Patent Description:
In some cases, a cement restrictor may be inserted in the cavity before the cement is introduced. The cement restrictor may serve various purposes. The cement restrictor may provide a solid foundation against which cement may be pressurised in order to ensure good introduction of cement into the cavity. Additionally, or alternatively, the cement restrictor may prevent, or reduce the amount of, cement passing beyond it and further into the prepared cavity. An excess of cement in the cavity may introduce difficulties should revision surgery be required later on, for example, requiring the excess cement to be removed from the cavity during revision surgery.

Irrespective of the reason for using the cement restrictor, there is generally a preferred position or depth within the cavity at which the cement restrictor should be placed. This preferred position or depth may be related to the position of the prosthetic implant in order to try and ensure that there is a preferred amount of cement between the cement restrictor and the prosthetic implant. Too much cement between the cement restrictor and implant gives rise to the same potential difficulties for revision surgery mentioned above and too little may reduce the ability for the prosthetic implant to settle properly after insertion and/or properly to fix the implant within the cavity.

Hence, correctly positioning the cement restrictor is generally desirable. However, the correct position of the cement restrictor may be a function of the size and/or type of implant being used. Also, the surgeon has no easy way of visualising the position of the cement restrictor during insertion as the cement restrictor will be hidden from view within some cavity.

Introducers for cement restrictors have been provided with various markings thereon to provide some guidance to the surgeon as to the depth to which the cement restrictor has been inserted. However these marking may be difficult to see and/or read during surgery. Also, the anatomical feature against which these markings should be aligned may be hard to visualise at the surgical site and/or ill defined. Also, there may be no clear relationship between the various markings and the insertion depth that the surgeon is currently trying to achieve for the intended prosthetic implant. It may be difficult for the surgeon reliably to recall which of the multiple markings they should currently be using. This issue is exacerbated for more sophisticated implant systems in which the appropriate position for a cement restrictor varies in a more complex way with the different sizes of implants that may be available.

The <CIT> discloses a cement restrictor inserter instrument of the type claimed. This known instrument comprises an inserter having a handle at a proximal end, a cement restrictor attachment formation at a distal end for releasably attaching a cement restrictor, a shaft and a stop on the shaft and between the proximal end and the distal end and a body having a shape corresponding to a proximal part of a corresponding orthopaedic prosthetic implant. It further comprises a visible depth guide feature wherein the visible depth guide feature is aligned with a feature of a bone of a patient in which the cement restrictor is to be inserted.

Further cement restrictor inserter instruments are known from <CIT>, <CIT>, <CIT> and <CIT>.

Hence, instruments and methods which may facilitate the ease and/or reliability with which cement restrictors may be positioned would be beneficial.

According to the present invention there is provided a cement restrictor inserter instrument, as defined in claim <NUM>. Optional further features of the cement restrictor inserter instrument are defined in the dependent claims.

The cement restrictor inserter instrument comprising: an inserter having a handle at a proximal end, a cement restrictor attachment formation at a distal end for releasably attaching a cement restrictor, a shaft extending from the proximal end to the distal end and a stop on the shaft and between the proximal end and the distal end; and a body having a shape corresponding to a proximal part of a corresponding orthopaedic prosthetic implant, a spacer, a visible depth guide feature and a releasable attachment mechanism by which the body is releasably attachable to the rod, and wherein the spacer is configured to position the visible depth guide feature at a fixed position relative to the inserter when the spacer abuts the stop corresponding to a target cement restrictor position when the visible depth guide feature is aligned with a feature of a bone of a patient in which the cement restrictor is to be inserted.

The releasable attachment mechanism may include a push fit or snap fit mechanism.

The stop may include an attachment formation and the releasable attachment mechanism may interact with the attachment formation.

The releasable attachment formation may include a C-clip or circlip and a groove arranged to receive the C-clip or circlip. The C-clip or circlip may be within a part of the stop and/or the releasable attachment mechanism of the body may include the groove.

The body may define an open channel or a closed channel and configured to accept the shaft. The channel may extend along a longitudinal axis of the body and/or extend along an axis parallel to a longitudinal axis of the shaft.

The releasable attachment mechanism may be a rotary releasable attachment mechanism. The releasable attachment mechanism may permit rotation of the shaft relative to the body.

The cement restrictor attachment formation may comprise a push fit formation.

The cement restrictor attachment formation may comprise a rotary attachment mechanism. The rotary attachment mechanism may be a screw thread.

The visible depth guide feature may comprise a surface or an edge of a part of the body.

The visible depth guide feature may comprise a marking on a surface of a part of the body.

The visible depth guide feature may comprise a plurality of markings on the surface of the part of the body. Each of the plurality of markings may correspond to a different position, or depth of insertion, of the orthopaedic prosthetic implant relative to the bone of the patient.

The orthopaedic prosthetic implant may be a humeral stem, a shoulder component, a femoral stem, a femoral component of a knee or a tibial component.

The body may have a size corresponding to the size of the orthopaedic prosthetic implant.

The body may have a size with dimensions corresponding to the size of the orthopaedic prosthetic implant to within <NUM>, <NUM>, <NUM>, <NUM> or <NUM>.

The body may be mounted on the inserter with the spacer abutting or engaging or mating with the stop.

A further embodiment provides a kit of surgical instrument parts comprising:
the cement restrictor inserter instrument of the first aspect; and a further body having a shape corresponding to the shape of the orthopaedic prosthetic implant, a further spacer, a further visible depth guide feature and a further releasable attachment mechanism by which the further body is releasably attachable to the shaft. The further body may have a different size to the body. The further body may have a different length and/or a different width. The further body may be larger or smaller than the body. A plurality of further bodies may be provided and each body may have a different size and/or the same shape. The further body may have a different size to the body and may correspond to the shape of a different size of the orthopaedic prosthetic implant. The further spacer may have a different size to the spacer and may be configured to position the further visible depth guide feature at a different fixed position relative to the inserter when the further spacer abuts the stop corresponding to the target cement restrictor position when the further visible depth guide feature is aligned with the feature of the bone of the patient in which the cement restrictor is to be inserted.

A method of inserting a cement restrictor in a cavity in a bone of a patient, which is useful as background information to the disclosure, is disclosed, the method comprising: selecting a body having a shape corresponding to the shape of an orthopaedic prosthetic implant to be implanted in a cavity in a bone of a patient, wherein the body includes a visible depth guide feature; releasably attaching the body to a shaft of a cement restrictor inserter at a pre-determined position; attaching a cement restrictor to a distal end of the shaft of the cement restrictor inserter; inserting the cement restrictor inserter with the body mounted thereon into the cavity to a depth determined by the visible depth guide feature being aligned with a feature of the bone of the patient.

The method may further comprise rotating the shaft of the cement restrictor inserter relative to the body to detach the cement restrictor from the distal end of the rod; and withdrawing the cement restrictor inserter from the cavity.

Selecting the body may further comprise selecting the body having a size corresponding to the size of the orthopaedic implant to be implanted in the cavity of the bone of the patient.

The method may further comprise: determining the size of the orthopaedic implant to be implanted is based on a final trial component or a final broach or a final reamer or a final cutting instrument, before selecting the body.

The method may further comprise attaching a cement restrictor trial to the distal end of the shaft and inserting the cement restrictor inserter into the cavity to trial a size for the cement restrictor, after attaching the body and before attaching the cement restrictor.

The feature of the bone of the patient may be an anatomical feature of the bone of the patient.

The feature of the bone of the patient may be a resected surface or edge or rim of the bone of the patient.

The visual depth guide may be a surface or an edge of the body.

The visual depth guide feature may be a marking on a surface of the body.

The visual depth guide feature may comprise a plurality of markings on a surface of the body. Each marking may correspond to a different position of the orthopaedic prosthetic implant relative to the bone of the patient, for example a depth of insertion. The method may further comprise using the marking corresponding to a selected one of the different positions to determine the depth to which the cement restrictor inserter is inserted.

The prosthetic orthopaedic implant may be a femoral stem. The feature of the bone of the patient may be a proximal resection of the femur or a neck resection of the femur.

The prosthetic orthopaedic implant may be a tibial component. The feature of the bone of the patient may be a proximal resection of the tibia.

The prosthetic orthopaedic implant may be a humeral stem. The feature of the bone of the patient may be a proximal resection of the humerus or a rim of a cavity reamed in the proximal humerus.

Embodiments 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, the same reference numerals are used to refer to refer to like parts unless indicated otherwise.

With reference to <FIG>, there is shown a view of a hip joint of a patient <NUM> which has undergone a total hip replacement surgical procedure. The prosthetic components include an acetabular cup <NUM> implanted in the prepared acetabulum of the pelvis <NUM> of the patient. As illustrated in <FIG>, the acetabular cup <NUM> includes a liner <NUM> providing an articulating surface. A cross section view of the proximal part of the femur <NUM> of the patient is also shown. The femoral part of a prosthesis includes a femoral head <NUM> mounted on a femoral stem <NUM> via a neck <NUM>. A distal end of the femoral stem <NUM> includes a centraliser <NUM>. The femoral stem <NUM> is located within a cement mantel <NUM> within an intramedullary cavity of the femur. Toward the distal end of the intramedullary cavity there is provided a cement restrictor <NUM>. As illustrated in <FIG>, there is a gap between the distal most part of the femur (stabiliser <NUM>) and the cement restrictor <NUM> of side <NUM> which is preferably approximately <NUM>-<NUM>.

Preferably, the cement mantel <NUM> has a thickness of a few millimetres, e.g. approximately <NUM>, around the stem <NUM> which is generally centrally located within the intramedullary cavity of the femur. Also, preferably, the distance between a distalmost portion of the stem and the cement restrictor <NUM> is sufficient to allow the stem <NUM> to settle within the cement. However, it is not so great that excess cement is present within the intramedullary cavity, for example, to avoid difficulties in removing that cement, should revision surgery subsequently be required. In practice, the distance <NUM> is preferably approximately <NUM>.

The use of cement restrictors is generally understood by a person of ordinary skill in the art, and cement restrictors can be used in other orthopaedic procedures in which some prosthetic component is cemented in place within a cavity of a patient's bone. As briefly discussed above, preferably, there is some finite distance between the cement restrictor and distal most part of the prosthetic implant component. However, the difficulty arises in trying to ensure that the cement restrictor <NUM> is placed at a depth within the cavity likely to give rise to the preferred separation <NUM> between the end of the prosthetic component and the cement restrictor. This is not something that can be achieved visually as the cement restrictor <NUM> is hidden from view when inserted into the cavity prior to cementation.

<FIG> shows a side view of a cement restrictor inserter instrument <NUM> according to a first embodiment and having a cement restrictor <NUM> attached to a distal end thereof. The cement restrictor inserter instrument <NUM> has a handle <NUM> at a proximal end and an attachment formation at a distal end <NUM> (not visible in <FIG>) via which the cement restrictor <NUM> can releasably attach to the inserter instrument <NUM>. A shaft <NUM> extends from the handle <NUM> to the distal end <NUM>. A stop <NUM> is provided on the shaft between the proximal and distal ends. A body <NUM> is provided on the shaft <NUM>. The position of the body <NUM> along the shaft <NUM> is controlled by stop <NUM> abutting a spacer part <NUM> of body <NUM>.

<FIG> shows a side elevation of the cement restrictor inserter <NUM> being part of the overall instrument <NUM>, omitting the body <NUM>. Hence, the overall instrument <NUM> may be considered an assembly of the body <NUM> and the inserter <NUM>. As illustrated in <FIG>, the inserter <NUM> has a generally T-bar construction. Handle <NUM> is in the form of a circular cylindrical cross bar attached to the proximal end of the shaft <NUM>. Shaft <NUM> has a generally circular rod form. As illustrated in <FIG>, an attachment formation <NUM> is provided at the distal end <NUM> of the shaft <NUM> and in the illustrated embodiment, may take the form of a screw thread. However, in other embodiments, the attachment formation may provide a push fit interface with a corresponding femur feature in the cement restrictor <NUM>.

The stop <NUM> has a flared portion extending to a greater diameter than shaft <NUM> and provides an abutting shoulder portion <NUM>. A circular cylindrical boss <NUM> extends toward the distal end and defines a groove or recess <NUM> therein. A C-clip or circlip <NUM> is located within circular groove <NUM>. Circlip <NUM> is generally in the form of a C or split ring of a resilient material, such as a metal, for example stainless steel. The inserter part <NUM> of the cement restrictor inserter instrument illustrated in <FIG> may be made from a suitable metal or alloy, for example stainless steel.

<FIG> show various views of a further body <NUM>, generally similar to body <NUM> illustrated in <FIG>. As explained in greater detail below, the major difference between the body <NUM> shown in <FIG> and the body <NUM> shown in <FIG> is the length of the spacer element along a direction parallel to the axis of the shaft <NUM> of the inserter <NUM>. <FIG> shows a side elevation of body <NUM> (generally in the anterior-posterior direction) and <FIG> shows a side elevation. <FIG> shows a cross-sectional view through the body along line L-L'. <FIG> shows a perspective view of the body <NUM> and <FIG> shows an expanded cross sectional view of a part <NUM> of the cross section of <FIG>.

As best illustrated in <FIG>, the body <NUM> generally has the same shape as the proximal part of the femoral stem <NUM> illustrated in <FIG>. However, the body <NUM> corresponds to the proximal part only of the stem <NUM> and is distally truncated, in that that distal part of the prosthetic stem <NUM> is not present. Also the body <NUM> is truncated at the part corresponding to the neck <NUM> of the prosthetic stem <NUM>. The part <NUM> of the body corresponding to the proximal part of the stem <NUM> may also have substantially the same dimensions as the proximal part of the stem <NUM>. That is, the body <NUM> has generally the same shape and size as the proximal part of the corresponding prosthetic component <NUM>.

It is not essential that the dimensions of the body and corresponding prosthesis are identical. The body may be a simplified version of the proximal part of the stem which has generally the same form or shape and which would be easier and cheaper to machine. Hence, generally speaking, the body should be as close in geometry as is economically reasonable to the corresponding prosthesis. However, the body should not be longer or wider or thicker than the final broach or trial or cutting instrument used to form the femoral cavity otherwise the body would contact the interior walls of the femoral cavity prematurely and prior to the cement restrictor having been inserted to the desired depth.

A spacer part <NUM> extends from a proximal part of the body <NUM> and generally along a longitudinal axis <NUM> of the body which is generally parallel to the longitudinal axis of the shaft <NUM> of the inserter <NUM>. As best illustrated in <FIG>, the body <NUM> defines a channel <NUM> extending generally along the longitudinal axis and between a lower opening <NUM> and upper opening <NUM> of the spacer <NUM>.

The spacer element <NUM> has a generally circular cylindrical construction and defines a slightly tapered cavity <NUM> therein. As best illustrated in <FIG>, an inner wall <NUM> of the spacer defines a groove <NUM> therein extending around the longitudinal axis. Cavity <NUM> is sized to snugly received boss <NUM> therein and groove <NUM> is positioned and dimensioned to receive circuit <NUM> therein to provide a releasable attachment mechanism between the body <NUM> and remainder of the cement restrictor inserter <NUM>.

Hence, the body <NUM> may be slid along shaft <NUM> of the inserter until the spacer <NUM> abuts the stop <NUM> to fix the position of the body relative to the remainder of the inserter. The releasable attachment mechanism prevents the body from being unintentionally removed from the shaft during handling.

As best illustrated in <FIG>, a visual depth guide feature <NUM> is provided on an anterior surface <NUM> of the body. A similar alignment feature is provided on the posterior side which is not visible in the Figures.

In the illustrated embodiment, the visual depth guide feature <NUM> is in the form of a plurality of markings <NUM>, <NUM>, <NUM>, each comprising a linear section. The linear sections are arranged generally perpendicularly to the direction of the neck axis of the corresponding stem component <NUM>. Indeed, corresponding markings <NUM> can be seen on the prosthetic stem component <NUM> in <FIG>.

As described above, the body part <NUM>, <NUM> of the inserter instrument <NUM> is releasably attachable to the inserter <NUM> by being slid along the shaft <NUM> and releasably attaching to the stop <NUM>. In practice, a plurality of body parts each corresponding to a different size of prosthetic component may be provided. For example, <FIG> shows a first body <NUM>, a second body <NUM> and a third body <NUM> each corresponding to a different sized prosthetic femoral stem. It will be appreciated that in other embodiments, a greater or lesser number of bodies may be provided. In this described example, the first body <NUM> corresponds to a smallest stem, the second body <NUM> corresponds to a medium sized stem and the third body <NUM> corresponds to a largest stem.

Generally speaking, the size of a stem is determined by its size in the medial-lateral direction. The length of the stem may also vary with the size of the stem such that a smaller stem will have a lesser length in the anterior-posterior direction than a larger sized stem. Therefore, the first body <NUM> corresponds to a prosthetic femoral stem having a smallest length in the inferior-superior direction, second body <NUM> corresponds to a second prosthetic femoral stem having a greater length in the inferior-superior direction than the first, and the third body <NUM> corresponds to a largest prosthetic femoral stem having a greatest length in the inferior-superior direction.

As the distance between the stop <NUM> and the distal end <NUM> of the inserter to which the cement restrictor is attached is fixed, the length of the spacer part of each body decreases as the size of the corresponding stem increases. In this way, the inserter <NUM> can be used to reliably position the cement restrictor <NUM> with the preferred separation from the distal-most point of the prosthetic implant by using the visual depth guide feature to be used to control the depth of insertion of the cement restrictor <NUM>.

The first body <NUM> corresponds to a prosthetic stem with the shortest length in the inferior-superior direction and therefore has the longest spacer part <NUM> so as to position the visual depth guide features further down the shaft relative to the stop <NUM>. The medium sized body <NUM> corresponds to a femoral stem having a greater length in the inferior-superior direction than the femoral stem corresponding to the first body <NUM> and therefore has a shorter spacer <NUM> so as to position the visual depth guide features <NUM> closer to the stop <NUM>.

The third body <NUM> corresponds to a femoral stem having a greatest length in the inferior-superior direction and therefore has a shortest spacer <NUM> so as to position the visual depth guide feature <NUM> closest to the stop <NUM>.

By varying the length of the spacer part along the longitudinal axis of the body, to compensate for the different lengths in the inferior-superior direction of the stems corresponding to the bodies, the visual depth guide features may be used to guide insertion of the cement restrictor <NUM> to a depth within the cavity corresponding to the desired separation <NUM> between the cement restrictor and the distal-most part of the prosthetic stem, when implanted.

With reference to <FIG> there is shown a flow chart illustrating a method <NUM> of using the cement restrictor inserter instrument <NUM> in order to insert a cement restrictor <NUM> at the appropriate depth within the intramedullary cavity of a femur. Various parts of the overall hip replacement procedure are omitted for the sake of clarity but are generally known to a person of ordinary skill in the art. Therefore, <FIG> illustrates merely those parts of the total hip replacement procedure useful to explaining the use of the inserter instrument <NUM>. At <NUM>, the femur is prepared. This may include resection of the native neck of the femur and also forming an intramedullary cavity extending generally along the proximal anatomical axis of the femur. Various cutting instruments such as brooches and rasps may be used to form the intramedullary cavity. In some embodiments, a trial femoral stem component which also functions as a final brooch may be used to form the cavity within the femur.

For example, <FIG> shows a cross sectional view of a proximal part <NUM> of the patient's femur and shows the resection plane <NUM> resulting from resection of the native femoral neck. A trial femoral stem <NUM> is shown having a neck <NUM> and cutting teeth <NUM> disposed on the stem and which has been used to brooch the femoral cavity. An anterior side wall of the trial stem <NUM> includes a visual depth guide feature <NUM> similar to those present on the bodies, e.g. body <NUM> and the corresponding prosthetic femoral stem component <NUM>. The visual depth guide feature <NUM> is similarly in the form of three parallel lines generally perpendicular to the neck axis of the stem. Each of the lines corresponds to a different amount of offset of the femur relative to the pelvis in the medial-lateral and inferior-superior directions. The middle line <NUM> may correspond to a neutral amount of medial-lateral offset and inferior-superior offset (also referred to leg length). The upper line <NUM> may correspond to a reduced amount of inferior-superior offset and medial-lateral offset. The lower line <NUM> may correspond to an increased amount of medial-lateral and inferior-superior offset. Hence, the surgeon may use trial stem <NUM> to complete broaching of the intramedullary cavity of the femur until a one of the markings corresponding to the desired change, if any, in the offset is aligned with the plane of the femoral resection. As illustrated in <FIG>, the neutral offset line <NUM> is generally aligned with the resection plane <NUM> of the femur.

The femoral trial <NUM> has a correspondingly sized prosthetic femoral stem <NUM>. However, the prosthetic femoral stem <NUM> has a slightly smaller size than the trial stem <NUM> in order to provide for the cement mantel <NUM> surrounding the prosthetic stem <NUM>. Hence, once trialling has been completed at <NUM>, the surgeon may determine the size of prosthetic femoral stem corresponding to the trial femoral stem <NUM>.

As further illustrated in <FIG>, body <NUM> has a shape and size corresponding to the prosthetic femoral stem <NUM>. Hence at <NUM>, the surgeon may select the body for the inserter corresponding to the selected size of the prosthetic femoral stem <NUM>.

At <NUM>, the selected body <NUM> may be attached to the inserter <NUM> by being slid along the shaft and attached via the releasable attachment mechanism. As discussed above, the position of the body <NUM> along the longitudinal axis of the inserter is determined by abutment of the spacer part <NUM> with the stop <NUM>.

A cement restrictor trial may then be attached to the distal end of the inserter instrument <NUM> at <NUM>. The inserter instrument <NUM> may then be used to introduce the cement restrictor trial into the intramedullary cavity of the femur. Generally, the purpose of the cement restrictor trial is to gauge the appropriate diameter of the cement restrictor to be used. Hence, the surgeon may move the cement restrictor trial distally into the intramedullary cavity in order to gauge the diameter of the intramedullary cavity near the intended target position of the cement restrictor. As the exact positioning of the trial is not essential, this may be simply done by feel. Alternatively, or additionally, at <NUM>, the surgeon may use the visual depth guide feature <NUM> on the anterior surface of the body by comparing the position of the marking corresponding to the previously planned position, e.g. marking <NUM>, relative to the resection plane <NUM> of the femur.

At <NUM>, the surgeon may determine whether the cement restrictor trial has the appropriate diameter for the target insertion depth. If not, then the method may return, as illustrated by flow line <NUM> back to step <NUM> and a different cement restrictor trial may be attached to the distal end of the introducer of a greater or lesser diameter. Hence, the method may repeat until a diameter of the cement restrictor has been successfully determined.

At <NUM>, a cement restrictor having the diameter determined from the trialling is releasably attached to the distal end of the rod, after having removed the cement restrictor trial. In embodiments in which a threaded connection is used, then the cement restrictor is screwed on to the screw formation at the distal end <NUM> of the inserter instrument <NUM>. In other embodiments, in which a push fit attachment mechanism is used, then the cement restrictor <NUM> may simply be pushed on to the distal end <NUM> of the inserter instrument <NUM>. Then at <NUM>, the cement restrictor <NUM> is introduced into the intramedullary cavity and the inserter <NUM> is used to insert the cement restrictor <NUM> into the intramedullary cavity. The shape of the body <NUM> helps to ensure that the longitudinal axis of the inserter <NUM> is generally aligned with central axis of the cavity rather than being tilted in the coronal plane. However, the dimensions of the body <NUM> are smaller than the dimensions of the trial stem <NUM> and therefore do not themselves limit the insertion depth of the cement restrictor. Rather, the shape of the body helps to provide visual context to the surgeon as to the correct depth of insertion of the cement restrictor. In particular, the visual depth guide features on the body <NUM> correspond to visual depth guide features <NUM> on the trial stem and also the visual depth guide features <NUM> on the prosthetic stem.

Hence, the surgeon may progress the inserter instrument into the intramedullary canal until the marking corresponding to the previously trialled marking, the central line in this example, is aligned with the resection plane <NUM> of a femur. The surgeon may now be confident that the cement restrictor <NUM> has been positioned at a target depth within the intramedullary canal of the femur which will have the appropriate degree of separation <NUM> from the distalmost part of the prosthetic stem <NUM> when inserted in the intramedullary canal at the corresponding position, as defined by the same middle line of the visual depth guide features <NUM> being aligned with the resection plane <NUM>.

Hence, in embodiments in which a push-fit is used, the greater frictional force between the inner walls of the femur and the outer surface of the cement restrictor will overcome the frictional force of the push-fit interface between the distal end of the inserter and the cement restrictor and so the inserter instrument <NUM> may simply be withdrawn from the intramedullary cavity leaving the cement restrictor <NUM> secured in place at the target depth.

Alternatively, if a screw threaded attachment is used, then the handle <NUM> may be used to rotate the shaft <NUM> which may rotate relative to the body <NUM> thereby allowing the distal end <NUM> of the inserter to be detached from the cement restrictor <NUM>. The circlip and groove releasable attachment mechanism permits rotation of the shaft <NUM> relative to the body thereby permitting disengagement of the screw thread attachment mechanism. Hence, at <NUM>, the inserter is detached from the cement restrictor, which is left in place at the target depth, as illustrated in <FIG>.

Consequently, cement may be introduced into the intramedullary canal and then the prosthetic stem <NUM> introduced and positioned with the central markings of its corresponding visual depth guide features aligned with the resection plane <NUM> of the femur.

With reference to <FIG> there are shown side and perspective views of a further embodiment of a body <NUM> which may be used as part of the cement restrictor inserter instrument. Body <NUM> is generally similar to the first embodiment described above other than the releasable attachment mechanism by which the body is releasably attached to the stop of the inserter. The body <NUM> shown in <FIG> has generally the same geometry and size as the body <NUM> shown in <FIG>, <FIG>. The body <NUM> generally has a shape and size corresponding to the proximal part of a corresponding femoral stem <NUM>. A visual depth guide feature <NUM> in the form of a plurality of markings each including a line is provided on an anterior surface <NUM> of the body <NUM>.

Similarly, a spacer <NUM> extends from a superior part of body <NUM> generally along the longitudinal axis of the body and defines a circular cylindrical cavity therein for receiving the shaft <NUM> of the inserter <NUM> in use. A proximal end of spacer <NUM> defines a shoulder <NUM> arranged to abut against the stop <NUM> of the inserter. However, in the illustrated embodiment, instead of using a circlip and groove, the releasable attachment mechanism <NUM> is in the form of a snap fit connector including four resilient tongues. The stop <NUM> of the inserter <NUM> defines a generally annular cavity therein and also a groove within an inner wall of the spacer configured to receive the protrusions at the free ends of the tongue, e.g. protrusion <NUM> of tongue <NUM>. Hence, body <NUM> can be used generally similarly to the first embodiment described above. Again, the snap fit piece of attachment mechanism allows the shaft of the inserter to rotate relative to the body and therefore the cement restrictor inserter provided using this body can be used with cement restrictors attached via a push fit or screw fit connection.

<FIG> show side and perspective views of a third embodiment of a body <NUM>. Again, body <NUM> has the shape and dimensions of a corresponding prosthetic femoral stem <NUM> and include a visual depth guide feature <NUM> on an anterior surface <NUM> thereof. In the illustrated embodiment, the visual depth guide feature <NUM> is in the form of a plurality of circles or dots equally spaced along an axis parallel to the longitudinal axis of the body <NUM>. Body <NUM> generally corresponds to body <NUM> and similarly includes a spacer element <NUM> extending from a superior end of body <NUM>. A proximal surface <NUM> of spacer <NUM> is arranged to abut the stop <NUM> of the inserter to control the position of the body relative to the inserter instrument.

However, as best illustrated in <FIG>, the releasable attachment mechanism of the body <NUM> is provided by a generally open channel <NUM> being defined by portions of the anterior <NUM> and posterior <NUM> surfaces of the body. The channel <NUM> extends generally along the longitudinal axis of the body and is dimensioned to receive the shaft <NUM> of the inserter <NUM> immediately below the stop <NUM>. When using this body, the inserter <NUM> omits boss <NUM> such that the body <NUM> may simply be clipped onto the shaft <NUM> of the inserter with the spacer <NUM> abutting the distalmost surface of the stop <NUM>. The body <NUM> is made from a suitable plastic material in order to provide a snap fit releasable attachment mechanism. As also illustrated in <FIG>, a groove <NUM> may be defined by an inner surface wall <NUM> of the channel <NUM>. A proud ring may extend around the shaft <NUM> of the inserter <NUM> and positioned to be received within groove <NUM> when surface <NUM> abuts the distal surface of stop <NUM> to ensure correct relative positioning of the body <NUM> relative to the stop <NUM> and prevent the body from being slid distally down the shaft <NUM> into an incorrect relative position. The ring of material may be an integral part of the shaft having been formed by machining rather than being some separate part subsequently attached to the shaft.

It will be appreciated that the use of cement restrictors is not limited to femoral stems and indeed may be used for other cemented orthopaedic implants having some stem like portion which extends into a cavity and which is not visible to a surgeon. The use of a body having the same shape and dimensions as a proximal part of the corresponding prosthetic implant is intended to help the surgeon to better understand and/or recollect whether the cement restrictor insertion depth is correct by using some visual depth guide feature to be compared with some part of the patient's bone but within the common context of the body and corresponding prosthetic implant. In many embodiments, the body is not itself used to control the depth of insertion. Rather, the body will have smaller dimensions than the cavity owing to the gap required between the walls of the cavity and the prosthetic implant to receive the cement cavity. The body may help with some centralisation of the inserter by partially filling the proximal part of the cavity. However, the shape and size of the body is more intended to provide visual and contextual feedback to the surgeon so that they can immediately understand that the body is at the correct position as the implant will be at that same position.

The relative position of the cement restrictor for the currently select body size is taken care of by the correct positioning of the body on the rod owing to the length of the spacer element and the position of the visual depth guide features on the body along an axis generally parallel to the longitudinal axis of the shaft of the inserter. Hence, the same inserter shaft can be used with multiple different bodies corresponding to different sized prosthetic implants with different sized stem lengths.

Therefore one embodiment of the present invention also relates to a kit of parts or surgical system including the inserter instrument, multiple bodies of different sizes and optionally multiple corresponding prosthetic implants of different sizes.

Other common orthopaedic implants which may use cemented stems, include humeral stems, both conventional and reverse shoulder, and also the tibial component and the femoral component of a knee prosthesis. Some femoral components include a cemented stem, especially those used in revision surgery.

For example, a body <NUM> having the shape and size of a corresponding prosthetic tibial component is illustrated in <FIG>. The prosthetic tibial component may generally have the form of a tibial tray with a stem extending from an inferior surface and providing an attachment mechanism for a bearing surface on a superior side. Hence, when a tibial tray with a cemented stem is being used, then the same general approach may also be used in which the body <NUM> has the shape and dimension of a proximal part of the tibial prosthesis, i.e. not including at least the distalmost portion of the stem.

For example, as illustrated in <FIG>, the body <NUM> includes a tibial tray part <NUM> having the general shape and size of the tibial tray of the corresponding prosthetic component. At least a part of a tibial stem <NUM> extends in an inferior direction from an inferior side <NUM> of the tibial tray part <NUM>. A pair of wings or flanges <NUM>, <NUM> extend between the stem <NUM> and the inferior side <NUM> of the tray <NUM>. Similarly to the bodies described above, a spacer <NUM> extends from a superior surface <NUM> of the tray <NUM> generally in the direction of the inferior-superior axis and parallel to the longitudinal axis of the shaft <NUM> of the inserter <NUM>. The spacer <NUM>, tray part <NUM> and stem part <NUM> between them define a central circular cylindrical cavity <NUM> within which the shaft <NUM> of the inserter <NUM> is inserted in use. An inner surface <NUM> of the spacer <NUM> defines a groove <NUM> arranged to receive the circlip of the inserter <NUM> to provide a releasable attachment mechanism which also permits rotation of the shaft <NUM> relative to the body <NUM>.

The length of the spacer <NUM> in the direction of the longitudinal axis of the shaft <NUM> is selected such that when the free end of the spacer <NUM> abuts the stop <NUM> when mounted on the inserter <NUM>, the cement restrictor would be located at the appropriate distance <NUM>, within the tibial intramedullary cavity, from the distal most part of the stem of the corresponding prosthetic component when the underside or inferior surface <NUM> of the tray <NUM> is seated on the resected surface of the tibia (resulting from the proximal tibial cut). Hence, in this embodiment correct positioning of the cement restrictor is determined by the surgeon observing that the tibial tray part <NUM> is seated flush on the resected tibial surface, rather than comparing a marking on, or structural part of, the body with some part of the bone of the patient. Hence, in this embodiment, the under surface or inferior surface <NUM> of the tray part <NUM> provide the visual depth guide feature of the body <NUM> by which the insertion depth of the cement restrictor may be visually assessed by the surgeon.

By way of further example, <FIG> shows a further embodiment of a cement restrictor inserter instrument <NUM> including a body <NUM> generally having the shape and dimensions of a humeral stem or shoulder stem prosthesis. The shoulder stem prosthesis is typically used in a reverse shoulder arthroplasty procedure. The shoulder stem prosthesis is inserted in an intramedullary cavity within the humerus of the patient to provide a shallow cup into which a bearing component may be inserted to provide an articulating surface for a corresponding ball type prosthetic implant located within the shoulder of the patient. Hence, body <NUM> generally has the shape and form of the humeral prosthetic implant including a part of the stem <NUM> and a cup like portion <NUM>. The cup portion <NUM> includes a generally annular wall <NUM> an upper edge or surface <NUM> of which provides the visual depth guide feature used to assess correct positioning of the cement restrictor inserter within the intramedullary cavity of the humerus. Similarly, a spacer part <NUM> extends from a superior part of the body <NUM> with a groove <NUM> defined within an interior surface <NUM> of the spacer part <NUM> therein for releasably attaching the body <NUM> to the circlip of the inserter <NUM>. The spacer <NUM>, cup part <NUM> and stem part <NUM> between them define a central circular cylindrical cavity <NUM> within which the shaft <NUM> of the inserter <NUM> is inserted in use.

The length of the spacer <NUM> in the direction of the longitudinal axis of the shaft <NUM> is selected such that when the free end of the spacer <NUM> abuts the stop <NUM> when mounted on the inserter <NUM>, the cement restrictor would be located at the appropriate distance <NUM>, within the humeral intramedullary cavity, from the distal most part of the stem of the corresponding prosthetic component when the surface <NUM> of the wall <NUM> is aligned with the rim of the cavity formed in the proximal part of the humerus. Use of the cement restrictor inserter instrument <NUM> illustrated in <FIG> is generally similar to that described above with reference to <FIG> other than the correct depth of insertion of the cement restrictor <NUM> being determined by the edge or surface <NUM> of the body being aligned with a resected or otherwise prepared part of the humerus of the patient.

The body parts described above may be made from various materials and various plastics, especially polymeric plastics, are particularly suitable. For example, the body part may be made from Acetal or Polyoxymethylene (POM), Polyphenylsulphone (PPS), Polyetheretherketone (PEEK), Polyaryletherketone (PAEK) or similar and also filled versions of those plastics or similar.

Hence, it would be apparent that there are a number of different benefits provided by the various sets of instrumentation described herein and methods enabled thereby.

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.

Claim 1:
A cement restrictor inserter instrument (<NUM>) comprising:
an inserter (<NUM>) having a handle (<NUM>) at a proximal end, a cement restrictor attachment formation (<NUM>) at a distal end (<NUM>) for releasably attaching a cement restrictor, a shaft (<NUM>) extending from the proximal end to the distal end (<NUM>) and a stop (<NUM>) on the shaft (<NUM>) and between the proximal end and the distal end (<NUM>); and
a body (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having a shape corresponding toa proximal part of a corresponding orthopaedic prosthetic implant, a spacer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), a visible depth guide feature (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and a releasable attachment mechanism (<NUM>, <NUM>) by which the body is releasably attachable to the shaft (<NUM>), and wherein the spacer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) is configured to position the visible depth guide feature (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) at a fixed position relative to the inserter (<NUM>) when the spacer (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) abuts the stop (<NUM>) corresponding to a target cement restrictor position when the visible depth guide feature (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) is aligned with a feature of a bone of a patient in which the cement restrictor (<NUM>) is to be inserted.