Patent Description:
Hip replacement is a surgical procedure in which the hip joint is replaced by a prosthetic implant. In total hip replacement surgery, a patient's natural hip is replaced by an acetabular cup component that replaces the acetabular socket and a femoral component that replaces the femoral head.

During such a surgical procedure, a diseased portion of the femur is excised, usually by resecting along a portion of the femoral neck. A prosthetic femoral component and a prosthetic femoral head replace the natural structures that are surgically removed. The positioning of the femoral component of the prosthesis is important to ensure proper fit and smooth rotation of the femoral head within its socket (i.e., the acetabular shell).

When performing joint reconstruction, such as hip replacement surgery, it is important that the pre-surgical geometry of the bone structure is replicated in the post-surgical structure. It is important to maintain the natural joint biomechanics, ensuring proper joint and soft tissue balancing. If this is not achieved, the result can be higher joint forces, and overall joint instability.

It is therefore necessary to ensure that orthopedic implant structures are properly placed within a patient. In the case of hip joint prostheses, it is important that the native anatomic centre of rotation of the femoral head within the acetabular shell be located and maintained during the implantation of the replacement structure. Misplacement of the centre of rotation during implantation of the femoral component of the hip joint prosthesis can affect the patient's leg length can lead to a very unsatisfactory result for the patient.

It is important in primary total hip arthroplasty to determine the natural offset and neck length of the femoral head by measurement. Offset can be measured from a point on the greater trochanter to the centre of the femoral head. Neck length can be measured from a point of the lesser trochanter to the centre of the femoral head.

<CIT> discloses an orthopaedic instrument for comparing post-surgical joint geometry to pre-surgical joint geometry. The instrument includes a head chuck that can be secured to the ball of a ball joint, and an arm having reference indicia thereon. Markings indicative of the pre-surgical joint geometry are made on the bone with reference to the centre of the ball joint. After replacement with a prosthetic ball, the post-operative geometry is verified by securing the head chuck to the prosthetic ball, and comparing the location of the bone markings against the reference indicia on the arm. As needed, adjustments are made in the prosthetic components.

<CIT> discloses an osteotomy guide assembly for femoral neck osteotomy which includes a saddle locator assembly and a saw guide attachment. The saddle locator assembly includes a barrel-shaped locating device that locates the saddle region of the proximal femur. The barrel further includes a transverse support bar extending from the barrel. The barrel is positioned over an intramedullary shaft which is temporarily positioned in and extends from the medullary canal of the femur. A saw guide is used in conjunction with the saddle locator assembly. The saw guide is attached to the support bar by a single locking means which provides for positional adjustment of the saw guide relative to the support bar in two directions, including adjustment in the anterior-posterior direction along the transverse support bar and axially along the femur via a post which extends from the saw guide.

Image based systems are also widely used within hip arthroplasty to locate the femoral head centre. There systems require pre-operative imaging and intra-operative verification.

There remains a need for surgical instruments that will assist a surgeon to measure the femoral head offset, without the need for error-prone complex mathematical calculations to be performed during surgery. There also remains a need for surgical instruments to assist a surgeon in resecting the femoral neck at the appropriate resection plane in order to reproduce within the artificial joint the hip's anatomic centre of rotation.

The invention relates to a surgical apparatus as defined in claim <NUM>.

There is provided a surgical apparatus for performing a controlled resection of the neck of a femur during a hip replacement procedure, the surgical apparatus comprising:.

The surgical apparatus according to the invention is a femoral neck resection jig. The apparatus is a "reality based" rather than an "image based" system for determining the femoral head centre. This is because apparatus uses the actual in situ femoral head to locate the femoral head centre, prior to its resection. As such, the surgical apparatus as described herein provides at least a quicker, cheaper, easier to use, and more accurate means of locating this key anatomical parameter, than conventional "image based" systems.

The concept is based around finding the femoral head centre and then making a neck resection in relation to that femoral head centre.

The frame is a simple ring structure dimensioned to be removably mountable onto the femoral head. The aperture of the frame positions the body portion of the apparatus with respect to a centre of the femoral head. The frame may be referred to by those skilled in the art as a "spherometer". It has been demonstrated that the posterior aspect of the femoral head can be used to determine femoral head centre even during the late stages of osteoarthritis, as it seems to maintain its sphericity more so in comparison to the anterior aspect. However, use of the surgical apparatus is not limited to the mounting of the frame on the posterior aspect of the femoral head, and it is also envisaged that the frame may be mounted on the anterior aspect of the femoral head.

The frame may include a pin hole configured for removable receipt of a bone pin for removably mounting the frame on the femoral head.

The pin holes may be angled such that the pin hole points towards the centre of the femoral head (i.e., the drill guide hole is orientated at <NUM> degrees to the surface of femoral head).

Optionally, the frame also includes "R" and "L" labels adjacent to the pin holes. These labels refer to the "Right Hip" or the "Left Hip". Due to the angulation of the pin holes, the labels inform the surgeon which pin hole to use, depending on whether the surgery is being performed on the left hip or the right hip. This ensures that when the bone pins are inserted into the pin holes, the pins are directed towards rather than away from the femoral head.

The resection guide extends from the frame. The resection guide may include a first longitudinal outer edge that defines a first resection guide surface for indicating a position of a first resection plane on the femoral neck.

The resection guide may include a second longitudinal outer edge that defines a second resection guide surface for indicating a position of a second resection plane on the femoral neck.

The first resection guide surface may be located proximal of the second resection guide surface, such that the first resection guide surface represents a resection plane that corresponds to a standard offset neck resection plane, and the second resection guide surface represents a resection plane that corresponds to a high offset neck resection plane.

In some constructions of the resection guide, the first and second resection guide surfaces are parallel.

The resection guide may include a first resection guide slot and second resection guide slot. The first and/or the second resection guide slot may be configured as a cutting slot, dimensioned for receipt of a blade of a cutting tool.

The first resection guide slot may be located proximal to the second resection guide surface, such that the first resection guide slot represents a resection plane that corresponds to a standard offset neck resection plane, and the second resection guide slot represents a resection plane that corresponds to a high offset neck resection plane.

The first and second resection guide slots may be substantially parallel.

The resection guide slot may be colour coded to help the surgeon to visually distinguish which slot indicates a standard offset neck resection plane, and which slot indicates a high offset neck resection plane. For example, the peripheral edges of the slots may be provided with a colour. A slot having green peripheral edges may be used to visually indicate the slot to be used for a standard offset neck resection plane. A slot having red peripheral internal edges may be used to visually indicate the slot to be used for a high offset neck resection plane.

The markings on the arm that enable a surgeon to visualise the true femoral neck offset may be in the form of a scale (e.g., graduated lines). For example, the scale may be graduated in <NUM> increments. The scale may start at, for example <NUM> and end at <NUM>. This is a non-limiting example.

The markings may be associated with a colour coding which allows the surgeon to visually identify whether the measured femoral neck offset is a standard offset and/or a high offset.

A first series of markings on the arm that represent a femoral head offset within a first range (e.g., between <NUM> and <NUM>) may be associated with a first colour (e.g., green). The markings may be provided in the first colour (e.g., coloured ink), or may be provided on a background of the first colour. If the connector's pointer indicates that the measured femoral head offset is within this first range, the surgeon will use the standard offset resection guide surface/slot.

A second series of markings on the arm that represent a femoral head offset within a second range (e.g., between <NUM> and <NUM>) may be associated with a second colour (e.g., amber). The markings may be provided in the second colour (e.g., coloured ink), or may be provided on a background of the second colour. If the connector's pointer indicates that the measured femoral head offset is within this second range, the surgeon will need to know the planned stem size in order to decide whether to use the standard offset resection guide surface/slot or the high offset resection guide surface/slot.

A third series of markings on the arm that represent a femoral head offset within a third range (e.g., between <NUM> to <NUM>) may be associated with a third colour (e.g., red). The markings may be provided in the third colour (e.g., coloured ink), or may be provided on background of the third colour. If the connector's pointer indicates that the measured femoral head offset is within this third range, the surgeon will use the high offset resection guide surface/slot.

The markings may be provided on opposing surface of the arm. This enables the arm to be used on either a right or a left femoral head.

The connector has a proximal end and a distal end, and a longitudinal axis extending therebetween. When the connector is mounted onto an intramedullary rod, the longitudinal axis of the connector is substantially parallel with the femoral shaft axis.

In some constructions, the connector may be configured to ride up and down the intramedullary rod. This can be used to ensure that the frame is at the correct height to locate femoral head centre.

The arm may be retained in the slot of the connector via a friction-fit. Optionally, the connector further comprises a locking mechanism for locking the connector at a location along the length of the arm. This locking mechanism make take the form of a locking screw.

In order that the markings on the arm are visible to the surgeon when the arm is assembled with the connector, the connector may include a viewing window through which at least a portion of the markings are visible.

In some constructions, the pointer may be in the form of a line that extends in a proximal direction and/ or a distal direction from the viewing window.

Optionally, the pointer may be defined as a pointed projection.

The connector may further include a resection slot or resection guide for indicating a position of a vertical resection plane on the femoral neck. In some constructions, the connector has an inferior surface and the resection guide extends in a superior direction from the inferior surface. This guides a surgeon for the placement of a vertical femoral neck cut.

The resection guide may be a cutting slot for receiving a blade of a cutting device during resection of the neck.

According to an example there is provided a method for performing a controlled resection of the neck of a femur during a hip replacement procedure using a surgical apparatus comprising:.

The frame may be removably mounted on a posterior aspect of the femoral head. Alternatively, the frame may be removably mounted on an anterior aspect of the femoral head.

The connector may include a slot configured for slidable receipt of the arm, and the step of assembling the connector with the arm includes the step of slidably inserting the arm into the slot.

The frame may include a pin hole configured for removable receipt of a bone pin for removably mounting the frame on the femoral head, and wherein the step of mounting the frame on the femoral head includes the step of inserting a bone pin through the pin hole.

Constructions of the present invention will be described hereinafter, by way of example only, with reference to the accompanying drawings in which like reference signs relate to like elements and in which:.

The surgical apparatus <NUM> as shown in <FIG> includes a body <NUM>. The body includes a frame <NUM>, a resection guide <NUM> and an arm <NUM>. The surgical apparatus also includes a connector <NUM> which is used to mount the body portion of the surgical apparatus onto an intramedullary rod. The body may be a unitary piece. This is advantageous in terms of manufacturing, and also for sterilisation of the apparatus. The body may be manufactured from metal, for example stainless steel. A non-limiting example of a suitable thickness of metal is about <NUM>.

The frame <NUM> is mountable on the femoral head of the femur. The frame is used to position the body portion with respect to the centre of the femoral head.

The frame includes pin holes <NUM>, each of which is dimensioned for receipt of a bone pin for removably mounting the frame to the femoral head. The pin holes may be angled such that the drill guide hole points towards the centre of the femoral head (i.e., the drill guide hole is orientated at <NUM> degrees to the surface of femoral head).

The frame also includes "R" and "L" labels adjacent to the pin holes. These labels refer to the "Right Hip" or the "Left Hip". Due to the angle of the pin holes, the labels inform the surgeon which pin hole to use, depending on whether the surgery is being performed on the left hip or the right hip. This ensures that when the bone pins are inserted into the pin holes, the pins are directed towards the femoral head rather than away from it.

The resection guide <NUM> visually indicates to the surgeon the position of a resection plane on the femoral neck. In the construction shown, the resection guide includes two, substantially parallel, resection guide slots <NUM>, <NUM>. Each resection guide slot is configured to receive a blade of a cutting device during the resection of a femoral neck.

Resection guide slot <NUM> indicates a standard offset neck resection plane. Resection guide slot <NUM> indicates a high offset neck resection plane. The difference between the standard offset neck resection plane and the high offset neck resection plane will be about <NUM>. Resection of the femoral neck using the resection guide slots <NUM>, <NUM> is further illustrated below with reference to <FIG>. The design is closed medially over the calcar and open laterally towards the trochanter. Use of either of the resection guide slots <NUM>, <NUM> will result in a femoral neck resection that is <NUM> conservative of the planned neck resection. This will allow the use of a calcar reamer after preparation of the femoral canal.

The arm <NUM> includes markings <NUM> that are used to read off the femoral head offset. The markings in this construction take the form of a graduated scale. The scale shown in this construction is in <NUM> increments, starting at <NUM> (i.e., a <NUM> femoral head offset) and ending at <NUM> (i.e., a <NUM> femoral head offset). The same scale may be provided on opposing surfaces of the arm. A marking, for example "R" for right, or "L" for left, provided on the arm will indicate to the surgeon which side of the arm use.

The connector <NUM> is used to mount the body portion of the surgical apparatus on an intramedullary rod. In the construction shown, the connector is designed to be mounted on the intramedullary rod, but not locked onto it. The mounting may be via a friction-fit. This allows the connector to be moved up and down the intramedullary rod. Optionally, locking mechanisms may be included to lock the connector to the intramedullary rod.

The connector includes a slot <NUM> configured for slidable receipt of the arm <NUM>. The slot <NUM> has a slot axis (X) which traverses the longitudinal axis (Y) of the connector. In the construction shown, the slot axis is angled at about <NUM> degrees with respect to the longitudinal axis of the connector.

The connector also includes a generally rectangular viewing window <NUM>. The dimensions of the viewing window are such that the surgeon can view at a portion of the adjacent markings <NUM> on the arm <NUM>. For example, the surgeon can view at least two adjacent markings. As shown in this first construction of the surgical apparatus, the viewing window is sufficiently large enough for the surgeon to be able to see the markings from <NUM> to <NUM>.

The connector also includes a pointer <NUM>, shown here in the form of a line extending between the proximal end of the connector and the proximal surface of the viewing window <NUM>. The position of the line <NUM> on the connector relative to the markings <NUM> on the arm provides the surgeon with an immediate visual readout of the femoral head offset. In the construction shown, the line <NUM> is aligned with the <NUM> increment of the graduated scale. Accordingly, the surgeon can see that the femoral head offset is <NUM>. Advantageously, by using the surgical apparatus of the invention the surgeon does not need to undertake any mental arithmetic, which as well as being time-consuming, may be prone to human error.

The connector may include a "R" and a "L" label. These refer to "Right Hip" and "Left Hip". As the arm is symmetrical, the connector can be flipped over for use on either the left hip or the right hip,.

As shown in this construction, a locking mechanism <NUM> is provided on the connector, which can be used to lock the arm <NUM> and the connector <NUM> together. This prevents any inadvertent sliding movement of the arm relative to the connector, thereby ensuring an accurate reading of femoral head offset is made. In the construction shown, the locking mechanism is in the form of a locking screw provided at the proximal end <NUM> of the connector. This locking screw is configured for locking engagement within a groove provided on the proximal and/or distal surface of the arm. This groove is shown in <FIG>. The groove shown this construction does not extend to the medial and lateral ends of the arm. The groove is therefore a captive groove. This ensures that whilst the arm is free to slide within the connector, until locked in place, the connector will not inadvertently fall off the end of the arm during surgery. Optionally, the groove may extend along the entire length of the arm.

Provided at the distal end <NUM> of the connector is a cutting slot <NUM>. This slot may be used to perform a vertical resection of the femoral neck. This is illustrated below with reference to <FIG>.

A second construction of the surgical apparatus <NUM> is shown in <FIG>. The construction is essentially the same as the first construction, apart from the use of colour coding to visually help the surgeon. Like parts in this construction of the surgical apparatus are referenced using the same reference numbers as in <FIG>, incremented by <NUM>.

The markings <NUM> are associated with a colour coding which allows the surgeon to visually identify whether the measured femoral neck offset is a standard neck offset and/or a high neck offset.

A first series of markings 242a provided on the arm <NUM> represent a femoral head offset within a first range of between <NUM> and <NUM>. The markings are black, and are provided on a green background. This is referred to as the "green range" of femoral head offset.

A second series of markings 242b provided on the arm <NUM> represent a femoral head offset within a second range of between <NUM> and <NUM>. The markings are black, and are provided on an amber background. This is referred to as the "amber range" of femoral head offset.

A third series of markings 242c provided on the arm <NUM> represent a femoral head offset within a second range of between <NUM> and <NUM>. The markings are black, and are provided on a red background. This is referred to as the "red range" of femoral head offset.

The resection guide slots <NUM>, <NUM> are colour coded in a similar manner to the markings (242a, 242c). As such, the resection guide slot <NUM> (indicating a standard offset resection plane) is edged with green, and the resection guide slot <NUM> (indicating a high offset resection plane) is edged with red.

During use, if the connector's pointer <NUM> indicates that the measured femoral head offset is within the green range of femoral head offset, the surgeon marks the neck resection plane using the green resection guide slot <NUM>.

During use, if the connector's pointer <NUM> indicates that the measured femoral head offset is within the red range of femoral head offset, the surgeon marks the neck resection plane using the red resection guide slot <NUM>.

During use, if the connector's pointer <NUM> indicates that the measured femoral head offset is within the amber range of femoral head offset, the surgeon will need to know the planned stem size in order to decide whether to mark the neck resection plane using the green resection guide slot <NUM>, or the red resection guide slot <NUM>.

<FIG> illustrate the third to eighth constructions of the surgical apparatus according to the invention. The body (<NUM><NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) of the surgical apparatus includes a frame (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), a resection guide (<NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>), and an arm (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) as discussed above with reference to <FIG> and <FIG>. Each construction of the surgical apparatus also includes a connector (<NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>). Different designs of the connector are shown in each of the third to eighth constructions of the surgical apparatus. For example, each connector varies in the mechanism by which it is mounted to an intrameduallary rod. In addition, each connector varies in the design of the pointer.

<FIG> provides a non-limiting example of a flow of surgical steps in which the second construction of the surgical apparatus of the invention is used during hip arthroplasty.

<FIG>: An intramedullary rod (having a fully rounded collar) is inserted into the femoral canal;
<FIG>: The surgical apparatus according to the invention is pre-assembled. This involves sliding the arm of the body into the slot of the connector.

<FIG>: The connector <NUM> of the assembled surgical apparatus is then mounted onto the intramedullary rod. The surgeon the slides the arm <NUM>, in a generally medial/lateral direction, until the frame <NUM> is mounted on the femoral head. The arm is then locked in position by rotating the knob of the locking screw <NUM> in a clockwise direction.

<FIG>: Drill holes are drilled into the femoral head using the pin holes <NUM> on the frame. Pins are then inserted at an angle into the femoral head to secure the frame.

<FIG>: The surgeon takes a true femoral head offset measurement by looking at the relative location of the pointer <NUM> with the markings <NUM> on the arm. As shown, the pointer <NUM> is aligned the marking that indicated <NUM> femoral head offset. Notably, this is within "amber range" of femoral head offset.

<FIG>: The intramedullary nail/rod is removed from the femur.

Claim 1:
A surgical apparatus (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) for performing a controlled resection of the neck of a femur during a hip replacement procedure, the surgical apparatus (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
a body portion (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
a frame (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising an aperture, wherein the aperture is dimensioned for receiving a femoral head of the femur to position the body portion (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) with respect to a centre of the femoral head;
a resection guide (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) for indicating a position of a resection plane on the femoral neck, and
an arm (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) extending from the frame (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and including markings (<NUM>, <NUM>, 242a, 242b, 242c) for reading off a femoral head offset,
a connector (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) for mounting the body portion (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) on an intramedullary rod located in an intramedullary canal of the femur, and for slidably receiving the arm (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>),
wherein the connector (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) includes a pointer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), the femoral head offset being indicated by reading the position of the pointer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) relative to the markings (<NUM>, <NUM>, 242a, 242b, 242c) on the arm (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>).