WO2024200544A1

WO2024200544A1 - A distraction spacer for a joint implant

Info

Publication number: WO2024200544A1
Application number: PCT/EP2024/058304
Authority: WO
Inventors: Gerry Clarke; Filip STOCKMANS; Maria Larkin
Original assignee: Loci Orthopaedics Ltd
Current assignee: Loci Orthopaedics Ltd
Priority date: 2023-03-31
Filing date: 2024-03-27
Publication date: 2024-10-03
Anticipated expiration: 2025-09-30
Also published as: WO2024200540A1

Abstract

A distraction spacer (1) is for use in insertion of an implant into a CMC joint. It has a proximal component (2) having a curved proximal surface (6) shaped for sliding movement over a trapezium. A neck (3) extends distally and there is a head (4) at the distal end having a distal spherical surface for contacting a resection plane of the metacarpal (M). The proximal saddle-shaped surface (6) and the distal spherical surface (8) allow accuracy and convenience during surgery, helping to reduce surgery time and risk of error.

Description

“A Distraction Spacer for a Joint Implant”

Introduction

The present invention relates to joint implants and surgery to insert them.

W02020/193078 (Loci Orthopaedics Ltd.) describes a bone joint implant for the Carpometacarpal (CMC) joint. When the surgeon is preparing the joint for insertion of the implant it is important to ensure that the bones are spaced (distracted) by the desired distance.

The present invention is directed towards achieving accurate and convenient maintenance of a desired gap during surgery. It is particularly directed towards maintenance of a desired gap during surgery to insert an implant in a joint having multiple axes of rotation, such as those in which there is a dual axis hemi-arthroplasty with two axes of rotation such as in the CMC joint.

Summary of the Invention

We describe a distraction spacer for insertion of an implant into a bone joint, the spacer comprising: a proximal component having a curved proximal surface shaped for sliding movement over a trapezium, and a head distally of the proximal component in a longitudinal direction, the head having a distal surface which has a convex curvature, wherein the spacer has a longitudinal dimension L between a distal-most part of the proximal component proximal surface and the distal-most part of the head distal surface in the range of 7 mm to 9 mm, and wherein the head has a maximum lateral width dimension W1 in the range of 6 mm to 14 mm.

In some preferred examples, the head is joined to the proximal component by a neck having a smaller lateral dimension than the head. In some preferred examples, the head has a substantially spherical distal surface.

In some preferred examples, the proximal component proximal surface has a curvature with convex and concave portions, providing a saddle shape. In some preferred examples, the spacer has a longitudinal dimension L between a distal-most part of the proximal component proximal surface and the distal-most part of the head distal surface in the range of 7.10 mm to 8.10 mm.

In some preferred examples, the head has a maximum lateral width dimension W1 in the range of 8 mm to 12 mm. In some preferred examples, the proximal component has a maximum width dimension W2 in the range of 10 mm to 16 mm, preferably 12 mm to 14 mm.

In some preferred examples, at least some of the spacer is of one or more selected from a Cobalt Chrome alloy, Titanium, a Titanium alloy, and a stainless-steel alloy.

In some preferred examples, the head distal surface and the proximal component proximal surface have a surface roughness which are both less than a surface roughness of the neck. Preferably, the head distal surface and the proximal component proximal surface each have a surface roughness in the range of 0.1 pm to 0.2 pm Ra, and the surface roughness of the neck is in the range of 0.2 pm to 4.0 pm Ra.

The neck may include at least one pair of opposed flats for gripping by a tool.

Additional Statements

We describe a distraction spacer for insertion of an implant into a bone joint, the spacer comprising: a proximal component having a curved proximal surface shaped for sliding movement over a trapezium, and a head distally of the proximal component in a longitudinal direction, the head having a distal surface which has a convex curvature.

In some examples, the head is joined to the proximal component by a neck having a smaller lateral dimension than the head.

In some examples, the head has a substantially spherical distal surface. In some examples, the proximal component proximal surface has a curvature with convex and concave portions, providing a saddle shape.

In some examples, the spacer has a longitudinal dimension (L) between a distal-most part of the proximal component proximal surface and the distal-most part of the head distal surface in the range of 7 mm to 9 mm, preferably 7.10 mm to 8.10 mm.

In some examples, the head has a maximum lateral width dimension (Wl) in the range of 6 mm to 14 mm, preferably 8 mm to 12 mm.

In some examples, the proximal component has a maximum width dimension (W2) in the range of 10 mm to 16 mm, preferably 12 mm to 14 mm.

We also describe a method of performing surgery to insert a hemiarthroplasty implant in a joint between a proximal bone and a distal bone, the method comprising performing a resection across a proximal end of the distal bone (M), inserting a distraction spacer of any example described herein into the gap between the proximal bone and the distal bone with the proximal component in sliding engagement with a distal surface of the proximal bone (T) and the head in contact with the resection plane of the distal bone (M), and determining correctness of the location of the distal bone resection according to how the spacer fits between said bones.

In some examples, the distal bone is the metacarpal and the proximal bone is the trapezium.

In some examples, the distraction spacer is chosen from a set of spacers, each one sized to match the distraction space of a particular implant.

Detailed Description of the Invention

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which:

Fig. 1 is a side view of a distraction spacer of the invention, for use with a CMC joint implant surgery, Fig. 2 is a top plan view of the spacer,

Fig. 3 is a front view of the spacer,

Fig. 4 is an underneath plan view of the spacer,

Fig. 5 is a sectional view in the direction of the arrows A-A of Fig. 2,

Fig. 6 is a sectional view in the direction of the arrows B-B of Fig. 3, and

Fig. 7 is a diagram illustrating use of the spacer of the invention, in which it is maintaining a gap between the trapezium and the metacarpal in the CMC joint.

Referring to Figs. 1 to 6 a distraction spacer 1 of the invention comprises a proximal part 2 which is saddle shaped, for moving on the trapezium in a sliding action. A proximal surface 6 of the saddle-shaped component 2 has both concave and convex curves, for optimum sliding over the trapezium of the applicable size.

A neck 3 extends distally from the proximal component 2, and this defines the longitudinal axis of the implant. There is a head 4 on the neck 3, and this is of hemi- spherical shape, having a distal surface 8 with a spherical curvature. The head 4 also has a proximal rim 7 which is curved inwardly and proximally to provide a rounded corner. Overall, the spacer 1 has rounded edges.

The spacer may be of any biocompatible material, on the basis that it is not part of the implant, merely being used temporarily during surgery. The preferred materials are Cobalt Chrome alloys, Titanium or Type 316 stainless steel alloys.

Referring to Fig. 3 key dimensions of the spacer 1 are:

L: 7 mm to 9 mm. Length along the longitudinal axis from the distal-most part of the proximal surface 6 of the proximal component 2 to the tip of the spherical surface 8 of the head 4.

W1 : 6 mm to 14 mm, maximum width, or diameter, of the head 4.

W2: 10 mm to 16 mm, maximum width of the proximal component More preferred ranges for these parameters are:

L: 7.10 mm to 8.10 mm.

Wl : 8 mm to 12 mm.

W2: 12 mm to 14 mm.

In use, the surgeon prepares the joint, in this example the CMC joint by performing resection across the proximal end of the metacarpal M, as shown diagrammatically in Fig. 7. The spacer 1 is placed in position, with the proximal component 2 resting on the distal surface of the trapezium and the head 4 contacting the resection plane of the metacarpal. The surgeon first makes a small, conservative orthogonal cut at the base of the metacarpal. The surgeon then inserts the distraction spacer 1 between the two bones, trapezium and metacarpal. The distraction spacer mimics the space between the two bones which the implant will eventually occupy. The surgeon may choose the distraction spacer from a set of such spacers to suit the size of the implant to be used. The implant may be the proximal implant component as described in W02020/193078, having a proximal saddle-shaped component and a ball on a neck. If the initial orthogonal cut at the base of the metacarpal is too conservative, the joint will be “over-stuffed” and the distraction spacer will pop out of the joint, indicating that the surgeon should perform a second orthogonal cut and repeat the process. On the other hand, if the surgeon’s evaluation using the distraction spacer is that there is too much laxity in the joint when the distraction spacer is deployed, then the indication will be that the metacarpal cut length is appropriate but a longer neck trial head should be sought when the distraction spacer is removed and the metacarpal has been broached to receive a stem and a trial head can be utilized.

Other features and advantages of use of the spacer include providing a means of optimizing the eventual fit of the implant within the joint and minimizing the theatre time in which the patient is under anaesthetic. The shape of the spacer distal surface (spherical curvature) allows convenience for the surgeon in placing the spacer into position pressing against the resection plane. The metacarpal, when resected, constitutes hard, cortical bone around the periphery of the cut and softer cancellous bone in the centre. To avoid the possibility of the distal surface of the distraction spacer sinking into the cancellous bone, the spherical curvature of the distal surface (Wl) should be at least 6 mm and preferably in the range of 8 mm to 12 mm. When temporarily installed in the distraction space, the distraction spacer allows the surgeon to manipulate the metacarpal to sufficient extent to gauge the laxity within the joint space and determine whether a subsequent orthogonal resection of the metacarpal is required, without risk of the distal surface of the distraction spacer migrating into the softer cancellous bone of the metacarpal.

In another embodiment, the head distal surface and the proximal component proximal surface have a surface roughness which are both less than a surface roughness of the neck. This allows them to engage effectively with the opposed surfaces of the bones that the spacer is separating, but it allows easier gripping of the spacer at the neck by the surgeon. The higher roughness of the neck makes it easier to grip by a tweezers or indeed manually. In preferred examples, the head distal surface and the proximal component proximal surface each have a surface roughness in the range of 0.1 pm to 0.2 pm Ra, and the surface roughness of the neck is in the range of 0.2 pm to 4.0 pm Ra.

In another embodiment, the neck includes at least one pair of opposed flats for gripping by a tool such as a long-nosed pliers. Such flats may be on an enlarged neck portion in the event that the neck is very thin for such a feature to be practical.

Components of embodiments can be employed in other embodiments in a manner as would be understood by a person of ordinary skill in the art. The invention is not limited to the embodiments described but may be varied in construction and detail.

Claims

1. A distraction spacer for insertion of an implant into a bone joint, the spacer comprising: a proximal component (2) having a curved proximal surface (6) shaped for sliding movement over a trapezium, and a head (4) distally of the proximal component in a longitudinal direction, the head having a distal surface which has a convex curvature, wherein the spacer has a longitudinal dimension (L) between a distal-most part of the proximal component proximal surface (6) and the distal-most part of the head distal surface (8) in the range of 7 mm to 9 mm, and wherein the head has a maximum lateral width dimension (Wl) in the range of 6 mm to 14 mm.

2. A distraction spacer as claimed in claim 1, wherein the head is joined to the proximal component by a neck (3) having a smaller lateral dimension than the head.

3. A distraction spacer as claimed in claim 1 or claim 2, wherein the head (4) has a substantially spherical distal surface (8).

4. A distraction spacer as claimed in any preceding claim, wherein the proximal component proximal surface (6) has a curvature with convex and concave portions, providing a saddle shape.

5. A distraction spacer as claimed in any preceding claim, wherein the spacer has a longitudinal dimension (L) between a distal-most part of the proximal component proximal surface (6) and the distal-most part of the head distal surface (8) in the range of 7.10 mm to 8.10 mm.

6. A distraction spacer as claimed in any preceding claim, wherein the head has a maximum lateral width dimension (Wl) in the range of 8 mm to 12 mm.

7. A distraction spacer as claimed in any preceding claim, wherein the proximal component has a maximum width dimension (W2) in the range of 10 mm to 16 mm, preferably 12 mm to 14 mm.

8. A distraction spacer as claimed in any preceding claim wherein at least some of the spacer is of one or more selected from a Cobalt Chrome alloy, Titanium, a Titanium alloy, and a stainless-steel alloy.

9. A distraction spacer as claimed in any of claims 2 to 8, wherein the head distal surface and the proximal component proximal surface have a surface roughness which are both less than a surface roughness of the neck.

10. A distraction spacer as claimed in claim 9, wherein the head distal surface and the proximal component proximal surface each have a surface roughness in the range of 0.1 pm to 0.2 pm Ra, and the surface roughness of the neck is in the range of 0.2 pm to 4.0 pm Ra.

11. A distraction spacer as claimed in any of claims 2 to 10, wherein the neck includes at least one pair of opposed flats for gripping by a tool.

12. A method of performing surgery to insert a hemiarthroplasty implant in a joint between a proximal bone and a distal bone, the method comprising performing a resection across a proximal end of the distal bone (M), inserting a distraction spacer (1) of any preceding claim into the gap between the proximal bone and the distal bone with the proximal component in sliding engagement with a distal surface of the proximal bone (T) and the head (2) in contact with the resection plane of the distal bone (M), and determining correctness of the location of the distal bone resection according to how the spacer fits between said bones.

13. A method as claimed in claim 12, wherein the joint is the CMC joint, the distal bone is the metacarpal and the proximal bone is the trapezium.

14. A method as claimed in claim 12 or claim 13, wherein the distraction spacer is chosen from a set of spacers, each one sized to match the distraction space of a particular implant.