The present invention relates to apparatus and methods for hip surgery and in particular to apparatus and methods for providing surgeons with visual guidance for the positioning of acetabular cups during hip replacement surgery.

The reasons for hip replacement surgery may vary between patients, but a common reason is degradation of the bone in the hip joint. Hip replacement surgery generally involves the replacement of one or more parts of the hip joint with prosthetic components. The natural hip joint is a ball and socket joint in which the femoral head articulates within the acetabulum of the pelvis. A total hip replacement involves the replacement of the native femoral head with a prosthetic femoral head and replacement of the acetabulum with a prosthetic acetabular cup. In some instances the prosthetic acetabular cup may comprise a shell and a liner which provides the articulating surface. A partial hip replacement generally involves replacement of the acetabulum only.

The femoral component for implanting in the patient's femur often includes a stem which is located in cavity formed during surgery in the femoral intramedullary canal. The femoral head is often attached to the stem by a neck so that the femoral head is located superiorly and medially of the stem and provides a convex articulation surface. The femoral head is received in the cup component with the convex articulation surface of the head in contact with the concave articulation surface of the cup component.

It is important to ensure that the acetabular cup component is oriented appropriately so that the resulting prosthetic hip joint behaves well, for example has good stability and a sufficient range of motion during articulation. The orientation of the cup component is generally defined by two angles: its version and its abduction. Generally speaking the version of the acetabular cup is the angular amount by which the cup is pivoted toward the anterior of the patient (referred to as anteversion) or toward the posterior of the patient (referred to as retroversion). The abduction, or inclination, is the angular amount by which the cup is tilted in the inferior direction. Assessment of the orientation of a cup component intraoperatively is often done by the surgeon by eye, and based on experience, and can have varying degrees o success. Typically this involves an estimate of the orientation of the native acetabulum from a pre-operative X-ray o the hip joint and then taking that native orientation into account when placing the cup component during surgery.

The positioning of each o the femoral component in the femur and the acetabular cup in the pelvis is important so as to provide good joint stability and avoid impingement of the femoral neck and cup which could otherwise be a cause of dislocation, accelerated wear, and pain in patients.

Hip joint replacement procedures can be carried out with the patient in a number of di fferent positions, for example lying on their side in a lateral position or lying on their back in a supine position. The position of the patient will determine how the surgeon is positioned, the surgeon's field of view of the surgical site, the surgeon's physical access to the surgical site and the way in which the surgeon can make an assessment of the orientation of the acetabular cup. When the patient is lying laterally, the surgeon may use a posterior approach in which an incision is made on a posterior region of the hip of the patient. When the patient is supine, the surgeon may use an anterior approach in which the surgeon makes an incision on an anterior region of the patient's hip. The surgeon may also use a direct lateral approach when the patient is either in the lateral or supine positions. The view of the hip joint, the pelvis and in particular the acetabulum will vary depending upon where the surgeon is standing and this can affect how the surgeon assesses the orientation of the acetabular component.

Hence, instruments and/or methods which would assist a surgeon in more reliably orienting an acetabular cup and/or assessing acetabular cup orientation during a hip replacement procedure would be beneficial.

A first aspect of the invention provides an alignment guide for guiding insertion of an indicator component into the pelvis of a patient during a hip replacement surgical procedure, comprising: a support attachable to a femoral neck along a neck axis of the femoral neck; and a guide connected to the support, the guide being configured to orient the indicator component along an insertion axis, wherein the insertion axis and neck axis subtend an acute angle corresponding to a target combined anteversion of the hip joint.

The indicator component may be a pin.

The acute angle may be in the range of 10° to 50°, or .25° to 45°. The acute angle may be substantially 35°.

The alignment guide may include a further guide connected to the support. The further guide may be configured to orient a further indicator component along the neck axis, when the alignment guide is attached to the femoral neck in use. The further guide may be in the form of a channel. The channel may be directed along the neck axis and may also extend in a direction perpendicular to the neck axis so that the position of the further indicator component can be varied.

The or each guide may be a mechanical guide.

The or each mechanical guide may be a channel directed along the insertion axis. The channel may be a closed channel or an open channel.

The guide may be a visual guide.

The visual guide may include an indicium corresponding to the insertion axis.

The visual guide may include further indicia each corresponding to a different acute angle. The or each indicium may be in the form of a line. The or each indicium may be provide by a male formation, such as a rib or similar, or a female formation, such as a groove or similar, or a combination of male and female formations. The alignment guide may further comprise a yet further guide.

The yet further guide may be a visual guide.

The visual guide may comprise a plurality of indicia each corresponding to a different acute angle to the neck axis.

The support may include at least one attachment formation or a plurality of attachment formations. The or each attachment formation may be configured to penetrate bone. The or each attachment formation may be a spike or spiked male formation.

The or each attachment formation may be configured to interact with a trial femoral neck to mount the alignment guide on the trial femoral neck. The trial femoral neck may include a corresponding attachment formation. The or each corresponding attachment formation may be a female formation.

The support may be configured to be attachable to a superior surface of the femoral neck. The hip replacement surgical procedure may use a posterior approach. A second aspect of the invention provides an alignment guide for guiding insertion of an indicator component into the pelv is of a patient during a hip replacement surgical procedure, comprising: a support attachable to a femoral neck along a neck axis of the femoral neck; and a guide connected to the support, the guide being configured to orient the indicator component along an insertion axis, wherein the insertion axis and neck axis are perpendicular.

The indicator component may be a pin. The guide may be a mechanical guide.

The mechanical guide may be a channel directed along the insertion axis. The channel may be a closed channel or an open channel.

The guide may be a visual guide.

The visual guide may include an indicium corresponding to the insertion axis.

The alignment guide may further include an adjustment mechanism whereby the position of the guide is adjustable relative to the support.

The adjustment mechanism may be an articulated limb. The articulated limb may include a first arm pivotably connected to the support. The articulated limb may include a second arm pivotably connected to the first arm. A free end of the second arm may include the guide.

The support may include one or a plurality of attachment formations each configured to penetrate bone and the femoral neck may be a native femoral neck.

The or each attachment formation may be configured to interact with a trial femoral neck to mount the alignment guide on the trial femoral neck. The support may be configured to be attachable to an inferior surface of the femoral neck.

The hip replacement surgical procedure may use an anterior approach.

Preferred features of the first aspect may also be preferred features of the second aspect and vice versa. A third aspect of the invention provides a kit of parts comprising: the alignment guide of the first aspect or the second aspect and a trial femoral neck.

The kit of parts may further comprise an indicator component or a plurality of indicator components. The or each indicator component may be a pin.

When the kit of parts includes the alignment guide of the second aspect, the kit of parts may further comprise a cup inserter guide including a guide formation defining an inserter guide axis and configured to guide a cup inserter instrument along the insertion axis.

The cup inserter guide may include a handle. The guide formation may be a ring or a cylinder.

The kit of parts may further comprise an acetabular cup inserter.

The kit o parts may further comprise a trial femoral head.

The kit of parts may further comprise a femoral broach. The femoral broach may include a releasable attachment mechanism by which the trial femoral neck can be releasably attached to the femoral broach.

A fourth aspect of the invention provides an assembly of the kit of parts o the third aspect. The indicator component may be oriented along the insertion axis by the guide.

A fifth aspect of the invention provides a femoral neck for guiding insertion of an indicator component into the pelvis of a patient during a hip replacement surgical procedure, comprising: a base which is releasably attachable to a broach; a shaft extending along a neck axis; an attachment formation for releasably attaching a femoral head at a free end of the shaft; and a guide on the shaft, the guide being configured to orient the indicator component along an insertion axis, wherein the insertion axis and neck axis subtend an acute angle corresponding to a target combined anteversion of the hip joint.

The femoral neck may comprising a further guide on the shaft, the further guide being configured to orient the indicator component along a further insertion axis, wherein the further insertion axis and neck axis subtend an acute angle corresponding to a target combined anteversion o the hip joint. The guide may be configured for use of the femoral neck with a right hip and the further guide may be con figured for use of the femoral neck with a left hip.

The guide and the further guide may be on a superior surface f the neck.

The guide and the further guide may be on an inferior surface f the neck. The or each guide may be a visual guide.

The visual guide may be or may include at least one indicium aligned with the insertion axis. The femoral neck may be a trial femoral neck.

The femoral neck may be or may be part of a femoral prosthesis.

A sixth aspect of the invention provides a kit of parts comprising the femoral neck of the fifth aspect and a pin.

A seventh aspect of the invention provides an assembly of: the femoral neck of the fifth aspect and a trial femoral head and/or a femoral part receivable within the femur of a patient. The femoral part may be a femoral broach.

An eighth aspect of the invention provides a surgical method for replacin a hip of a patient having a femur and a pelvis, comprising: positioning the femur and the pelvis of the patient so that the hip is in an anatomical position; using an alignment guide of a femoral neck attached to the femur to orient an indicator component relative to the pelvis and along an insertion axis; inserting the indicator component along the insertion axis into a bony part of the pelvis adjacent the acetabulum; orienting an acetabular cup inserter holding an acetabular cup relative to the indicator component to set an insertion axis; and inserting the acetabular cup into the acetabulum along the insertion axis to place the acetabular cup in the acetabulum with an orientation corresponding to a target combined anteversion for the hip. The anatomical position may corresponds substantially to 0° extension/flex i on of the leg, 0° abduction/adduction of the femur and 0° rotation of the femur.

The surgical method may use a posterior approach. The acetabular cup inserter may be oriented to be parallel to an axis of the indicator component to set the insertion axis.

The insertion axis may subtend an acute angle with a neck axis of the femoral neck when the hip is in the anatomical position.

The surgical method may further comprise: using the alignment guide to orient a further indicator component along further insertion axis parallel to the neck axis of the femoral neck; and inserting the further indicator component along the further insertion axis into a bony part of the pelvis adjacent the acetabulum to record the orientation of the neck axis relative to the pelvis.

The surgical method may further comprise attaching the alignment guide to the femoral neck. The surgical method may further comprise attaching the alignment guide to a superior surface of the femoral neck. The femoral neck may be a native femoral neck or a trial femoral neck. The alignment guide may be a part of the femoral neck. The alignment guide may be an integral or unitary part of the femoral neck. The alignment guide may be provided by a part of a shaft of the femoral neck.

The surgical method uses an anterior approach.

An inserter guide may be used to orient the acetabular cup inserter relative to the indicator component to set the insertion axis.

The inserter guide may have a handle defining a handle axis. Orienting the acetabular cup inserter may include positioning the handle so that the handle axis subtends an acute angle with the indicator component. The acute angle may correspond to the target combined anteversion. The acute angle and target combined anteversion may be substantially 35°.

The insertion axis may subtend a right angle, or substantially 90°, with a neck axis of the femoral neck when the hip is in the anatomical position. The surgical method may further comprise attaching the alignment guide to the femoral neck.

The surgical method may further comprise attaching the alignment guide to an inferior surface of the femoral neck. The femoral neck may be a native femoral neck or a trial femoral neck.

The target combined anteversion may be in the range of 25° to 45°.

The target combined anteversion may be substantially 35°.

Embodiments of the invention will now be described in detail, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 shows a schematic illustration of a human femur;

Figure 2 shows a schematic illustration from above of the femoral head and neck of the femur shown in Figure 1 ;

Figure 3 shows a perspective view of an assembly according to the invention including a first embodiment of a guide according to the invention;

Figure 4 shows a perspective partially exploded view of the assembly of Figure

3;

Figure 5 shows a cross-section o the assembly of Figure 3 along the line A-A; Figure 6 shows a magnified perspective view of a proximal part of the assembly of Figure 3;

Figure 7 shows side view of a second embodiment of an assembly according to the invention including a second embodiment of a guide according to the invention;

Figure 8 shows an end view of the assembly of Figure 7:

Figure 9 shows a perspective view of the assembly of Figures 7 and 8;

Figure 10A show a perspective view of a cup inserter instrument guide for use with the assembly shown in Figures 7 to 9;

Figures 1 OB to I OC illustrate use of the cup inserter instrument guide of Figure 1 OA to orient a cup using an indicator component positioned using the assembly of Figures 7 to 9;

Figures 1 1 A to 1 1C show perspective, superior plan and inferior plane views of a trial neck including a guide according to a third embodiment of the invention;

Figure 12 shows a flow chart illustrating a first hip replacement surgical procedure using the first assembly as shown in Figures 3 to 6;

Figure 13 shows a flow chart illustrating a second hip replacement surgical procedure using the second assembly as shown in Figures 7 to 9; and

Figure 14 shows a flow chart illustrating a third hip replacement surgical procedure using the third assembly as shown in Figures 1 1 A to 1 1 C.

Figures 1 and 2 respectively show an anterior view and superior view of a human femur 1. The human femur 1 generally comprises a main shaft 2 with a femoral neck 3 and femoral head 4 at a proximal end. The femoral head 4 engages within the acetabulum of the human pelvis to form the hip which acts as a ball and socket joint. At the distal end of the femur are the medial 5 and lateral 6 condyles which form part of the knee joint.

Figure 2 is an illustration of the femur 1 as viewed from a superior direction showing the medial 5 and lateral condyles 6, the femoral neck 3 and femoral head 4. In Figure 2, the midline of the neck 3, corresponding to line 7, is naturally anteverted with a degree of antcversion, Θ, relative to a line 8, which is parallel to dashed line 9 which is tangential to the posterior of the medial 5 and lateral 6 condyles. The degree of anteversion varies from person to person but is typically around 15°.

When preparing a femur 1 for implantation of a femoral component of a hip prosthesis, the femur 1 is resected to remove the femoral neck 3 and head 4 and the femoral intramedullary canal is prepared by inserting increasing sized broaches into the femoral intramedullary canal. The final broach generally has the same shape and configuration as the stem of the hip prosthesis (not shown). Usually a number of broaches of successive sizes are used until the required size of cavity within the femoral intramedullary canal is achieved, at which point the cavity is cleaned and prepared prior to implantation of the stem.

As part of the surgical procedure, and prior to implantation of the hip prostheses, different size replacement femoral heads may be tri l led using different sized trial heads. To do this, a trial neck may be attached to the broach and various trial heads mounted on the trial neck.

However, once the native femoral neck 3 has been resected, all information about the native femoral neck anteversion has been lost. It is believed that the performance of a prosthetic hip joint depends on the anteversion of the femoral component and the antcversion of the acetabular cup. Hence, it is the combined version of the hip joint, and not simply the anteversion of the femoral neck or acetabular cup alone, which should be considered by the surgeon. The overall geometry of the hip joint arises from the orientation of the acetabulum relati ve to the pelvis and also the orientation of the femoral neck relative to the femur. The overall or combined anteversion of a hip joint is the combination of the acetabular anteversion, which may be about 20°, and the amount of femoral anteversio projected into the same plane, which may be approximately 11°. Hence, the combined anteversion o the hip joint measured in that plane would be 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 o the acetabulum relative to the pelvis. More specifically, for non-extreme cases, combined anteversion may also refer to a general rule o 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 o 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.

Hence, to assist the surgeon in taking femoral neck version into account when positioning the acetabular cup, a trial neck assembly and/or a guide component may be used.

With reference to Figures 3 to 6, there is shown a first embodiment of a trial neck assembly 100, which includes a trial neck 12, a broach 10, a trial head 1 1 and a guide component 16. The trial neck 12 extends along a longitudinal axis, A, and comprises an elongate body portion, a shoulder 13 at a first end and a head receiving formation 14, in the form of a taper, at second end configured to be received within a bore o a trial head 1 1. An attachment formation 15 extends from the shoulder 13, as best illustrated in Figure 5, for releasably attaching the trial neck 12 to a femoral broach 10. The trial neck 12 also includes a pair of apertures 17, 18 positioned on, and spaced apart along, the midline of the trial neck and extending through the trial neck from a superior surface 19 to an inferior surface 20. Hence, the apertures 17, 18 are arranged on, and spaced apart along, the longitudinal axis of the trial neck. Figures 3 to 6 show a first embodiment of a guide component 16 according to the invention. The guide component 16 is in the form of a generally L-shaped member comprising a first guide portion 21 , defining a guide channel in the form of an extended slot 22, having a first guide axis which is generally parallel to the mid-line and longitudinal axis of the trial neck 12. An indicator portion 23 is borne by an upper part of the first guide portion 21 and has an inferior surface 24 and a superior surface 25. The superior surface 25 defines an indicator surface.

The slot 22 defines a guide plane B, as illustrated in Figure 6, within which a first indicator component can be directed as will be described in further detail below. An example of a suitable first indicator would be a Steinmann pin although any suitable indicator component could be used. The indicator surface 25 extends in an indicator plane C which is generally perpendicular to the guide plane B, as illustrated in Figure 6. The indicator surface has a plurality of markings, including a first indicator marking 26 aligned with the slot 22, and axis A, to provide a visual indication of the direction of guide plane B, and the longitudinal axis A. The further indicator markings 26'are oriented at predetermined angles with respect to the first indicator marking 26. For example, the angled indicator markings 26' are marked at 5° increments from the 0° first marking 26 to 45°. The first marking 26 and alternate ones of the further indicator markings 26' may be in the form of grooves which may be used to guide placement of one or more further indicator components, e.g. a second and/or a third Steinmann pins, as described in greater detail below.

The inferior surface 24 defines a semi-circular groove 27 which provides a second guide channel. The semi-circular groove is titled by a pre-selected angle, e.g. 35°, relative to the first guide marking 26, and hence also relative to the longitudinal axis A. The second guide channel 27, may be used additionally or alternatively, to grooves 26' to guide placement of one or more further indicator components, e.g. a second and/or a third Steinmann pins, as also described in greater detail below.

A pair of spiked legs 28 extend from a lower end 29 of the guide portion 21. Spiked legs 28 are sufficiently sharp to allow the guide component 16 to be securely, but releasably, attached to the superior surface of the native femoral neck prior to resection of the femur as described in greater detail below. Hence, the same parts of the guide component 16 are used to attach the guide component initially to the midline of the native femoral neck and also, subsequently, to the midline of the trial neck 12, by being received in the pair of apertures 17, 1 8. A pair of spiked legs helps to prevent the guide component from being rotated under load when attached to the native neck.

The guide portion 21 has ribbed exterior side surfaces which assist with manual gripping and manipulation of the guide component 16, in case it becomes slippery during surgery.

In use, the guide component 16 can be releasably attached to the midline of the trial neck 12 by inserting the pair of spiked legs 28 into the apertures 17, 18. Hence, the pair of spiked legs 28 define a guide attachment formation configured for releasable attachment of the guide component 16 to the trial neck 12.

In this first embodiment, the guide component 16 is mounted on the superior surface 19 of the trial neck 12. The guide component 16 and assembly 100 of the first embodiment are particular suitable for use in a posterior approach hip replacement procedure as described in greater detail below with reference to Figure 12.

As the pair of apertures 17, 1 8 are arranged along, and aligned with, the midline and longitudinal axis A of the trial neck, when the guide component 16 is attached to the trial neck 12, the trial neck longitudinal axis A of the neck falls within plane B and slot 22 is aligned with the trial neck longitudinal axis A.

Hence, while the native joint is reduced, as the guide 16 mounted on the mid-line of the native neck, a surgeon can insert an indicator component, such as a Steinmann pin, into the slot 22, which will direct the Steinmann pin in alignment with the native neck axis. A surgeon can therefore, use the assembly to place an indicator component, such as a Steinmann pin, in the pelvis, which provides a visual indication of the version of the native neck. Hence, a Steinmann pin inserted through slot 22 and into the bone of the pelvis around the acetabulum will provide a clear visual indication of the native neck version and which the surgeon can use to help assess the appropriate cup version when inserting the cup prosthesis.

Additionally, or alternatively, when the trial joint is reduced, when the guide 16 is mounted on the mid-line of the trial neck, a surgeon can insert an indicator component, such as a Steinmann pin, into the slot 22, which will direct the Steinmann pin in alignment with the trial neck axis. A surgeon can therefore, use the assembly to place an indicator component, such as a Steinmann pin, in the pelvis, which provides a visual indication of the version of the trial neck. Hence, a Steinmann pin inserted through slot 22 and into the bone of the pelvis around the acetabulum will provide a clear visual indication of the trial neck version and which the surgeon can use to help assess the appropriate cup version when inserting the cup prosthesis. Additionally, or alternatively, the surgeon can use the indicator markings 26, 26' to prov ide the visual indication or a further visual indication of neck version by inserting Steinmann pins in the pelvis in alignment with one or more of the indicator markings 26, 26', and line-of-sight assessment. For example a second Steinmann pin may be inserted in the pelvis via guide 22 and which represents the trial neck version and then a third Steinmann pin may be place in the pelvis using a further marking 26 'groove at an angle of 10° to the second pin. The second and third pins may then provide further visual guidance to the surgeon when positioning the acetabular cup.

Additionally, or alternatively, the second alignment groove 27 can be used to align a third Steinmann pin at some pre-selected version angle relative to the trial neck axis version. In the described embodiment, the pre-selected version angle may be 35°, relative to the trial neck axis version. This pre-selected angle may be selected to provide a good range of motion for the hip joint without impingement, for a cup positioned with a version so that the cup axis (defined by a line passing through the pole of the cup and the centre of the mouth of the cup and perpendicular to the plane of the mouth of the cup) is parallel to the pin. With reference to Figures 7 to 9 there is shown a second embodiment o an assembly 110 including a second embodiment of the guide component 1 16. Figure 7 shows a side elevation in a generally anterior-posterior direction in use, Figure 8 a side elevation in a generally medial-lateral direction in use and Figure 9 a perspective view which also includes a guide pin 150 received in the guide component 1 16. The assembly 1 10 includes the same broach 10, a similar trial neck 1 12 and a trial head 1 1 as the first assembly 10, but a different guide component 1 16. in the second embodiment of the guide component 1 16, the guide component 1 16 is articulated and comprises a first portion 1 0 and a second portion 13 1 which are pivotally connected to each other. A guide attachment member in the form of an attachment plate 132 also has a pair of spiked legs and is pivotally connected to one end of the first portion 130. The first portion 130 provides an articulating link between the base or attachment plate 132 and the second or guide portion 13 1. The attachment plate 132 has a central bore having an axis D extending in a direction generally perpendicular to the plane of the broach and neck as shown in Figure 7. The first portion 130 includes a circular shaft 133 extending laterally o the first portion 130. The attachment plate 132 is mounted around the shaft 133 so that the first link portion 130 is pivotable with respect to the attachment plate 132 around axis D. A pair of spiked legs extend from an upper surface of the base 132 and can be received in the pair of channels 17, 18 in the trial neck 112 to allow the guide 1 16 to be releasably attached to the inferior side 137 of trial neck 1 12. The second or guide portion 131 includes a guide channels in the form of bore 135 defined toward a free end of guide portion 131 and which also extends generally parallel to the direction of axis D, along axis F (shown in Figure 9) and generally perpendicularly to a mid-plane of the broach and trial. The bore 135 is directed generally perpendicularly to the direction of the neck axis A in Figure 8.

Similarly to the first embodiment described above, the guide channel 1 5 defines an axis within which an indicator component, such as guide pin 150, can be directed as will be described in further detail below. As before, an example of a suitable indicator component would be a Steinmann pin although any suitable indicator component could be used.

In this configuration, the guide channels 135 in the second portion 131 of the guide component 116, and the corresponding guide axis defined by guide channel 135, is in a direction substantially transverse to the longitudinal neck axis A of the trial neck 1 12 when the guide component 1 16 is attached to the trial neck 112.

This second embodiment is particularly suitable for use in an anterior approach hip replacement procedure, for example when the patient is in the supine position. In this position, it is not feasible for the surgeon to use a guide component mounted on the trial neck 1 12 at the superior surface 138 of the trial neck as this would not be accessible. In this instance, the second guide component 1 16 enables the guide component 1 16 to be mounted on the trial neck 1 12 on its inferior surface 137 which is more accessible for the surgeon. In this scenario, the neck version is indicated by a pin 150 at right angles to the longitudinal axis A of the trial neck 1 12. The provision of the articulated guide component 1 16 allows the position of the guide pin in the pelvis to be adjusted so that the guide pin can be inserted in suitable bone of the pelvis near the acetabulum while its direction is maintained as perpendicular to the neck axis A.

A hip replacement surgical procedure using a posterior approach and the first guide component 16 will now be described with reference to Figure 12. Figure 12 shows a flowchart illustrating a first hip replacement surgical method 200. At 202, the patient is positioned on the operating table with a position suitable for a posterior approach, such as laterally. At 204, the surgeon exposes the surgical site to provide access to the hip joint. At 206, the guide component 16 is attached to the native or natural femoral neck, by forcing spikes 28 into the superior surface of the native femoral neck and generally aligned with the mid-line of the femoral neck. The patient's hip joint is then placed in an anatomical position which may include checking and adjusting the position of the patient's pelvis on the operating table.

In the anatomical position, the patient's leg is placed with the femur in 0° of flexion / extension, 0° f 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. When 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.

Hence the patient's pelvis and the patient's leg are manoeuvred so that femur has substantially zero degrees of abduction, zero degrees of flexion and zero degrees of internal rotation. With the hip joint in this prc-selectcd anatomical position, at 208, a first pin is inserted into guide slot 22, which controls the orientation of the first pin, and its position along the guide slot can be adjusted so that they pin can be inserted into a suitable bony part of the pelvis adjacent the natural acetabulum. Hence, the first guide pin provides a visual indication of the natural or native anteversion of the femoral neck.

The guide component 16 is then removed from the native femoral neck and the surgeon can then separate the hip joint and prepare the femur and the acetabulum in a usual way at 210. This may include removing soft tissues from the acetabulum and reaming a hemispherical cavity in the native acetabulum for receiving a trial cup. This may also include resecting the native femoral neck and head and creating a cavity for receiving a femoral stem using one or more broaches of increasing size. The largest sized broach 10 is then left in the femoral cavity and a broach handle removed. At 212 a trial acetabular cup may be placed in the acetabular cavity. At 214, the trial neck 12 is attached to the broach 10 and a trial head 1 1 of a matching size to the trial cup is attached to the trial neck. The guide component 16 is also attached to the superior side of the trial neck, either before or after the trial neck is attached to the broach. The trial joint is then reduced at 216 and the patient's pelvis and/or leg are again manipulated to put the trial hip joint in the same anatomical position as previously. At 21 8. a second guide pin may be inserted via slot 22 and inserted in a bony part of the patient's pelvis to provide a visual indication of the trial neck anteversion. The anteversion of the trial neck may be different to the anteversion of the native neck either purposefully or simply owing to surgical technique. The placement of the first and/or second guide pins may be optional in some embodiments.

At 218, the surgeon uses the guide component 16 to place a third guide pin. For example, the semi-circular groove 27 may be used to place a third guide pin at a pre-selected anteversion angle, e.g. +35°, from the direction of the trial neck axis A, and which anteversion angle has been pre-selected so as to provide a target combined anteversion of the hip joint for a cup orientation substantially aligned with the third pin. This cup orientation may also provide good joint stability and range of motion for a cup oriented in alignment with the third guide pin. Additionally, or alternatively, at 218, the surgeon may use markings 26' and/or the associated grooves to guide placement of one or more further guide pins in the bone adjacent the acetabulum at some other anteversion angle or angles, and which may be useful subsequently in helping to guide or assess the orientation o an acetabular cup, e.g. +10°. This may help the surgeon quantitatively or more accurately assess whether the actual cup orientation achieved is within a safe or preferred range of deviation from the target anteversion. For example if the target combined anteversion is 35°, as indicated by the third pin, then fourth and fifth pins may optionally be placed at 218 to indicate combined anteversions of 25° and 45° respectively.

After however many guide pins as the surgeon determines to be useful have been inserted in the pelvis at 218, the trial joint is separated and the trial femoral and acetabular components are removed at 219. Then at 220, the prosthetic acetabular cup can be implanted suing a cup inserter. The guide pins provide the surgeon with a visual indication of optionally the native neck anteversion, optionally the trial neck anteversion and the target combined anteversion, e.g. 35°. The surgeon can use one or more of these to guide the orientation and hence anteversion of the prosthetic acetabular cup, for example by aligning the shaft of the cup inserter, which is generally co-linear with the cup axis (passing through the pole of the cup and perpendicularly to the centre of the mouth of the cup) with the third guide pin, and before impacting the cup inserted and implanting the cup. Additionally, or alternatively, the surgeon may use any one or more of the other guide pins to help assess and guide the anteversion of the prosthetic cup as it is implanted. Once the cup has been implanted, the surgeon can visually assess the achieved cup orientation by comparing the axis of the cup inserted with one or more o the guide pins either to provide real-time intraoperative feedback and/or to consider whether any further action may be required, such as re-positioning the cup and/or adjusting one or more parts of the joint, for example changing a neck length or off set or similar. At 222, the femoral prosthesis is implanted and then the prosthetic hip joint can be reduced and the procedure completed in a usual manner. A hip replacement surgical procedure using an anterior approach and the second guide component 1 ! 6 will now be described with reference to Figure 13. Figure 13 shows a flow chart illustrating a second hip replacement surgical method 240, some of which is similar to the method 200 illustrated in Figure 12. At 242, the patient is positioned on the operating table with a position suitable for an anterior approach, such as supine. The surgical site is exposed at 224 and the hip joint separated. At 246, the guide component 1 16 is attached to the interior surface of the natural femoral neck, along its midline, using the spikes. The hip is placed in the anatomical position similarly to as described above, but taking into account the changed position of the patient's pelvis.

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. When 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.

Then guide bore 135 may optionally be used at 248 to place a first guide pin in a bony part of the pelvis adjacent to the acetabulum but at an angle of 90° to the native anteversion of the femoral neck. This 90° rotation of the indicator guide pin is owing to the reduced access to, and smaller exposure of, the hip when an anterior approach is used.

The guide component 1 16 is then removed from the native femoral neck and at 250 the femur and acetabulum can be prepared in a conventional manner for an anterior approach. At 252 the trial cup is placed in the prepared acetabulum and at 254, the trial neck 1 12, trial head 1 1 and guide component 1 16 are assembled on the broach 10, while located within the femoral cavity. At 256, the trial joint is reduced and the hip is again placed in the anatomical position. Then at 258 a guide pin is inserted into the bone of the pelvis adjacent the trial cup via guide 135 so as indicated a direction generally perpendicular to neck axis and the mid-plane of the neck and broach the for the hip in the anatomical position.

Then at 260 the trial components are removed and at 262 the acetabular cup can be inserted using an inserter, an inserter guide and using the guide pin 150 inserted at step 258 to guide orientation of the cup before insertion.

Figure 1 OA shows a perspective view of an inserter guide 160 used to guide the direction of a cup inserter instrument. Cup inserter instruments generally have a shaft extending along a longitudinal axis and aligned with or parallel to an insertion axis f the inserter instrument and an acetabular cup axis (which passes though the pole of the cup and the centre of the mouth of the cup and hence perpendicularly to the plane of the mouth of the cup). The inserter guide 160 includes a handle 162 and a guide formation which may be in the form of a ring or circular cylinder 164 defining a circular aperture or bore 166. An inserter guide axis 168 extends along the centre of bore 166 and perpendicularly to the plane f the mouth of the bore 166, and hence also perpendicularly to the longitudinal axis of the handle 162. Ring 164 is dimensioned to receive the shaft of the inserter instrument snugly therein and so that the shaft of the inserter instrument can translate smoothly relative to ring 164 along the inserter guide axis 168.

Figures l OB, I OC and 10D illustrate how a guide pin 150 inserted using the guide 1 16 can be used with inserter guide 1 0 to guide insertion of an acetabular cup using a cup inserter (not shown).

Figure l OB illustrates the situation in which the handle 162 of the inserter guide 160 is parallel to the axis of the guide pin 150 and hence the inserter guide axis 158 is generally parallel to the neck axis. In this case, the antcversion arising from an acetabular cup implanted in this direction would be approximately 0°. Figure 10C illustrates the situation in which the handle 162 of the inserter guide 160 is not parallel to the axis of the guide pin 150, for example subtends an acute angle with the axis of the guide pin 150 of approximately 10°. In this case, the insertion axis 168 will subtend an acute axis of approximately 10° with the neck axis. A, and the anteversion arising from an acetabular cup implanted in this direction would be approximately 10°, and which may differ from the target combined anteversion of, for example,

approximately 35°.

Figure 1 OD illustrates the situation in which the handle 162 of the inserter guide 160 is not parallel to the axis of the guide pin 150 and subtends an acute angle with the axis of the guide pin 150 of approximately 35°. In this case the insertion axis 168 will subtend an acute angle of approximately 35° with the neck axis A, and the anteversion arising from an acetabular cup implanted in this direction would be approximately 35° and hence corresponds to the target combined anteversion of approximately 35°.

Hence, the guide pin 150 placed using guide 1 16 at step 258 can be used together with inserter guide 160 to guide cup insertion so as to better achieve a target orientation of the acetabular cup in the pelvis. Once the acetabular cup has been appropriately oriented using guide pin 150, inserter guide 160 and the inserter instrument at 262, then the inserter instrument may be impacted by the surgeon, for example using a slap hammer or mallet, so as to implant the acetabular cup. The prosthetic femoral components may be implanted at 264 and the joint reduced and any further typical surgical steps carried out to complete the method 240.

Figures 1 1 A, 1 1 B and 1 1 C show various views of a third embodiment of the invention in which the guide component 3 10 is integrated into the trial neck 312. Figure 1 1 A shows a perspective view of an assembly 300 of a broach 10, trial neck 312 and trial femoral head 1 1. Figure 1 1 B shows a generally superior view of the assembly 300 and Figure 1 1 B shows a generally inferior view of the assembly. As in the other embodiments, a neck axis extends generally along the neck and is denoted by A. The trial neck 312 has a superior surface 314 bearing a first alignment guide indicium 3 16 and a second alignment guide indicium 318. Each indicium 316, 318 is respectively in the form of a line and each generally subtends an acute angle of approximately 35° with the mid-line 315 of the trial neck and consequently the neck axis A. The trial neck 312 also has an inferior surface 320 bearing a third alignment guide indicium 322 and a fourth alignment guide indicium 322. Each indicium 320, 322 is respectively in the form of a line and each generally subtends an acute angle of approximately 35° with the mid-line 3 15 of the trial neck and consequently the neck axis A. The first alignment guide 316 and the second alignment guide 318 can be used for left and right hip joints respectively and for a posterior surgical approach. The third alignment guide 322 and the fourth alignment guide 324 can be used for left and right hip joints respectively and for an anterior surgical approach.

The third embodiment can be used similarly to the first embodiment, but rather than using a mechanical guide to guide placement of the pin indicating the target anteversion angle, an appropriate one of the visual alignment guides 316, 3 18, 322, 324 is used to guide pin placement at the appropriate part of the surgical method. Hence, visual alignment guide 316 corresponds generally to mechanical alignment guide 27 in the first embodiment.

Use of the third embodiment is generally similar to the first embodiment and will be described briefly with reference to Figure 14 which shows a flow chart illustrating a surgical method 280 for guiding acetabular cup placement.

A hip replacement surgical procedure 280 using a posterior approach and the third guide component 301 starts at 282 with positioning the patient on the operating table with a position suitable for a posterior approach, such as laterally. At 284, the surgeon exposes the surgical site to provide access to the hip joint. At 286 the femur and acetabulum are prepared and at 288 a trial acetabular cup is implanted. Then at 290 the trial neck 12 is mounted on the broach 10 and the trial head 1 1 is mounted on the taper at the free end of the trial neck 3 12. The trial joint is reduced at 292 and the patient ^' s hip joint is then placed in an anatomical position which may include checking and adjusting the position of the patient's pelvis on the operating table and positioning the femur relative to the pelvis as described above. Then at 294 a guide pin is inserted into the bone of the pelvis adjacent the acetabular cup by aligning the guide pin with the appropriate one of the visual alignment guides 316, 318. Hence, the guide pin when so implanted provides a visual indication of a direction generally subtending an angle of 35° to the neck axis direction for the hip in the anatomical position. At 296 the trial components are removed and then at 298 the prosthetic acetabular cup can be implanted by aligning the cup insertion axis of the inserter instrument with the axis of the guide pin before impacting the inserter instrument to implant the cup. Hence, the orientation o the acetabular cup can be closer to that corresponding to a target combined anteversion angle, for example 35°. The femoral prosthetic components can then be implanted at 299 before the surgical method is completed by any further typical steps of such methods.

Hence, the guide components 16, 1 16, 310 and assemblies 10, 1 10, 300 may be used to place one or more visual indicators of anteversion angles which the surgeon can subsequently use as a reference while implanting the acetabular cup prosthesis and/or to assess the anteversion of the acetabular cup prosthesis after it has been impacted.

Providing a reliable visual indication of the neck anteversion adjacent the acetabulum can therefore help improve the anteversion orientation of the acetabular cup so that the resulting prosthetic hip has or is closer to a target combined anteversion.

As discussed above, during hip joint replacement surgery, after the femur has been resected and the broach inserted, the trial neck can then be attached to the broach and the guide mounted on the trial neck. The surgeon then returns the reduced trial joint to the anatomical position. Using the guide a surgeon is able optionally to place a further indicator component, generally in the form of a pin, into the pelvis adjacent the acetabulum and oriented along the neck axis. This provides, for the surgeon, a visual indication, or record, of the neck axis f the trial neck and thus of the degree of restored version of the replacement femoral head and neck. The presence of the pin in the pelvis provides a clearer visual indication of the amount of version in the broach. This can facilitate decision making for the surgeon as to the next steps in the hip replacement process, such as correct alignment of the acetabular cup. 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.