REFERENCING APPARATUS

A referencing apparatus for application onto a patient, the referencing apparatus including: a support plate; a first locating element extending from the support plate; a second locating element extending from the upper support plate; a third locating element extending from the upper support plate; and an electronic orientation monitor housing adapted to receive an electronic orientation monitor; a docking station adapted to receive the housing and thereby define a reference point external to and relative to the patient's anatomy; wherein the first locating element, the second locating element and the third locating element are arranged to be pushed down onto a patient to provide a reference orientation for the electronic orientation monitor with respect to a predetermined anatomical site.

FIELD OF THE INVENTION

The present invention relates to surgical implements and surgical methods and in particular to a referencing apparatus that may be applied to a patient prior to, or during, surgical procedures, for example hip surgery involving prosthetic components.

BACKGROUND

The discussion of the prior art within this specification is not, and should not be taken as, an admission of the extent of common general knowledge in the field of the invention. Rather, the discussion of the prior art is provided merely to assist the addressee to understand the invention and is included without prejudice.

Whilst the following discussion is with respect to hip replacement surgery, a person skilled in the art will appreciate that the present invention is not limited to this particular field of use and may be adapted to use with any bone structure or various types of surgery.

Hip replacement surgery involves the use of a prosthetic cup (acetabular cup) or a prosthetic ball (femoral stems) or both to restore the ball and cup joint functionality of the hip. The ball and cup joint enable the hip to rotate in different directions to various degrees (in contrast to the relatively limited rotation of a knee joint).

Historically, hip replacement (arthroplasty) surgery required up to a 40 cm (7 to 12 inches) curved incision to provide sufficient access for the surgeon to manually access and manipulate the hip and femur. A prosthetic cup was attached to the hip socket or the head of the femur removed and replaced with a prosthetic ball, or both.

After the incision is made, the ligaments and muscles are separated to allow the surgeon access to the bones of the hip joint. It is typically this part of the surgery that makes the ligaments and muscles somewhat weak after surgery. Until they heal, which often takes about a month to six weeks, the patient must follow special hip precautions to prevent dislocation of the new hip joint.

Typical steps in hip replacement surgery include the following:Removing the Femoral Head: Once the hip joint is entered, the femoral head is dislocated from the acetabulum. Then the femoral head is removed by cutting through the femoral neck with a power saw.Reaming the Acetabulum: After the femoral head is removed, the cartilage is removed from the acetabulum using a power drill and a special reamer. The reamer forms the bone in a hemispherical shape to exactly fit the metal shell of the acetabular component.Inserting the Acetabular Component: A trial component, which is an exact duplicate of the patient's hip prosthesis, is used to ensure that the joint received will be the right size 5 and fit. Once the right size and shape is determined for the acetabulum, the acetabular component is inserted into place. In the uncemented variety of artificial hip replacement, the metal shell is simply held in place by the tightness of the fit or with screws to hold the metal shell in place. In the cemented variety, a special epoxy type cement is used to “glue” the acetabular component to the bone.Preparing the Femoral Canal. To begin replacing the femoral head, special rasps are used to shape and hollow out the femur to the exact shape of the metal stein of the femoral component. Once again, a trial component is used to ensure the correct size and shape. The surgeon will also test the movement of the hip joint.Inserting the Femoral Stem: Once the size and shape of the canal exactly fit the femoral component, the stem is inserted into the femoral canal. Again, in the uncemented variety of femoral component the stem is held in place by the tightness of the fit into the bone (similar to the friction that holds a nail driven into a hole drilled into wooden board—with a slightly smaller diameter than the nail). In the cemented variety, the femoral canal is rasped to a size slightly larger than the femoral stem. Then the epoxy type cement is used to bond the metal stem to the bone.Attaching the Femoral Head. The metal ball that replaces the femoral head is attached to the femoral stem.The Completed Hip Replacement: Before the incision is closed, an x-ray is taken to make sure the new prosthesis is in the correct position.

Such surgery had a number of problems including:a hospital stay of three days or more, post-operative pain and weeks of rehabilitation;each cm of incision has a tenfold increase in the risks of blood clotting and infection post-surgery;the surgeon was reliant on his experience and eye to ensure accurate placement of the cup into the three dimensional hip socket and alignment of the cup with the ball/femur to enable proper function of the joint. Misalignment may lead to post-operative complication such as misalignment of the leg, incorrect leg length and/or incorrect soft tissue tension. The long-term effects of misaligned prosthetic components can also include accelerated wear of the components, aseptic loosening of the components and potentially early repetition of the surgery.

Attempts to overcome these problems include:WO 2003/037192 which discloses a jib (impaction tool) for use in bone surgery and thus enables the use of a smaller incision. For hip replacement surgery, the jig enables the use of a 4 to 7 cm (2 to 3 inch) incision, i.e. keyhole surgery. Other benefits include a shorter stay in hospital, less blood loss, less pain, fewer postoperative dislocations and faster recovery; andWO 2005/046475 which discloses a gauge to assist the surgeon with accurate placement of a prosthetic when using a jig in keyhole surgery as the surgeon is no longer able to see the fit of the cup into the hip socket or the fit between the ball and cup.WO 2010/031111 which discloses a brace designed to define a reference point with respect to the patient in use to define the location for prosthetic placement.

The gauge provided in WO 2005/046475 has enabled efficient use of the impaction tool of WO 2003/037192. Commercial examples include the NivNav Hip System available from MAC Surgical. However, the gauge only works in two dimensions and there is still a heavy reliance on the surgeon's eye and experience for optimal placement of the cup into the hip.

A further attempt to overcome these problems was provided by WO 2010/031111, the contents of which are hereby incorporated in their entirety into this specification by way of cross reference. This prior art document discloses a brace (3) in the form of a clamp that is attachable to a patient to define a reference point relative to the patient's anatomy. This prior art clamp has a number of pads (14,16,17and18) that are positioned against various points of the patent's anatomy. However, it has been appreciated by the present inventor that this clamp is likely to be obstructive to at least some surgical procedures and does not readily accommodate the surgical drapes that are typically used in many surgical settings.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a referencing apparatus for application onto a patient. The referencing apparatus may include a support plate. The referencing apparatus may further include a first locating element extending from the support plate. The referencing apparatus may further include a second locating element extending from the upper support plate. The referencing apparatus may further include a third locating element extending from the upper support plate. The referencing apparatus may further include an electronic orientation monitor housing adapted to receive an electronic orientation monitor. The referencing apparatus may further include a docking station adapted to receive the housing and thereby define a reference point external to and relative to the patient's anatomy. The first locating element, the second locating element and the third locating element may be arranged to be pushed down onto a patient to provide a reference orientation for the electronic orientation monitor with respect to a predetermined anatomical site.

According to a particular arrangement of the first aspect, there is provided a referencing apparatus for application onto a patient, the referencing apparatus including: a support plate; a first locating element extending from the support plate; a second locating element extending from the upper support plate; a third locating element extending from the upper support plate; and an electronic orientation monitor housing adapted to receive an electronic orientation monitor; a docking station adapted to receive the housing and thereby define a reference point external to and relative to the patient's anatomy; wherein the first locating element, the second locating element and the third locating element are arranged to be pushed down onto a patient to provide a reference orientation for the electronic orientation monitor with respect to a predetermined anatomical site.

The housing may be a sterile housing. The housing may comprise: a body comprising an opening adapted for receiving the orientation monitor; a load funnel comprising an angled, leading wall, and an insertion wall for enabling a non-sterile orientation monitor to be inserted into the sterile housing whilst preventing contamination of the sterile housing; and a locking means comprising an enclosed frame adapted for engagement with the docking station, wherein the frame is pivotally attached to the body of the housing. The housing may be a clamshell housing.

The load funnel may be a transfer shield adapted to be placed over the opening of the housing to protect the sterile components of housing in use whilst the monitor is inserted through the shield and into the housing.

The locking means may comprise a central aperture shaped to receive the docking station within it, thereby to fix the orientation monitor to the reference apparatus to orient the electric orientation monitor with respect to the patient.

The first and second locating elements may be first and second anterior superior iliac spine locating elements. The third locating element may be a pubis locating element. The first and second locating elements may include a patient connecting plate. The patient connecting plate maybe arranged to fix to a patient above the anterior superior iliac spine.

An electronic orientation monitor may be dockable with the docking station in either a first docking configuration or a second docking configuration. The electronic orientation monitor may be housed in an electronic orientation monitor housing. The electronic orientation monitor housing may be arranged to engage the support plate to provide the reference orientation for the electronic orientation monitor.

The first docking configuration may define a first orientation of the electronic orientation monitor relative to the referencing apparatus. The second docking configuration may define a second orientation of the electronic orientation monitor relative to the referencing apparatus.

According to a second aspect of the invention, there is provided a method of using a referencing apparatus as defined in the first aspect to calibrate an electronic orientation monitor. The method may include the step of positioning a patient connector plate over the left anterior superior iliac spine. The method may include the further step of positioning a patient connector plate over the right anterior superior iliac spine. The method may include the further step of connecting the first and second locating elements to respective patient connector plates. The method' may include the further step of positioning the third locating element against the pubis. The method may include the further step of placing an electronic orientation monitor into a sterile housing comprising means for receiving the non-sterile monitor whilst preventing contamination with the sterile housing. The method may include the further step of engaging the housing comprising the monitor housed therein to a docking station disposed on the referencing apparatus to assume a reference orientation external to and relative to the patient. The method may include the further step of calibrating the electronic orientation monitor.

According to a particular arrangement of the second aspect, there is provided a method of using a referencing apparatus as defined in the first aspect, to calibrate an electronic orientation monitor, the method including the steps of: positioning a patient connector plate over the left anterior superior iliac spine; positioning a patient connector plate over the right anterior superior iliac spine; connecting the first and second locating elements to respective patient connector plates; positioning the third locating element against the pubis; placing an electronic orientation monitor into a sterile housing comprising means for receiving the non-sterile monitor whilst preventing contamination with the sterile housing; engaging the housing comprising the monitor housed therein to a docking station disposed on the referencing apparatus to assume a reference orientation external to and relative to the patient; and calibrating the electronic orientation monitor.

The referencing apparatus may be disposed anterior to the patient during the steps of pressing the referencing apparatus into engagement with the surgical drapes and during calibration of the electronic orientation monitor. An anterior approach may be used for surgical access to the patent's acetabulum.

The patient may be positioned such that they lie in a face up position during the above method steps.

According to a third aspect of the invention, there is provided a method of using a referencing apparatus as defined in the first aspect, to calibrate an electronic orientation monitor. The method may include the step of positioning surgical drapes onto a patient. The method may include the further step of engaging the plurality of locating elements against the surgical drapes such that the surgical drapes are disposed intermediate the plurality of locating elements and a respective plurality of predefined anatomical sites on the patient so as to cause a docking station disposed on the referencing apparatus to assume a reference orientation relative to the plurality of predefined anatomical sites. The method may include the further step of placing an electronic orientation monitor into a sterile housing comprising means for receiving the non-sterile monitor whilst preventing contamination with the sterile housing and docking the housing with the docking station so as to orient the electronic orientation monitor in a reference orientation. The method may include the further step of calibrating the electronic orientation monitor.

According to a particular arrangement of the third aspect, there is provided a method of using a referencing apparatus as defined in the first aspect, to calibrate an electronic orientation monitor, the method including the steps of: positioning surgical drapes onto a patient; engaging the plurality of locating elements against the surgical drapes such that the surgical drapes are disposed intermediate the plurality of locating elements and a respective plurality of predefined anatomical sites on the patient so as to cause a docking station disposed on the referencing apparatus to assume a reference orientation relative to the plurality of predefined anatomical sites; placing an electronic orientation monitor into a sterile housing comprising means for receiving the non-sterile monitor whilst preventing contamination with the sterile housing and docking the housing with the docking station so as to orient the electronic orientation monitor in a reference orientation; and calibrating the electronic orientation monitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Broadly, the present invention relates to a referencing apparatus100that is for application onto a patient for hip surgery such as, but not limited to, a hip replacement. Referring to the drawings, the referencing apparatus100of the present invention is used for assisting a surgeon to orient a prosthetic component relative to a patient's anatomy during surgery. The referencing apparatus100is able to be placed over the patient by a surgeon allowing for the easy and reliable orientation of an electronic orientation monitor46in housing12. When oriented, the electronic orientation monitor can be disengaged from the referencing apparatus100and attached to the prosthetic component to provide position details of the prosthetic component for reliable and accurate insertion of the prosthetic component into the patient. The prosthetic component may, for example, be a surgical impactor which is used to place the prosthetic component into the patient. The orientation monitor provides position details of the impactor which is equivalent to the position of the prosthetic to ensure accurate placement of the prosthetic component within the patient orientation monitor46comprises an inertial measurement unit (IMU) including a tri-axial digital gyroscope and tri-axial digital accelerometer. In particular embodiments, the IMU is an integrated digital gyroscope and accelerometer sensor specifically designed for inertial measurements and provides increased dynamic range, improved sensitivity, greater accuracy, lower bias and lower drift when compared with prior gyroscope/accelerometer implementations. In particular embodiments, the IMU selected enables precise positional awareness and determination without the need for additional navigational components, such as, for example, magnetometer or compass components which may experience interference from localised magnetic fields (e.g. from medical imaging equipment) which would adversely affect the accuracy of the critical orientation parameters which must be determined by the orientation monitor46. In particular embodiments, the surgeon may be provided with the ability to select or enter specific prosthetic angles and related data to the orientation monitor46to assist and fine tune the orientation calibration with respect to the patient's unique anatomy.

The preferred embodiment is particularly suited for assisting surgeons to properly locate an acetabular cup into a reamed acetabulum during hip surgery, such as total or partial hip replacements or revisions. When used in this context, the reference apparatus100is pushed down from above onto the patient's pelvis to assume a reference position to orient an electronic orientation monitor46to assist in the positioning of surgical impactors and prosthetic components.

This detailed description shall describe the use of the referencing apparatus100and electronic orientation monitor46as an aid in the insertion of a prosthetic component in the form of an acetabular cup, into a reamed acetabulum of a patient's pelvis wherein an anterior approach is used for surgical access to the patent's acetabulum. An important part of this process is the use of the referencing apparatus100to calibrate an electronic orientation monitor46, which may be similar to the monitor as disclosed in applicant's prior application no. WO 2010/031111, the contents of which have been incorporated in their entirety into this specification by way of cross reference. However, it will be appreciated by those skilled in the art that the invention may be used in other surgical contexts.

With reference to the Figures, the referencing apparatus100comprises the following components:a frame10, for positioning of the electronic orientation monitor in a reference position with respect to the patient;first and second anterior superior iliac spine (ASIS) locating elements14;a third, pubis locating element16;an electronic orientation monitor46; andelectronic orientation monitor housing12.

The frame10includes an upper support plate in the form of channel section11and T channel

section15extending perpendicularly from the channel section11. A first ASIS locating element14extends outwardly from the base of one longitudinal end of the channel section11and the second ASIS locating element14extends from the opposite longitudinal end of the channel section11. The third, pubis locating element16extends outwardly from the base of the T channel section15.

A force applying plate13forms part of the channel section11and provides an interface for downwards force to be applied to the referencing apparatus100onto the patient through the locating elements14,16to orient the electronic orientation monitor46.

The first and second ASIS locating elements14connect to the channel section11and extend outwards and generally perpendicularly to the channel section11. In one embodiment, to provide the ability to use a single sized referencing apparatus100on different sized and hip profile patients, the first and second ASIS locating elements14attach to the channel section11so that they can be fixed at different positions. In one embodiment, the connecting face of the channel section11has a number of fixing points that can be selected from to attach the first and second ASIS locating elements14. In an alternative embodiment the underside of the channel section11includes a rail with an attachment point for the first and second ASIS locating elements14. The attachment point can be locked in place as desired.

The third, pubis locating element16connects to the T channel section15and extend outwards and generally perpendicularly to the T channel section15. In one embodiment, to provide the ability to use a single sized referencing apparatus100on different sized and hip profile patients, the third, pubis locating element16is attached to the T channel section15so that it can be fixed at different positions. In one embodiment, the connecting face of the T channel section15has a number of fixing points that can be selected from to attach the third, pubis locating element16.

In an alternative embodiment the underside of the T channel section15includes a rail with an attachment point for the third, pubis locating element16. The attachment point can be locked in place as desired.

Extending from the channel section11are docking stations19shaped to receive the electronic orientation monitor46contained within the housing12. Docking stations19are designed to be highly toleranced and locate the monitor46in a precisely defined position so as not to compromise the accuracy of the measuring system. Engaging either one of the docking stations19with the electronic orientation monitor46contained within the housing12defines a reference point relative to the patient's anatomy. This reference point is external of the patient and is used to orient the electronic orientation monitor46into a reference orientation. Whilst in this orientation the electronic orientation monitor46acquires reference orientation information which is used to calibrate electronic orientation monitor46to the reference orientation. In one embodiment, as shown in inFIG.1, the docking station19of frame10includes a central aperture17and the docking station19is profiled to receive and fix in place the electronic orientation monitor46. In further embodiments of the frame, e.g. frame70ofFIG.2B, docking stations19do not comprise an aperture therein.

First and second ASIS locating elements14include a rod extension20that extends from the base of the channel section11, a base21and patient connecting plate18. The patient connecting plate18is arranged to be fixed to the patient's body over the patient's ASIS. The position of the patient connection plate18defines where the first and second ASIS locating elements14will be placed on the patient.

The pubis locating element16extends as a bar from the channel section11and ends in pubis probe23. The pubis probe23is shaped to nestle within the ridges of the pubis of the patient in use. With the pubis probe23nestled between the pubis ridges on the patient and the first and second ASIS locating elements14in place on the connection plates18, a known reference position of the channel section11and referencing apparatus100as a whole, with reference to the patient, is then known.

In this known position, the electronic orientation monitor46can be placed on the docking station19in the electronic orientation monitor housing12appropriate for the hip side that they are to operate on in accordance with the surgeon's personal preference i.e. regardless of the hip which the surgeon in to operate on, the surgeon may place the orientation monitor46in housing12and attach the housing to either of the two docking stations19(on either the left or right side of frame10,70) of the referencing apparatus100. In practice, the range of desired locations selectable by the surgeon for the orientation monitor46is limited by the anatomy of the patient and clinical efficacy. The location selected by the surgeon is determined by a combination of the type of implant and the patient's anatomy tempered by the surgeon's clinical judgement. The referencing apparatus100can be considered to establish a commonly used/accepted pre-defined orientation with respect to the patient's anatomy. The addition of the orientation monitor46to the apparatus100provides the surgeon with live positional feedback, which enables the surgeon to position the implant in a desired location which may differ from the pre-defined position, should the surgeon think this appropriate.

FIG.2Ashows an alternate embodiment50of frame10wherein channel section11and T-channel section15of the prior embodiment are replaced with rigid non-channel arms51and52respectively are replaced with a non-channel frame50. Adjustment slots52and53are provided in at least one of arms51, and also in T-section54for adjustment of the spacing between the first and second ASIS locating elements14having feet22, and also for adjustment of pubis locating element16with respect to the patient's unique anatomy. The particular embodiment show inFIG.2Ais described in greater detail in Australian Patent No. AU2013204941, the contents of which are entirely incorporated herein by cross reference.

FIG.2Bshows an alternate embodiment70of frame10and frame50wherein, again a channel section frame is not used but rather slots71and72on the arms74of frame70and also, slot75on T-section76(similar in nature to slots52and53ofFIG.2A) are provided. In this present embodiment, ASIS locating elements14terminate in a lever lock system which engages with slots71and72respectively of frame70. Similarly, pubis locating element16terminates in a lever lock system which engages with slot75so that the ASIS locating elements14and pubis locating element16can be adjusted to locate the anatomical features of the patient and then be locked in position. As shown inFIG.2A, slots71and72of arms74and slot75of T-section76may optionally comprises a series of regularly spaced detents to assist in correctly locating the locating elements14and16and also to aid the locking clamps to secure the locating elements14and16in place.

Docking stations19of the embodiment shown inFIG.2Balso comprises magnet locating features77. Locating features77are sensed by the orientation monitor46when engaged with either of the docking stations19. Locating features77sense placement of the orientation monitor housing12including the orientation monitor46and assist in ensuring that referencing apparatus100is used as intended and to avoid error, for example, which may arise if the monitor46or the frame10,50,70, is used before it has been properly calibrated.

As best shown inFIGS.3and4, the patient connecting plate18includes a central ring protrusion29defined by the perimeter22of the first and second ASIS locating elements14, a central aperture30defined by the central ring protrusion29, a base27and base protrusions28. The central ring protrusion29acts to be received in the recess32defined by the perimeter22of the first and second ASIS locating elements14. With a patient connecting plate18fixed in place on both the left and right second ASIS, the recesses32on first and second ASIS locating elements14can be placed over the central ring protrusions to place the referencing apparatus100in a reference orientation when the pubis locating element16is also in place. The ring structure of patient connecting plate18also allows the surgeon to easily place the patient connecting plate18directly over the patient's ASIS when the patient is covered by surgical drapes

FIG.4illustrates the fixing of the patient connecting plate18to the patient. An adhesive sterile film35is attached to the patient's skin36. A connector plate adhesive34is stuck to the adhesive film35over the anterior superior iliac spine and fixes external of the patient and is used to orient the electronic orientation monitor46into a reference orientation. Whilst in this orientation the electronic orientation monitor46acquires reference orientation information which is used to calibrate electronic orientation monitor46to the reference orientation. A patient covering sheet33can be accommodated between the patient connecting plate18and the first and second anterior superior iliac spine locating elements14.

FIGS.5to8illustrate the electronic orientation monitor46and the electronic orientation monitor housing12. The electronic monitor housing12is a sterile housing so that the electronic orientation monitor46need not be sterile for use on a patient. In one embodiment, the electronic monitor housing12is a clamshell housing. The electronic monitor housing12includes a body24for receiving the electronic orientation monitor46, a lid41, a load funnel37and a locking means80.

The clamshell housing12performs three main functions:1. It provides a physical barrier against biological contamination of the orientation monitor.2. It provides physical vibration isolation from high levels of shock for the orientation monitor that it would otherwise experience when being used.3. It maintains proper alignment of the orientation monitor. The accuracy of orientation monitor is highly sensitive to any misalignment so the clam-shell has alignment features built in to maintain proper alignment during use.

The clam-shell housing12is preferably designed to be supplied as a sterilised, single use part. Re-using a clam-shell housing12can pose a safety risk for the patient through one or more of:misalignment caused by wear and tear from re-use;misalignment because of deformation from cleaning or handling;contamination leading to infection because of incorrect or poor re-sterilisation.

The load funnel37includes an angled leading wall38and an insertion wall39. The load funnel is sterile and prevents non-sterile components touching sterile components of the electronic orientation monitor housing12. The load funnel is inserted into the electronic orientation monitor housing12to allow the non-sterile electronic orientation monitor46to be inserted into the electronic orientation monitor housing12. When in the electronic orientation monitor housing12, the non-sterile electronic orientation monitor46can be used in a sterile environment and can withstand forces applied to the electronic orientation monitor housing12as discussed further below. Housing12also preferably includes one or more internal locating features adapted to ensure the correct alignment of the monitor46within housing12, and thus to ensure repeatable and accurate orientation measurements.

In an alternative embodiment shown inFIG.5A, load funnel37is replaced with a transfer shield60. Shield60is placed over the opening of housing12to protect the sterile components of housing12whilst monitor46is inserted through shield60and into housing12. Shield60provides for improved protection to the sterile components of housing12during insertion of the monitor46than the load funnel37ofFIG.5. The housing12protects the navigation unit during use to provide impact isolation and a physical barrier to bio-contamination.

The electronic orientation monitor housing12includes body24, cap41, clip42and clip lock47arranged to receive and lock the clip42and cap41in place to seal the body24. The cap41, clip42and clip lock47are part of lid43of the electronic orientation monitor housing12. The cap41pivots around a connection with the lid43to seal the body24.

Locking means80extends from the base of the electronic orientation monitor housing12to engage with the docking stations19to fix the electronic orientation monitor46to the reference apparatus100for obtaining a reference orientation.

The locking means80includes perpendicular extension members25that extend perpendicularly

from the body24. There are a forward and rear pair of perpendicular extension members25that form a square profile. Support frame member26extends between forward and rear perpendicular extension members25to form an enclosed frame. The perpendicular extension members25are attached to the body at upper pivot points45. This allows the perpendicular extension members25to rotate around upper pivot points45. The support frame member26is attached to the perpendicular extension members using lower pivot points44. This allows the ends of the perpendicular extension members25to pivot around the support frame member26. The attachment means is further adapted to engage with a mounting frame90includes vibration isolation features to absorb forces applied to the electronic orientation monitor housing12longitudinally will be described below. Isolation features in particular embodiments include spring features91as discussed below and shown, for example, inFIG.5B.

The enclosed frame of locking means80includes a central aperture48that is shaped to receive the docking station19within it to fix the electronic orientation monitor46to the reference apparatus100to orient the electric orientation monitor46with respect to a patient for further surgical use.

A further embodiment of electronic monitor housing12is shown inFIGS.5A to5C. In this further embodiment, the angle of the housing24is set at an inclined angle by mounting frame90to permit easier viewing by the surgeon and surgical staff. Mounting frame90is configured to precisely engage with docking stations19of the referencing apparatus100. Spring features91of the mounting frame90act to isolate the orientation monitor housing12and installed orientation monitor46from environmental vibrations during operation to improve the positional accuracy able to be provided by the orientation monitor46.

FIGS.6and7show further views of the clamshell housing12disclosed above.FIGS.8A and8Bdepict the clamshell housing12engaged with frame70of referencing apparatus100.

Referring toFIG.9, with an orientation assumed by the electrical orientation monitor46, the electronic orientation monitor housing12with the electronic orientation monitor46inserted is attached to an insertion implement52having an acetabular cup54. The surgeon manipulates the insertion implement52into a position whereby the cup is adjacent the acetabulum of the patient and a display (not shown) on the electronic orientation monitor46guides the surgeon to orient the insertion implement such that the current orientation of the electronic orientation monitor46is equal to the reference orientation (or such that the current orientation has some other desired relationship to the reference orientation). The display provides positional and orientational information to the surgeon including: yaw/inclination axis orientation and anteversion/pitch axis orientation to allow the surgeon to orient the prosthetic tool precisely with the patient's unique anatomical structure. The orientation monitor46may provide orientation information to the surgeon in a number of different ways, depending on the particular surgeon's preference. For example the orientation of the insertion implement52with respect to the patient's acetabulum may be conveyed to the surgeon through a simple target display, where the degree the implement56is off-target, may be conveyed visually. Further examples of an orientation display may include a “bubble-level” visual display, or a numerical display depending upon the surgeon's personal preference.

Once the desired orientation has been achieved, the electronic orientation monitor46provides an indication to the surgeon, such as a visual indication on the display and/or an audible indication, and this prompts the surgeon to either assess the trial cup, or to hit the impactor plate55to transfer force through the shaft53to impact the acetabular cup54into the patient's reamed acetabulum.

When placed on the insertion implement52, the electrical orientation monitor housing12is arranged to isolate shock from the electronic orientation monitor46. The perpendicular extension members25pivot around pivot points44and45to move the support frame member26forwards or backwards to isolate force applied to the impactor plate55from the electronic orientation monitor46. Spring formations91of the embodiment of housing12as seen inFIG.5Bare particularly adapted for shock isolation from the insertion implement during use.

From the foregoing description it will be appreciated that the referencing apparatus100is configured for solely anterior engagement with the patient and the patient connector plates18that are on the patient during the steps of pressing the referencing apparatus into engagement with the surgical drapes and during calibration of the electronic orientation monitor. This compares favourably with the clamp disclosed in WO 2010/031111, which requires both anterior and posterior engagement with the patient. This is because it has been appreciated by the present inventor that in practice the clamp of WO 2010/031111 may cause an undesirable obstruction to the surgeon.

Whilst the invention has been described with reference to specific examples, those skilled in the art will appreciate that it may be embodied in many other forms.