Version protractor

An apparatus and method for measuring a version angle of a restored neck of a femur during a hip replacement procedure. The apparatus includes a broach. The broach has a distal end that is insertable into a medullary canal of the neck of the femur. The broach also has a proximal end that extends along a neck axis of the broach. The apparatus also includes a protractor. The protractor includes a rod which is attachable to the proximal end of the broach to extend away from the neck axis of the broach for measuring the version angle of the restored neck of the femur relative to a vertical direction. The method includes inserting the broach, flexing the knee at approximately ninety degrees, orienting the tibia vertically, attaching the protractor to the proximal end of the broach and using it to measure the version angle.

BACKGROUND

The present specification relates to an apparatus for measuring a version angle of a restored neck of a femur during a hip replacement procedure, and to a method of measuring a version angle of a restored neck of a femur of a leg of a patient during a hip replacement procedure.

Hip replacement is a surgical procedure in which the hip joint is replaced by a prosthetic implant. As part of the hip replacement procedure, the femoral head is replaced with a femoral prosthetic that includes a stem which is inserted into the medullary canal at the neck of the femur. The femoral prosthetic also includes a bearing surface, which is received within the acetabulum of the patient. The procedure may in some cases also involve inserting an acetabular cup into the acetabulum of the patient, for receiving the bearing surface of the femoral prosthetic.

It is important that the size, shape, orientation and alignment of the femoral prosthetic and the acetabulum (or acetabular cup, where one is used) are determined correctly, to ensure correct operation of the hip joint. For instance, misalignment between the femoral prosthetic and the acetabulum (or acetabular cup, where one is used) may lead to complications such as increased wear and tear of the bearing surfaces and/or unbalanced tension in the surrounding ligaments.

As part of this, it is important that the version angle of the restored neck of the femur is determined correctly for the patient in question. A typical version angle for many patients is around 15 degrees of anteversion, however this can vary between patients.

SUMMARY

Aspects of the present invention are set out in the accompanying independent and dependent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as appropriate and not merely as explicitly set out in the claims.

According to an aspect of the invention, there is provided an apparatus for measuring a version angle of a restored neck of a femur during a hip replacement procedure, the apparatus comprising:

a broach comprising a distal end insertable into a medullary canal of the neck of the femur and a proximal end extending along a neck axis of the broach; and

a protractor comprising a rod which is attachable to the proximal end of the broach to extend away from the neck axis of the broach for measuring the version angle of the restored neck of the femur relative to a vertical direction.

According to another aspect of the invention, there is provided a method of measuring a version angle of a restored neck of a femur of a leg of a patient during a hip replacement procedure, the method comprising:

inserting a distal end of a broach into a medullary canal of the neck of the femur;

flexing a knee of the patient at approximately ninety degrees;

rotating the leg of the patent to orient a tibia of the leg along a vertical direction;

attaching a protractor comprising a rod to a proximal end of the broach to extend away from the neck axis of the broach; and

using the protractor to measure the version angle of the restored neck of the femur relative to the vertical direction.

Embodiments of this invention may conveniently allow a version angle of a restored neck of a femur of a leg of a patient to be measured during a hip replacement procedure. This can allow misalignment to be avoided between a femoral prosthesis located in the restored neck and the acetabulum of the patient (or acetabular cup, where one is used), which receives a bearing surface of the femoral prosthesis. In the event that the measured version angle differs from an intended or “normal” angle, measures may be taken to accommodate for this, such as adjusting the alignment of the acetabular cup or choosing a different femoral implant for the replacement hip.

The protractor may include a pendulum pivotably mounted on the rod to hang vertically for measuring the version angle relative to the vertical direction. The method may include allowing the pendulum to hang vertically, for measuring the version angle relative to the vertical direction. Accordingly, with the tibia held vertically, gravity may conveniently be used to define the vertical direction relative to which the version angle is measured.

A stationary marker may be attached to the rod for reading off a measurement of the version angle relative to the vertical direction. The method may further include reading off a measurement of the version angle relative to the vertical direction by determining the location of the stationary marker in relation to the orientation of the pendulum.

In some embodiments, the protractor may include a sleeve portion located on the rod. The sleeve portion may include the stationary marker. The pendulum may be pivotably attached to the sleeve portion.

In one embodiment, the protractor may include a bubble level attached to the rod. The method may further include using the bubble level to read off the version angle relative to the vertical direction.

In some examples, the protractor may include one or more indicia for reading off a measurement of the version angle relative to the vertical direction. The method may further include reading off a measurement of the version angle relative to the vertical direction using the indicia. In some examples the indicia may include a plurality of tick marks for reading off a numerical measurement of the version angle in degrees. The method may further include reading off a numerical measurement of the version angle in degrees using the tick marks. In some examples, the indicia may include one or more zonal markers. The zonal markers may each correspond to a range of version angles. For instance, the range may be a normal range, a high range (within which the version angle is higher than normal) and/or a low range (within which the version angle is lower than normal). The method may further include reading off a zonal measurement indicating that the version angle falls within either a normal range, a high range and/or a low range using the zonal marker(s). In some examples, the indicia may further include a marker for indicating the vertical direction. The marker may, for instance be a line extending across the pendulum, such that the line is vertically oriented when the pendulum is allowed to hang vertically.

In some embodiments, the protractor may include an electronic inclinometer attached to the rod. The method may further include using the electronic inclinometer to read off the version angle.

In one embodiment, the rod may include an elongate section set at a predetermined angle relative to the broach. The predetermined angle may correspond to a normal version angle for a patient (e.g. 15 degrees). The method may further include measuring the version angle by judging (e.g. simply by line of sight) the orientation of the elongate section relative to the vertical direction.

In one embodiment, the proximal end of the broach may include a connection member for connecting a neck trial to the broach. The apparatus may further include a neck trial attached to the connection member of the broach. Attaching the protractor to the proximal end of the broach may include attaching the rod to the connection member or to the neck trial.

In some embodiments, the proximal end of the broach (e.g. the connection member and/or the neck trial) may include an aperture for receiving the rod. Attaching the protractor to the proximal end of the broach may include inserting the rod in the aperture.

DETAILED DESCRIPTION

Embodiments of this invention are described in the following with reference to the accompanying drawings.

FIGS. 1 to 4show various views of a protractor according to an embodiment of this invention. The protractor10in this example includes a rod2which, as described below is attachable to the proximal end of a broach for use in measuring a version angle of a restored neck of a femur during a hip replacement procedure. The rod is elongate and may, for instance, be circular in cross section.

The protractor10in this example includes a pendulum20, which is pivotably mounted on the rod2. As will be described below, the pendulum20may be arranged to hang vertically from the rod2for measuring the version angle relative to the vertical direction.

The protractor10may include a sleeve24, which may also be elongate. The sleeve24includes a bore22, through which the rod2may be received, thereby to attach the sleeve24to the rod2. The bore22may be sized so as to provide a firm friction fit between the sleeve24and the rod2. The fit between the sleeve24and the rod2may be tight enough to hold the sleeve24in a fixed position relative to the rod2. The fit between the sleeve24and the rod2may still be loose enough to allow the surgeon manually to adjust the location and orientation of the sleeve24relative to the rod2(e.g. the rotational position of the sleeve24around the longitudinal axis of the rod2and/or the position of the sleeve24along the length of the rod2).

In this example, the pendulum20is attached to the sleeve24by a pivot4, which may be located at or near to the top of the pendulum20. The pivotal attachment of the pendulum20to the sleeve24in this example implements the pivotal mounting of the pendulum20on the rod2noted above.

The pendulum20may include a front face8and a rear face18. The pendulum20may be provided with one or more indicia for reading off a measurement of the version angle relative to the vertical direction. These indicia may be provided on the front face8and/or the rear face18of the pendulum20.

The protractor10may also include a stationary marker6. In the present example, the stationary marker6is located on the sleeve24. The stationary marker may, for instance, be a needle or arrow pointing towards a lower edge19of the pendulum20. As the pendulum20rotates around the pivot4(under the force of gravity, thereby to hang vertically) the indicia move relative to the stationary marker6, allowing the version angle to be read off from the protractor10by noting the position of the stationary marker6relative to the indicia at the lower edge19of the pendulum20.

In the present example, the indicia include a pair of zonal markers16for reading off a zonal measurement indicating that the version angle falls within either a normal range, a high range and/or a low range. Each zonal marker16may, for instance comprise an area on the front face8(and/or rear face18) of the pendulum20which indicates a range of angles (e.g. a 5 degree or 10 degree band). Each zonal marker may, for instance, be coloured differently to the surrounding area of the pendulum to allow to be viewed easily.

The zonal markers16may be provided with one or more tick marks17, for indicating e.g. a mid-point of the zone covered each the zonal marker16. In the example shown inFIGS. 1 to 4, two zonal markers16are included on the front face8of the pendulum20, with each zonal marker being centred around a 15 degree angle of rotation of the pendulum20relative to the rod2. The angle of 15 degrees is chosen in this example since this is often considered to be the “normal” version angle for a patient. It is envisaged that angle other than 15 degrees may be chosen. The zone covered by each zonal marker16may be chosen to provide an acceptable amount of tolerance either side of the “normal” version angle (e.g. ±2.5 degrees, or ±5.0 degrees), within which it may be determined that the version angle provided by the restored neck of a femur is acceptable.

One or more numerical indications14of the angle(s) covered by each zonal marker16may be provided on the front face8of the pendulum20. In the present example, the numerical indication14specifies the central angle of 15 degrees around which each zonal marker16is centred. Similar numerical indication may also be provided at the edges of each zonal marker16.

Note that the zonal markers16may be arranged symmetrically on either side of the front face8of the pendulum20, so that one of the zonal markers16may be used for carrying out a procedure on the left leg of a patient while the other of the zonal markers16may be used for carrying out a procedure on the right leg of a patient.

In the present example, the pendulum20is substantially triangular, with an upper apex of the triangle being located at or near the pivot4. The lower edge19of the triangle, which may correspond to a side of the triangle opposite the upper apex including thee pivot4may be curved (convex), so that the distance between the lower edge19and the stationary marker6remains substantially unchanged as the pendulum20rotates around the pivot4. In the present example, the zonal markers are recessed slightly with respect to the lower edge19of the pendulum20, so as to emphasise their position relative to the stationary marker6.

Instead of (or as well as) the zonal markers16described above, it is envisaged that the indicia may include a plurality of tick marks for reading off a numerical measurement of the version angle in degrees or radians. These tick marks may be located at the bottom edge19of the pendulum to allow the angle to be conveniently read off using the stationary marker6. The tick marks may be spaced at regular intervals (e.g. every 1, 2, or 5 degrees). The tick marks may be provided with numerical indications of the angle associated with each tick mark.

In some embodiments, the pendulum20may be provided with a further marker26for indicating the vertical direction when the pendulum20hangs vertically under the force of gravity. The further marker26may for instance include a line which extends along the front face8of the pendulum20. In the example ofFIGS. 1 to 4, the further marker26extends along the front face8, in between the zonal markers16. The further marker26may also pass through the pivot4, as shown inFIG. 1. As will be described below, the further marker26may be used by a surgeon to determine the vertical direction when using the protractor10, for instance to check whether the tibia of the patient is oriented vertically while he or she is reading off the version angle.

The rod2may, for instance, comprise Precipitation Hardened Stainless Steel e.g. 17-4PH Grade of Stainless Steel. The pendulum20and sleeve24may comprise engineering plastic such as Polyphenylsulphone (PPS), commonly known by the brand “Radel” from Solvay Chemicals, Modified PolyArylEtherKetone/PolyEtherEtherKetone (mPEEK), commonly known by the brand “Avaspire” from Solvay Chemicals or PolyAcetal/PolyOxyMethylene (POM), Commonly known as “Acetal” or by the brand name “Celcon”. There are other options—Propylux, Nylon 66, or other polymers that may normally be used for single-use applications. The sleeve24may alternatively be made from Stainless Steel 17-4PH.

FIGS. 5 to 7show various views of the protractor10ofFIGS. 1 to 4assembled together with a broach30according to an embodiment of this invention.

The broach30in this example is a trial femoral broach which is sized and shaped to be received in the medullary canal of the neck of the femur during a hip replacement procedure. In particular, the broach30has a distal end including a cutting portion36and a tip34, both of which may be inserted into the medullary canal, and a proximal end including a trial neck portion32. The cutting portion36may include a surface comprising a plurality of teeth which may, as is known in the art, be used to remove bone from the femur during a hip replacement procedure, thereby the prepare the femur to receive the stem of a femoral prosthetic. The distal end of the broach30may extend along a longitudinal axis thereof, which is labelled using reference numeral33inFIG. 7. The broach30may, for instance, comprise Precipitation Hardened Stainless Steel e.g. 17-4PH Grade of Stainless Steel, 404 Grade of Stainless Steel, 300 series (e.g. 316 or 303 stainless steel), Nitronic 60 Stainless Steel, Cobalt-Chrome alloy, Titanium alloy, Fibre-reinforced PEEK polymer, PEEK polymer or a ceramic material such as alumina [aluminum oxide] and zirconia [zirconium oxide].

The trial neck extends along a neck axis31of the broach30. The neck axis31is typically set at an angle (denoted “θ” inFIG. 7) to the longitudinal axis33of the distal end. The trial neck portion32may be removably attached to a connection member of the broach (this will be described below in more detail in relation toFIG. 15). This may allow trial neck portions of different sizes and lengths to be used with the broach30, according to the chosen dimensions of the femoral implant. It is also envisaged that the trial neck portion32may be integrally formed with the distal end of the broach30.

The distal end of the broach30may be dimensioned similarly to the stem of the femoral implant, and the trial neck portion32may be dimensioned and oriented similarly to the neck of the femoral implant, so that the broach30may also be used as a trial during the procedure, the determine the position and orientation of the femoral implant once it has been installed. Note that the angle at which the neck axis31of the broach31is set relative to the distal end of the broach30may correspond to the angle of the neck axis of the femoral implant relative to the stem of the femoral component.

To use the broach30as a trial, the surgeon may, as part of the procedure for removing bone from the femur to prepare it to receive the femoral implant, periodically insert the distal end of the broach30into the femur to judge the fit of the implant in the prepared femur. As part of this, the protractor10described above may be attached to the proximal end of the broach30as indicated inFIGS. 5-7to allow the surgeon to measure the anticipated version angle of the restored neck of a femur, once the femoral implanted has been installed. This can allow the surgeon to check that the version angle for the restored neck of the femur will be correct (e.g. within a certain tolerance) for the patient. The process for measuring the version angle using the protractor10and broach30will be described in more detail below in relation toFIGS. 11-13.

As can be seen inFIGS. 5-7, the neck trial32of the broach30is configured to allow the protractor10to be attached to it so that the rod2extends away from the proximal end of the broach30. InFIG. 7it is shown that, in the present embodiment, when the protractor10is attached to the neck trial32, the longitudinal axis of the rod2is oriented substantially orthogonal to the neck axis31. The rod2may also be oriented so that it extends substantially perpendicular the plane containing the neck axis31and the longitudinal axis33of the distal end of the broach30.

To allow attachment of the protractor10to the neck trial32, the neck trial32in this example is provided with an aperture38through which the rod2of the protractor10may be received. The aperture38passes through the neck trial32from a posterior face to an anterior face thereof, and may optionally also pass through a point on the neck axis31as can be seen inFIG. 7. Note that when the protractor10is attached to the neck trial32in this example, the longitudinal axes of the rod2, the bore22and the aperture38are all aligned with each other. The aperture38may be sized so as to provide a firm friction fit between the aperture38and the rod2. The fit between the aperture38and the rod2may be tight enough to hold the rod2in a fixed position relative to the neck trial32. The fit between the aperture38and the rod2may still be loose enough to allow the surgeon manually to adjust the location and rotational orientation of the rod2relative to the neck trial32.

When the broach30is inserted into the medullary canal of the femur, the plane containing the axes31and33is tilted by a certain an amount, according to the version angle of the restored neck of the femur. This tilting of the broach30also causes the rod2to tilt, while the pendulum20of the protractor10rotates around the pivot4to maintain its vertical orientation. As will be described below this can, by correct orientation of the leg by the surgeon so that the tibia points along the vertical direction, allow the protractor10to be used to measure the version angle of the restored neck of the femur.

FIGS. 8 to 10show various views of the protractor10and broach30ofFIGS. 5 to 7in situ during part of a hip replacement procedure according to an embodiment of this invention. As part of a hip replacement procedure, the distal end of the broach30is inserted within the medullary canal of the neck of the femur100. The knee joint110and tibia120of the leg are also shown inFIGS. 8-10. The procedure also includes (either before or after the broach30has been inserted) flexing the knee110of the patient at approximately ninety degrees and rotating the leg of the patent to orient a tibia120along the vertical direction. Note that it is envisaged that in some examples, the leg would be rotated first, prior to flexing the knee110of the patient at approximately ninety degrees. This manipulation of the leg and the use of the protractor10for measuring the version angle of the restored neck of the femur may be included as part of a hip replacement procedure following the so called “posterior approach”, although in principal it may also be included in a hip replacement procedure following other approaches such as the anterior approach, the lateral approach, direct lateral approach, direct anterior approach, or postero-lateral approach.

As can be seen inFIGS. 8 to 10, as part of the procedure, the protractor10is attached to the broach30, so that the pendulum20(and sleeve24) of the protractor10is located posteriorly with respect to the broach30. Typically, the protractor10may be attached to the broach30after once the leg has been manipulated to so point the tibia120along the vertical direction as described above, although it is also envisaged that the protractor10could instead be attached prior to the manipulation of the leg. With the pendulum20of the protractor10located posteriorly with respect to the broach30, the pendulum20hangs vertically. As can be seen inFIG. 8, the further marker26is aligned parallel with the vertical direction, which is represented inFIG. 8by the dotted line126.

In this position, with the tibia oriented vertically, the version angle of the restored neck of the femur100causes the broach30and consequently the rod2of the protractor to tilt. The amount of tilting corresponds to the version angle of the version angle of the restored neck of the femur100, which may read off from the protractor10using the stationary marker6. Some examples of this are shown inFIGS. 11 to 13.

The view of the leg, broach30and protractor10inFIGS. 11-13is along the femoral axis, looking down towards the knee110from the neck of the femur100. Note that the tibia120is oriented vertically as discussed above. The broach30is inserted into the medullary canal at the restored neck of the femur100and the protractor10is attached to the broach30so that the pendulum20is located posteriorly with respect to the femur100and the broach30. As the pendulum20of the protractor10hangs along the vertical direction126, the surgeon may compare the position of the stationary marker6with respect to the indicia on the pendulum, thereby to measure the version angle. In the examples shown inFIGS. 11 to 13, the indicia include a pair of zonal markers of the kind discussed above, although again it is envisaged that other kinds of indicia, such as tick marks may be provided on the protractor10.

InFIG. 11, the position of the stationary marker6relative to the zonal marker16indicates that the version angle falls outside the acceptable range indicated by the zonal marker16. In particular,FIG. 11shows an example in which the version angle of the restored neck of the femur is non-zero, but is too low. The broach30inFIG. 11is thus retroverted relative to the amount of anteversion that would normally be considered to be within the normal range.

On the other hand,FIG. 12shows an example in which the version angle of the restored neck of the femur falls within the acceptable range covered by the zonal marker16. This indicates that the broach30is anteverted by an amounted that would be considered normal. In fact, in the example ofFIG. 12, the version angle is approximately 15 degrees (which, as discussed above, may be considered to be roughly average for a human leg), which can be determined from the fact that the stationary marker6is substantially aligned with the central tick mark17.

FIG. 13shows an example in which the version angle of the restored neck of the femur is even lower than that of the example ofFIG. 11. InFIG. 13, the broach30is thus significantly retroverted relative to the amount of anteversion that would normally be considered to be within the normal range (note that the stationary marker6inFIG. 13is located slightly to the right of the further marker26, instead of to the left of the further marker26as shown in the examples ofFIGS. 11 and 12).

FIG. 14shows another example of an apparatus for measuring a version angle of a restored neck of a femur during a hip replacement procedure. As described previously, the apparatus includes a broach30. The broach30in this example is substantially the same as that described above in relation toFIGS. 5-7.

The apparatus inFIG. 14also includes a protractor10. In this embodiment, the protractor includes a rod2, which includes a first section42, a second section46and a third section44. The third section44is elongate, the first42and second44sections may also be elongate. As described previously, the protractor10may be attached to the broach30by inserting the rod2into the aperture38of the neck trial32of the broach30. In this example, the rod2is bent in two places so as to produce the first42, second46and third44sections, with the third section44set at a predetermined angle relative to the broach30when the rod2is attached to the broach30. It is envisaged that the rod may include further sections and bends.

The predetermined angle at which the third section44is set relative to the broach30may correspond to a normal version angle for a patient, for example 15 degrees.FIG. 16shows the use of the broach30and attached protractor10ofFIG. 14for measuring the version angle of the restored femoral neck of the femur. As withFIGS. 11 to 13, the view of the leg, broach30and protractor10inFIG. 16is along the femoral axis, looking down towards the knee110from the neck of the femur100. Again, note that the tibia120is oriented vertically by rotation of the leg and flexing of the knee as discussed above. The broach30is inserted into the medullary canal at the restored neck of the femur100and the protractor10is attached to the broach30so that the third section44, which is elongate, is located posteriorly with respect to the femur100and the broach30.

With the broach30and protractor10in place as shown inFIG. 16, and with the tibia120oriented vertically, the surgeon may inspect the third section44to judge its orientation relative to the vertical direction. In this way, he or she may measure the version angle of the restored neck of the femur100. For instance, in the example shown inFIG. 16, the tilting of the broach30and the consequent tilting of the protractor30according to the version angle of the restored neck of the femur as explained previously orients the third section44of the protractor10such that it is substantially parallel to the vertical direction126. Since the angle at which the third section is set with respect to the broach30in this example is approximately 15 degrees, this orientation of the third section44allows the surgeon to determine that the version angle is normal. On the other hand, should the surgeon observe that the third section44is not oriented vertically, this would allow him or her to determine that the version angle differs from the predetermined angle of the third section44.

The surgeon may also judge, by comparing the orientation of the third section44with respect to the vertical direction, whether the version angle of the restored femoral neck of the femur falls within an acceptable range. In some examples, a surgical kit may include a plurality of protractors10of the kind shown inFIG. 14, each protractor10having a third section44which is set at a different predetermined angle. In this way the surgeon may be able to swap between different protractors10until the third section44of the chosen protractor10aligns vertically when the tibia120is aligned vertically. The surgeon may then determine the version angle according to the predetermined angle of the third section44of the chosen protractor10.

In the examples described above, the protractor10is attached to the broach by inserting the rod2into an aperture38that passes through the neck trial32of the broach30, from an anterior face of the neck trial32to a posterior face of the neck trial32. It is envisaged that the apparatus described herein may include a broach30having a detachable neck trial32, to allow differently configured neck trials32to be used (e.g. neck trials32of different sizes and/or having a different version angle). A surgical kit according to an embodiment of this invention may include one or more such broaches30(e.g. of different sizes) and one or more such neck trials32for attachment to each broach30.

To implement this, the proximal end of the broach30may be provided with a connection member39of the kind shown inFIG. 15. The neck trials32used with a broach30of the kind shown inFIG. 15may include a corresponding (female) connector for receiving the connection member39, thereby to allow the neck trials32to be attached at the proximal end of the broach30.

As shown inFIG. 15, instead of attaching the protractor10to the neck trial32of the a broach30as described previously, it is envisaged that the protractor10may instead be attachable to the connection member39at the proximal end of the broach30. For instance, inFIG. 15, an aperture38is located in the connection member39, which passes through the connection member39from an anterior side to a posterior side thereof, for receiving the rod2of the protractor10. It is envisaged the a connection member configured in this way may allow any of the protractors30described herein to be attached to the broach30, although inFIG. 15a protractor10of the kind shown inFIGS. 14 and 16is provided.

FIG. 17show a protractor20according to a further embodiment of this invention. In common with the previously described embodiments, the protractor10in this example includes a rod2which, as described below is attachable to the proximal end of a broach for use in measuring a version angle of a restored neck of a femur during a hip replacement procedure. The rod2is elongate and may, for instance, be circular in cross section.

The protractor10in this example includes a pendulum20, which is pivotably mounted on the rod2. The pendulum20may include an arm98having an elbow90and an angled member96set at an angle (e.g. around 90 degrees) to the arm98. The arm98may include (e.g. at a top end thereof) a pivot point94which can rest upon an end of the rod2distal the broach with which the protractor10is used, so that the pendulum20can rotate freely about the point94under its own weight. To facilitate free hanging of the pendulum20under gravity, the end of the rod2may be rounded (e.g. hemispherical). Correspondingly, the pivot point94may for instance be formed from a curved (e.g. hemispherical) socket, which receives the end of the rod2. Accordingly, in common with the embodiment ofFIGS. 1 to 13, the pendulum20may be arranged to hang vertically from the rod2for measuring the version angle relative to the vertical direction. In the present embodiment, as the pendulum20hangs vertically under its own weight, the arm98may extend substantially along the vertical direction126.

The angled member96may be bifurcated into two parts96A,96B. In use a space or slot located in between the two parts96A,96B may receive the rod2, thereby allowing the pendulum20to rotate freely relative to the rod2while preventing movement of the pendulum20outside the plane containing the rod2and the vertical direction126.

As can be seen inFIG. 17, the pendulum20may be provided with indicia for reading off a measurement of the version angle relative to the vertical direction. The indicia may be provided on a front face8of the pendulum and/or on a rear face of the pendulum20. In the present example, the indicia include numerical indications14of angle relative to the vertical direction (note that the “0” point shown inFIG. 17coincides with the vertical direction) and a plurality of corresponding tick marks. To read off the version angle, the surgeon may note the position of the rod2relative to the angled member96using the tick marks and numerical indications14. It is envisaged that in other examples, zonal markers of the kind described above may be provided on the front face8and/or rear face of the pendulum20(e.g. on the angled member96) for measuring the version angle.

The protractor10shown inFIG. 17may be used in much the same way as the protractor described in relation toFIGS. 1 to 13for measuring the version angle, by attaching the rod to the proximal end of a broach to and allowing the pendulum20to hang vertically.

In accordance with an embodiment of the invention, a protractor may include alternative means for measuring the version angle.

For instance, in one embodiment, the protractor may include a bubble level which may be attached to the proximal end of the broach. The bubble level may be located on a rod of the kind described above, which again may be inserted into an aperture located either in the neck trial or connection member (e.g. so that the bubble level is located posteriorly with respect to the femur and broach). The bubble level may be curved (e.g. substantially C-shaped), so that the location of the bubble can be used to read off the particular angle at which the bubble level is oriented relative to the vertical direction. As explained previously, this angle would correspond to the version angle of the restored neck of the femur during. The bubble level may be provided with indicia of the kind described above, including zonal markers and/or one or more tick marks positioned to allow the position of the bubble in the bubble level to be used to read off the version angle and/or determine whether the version angle falls within an acceptable range.

In another example, the protractor may include an electronic inclinometer which may be attached to the proximal end of the broach. The electronic inclinometer may be located on a rod of the kind described above, which again may be inserted into an aperture located either in the neck trial or connection member (e.g. so that the electronic inclinometer is located posteriorly with respect to the femur and broach). The electronic inclinometer may be configured to measure its orientation relative to the vertical direction, thereby to measure the tilting of the broach according to the version angle of the restored neck of the femur as explained previously. The electronic inclinometer may include a display for displaying the measured angle and/or indicating whether the version angle falls within an acceptable range. In some examples, instead of, or in addition to including a display, the electronic inclinometer may be configured to send the measured angle via a wired or wireless connection to a separate computing device for display and/or use in making recommendations on a pre-operative plan and the desired outcome for the patient.

In the event that the measured version angle does not correspond to an anticipated/intended value and/or does not fall within an acceptable range of “normal” angles, there are various actions that may be taken.

For instance, in one example, an iterative approach may be taken in which the procedure described herein is repeated a plurality of times as the neck of the femur100is being prepared to receive the femoral implant. For instance, while using broaches of different sizes to remove bone from the femoral neck, each broach may be inserted (typically starting with the smallest, thereafter in order of increasing size as more bone is removed) into the medullary canal so that the version angle may be measured using a protractor of the kind described herein. In this way, the surgeon may use the measured version angle as a guide for the subsequent removal of bone from the femur, thereby to attempt to arrive at a finally prepared femur which has an acceptable version angle when the femoral implant is installed.

In another example, the orientation and/or configuration of the acetabular cup implant that may be installed in the acetabulum of the patient as part of the hip replacement procedure may be altered to accommodate the version angle of the restored neck of the femur. In particular, the cup anteversion angle at which the cup implant is installed in the acetabulum may be altered accordingly and/or a different liner may be used in the cup implant.

In a further example, a different femoral implant may be selected for use in the hip replacement procedure. The selected femoral implant may be configured (shaped and dimensioned) such that the version angle of the restored neck of the femur corresponds to an acceptable value. It is envisaged that in order to choose an appropriate implant, broaches30of various configurations (e.g. incorporating different degrees of anteversion) may be trialled by inserting them into the medullary canal at the neck of the femur100and by using the protractor to measure the version angle. At the end of this process, a femoral implant corresponding to the configuration (e.g. degree of anteversion) of the most appropriate broach may be selected for the prosthetic hip. In a similar approach, a different femoral neck portion may be selected for the femoral implant, to produce a normal amount of anteversion for the implant. Again, the appropriate femoral neck portion may be selected by trialling using different broaches, or a single broach having a connection member for the attachment of different kinds of neck trial portion having different amounts of anteversion.

In another example, an abnormal version angle may be accommodated by adjusting the tension in the soft tissues of the leg (e.g. the abductor muscles, flexors or capsule).

It is envisaged that combinations of the approaches set out above may be used. For instance, in the event that the iterative approach described above does not result in an acceptable version angle, the anteversion angle of the acetabular cup may be altered and/or the tensions in the soft tissues surrounding the hip may be altered.

Accordingly, there has been described an apparatus and method for measuring a version angle of a restored neck of a femur during a hip replacement procedure. The apparatus includes a broach. The broach has a distal end that is insertable into a medullary canal of the neck of the femur. The broach also has a proximal end that extends along a neck axis of the broach. The apparatus also includes a protractor. The protractor includes a rod which is attachable to the proximal end of the broach to extend away from the neck axis of the broach for measuring the version angle of the restored neck of the femur relative to a vertical direction. The method includes inserting the broach, flexing the knee at approximately ninety degrees, orienting the tibia vertically, attaching the protractor to the proximal end of the broach and using it to measure the version angle.

Although particular embodiments of this invention have been described, it will be appreciated that many modifications/additions and/or substitutions may be made within the scope of the claims.