Patent ID: 12208024

Similar items in the different Figures share common reference signs unless indicated otherwise.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the invention will be described within the context of orthopedics and in particular in relation to a hip joint. However, it will be appreciated that the invention is not necessarily limited in application to hip joints and may also be used in other ball and socket type joints.

As explained in greater detail below, one or more vertical lines (i.e. parallel to the inferior-superior axis of the patient's body in use) may be used to represent an amount of tension introduced into the joint owing to movement of the patient's limb along the medial-lateral axis, and which may be referred to as limb offset. Movement of the limb relative to the body in the medial direction will generally decrease tension and movement of the limb relative to the body in the lateral direction will generally increase tension. One or more horizontal lines (i.e. parallel to the medial-lateral axis of the patient's body in use) are used to represent an amount of tension introduced into the joint owing to movement of the patient's limb along the inferior-superior axis, and which may be referred to as limb length. Movement of the limb relative to the body in the superior direction will generally decrease tension and movement of the limb relative to the body in the inferior direction will generally increase tension. One or more diagonal lines (which may be generally perpendicular to the neck axis in use) may be used to represent an amount of tension introduced into the joint owing to movement of the patient's limb (arm or leg) along both the medial-lateral axis and the inferior-superior axis.

In the following, the “line” or “lines” will generally be used to indicate any linear indicium or linear indicia which can be discerned by a user. The line may have various forms, e.g. solid, broken, chain, etc. and may be embodied in various ways, e.g. by printing or marking or similar, and/or by various physical features, e.g. ridges, ribs, groove or channels or similar. Hence, although line will be used below for the sake of clarity, it will be appreciated that any linear indicium or indicia may be used in practice.

With reference toFIGS.1A to1C, there is shown a kit of parts100according to an embodiment of the invention. The kit of parts100comprises a plurality of different types of trial component which can be used during a trialling stage of a surgical procedure, such as a hip replacement procedure. The kit of parts100can be provided as a trialling kit within a tray which can be provided to the operating theatre staff for use during the surgical procedure. The kit of parts100illustrated inFIGS.1A to1Cis for a particular head size or diameter. A similar kit of parts can be provided for other different head diameters. Also, the kit of parts100is for a particular implant system having a particular set of necks and neck geometries. A similar kit of parts can be provided for other different implant systems having a different neck or set of necks.

As illustrated inFIG.1A, the trialling kit100may include one or a plurality of liner trials110. Three different liner trials112,114and116are provided. Each liner trial includes one or more lines as described in greater detail below. A first liner trial112has a body with a rim118defining a generally hemispherical cavity in which a head trial can be received in use. The circular rim118extends around and defines a mouth of the liner trial. A line, in the form of a solid line120, is provided on an outer surface of the liner trial and extends around the periphery of the mouth, adjacent and parallel to the plane of the rim118. The first liner trial112has a minimal or smallest thickness of the liner trials110provided in the kit. The thickness of the first liner trial112may correspond to an increase in overall neck length of approximately 2 mm.

The second liner trial114is generally similar to the first liner trial112. However, the second liner trial114is an augmented liner trial which has a further segment124extending away from the rim122so as to define a slightly greater than hemispherical cavity within the liner trial114. This augmented liner trial114may be used in circumstances in which the trial cup has been placed with a relatively vertical orientation i.e. without much inclination relative to the patient's pelvis. Hence, the segment124helps to avoid dislocation of the head. The second liner trial114also includes a single line126on an outer surface and extending around the mouth of the liner trial and adjacent and generally parallel to the plane of the rim122. The second liner trial114has generally the same thickness as the first liner trial112. Hence, the thickness of the second liner trial114may correspond to an increase in overall neck length of approximately 2 mm.

The third liner trial116is generally similar to the first liner trial112and also includes a rim128extending around a mouth of hemispherical cavity defined by the body of the liner trial116. However, liner trial116includes a first line130and a second line132, each in the form of a solid line. Liner trial116has a greater thickness than the first112and second114liner trials. Hence, when inserted in a trial cup, the third liner trial116modifies the position of the centre of rotation of the joint in a direction away from the pelvis in both the lateral and inferior directions, and generally along the neck axis compared to the first or second liner trials.

In other embodiments, the liner trial116may be adapted otherwise to modify the position of the centre of rotation along the neck axis. For example, rather than having a different thickness, other features of the liner trial may be modified in order to change the position of the centre of rotation of a head trial in use. For example, third liner trial116may move the centre of rotation approximately 2 mm further along a cup axis (defined by a line passing through the centre of the mouth of the cup and liner and perpendicular to the plane of the mouth of the liner and cup), compared to the first and second liner trials. Hence, the thickness of the third liner trial116may corresponds to an increase in overall neck length of approximately 4 mm.

Hence, each liner trial includes at least one line and the number of lines on any liner trial is proportional to, or otherwise corresponds to, an amount of distance introduced into the trial joint assembly, and corresponding tension in the trial joint assembly, by use of that liner trial in the trial joint assembly.

Each of trial liners112,114,116defines a generally hemispherical cavity having an inner diameter of approximately 32 mm, for example. The trialling kit100also includes a plurality of head trials140as illustrated inFIG.1B. In the illustrated embodiment, six head trials142,144,146,148,150,152are provided. Each head trial has a generally truncated spherical form and has the same outer diameter of approximately 32 mm. Hence, each of head trials142to152can be received in any respective one of the liner trials112,114,116of the kit.

The liner trials and head trials ofFIG.1, therefore correspond to a first size. A plurality of sets of liner trials and head trails can be provided, with each set corresponding to a different size. For example, liner trial inner diameters and head trial outer diameters of approximately 22 mm, 28 mm, 32 mm, 36 mm and 40 mm may be provided for corresponding sized prosthetic components. As will be appreciated from the following, the same neck trials can be used with liner trials and head trials of different sizes.

The body of each head trial defines a respective cavity therein for receiving a free end of a neck trial. Each cavity extends generally along a head axis, e.g.154, which passes through the centre of the head trial, and generally perpendicularly to a flat underside thereof and through a pole of the head trial.

Each of the head trials142to152is generally similar other than the position along the head axis154of the respective cavities is different for each of the head trials so that the centre of rotation of each head trial can adopt a different position along the neck axis when assembled on a neck trial in use. Also, each head trial includes a different number of lines and the number of lines is proportional to, or otherwise corresponds to, the resulting position along the neck axis arising from the position of the cavity within the head trial. Hence, each head trial includes at least one line and the number of lines indicates the amount by which the trial joint assembly will change along the neck axis, and with a corresponding change in soft tissue tension, owing to use of that head trial in the trial joint assembly.

For example, the first head trial142has a single line156generally in the form of a solid line extending at least partially around the head axis154and in a plane generally perpendicular to the head axis154. This first head trial142corresponds to a smallest neck length which may be less than a normal or default neck length and hence can be used to reduce an overall neck length in use.

A second head trial144includes first and second lines158,160and has a cavity arranged to position the centre of rotation of head trial144further away from the neck trial along the neck axis when assembled thereon in use compared to the first head trial142. For example, the difference in position along the neck axis between the first head trial142and second head trial144may be approximately 3.5 mm. Similarly, each of the third, fourth, fifth and sixth head trials have an incremental number of lines and each have respective cavities configured to position the centre of rotation of the head trial further along the neck axis and away from the neck trial. For example, the sixth head trial152has six lines162and corresponds to the greatest neck length which may be approximately 17.5 mm longer than a corresponding neck length arising from use of a first head trial142on the same neck trial.

It will be appreciated that each line does not need to correspond to the same change in neck length. For example, each additional line may not correspond to a same 3.5 mm change in neck length. Rather, the amount of the change in neck length may vary for addition or omission of a line. It is simply that the number of lines indicates or corresponds to the change in the neck length resulting from use of that particular trial head. The greater the number of lines, the greater the neck length and the fewer the number of lines, the less the neck length.

As noted above, each head trial has the same outer diameter and the outer diameter of each head trial matches the inner diameter of each of the liner trials so that any one of head trials140to152can be used with any one of liner trials112to116. This compatibility between the head trials and liner trials can be indicated by making the colour of the head trials and the colour of the liner trials the same. For example, 22 mm diameter liner trials and head trials may all be tan coloured, 28 mm diameter liner trials and head trials may all be green coloured, 32 mm diameter liner trials and head trials may all be blue coloured, 36 mm diameter liner trials and head trials may all be orange coloured and 40 mm diameter liner trails and head trials may all be pink coloured.

Hence, for a particular size of head, the compatibility between the head trials and liner trials may be indicated by the head trials and liner trials all having the same matching colour.

In some embodiments, the head trials and the liner trials may be made from suitable plastics and polymers such as Polyphenylsulfone (PPSU) or Polyoxymethylene (POM) or similar.

A trialling kit for a different sized head may include similar components but having different inner and outer diameters and each of the head trials and liners trials for the second trialling kit may have a matching colour different to the matching colour of the first trialling kit. It will be appreciated that typically a reasonable number of different sized heads may be provided by an orthopedics manufacturer (for example approximately five different sized femoral heads of approximately 22 mm, 28 mm, 32 mm, 36 mm and 40 mm) and each trialling kit for each head size may have its own colour which matches within the kit but differs between kits, as described above.

The trialling kit100also includes a plurality of neck trials170as illustrated inFIG.1C. In the embodiment illustrated inFIG.1C, the trialling kit100includes five neck trials172,174,176,178and180. Each neck trial has a generally similar overall construction but a different geometry.

For example, with reference to the first neck trial172, each neck trial has a body182with a male formation184extending from an underside thereof. A neck portion186extends away from the body182and along a neck axis190. A taper188is provided at a free end of the neck186for releasably attaching a head trial thereto in use. The first neck trial has a neck-stem angle of approximately 135°.

First neck trial172is illustrated inFIG.1Cso as to form a part of a right hand hip joint in use. Hence, surface192is a generally anterior facing surface of the neck trial172. Anteriorly facing surface192bears a first line194and a second line196, each of which is in the form of a solid line.

The first line194is arranged to extend in a first direction generally parallel to the inferior-superior axis of a patient's body in use. The second line196is arranged to extend generally parallel to the medial-lateral axis of a patient's body in use.

The first line194indicates the extent to which the neck trial172will change the medial-lateral offset of the patient's leg. The second line196indicates the extent to which the neck trial172will change the leg length of the patient in use. As illustrated inFIG.1C, the first neck trial172has only a single first line194and a single second line196. The single second line196indicates that this trail neck172provides the minimal amount of change in the leg length of the patient in use.

As also illustrated inFIG.1, there is a gap198between a superior the end of the first line194and a medial end of the second line196. The gap198signifies the position of the first line194relative to the second line196and in particular that the first line194is positioned more medially than the medial end of the second line196. This arrangement of the first line194relative to the second line196signifies or indicates that the first neck trial172will result in the minimal medial-lateral distance. In particular, the gap198signifies that the first neck trial172will provide a smaller media-lateral offset than a second neck trial174. In particular, the first neck trial will move the limb approximately 5 mm in the medial direction along the medial-lateral axis relative to the pelvis.

Second neck trial174is generally similar to first neck trial172except that the position of its neck186′ relative to its body182′ is different such that the position of the taper188′ will move the limb relative to the pelvis further in the lateral direction compared to the first neck trial172. The neck-stem angle for the second neck trial174is approximately 125°. As can be seen inFIG.1C, the superior end of the first line200is connected to the medial end of the second line202and the absence of the gap198compared to the first neck trial172, signifies that the second trial neck174will result in a greater offset in the lateral direction, approximately 5 mm, compared to the first trial neck172.

The second neck trial174can be considered a neutral neck trial. In that case, the first neck trial172can be considered a reduced off-set neck trial as the first neck trial172will move the femur medially, by approximately 5 mm, compared to the second neck trial174.

Further, the anterior facing surface of the second neck trial174includes one second line202parallel to the medial-lateral axis similarly to the first neck trial172and at the same position on the body182′ of the second neck trial as the second line196on the body182of the first neck trial172. This combination and configuration of lines indicates that the second neck trial174provides the same leg length position as the first neck trial172, but increases the medial-lateral offset of the leg (in the lateral direction) compared to the first neck trial172.

The connected single first line200and single second line202may be used to indicate that the second neck trial is a neutral neck and hence positions the femur at a neutral leg-length and a neutral medial-lateral position. This may correspond to a standard or default neutral leg position for a surgical procedure.

For example, the second neck trial174may increase the medial-lateral offset, in the lateral direction by approximately 5 mm, compared to the first neck trial172. Further, the second neck trial174has a slightly reduced neck-stem angle, compared to the first neck trial172. The first neck trial172may have a neck stem angle of approximately 135° whereas the second neck trial174has a smaller neck-stem angle of approximately 125°.

The third neck trial176is generally similar to the first and second neck trials other than the neck is arranged relative to its body to position the leg relative to the pelvis further laterally along the medial-lateral axis of a patient in use, compared to the first and second neck trials. The third neck trial176may have a stem-neck angle of approximately 125°, similarly to the second neck trial, but be a high-offset neck trial. The third trial neck results in a femur positioned approximately 7 mm more laterally in the medial-lateral direction than the second trail neck176. This further increase of the resulting medial-lateral offset of the patient's femur arising from the third neck trial176is represented by the presence of two first lines204,206generally parallel to the superior-inferior axis on the anteriorly facing surface. Again, there is only a single second line208indicating that the third neck trial neck does not result in a chance of the leg-length compared to the first neck trial172or the second neck trial174. The first first line204has the same position on the anterior surface as the first line200of the second neck trial, whereas the second first line206is more laterally positioned on the anterior surface of the third neck trial compared to the first line200.

Fourth neck trial178is generally similar to second neck trial174except that the neck portion is arranged relative to the body portion to move the leg more inferiorly relative to the pelvis along the inferior-superior axis than the first, second or third neck trials. The fourth neck trial may have a stem-neck angle of approximately 135° and may move the leg approximately 5 mm inferiorly compared to the first to third neck trials. This is indicated by the presence of a single first line210and a first212and a second214second line on the anteriorly facing surface. The first second line212has the same position on the anterior face of the fourth neck trial as the first second line298on the third neck trial, whereas the second second line214is positioned more inferiorly on the fourth neck trial compared to the first second line208on the third neck trial. The fourth neck trial will result in the same medial-lateral position of the leg as the second neck trial174as indicated by the single first line210.

The fifth neck trial180is generally similar to the fourth neck trial178other than the neck being arranged relative to the body so as to increase the medial-lateral offset of the femur in the lateral direction compared to the second and fourth neck trials. The fifth neck trial may have a stem-neck angle of approximately 135°. The resulting leg position in the inferior-superior direction is the same as for the fourth neck trial, i.e. approximately 5 mm more inferior, as indicated by the first220and second222second lines, and which have the same position on the anterior face of the fifth neck trial as lines212and214on the fourth neck trial. The amount of lateral offset in the medial-lateral direction is indicated by the presence of first216and second218first lines generally parallel to the superior-inferior axis and similarly to the third neck trial176. Hence, the fifth neck trail may move the femur approximately 7 mm laterally and 5 mm inferiorly compared to the second neck trial174.

The second neck trial174(having a stem-neck angle of approximately) 125° may be taken as a reference or neutral which provides a neutral or first amount of off set and a neutral or first amount of leg length. Compared to the second neck trial, the first neck trial172(having a stem-neck angle of approximately) 135° may move the leg approximately 5 mm medially, as reflected by the gap between, and relative position of, the vertical line194and the horizontal line196compared to the connected vertical line200and horizontal line202on the second neck trial, and does not change the leg length as reflected by the single horizontal line196,202on each of them and at the same position on the anterior faces.

Compared to the second neck trial174, the third neck trial176(having a stem-neck angle of approximately) 125° may move the leg approximately 7 mm laterally, as reflected by the two vertical lines204,206compared to the one vertical line200on the second neck trial174, and does not change the leg length as reflected by the single horizontal line on each of them. Hence, in this example, the second vertical line206on the third trial176indicates a change of 7 mm laterally compared to the second neck trial174, whereas the gap and relative positions of the vertical line194and horizontal line196on the first neck trial172corresponds to a change of 5 mm medially compared to the second neck trial.

Compared to the second neck trial174, the fourth neck trial178(having a stem-neck angle of approximately) 135° may move the leg approximately 5 mm inferiorly along the inferior-superior axis, as reflected by the two horizontal lines212,214compared to the one horizontal line202on the second neck trial174, and does not change the leg length as reflected by the single vertical line on each of them.

Compared to the second neck trial174, the fifth neck trial180(having a stem-neck angle of approximately 135°) may move the leg approximately 5 mm inferiorly along the inferior-superior axis, as reflected by the two horizontal lines220,222compared to the one horizontal line202on the second neck trial, and also moves the leg approximately 7 mm laterally as reflected by the two vertical lines216,218on the fifth neck trial compared to the one vertical line200on the second neck trial174.

Hence, the number of lines and/or relative position of the lines, is generally proportional to or corresponds to the change in the position of the leg (the more lines, the greater the change, the fewer lines the less the change). Each line, or relative position, may not corresponds to the same amount of change. For example the second vertical line206on the third neck trail corresponds to a change of 7 mm, compared to the second neck trial, whereas the gap198on the first neck trial172corresponds to a change of 5 mm compared to the second neck trial174.

The same arrangements of linear indicia may be provided on the posteriorly facing surface of the neck trials as illustrated inFIG.1C. Hence, those markings may be used when the neck trials are used for a left hand hip joint.

FIG.1Dshows a further set of neck trials230which may be provided additionally or alternatively to the neck trials170illustrated inFIG.1C. For example, neck trials230may correspond to a different implant system to that of neck trials170and hence may be used instead of neck trials170with the liner trials110and head trials140shown inFIGS.1A and1B.

The further neck trials230comprise a first neck trial232and a second neck trial234which are generally similar to those shown inFIG.1C. First neck trail232and second neck trail234each have the same stem-neck angle of approximately 130°. First neck trial232includes a single vertical line236and a single horizontal line238and second neck trial234has a two vertical lines240,242and a single horizontal line244. Similarly to above, the single horizontal line on each neck trial indicates that each neck trial results in the same leg position along the inferior-superior axis, whereas the two vertical lines240,242compared to the single vertical line236indicates that the second neck trial234results in a greater offset of the leg laterally compared to the first neck trial232.

For example, the first neck trial232can be considered a neutral neck trial which has a standard off set positon of the leg as reflected by the single vertical line, whereas the second neck trial234can result in a high offset position as it moves the leg laterally, e.g. by approximately 4 mm to 8 mm, compared to the first trial neck232.

An implant system may provide a different sizes of prosthesis and a pair of neck trials232,234may be provided corresponding to the smaller sized prostheses and the larger sized prostheses. For example, for a first implant system, the second neck trial234for the smaller sized prostheses may move the leg 6 mm laterally whereas the second neck trial234for the larger sized prostheses may move the leg 8 mm laterally. For example, for a second implant system, a pair of neck trails232,234may be provided for each of five different sizes of prostheses, and the lateral movement provided by the second neck trial234may be 4 mm, 5 mm, 6 mm, 7 mm and 8 mm for the smallest to the largest of the five sizes of prostheses.

The neck trials may be made from any suitable material, such as surgical grade stainless steel or various suitable polymers such as Polyetheretherketone (PEEK), or Polyaryletherketone (PAEK) or similar. The linear indicia may be provided on the anterior and/or anterior facing surfaces of the neck trials using laser marking.

The lines or linear indicia can be provided on the various trials as simple and high contrast markings which are easy to visualise by a user in order to understand the effect of the trial components on the trial joint assembly. The colour of the liners and/or heads can also be used to encode and communicate size information to the user.

FIG.2shows a perspective view of an example trial hip joint250that may be constructed using a selection of the trial components illustrated inFIGS.1A to1C. The trial hip joint250includes a final broach260which has been used to prepare a femoral cavity within the femur of the patient. It will be appreciated that in other embodiments, other femoral parts may be used instead of a femoral broach. For example, a trial femoral stem may be used. In other embodiments, a prosthetic femoral stem may be used. Also, other instruments and/or tools used during preparation of the femur may be used instead.

The third neck trial176is releasably mounted on a proximal surface262of femoral broach260. The proximal surface262has an aperture for receiving the male member184extending from the distal surface of the neck trial176. In other embodiments, a male member may be provided on the proximal surface262to be received within a corresponding female formation within the body of the neck trial176. The third head trial146is releasably attached to the taper of the neck trial176. The head trial146is received within the cavity defined by the body of the augmented liner trial114. The augmented liner trial114is received within a trial acetabular cup264which may be provided in the form of a shell as illustrated inFIG.2. In other embodiments, the liner trial114may be received in the prosthetic shell or cup.

As discussed above, each of the trial components of the trialling kit100includes a number of lines or linear indicia and the number of lines or linear indicia, and/or the relative position of the horizontal and vertical lines, visually indicates the effect of each trial component on a particular property of the resulting joint. The linear indicia are a visual representation or indication of both the amount and direction of tension which is being applied to the resulting joint by each of the trail components in the trial joint assembly.

As illustrated inFIG.2, the line126on augmented trial liner114is visible as are the three lines266on the head trial146. Each of these are generally perpendicular to the neck axis190and indicate the amount by which the neck length is affected by each of these trial components. The linear indicia on the neck trial176indicate that the neck trial176has a minimal effect on the leg length, but have an increased effect on the medial-lateral offset of the resulting joint.

This is further illustrated inFIG.3which shows a graphical representation270of the relationship between the linear indicia on the trial components and the changes to the resulting joint.

The number of linear indicia extending in the superior-inferior direction effects the medial-lateral offset of the leg of the patient as illustrated by line A inFIG.3. The greater the number of vertical lines on the neck trial, the greater the offset of the patient's leg laterally along the medial-lateral axis, as indicated by arrow272. Similarly, the greater the number of horizontal lines, parallel to the medial-lateral direction, the greater the effect of the neck trial on the leg length of the patient, as illustrated by line B inFIG.3. The greater the number of lines parallel to the medial-lateral axis, the greater the change in leg length in the inferior direction illustrated by line274inFIG.3.

Further, the number of linear indicia on the liner trial and/or neck trial of the joint, the greater the change in neck length along line C ofFIG.3.FIG.3extends generally in the direction of the neck axis190and can increase tension in the hip joint in the direction illustrated by line276inFIG.3. As will be appreciated from a comparison ofFIGS.2and3, the linear indicia on the head trial146and liner trial114are generally perpendicular to the direction of the neck axis190.

If the head trial and/or liner trial are changed to alter the neck length, C, then as illustrated inFIG.3, this can also have an effect on the leg length, B, and offset, A. For example, reducing the overall neck length has the effect of reducing the offset A and the leg length B. Similarly, increasing the overall neck length has the effect of increasing the offset A and leg length B.

Similarly, increasing the offset A will increase the neck length C slightly, but not necessarily also the leg length B. Similarly, increasing the leg length B will increase the neck length C slightly but may not change the offset A in the medial-lateral direction.

The visual indicia included on the trialling components therefore provides an easily understandable system for allowing the surgeon to immediately understand the contribution which each of the trial components provides to the trial joint in terms of offset and/or leg length and/or neck length. A surgeon can therefore easily determine which one or more of the trial components to change in order to improve the likely outcome of the procedure by visually inspecting the trial components used in the trial joint.

Further, the surgeon can easily determine which of the trial components in the kit to use for a further trial assembly, in order to re-trial the joint with a modified trial joint, using other trialling components from the kit.

For example,FIG.4Ashows a view in the generally anterior-posterior direction of a right hand hip trial joint280, similar to that shown inFIG.2. The trial joint280includes trial shell264, first trial liner112, fifth trial head150and second trial neck174.

As indicated by the visual indicia200,202on the trial neck174, the current trial neck174has a neutral impact on the leg length and the offset. The single linear indicia on the liner trial112shows that the liner trial is providing a minimal contribution to the overall neck length whereas the five linear indicia on the head trial150shows that the head trial is contributing significantly to the overall neck length. Hence, if the surgeon wishes to reduce the overall neck length, for example because of significant tension in the soft tissues of the reduced trial joint, then the surgeon may quickly understand, by inspection of the trial joint280that the trial head150is contributing significantly to the tissue tension.

Hence, the surgeon may replace the trial head150with the third trial head146so as to reduce the overall neck length and resulting in the trial joint282illustrated inFIG.4B.

However, by reducing the overall neck length, along direction C inFIG.3, the surgeon has now also reduced the offset by moving the leg medially along the medial-lateral axis A. Therefore, the medial-lateral offset of the patient's leg has now been reduced by the trail joint assembly282compared to the situation for the trial joint assembly280ofFIG.4A. The surgeon may determine that it is desirable to increase the medial-lateral offset laterally. By inspecting the trialling kit100, the surgeon can immediately see that the third neck trial176increases the medial-lateral offset laterally by virtue of the two lines204,206parallel to the inferior-superior axis.

Hence, the surgeon may replace second trial neck174with third trial neck176so as to arrive at the trial joint284illustrated inFIG.4C. Hence, in the third trial joint284, the overall neck length has been reduced compared to the first trial assembly280and the medial-lateral offset increased by the third neck trial176so as to better reproduce the intended medial-lateral offset and to compensate for the reduction in medial-lateral offset by the use of the third head trial146in the place of the fifth head trial150to reduce the overall neck length.

As can be seen inFIGS.4A to4C, the number of linear indicia generally perpendicular to the neck axis (those on the liner trial and the head trial) are representative of the amount of tension in the trial joint. The number of linear indicia extending in the inferior-superior direction are generally indicative of the amount of offset of the trial joint. The number of linear indicia in the medial-lateral direction are indicative of the amount of leg length in the trial joint. Hence, the linear indicia provide an easy to see and simple to understand indication of the effect of each of the different trialling components on the likely surgical outcome for such a hip joint.

Furthermore, not only do the linear indicia allow the surgeon to understand which trialling components are contributing what effect to the hip joint, the surgeon can also use the visual indicia to easily and accurately determine which of the other trial components to select to use to retrial the joint in order to correct for any undesirable properties of the current trial, e.g. in terms of offset, leg length and/or tissue tension. This will be explained in greater detail with reference toFIG.5.

FIG.5illustrates a flow chart illustrating a method300of using the trialling kit100according to a further embodiment of the invention. A number of the steps of the surgical procedure for replacing a hip joint are generally known, and are not described in detail so as not to obscure the present invention. The present invention is particularly relevant to the trialling stage of a hip replacement surgical procedure.

The method300begins with preparation of the acetabulum at302. This may include removing the various soft tissue structures surrounding the acetabulum and using an acetabular grater and/or reamer in order to prepare a substantially hemispherical cavity within the acetabulum of the patient's pelvis.

At304, the femur of the patient is prepared. This can include resecting the femoral head and the proximal part of the femur. Various tools and instruments commonly known in the art may be used to initiate and prepare an intramedullary cavity extending generally along the proximal part of the femoral axis. At some stage in the preparation of the femur, a final size broach may be used306to finally prepare the femoral cavity. A handle may then be removed from the broach and the broach may be left within the femur. For example, broach260is shown inFIG.2.

At308, according to a planned surgical procedure, a cup trial, e.g. trial264, may be selected and inserted in the prepared acetabular cavity. At step310, a liner trial can be selected from the trialling kit which corresponds to the pre-planned cup and head size for the patient. If the cup trial has been inserted with a significant vertical orientation or there is a risk of the patient dislocating, then augmented liner114may be used. Otherwise, the surgeon may select a standard liner trial for insertion in the cup trial.

At312, a one of the neck trials170can be selected in accordance with the pre-planned surgical procedure and releasably attached to the broach260at step312.

At314, a selected one of the head trials140can be selected and attached to the taper of the neck trial at314. Then at316the trial joint can be reduced and has the general structure illustrated inFIGS.2and4A to4C.

At318, the surgeon can assess the properties of the resulting trial joint. This can include assessing the tension in the soft tissues of the hip joint. This may also include assessing the resulting leg length of the patient, along the generally inferior-superior axis of the patient. This may also include assessing the offset of the patient's leg along the medial-lateral axis. Step318may also include carrying out a range of motion (ROM) assessment to determine any likely impact between the trial components and also to assess the tissue tension arising from the currently selected trial components. At step320, the surgeon may determine, based on experience or other factors, whether the hip joint arising from this selection of components is acceptable or not. If it is acceptable, then at322, the trial components can be removed. The trial components can then be replaced with prosthetic components having generally the same size, position and/or orientation as the trial components.

Alternatively, the surgeon may select prosthetic components having slightly different geometries to compensate for any properties of the hip joint determined during the assessment stage318instead of selecting prosthetic components identical to the trial components. For example, if the surgeon determines at318that the tissue tension is slightly too great, than at322, the surgeon may select to use a slightly shorter neck length for the femoral prosthesis in order to help reduce the tissue tension.

Returning to step320, if the surgeon determines that the joint is not acceptable in some way, then at324, the surgeon can inspect the trial joint in situ. For example, if at318, the surgeon assesses the joint and determines that the tissue tension is too loose and also the medial-lateral offset is too small for the current trial assembly then the surgeon can inspect the trial construct at324to determine how the trial construct might be modified. For example,FIG.6shows a view of a trial assembly340comprising the third head trial146mounted on the second neck trial174mounted on femoral broach260. As can be seen from the number of linear indicia on the head trial146, the head trial is contributing a moderate amount to the overall neck length and, from the linear indicia on the neck trail174, the neck trial174is contributing neutral amounts to the leg length and offset. Hence, the surgeon can easily understand how the current trial components are impacting on the trial joint performance.

Hence, at326, the surgeon can separate the trial joint and select one or more trial components from the trialling kit100in order to rectify the surgical outcome. For example, if the surgeon considers that the tissue tension is slightly too loose and the medial-lateral offset is too small, the surgeon can easily determine, from inspecting the trialling kit100which of the other neck trials can be used to increase the medial-lateral offset but without increasing the leg length. As noted above, increasing the medial-lateral offset will also increase the overall neck length slightly. Hence, at326, the surgeon may disassemble the initial trial assembly340and replace neck trial172with the third neck trial176to arrive at the trial assembly350illustrated inFIG.7.

Hence, process flow can return as illustrated by process flow line328to step316at which the surgeon can reduce the trial joint with the new trial assembly350. The effect of replacing neck trial174with neck trial176is illustrated inFIG.7. The previous position of the femoral broach260is indicated in shadow and the new position of femoral broach is indicated in darker form260′. Hence, the effect of replacing neck trial174with neck trial176is to move the patient's leg laterally along the medial-lateral axis by increasing the offset by about 7 mm, but while maintaining the leg length. InFIG.7, the linear indicia on the anteriorly facing surface of the neck trial176indicate that the neck trial has the effect of moving the patient's leg laterally relative to the centre of rotation of the hip joint.

Hence, the reduced replacement trial joint350can be assessed again at step318and the surgeon may determine that the second trial hip joint350is likely to lead to a satisfactory surgical outcome and therefore may be adopted for the final prosthetic implants.

As another example, returning to step318, if it were determined at318that the tissue tension were too great and the medial-lateral offset were too small at318for the initial trial assembly340, then at324, the surgeon can immediately understand from the linear indicia on the initial trial head146that the trial head is contributing significantly to the neck length and therefore to the tension. Hence, at326, the surgeon may easily determine that a trial head which reduces the tissue tension could be tried and can easily identify, e.g., the second trial head144owing to the reduced number of linear indicia thereon. The surgeon can also easily identify that trial neck176may be considered as that will increase the medial-lateral offset (two vertical lines204,206) without changing the leg length (one horizontal line208). Hence, the surgeon may select the second trial head144and the third trial neck176and assemble trial assembly360as illustrated inFIG.8.

Process flow returns as indicated by line328to316and the trial joint can be reduced again and further assessed at318. The surgeon may then determine that the tissue tension is now appropriate and also that the offset is appropriate at320. As illustrated inFIG.8, the second head trial144has the effect of reducing the overall neck length while the third neck trial176has the effect of increasing the offset laterally, without changing the leg length, and slightly contributing to the overall neck length.

Further, the angle between the linear indicia on the liner trial and the linear indicia of the head trail can be used to help assess whether an augmented liner trial might be used. For example, assuming a neutral liner trial is currently being used, then during the assessment at318, the surgeon may place the femur in the Ranawat sign position (generally the operated leg is placed in extension and internally rotated by 45°). The surgeon may then assess whether the linear indicium on the liner trial are sufficiently parallel to the linear indicia on the head trial. If they are, for example because the acute angle subtended between them is less than a few degrees, for example less than about 10°, then the surgeon may determine that the risk of dislocation is low and select to use a normal liner. Alternatively, if the acute angle subtended between them is greater than about 10°, for example, then the surgeon may determine that the risk of dislocation is high and the surgeon may select to use an augmented liner instead. Hence, the linear indicia of tension in the joint can also be used to assess the risk of dislocation and hence whether to use an augmented liner or not.

Hence, the number of linear indicia in the first and second directions on the neck trial indicate the amount to which the neck trial contributes to the position of the patient's leg in the offset and leg length directions. The number of linear indicia on the head trial and/or liner trial are representative of the amount by which these components contribute to the neck length. Therefore, the surgeon can easily understand by visual inspection how each of the different trial components are contributing to the behaviour of the trial joint simply by inspecting them in situ.

Further, the linear indicia can easily be used to select a one or more replacement trial components in order to compensate for any potential deficiencies in a current trial joint and allow a further trial assembly to be assembled likely to reduce any deficiencies in the joint.

Further, as the liner trials and head trials of any particular head size are colour coded, a surgeon can easily ensure that the trial head size and trial liner size match for any trialling kit. Hence, if a trialling kit is provided with liner trials and head trials of different sizes, such that a surgeon decides to use a different sized liner trial, then the surgeon can easily determine which head trials match the different sized liner based on their matching colours.

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

Any instructions and/or flowchart steps can be executed in any order, unless a specific order is explicitly stated or implicitly required. Also, those skilled in the art will recognize that while one example set of instructions/method has been discussed, the material in this specification can be combined in a variety of ways to yield other examples as well, and are to be understood within a context provided by this detailed description.

While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and described in detail. It should be understood, however, that other embodiments, beyond the particular embodiments described, are possible as well. All modifications, equivalents, and alternative embodiments falling within the scope of the appended claims are covered as well.