An implant as claimed in any of Claims 1 to 6, wherein the first component (9) and/or the second component (10) comprises one or more radial projections in the form of any or a combination of fins, pins and tines.

8. An implant as claimed in any of Claims 1 to 7, wherein the first and second components (9, 10) form a joint.

9. An implant as claimed in Claim 8, wherein the joint between the first and second components is in the form of a mortise and tenon joint or a tongue and groove joint.

10. An implant as claimed in Claim 9, wherein the first component (9) defines the mortise or groove (13) and the second component (10) defines the tenon or tongue or vice versa.

11. An implant as claimed in any of Claims 1 to 10, wherein the first and second components (9, 10) are adapted to be secured together by means of one or more fasteners.

12. An implant as claimed in any of Claims 1 to 11, wherein the first and second components are adapted to be secured together after implantation by one or more screw fasteners.

13. An implant as claimed in any of Claims 1 to 12, wherein the first component (9) comprises a geometry that enables bone chip breaking and/or tissue collection when screwing the first component (9) during implantation.

14. An implant as claimed in any of Claims 1 to 13, wherein the first component (9) * comprises a geometry defining one or more grooves (12), columns and/or recesses diat enables bone chip breaking and/or tissue collection when screwing the first component (9) during implantation.

15. An implant as claimed in any of Claims 1 to 14, that is modular whereby the first and second components (9, 10) are connectable to a range of differendy shaped and/or sized second and first components (10,9) respectively.

16. An implant as claimed in any of Claims 1 to 15, wherein the first component (9) is a distal component and the second component (10) is a proximal component.

17. An implant as claimed in any of Claims 1 to 16, wherein the first and/or second component (9, 10) defines slots and/or apertures and/or channels adapted for connection of the component to another component adapted to resist translational and/or rotational movement of the first and/or second component after implantation.

18. An implant as claimed in Claim 17, comprising wherein said other components comprise fasteners, pins and/or tines adapted to engage the osseous walls of the bone cavity.

19. An implant as claimed in any of Claims 1 to 17, wherein the first and/or second component (9, 10) defines at least one channel communicating widi apertures or pores at the surface of the component (9,10) for the intra- operative or postoperative drainage of collected materials or the introduction of fluent materials.

20. An implant as claimed in any of Claims 1 to 19, wherein each of the first and second components (9, 10) is comprised of bio-compatible materials diat include any or a mixture of any of the following, namely titanium, titanium alio}', stainless steel, stainless steel alloy, cobalt chrome alloy; a polymer or a polymer composite, a ceramic or a ceramic composite, and a metal composite.

21. An implant as claimed in any of Claims 1 to 20, wherein the self-tapping thread (11) comprises a cutting tip made from any of the following, namely a ceramic material, a ceramic composite material, a metal, a metal composite, and a polymer composite.

22. An implant as claimed in any of Claims 1 to 21, comprising a bone graft or a bioabsorbable material,

23. An implant as claimed in any of Claims 1 to 22, wherein either or bodi of the first and second components (9, 10) comprises a biocompatible pliable, flexible or viscoelastic material adapted to impart flexibility to the implant.

24. An implant as claimed in any of Claims 1 to 23, wherein the first and/or the second component (9, 10) has been treated to assist osteointegration of the implant by any or a combination of the following treatments:-

(i) addition of a surface layer of titanium, hydroxyapatite or a biocompatible phase-transforming material;

(ii) pressure or grit blasting witli zirconium oxide or another grit material; and

(iii) production of a surface by a rapid prototype manufacturing procedure.

25. An implant as claimed in any of Claims 1 to 24, that comprises or is at least partially comprised of a radiographic material or a radiographic marker.

26. An implant as claimed in any of Claims 1 to 25, that comprises the distal components of an arthrodesis.

27. An implant as claimed in any of Claims 1 to 26, diat comprises an arthroplasty implant or a part dicreof.

28. An implant as claimed in any of Claim 1 to 27, that comprises or forms a part of an implant (1) adapted for implantation in a long bone.

29. A system as claimed in any of Claims 1 to 28, wherein said implant comprises or forms a part of an implant adapted for implantation in one of a hip joint, a knee joint, an ankle joint, a toe joint, a shoulder joint, an elbow joint, a wrist joint, a hand joint, a finger joint, and the spine,

30. An implant as claimed in Claim 29, that comprises a femoral stem (1) of a hip joint pros thesis.