Patent Description:
A variety of different hip replacement procedures are known generally. Some of these involve removing the native femoral head and replacing it with a prosthetic femoral head. Often a stem is used including a prosthetic femoral neck to which the prosthetic femoral head is attached. Sometimes an acetabular cup may also be used to replace the native acetabulum of the patient's pelvis. The specific details may vary depending on the implant system being used.

The positioning of the prosthetic components can be an important factor in the outcome of the hip replacement procedure. A variety of different philosophies or approaches to implant placement exist and may vary depending on the implant system and/or the individual circumstances of the patient.

One approach is a restorative approach in which the surgeon tries to replicate or restore the native anatomy of the patient prior to the hip replacement procedure.

For example, pre-operative images, such as X-ray images or CT scans, may be used to determine the anatomy of the patient's femur and then used to plan the prosthetic implant components and their positioning so as to attempt to restore the patient's native anatomy. However, such approaches require the availability of imaging apparatus, may take more time, may be more complicated, and may require greater surgeon experience or skill.

Therefore, simpler approaches to helping to restore native anatomy would be beneficial.

<CIT> provides a surgical instrument according to the preamble of claim <NUM>.

The present disclosure is directed to surgical instruments, apparatus and kits of parts which may provide a simple and/or easy to use approach to restoring the native femoral head position during a hip replacement surgical procedure.

A first aspect of the present disclosure provides a surgical instrument for assessing restoration of the femoral head centre, comprising: a body having a first connector for attaching the body to a femoral part, and wherein the body defines a plurality of apertures therein, wherein each aperture corresponds to a respective femoral head centre arising from a respective corresponding femoral neck; and a gauge, wherein the gauge includes a pin at a first end and an arm extending transversely from the pin and wherein the pin is receivable in each of the plurality of apertures and wherein the arm bears a scale indicating a distance from the pin.

The plurality of apertures may include apertures corresponding to femoral necks having different medial-lateral offsets.

The plurality of apertures may include apertures corresponding to femoral necks having different stem-neck angles.

The plurality of apertures may include apertures corresponding to femoral necks having different leg-lengths.

The body may have an anterior face and the anterior face may include at least a first linear indicium extending parallel to a medial-lateral axis and passing through at least a first of the plurality of apertures and corresponding to a first position on a superior-inferior axis.

The anterior face may include at least a second linear indicium extending parallel to the medial-lateral axis and passing through at least a second of the plurality of apertures and corresponding to a second position on the superior-inferior axis.

The body may have a posterior face and the posterior face may include the same indicia as the anterior face and may be configured so that the same body is useable for right hand hips and left hand hips.

The body may have a posterior face and the posterior face may define a posterior plane and the anterior face may define an anterior plane and the anterior plane may be parallel to the posteriori plane.

Each of the plurality of apertures may comprise a channel passing through the entire thickness of the body. Each channel may pass from the anterior face through the body to a or the posterior face.

A second aspect of the disclosure provides a surgical instrument system comprising: the surgical instrument of the first aspect; and a centre finder. The centre finder may include a plurality of indicia configured to indicate the centre of the centre finder.

The centre finder may comprise a circular ring. The plurality of indicia may comprise a first pair of diametrically opposed indicia and/or a second pair of diametrically opposed indicia.

The surgical instrument system may further comprise a broach. The broach may include a second connector configured to engage the first connector to attach the body to the broach.

The surgical instrument system may further comprise a plurality of femoral necks. Each neck may give rise to a different femoral head centre position.

The plurality of femoral necks may include femoral necks having different offsets along the medial-lateral axis.

The plurality of femoral necks may include femoral necks having different stem-neck angles.

The plurality of femoral necks may include femoral necks having different leg lengths along the superior-inferior axis.

The femoral necks may be trial necks or prosthetic necks.

The invention may be used in a method for assessing restoration of the femoral head centre for a femur of a patient. The method may include one or more of: determining the centre of the native femoral head of the femur of the patient; marking the position of the centre of the native femoral head on the native femoral head; marking a position on the greater trochanter of the femur relative to the centre of the native femoral head with a known separation along the medial-lateral axis from the centre of the native femoral head and at the same position along the superior-inferior axis as the centre of the native femoral head; resecting the native femoral neck; attaching a body to the resected femoral neck, wherein the body defines a plurality of apertures, each aperture corresponding to a respective femoral head centre arising from a respective corresponding femoral neck; attaching a gauge including a scale to the body using a first one of the plurality of apertures; and using the gauge to determine whether the femoral head centre arising from a first femoral neck corresponding to said first one of the plurality of apertures would restore the native femoral head centre.

The method may further comprise; attaching the gauge to the body using a second one of the plurality of apertures; and using the gauge to determine whether the femoral head centre arising from a second femoral neck corresponding to said second one of the plurality of apertures would restore the native femoral head centre.

The method may further comprise: aligning the gauge with a linear indicium on the body which is parallel to the medial-lateral axis of the femur.

The method may further comprise; using the scale on the gauge to determine whether the femoral head centre arising from the femoral neck corresponding to said one of the plurality of apertures would have a separation restoring the known separation.

The method may further comprise: using a centre finding guide placed on the native femoral head to determine the centre of the native femoral head and/or to mark the position of the centre of the native femoral head.

An embodiment will now be described in detail, by way of example only, and with reference to the accompanying drawings, in which:.

In the Figures of drawings, like items in the different Figures share common reference signs unless indicated otherwise.

With reference to <FIG> there is shown a side elevation of a first part <NUM> of a head centre restoration instrument. The first part of the instrument <NUM> provides a body of the head centre restoration instrument. The body includes a main portion <NUM> and a connection portion <NUM> by which the body <NUM> may be attached to a femoral part in use as described in greater detail below.

The main part <NUM> of the body <NUM> defines a plurality of apertures therein. In the illustrated embodiment, five apertures <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are defined by the body. Each of the apertures passes entirely through the entire width of the main part of the body <NUM> also has to have an opening on either side of the body. It will be appreciated that five apertures is simply an example, and in other embodiments, a greater or lesser number of apertures may be provided. As described in greater detail below, the position of each aperture corresponds to a corresponding femoral neck, and in particular, to the centre of a femoral component when mounted on the corresponding neck. Hence, in the illustrated embodiment, as there are five apertures, there are also five femoral necks. Each femoral neck has a geometry corresponding to a slightly different position of the centre of the femoral component when mounted on the respective necks. The femoral necks may have differing stem-neck angles, e.g. <NUM>° or <NUM>°, and / or differing medial-lateral offsets and / or differing leg lengths.

For example, the fourth aperture <NUM> may correspond to a fourth femoral neck which may be considered a standard or reference femoral neck. The standard femoral neck may have a stem-neck angle of <NUM>° and give rise to a femoral component centre at a standard position in terms of medial-lateral offset and leg length. The standard femoral leg may be referred to as providing a low femoral head position.

The third aperture <NUM> may be associated with a third femoral neck also having a stem-neck angle of <NUM>°. However, the femoral neck gives rise to a centre of the femoral component giving rise to a lateral offset of the femur relative to the pelvis. For example, the amount of the increased lateral offset may be approximately <NUM>.

The fifth aperture <NUM> may correspond to a fifth femoral neck again having a neck-stem angle of <NUM>°. However, the femoral neck gives rise to a centre of the femoral component having a reduced distance in the medial-lateral direction and corresponding to a medial offset of the femur relative to the pelvis. The amount of the medial offset may be approximately <NUM>, for example.

The second aperture <NUM> may correspond to a second femoral neck having a stem-neck angle of <NUM>°. The second femoral neck may give rise to the same medial-lateral position as the standard femoral neck, but give rise to a centre of a femoral head giving rise to an increased leg length in the inferior-superior direction. For example, the amount of the increase in leg length may be approximately <NUM>.

The first aperture <NUM> may correspond to a first femoral neck also having a neck-stem angle of <NUM>°. The first femoral neck gives rise to a femoral head centre having an increased leg length, relative to the standard neck, and also an increased lateral offset relative to the standard neck. The amount of the increase in leg length may be approximately <NUM> and similarly the amount of the lateral offset may be approximately <NUM>.

The first and second femoral necks may be referred to as "high" femoral necks, and the third, fourth and fifth femoral necks may be referred to as "low" femoral necks.

As indicated in <FIG>, various indicia and markings may be provided on an anterior surface <NUM> of the main body part <NUM> indicating to the user the femoral neck associated with each of the respective apertures. Similar markings may also be provided on the posterior surface of the main body as illustrated in <FIG>, and which posteriori surface is generally parallel to the anterior surface. Hence, the same body may be used for right hand hips and left hand hips, or for anterior or posterior approaches, as it is essentially symmetric about the central plane parallel to the anterior and posterior surfaces of the body.

As also illustrated in <FIG>, a first linear indicium <NUM> and a second linear indicium <NUM> is also provided on the anterior surface <NUM>. The first linear indicium <NUM> passes through the first and second apertures and extends generally along the medial-lateral axis of the patient's anatomy when the body <NUM> is mounted on the patient's femur in use. Similarly, second linear indicium <NUM> extends through the third, fourth and fifth apertures and again extends generally parallel to the medial-lateral axis of the patient's anatomy when body <NUM> is mounted on the patient's femur in use.

The connecting or foot portion <NUM> defines a peg <NUM> and cavity <NUM> providing first and second attachment features for releasably attaching the body <NUM> to a femoral component in use. The provision of a peg and cavity helps to ensure that the body <NUM> is attached correctly to the femoral part in use.

<FIG> shows as perspective view of a gauge <NUM> part of the head centre restoration instrument. The gauge <NUM> has a pin <NUM> at a first end. The pin <NUM> is dimensioned to be snuggly received in any one of the plurality of apertures of the body <NUM>. As illustrated in <FIG>, the peg has a generally right circular cylindrical form.

The gauge <NUM> also includes an arm or member <NUM> extending generally transversely to a longitudinal axis of the pin <NUM>. The arm includes a plurality of indicia on a first <NUM> surface and also on the reverse surface <NUM>. As illustrated in <FIG>, the indicia provided on the arm <NUM> provide a scale indicating a distance or separation between an origin defined by the location of the pin <NUM> and the transverse distance along the longitudinal axis of the arm <NUM>.

In some embodiments, as illustrated in <FIG>, the scale may also provide a ruler and include numerals indicating the magnitude of the distance. For example, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. However, in other embodiments, the gauge may not be in the form of a ruler and may simply include any markings which allow a visual assessment of the distance between a point on the arm <NUM> and the position of the pin <NUM>.

<FIG> shows a perspective view of the head centre restoration instrument <NUM> comprising the gauge <NUM> mounted on the body <NUM>. As illustrated in <FIG>, the pin <NUM> is received within the first aperture <NUM>. The longitudinal axis of the pin extends substantially transversely to the plane of the anterior surface <NUM> of the body. As also illustrated in <FIG>, the longitudinal axis of the arm <NUM> is substantially parallel to the first linear indicium <NUM>.

The configuration of the body and gauge illustrated in <FIG> corresponds to the relative position of the body and gauge in use, as described in greater detail below.

<FIG> shows a flow chart illustrating a general method of use of the head centre restoration instrument <NUM> illustrated in <FIG> as part of a hip replacement procedure. Various parts of the hip replacement procedure are generally known to a person of ordinary skill in the art, and therefore are not shown in the flow chart illustrated in <FIG>. Hence, <FIG> shows merely a sub-set of the surgical method so as not to obscure the description of the present invention. The method <NUM> illustrated in <FIG> will now be described in greater detail with further reference to <FIG>.

<FIG> shows an anterior-posterior view of the approximal part of a femur <NUM> of a patient. Line <NUM> is generally parallel with the anatomical axis of the femur <NUM>. The proximal part of the femur <NUM> generally comprises the native femoral head <NUM>, the native femoral neck <NUM> and the native greater trochanter <NUM>.

<FIG> also shows a guide component <NUM> which may optionally be used to improve the overall accuracy of the procedure. The guide component <NUM> includes a centre finding part <NUM>, a first arm <NUM> and a second arm <NUM>. The centre finding part <NUM> generally has a circular annular construction. Hence, as it is in the form of a generally circular ring, when the centre finding part <NUM> is mounted on the femoral head <NUM>, which is approximately spherical, it will naturally sit with its centre generally aligned with the centre of the native femoral head <NUM>. The first arm <NUM> is aligned to lie parallel to the anatomical femoral axis <NUM>. The length of the first arm <NUM> and the angle between the second arm <NUM> and the first arm <NUM> is predefined so as to indicate a preferred resection height and angle for resecting the native femoral neck <NUM>. An upper edge <NUM> of the second arm <NUM> may be used to define a first resection height (a standard resection height) and a lower edge <NUM> may be used to define a second resection height (corresponding to a high neck resection).

At <NUM>, the guide <NUM> is positioned on the native femoral head and oriented so that the first arm <NUM> is generally parallel to the anatomical axis of a femur <NUM>, as illustrated in <FIG>. Then, at <NUM>, the second arm <NUM> may be used to mark a resection height and angle on the native femoral neck as illustrated in <FIG>. For example, a chisel instrument <NUM> may be positioned on the femoral neck using the upper edge <NUM> of the second arm <NUM> and used to mark the neck resection height and angle on the native femoral neck <NUM>.

The guide <NUM> is then used at <NUM> to mark the approximate centre of the native femoral head <NUM>. As illustrated in <FIG>, the annular ring <NUM> of the guide component <NUM> includes four indicia, each in the form of an arrow, e.g. <NUM>. A first pair of indicia or markings define a first axis substantially parallel to the axis of the first arm <NUM>, or the inferior-superior axis of the patient's femur. A second pair of markings define a second axis substantially perpendicular to the first axis and the longitudinal axis of the first arm <NUM>, and generally parallel to the medial-lateral axis of the patient's femur. Hence, the second pair of markings define a second axis generally parallel to the medial-lateral axis of the native femur. Hence, at <NUM>, the surgeon may mark the approximate centre of the native femoral head by drawing a first line <NUM> between the first pair of markings and a second line <NUM> between the second pair of markings. As the markings of each pair of markings are diametrically opposed, the intersection of the two lines generally corresponds to the centre of the annular ring <NUM> and therefore also generally to the approximately centre of the native femoral head <NUM>.

After the centre of the femoral head has been marked, the guide <NUM> may be removed. <FIG> shows the native femur after removal of the guide <NUM> and shows the marking on the native femoral neck <NUM> indicating the preferred neck resection height and angle. At <NUM>, a mark is made on a part of the native femur which will remain after resection of the native femoral head. The marking may be made in any suitable part of the remaining femur and as illustrated in <FIG> is generally in the region of the greater trochanter. As illustrated in <FIG>, the marking on the greater trochanter is made at a known distance from the marked centre of the native femoral head. The marking may be made by placing the gauge <NUM>, or a rule, or similar, adjacent the native femoral head <NUM> and generally aligned with the second line <NUM> and hence the medial-lateral axis of the native femur. The marking <NUM> on the greater trochanter <NUM> includes a first line <NUM> generally parallel to the medial-lateral axis and a second line <NUM>, perpendicular thereto, clearly indicating the separation between the marking <NUM> on the greater trochanter <NUM> and the centre of the native femoral head <NUM>. The distance along the medial-lateral axis is arbitrary and the position of the vertical marking <NUM> may be determined more by which part of the greater trochanter is more accessible. The position of the vertical marking <NUM> does not need to correspond to any particular value of distance. It is simply that the vertical marking provides a fixed separation to the centre of the native femoral head and which distance is known. For example, as illustrated in <FIG>, the distance between the centre of the native femoral head and the marking <NUM> is approximately <NUM>.

After the greater trochanter has been marked, at <NUM>, the femoral neck may be resected using the neck resection marking <NUM> to achieve the desired neck resection height and angle. The intramedullary canal of the femur may then be formed as generally known in the art. Forming the intramedullary canal may involve using various cutting instruments such as rasps and broaches. Eventually, a final broach may be used once the cavity has the size desired for the intended prosthetic implant.

<FIG> illustrates the femur and shows the marking <NUM> on the remaining part of the native femur and also a final broach <NUM> located within the intramedullary canal. As illustrated in <FIG>, the final broach <NUM> includes a male attachment formation <NUM> extending therefrom and also includes a female attachment formation (not visible) positioned and configured to mate with male attachment formation <NUM> on the body <NUM>. In other embodiments the attachment formations on the broach and on the body can be swapped. For example is a female broach were used instead, then a male attachment formation would be provided on the body to engage therewith.

At <NUM>, the body <NUM> is mounted on the broach <NUM> as illustrated in <FIG>. If desired, the marking <NUM> may have the vertical line extended, generally parallel to the anatomical femoral axis, as illustrated in <FIG>. Then at <NUM>, the gauge <NUM> may be attached to the body <NUM> by inserting the pin <NUM> in a respective one of the apertures <NUM> to <NUM>, each corresponding to a different femoral neck. As illustrated in <FIG>, the pin <NUM> has been inserted in the first aperture <NUM> and hence corresponds to a femoral neck with a stem neck angle of <NUM>° and being a high neck compared to a standard neck. The arm <NUM> is aligned with the first linear indicium <NUM> so as to be generally parallel to the medial-lateral axis. As illustrated in <FIG>, the arm <NUM> of the gauge generally overlies the horizontal line of marking <NUM>. Hence, this indicates to the user that the femoral neck corresponding to the currently used aperture would give rise to a femoral head centre substantially reproducing the position of the centre of the native femoral head in the inferior-superior direction.

Hence, at <NUM>, the surgeon uses the gauge <NUM> to assess which of the apertures in the body <NUM> may most closely position a prosthetic femoral head closest to the centre of the native femoral head so as to restore the native femoral head. At <NUM> the surgeon may look at the scale on the gauge <NUM> to assess the position in the medial-lateral direction. For example, if the scale on the arm <NUM> indicates that the separation in medial-lateral direction would be approximately <NUM>, then the surgeon may determine at <NUM> that the femoral neck corresponding to the first aperture may not be appropriate as previously the preferred separation between the centre of the femoral head and the marking on the trochanter has been determined to be approximately <NUM>. Hence, at <NUM>, if the surgeon determines that a femoral neck corresponding to the currently used aperture may not be appropriate, then the method returns, as illustrated by process flow line <NUM> to step <NUM>. At <NUM>, the surgeon may remove the gauge <NUM> from the body <NUM> and engage the pin <NUM> in another one of the plurality of apertures. For example, if the surgeon positions the gauge with the pin <NUM> in the second aperture <NUM>, then this will reduce the medial-lateral offset of a femoral head placed on the corresponding femoral neck. As discussed above, the second aperture <NUM> may correspond to a femoral neck giving rise to a reduced separation in the medial-lateral direction of approximately <NUM>. Hence, the surgeon may position the gauge <NUM> aligned with the first linear indicium <NUM>, and determined using the scale on the gauge that the resulting separation would be approximately <NUM>. This may then be considered to be acceptable at <NUM> as the originally determined ideal separation to restore the native femoral head was determined to be approximately <NUM>. Hence, at step <NUM>, an acceptable femoral neck has been identified, approximately restoring the centre of the native femoral head, and therefore the remainder of the neck replacement procedure may be continued with at <NUM>.

Additionally or alternatively, at <NUM>, it may be determined that the femoral neck corresponding to the currently selected aperture in the body would position the femoral head at the wrong position in the inferior-superior direction as the gauge, when aligned with the linear indicium <NUM> is offset from the marking <NUM>. Hence, the surgeon may select another one of the apertures, e.g. the aperture <NUM> and attach the gauge with its pin in that aperture with the arm of the gauge <NUM> aligned with the second linear indicium <NUM>. The surgeon may then visually inspect the marking <NUM> to assess whether the corresponding femoral neck gives rise to a femoral head position sufficiently close in the inferior-superior and medial-lateral directions. If the arm <NUM> of the gauge is sufficiently close to the horizontal part of marking <NUM> and the vertical part of marking <NUM> corresponds to a sufficiently close separation in the medial-lateral axis, then the surgeon may select the corresponding femoral neck accordingly.

Hence, the plurality of apertures in the body <NUM> and the gauge <NUM> may be used to determine which of the plurality of femoral necks will give rise to a replacement femoral head with a centre most closely matching the centre of the native femoral head. This is achieved by providing a marking on the remaining part of the native femur <NUM> having a known positional relationship to the centre of the native femoral head. The gauge <NUM> and the apertures and linear indicia <NUM>, <NUM> hence permit the surgeon to compare the resulting leg length and medial-lateral offset arising from the various femoral necks corresponding to the various apertures in the body.

Although the use of a scale and measuring specific distances is described above, it will be appreciated that this is not essential. Rather, the scale may simply use different markings indicating different amounts of separation. Absolute values of distance are not essential.

Also, as noted above, although the described embodiment uses five apertures each corresponding to a different femoral neck, a greater or lesser number of apertures of corresponding femoral necks may be used. Also, the specific geometries of the femoral necks described, in terms of their stem-neck angle and variations in leg length and medial-lateral offset are not essential.

Further, although a specific guide is illustrated in <FIG> as being used to determine the approximate centre of the native femoral head, the use of such a guide is not essential. Any device that may be used to approximately identify the centre of the femoral head may be used. The identification of the preferred neck resection height and angle is merely incidental and is not essential in order to achieve the benefits of approximately restoring the centre of the femoral head.

In this specification, example embodiments have been presented in terms of a selected set of details. However, a person of ordinary skill in the art would understand that many other example embodiments may be practiced which include a different selected set of these details. It is intended that the following claims cover all possible example embodiments.

Any instructions and/or flowchart steps can be executed in any order, unless a specific order is explicitly stated.

Claim 1:
A surgical instrument for assessing restoration of the femoral head centre, comprising:
a body [<NUM>] having a first connector [<NUM>] for attaching the body [<NUM>] to a femoral part, and wherein the body [<NUM>] defines a plurality of apertures [<NUM>, <NUM>, <NUM>, <NUM>, <NUM>] therein, wherein each aperture [<NUM>, <NUM>, <NUM>, <NUM>, <NUM>] corresponds to a respective femoral head centre arising from a respective corresponding femoral neck; and
a gauge [<NUM>], wherein the gauge [<NUM>] includes a pin [<NUM>] at a first end and an arm [<NUM>] extending transversely from the pin [<NUM>] and wherein the pin [<NUM>] is receivable in each of the plurality of apertures [<NUM>, <NUM>, <NUM>, <NUM>, <NUM>] and
characterized in that:
the arm [<NUM>] bears a scale indicating a distance from the pin [<NUM>].