WO2019015962A1

WO2019015962A1 - Apparatus and method for hip surgery

Info

Publication number: WO2019015962A1
Application number: PCT/EP2018/068073
Authority: WO
Inventors: Lewis BUTLER; Stephanie Prince; Duncan Young
Original assignee: Depuy Ireland Unlimited Company
Priority date: 2017-07-21
Filing date: 2018-07-04
Publication date: 2019-01-24
Also published as: GB201711812D0

Abstract

Instrumentation (400) for implanting a prosthetic acetabular cup in an acetabulum of a patient and methods of use are described. A first version of the instrumentation comprises an inserter (410) having a handle (414) at a proximal end and an impaction head (418) at a distal end, configured to couple with an acetabular cup and to transmit an impaction force to the acetabular cup. The handle and impaction head define an impaction axis. A first attachment formation (416) is provided at the distal end of the inserter and a femoral part has a second attachment formation (424) releasably attachable to the first attachment formation. When the femoral part is attached to the inserter by the first and second attachment formations in use, a change in orientation of the femoral part causes a change of orientation of the inserter and the impaction axis. In a second version, the femoral part is attached to the distal end of the inserter, and, in use, a change in orientation of the femoral part causes a change of orientation of the inserter and the impaction axis.

Description

Apparatus and Method for Hip Surgery

The present invention relates to apparatus and methods for hip surgery, and in particular to instrumentation for placing a component of a hip joint and/or methods of hip surgery using such instrumentation.

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 only the articulating surface 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 one or both 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 o the surgeon to place the acetabular cup so that it is pointing generally in a preferred direction or range of directions. The orientation of an acetabular cup is often defmed in terms of an angle of abduction (or inclination) and an angle of antcversion.

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 o 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 co- planar 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 hav e 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 angular position of the acetabular cup relative to 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 leam. 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 placement of an acetabular cup simpler, easier and/or more reliable would be beneficial. A first aspect of the invention provides instrumentation for implanting a prosthetic acetabular cup in an acetabulum of a patient, including: an inserter, comprising: a handle at a proximal end of the inserter; an impaction head at a distal end of the inserter, wherein the impaction head is configured to couple with an acetabular cup in an acetabulum of a patient and to transmit an impaction force to the acetabular cup and wherein the handle and the impaction head are arranged to define an impaction axis of the inserter extending along the inserter; and a first attachment formation at the distal end of the inserter; and a femoral part attachable to a femur of the patient and having a second attachment formation which is releasably attachable to the first attachment formation, wherein when the femoral part is attached to the inserter by the first attachment formation and the second attachment formation in use, a change in orientation of the femoral part causes a change of orientation of the inserter and the impaction axis.

The femoral part may extend at least partially, or wholly, along a femoral neck axis and the femoral neck axis may be collinear with the impaction axis.

The femoral part may extend at least partially, or wholly, along a femoral neck axis and the femoral neck axis and the impaction axis may subtend an acute angle in the range of 10° to 50°. The impaction axis may subtend an acute angle in the range of 15° to 45°. The impaction axis may subtend an acute angle in the range of 10° to 40°. The impaction axis may subtend an acute angle in the range of 20° to 50°.

The femoral part may extend at least partially, or wholly, along a femoral neck axis and the femoral part may be configured such that the femoral neck axis and the impaction axis pass through a common pivot point corresponding to the centre of a sphere corresponding to the acetabular cup.

The inserter may include a third attachment formation at the distal end of the inserter. The second attachment formation may be releasably attachable to the third attachment formation. The femoral part may be attached to the inserter by the first attachment formation and the third attachment formation in use and a change in orientation of the femoral part may cause a change of orientation of the inserter and the impaction axis. The first attachment formation and the third attachment formation may be positioned to correspond to different anteversion angles of the acetabular cup.

The first attachment formation and the third attachment formation may be positioned to correspond to different surgical approaches to implanting the acetabular cup.

The first attachment formation may correspond to a right hip and/or the third attachment formation may correspond to a left hip. The first attachment formation may correspond to an anterior approach and/or the third attachment formation may correspond to a posterior approach.

The inserter may include a plurality of groups of further attachment formations at the distal end of the inserter. Each group of further attachment formations may comprise a plurality of different attachment formations. The second attachment formation may be releasably attachable to any o the further attachment formations. Each different attachment formation of a group may correspond to a different anteversion angle of the acetabular cup. Each group of attachment formations may correspond to one or more of: different surgical approaches to implanting the acetabular cup; a right hip and/or a left hip; and an anterior approach and/or a posterior approach.

The impaction head may have a hemispherical shape or part configured to be received within an acetabular cup cavity. The impaction head may have a circular and/or disc shape or part configured to engage with an acetabular cup mouth.

The inserter may include an intermediate portion between the handle and the impaction head and the intermediate portion may be offset to the impaction axis.

The first attachment formation may be a part of the impaction head. The inserter may include an inserter body. The first attachment mechanism may be a part of a distal end of the inserter body.

The inserter may include an inserter body. The impaction head may be releasably attachable to a distal end of the inserter body

The impaction head may be, or include, a liner or a trial liner for an acetabular cup.

The liner or the trial liner may include an apical formation arranged to releasably attach to a distal attachment formation at the distal end of the inserter body. The apical formation may be a clip, a fastener or a push fit attachment mechanism.

The femoral part may extend at least partially along a femoral neck axis. The second attachment mechanism may extend along an attachment axis, and the femoral neck axis and the attachment axis may subtend an acute angle in the range of 10° to 50°. The attachment a is may subtend an acute angle in the range of 15° to 45°. The attachment axis may subtend an acute angle in the range of 10° to 40°. The attachment axis may subtend an acute angle in the range of 20° to 50°. The femoral part may be, or include, a femoral neck.

The second attachment formation may be a taper at a free end of the femoral neck. The first attachment formation may be a socket configured to releasably receive the taper therein.

The first attachment mechanism may be operable by a user to secure and/or release the second attachment mechanism.

The first attachment formation may include a translatable collar and a curved wall. A curved portion o the translatable collar and the curved wall may define the socket.

The femoral neck may be a trial femoral neck. The femoral part may also include an insert configured to be received within a cavity with the femur of the patient. The insert may include an insert attachment formation by which the trial femoral neck is attachable to the insert. The insert may be selected from: a femoral broach; a femoral rasp; a trial femoral stem; and a prosthetic femoral stem.

The taper may be tilted relative to a body of the femoral neck. The instrumentation may be configured to orient the acetabular cup for implantation in the acetabulum of the patient with a target anteversion angle when the femur of the patient is positioned at a preselected position relative to the pelvis o the patient.

The target anteversion angle may be in the range of 5° to 60° of combined anteversion, and preferably 15° to 45° of combined anteversion.

The preselected position may be the Ranawat sign position.

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

The femoral part may be attached to the inserter by the first attachment formation and the second attachment formation.

A second aspect of the invention provides an assembly of the instrumentation o the first aspect of the invention, wherein the femoral part is attached to the inserter by the first attachment formation and the second attachment formation. 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 instrumentation for implanting a prosthetic acetabular cup in an acetabulum of a patient, including: an inserter, comprising: a handle at a proximal end of the inserter; and an impaction head at a distal end of the inserter, wherein the impaction head is configured to couple with an acetabular cup in an acetabulum of a patient and to transmit an impaction force to the acetabular cup and wherein the handle and the impaction head are arranged to define an impaction axis of the inerter extending along the inserter; and a femoral part attachable to a femur of the patient and attached to the distal end of the inserter, wherein, in use, a change in orientation of the femoral part causes a change of orientation of the inserter and the impaction axis.

Preferred features of the first aspect o f the invention may also be preferred features of the third aspect of the invention. A fourth aspect of the invention provides a method for implanting a prosthetic acetabular cup in an acetabulum of a patient using an inserter comprising a handle at a proximal end of the inserter and an impaction head at a distal end of the inserter wherein the handle and the impaction head are arranged to define an impaction axis of the inerter extending along the inserter, the method comprising: coupling the impaction head to an acetabular cup to be implanted in an acetabulum of a pelvis of the patient; moving a femur of the patient relative to the pelvis, wherein the femur has a femoral part attached thereto and also attached to the distal end of the inserter, to pivot the acetabular cup in the acetabulum into a preselected anteversion angle; and impacting the inserter to impart an impaction force to the acetabular cup along the impaction axis so as to implant the acetabular cup in the acetabulum.

Moving the femur of the patient relative to the patient may comprise moving the femur into a preselected position relative to the pelvis of the patient. Moving the femur of the patient relative to the patient may comprise moving the femur into the Ranawat sign position. Moving the femur of the patient relative to the patient may comprise moving the femur into 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 method may further comprise releasably attaching the femoral part to the distal end of the inserter.

The femoral part may be attached to the distal end of the inserter at an acute angle relative to the impaction axis of 0° .

The femoral part may be attached to the distal end of the inserter at an acute angle relative to the impaction axis. The acute angle may be in the range of from 5° to 60°, or in the range of from 15° to 45°.

Attaching the femoral part to the distal end of the inserter may comprise attaching the femoral part to a selected one of a plurality of attachment formations at the distal end of the femur. Each of the plurality of attachment formations may correspond to a different anteversion angle and the selected one may correspond to the preselected anteversion angle.

The preselected anteversion angle may be in the range of 15° to 45°. The femoral part may be or may include a femoral neck. The femoral neck may be a trial femoral neck.

The femoral neck may include a taper at a free end. The femoral neck may be attached to the distal end of the inserter by the taper.

The taper may extend along a taper axis and a body of the femoral neck may extend along a neck axis and the taper axis and neck axis may subtend an acute angle corresponding to the preselected anteversion angle. The method may further comprise attaching the femoral neck to a femoral broach located in the femur of the patient. The impaction head may be in the form of a liner or a trial liner. The impaction head may be releasably attachable to the distal end of the inserter. The method may further comprise detaching the liner or trial liner from the distal end of the inserter and leaving the liner or trial liner in the acetabular cup after impacting the inserter. Preferred features of the first aspect of the invention may also give rise to be preferred method features of the fourth aspect of the invention.

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 I 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 1 1 shows a partial cross sectional perspective view of the pelvis along line C-C of Figure 10;

Figure 12 shows a perspective exploded view of an embodiment of an assembly according to an aspect of the invention and including an embodiment of an instrument according to an aspect of the invention; Figure 13 shows a first side elevation of a part of the instrument shown in Figure

12;

Figure 14 shows a second side elevation of the part of the instrument shown in Figure 13;

Figure 15 shows a plan view from a proximal end and along a longitudinal axis of the assembly shown in Figure 12 when assembled;

Figure 16 shows a first side elevation of the assembly shown in Figure 12 when assembled;

Figure 17 shows a second side elevation of the assembly shown in Figure 16; Figure 18 shows a cross-section along line A-A of Figure 17 of a distal part of the assembly of Figure 17;

Figure 19 shows a perspective view of the assembly shown in Figures 12, 15, 16 and 17 when assembled;

Figure 20 shows a flow chart illustrating an embodiment of surgical method according to an aspect of the invention in which the assembly may be used to position and implant an acetabular cup;

Figure 21 shows a perspective view of a part of a second embodiment of the assembly according to the invention in a first attachable state;

Figure 22 shows a perspective view of the of Figure 21 in a second detachable state;

Figure 23 shows a perspecti ve view of a distal part of a second embodiment of the instrument of the second embodiment of the assembly;

Figure 24 shows a perspective view of a distal part of the second embodiment of the assembly;

Figure 25 shows a side elevation of a part of a third embodiment of the assembly according to the invention for positioning an acetabular cup with a first selected orientation; and

Figure 26 shows a side elevation of a further part of a third embodiment of the assembly according to the invention for positioning an acetabular cup with a second selected orientation.

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 ML 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 postoperatively 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 1 10 and the medial femoral epicondyle 1 12. The femur 100 also has an anatomic axis 1 14 extending between, for example, the distal femur intercondylar notch 1 16 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 1 14 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 1 14, 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 1 14 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 o 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 ML 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-operativcly 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 ΛΡΡ 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 antevcrsion 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 1 1 , 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 1 1 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 1 1 is generally perpendicular to the direction of the inclination axis 222 of the acetabular cup. As illustrated in Figure 1 1 , 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 1 1 °.

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 antevcrsion projected into the same plane, which in this example is approximately 1 1 °. Hence, the combined anteversion of the hip joint 300 in this plane is about 3 1 °. 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 an exploded perspective view of

instrumentation 400 for inserting an acetabular cup according to a first embodiment of the invention. The instrumentation 400 generally comprises an inserter 410 and a femoral part 420. As illustrated in Figure 12, the femoral part 420 includes a first femoral part 422 which is receivable within a cavity formed within the intramedullary canal of a patient's femur. In the illustrated embodiment, the first femoral part 422 is in the form of a femoral brooch. However, in other embodiments, the first femoral part 422 may have other forms, such as a femoral stem, including prosthetic and trial components, or other femoral cutting devices or instruments which can be located in the femur or attached to the femur as part of a surgical procedure. The femoral component 420 also includes a second femoral part 424 which in the illustrated embodiment is in the form of a trial femoral neck. The trial femoral neck 424 is releasably attachable to a proximal, superior part of the femoral broach 422 via cooperating male and female attachment formations. A free end of the trial femoral neck 424 is in the form of a taper 426 on to which a trial femoral head may be releasably attached. In other embodiments, the femoral neck 424 may be attachable directly to a resected part of the femur of the patient rather than being mounted on a component inserted or implanted into the femur.

With further reference to Figures 13 and 14, the inserter 410 includes a main body 412 having a handle 414 at a proximal end and a releasable attachment mechanism 416 at a distal end for releasably attaching an impaction head 418. As illustrated in Figure 12, the impaction head 418 may be in the form o a liner and in particular a trial liner for an acetabular cup.

As best illustrated in Figure 12, the releasable attachment mechanism 416 comprises an end cap 430, a wave spring 432, illustrated in magnified form in Figure 12, a generally annular or ring shaped collar 434 and a formation 436 at a distal end of the main body 412. Wave spring 432 is provided between end cap 430 and collar 434 and acts to bias the collar away from the end cap 430 in the direction of the handle 414. A distal or end surface of end cap 430 bears a plurality o resilient wall members providing part of a push fit mechanism for releasably attaching the impaction head 418 to the remainder of the inserter 410 via a polar aperture 419 of the impaction head 418. End formation 436 includes a generally cylindrical wall 438 defining a cavity therein shaped and configured to receive a corresponding male feature 431 of the end cap 430 as best illustrated in Figure 18. The impaction force is transferred largely by parts 438 and 430 to the impaction head 418.

End formation 436 also includes a curved wall section 437 which co-operates with an 5 inner curved wall section of collar 434 to define a cavity into which the taper 426 can be releasably received in use. The user can push on the collar 434 against wave spring 432 to translate the collar slightly along the impaction axis 448 as illustrated n Figure 13. The taper 426 of the femoral component can then be placed adjacent curved wall 437 and the collar 434 released. The wave spring 432 acts to return the collar to surround curved wall 10 437 and close around the taper 426 thereby releasably connecting the femoral part to the inserter.

As best illustrated in Figures 1 and 14, the main body 412 of the inserter 410 includes a handle portion 414 at a proximal end which may be formed externally from a suitable

15 grippy material, such as a synthetic rubber or plastic. The body 412 of the inserter

instrument may extend through the outer handle and be formed from a harder material, such as a biocompatible metal or alloy, such as surgical grade stainless steel. A proximal free end of the main body 412 may extend slightly proud of the handle 414 to provide a strike element 440 to which an impaction force can be applied using a manual instrument, 0 such as a mallet or slap hammer or similar.

The linear handle portion of the main body 412 develops into a first diagonal portion 442, which develops into a second intermediate linear portion 444 which develops into a second diagonal portion 446 with the distal releasable attachment mechanism 416 at the 5 distal end thereof. As illustrated in Figure 14, and 17, the handle part 414 and distal part 416 of the inserter 410 are co-linear and each extend generally along an impaction axis 448 which extends generally longitudinally along the inserter instrument.

Figures 15, 16 and 17 show plan, first side elevation and second side elevation views of 0 the assembled instrumentation 400. As illustrated in Figures 15, 16 and 17, the impaction head 418 may be releasably attached to the detachment mechanism 416 at the distal end of the main body 412 of the inserter 410. As best illustrated in Figure 17, a polar axis of the impaction head 418, extending through the pole of the liner and passing perpendicularly to the plane of the mouth of the liner is co-linear with the impaction axis 448 of the inserter 410. Hence, if an impaction force is applied to the plate 440 then the impaction force is transmitted along the impaction axis 448 and generally along the polar axis of the impaction head 418. The impaction head 418 is shaped and dimensioned to be received within and coupled to an acetabular cup so as to allow the impaction force to be transmitted from the impaction head 418 to the acetabular cup in use.

As illustrated in Figures 15, 16 and 17, in the assembly 400 of the instrumentation, the femoral part 420 is releasably attached to the impaction head 418 via the taper 426 of the femoral neck being inserted within the socket defined by curved wall 438.

Figure 18 shows an expanded cross sectional view through the distal part of the instrumentation shown in Figure 17 along line A-A. In the assembled configuration, the taper 426 of the trial head is received within a socket formation formed by the collar 434 and the curved wall 437, the end face of the taper abuts part 438 and the end cap 430 abuts the inner surface of the trial liner so as to transfer the impaction force to the impaction head with the end cap 430 seated at a polar region of the impaction head with the flexible tabs engaged in the polar cavity 419 to releasably attach the liner 418 to the remainder of the inserter 410. The biasing wave spring 432 acts to urge the collar 434 away from the end cap 430 to form the socket in which the taper is received. When the releasable attachment mechanism is first introduced into the liner, the cap 430 and flexible tabs can be initially push fit into the polar cavity 419 and seat at the polar region of the liner. Wave spring 432 causes collar 434 to 'pop up' to capture the taper of the neck 426 against the cylindrical face 437. Initially the user puts the acetabular cup loosely into the patient's acetabulum and then brings the femoral component 420 generally into alignment. The user pushes down on the collar 434 against the action of wave spring 432 to allow the neck 424 and taper 426 to be correctly positioned without having to distract the femur excessively. The user can then release the collar 434, thereby capturing the femoral component into the assembly. The same process is used in reverse to disengage the femoral component after impaction. As particularly illustrated in Figure 17, the majority of the inserter between the handle 414 and the impaction head 418 is offset laterally, or to the side, of the impaction axis 448. As illustrated in Figures 15, 16 and 17, the broach 422 extends partially along the impaction axis 448 and also laterally thereto and in use will be received in the

intramedullary cavity of a patient's femur. Hence, the lateral offsetting of the majority of the body of the inserter instrument can accommodate the patient's femur and any other local parts of the patient's anatomy during use of the inserter to implant an acetabular cup, as described in greater detail below. Figure 19 shows a perspective view of an assembly 400 of the instrumentation according to the invention including the inserter instrument 410 and the femoral part 420. As illustrated in Figure 1 and particularly in Figures 16 and 17, the neck axis, extending generally along the neck of the trial neck 424 of the femoral part, is also co-linear with the impaction axis 448 of the inserter instrument 410.

The first embodiment of the instrumentation 400 illustrated in Figures 12 to 19 is particularly suitable for use in a surgical procedure utilising the Ranawat sign approach as will now be described in greater detail below. With reference to Figure 20 there is shown a flow chart illustrating a hip replacement surgical procedure 500 in which the inserter instrument 410 and instrumentation assembly 400 may be used to implant a prosthetic acetabular cup. As will be apparent to a person of ordinary skill in the art from the following, the order of some of the steps is not relevant, but the order of some of the steps may be relevant as will become apparent from the following description. Also, some of the described steps may be optional, and may be omitted, depending on a particular workflow that a surgeon may prefer. Also, some of the details of the procedure and steps are omitted for the sake of clarity or explanation of the present apparatus. At 502, the femur is prepared in a generally conventional manner, which may include resecting the native femoral neck and head. Then, at 504, a cavity is formed generally along the intramedullary canal which will later be used to accept a femoral stem implant. Preparation of the cavity typically includes the use of one or more brooches and / or rasps. When a final sized broach, e.g. broach 422, has been used, then a broach handle is removed and the broach 422 is left in the femur. At 506, the acetabulum is prepared in a generally conventional manner which may include removing soft tissues and forming a hemispherical cavity within the native acetabulum using an acetabular femur. After the acetabulum has been prepared, then at 508, the acetabular cup implant, i.e. the final cup rather than a trial cup, is generally placed loosely in the acetabulum and manually oriented in the generally appropriate orientation relative to the patient's pelvis, but not yet impacted in position. The patient has already been positioned on the operating theatre table with the pelvis in a lateral decubitus position in which the patient is lying laterally (i.e. on their side) so that their ASIS-AS1S axis (transverse axis) is generally vertical and their sagittal plane is generally parallel to the floor. Preferably, their pelvis should not be rotated or flexed, that is their inferior-superior axis should be pointing up the table towards their head.

At 510, the assembly 400 of the instrumentation is put together. The trial femoral neck 424 is attached to the broach 422 which is located in the patient^'s femur. The trial liner 418 is clipped to the end of the inserter 410 via the releasable attachment mechanism 416. The trial liner 418 is then introduced into and coupled to the prosthetic acetabular cup which has been loosely placed in the patient's acetabulum. The patient's femur is then manipulated so as to position the taper 426 of the trial neck 424 adjacent the socket defined in the impaction head 418. The collar 434 is pushed against wave spring 432 and the taper 426 located against curved wall 437 before the collar is released to capture the taper 426 so as to form the assembly 400. At this stage, the hip joint has effectively been reduced, corresponding to step 512 with the hip joint being generally formed by the femoral part 420, the impaction head 418, in this case in the form of a trial liner, and the acetabular cup which has not yet been implanted.

Then, at 514, the surgeon can manipulate the pelvis and / or the patient's femur so as to position the femur relative to the pelvis in the Ranawat Sign position are generally known in the art. More specifically, with the patient in the true lateral decubitus position as described above, the femur is internally rotated without hip flexion until the impaction axis is generally perpendicular to the plane of the mouth o the acetabulum. The amount of internal rotation necessary to achieve this corresponds to the Ranawat sign and relates to the combined anteversion of the femoral and acetabular components

As the femoral part 420 is received in the femur of the patient, and as the femoral part 420 is coupled to the inserter instrument 410, and as the impaction head 418 is coupled to the acetabular cup, as the femur is moved relative to the pelvis, the acetabular cup will pivot within the acetabulum, similarly to a ball and socket joint. Hence, the patient's femur is effectively used as a long and accurate lever to pivot the acetabular cup within the acetabulum. Once the patient's femur is placed in the Ranawat Sign position relative to the pelvis with the impactor axis generally perpendicular to the plane of the mouth of the patient's acetabulum, then the surgeon can determine that the orientation of the acetabular cup relative to the patient^'s pelvis is appropriate. Hence, at 514, the surgeon can manipulate the patient's pelvis and / or the femur to adopt the Ranawat Sign position and effectively use the patient^'s femur to correctly orient the acetabular cup relative to the pelvis.

At 516, with the acetabular cup in the appropriate position, the surgeon can then use a mallet, slap hammer or similar, to implant the acetabular cup by striking the plate 440 at the proximal end of the inserter 410 so as to impact and implant and acetabular cup in the patient's acetabulum. Hence, the instrumentation assembly 400 can be used together with the patient's femur, to correctly orient the acetabular cup relative to the patient's pelvis before implantation.

The assembly of instrumentation may then be disassembled. The collar 434 is pushed against the wave spring 432 to release the taper 424. In embodiments in which the impaction head 418 is in the form of a trial liner, as illustrated in Figures 12 to 19, then the remainder of the inserter 410 may be detached from the trial liner 418 which is left in place in the implanted acetabular cup. In other embodiments in which the impaction head is not a trial liner, then a trial liner may optionally be added to the acetabular cup, if used. In other embodiments, no trial liner may be used. Further, at 51 , in embodiments in which the femoral component does not include a trial neck, but some other attachment mechanism for attaching the femoral component to the inserter, then a trial neck may be attached to the femur. A trial femoral head may then be attached to the taper 426 of the trial neck and the trial joint reduced at 518. At 520, optionally, a range of motion assessment may be carried out and / or other assessments of the trial joint carried out. At 522, the trial components may be removed, and the broach 422. At 524, the trial liner may be removed and a final liner may be introduced into the implanted acetabular cup. The femoral stem and head may be implanted at 526 into the femur. Finally, the final joint reduction may be carried out at step 530 after which the surgical procedure is generally finished and ends in a conventional manner.

It will be appreciated that some of the trial! ing steps, e.g. 518 to 522 are entirely optional as is the use of a liner which will depend on the particular prosthetic system being used.

Hence, the instrumentation 400 of the first embodiment of the invention is particularly suitable when the patient's joint is placed in the Ranawat Sign position in order to implant the acetabular cup. Other embodiments of the instrumentation may be used and / or be particularly suitable for other hip positions so to similarly orient the acetabular cup using the instrumentation which is driven by the position of the patient's femur so as to correctly orient the acetabular cup relative to the patient's pelvis.

With reference to Figures 21 to 24, there are shown various parts of a second embodiment of the instrumentation according to the invention.

Figure 21 shows a second embodiment of the femoral part which includes the femoral broach 422 and a second embodiment of the releasable attachment part 550 of the femoral part 420. Similarly to the trial femoral neck 424, the second part of the femoral part 420 is releasably attachable to an upper or superior part of the femoral broach 422. However, in the second embodiment, the second part 550 includes a housing 552 which houses a retractable pin 554 which is actuable via a slider 556. As illustrated in Figure 21 , in a first state, the pin 554 protrudes from the housing 552. In a second state, illustrated in Figure 2, by operating slider 556, the pin 554 can be retracted into the housing 552.

Figure 23 shows a perspective view of the impaction head 560 of a second embodiment of the inserter 410. In the second embodiment, the impaction head 560 has the form of a generally disc shaped member and includes a plurality of tongues, e.g. tongue 562 extended from a side wall 564 and that a plurality of angular positions around the impaction head 560. The tongues 562 may provide an anti-rotation device and may be arranged to interact with correspondingly shaped and positioned recesses defined within the rim of the acetabular cup and in order to control the angular position of the impaction head 560 relative to the acetabular cup (not shown). As can be seen in Figure 23, the distal diagonal limb 446 of the main body 412 of the inserter is permanently attached to an upper surface of the impaction head 560.

The upper surface of the impaction head 560 has a generally convex or dome shaped surface and includes a plurality of recesses defined therein. Each of the plurality of recesses provides an attachment formation into which the pin 554 of the femoral part 420 can be introduced to releasably attach the femoral part to the impaction head of the inserter. For example, a first recess 570 is positioned generally at the apex of the upper surface and at the centre of the impaction head 560.

Hence, when the pin 554 is inserted in the apical recess 570, an arrangement similar to that shown in Figures 15 to 19 is achieved in which the neck axis of the femoral component is co-linear with the impaction axis 448 of the inserter. Hence, in this configuration, the instrumentation may be used in a similar manner to that described above with the patient femur in the Ranawat Sign position so as to appropriately set the desired level of anteversion of the acetabular cup before impacting the cup. The provision of a plurality of recesses in the impaction head 560 allows the femoral part 420 to be releasably attached to the impaction head 560 with a plurality of different orientations. The domed upper surface of the impaction head 560 has a radius of curvature such that each of the cavities is oriented toward a common centre of rotation and which generally corresponds to the centre of the mouth of the acetabular cup with which the impaction cap 560 is going to be used. In other embodiments, a flat planar face could be used but with the holes drilled in at an angle directed toward the common centre of rotation. However, the use of a spherical face may be preferable as it may help to keep the joint tension similar no matter which hole is selected. The plurality of attachment points for the femoral part 420 means that the same instrumentation can be used for different surgical approaches and / or different relative positions of the femur and pelvis and / or different anteversion angles of the acetabular cup as described in greater detail below.

As illustrated in Figure 23, seven groups of four attachment locations are provided on the impaction head 560. Each group comprises four attachment points located along a common radial direction. Each group of four attachment points is positioned at a different angular position about the centre of the impaction head 560. Each radial position may correspond to a different anteversion angle of the acetabular cup. For example, for a first group of four attachment points 572, the innermost cavity corresponds to a combined anteversion angle of approximately 15°, the next to a combined

anteversion angle of approximately 25°, the next to a combined anteversion angle of approximately 35° and an outermost one to a combined anteversion angle of

approximately 45° for the acetabular cup and femoral component.

The instrumentation is generally intended to make angular adjustments around the version axis (the axis created by an intersection of the cup face and the coronal plane of the patient). If the stem-neck angle is 135° and the cup inclination is 45° then the neck axis and the cup axis would be perfectly aligned and the angular values of the different attachment points would be true and exact. That is, the attachment point corresponding to 15° anteversion would subtend an angle of 15° relative to attachment point 570, and similarly for the other anteversion angle attachment points.

However, the target inclination for an acetabular cup is generally closer to 40° and, depending on the implant system, the stem -neck axis may be 125°, 130° or 135°. Hence, in practice the neck axis and cup axis may not be perfectly aligned. However, in practice any differences in alignment of the cup axis and the stem-neck axis are small and the same head 560 may be used for a 40° cup inclination and a variety of stem-neck angles. In other embodiments, the angular separation between the attachment points may be adjusted to compensate for the non-alignment of the cup axis and neck axis so that they are appropriately angled to arrive at a cup anteversion angle sufficiently close to the indicated total anteversion angles of 15°, 25°, 35° and 45° for a specific stem-neck angle and a cup inclination of 40°.

In the method illustrated in Figure 20, rather than placing the patient's femur in the Ranawat Sign position, the patient's femur may be placed in an anatomical position defined as follows. In the anatomical position, the patient's leg is placed with the femur in 0° of flexion / extension, 0° of adduction / abduction and 0° of internal / external rotation. Assuming that the pelvis on the operating table has taken up an approximately neutral amount of pelvic tilt, then the anatomical position can be achieved by comparing the following 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. An internal / external rotation angle of 0° can be checked using the epicondyle 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 epicondyle 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 of the femoral articular axis which would indicate any internal / external rotation of the femur. Hence, depending on the orientation of the patient on the table, the patient^'s legs may be placed in appropriate positions to provide 0° of flexion / extension, 0° of abduction / adduction and 0° of internal / external rotation of the femur with respect to the pelvis. With the patient's leg in this anatomical position, the acetabular cup may be oriented relative to the patient's pelvis at step 514 using the instrumentation.

If the desired combined anteversion for the cup is 35° then the femoral component 420 is attached to the impaction head 560 by inserting the pin 554 in the cavity, e.g. 576, corresponding to 35° of combined anteversion for the acetabular cup. Hence, by moving the patient's leg and femur into the anatomical position, the acetabular cup will pivot within the patient's acetabulum similarly to a ball and socket joint in which the patient's femur acts as the lever to drive the orientation of the acetabular cup relative to the pelvis. Once the patient's leg has been appropriately positioned in the anatomical position, then the acetabular cup can be inserted by impacting the inserter instrument as described above.

The different angular positions of the groups of attachment positions, e.g. second group 5 574, allows the same instrumentation to be used for different approaches. For example, the first set of four attachment positions, 572 may be suitable for a right anterior approach, whereas the second group of four attachment positions 574 may be more suitable for a left anterior approach. The groups of attachment positions 577 and 578 adjacent the impactor limb 446 may be more suitable for posterior-lateral approaches.0 Hence, the multiple groups of attachment positions allows the same set of instrumentation to be used for right or left hip joints, with different surgical approaches and/or different patient positions on the operating theatre table.

Therefore, using the first instrumentation, the patient's leg is generally used to pivot the acetabular cup to provide the desired level of anteversion using the Ranawat Sign technique before impacting the cup into position. Using the second embodiment, the patient^'s leg is similarly used to pivot the acetabular cup, but the leg can be kept in full extension with generally neutral version which can be easier and more repeatable for the surgeon. In this second embodiment, the user can select the desired angle of combined anteversion by selecting the appropriate attachment location of the femoral part to the impaction head which effectively varies the angle subtended between the polar axis or the acetabular cup and the neck axis of the femur. As noted above, the impaction axis 448 of the inserter remains generally aligned with the acetabular cup axis throughout and therefore once the patient's leg has been appropriately positioned to set the appropriate orientation of the acetabular cup, the surgeon can simply impact the cup into position by striking on plate 440.

Figure 24 shows a perspective view of the distal end of the instrumentation when assembled with the femoral part 420 attached to the impaction head 560 at a position corresponding to a combined anteversion angle of 35° for the acetabular cup and with the impaction head 560 coupled to an acetabular cup 580. In a third embodiment of the instrumentation according to the invention, the femoral part may be varied as to as to use the instrumentation with the patient's leg in an anatomical position. Similarly to the second embodiment, the anteversion angle of the acetabular cup may be selected by using different parts. Essentially, the first embodiment is modified so that the femoral component 420 is attachable to the impaction head 418 so that it is not parallel with the impaction axis 448. Rather, the femoral component 420 is modified so that the neck axis of the femoral component and the impaction axis 448 of the

instrumentation subtends an acute angle generally corresponding to the intended combined anteversion angle of the acetabular component.

One way of achieving this effect is to use a bent trial neck in which the free attachment end is tilted relative to the neck axis o the femoral part 420.

For example, Figure 25 shows a view in the generally lateral to medial direction of a further embodiment of the femoral part 600 including the femoral broach 422 and a further embodiment o the trial neck 610. Similarly to trial neck 424, trial neck 610 includes a body 612 which is releasably attachable to a superior part of broach 422 via mating male and female formations. The body 612 extends generally along the neck axis 614. However, the neck 610 is bent such that the taper 426 at a free end of the trial neck 610 is tilted relative to the neck axis 614. As illustrated in Figure 25, the taper (not shown) extends along a taper axis 616 which is tilted relative to the neck axis 614 and which subtend an acute angle of approximately 35°.

Figure 25 shows selected components of the resulting trial joint arising from use of the bent trial neck 610. When the bent trial neck 10 is used in place of straight trial neck 424 in the instrumentation shown in Figure 400, then the patient^'s leg can be placed in the anatomical position in order to rotate the acetabular cup within the prepared acetabulum to adopt a combined anteversion angle of approximately 35° for impaction. The trial liner 418 generally adopts the same orientation as the same acetabular cup (not shown in Figure 25). As illustrated in Figure 25, a trial femoral head 61 8 has been mounted on the bent trial femoral neck 610 at step 518 to form the trial joint. As can be seen, with the patient^'s leg in the anatomical position, the acetabular cup, with the trial liner 418 provided therein, may be implanted with a combined anteversion angle of approximately

35°.

As discussed above, depending on the design of the implant neck, the stem-neck can be at 125, 130 or 145 degrees and typically cups are put in at 40 degrees of inclination, and not 45°. So for a cup 418 inclined at 40°, the 35° of neck tilt in Figure 25 would not correspond exactly to 35° combined anteversion but would be sufficiently close for practical purposes. In other embodiments, the tilt angle may be adjusted away from 35° to compensate for the non-alignment of the neck and cup axis and so that the cup anteversion angle will be even closer to the target combined anteversion angle of 35°.

For other preselected positions of the patient's femur relative to the pelvis and / or for the same anatomical position but with a different desired combined anteversion angle, a different bent trial neck may be used. For example, Figure 26 shows a further bent trial neck 620 mounted on the femoral broach 422. Again, trial neck 620 includes a body 622 extending generally along the neck axis 614. The trial neck taper is tilted relative to the neck axis 614 and the taper axis 626 subtends an acute angle of approximately 20° with the neck axis 614. Hence, the second bent trial neck 620 may be used with the instrumentation illustrated in Figure 12 to implant an acetabular cup at a combined anteversion angle of approximately 20° when the patient's hip joint is placed in the anatomical position by suitable manipulating the patient^'s pelvis and / or femur.

It will be appreciated that other bent trial necks defining other anteversion angles may be provided, for example as a kit of parts so that he searching can select which bent trial neck to use during the procedure depending on the position of the patient and / or the surgical approach and / or the desired anteversion angle of the acetabular cup.

It will be appreciated that other specific forms of the instrumentation can be provided and used. For example, in other embodiments, the femoral part may be permanently, or non- releasably, attached to the distal end of the inserter. Hence, the femoral part of the instrumentation is then coupled to the patient^'s femur in use, for example by being screwed or otherwise fixed or fastened to the femur or by coupling to some other femoral part attached to the femur, such as a femoral tool, instrument or implant, for example a rasp, a broach, or a femoral stem. All that is required is that there is some mechanism for transferring the torque arising from moving the patient's femur to the inserter and impaction head so as to cause the acetabular cup to pivot within the acetabulum as the orientation of the femur relative to the pelvis is varied.

Also, in embodiments in which the femoral part is releasably attachable to the distal end of the inserter, other attachment formations and mechanism different to those specifically described may also be used. The instrumentation may therefore be used with the patient in different positions and/or using different surgical approaches and/or to place acetabular cups with various different target cup anteversion angles for a wide range of patients.

Hence, the invention improves the reliability with which a prosthetic acetabular cup may be implanted in a patient with a target orientation relative to the pelvis and in particular with a specific anteversion.

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. Instrumentation for implanting a prosthetic acetabular cup in an acetabulum of a patient, including:

an inserter, comprising:

a handle at a proximal end of the inserter;

an impaction head at a distal end of the inserter, wherein the impaction head is configured to couple with an acetabular cup in an acetabulum of a patient and to transmit an impaction force to the acetabular cup and wherein the handle and the impaction head are arranged to define an impaction axis of the inserter extending along the inserter; and

a first attachment formation at the distal end of the inserter; and a femoral part attachable to a femur of the patient and having a second attachment formation which is releasably attachable to the first attachment formation, wherein when the femoral part is attached to the inserter by the first attachment formation and the second attachment formation in use, a change in orientation of the femoral part causes a change of orientation of the inserter and the impaction axis.

2. Instrumentation as claimed in claim 1 , wherein the femoral part extends at least partially along a femoral neck axis and wherein the femoral neck axis is collinear with the impaction axis.

3. Instrumentation as claimed in claim 1, wherein the femoral part extends at least partially along a femoral neck axis and wherein the femoral neck axis and the impaction axis subtend an acute angle in the range of 15° to 45°.

4. Instrumentation as claimed in claim 1 , wherein the femoral part extends at least partially along a femoral neck axis and wherein the femoral part is configured such that the femoral neck axis and the impaction axis pass through a common pivot point corresponding to the centre of a sphere corresponding to the acetabular cup.

5. Instrumentation as claimed in any of claims 1 to 4, wherein the inserter includes a third attachment formation at the distal end of the inserter and wherein the second attachment formation is releasably attachable to the third attachment formation and wherein when the femoral part is attached to the inserter by the first attachment formation and the third attachment formation in use, a change in orientation of the femoral part causes a change of orientation o the inserter and the impaction axis.

6. Instrumentation as claimed in claim 5, wherein the first attachment formation and the third attachment formation are positioned to correspond to different anteversion angles of the acetabular cup.

7. Instrumentation as claimed in claim 5 or 6, wherein the first attachment formation and the third attachment formation are positioned to correspond to different surgical approaches to implanting the acetabular cup.

8. Instrumentation as claimed in claim 5 or 6, wherein the first attachment formation corresponds to a right hip and the third attachment formation corresponds to a left hip.

9. Instrumentation as claimed in claim 7 or 8, wherein the first attachment formation corresponds to an anterior approach and the third attachment formation corresponds to a posterior approach.

10. Instrumentation as claimed in any preceding claim, wherein the impaction head has a hemispherical shape configured to be received within an acetabular cup cavity.

11. Instrumentation as claimed in any preceding claim, wherein the impaction head has a circular disc shape configured to engage with an acetabular cup mouth.

12. Instrumentation as claimed in any preceding claim, wherein the inserter includes an intermediate portion between the handle and the impaction head and wherein the intermediate portion is offset to the impaction axis.

13. Instrumentation as claimed in any preceding claim, wherein the first attachment formation is part of the impaction head.

14. Instrumentation as claimed in any of claims 1 to 12, wherein the inserter includes an inserter body and wherein the first attachment mechanism is part of a distal end of the inserter body.

15. Instrumentation as claimed in any preceding claim, wherein the inserter includes an inserter body and wherein the impaction head is releasably attachable to a distal end of the inserter body

16. Instrumentation as claimed in claim 15, wherein the impaction head is a liner or a trial liner for an acetabular cup.

17. Instrumentation as claimed in claim 16, wherein the liner or the trial liner includes an apical formation arranged to releasably attach to a distal attachment formation at the distal end of the inserter body.

18. Instrumentation as claimed in any preceding claim, wherein the femoral part extends at least partially along a femoral neck axis and wherein the second attachment mechanism extends along an attachment axis, and wherein the femoral neck axis and the attachment axis is subtend and acute angle in the range of 15° to 45°.

19. instrumentation as claimed in any preceding claim, wherein the femoral part is or incudes a femoral neck.

20. Instrumentation as claimed in claim 19, wherein the second attachment formation is a taper at a free end of the femoral neck and wherein the first attachment formation is a socket configured to releasably receive the taper therein.

21. Instrumentation as claimed in claim 20, wherein the first attachment formation includes a translatable collar and a curved wall and wherein a curved portion of the translatable collar and the curved wall define the socket.

22. Instrumentation as claimed in claim 20, wherein the femoral neck is a trial femoral neck.

23. Instrumentation as claimed in claim 22, wherein the femoral part also includes an insert configured to be received within a cavity with the femur of the patient and wherein the insert includes an insert attachment formation by which the trial femoral neck is attachable to the insert.

24. Instrumentation as claimed in claim 23, wherein the insert is selected from: a femoral broach; a femoral rasp; a trial femoral stem; and a prosthetic femoral stem.

25. Instrumentation as claimed in any of claims 20 to 24, wherein the taper is tilted relative to a body of the femoral neck.

26. Instrumentation as claimed in any preceding claim, wherein the instrumentation is configured to orient the acetabular cup for implantation in the acetabulum of the patient with a target anteversion angle when the femur of the patient is positioned at a preselected position relative to the pelvis of the patient.

27. Instrumentation as claimed in claim 26, wherein the target anteversion angle corresponds to a combined anteversion of 15° to 45°.

28. Instrumentation as claimed in claim 27, wherein the preselected position is the Ranawat sign position.

29. Instrumentation as claimed in claim 27, wherein, wherein the preselected position is the anatomical position.

30. Instrumentation as claimed in claim 29, wherein the anatomical position corresponds substantially to 0° extension/flexion of the leg of the patient, 0°

abduction/adduction of the femur and 0° rotation of the femur.

31. An assembly of the instrumentation of any preceding claim, wherein the femoral part is attached to the inserter by the first attachment formation and the second attachment formation.

32. Instrumentation for implanting a prosthetic acetabular cup in an acetabulum of a patient, including:

an inserter, comprising:

5 a handle at a proximal end of the inserter; and

an impaction head at a distal end of the inserter, wherein the impaction head is configured to couple with an acetabular cup in an acetabulum of a patient and to transmit an impaction force to the acetabular cup and wherein the handle and the impaction head are arranged to define an impaction axis of the inerter 10 extending along the inserter; and

a femoral part attachable to a femur of the patient and attached to the distal end of the inserter, wherein, in use, a change in orientation of the femoral part causes a change of orientation of the inserter and the impaction axis.

15 33. A method for implanting a prosthetic acetabular cup in an acetabulum of a patient using an inserter comprising a handle at a proximal end of the inserter and an impaction head at a distal end of the inserter wherein the handle and the impaction head are arranged to define an impaction axis of the inerter extending along the inserter, the method comprising:

0 coupling the impaction head to an acetabular cup to be implanted in an

acetabulum of a pelvis of the patient;

moving a femur of the patient relative to the pelvis, wherein the femur has a femoral part attached thereto and also attached to the distal end of the inserter, to pivot the acetabular cup in the acetabulum into a preselected anteversion angle; and

5 impacting the inserter to impart an impaction force to the acetabular cup along the impaction axis so as to implant the acetabular cup in the acetabulum.

34. The method of claim 33, wherein moving the femur of the patient relative to the patient comprises moving the femur into the Ranawat sign position.

0

35. The method of claim 33, wherein moving the femur of the patient relative to the patient comprises moving the femur into an anatomical position 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.

36. The method of any of claims 33 to 35, and further comprising releasably attaching 5 the femoral part to the distal end of the inserter.

37. The method of claim 36, wherein the femoral part is attached to the distal end of the inserter at an acute angle relative to the impaction axis of 0° or in the range of from 15° to 45°.

10

38. The method of claim 36 or 37, wherein attaching the femoral part to the distal end of the inserter comprises attaching the femoral part to a selected one of a plurality of attachment formations at the distal end of the femur.

15 39. The method of claim 38, wherein each of the plurality of attachment formations corresponds to a different anteversion angle and the selected one corresponds to the preselected anteversion angle.

40. The method of any of claims 33 to 39, wherein the preselected anteversion angle 20 is in the range of 15° to 45°.

41. The method of any of claims 33 to 40, wherein the femoral part is or includes a femoral neck.

25 42. The method of claim 41 , wherein the femoral neck includes a taper at a free end and wherein the femoral neck is attached to the distal end of the inserter by the taper.

43. The method of claim 42, wherein the taper extends along a taper axis and a body of the femoral neck extends along a neck axis and wherein the taper axis and neck axis

30 subtend an acute angle corresponding to the preselected anteversion angle.

44. The method of any of claims 4! to 43, and further comprising attaching the femoral neck to a femoral broach located in the femur of the patient.

45. The method of any of claims 33 to 44, wherein the impaction head is in the form of a liner or a trial liner and wherein the impaction head is releasably attachable to the distal end of the inserter, and further comprising:

detaching the liner or trial liner from the distal end of the inserter and leaving the liner or trial liner in the acetabular cup after impacting the inserter.