WO2019038032A1

WO2019038032A1 - Trial shell with window connection features

Info

Publication number: WO2019038032A1
Application number: PCT/EP2018/070686
Authority: WO
Inventors: Clinton Beck; Larry Mccleary; Stephanie Prince; Duncan Young; Stephen Robinson
Original assignee: Depuy Ireland Unlimited Company
Priority date: 2017-08-22
Filing date: 2018-07-31
Publication date: 2019-02-28

Abstract

A system that includes a trial acetabular cup liner (10) and an acetabular cup (40), and methods of trialing the hip system, are described. The hip system comprises a trial liner configured to be received within an acetabular cup. The trial liner comprises a convex outer surface (12) configured to be engaged with the acetabular cup, the convex outer surface having a plurality of barbs (14) circumferentially arranged thereon. The trial liner also comprises a concave inner surface configured to receive a femoral head. The hip system further includes a trial acetabular cup configured to receive the trial liner. The acetabular cup comprises a shell (42) with a convex outer surface configured to be engaged with an acetabulum, and a concave inner surface configured to be engaged with the convex outer surface of the trial liner. The shell has a plurality of circumferentially arranged windows (54), and at least one of the plurality of barbs on the convex outer surface of the trial liner is configured to be engaged with an edge of one of the plurality of windows in the shell when the trial liner is received within the acetabular cup.

Description

TRIAL SHELL WITH WINDOW CONNECTION FEATURES

Field of the invention

This invention relates to the field of orthopaedics, and more particularly to system that includes a trial acetabular cup liner and an acetabular cup.

Background of the invention

Patients who suffer from hip pain and immobility caused by arthritis and rheumatoid arthritis have an option of hip replacement surgery or hip arthroplasty in which a diseased and/or damaged hip joint is replaced with a prosthetic hip joint. In a typical hip joint arthroplasty, a proximal portion of the femur is resected and a distal portion of the acetabulum is milled. A prosthetic hip cup is attached to the acetabulum and a hip stem is attached to the femur.

Typical prosthetic hip cups include a shell or a cup that is secured to the milled portion of the acetabulum by bone cement, fasteners and/or features on the cup surface and a bearing or liner which includes a convex outer periphery that is secured to a concave inner periphery of the cup. Typically the liner is secured to the cup by fixed barbs on the convex outer periphery of the liner that fit into a circumferential groove positioned in the concave inner periphery of the cup.

The liner, typically made of polyethylene, is pressed into the cup, typically made of metal, with the aid of a mallet. During installation the barbs are deformed to pass the lip of the cup and then enter the groove of the cup.

The formation of a circumferential groove within the concave inner periphery of an acetabular cup during manufacture of the cup by Metal Injection Moulding (MEVI) increases, amongst of things, the complexity of the manufacturing process and the cost. Conventional trial liners include viewing widows that enable a surgeon to visualise the interior of the acetabular cup. It has been found that by altering the geometry of these viewing windows, the engagement mechanism between the trial liner and the trial cup can be based on the engagement of the barbs with the edge of the windows. This provides the viewing windows with dual functionality: the original visualisation function and in addition a connection function.

Advantages of this arrangement include, but are not limited to: reducing the production cost because the creation of the circumferential groove is not required; reducing the overall mass of the trial liner which reduces the production costs and time and also the weight of the instrument tray; improvements in the ease of cleaning of the trial liner because it is no longer necessary to clean within a circumferential groove.

Summary of the invention

According to an aspect of the invention there is provided a hip system comprising:

(a) a trial liner configured to be received within an acetabular cup, the trial liner comprising:

a convex outer surface configured to be engaged with the acetabular cup, the convex outer surface having a plurality of barbs circumferentially arranged thereon, and

a concave inner surface configured to receive a femoral head;

(b) a trial acetabular cup configured to receive the trial liner, the acetabular cup comprising:

a shell comprising:

a convex outer surface configured to be engaged with an acetabulum, and a concave inner surface configured to be engaged with the convex outer surface of the trial liner,

in which the shell includes a plurality of circumferentially arranged windows, and in which at least one of the plurality of barbs on the convex outer surface of the trial liner is configured to be engaged with an edge of one of the plurality of windows in the shell when the trial liner is received within the acetabular cup. In some constructions of the hip system, each of the plurality of barbs on the trial liner has a cup contacting face configured to be seated on the edge of one of the plurality of windows of the acetabular cup when the trial liner is received within the acetabular cup. In particular, in some constructions of the hip system, the trial acetabular cup includes a circumferential rim and the edge of at least one of the plurality of windows which engages at least one of the barbs on the convex outer surface of the trial liner is substantially parallel to the circumferential rim. Accordingly, the edge of the window may act as a ledge on which the liner contacting face of a barb can be seated when the liner is inserted into the acetabular cup. This prevents the disengagement of the trial liner from the trial acetabular cup during range of motion assessment.

In some constructions of the hip system, the shell of the trial acetabular cup comprises a frame having a plurality of arms. An arm of the plurality of arms separates each of the circumferentially arranged windows. Advantageously, each of the plurality of barbs is spaced apart on the convex outer surface of the trial liner from a neighbouring barb such that a space is provided in between neighbouring barbs which is dimensioned to receive an arm of the frame. This is particularly advantageous in hip systems that rely on the interaction of a plurality of spaced apart complimentary anti-rotation devices (ARDs) provided on the convex outer surface of the liner with a plurality of spaced apart recesses formed in the concave inner surface of the shell to prevent the relative rotation of the two components. The ability for a surgeon to be able to position any of the ARDs on the trial liner in any of the spaced apart recesses on the acetabular cup, rather than being restricted to positioning the trial liner in a specific orientation within the acetabular cup is advantageous in hip systems in which the convex outer surface of the trial liner is not entirely spherical, for example, in the case of a trial augmented liner. In some constructions of the hip system, each barb of the plurality of barbs may have the same circumferential arc length.

In some constructions of the hip system, the space between each of the neighbouring barbs is the same about the circumference of the trial liner.

In some constructions of the hip system, each arm of the plurality of arms may have the same circumferential arc length.

In some constructions of the hip system, the space between each of the neighbouring barbs is greater than the circumferential arc length of each arm of the plurality of arms.

In some circumstances, the surgeon may inadvertently insert the trial acetabular liner of the aforementioned hip system into a definitive acetabular cup prosthesis. In many of the available hip systems, this definitive acetabular cup prosthesis is provided with a circumferential groove on its inner concave surface which is dimensioned to receive a plurality of barbs on the definitive acetabular liner. Receipt of the barbs within this circumferential groove retains the definitive acetabular liner within the definitive acetabular cup. In order to mitigate the risk that the trial acetabular liner is inadvertently inserted in the definitive acetabular cup, it is particularly advantageous that the barbs on the trial liner are not only configured for engagement with an edge of a window in the trial acetabular cup, but also configured for engagement within the circumferential groove of the definitive acetabular cup. Accordingly, the aforementioned hip system also comprises a second acetabular cup. This second acetabular, which may be the final or definitive acetabular cup, comprises:

a shell comprising:

a convex outer surface configured to be engaged with an acetabulum, and a concave inner surface configured to be engaged with the convex outer surface of the trial liner, in which the shell includes a circumferential groove, and in which at least one of the plurality of barbs on the convex outer surface of the trial liner is configured to be engaged with the circumferential groove in the shell when the trial liner is received within the acetabular cup.

According to a further aspect of the invention, there is provided a method of trialing, comprising the steps of:

(i) using a trial liner comprising:

a concave inner surface configured to receive a femoral head;

(ii) inserting the trial liner into an acetabular cup within a joint of a

patient's limb, the acetabular cup comprising: a shell comprising: a convex outer surface configured to be engaged with an acetabulum, and

a concave inner surface configured to be engaged with the convex outer surface of the trial liner,

in which the shell includes a plurality of circumferentially arranged windows, and in which at least one of the plurality of barbs on the convex outer surface of the trial liner is configured to be engaged with an edge of one of the plurality of windows in the shell when the trial liner is received within the acetabular cup, whereby during insertion of the trial liner into the acetabular cup the at least one of the plurality of barbs on the convex outer surface of the trial liner engages with the edge of one of the plurality of windows in the shell.

Brief Description of the Drawings

Constructions of the hip system will be described hereinafter, by way of example only, with reference to the accompanying drawings in which like reference signs relate to like elements and in which: FIG. 1 is a perspective view of a first construction of the trial liner inserted into a trial acetabular cup;

FIG. 2 is a top view of the construction shown in FIG. 1 demonstrating that (a) due to the positioning of the barbs provided on the outer convex surface of the trial liner within the windows of trial acetabular cup, the anti-rotation devices (ARDs) provided on the outer convex surface of the trial liner are not able to be seated within each of the complementary recesses provided on the inner concave surface of the trial acetabular cup, and; (b) rotation of the ARD position is required in order to seat the anti-rotation members within the complementary recesses provided on the inner concave surface of the trial acetabular cup.

FIG. 3 is a perspective view of a second construction of the trial liner inserted into a trial acetabular cup;

FIG. 4 illustrates the possible dimensions of the barbs in the second construction of the trial liner for a given size of construction.

Detailed Description

Illustrative constructions of the trial acetabular liner and the trial acetabular cup are described in the following with reference to the accompanying drawings.

FIGs. 1 and 2 shows a first construction of a hip system according to the invention. This system includes a trial acetabular liner 10. The liner illustrated is a size 44-28 liner. The liner is received within a trial acetabular cup 40.

The trial liner 10 has an outer convex surface 12 which is configured to be engaged with an inner concave surface (not shown) of the trial acetabular cup. The outer convex surface of the trial liner is provided with a plurality of barbs 14 that are

circumferentially arranged thereon. Each barb includes a cup contacting surface 16. An exemplary construction of the trial acetabular cup 40 is also shown. The construction shown is a size 44. The cup includes a shell in the form of a frame 42. The frame has a pole 46 which defines a pole axis X. The pole may include a screw hole 48 dimensioned for receipt of a screw (not shown) for securing the acetabular cup to the acetabulum. The frame includes six (6) arms 50 that radiate from the pole 46 towards an annular rim 52.

Neighbouring arms 50 define a window 54. The construction shown has six generally triangular- shaped windows 54 that are circumferentially arranged about the frame. In the construction shown, each arm has a circumferential width of 4 mm.

Each window includes an edge 56 which engages with at least one barb 14 of the trial acetabular liner 10. In the particular construction of the hip system shown, the cup contacting face 16 of each barb makes contact with (e.g., is seated on) the edge 56 of a window 54. More particularly, the edge 56 of the window 54 on which the cup contacting face 16 of each barb contacts is substantially parallel to the annular rim 52.

The seating of the cup contacting face 16 of a barb 14 against the edge 56 of a window 54 prevents any distal movement of the trial acetabular liner relative to the trial acetabular cup along the pole axis X. This ensures that the trial liner does not become inadvertently pulled out of the trial acetabular cup during range of motion studies.

In the construction shown in FIG. 2, the anti-rotation devices (ARDs) on the trial acetabular liner take the form of generally semi-circular protrusions 18 extending outwardly from the outer convex surface 12 of the trial liner. As shown, the trial liner includes four (4) generally semi-circular protrusions 18 which are configured to be received within complementary-shaped recesses 58 disposed within the rim 52 of the trial acetabular cup. In the particular construction shown, the rim is provided with twelve (12) substantially scallop-shaped recesses 58. This allows for 12 possible rotational positions of the trial acetabular liner within the trial acetabular cup. As shown in FIG. 1, each barb 14 has an arc length (approximately 15mm) that is substantially the same as the arc length of the edge 56 of the window 54. However, as shown in FIG. 2a the selection of this barb arc length limits the possible rotational positioning of the liner within the cup. This is because not every protrusion 18 is able to be lined up and consequently received within each one of the recesses 58 due to a clash between the barbs 14 and the arms 50 of the frame 42. As shown in FIG. 2b, the surgeon must rotate the cup by 15° (either in a clockwise or anticlockwise direction) in order to line up each of the protrusions with each of the recesses. This is a disadvantage for augmented trial liners, because the surgeon is limited in the rotational positioning of the liner within the cup. This means that a surgeon may not be able to position an augmented section of the liner in the desired location within the acetabulum cup.

This problem is addressed by the design of the second construction of the trial liner, as shown in Figure 3. The difference between the trial liners 10, 20 of the first and second constructions is the barb arc length. In the second construction, the circumferential arrangement of the barbs 14 about the convex outer surface 12 of the liner 10 is such that the spacing (i.e., the barb gap (Bg)) between each neighbouring barb 14 is dimensioned to receive an arm 50 of the frame 42 of the shell of the acetabular cup. Each barb in the illustrative construction of the size 44 trial acetabular liner has the following dimensions:

barb tip (B_t): approximately 3 mm;

barb base (Bt>): approximately 6 mm;

barb gap (B_g): approximately 6.5 mm.

This construction of the trial acetabular liner prevents any clashing between the barbs and the arms of the window frame. The illustrated size and arrangement of the barbs 14 allows for each protrusion (i.e., the ARDs) to be received in each one of the recesses. This means that all 12 rotational positions can be achieved by the trial liner, rather than the 6 positions that the first construction of the liner is restricted to. Although particular constructions of the invention have been described, it will be appreciated that many modifications/additions and/or substitutions may be made within the scope of the claimed invention.

Claims

1. A hip system comprising:

a concave inner surface configured to receive a femoral head;

a shell comprising:

in which the shell includes a plurality of circumferentially arranged windows, and in which at least one of the plurality of barbs on the convex outer surface of the trial liner is configured to be engaged with an edge of one of the plurality of windows in the shell when the trial liner is received within the acetabular cup.

2. The hip system of claim 1, in which each of the plurality of barbs has a cup contacting face configured to be seated on the edge of one of the plurality of windows of the acetabular cup when the trial liner is received within the acetabular cup.

3. The hip system of claim 1 or 2, in which the trial acetabular cup further comprises a circumferential rim, the edge of at least one of the plurality of windows which engages at least one of the barbs on the convex outer surface of the trial liner being substantially parallel to the rim.

4. The hip system of claim 1, in which the shell comprises a frame having a plurality of arms, an arm of the plurality of arms separating each of the circumferentially arranged windows, and in which each of the plurality of barbs is spaced apart on the convex outer surface of the trial liner from a neighbouring barb such that a space is provided in between neighbouring barbs which is dimensioned to receive an arm of the frame.

5. The hip system of claim 4, further comprising:

a plurality of spaced apart anti-rotation members provided on the convex outer surface of the liner, and

a plurality of spaced apart recesses formed in the concave inner surface of the shell, each of the plurality of recesses having a size and shape complementary to an anti-rotation member,

in which an arm of the plurality of arms of the frame is located between the plurality of spaced apart recesses formed in the concave inner surface of the shell.

6. The hip system according to any of claims 1 to 5, in which the system further comprises a second acetabular cup, the second acetabular cup comprising:

a shell comprising:

in which the shell includes a circumferential groove, and in which at least one of the plurality of barbs on the convex outer surface of the trial liner is configured to be engaged with the circumferential groove in the shell when the trial liner is received within the second acetabular cup.

7. A method of trialing, comprising the steps of:

(i) using a trial liner comprising:

a concave inner surface configured to receive a femoral head; (ii) inserting the trial liner into an acetabular cup within a joint of a patient's limb, the acetabular cup comprising: a shell comprising:

a convex outer surface configured to be engaged with an acetabulum, and