GB2564718A

GB2564718A - Apparatus and method for hip surgery

Info

Publication number: GB2564718A
Application number: GB1711805.0A
Authority: GB
Inventors: Young Duncan
Original assignee: DePuy Ireland ULC
Current assignee: DePuy Ireland ULC
Priority date: 2017-07-21
Filing date: 2017-07-21
Publication date: 2019-01-23
Also published as: GB201711805D0

Abstract

A liner 430 for an acetabular cup for assessing anteversion of the acetabular cup in a patients pelvis. Liner 430 comprising: a body 432 having a rim 436 defining a mouth to a liner cavity 434 adapted to receive a trial head 416 within the liner 430; and a visual alignment guide 450 configured to define a guide plane tilted with respect to a plane defined by a mouth of the acetabular cup when the liner 430 is received in the acetabular cup and to subtend an acute angle with the plane defined by the mouth of the acetabular cup, where the acute angle corresponds to a target combined anteversion for a hip joint when the acetabular cup is in the pelvis. Liner 430 may include an anti-rotation device engageable with the acetabular cup preventing liner 430 rotation. Visual alignment guide 450 may include a plurality of indicia providing a scale indicating different amounts of combined anteversion of the hip-joint. Liner 430 may include a formation for releasably attaching a handle. Visual alignment guide 450 may be releasably attached to rim 436 of the liner 430. Liner 430 may be a trial liner. Liner 430 may be a prosthetic liner.

Description

Apparatus and Method for Hip Surgery

The present invention relates to apparatus and methods for hip surgery, and in particular to one or more components of a hip joint and/or methods of hip surgery using such components.

A variety of methods of hip surgery are generally known. The hip joint may generally be considered a ball and socket joint in which the head of the femur articulates within the acetabular cavity of the pelvis. Some methods of hip surgery may involve the replacement of one or more parts of the hip joint with one or more prosthetic components. This may be to replace damaged, worn, diseased or otherwise imperfect parts of the hip joint including the respective articulating surfaces of the acetabular cavity and/or femoral head.

Different surgical procedures may involve replacement of a part of the acetabulum or the femoral head or both. Some procedures, sometimes referred to as resurfacing procedures, may involve replacement of or all of the articulating surface only of the femoral head. Other procedures may involve replacement of the entire femoral head. Such procedures often also use a stem component which is implanted in the resected femur and having a neck to which the femoral head is attached. In some procedures, a prosthetic cup may be implanted in a prepared acetabular cavity to provide a cavity in which the femoral head or prosthetic femoral head may articulate when the joint is reduced. Surgical procedures in which both the acetabulum and at least a part of the femoral head are replaced with prosthetic components are generally referred to as total hip replacement procedures.

During hip surgery procedures, some surgeons may sometimes use one or more trial components, which have the same geometry and size as the intended prosthetic components, so that the surgeon may trial the joint before final implantation of the prosthetic components. For example, the surgeon may use trial components to check that the size, position or orientation of one or more of the components is suitable. Other surgeons may opt not to use trial components or may use them occasionally based on their professional judgement.

One of the considerations in hip surgery is the angular orientation of the acetabular cavity. When the acetabulum is replaced with an acetabular cup, then it is often an aim of the surgeon to place the acetabular cup so that it is pointing generally in a preferred direction or range of direction. The orientation of an acetabular cup is often defined in terms of an angle of abduction (or inclination) and an angle of anteversion.

A variety of approaches have been used to try and assess the angular orientation of an acetabular cup, either a trial or a prosthesis, after placement in the acetabular cavity.

Anatomical approaches may be used in which the surgeon uses either their experience and/or a piece of instrumentation, in order to gauge, by inspection or instrumentation, the angular orientation of the acetabular cup relative to one or more anatomical features of the patient’s pelvis. However, there is often limited access to the surgical site, particularly for minimally invasive approaches, and therefore this is often not easy nor accurate.

Other approaches may use markings or other features on the trial or prosthetic components in order to gauge the angular orientation of the acetabular cup relative to the patient’s pelvis.

For example “The Ranawat Sign A Specific Maneuver to Assess Component Positioning in Total Hip Arthroplasty”, Lucas, David H., and Scott, Richard D., Journal of Orthopaedic Techniques, Vol. 2, No. 2, June 1994, describes a method of intraoperative assessment of component orientation for total hip arthroplasty. With the patient in the true lateral decubitus position, the femur is internally rotated without hip flexion until a flat underside of the prosthetic head (generally perpendicular to the femoral neck) is coplanar with a rim of the acetabular cup. The amount of internal rotation necessary to achieve this position is known as the Ranawat sign and relates to the combined anteversion of the acetabular and femoral components of the joint. For example a Ranawat sign of 45° may correspond to a cup anteversion of 30° and a femoral anteversion of 15°. However, any knee laxity or deformity can influence the interpretation of this value. Also, there may be difficulty in assessing the actual magnitude of the angle of internal rotation. Further, different surgeons may have different approaches to manipulating the patient’s leg and also any one surgeon’s approach may not easily be reproducible from patient-to-patient either by that same surgeon or by other surgeons.

WO 2009/108683 describes another approach in which markings are applied to a femoral head and in which the surgeon again applies an amount of internal rotation to the patient’s leg, during trial reduction, so that the angle between the rim of the acetabular cup and various markings on the femoral head indicates the relative angular position of the acetabular cup in the patient’s pelvis. A neutral leg position is used in which the patient’s leg is in full relaxed extension at zero degrees abduction, zero degrees anteversion and approximately 15° internal rotation or otherwise internally rotated by an amount equal to the amount of version of the natural or artificial femoral neck. Hence, this approach also requires the surgeon to apply a specific amount of internal rotation to the patient’s leg. Again, it may be difficult to apply the correct amount of internal rotation, there may be inaccuracies introduced by deformities of the patient’s leg and the surgical technique may be difficult to reproduce and/or reliably learn. This is particularly the case for a relatively small angle, 15°, as even a relatively small error in the amount of internal rotation, for example 5°, is a large proportion (33%) of the target internal rotation.

Other approaches and associated instrumentation are described in US 2005/0107799. An accessory for implanting a hip cup, includes a manipulable cup, a manipulation head having a hemispherical portion and a circular rim around it for aligning the manipulable cup in the acetabulum. A device for immobilizing the aligned position of the manipulable cup is provided and allows a guide to be set for alignment of a bone bur and a drive-in instrument for reaming placing the acetabular cavity and placing the cup. In another approach, a manipulable cup is located in the acetabulum and its orientation can be adjusted by a handle until a lip of the manipulable cup is parallel with an equatorial line on a femoral head or a plane on the reverse of a femoral head

Hence, apparatus and/or methods making accurate intraoperative assessment of acetabular cup placement simpler, easier and/or more reliable would be beneficial.

A first aspect of the invention provides a liner for an acetabular cup for assessing anteversion of the acetabular cup in a pelvis of a patient, the liner comprising: a body having a rim defining a mouth to a liner cavity adapted to receive a trial head within the liner; and a visual alignment guide configured to define a guide plane tilted with respect to a plane defined by a mouth of an acetabular cup when the liner is received in the acetabular cup in use and to subtend an acute angle with the plane defined by the mouth of the acetabular cup, wherein the acute angle corresponds to a target combined anteversion for a hip joint when the acetabular cup is in the pelvis.

The visual alignment guide may be an integral or unitary part of the liner.

The visual alignment guide may be an ancillary or separate part of the liner and which is attachable to the liner.

The liner may include an anti-rotation device engageable with the acetabular cup to prevent or control rotation of the liner about a polar axis of the liner or acetabular cup. This can help improve reliability of placement of the liner in the cup in the acetabulum so as to more accurately assess the combined anteversion of the hip joint.

The acute angle may be in the range 15° to 55°, or in the range 25° to 45°, or in the range 30° to 40°. The acute angle may be substantially 35°.

A portion of a wall of the body at a position on the rim diametrically opposed to a position on the rim at which the visual alignment guide is provided may be lower than a liner plane defined by the mouth of the liner. This may help to provide visual access to a portion of the interior of the liner and/or to different parts of a trial head to be used with the liner.

The visual alignment guide may include an indicium, or a plurality of indicia, arranged to provide a scale indicating an amount, or different amounts, of combined anteversion of the hip joint.

The scale may include a number, or a plurality of numbers, indicating the quantitative amount of the degree of combined anteversion of the hip joint. The scale may extend from 5° to 65° and may include 5° or 10° or 15° steps, or from 15° to 55° and may include 5° or 10° steps, or from 15° to 45° and may include 5° or 10° steps.

The visual alignment guide may include a curved member.

The curved member may have a radius of curvature centred on the centre of the mouth of the body.

The visual alignment guide may be in the form of a curved wire.

The curved wire may include a first leg and a second leg by which the curved member is mounted away from the rim. The first leg and the second leg may each have a free end or a foot which are respectively receivable in corresponding formations or holes in the rim of the liner or in a side wall of the liner adjacent the rim of the liner.

The visual alignment guide may be in the form of a curved and tapering member or block.

The liner may include a formation for releasably attaching a handle. The formation may be a female formation.

The female formation may be formed within the wall of the body and/or may have an opening in the rim.

The female formation may be formed within the visual alignment guide.

The liner may include a connector of fastener for releasably attaching the liner to the acetabular cup.

The connector or fastener may comprise a threaded member. The threaded member may pass through an aperture defined at the pole of the liner and/or may extend from a rear side of the liner and/or may extend along a polar axis of the liner.

The visual alignment guide may be releasably attached to, or adjacent, the rim of the liner.

The visual alignment guide may include at least one male formation and the liner may include at least one female formation adapted to receive the at least one male formation to releasably attach the visual alignment guide to the liner. The male formation and female formation may co-operate to form a push fit or snap fit fastening or a clip.

The visual alignment guide may be an integral or permanent part of the liner.

The liner and visual alignment guide may be unitary.

The visual alignment guide may be configured and/or arranged and/or positioned to coincide with an indicium of a trial head when located in the liner in use. The indicium may be an equatorial line on the trial head. The indicium may be a distal face of a trial head.

The liner may include a further visual alignment guide configured to define a further guide plane tilted with respect to the plane defined by the mouth of an acetabular cup when the liner is received in the acetabular cup in use and to subtend the acute angle with the plane defined by the mouth of the acetabular cup. The guide plane may coincide with a first indicium of the trial head and the further guide plane may coincide with a second indicium of the trial head.

One or a plurality of visual alignment guides may be provided.

The, or each, visual alignment guide may be provided by a flat surface of a male formation.

The, or each, visual alignment guide is provided by a flat surface of a female formation.

The liner may include a first anti-rotation device and a second anti-rotation device positioned about the rim. The first anti-rotation device and the second anti-rotation device may be positioned about the rim diametrically opposite each other.

The visual alignment guide may be positioned equidistantly at or around the rim between the first anti-rotation device and the second anti-rotation device.

The liner may be adapted to pivot within the acetabular cup. A portion of the rim of the liner may provide the visual alignment guide.

The liner may include a slot or a channel defined in and by a base of the liner. A fastener may be received in the slot or channel, and may be adapted to travel in the slot or channel, and be for attaching the liner to the acetabular cup in use.

The liner may include a first anti-rotation device and a second anti-rotation device arranged to define a pivot axis about which the liner can pivot in use.

The pivot axis may be substantially perpendicular to a longitudinal axis of the slot.

The liner may be a trial liner.

The liner may be a final or a prosthetic liner.

The acute angle may be fixed.

The acute angle may be variable. The acute angle may be discretely variable. The acute angle may be continuously variable.

The acute angle may define a target combined anteversion of the hip of the patient when a trial head is located in the cavity and is attached to a neck of a stem component inserted in a femur of the patient and the femur is placed in an orientation corresponding to a preselected position of the leg of the patient. The preselected position may be an anatomical position.

The anatomical position may corresponds substantially to 0° extension/flexion of the leg and/or 0° abduction/adduction of the femur and/or 0° rotation of the femur.

The acetabular cup may be a trial acetabular cup or shell.

The acetabular cup may be a prosthetic acetabular cup or shell.

Any of, and any number of, the preferred features of the first aspect of the invention may be combined in any non-mutually exclusive or compatible way.

A second aspect of the invention provides a kit of parts comprising: the liner of the first aspect of the invention and/or an acetabular cup or shell defining a cup cavity adapted to receive the liner and/or a trial head having an indicium and adapted to be received within the liner cavity and/or a stem part having a neck with an attachment formation at a free end of the neck to which the trial head can be releasably attached.

The liner may be a trial liner.

The acetabular cup or shell may be a trial acetabular cup or shell or a prosthetic acetabular cup or shell.

The stem part may be a femoral broach or a trial femoral stem or a prosthetic femoral stem.

The acetabular cup or shell may include at least one anti-rotation formation configured to mate with an anti-rotation device of the liner.

The acetabular cup or shell may include a first anti-rotation formation configured to mate with a first anti-rotation device of the liner and a second anti-rotation formation configured to mate with a second anti-rotation device of the liner.

Any of the preferred features of the first aspect of the invention may also be preferred features of the second aspect of the invention.

A third aspect of the invention provides an assembly of the kit of parts of the second aspect of the invention.

A fourth aspect of the invention provides a method of assessing the anteversion of an acetabular cup within an acetabulum of a pelvis of a patient, comprising: reducing a trial hip joint comprising a liner within an acetabular cup within an acetabulum of a pelvis of a patient and a trial head having an indicium attached to the neck of a stem located within a femur of a leg of the patient; and comparing the indicium to a visual alignment guide part of the liner, wherein the visual alignment guide defines a plane subtending an acute angle with a plane of a mouth of the acetabular cup, the acute angle corresponding to a target combined anteversion of the hip joint of the patient.

The method may further comprise moving the leg of the patient into a preselected position before comparing the indicium to the visual alignment guide. The preselected position may be an anatomical position.

The anatomical position may correspond substantially to 0° extension/flexion of the leg and/or 0° abduction/adduction of the femur and/or 0° rotation of the femur.

The indicium may be an equatorial line of the trial head or a distal face of the trial head.

The liner may be a prosthetic liner and the acetabular cup may be a prosthetic acetabular cup and the method may further comprising: removing the visual alignment guide from the liner.

The acetabular cup may be a prosthetic acetabular cup and the method may further comprise: adjusting the orientation of the prosthetic acetabular cup based on the comparison of the indicium to the visual alignment guide.

The acetabular cup may be a trial acetabular cup and the method may further comprise: removing the trial acetabular cup; and implanting a prosthetic acetabular cup at an implantation orientation, wherein the implantation orientation is based on the comparison of the indicium to the visual alignment guide.

Any of the preferred features of the first aspect of the invention may also give rise to corresponding preferred method features of the fourth aspect of the invention.

A fifth aspect of the invention provides a kit of parts comprising: a liner; an acetabular cup having a rim defining a mouth of a cup cavity adapted to receive the liner; and a visual alignment guide releasably attachable to the acetabular cup and configured to define a guide plane tilted with respect to a plane defined by the mouth of the acetabular cup when the visual alignment guide is mounted on the rim of the acetabular cup in use and to subtend an acute angle with the plane defined by the mouth of the acetabular cup, wherein the acute angle corresponds to a target combined anteversion for a hip joint when the acetabular cup is in a pelvis of the patient.

The visual alignment guide may include a male formation having a surface which defines the guide plane.

The visual alignment guide may include a clip by which the alignment guide can be releasably attached to the rim of the cup.

The clip may be in the form of a ring, or a part of a ring.

The male formation may be in the form of a curved wedge.

A sixth aspect of the invention provides an assembly of the kit of parts of the fifth aspect of the invention. The assembly may include a liner within the acetabular cup.

A seventh aspect of the invention provides a trial femoral head having an equatorial indicium and wherein the equatorial indicium is provided by one or more features of the shape of the outer surface of the trial femoral head.

Embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 shows a coronal view of a femur;

Figure 2 shows a sagittal view of the femur of Figure 1;

Figure 3 shows a transverse view of the femur of Figures 1 and 2;

Figure 4 shows a view of the femur in a plane parallel to the anatomic axis and the neck of the femur;

Figure 5 shows a coronal view of a pelvis;

Figure 6 shows a sagittal view of the pelvis of Figure 5;

Figure 7 shows a transverse view of the pelvis of Figures 5 and 6;

Figure 8 shows a partial cross sectional perspective view of the pelvis along line A-A of Figure 5;

Figure 9 shows a perspective view of the pelvis;

Figure 10 shows a coronal view of a hip comprising the femur of Figures 1 to 4 and the pelvis of Figures 5 to 9;

Figure 11 shows a partial cross sectional perspective view of the pelvis along line C-C of Figure 10;

Figure 12 shows a perspective view of a first embodiment of a trial hip joint according to an aspect of the invention and including a first embodiment of a liner according to an aspect of the invention;

Figure 13 shows a view of the liner shown in Figure 12 ;

Figure 14 shows a perspective view of a second embodiment of a liner according to an aspect of the invention;

Figure 15 shows a partial cross-sectional view of a second embodiment of a trial hip joint including the liner shown in Figure 14 and a trial femoral head;

Figures 16A to 16C show various perspective and cross sectional views of a further trial femoral head according to an aspect of the invention, and which may be used in a trial hip joint of the invention and with the liner of the invention;

Figures 17A to 17D show various perspective and cross sectional views of a third embodiment of a liner of the invention;

Figures 18A to 18D show various perspective and cross sectional views of a fourth embodiment of a liner of the invention;

Figures 19A to 19D show various perspective and cross sectional views of a fifth embodiment of a liner of the invention;

Figures 20A to 20D show various perspective and cross sectional views of a fifth embodiment of a liner of the invention;

Figures 21A to 21D show various perspective and cross sectional views of an alignment guide and assemblies including the alignment guide according to aspects of the invention;

Figures 22A to 22D show various perspective and cross sectional views of a seventh embodiment of a liner of the invention;

Figure 23 shows a flow chart illustrating a first embodiment of a surgical method according to the invention in which the embodiments of the liner and trial hip joint may be used to assess a trial cup anteversion;

Figures 24A to 24C show views of the trial hip joint including the first embodiment of the liner and a trial femoral head illustrating use of the visual alignment guide to assess cup anteversion; and

Figure 25 shows a flow chart illustrating a second embodiment of a surgical method according to the invention in which the embodiments of the liner and trial hip joint may be used to assess a prosthetic cup anteversion.

Similar items in the different Figures share common reference signs unless indicated otherwise.

Before describing the apparatus and/or methods of the invention, the geometry of a hip joint will be discussed generally. In the below, a right hip joint is described, but it will be appreciated that a similar discussion applies to a left hip joint. Also, the following discussion is intended to relate to both the pre-operative natural or native, hip joint, as well as to the artificial, or prosthetic, hip joint. Hence, although the magnitude of the various angles may vary between the native hip joint and the prosthetic hip joint, the definitions of those angles may be generally the same for the native and prosthetic hip and may be determined by the positions and/or orientations of the various parts making up the native hip joint and prosthetic hip joint respectively.

With reference to Figures 1 to 4, there are shown various different views of a right femur 100. In particular Figure 1 shows a coronal view in the anterior to the posterior direction (generally herein the AP direction), Figure 2 shows a sagittal view in the medial to the lateral direction (generally herein the ME direction), Figure 3 shows a transverse view in the superior to the inferior direction, and Figure 4 shows a view of the femur in a plane parallel to the anatomic axis of the femur and the neck of the femur as explained in greater detail below. Pre-operatively, the proximal part of the femur 100 includes the native femoral neck and native femoral head. Intra-operatively and post-operatively the proximal part of the femur may include various trial or prosthetic parts or components providing trial or prosthetic femoral necks and femoral heads. The following will refer generally to femoral necks and femoral heads and is intended to include native, trial or prosthetic ones.

With particular reference to Figures 1 and 2, the proximal part 102 of femur 100 includes a femoral head 104 (represented by a sphere) attached to a femoral neck 126, best illustrated in Figure 4, having a neck axis extending generally in the direction of arrow 106. The femur 100 has an epicondylar axis 108 extending between the lateral femoral epicondyle 110 and the medial femoral epicondyle 112. The femur 100 also has an anatomic axis 114 extending between, for example, the distal femur intercondylar notch 116 and the piriformis fossa, close to the medial face of the greater trochanter. The femur 100 also has a mechanical axis 120 extending between, for example, close to the distal femur intercondylar notch 116 and the centre of the femoral head 104. The anatomical axis 114 and mechanical axis 120 of the femur 100 may be defined by other anatomical points in other embodiments.

With reference to Figure 3, a femoral neck anteversion angle 124 can be defined as the angle in the transverse plane subtended by the femoral neck axis 106 and the epicondylar axis 108. In practice, the femoral neck anteversion angle for the native neck is typically in the range of about 12° to 15°, but may have other values. Neck anteversion angle 124 is a measure of the anteversion of the femoral neck relative to the local anatomy of the femur 100.

Figure 4 shows a view of the femur 100 in a plane parallel to line BB of Figure 3, which is parallel to the femoral neck axis 106, and the anatomical axis 114, and which more clearly shows the femoral neck 126. Figure 4 also illustrates the neck angle 128 subtended between the femoral neck axis 106 and the anatomical axis 114 of the femur. The native neck angle 128 varies from patient to patient, but is typically about 130°. The neck angle 128 for a trial or prosthetic implant is usually fixed by the implant design, unless the implant is adjustable, and is often intended to approximately reproduce the native geometry and so may also be about 130°. In the following a neck angle 128 of 130° may be used as an example, but it will be appreciated that in other embodiments, other neck angle values may also be used.

Hence during hip surgery in which a prosthetic femoral component is used, one of the variables is the femoral neck anteversion angle 124, which generally measures how far forward the femoral neck 126 is directed compared to the medial-lateral axis of the femur.

With reference to Figures 5 to 9, there are shown various different views of a pelvis 200 and right acetabulum. In particular Figure 5 shows a coronal view in the anterior to the posterior direction (generally herein the AP direction), Figure 6 shows a sagittal view in the medial to the lateral direction (generally herein the ME direction), Figure 7 shows a transverse view in the superior to the inferior direction, Figure 8 shows a partial sectional view along line A-A of Figure 5, and Figure 9 shows a perspective view of the pelvis 200 with the anterior pelvic plane (APP) vertical and the transverse axis generally horizontal. Pre-operatively, the pelvis 200 includes an acetabulum which provides a native socket in which the native femoral head is received and articulates. Intra-operatively and/or postoperatively the pelvis may include various trial or prosthetic implants, such as trial or prosthetic acetabular cups (with or without liners depending on the specific implant system being used). The following will refer generally to the acetabulum or acetabular cup and is intended to include the native acetabulum as well as trial or prosthetic components.

As illustrated in Figure 5, the acetabulum 202 may be represented by a hemisphere or hemispherical cup which generally has a position and an orientation. The orientation or direction of the acetabulum may generally be defined by two angles. A first angle indicates how much the acetabulum is directed forward or backward (generally referred to as anteversion when pointing anteriorly and retroversion when pointed posteriorly) relative to the pelvis. A second angle indicates how much the acetabulum is pointing downward or in an inferior direction (generally referred to as inclination or abduction) relative to the pelvis. The direction of the acetabulum may be defined by an acetabular axis 204, best illustrated in Figure 9, which generally passes through the centre of the mouth of the acetabulum and perpendicular to the plane of the mouth of the acetabulum.

The pelvis 200 includes a transverse axis 206 passing between the right ASIS 208 and the left ASIS 210. An anterior pelvic plane 212 (generally referred to as APP in the following) is defined by the transverse axis 206 and first and second points on the symphysis pubis 214, 216.

As best illustrated in Figure 5, an inclination angle for the acetabulum or acetabular cup 202 may be defined by the angle 220 subtended by the transverse axis 206 and a long axis, or inclination axis, 222 of the acetabular cup 202 within, or parallel to, the anterior pelvic plane 212. In Fig. 5, the illustrated inclination angle 220 is approximately 40°. Figure 8 shows a view of a cross section of the pelvis 200 along line A-A in Figure 5 and in a direction along the long axis 222 of the acetabular cup 202. Hence, Figure 8 shows the plane generally perpendicular to the long axis 222 of the pelvic cup 202. From Figure 8, an anteversion angle 224 may be defined as the angle subtended between the plane 226 of the mouth of the acetabular cup and a plane 228 perpendicular to the anterior acetabular plane 212. Hence, as illustrated in Figure 8, the acetabulum or acetabular cup 202 has an anteversion angle 224 of approximately 20°.

Hence, as illustrated in the perspective view of the pelvis 200 in Figure 9, the acetabulum or acetabular cup 202 has an orientation corresponding to an inclination of 40° and an anteversion of 20°. These angles may be referred to as radiographic angles as they are based on the APP view of the pelvis illustrated in Figure 5 and which is the view of the pelvis typically radiographically imaged or X-rayed and which images are often used by surgeons pre-, intra- and/or post operatively to assess acetabular orientation.

With reference to Figures 10 to 11, there are shown various different views of a right hip joint 300 formed by femur 100 and pelvis 200. In particular, Figure 10 shows a coronal view in the anterior to the posterior direction (generally herein the AP direction), similar to Figures 1 and 5 combined. In Figure 10, the femur has been placed in an anatomical position as described in greater detail below. Figure 11 shows a partial section along line C-C of Figure 10 and viewed in a direction along the inclination axis 222 of the acetabular cup 202. Hence, the plane of Figure 11 is generally perpendicular to the direction of the inclination axis 222 of the acetabular cup.

As illustrated in Figure 11, the acetabular cup 202 has an anteversion angle 224 of 20° in the plane perpendicular to the inclination axis 222 of the acetabulum. Figure 11 also illustrates the femoral anteversion angle 230 in the plane perpendicular to the inclination axis of the acetabulum and being defined by the angle 230 subtended in that plane by the femoral neck axis 106 and the anterior pelvic plane 212. As illustrated in Figure 11, the apparent femoral anteversion angle 230 is approximately 11°.

Hence, as can be seen the overall geometry of the hip joint arises from the orientation of the acetabulum relative to the pelvis and also the orientation of the femoral neck relative to the femur. In the illustrated example, the overall or combined anteversion of the hip joint 200 shown in Figures 10 and 11 is the combination of the acetabular anteversion, about 20°, and the amount of femoral anteversion projected into the same plane, which in this example is approximately 11°. Hence, the combined anteversion of the hip joint 300 in this plane is about 31°.

However, in practice, when surgeons talk about a combined anteversion of about 35°, this may be arrived at by adding absolute values of angles in different planes, 15° anteversion of the neck relative to the femur in a first plane and 20° anteversion of the acetabulum relative to the pelvis in a second, different plane, to give approximately 35°. In practice, the combined anteversion is assumed to be in the range of approximately 30° to 40°, as being typically greater than 30° and less than 40°, and that any measurement or assessment is likely to be accurate to plus or minus a few degrees anyway and so measurement of the angles in different, non-parallel planes is not crucial.

Herein, combined anteversion may refer, depending on the context, to the general idea that the anteversion of a hip joint is the combined effect of the degree of anteversion of the femoral neck relative to the femur and also the degree of anteversion of the acetabulum relative to the pelvis. More specifically, for non-extreme cases, combined anteversion may also refer to a general rule of thumb that the sum of the acetabular anteversion and the femoral anteversion, measured in the same plane, should have a certain value, for example approximately 35°. Hence, if a low value of one occurs, then the other can be increased (or vice versa) in order to bring the combined anteversion closer to this target value.

While there can be a reasonable degree of adjustment of the orientation of the acetabular cup in the reamed acetabulum, there is less freedom to vary the orientation of the femoral stem. This is because once the proximal part of the femur has been resected and the intramedullary canal reamed or otherwise prepared, there is little remaining bone stock. Hence, there is little freedom in how the surgeon can orient the stem in order to adjust the version of the neck. Hence, in some surgical approaches, a “stem first” approach may be used in which the stem component’s position and orientation are determined first. Then, based on the position and orientation of the stem component, the position and/or orientation of the cup may be adjusted particularly as there is greater flexibility in the orientation of the cup within the acetabulum.

With reference to Figure 12, there is shown a perspective view of a trialling system 400 including a femoral part 410 and an acetabular liner 430.

The femoral part 410 includes a femoral broach 412 to which a trial femoral neck 414 is releasably attached and a trial femoral head 416 releasably attached to a free end of the femoral neck 414. A free end of neck 414 may include a taper which can be received within a corresponding female socket within the trial femoral head 416. The trial femoral head has a generally spherical shape and includes an indicia or marking 418 extending around its equator. The equator of the trial head 416 is generally perpendicular to a trial head axis passing through a pole 420 of the trial head and about which the trial head is rotatably symmetric. The trial head 418 includes a generally rotationally symmetric cavity for receiving the taper of the femoral neck 414. A handle may be attached to a proximal end of the broach 412 during broaching of the intramedullary canal of the femur subsequent to which the trial neck 416 may be attached. The trial head may be rotationally symmetric and the equatorial indicium or marking 418 is used to assess cup positioning subsequently. Hence, in the illustrated embodiment there is no need to use a specific rotational orientation of the trial head 418 about its polar axis.

In other embodiments, discussed below, the indicium of the trial head used to assess cup positioning may be additionally, or alternatively, the distal flat end 419 of the trial head. As will be appreciated the distal flat end face is generally parallel to the plane of the equatorial line and hence any indicium on the trial head which is generally parallel to this plane may be used.

Although a broach 412 is illustrated in Figure 12, it will be appreciated that the invention is not necessarily limited to mounting the neck 414 and/or trial head 416 on a broach. In other embodiments, the neck 414 and/or trial head 416 may be mounted on some other femoral too or instrument, or be provided on a trial stem component or a prosthetic stem component, depending on the precise details of the workflow. A femoral broach may conveniently be used as broaching of the intramedullary canal essentially determines the anteversion relative to the femur of the stem component which will subsequently be implanted in the broached femoral cavity.

The acetabular liner 430 is illustrated in the form of a trial liner. However, in other embodiments, the acetabular liner may be the final acetabular liner to be used with the final acetabular cup. The trial liner 430 has a body 432 in the form of a generally hemispherical cup. The trial liner 430 defines a generally hemispherical cavity 434 having a circular mouth defined by a rim 436 of the acetabular liner body. An arcuate socket 438 is defined within the rim 436 of the liner 430 for receiving a correspondingly shaped male attachment formation of a releasably attachable handle which may be used to guide liner insertion in the acetabular cup. An outer wall of the body 432 bears a first 440 and a second 442 male formations which provide anti-rotation devices (ARDs) so that the rotation of the liner about its central polar axis relative to the acetabular cup can be controlled.

A threaded boss or cup connector 444 extends from a rear face of the liner body 432 generally at the pole of the liner and is arranged to be received within, and co-operate with, a threaded bore at the pole of the acetabular cup. The liner 430 may be screwed into the acetabular cup so as to pull the anti-rotation features into corresponding shaped female features or notches positioned around the rim of the acetabular cup. A plurality of notches may be provided around the rim of the cup, e.g. twelve, and the user may select which two of the 12 notches the ARDs 440, 442 should be received in so as to correctly rotationally orient the liner within the cup.

The liner 430 also includes a visual guide 450 which is releasably attachable to the rim 436 of the liner.

In the illustrated embodiment, visual guide 450 is in the form of a wire having first and second leg portions 452, 454, between which a main body extends in a curved manner and generally having the form of an arc of a circle having a slightly greater diameter than the diameter of the hemispherical cavity and trial head 416. Free ends of the first and second legs 452, 454, are received within corresponding circular holes in the rim so that, optionally, the visual guide 450 may be removed from the liner 430. As described in greater detail below, at some times during the surgical procedure it may be preferable to use the liner without the guide 450, for example during a range of motion assessment during which no obstruction to the neck of the stem may be preferred, or with the guide 450 in place. When the visual guide 450 is made of wire, it may be made flexible and resilient so as to bend out of the way and also return to its original position during any range of motion assessment or owing to any other impingements, e.g. by other surgical tools or instruments. Hence, a resiliency deformable alignment guide 450 may be preferred as allowing range of motion assessment without having to remove the alignment guide.

Figure 13 shows a view of the liner 430 looking along an “anteversion axis” which is the axis created by the intersection of the coronal plane and a plane inclined at the inclination angle, e.g. 40 degrees, which corresponds to the direction of line 222 in Figures 10 and 11 above. As can be seen, the main body 456 of the visual guide generally defines a plane which is inclined at an acute angle 458 relative to the plane of the mouth of the hemispherical cavity of the liner and which corresponds to an intended or target combined anteversion angle for the hip joint. In this specific embodiment, the angle 458 is substantially 35°. This corresponds to a femoral neck anteversion angle of 15° relative to the femur and a acetabular anteversion angle of 20° relative to the pelvis (and assuming an acetabular abduction angle of 40° relative to the pelvis) and hence combined anteversion angle for the hip joint of approximately 35°, notwithstanding the local anteversion angles being defined in slightly differing planes, as discussed above. However, as will be understood from the above and the following discussion, that is simply an example angle and other angles may be appropriate depending on a number of factors, such as the target cup anteversion angle and/or the femoral anteversion angle, and/or the preselected hip joint position, as discussed above and below.

As the visual alignment guide is intended to allow a user to gauge the combined anteversion, it should be places so as to define an angle around the anteversion axis which is the axis formed by the inclined plane and the coronal plane of the patient and labelled as 222 in Figures 10 and 11 above. Hence, when the liner is within the acetabular cup or shell, the surgeon should try and locate the acetabular cup or shell in the acetabulum with ARD 440 at a most superior position. In other embodiments, in which a first ARD and a second ARD are provided diametrically opposed, as illustrated below, then the cup or shell should be placed in the acetabulum so that one of the ARDs is at the most superior position and the other of the ARDs is at the most inferior position. Which of the ARDs is superior and which of the ARDs is inferior will depend on whether the hip is a right hand or left hand hip. Figure 12 illustrates a right hand hip and so ARD 440 would be positioned most superior and ARD 442 will be pointing in a generally posterior direction.

By way of further example, the swing liner shown in Figs. 18A to 18D has two hinge ARDs and which are positioned inferior and superior so that the hinge axis is parallel to the coronal plane.

Returning to Figure 12, the liner 430 may be used in conjunction with a trial cup, again having a generally hemispherical cup shape and with a hemispherical cavity for receiving the liner 430. As noted above a threaded aperture is also provided in the trial cup positioned at the pole or apex of the cup and sized to receive the threaded boss 444. The outer surface of the cup may include formations to help secure the trial cup within the acetabulum. The cup may also include recesses or notches at its rim and around its inner walls to receive the anti-rotation devices 440, 442 so as to “clock” or lock the rotational orientation of the liner about is polar axis relative to the trial cup. These notches may be provided around the periphery of the mouth of the cup every 10°, 15°, 20° or 30°, depending on the level of accuracy desired.

Figure 14 shows a perspective view of a second embodiment of a liner 460. Liner 460 is generally similar to liner 430 and the common features will not be described in greater detail. However, line 460 includes a different visual alignment guide 470. Visual alignment guide 470 is provided in the form of a solid block having a generally arcuate form matching that of the rim 436 of the cup and also having a wedge shape tapering from a greater height toward the outer portion of the liner to a lesser height toward the inner portion of the liner 460. As best illustrated in Figure 15, upper surface 472 is inclined at an angle 474 relative to the plane of the mouth of the liner which again may be approximately 35°. As also best illustrated in Figure 15, the visual guide 470 may be releasably attached to the rim 436 of the liner via one or more male formations 476 received in a corresponding female formation within the rim of the liner. Also, as illustrated in Figure 14, one, or both, end faces e.g. 478, of the visual alignment guide 470 may include indicia 480 showing different angular positions of the cup. For example, if the upper surface corresponds to an angular position of 35° of anteversion, then a next indicium may correspond to an angle of 25° of anteversion and a further indicium to an angle of 15° anteversion. Hence, a scale of angular orientation of the acetabular cup may be included on the visual alignment guide 470.

As will be described in greater detail below, as illustrated in Figure 15, the visual alignment guide 470 provides a mechanism for allowing a surgeon to easily visually assess the total anteversion of the hip joint intraoperatively. If the equatorial marking 418 of the trial head 416 coincides with the plane defined by the visual alignment guide, then the surgeon is informed that the total anteversion of the hip has a particular value. The angle of tilt 474 of the alignment guide relative to the plane of the mouth of the cup when the liner is inserted in the cup, sets the target anteversion angle and therefore may vary depending on the target total anteversion and also the specific anteversion of the cup alone relative to the pelvis and the neck anteversion relative to the femur. If the equatorial marking 418 is reasonably close to being parallel to the plane defined by the visual alignment guide 470, then the surgeon may still be comfortable that the overall anteversion angle is acceptable. However, if there is a significant difference, either greater than or less than the angle of the plane defined by the visual alignment guide 470, then the surgeon may consider this to be an indication that the anteversion of the hip joint is not acceptable.

Further, liner 460 differs from trial liner 430 in having a section of the body of the trial liner cut away at a position 464 diametrically opposed to the position of the visual alignment guide 470 on the rim 436. This can provide improved visibility of the equatorial marking 418 on the trial head to further help assess the suitability of the total anteversion of the hip joint, when the equatorial marking 418 is not aligned with the alignment guide. For example, if the surgeon is trying to view the equatorial mark 418 on a trial head 416 when tilted at 35 degrees to the mouth of the liner, then the equatorial mark 418 may otherwise become obscured and not visible as soon as the trial head is tilted beyond this position. The cut-out portion 464 of the liner is arranged to permit the corresponding part of the equatorial line 418 remain visible to the surgeon.

For a posterior and an anterior approach which may allow the femoral head to be viewed from two opposing directions, then for one of those directions, the view via the cutaway 464 may provide the only feasible viewing angle. Other embodiments using this principle are described further below.

The liners described herein may be made from any suitable biocompatible material such as a plastic. For example, the trial liner may be made from a polyphenylsulphone material, such as that provided under the trade mark RADEE, Polyoxymethylene (POM) or Polyacetal. The liner may also be made from PEEK/PAEK, either glass filled or otherwise. Also, single use versions of the liner could be made from Nylon, POM, Polypropylene or similar.

Figures 16A and 16B show perspective views of a further embodiment of a trial femoral head and Figure 16C shows a cross sectional view of the trial femoral head along line G23

G’. As best illustrated in Figure 16A, the trial femoral head has an upper half 502 with a hemispherical shape and defining a generally hemispherical articulating surface 504. A lower half 506 includes a generally cylindrical wall 508 defining a cavity 510 configured to receive a taper at a free end of a femoral neck. As best illustrated in Figure 16B a plurality of ribs, e.g., rib 512, extend from an outer surface of cylindrical wall 508 and meet an underside 514 of the upper half 502. A channel 516 extends from a closed end of cavity 510 to the pole or apex of the trial femoral head at which the channel has an open mouth. Hence, channel 516 permits the egress of fluids from the cavity 510 as the trial femoral head 500 is mounted on the taper of a femoral neck in use.

The interface between the upper half 502 and the lower half 506, and in particular the change in geometry of the outer surface of the trial head 500, provides an indicium at the equator of the trial femoral head similar to equatorial marking 418 of the first trial head 416. However, in the trial femoral head 500 of Figures 16A to 16C, the equatorial indicium is provided by features of the shape of the outer surface of the trial femoral head rather than by some secondary or ancillary marking. Hence, there is no need to add some further marking during or after manufacturing and also there is no marking which can be rubbed off or otherwise fade with use. Also, the equatorial indicium provided by this abrupt change in geometry may have enhance visibility compared to a simple line marking and therefore may be easier for a surgeon to see during use in a surgical site. As discussed above the distal most end face of the trial head may additionally, or alternatively, provide the indicium with which the visual alignment guide is compared.

However, it will be appreciated that the trial head 416 illustrated in Figure 12 can also be used with any of the trial liners described herein.

Figures 17A to 17C show various perspective views of a third embodiment of a trial liner 520 according to the invention and Figure 17D shows a cross sectional view along line AA’ of the liner 520 when located within an acetabular cup 530. Many of the features of the third embodiment 520 are similar to those of the first and second embodiments. The alignment guide 524 is releasably attachable to the rim of the trial liner 522 and is generally in the form of a curved wedge having an upper surface 526 defining an alignment plane. As best illustrated in Figure 17D, the alignment guide is configured to position the upper surface 526 of the alignment guide 524 to define an alignment plane which subtends an acute angle 532 of substantially 35° with the plane 534 of the mouth of the liner, denoted by dashed line 534, and which is coincident with the plane of the mouth of the acetabular cup 530.

A linear feature 536, which may be in the form of an engraved line, is provided on the visual alignment guide, and is intended to help the user orientate the visual alignment guide within the acetabulum by positioning the line 536 so that it points along axis 222, so that the line 536 is generally parallel to the patient’s coronal plane.

The alignment guide 524 also includes an attachment formation 538 in the form of a threaded bore arranged to receive a threaded end part of a tool for a handle which may be used to insert the cup and liner assembly in the patient’s reamed acetabulum.

As noted above, the cup and liner assembly should be placed in the patient’s acetabulum with ARD 521 most superior and ARD 523 most inferior, for a right hip, to improve the accuracy of assessing combined anteversion.

A cut-out portion 539 is also provided on one side of the visual alignment guide to enhance grip and handling, and a flatter surface is provided for markings to be applied

In this embodiment, the plane defined by surface 526, while parallel to an equatorial line on the head 416, does not match up to an equatorial line, but rather to the flat face 419 on the inferior portion of the head. Hence, the visual alignment guide 524 is configured to align with a feature on the head that is completely outside the liner, allowing a comparison to without affecting the geometry of the cup 530.

In other embodiments, the alignment guide 524 may be releasably attachable to the rim of the acetabular cup or a trial cup.

Figures 18A to 18C show various perspective views of an assembly of a fourth embodiment of a trial liner 540 and Figure 18D shows a cross sectional view along line B-B’ of an assembly of the trial liner 540 and an acetabular cup 550. The assembly of trial liner 540 and acetabular cup 550 shown in Figure 18D also shows trial femoral head 500. Many of the features of the fourth embodiment 540 are similar to those of the other embodiments. However trial line 540 is configured to pivot or swing within the acetabular cup 550 such that a portion of the rim of the trial liner 540 provides the visual alignment guide.

The base of the trial liner 540 defines a generally arcuate slot 542 extending generally from a pole or apex of the trial liner and at least partially along a side wall part of the trial liner. A threaded member 544 is received within arcuate slot 524 and in use secures the trial liner within the cup 550 as best illustrated in Figure 18D. The threaded member can be tightened to fix the angle of the liner 540 relative to the cup 550. The liner 540 includes a first 546 and a second 548 male formation or lug and which are positioned generally diametrically opposed and perpendicular to the axis of the slot. Fugs 546, 548 also act as ARDs. When lugs 546, 548 are received in corresponding female formations in the rim of the cup, then the liner can pivot or swing about an axis between them (generally perpendicular to the plane of the section of Fig 18D) with the threaded member 544 travelling in slot 542. A superior portion of the rim of the trial liner includes a lip 547 which together with the adjacent portion of the rim defines a planar surface 549 being the visual alignment guide part of the trial liner 540.

The slot 542 in the base of the liner 540 contains the locking screw 544. Hence, the user can lock the liner 540 in the unswung (no indication) position in the cup 550 or in the swung, e.g. 35°, position as illustrated in Figure 18D in which it can be used for combined anteversion indication. The liner 540 can be locked at any incremental position in between 0° and 35°, or indeed greater, and can also be left slightly untightened so that it can freely pivot. The user can pivot the liner into either end of its two ranges of motion or any position therebetween. The locking screw 544 has a small flange on it which cooperates with the slot 542 and which may be in the form of a recessed keyway or channel.

As discussed above the first and second ARDs are received within corresponding notches in the rim of the cup and hence act as pivots or hinges to permit the liner to swivel or pivot about them within the cup. As also discussed above ARDs 546, 548 can be sued by the user to ensure correct positioning of the cup and liner assembly in the patient’s acetabulum. Hence, the pivoted rim of the trial liner provides the alignment guide 549 and defines an alignment plane. As best illustrated in Figure 18D, the pivoted trial liner positions the rim to define an alignment plane 549 which can subtend an acute angle of substantially 35° with the plane of the mouth of the acetabular cup 550 and against which an equatorial line of the trial head 500 can be compared.

Figures 19A to 19C show various perspective views of a fifth embodiment of a trial liner 570 according to the invention and Figure 19D shows a cross sectional view along line CC’ of an assembly of the liner 570 and a cup 589 together with a trial femoral head 500. Many of the features of the fifth embodiment 570 are similar to those of the preceding embodiments. The alignment guide 572 has a first formation 574 which is generally make and a second formation 576 which is generally female, as best seen in Figure 19D in the sense that it is recessed compared to the rest of the liner. The first formation and second formation are generally diametrically opposite. An upper surface 578 of the first curved male formation 574 defines a first visual alignment plane. As best illustrated in Figure 19D, the first male formation 574 is configured to position the upper surface 578 to define an alignment plane which subtends an acute angle of substantially 35° with the plane of the mouth of the remainder of the liner and which is generally coincident with the plane of the mouth of the acetabular cup 530. The upper surface 578 provides a first visual alignment guide against which an equatorial line on the trial head 500 can be compared to assess combined anteversion.

The female formation 576 also defines a planar surface 580. Surface 580 of the female formation 576 defines a second visual alignment plane. As best illustrated in Figure 19D, the female formation 576 is also configured to position the surface 588 to define an alignment plane which subtends an acute angle of substantially 35° with the plane of the mouth of the remainder of the liner and which is generally coincident with the plane of the mouth of the acetabular cup 530. The surface 580 provides a second visual alignment guide against which the flat inferior, distal or lower surface 516 of the trial head can be compared to assess combined anteversion. Surface 578 provides a visual alignment guide which is preferable for the anterior approach, and surface 580 provides a visual alignment guide which is more suitable for the posterior approach.

Figures 20A and 20C show various perspective views of a sixth embodiment of a trial liner 590 according to the invention and Figure 20B shows a plan view of an assembly of the liner 590 and an acetabular cup 530 together with a trial femoral head 500 and Figure 20D shows a stepped cross sectional view along line J-J’ of Figure 20B. Many of the features of the sixth embodiment 590 are similar to those of the preceding embodiments. The alignment guide 592 is permanently formed as part of the rim 591 of the trial liner 590 and includes a male part 594 and two female or cut-away parts 596, 598 in the side wall of the liner diametrically opposed to the male part 594 . An upper surface 595 of the male part 594 defines a fist alignment plane. The male part 594 is configured to position the upper surface 595 to define an alignment plane which subtends an acute angle of substantially 35° with the plane of the mouth of the liner and which is coincident with the plane of the mouth of the acetabular cup 530 as best illustrated in Figure 20D. The face 595provides a first visual alignment guide against which an equatorial line on the trial head 500 can be compared to assess combined anteversion.

The trial liner 590 also includes a first and a second female formation 596, 598 each having respective faces 597, 599 and which are also configured to subtend an angle 35° with the plane of the mouth of the liner and which is coincident with the plane of the mouth of the acetabular cup 530. The plane of surface 597 is best seen in the stepped cross section in Figure 20D. The faces 597 and 599 provide second and third visual alignment guides against which an equatorial line on the trial head 500 can additionally, or alternatively, be compared to assess combined anteversion as also best illustrated in Figure 20D.

Figures 21A shows a perspective views of a seventh embodiment of an alignment guide part 600, Figures 2IB and 21C show perspective views of a trial liner 620 and the alignment guide part 600 and Figure 21D shows a partial cross sectional view along line E-E’ of an assembly of the alignment guide 600, liner 620 in an acetabular cup 530, and a trial femoral head 500. Many of the features of the seventh embodiment 620 are similar to those of the preceding embodiments. The alignment guide part 600 is releasably attachable to the rim of the acetabular cup and is generally in the form of an annulus or ring 602 configured to push or snap fit onto the rim of the acetabular cup. The alignment guide part 600 includes a curved wedge shaped formation 604 having an upper surface 606 and configured to define an alignment plane. As best illustrated in Figure 21D, the wedge section 604 is configured to position the upper surface 606 of the alignment guide 600 to define an alignment plane which subtends an acute angle of substantially 35° with the plane of the mouth of the liner and which is generally coincident with the plane of the mouth of the cup.. Hence, the alignment guide part 600 may be used with a conventional trial liner or a final liner as it is adapted to attached to the rim of the acetabular cup. The acetabular cup may be a trial cup or shell or a prosthetic cup or shell. Hence, face 606 provides a visual alignment guide against which an equatorial line on the trial head 500 can be compared to assess combined anteversion.

Figures 22A to 22C show various perspective views of an eighth embodiment of a trial liner 640 according to the invention and Figure 22D shows a partial cross sectional view along line F-F’ of an assembly of the liner 640 within an acetabular cup 530 and a trial femoral head 500. Many of the features of the eighth embodiment 640 are similar to those of the preceding embodiments. The alignment guide 642 is releasably attachable to the rest of the trial liner 644 and is generally in the form of a curved wedge shaped formation 644 having an upper surface 646 and configured to define an alignment plane. The alignment guide sits on the rim of the trial liner and is releasably attached thereto be a clip or similar mechanism. As best seen in Figure 22B a window or aperture 648 is defined in a part of the side wall of the trial liner 640. A lower, resilient portion 645 of the alignment guide 642 is received within window 648 so as to clip the alignment guide 642 to the rim of the liner 640 as best illustrated in Figure 22D. The window or aperture 648 is located equidistant between first and second diametrically opposed ARDs 650, 652.

As best illustrated in Figure 22D, the wedge section 644 is configured to position the upper surface 646 of the alignment guide 642 to define an alignment plane which subtends an acute angle 648 of substantially 35° with the plane of the mouth of the liner. Hence, face 646 provides a visual alignment guide against which an equatorial line on the trial head 500 can be compared to assess combined anteversion.

Trial liner 640 can also be used with a wire like visual alignment guide similar to that shown in Figure 12. As can best be seen in Figures 22A and 22B a first hole 654 and a second hole 656 are provided in the rim of the trial cup 640 at the same positions as the first and second ARDs 650, 652. These holes can be sued to receive the free ends of a wire shaped similarly to that shown in Figure 12 but with radially directed feet to be received in hole s654 and 656. Hence, trial cup 640 can be used with either the wedge shaped visual alignment guide 642 or a wire form visual alignment guide similar to that shown in Figure 12.

Use of the trialling system including the various trial femoral heads and liners described above will now be described in greater detail with reference to Figures 23 to 25. It will be appreciated that the same general principal applies to all the embodiments of the liner 260 and femoral head as described herein.

Figure 23 shows a flow chart illustrating a method of carrying out a hip replacement surgical procedure 800 according to the invention and using the trialling system described previously, also according to the invention. Total hip replacement surgery is known generally in the art and may of the details are omitted from the following description so as not to obscure the nature of the invention.

The order of some of the steps may not be material but the order of some of the steps may be material as will become clear from the following description. Also, some of the described steps may be optional, depending on the specific workflow that a surgeon may prefer.

With reference to Figure 23, at 802, the femur is prepared, which may involve the resecting of the proximal part of the femur and planning or milling the resected surface to provide a flat surface. After the proximal part of the femur has been removed, at 804, a cavity is formed generally aligned with the local anatomical axis of the femur and generally along the intramedullary canal, ultimately to receive the stem of the prosthetic femoral components. Preparation of the cavity may include drilling and the use of various sized rasps and/or broaches to pre-form the appropriately shaped cavity.

Different sized broaches may be used up to a largest broach to form the cavity to accept the stem. For example, using the system illustrated in Figure 12, broach 412 may be used with a handle which is releasably attached to a proximal part of the broach 412. When broaching has been completed, then the handle may be removed and the broach 412 may be left in the femur for use during the trialling stage, to be described in greater detail below.

Either before or after preparation of the femur, the acetabulum of the pelvis is prepared. This may include cutting away soft tissue and using a hemispherical reamer to ream the acetabular cavity at 806 to form a substantially hemispherical cavity for receiving the acetabular component. After the acetabulum has been prepared, then at 808, a trial acetabular cup is inserted in the reamed acetabular cavity. At this stage, the position of the trial acetabular cup is largely determined by the depth to which the acetabular cavity has been reamed. However, the surgeon has some degree of flexibility in adjusting the orientation of the trial acetabular cup relative to the local anatomy of the pelvis. Hence, at this stage, the surgeon inserts the trial acetabular cup to try and produce a desired angle of anteversion and abduction. In particular, the surgeon attempts to insert the trial acetabular cup with an abduction or inclination angle of approximately 40° relative to the pelvis and an anteversion angle of approximately 20° relative to the pelvis. It will be appreciated that in other embodiments, a prosthetic cup may be inserted at this stage instead.

Generally, after trial cup has been inserted at 808, then the trial liner is inserted in the cup. However, in some embodiments, the trial liner may be inserted into the cup before insertion of the cup at 808, in which case step 810 is skipped. For some of the described embodiments, the trial liner thread 444 is screwed into a corresponding threaded bore at the pole of the cup. The angular orientation of the trial liner about its polar axis relative to the cup is limited, or fixed, by the anti-rotation devices on the liner, e.g., 440, 442, to ensure that the angular alignment guide is at the appropriate angular position about the polar axis of the cup so as to give rise to the geometry illustrated in Figure 13 above.

In particular, when the cup is inserted at 808 without a trial liner, a one of the cup ARDs is positioned as superior as possible and the other as inferior as possible. Then when the trial liner is placed in the cup at 810, the pair of liner ARDs, e.g., ARDs 650 and 652 in

Figure 22A to 22D, which define the appropriate axis of the liner are located in the most superior and most inferior cup ARDs. If the liner is inserted in the cup before placing the cup in the acetabulum then the cup is oriented in the acetabulum at 808 with the appropriate one of the liner ARDs as superior as possible and the other as inferior as possible.

At some stage, a trial femoral neck 414 may be attached to the broach and the trial head 416 is attached at 812 to the taper of the neck 414 on the broach which is located in the patient’s femur. Then, at 814, the hip joint is reduced and the patient’s leg is placed in an anatomical position. In particular, the patient’s leg is placed with the femur in an anatomical position with respect to the pelvis. Specifically, the femur is placed in 0° of flexion/extension, 0° of adduction/abduction and 0° of intemal/extemal rotation.

Assuming that the pelvis on the operating table has taken up an approximately neutral amount of pelvic tilt then this can be achieved by comparing the following three factors. The long axis of the leg relative to the longitudinal axis of the patient can be adjusted by pulling lightly on the lower limb to pull the leg into full extension. If an anterior approach is being used, with the patient supine, then the leg will naturally rest in full extension. Zero abduction / adduction of the legs can be achieved by placing both lower legs (tibia from knee to ankle) parallel and almost touching. 0° of internal / external rotation can be checked using the epicondylar axis of the knee relative to the transverse axis of the pelvis. If the pelvis is level (supine) or vertical (in a lateral decubitus approach) on the table, then the epicondylar axis can be compared to the table. If a posterior approach is being used, with the patient lateral, then the tibia can be flexed 90° to provide a more discernible indication on the femoral articular axis which will indicate any internal / external rotation of the femur. Hence, depending on the orientation of the patient on the table, the patient’s legs are placed in appropriate positions to provide 0° of flexion/extension, 0° of abduction/adduction and 0° of intemal/extemal rotation of the femur with respect to the pelvis. With the patient’s legs in this anatomical position, an assessment of the trial cup position can be carried out at step 816.

Optionally, at step 816 a range of motion assessment can also be carried out. This is generally known in the art and may involve articulating the hip joint to detect the likely range of articulation possible before impingement of the hip components.

Assessment of the cup orientation at 816, and in particular assessment of the anteversion of the cup, will now be described in greater detail with reference to Figures 24A to 24C. Figures 24A to 24C show schematic diagrams of the trial liner 430 and trial head 416 as described above and illustrated in Figure 13. As discussed above, the trial liner 430 is positioned within the trial cup at a specific clocked rotational position so as to arrive at the positional relationship illustrated in Figure 13 and 24A to 24C, and with the plane of the mouth of the liner co-incident with the plane of the mouth of the acetabular cup. With the hip joint in the anatomical position, described above, and with the liner in this position, the visual alignment guide 450 can be used to help assess the combined anteversion angle of the hip joint arising from the current trial component orientations. As noted above, there may be limited opportunity to modify the orientation and hence anteversion angle of the stem. Therefore, the assessment carried out at 816 may help the surgeon determine whether the anteversion of the cup is satisfactory or may need altering or simply to assess the cup position for an implanted prosthetic cup.

In greater detail, Figure 24A shows a schematic view of the trial cup 430, visual alignment guide 450, trial head 416 and equatorial marking on the trial head 418. As illustrated in Figure 24A, the equatorial mark 418 on the trial head 416 is not aligned with the plane of the visual alignment guide 450. In this instance, the trial cup may be in a position with too little anteversion compared to the target anteversion angle. That is, the trial cup may be pointing too much toward the lateral direction and not enough in the anterior direction.

Figure 24B illustrates a scenario in which the equatorial marking 418 is again not aligned with the plane of the visual alignment guide 450. Hence, this corresponds to a situation in which the trial cup position has greater anteversion than a target anteversion value. Hence, by visually inspecting the position of the equatorial alignment mark 418 compared to the visual alignment guide 450, the surgeon can assess the anteversion of the cup relative to the pelvis and also how the anteversion of the cup affects the combined anteversion of the hip joint. It may be that equatorial marking 418 is sufficiently close to the visual alignment guide 450 that no repositioning of the cup is merited.

Figure 24C illustrates a scenario in which the equatorial marking 418 is aligned with the plane of the visual alignment guide 450. Hence, the anteversion of the trial cup corresponds to a preferred or target anteversion value and so no repositioning of the cup may be needed.

It will be appreciated that for other embodiments of the trial liner and visual alignment guide, the flat rear or distal surface of the trial head is compared to the visual alignment guide, rather than the equatorial line or additionally to the equatorial line.

It is not necessary that the surgeon carries out any repositioning of the cup. The trial assessment at 816 may be carried out simply to assess the anteversion angle achieved with the current cup placements so as to provide immediate feedback to the surgeon to improve their experience. This is particularly the case if an implanted prosthetic cup is being assessed at 816. However, in other embodiments, the cup may be re-positioned, particularly if a trial cup is being assessed at 816.

At 818, all the trial components are removed from the acetabulum and/or femur. Then at 820, the actual prosthetic cup, if not already implanted, is implanted in the acetabular cavity with an orientation similar to that used for the trial cup, if the trial position was assessed to be satisfactory, or adjusted based on the results of the trial cup orientation assessment at 816. Then the final liner is inserted in the cup, once positioned. The femoral stem is then implanted at 822 together with the prosthetic femoral head. Then at 824, the joint can be reduced and optionally any range of motion trial carried out if desired. The surgical procedure then substantially ends.

Figure 25 shows a further embodiment of a method 840 for carrying out a hip replacement surgical procedure. Much of method 840 is similar to method 800 except in method 840, a final or prosthetic cup is implanted initially rather than using a trial cup. Hence, at step 842, instead of inserting a trial cup, the prosthetic cup is inserted. Then, at step 844, the trial components are removed but the implanted prosthetic cup may be left in place and at 846 the final liner is inserted into the cup which is kept in position. However, if at 816 the assessment is that the cup anteversion angle is too far from the target anteversion angle, then in some embodiments, the acetabular cup may be removed and implanted again with a different orientation at step 842.

Otherwise, the method and the assessment of the position of the implanted cup are generally similar to that described above in relation to method 800. However, in this approach, the surgeon may either use the assessment at 816 simply to assess the implanted cup position and not alter the implanted cup position or alternatively may decide to reposition the acetabular cup if its anteversion is too far from the target anteversion.

Hence, the visual alignment guide attached to the trial liner provides a robust mechanism for assessing the anteversion of an acetabular cup. There may be no need to use a specialised trial head with the liner as many trial heads already include an equatorial line 418. Also, there is no need for careful rotational positioning of the trial head on the neck of the femoral part, in the described approach, as may be required by other approaches in which special markings on the trial head are used instead to assess cup position.

Also, the visual alignment guide is provided in a more readily visible state, rather than having to rely on, for example, simply the rim of a cup or liner.

Also, as the visual alignment guide may be releasable attachable, in some embodiments, different target cup angles can be easily assessed by providing visual alignment guides with different angles and/or information which can be attached to the liner depending on the surgeon’s preferred approach.

As mentioned above, the specific value of the angle of the visual alignment guide depends on a number of factors. These include the anteversion of the femoral component relative to the femur and also the target anteversion of the cup relative to the pelvis.

In the above described embodiment, a 35° combined anteversion angle for the hip may correspond to an anteversion of the femoral neck relative to the medial-lateral axis of the femur of 15° an anteversion angle of the cup relative to pelvis of 20°. However, this same combined anteversion angle may also arise for a femoral neck anteversion angle relative to the femur of 5° and an acetabular anteversion angle relative to the pelvis of 30°, for example.

In other embodiments, different angles of tilt of the visual alignment guide relative to the plane of the mouth of the cavity of the liner may be used. For example, the tilt angel 458 of the visual alignment guide may be 30° for a target combined anteversion angle of 30°, corresponding, e.g. to a femoral neck has anteversion angle of 0°, and an anteversion angle of the cup relative to the pelvis is 30°. Hence, different tilt angles may be provided for the visual alignment guide of the liner depending on the target combined anteversion of the hip joint.

It would also be appreciated that other specific forms of the visual alignment guide can be used. All that is required is that there is some structure which provides a visual indication of a plane to which the equatorial alignment mark on the trial head can be compared to assess the anteversion angle of the cup. As noted above, markings can be provided to allow the surgeon to read angles from the visual alignment guide.

Also, in some embodiments, the liner may be the actual prosthetic liner rather than a trial liner. Typically, the alignment guide will then be releasable from the liner. In those circumstances, the surgical method 840, is modified accordingly such that the liner itself is inserted in the prosthetic acetabular cup after 842, rather than a trial liner, and the final liner is not removed during the trial component removal step 844 and the final liner insertion step 846 is omitted. Hence, in this instance, the visual alignment guide is releasably attachable to the liner so as to be removable after the trial joint assessment at 816.

In this approach, rather than providing special orientation markings on the trial head, the orientation datum is provided by a visual alignment guide on the liner component. If orientation markings were provided on a trial head instead, then as trial heads are typically mounted on a taper, this approach is inherently unable to force a single clocked orientation to the markings owing to the rotational symmetry of the taper and trial head attachment mechanism. Therefore a special neck with keying features or an additional component is provided to attach the trial head to a neck taper at a particular orientation. In the described approach, the trial liner may include one or more antirotation devices (ARDs), and so the rotational position of the liner relative to the polar axis of the acetabular cup can be fixed and so the datum provided by the visual alignment guide can be kept stable rotationally.

The user can orientate the liner/cup assembly relative to the version axis by aligning the liner/cup assembly relative to the anterior superior iliac spine (ASIS) of the pelvis or the lateral direction of the patient's pelvis as defined by other bony anatomical landmarks of the pelvis. As discussed above, the user can orientate the cup or trial cup relative to the patient’s pelvis by ensuring that the ARD recesses on the cup are placed with one as superior as possible and the other as inferior as possible. Thus when the liner is inserted into the cup, the ARDs of the liner that define the version axis can be positioned in these ARD recesses of the cup, ensuring that the visual alignment guide is correctly orientated.

Further, the anatomical position of the patient’s leg is easier to reliably and reproducible achieve during a surgical procedure, compared to other leg positions such as the Ranawat sign position or positions involving internal rotation of the femur.

Further, when the visual alignment guide is mounted on the rim of the liner, the visual alignment guide is away from the rim of the cup and therefore easier for the surgeon to visually inspect compared to trying to assess alignment relative to the rim of the cup which may be obscured, for example by soft tissues and/or bodily fluids.

Hence, the invention may improve the ability to assess the anteversion of trial or prosthetic acetabular cups implanted in the pelvis compared to other approaches, for example using a conventional pointer which can cause errors in inclination and anteversion. This is particularly, the case when the pelvis is mal-rotated relative to the global reference plane of the operating table or the operating room. In such instances the orientation of the cup often bears little, if any, relation to the orientation of the femur and lower limb.

Hence, the invention may make intra-operative acetabular cup orientation assessment easier, quicker, simpler, more reproducible, more quantitative and/or more useful to the surgeon.

In this specification, example embodiments have been presented as particular combinations of features. However, a person of ordinary skill in the art would understand that many other embodiments may be practiced which include a different combination of features, including fewer features or a greater number of features. It is intended that the following claims cover all possible embodiments.

Any instructions and/or flowchart steps may be carried out in any order, unless a specific order is explicitly stated or would be understood to be required from the context of the description. Also, those skilled in the art will recognize that while one example method has been discussed, a variety of other differing methods are possible based on other combinations and/or orders of method steps, and are to be understood within a context provided by this detailed description.

While the inventions are amenable to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and described in detail. It should be understood, however, that other embodiments, beyond the specific embodiments described, are possible as well. All modifications, equivalents, and alternative embodiments falling within the scope of the appended claims are covered as well.

Claims

CLAIMS:

1. A liner for an acetabular cup for assessing anteversion of the acetabular cup in a pelvis of a patient, the liner comprising:

a body having a rim defining a mouth to a liner cavity adapted to receive a trial head within the liner; and a visual alignment guide configured to define a guide plane tilted with respect to a plane defined by a mouth of an acetabular cup when the liner is received in the acetabular cup in use and to subtend an acute angle with the plane defined by the mouth of the acetabular cup, wherein the acute angle corresponds to a target combined anteversion for a hip joint when the acetabular cup is in the pelvis.

2. The liner as claimed in claim 1, wherein the liner includes an anti-rotation device engageable with the acetabular cup to prevent rotation of the liner about a polar axis of the liner.

3. The liner as claimed in claim 1 or 2, wherein the acute angle is in the range 20° to 50°.

4. The liner as claimed in claim 3, wherein the acute angle is substantially 35°.

5. The liner as claimed in any of claims 1 to 4, wherein a portion of a wall of the body at a position on the rim diametrically opposed to a position on the rim at which the visual alignment guide is provided is lower than a liner plane defined by the mouth of the liner to provide visual access to a portion of the interior of the liner.

6. The liner as claimed in any of claims 1 to 5, wherein the visual alignment guide includes a plurality of indicia arranged to provide a scale indicating different amounts of combined anteversion of the hip joint.

7. The liner as claimed in claim 6, wherein the scale includes a plurality of numbers indicating the quantitative amount of the degree of combined anteversion of the hip joint.

8. The liner as claimed in any preceding claim, wherein the visual alignment guide includes a curved member.

9. The liner as claimed in claim 8, wherein the curved member has a radius of curvature centred on the centre of the mouth of the body.

10. The liner as claimed in claim 9, wherein the visual alignment guide is in the form of a curved wire.

11. The liner as claimed in claim 10, wherein the curved wire includes a first leg and a second leg by which the curved member is mounted away from the rim.

12. The liner as claimed in claim 9, wherein the visual alignment guide is in the form of a curved and tapering block.

13. The liner as claimed in any preceding claim, wherein the liner includes a formation for releasably attaching a handle.

14. The liner as claimed in claim 13, wherein the formation is a female formation.

15. The liner as claimed in claim 14, wherein the female formation is formed within the wall of the body and has an opening in the rim.

16. The liner as claimed in claim 14, wherein the female formation is formed within the visual alignment guide.

17. The liner as claimed in any of claims 1 to 16, wherein the liner includes a connector for releasably attaching the liner to the acetabular cup.

18. The liner as claimed in claim 17, wherein the connector comprises a threaded member passing through an aperture defined at the pole of the liner and extending from a rear side of the liner and along a polar axis of the liner.

19. The liner as claimed in any of claims 1 to 18, wherein the visual alignment guide is releasably attached to the rim of the liner.

20. The liner as claimed in claim 19, wherein the visual alignment guide includes at least one male formation and the liner includes at least one female formation adapted to receive the at least one male formation to releasably attach the visual alignment guide to the liner.

21. The liner as claimed in any of claims 1 to 18, wherein the visual alignment guide is a unitary part of the liner.

22. The liner as claimed in any of claims 1 to 21, wherein the visual alignment guide is configured to coincide with an equator of a trial head when located in the liner in use.

23. The liner as claimed in any of claims 1 to 21, wherein the visual alignment guide is configured to coincide with a distal face of a trial head when located in the liner in use

24. The liner as claimed in any preceding claim and including a further visual alignment guide configured to define a further guide plane tilted with respect to the plane defined by the mouth of an acetabular cup when the liner is received in the acetabular cup in use and to subtend the acute angle with the plane defined by the mouth of the acetabular cup.

25. The liner as claimed in any preceding claim, wherein the visual alignment guide is provided by a flat surface of a male formation.

26. The liner as claimed in any of claims 1 to 24, wherein the visual alignment guide is provided by a flat surface of a female formation.

27. The liner as claimed in any preceding claim, wherein the liner includes a first antirotation device and a second anti-rotation device positioned about the rim diametrically opposite each other.

28. The liner as claimed in claim 27, wherein the visual alignment guide is positioned equidistantly at the rim between the first anti-rotation device and the second anti-rotation device.

29. The liner as claimed in claim 1, wherein the liner is adapted to pivot within the acetabular cup and wherein a portion of the rim of the liner provides the visual alignment guide.

30. The liner as claimed in claim 29, wherein the liner includes a slot in a base of the liner and a fastener received in the slot, and adapted to travel in the slot, for attaching the liner to the acetabular cup in use.

31. The liner as claimed in claim 30, wherein the liner includes a first anti-rotation device and a second anti-rotation device arranged to define a pivot axis about which the liner can pivot in use.

32. The liner as claimed in claim 31, wherein the pivot axis is substantially perpendicular to a longitudinal axis of the slot.

33. The liner as claimed in any preceding claim, wherein the liner is a trial liner.

34. The liner as claimed in any of claims 1 to 32, wherein the liner is a prosthetic liner.

35. The liner as claimed in any of claims 1 to 34, wherein the acute angle defines a target combined anteversion of the hip of the patient when a trial head is located in the cavity and is attached to a neck of a stem component inserted in a femur of the patient and the femur is placed in an orientation corresponding to an anatomical position of the leg of the patient.

36. The liner as claimed in claim 35, wherein the anatomical position corresponds substantially to 0° extension/flexion of the leg, 0° abduction/adduction of the femur and 0° rotation of the femur.

37. The liner as claimed in any preceding claim, wherein the acetabular cup is a trial acetabular cup.

38. The liner as claimed in any of claims 1 to 36, wherein the acetabular cup is a prosthetic acetabular cup.

39. A kit of parts comprising:

the liner as claimed in any of claims 1 to 38;

an acetabular cup defining a cup cavity adapted to receive the liner;

a trial head having an indicium and adapted to be received within the liner cavity; and a stem part having a neck with an attachment formation at a free end of the neck to which the trial head can be releasably attached.

40. The kit of parts as claimed in claim 39, wherein the liner is a trial liner.

41. The kit of parts as claimed in claim 39 or 40, wherein the acetabular cup is a trial acetabular cup or a prosthetic acetabular cup.

42. The kit of parts as claimed in claim 39, 40 or 41, wherein the stem part is a femoral broach or a trial femoral stem or a prosthetic femoral stem.

43. The kit of parts of any of claims 39 to 42, wherein the acetabular cup includes at least one anti-rotation formation configured to mate with an anti-rotation device of the liner.

44. The kit of parts of claim 43, wherein the acetabular cup includes a first antirotation formation configured to mate with a first anti-rotation device of the liner and a second anti-rotation formation configured to mate with a second anti-rotation device of the liner.

45. An assembly of the kit of parts of any of claims 39 to 44.

46. A method of assessing the anteversion of an acetabular cup within an acetabulum of a pelvis of a patient, comprising:

reducing a trial hip joint comprising a liner within an acetabular cup within an acetabulum of a pelvis of a patient and a trial head having an indicium attached to the neck of a stem located within a femur of a leg of the patient; and comparing the indicium to a visual alignment guide part of the liner, wherein the visual alignment guide defines a plane subtending an acute angle with a plane of a mouth of the acetabular cup, the acute angle corresponding to a target combined anteversion of the hip joint of the patient.

47. The method of claim 46, further comprising:

moving the leg of the patient into an anatomical position before comparing the indicium to the visual alignment guide.

48. The method of claim 47, wherein the anatomical position corresponds substantially to 0° extension/flexion of the leg, 0° abduction/adduction of the femur and 0° rotation of the femur.

49. The method of any of claims 46 to 48, wherein the indicium is an equatorial line of the trial head or a distal face of the trial head.

50. The method of any of claims 46 to 49, wherein the liner is a prosthetic liner and the acetabular cup is a prosthetic acetabular and cup further comprising:

removing the visual alignment guide from the liner.

51. The method of any of claims 46 to 49, wherein the acetabular cup is a prosthetic acetabular cup and further comprising:

adjusting the orientation of the prosthetic acetabular cup based on the comparison of the indicium to the visual alignment guide.

52. The method of any of claims 46 to 49, wherein the acetabular cup is a trial acetabular cup and further comprising:

removing the trial acetabular cup; and implanting a prosthetic acetabular cup at an implantation orientation, wherein the implantation orientation is based on the comparison of the indicium to the visual alignment guide.

53. A kit of parts comprising:

a liner;

an acetabular cup having a rim defining a mouth of a cup cavity adapted to receive the liner; and a visual alignment guide releasably attachable to the acetabular cup and configured to define a guide plane tilted with respect to a plane defined by the mouth of the acetabular cup when the visual alignment guide is mounted on the rim of the acetabular cup in use and to subtend an acute angle with the plane defined by the mouth of the acetabular cup, wherein the acute angle corresponds to a target combined anteversion for a hip joint when the acetabular cup is in a pelvis of the patient.

54. The kit of parts of claim 53, wherein the visual alignment guide includes a male formation having a surface which defines the guide plane and a clip by which the alignment guide can be releasably attached to the rim of the cup.

55. The kit of parts of claim 54, wherein the clip is in the form of a ring and wherein the male formation is in the form of a curved wedge.

56. An assembly of the kit of parts of any of claims 53 to 55.