WO2019057698A1

WO2019057698A1 - Adjustable trial neck

Info

Publication number: WO2019057698A1
Application number: PCT/EP2018/075178
Authority: WO
Inventors: Gary Moore; Stephanie Prince; Duncan Young
Original assignee: Depuy Ireland Unlimited Company
Priority date: 2017-09-19
Filing date: 2018-09-18
Publication date: 2019-03-28
Also published as: GB201715038D0

Abstract

A kit of parts and method for trialling a hip joint are described. The kit of parts comprises a femoral part (130) having first attachment formation (140) at a superior end (138) and a trial neck (100) having a second attachment formation (104) which is attachable to the first attachment formation at one of a plurality of attachment positions. The trial neck component includes a head attachment formation (106) at a free end (108) for releasably attaching a trial femoral head and an adjustment mechanism (112, 124) operable by a user to vary the separation between the head attachment formation and the second attachment formation to adjust the neck length. Each of the plurality of attachment positions corresponds to a different neck offset for an assembly of the femoral part and the trial neck.

Description

Adjustable Trial Neck

The present invention relates to trial necks and in particular to adjustable trial necks for use during a trialling stage of an orthopaedic surgical procedure.

During some orthopaedic procedures, in which one or more parts of a joint are replaced by artificial joint components, also referred to generally as prostheses or implants, trialling may be used. During trialling, the surgeon uses trial components, rather than the actual implants, to help assess whether any changes might be made to bone cuts and/or soft tissues and/or the implants originally planned to be used. Generally, this involves constructing a trial version of the intended implants, and reducing the joint to help assess whether the eventual prosthetic joint is likely to be suitable or not.

For example, during a hip arthroplasty procedure, the surgeon may attach a trial femoral head to a trial femoral neck and reduce the hip joint to see whether various properties of the hip joint are suitable, such as the size of the femoral head. Also, the orientation of the femoral head and/or position of the femoral head relative to the femur, may also be assessed and which are largely determined by the trial neck. In order to allow the trial construct to be optimised for each patient, modular systems may be provided including vary many different parts. For example, each head size and head offset combination may have its own dedicated trial neck, and each head offset may have its own trial head. Hence, the trays for the trial components can be very large and/or heavy and/or may have to hold a large number of different trial components which may be subtly different.

Typically a scrub nurse or other surgical assistant will assemble a trial construct and pass that to the surgeon. The large number of modular trial components can make selecting the correct ones difficult. Also the need to assemble the trial construct, trial the joint, disassemble, reassemble, re-trial, etc., can discourage iterative trialling in order to better assess the joint and the best final implant construction. US 7,425,214 describes a trial proximal femoral part including a trial femoral head which is coupled for selective movement relative to a femoral stem to vary the neck length.

However, these approaches require either a large number of different trial parts to be provided, many of which may be redundant, or do not permit sufficient trialling flexibility. Hence, a more efficient and/or reliable approach to trialling for ball and socket type joints would be beneficial.

According to a first aspect of the invention, there is provided a kit of parts for trialling a hip joint, comprising: a femoral part having first attachment formation at a superior end; and a trial neck having a second attachment formation, wherein the second attachment formation is attachable to the first attachment formation at one of a plurality of attachment positions, and wherein the trial neck component includes a head attachment formation at a free end for releasably attaching a trial femoral head and an adjustment mechanism operable by a user to vary the separation between the head attachment formation and the second attachment formation to adjust the neck length and wherein each of the plurality of attachment positions corresponds to a different neck offset for an assembly of the femoral part and the trial neck. The first attachment formation may be configured such that each of the plurality of attachment positions corresponds to the same leg length for an assembly of the femoral part and the trial neck.

The first attachment formation may be a female formation and/or the second attachment formation may be a male formation.

The first attachment formation may include a first plurality of ribs and grooves. The second attachment formation may include a second plurality of ribs and grooves. The first plurality of ribs and grooves may be arranged to define the plurality of different attachment positions. The second plurality of ribs and grooves may be arranged to cooperate with some of the first plurality of ribs and grooves to define a selected one of the plurality of attachment positions. The plurality of attachment positions may comprise only a first attachment position and a second attachment position.

The female formation may be in the form of a cavity defined by a base wall. The base wall may extend transversely to a longitudinal axis of the femoral part. The base wall may be arranged to act as a stop to control the depth of insertion of the second attachment formation.

The adjustment mechanism may be configured to be operable by a user to vary the separation continuously.

The adjustment mechanism may be a linear adjustment mechanism.

The adjustment mechanism may include a threaded shaft and a rotary threaded member arranged about the threaded shaft.

The adjustment mechanism may include an external interface arranged to receive a tool to operate the adjustment mechanism. The trial neck may include a scale. The scale may be arranged to indicate different neck lengths. The scale may be arranged to indicate head offsets corresponding to different neck lengths.

The trial neck may comprise a first part and a second part. The first part may be translatable relative to the second part by the adjustment mechanism. The head attachment formation may be provided at a free end of the first part. The second attachment mechanism may be provided toward a base or inferior end of the second part.

The kit of parts may further comprise a further femoral part having a third attachment formation at a superior end and wherein the second attachment formation is attachable to the third attachment formation at one of a plurality of further attachment positions. Each of the plurality of further attachment positions may correspond to a different neck offset for an assembly of the further femoral part and the trial neck. The first femoral part and the second femoral part may have different sizes.

The or each femoral part may be a femoral broach or a trial femoral stem or a femoral stem implant.

The kit of parts may further comprise a trial femoral head or a plurality of trial femoral heads. The or each trial femoral head may have a cavity arranged to receive the head attachment formation.

According to a second aspect of the invention there is provided an assembly of the kit of parts of the first aspect, wherein the trial neck is attached to the femoral part at a selected one of the plurality of attachment positions. According to a third aspect of the invention there is provided a method of trialling a hip joint during a hip replacement procedure being carried out on a patient, comprising:

attaching a trial neck to a femoral part at a selected one of a plurality of different positions each corresponding to a different neck offset; reducing a trial hip joint including a trial femoral head mounted on the trial neck; adjusting the length of the trial neck; and assessing the tension of the trial hip joint.

The method may further comprise shortening the length of the trial neck before reducing the trial hip joint. The method may further comprise shortening the length of the trial neck after assessing the tension of the trial hip joint; and dislocating the trial hip joint.

The method may further comprise: further adjusting the length of the trial neck after assessing the tension of the trial hip joint; and further assessing the tension of the trial hip joint.

A tool may be used to adjust or shorten the length of the trial neck while the trial hip joint is reduced. The method may further comprise: establishing a target geometry of the trial hip joint after assessing the tension; providing a femoral implant having a neck arranged to reproduce the target geometry; and implanting the femoral implant after the trial neck has been removed.

The femoral implant may be a femoral stem with a unitary neck or a femoral stem with a modular neck. The femoral part may be a femoral broach.

A fourth aspect of the invention provides a trial neck comprising: a femoral attachment formation at one end; a head attachment formation at a free end for releasably attaching a trial femoral head; and an adjustment mechanism operable by a user to vary the separation between the head attachment formation and the second attachment formation to adjust the neck length and wherein the femoral attachment mechanism is configured to releasably attach the trial neck to a femoral part at a selected one of a plurality of attachment positions, each attachment position corresponding to a different neck offset when the trial neck is attached to the femoral part in use.

Preferred features of the first aspect can give rise to preferred features of the fourth aspect.

An embodiment of the invention will now be described in greater detail, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 shows a perspective view of a trial neck according to the invention; Figure 2 shows an exploded perspective view of an assembly of the trial neck of Figure 1 and a broach according to the invention;

Figure 3 shows a perspective view of the assembly of Figure 2 and a tool for adjusting the trial neck;

Figure 4 shows a side elevation of the assembly of Figure 2;

Figure 5 shows a cross section of the assembly as shown in Figure 4; Figure 6 shows a side elevation of a further assembly of the trial neck and a further broach;

Figure 7 shows a cross section of the further assembly as shown in Figure 6; and Figure 8 shows a flow chart illustrating a method of use of the trial neck according to the invention.

Similar items in the different Figures of the drawings share like reference signs, unless indicated otherwise. With reference to Figure 1 there is shown a perspective view of an embodiment of a trial neck 100 according to the invention. The trial neck 100 includes a main body 102 having a male formation 104 at a first end. A taper 106 is provided toward a second free end of the trial neck. The taper 106 provides a releasable attachment formation to which a trial femoral head (not shown in Figure 1) can be releasably attached in use. The taper 106 can be translated relative to the main body 102 along a longitudinal neck axis of the trial neck to adjust the length of the trial neck in a continuous manner.

Figure 2 shows an exploded perspective view of an assembly 120 of the trial neck 100 and a femoral broach 130 better illustrating the adjustment mechanism by which the length of the trial neck can be continuously adjusted along the longitudinal neck axis 108. The main body 102 has a central aperture extending along its length and arranged to receive a partially threaded member 1 12 which extends from a lower side of the taper 106. Opposed side walls, e.g. wall 1 14 includes an indicium in the form of a line 1 16 which provides a datum for use with a scale 1 18 provided on the main body 102. The scale 118 is provided on the surface of a flat side wall of the main body, and may include a plurality of indicia each corresponding to a different amount of neck length or equivalently head offset, e.g. -3, 0, 3, 6, 9, in the illustrated embodiment. The indicia may be approximate dimensions or arbitrary numbers representing positions on a scale. Taper 106 includes opposed recesses 120, 122 defined by portions of its side wall and arranged to receive free ends of the upper part of the main body to provide a full range of length adjustment. The lower part of the main body 102 has curved side walls and includes a plurality of ribs and grooves on opposed faces. The ridges and grooves allow the male portion to be selectively engaged at a selected one of multiple positions within a cavity in the broach 130 as described in greater detail below. A toothed wheel or bevel gear 124 has an internally threaded bore, and is located in a slot within the main body and about the threaded shaft 1 12. The bevel gear 124 and the threaded shaft 1 12 co-operate to provide a drive mechanism by which the position of the taper can be continuously adjusted relative to the main body along the longitudinal neck axis 108 so as to vary the neck length. The toothed wheel 124 provides an external interface to the trial neck drive mechanism for a tool which allows the neck length to be adjusted while a trial joint is reduced as described in greater detail below.

As also illustrated in Figure 2, broach 130 generally includes an inferior stem part 132 which extends along a longitudinal stem axis 134 which generally extends in the inferior- superior direction in the intramedullary canal of the proximal part of a patient's femur in use. A superior part 136 of the broach 130 is generally in the form of a shoulder and includes a superior surface 138 which is tilted relative to the stem axis 134. A cavity 140 is defined in the superior part of the broach and includes a plurality of ribs. The cavity 140 provides a female part of an attachment mechanism and can receive the male part 104 of the trial neck at one of a plurality of distinct positions in order to change the neck offset of the assembly in a discontinuous manner.

Figure 3 shows a perspective view of the assembly 120 of the trial neck 100 and broach 130 with the trial neck inserted in the broach cavity at a position corresponding to a minimal neck offset. Figure 3 also shows a tool 180 which may be used to adjust the neck length along the neck axis 108. The tool 180 may be a power tool including a motor in a body 182 which can drive a rotating shaft 184 having a toothed wheel or bevel gear 186 at a free end. By coupling the teeth of tool bevel gear 186 with the teeth of neck bevel gear, and running the motor, the length of the trial neck can be increased or decreased to adjust the neck length. In other embodiments a manual tool may be used instead of a power tool. Figure 4 shows a side elevation of the assembly 120 with the trial neck 100 at a minimal neck offset position within the broach cavity 140. Figure 5 shows a cross section of the assembly shown in Figure 4. In the illustrated embodiment, the stem-neck angle, i.e. the angle subtended by the stem axis 134 and the neck axis 108 is approximately 135°. In other embodiments other stem-neck angle may be used and typical values include 130° and 140° depending on the implant system. As discussed above, in use the stem axis 134 is generally aligned with the inferior-superior axis of the patient. Double headed arrow 150 in Figures 4 and 5 indicates the direction of the medial-lateral axis of the patient. With the trial neck located in the first position within the femoral cavity 140, as illustrated in Figure 5, the taper has a first neck offset for a trial joint when a trial femoral head is mounted on the taper in use and the trial hip joint is reduced. The femoral broach cavity 140 and its ribs are arranged to interact with the ribs and grooves on the trial neck to define a plurality of different positions at which the trial neck can be inserted in the broach cavity 140 each giving rise to a different neck offset but not changing the leg length. As illustrated in Figures 4 and 5, if the trial neck is inserted in the broach cavity at a second position, indicated by dashed lines 100' in Figures 4 and 5, then the trial neck simply translates in the medial-lateral direction, as indicated by doubled headed arrow 152 being parallel to the medial-lateral axis 150. With the trial neck in the second position, the amount of neck offset is greater than for the trial neck in the first position, i.e. the femur has been moved laterally. However, there has been no change in leg-length as the position of the trial neck in the superior-inferior direction, 134, does not change. As will be appreciated, by operating the drive mechanism to adjust the neck length of the trial neck, both the offset (in the medial-lateral direction) and the leg length (in the inferior-superior direction) will be changed as the trial neck changes its length along the neck axis 108.

Hence, the assembly shown in Figures 4 and 5 allows the neck length to be adjusted continuously, but the neck offset to be altered or selected in a discontinuous or discrete manner.

Figure 6 shows a second assembly 160 of the trial neck 100 and a second femoral broach 170. The second femoral broach 170 has a different size to the first femoral broach 130 and extends in use generally along the inferior-superior axis of the patients femur 174. In the illustrated embodiment, the second femoral broach 170 is smaller than the first femoral broach. Similarly to the first femoral broach 130, the second femoral broach has a broach cavity including ribs and grooves arranged to define a plurality of different positions at which the trial neck 100 may be inserted in the broach cavity with different neck offsets. As illustrated in Figures 6 and 7, the trial neck 100 may be inserted at a first position corresponding to a minimal neck offset or a second position, indicated by dashed outline 100', corresponding to an increased neck offset in the medial-lateral direction 150 but no change in leg length. As illustrated in Figures 6 and 7, the trial neck 100 has been adjusted to increase its overall neck length compared to its neck length as illustrated in Figures 4 and 5.

Although the trial neck is illustrated being used in an assembly including a femoral broach above, it will be appreciated that the trial neck could alternatively or additionally be used with any other femoral component that may be provided in the femur during hip surgery. For example, in other embodiments, the femoral part may be a rasp, or any other femoral cutting tool or instrument commonly used in hip surgery, or may be a trial femoral stem implant or a prosthetic femoral stem implant. Hence, the adjustable trial neck and a single femoral part with multiple attachment positions for the trial neck may allow a trial hip joint to be realised with a reduced number of parts compared to conventional approaches. Further, a greater range of trial hip joints may be realised with a reduced number of parts compared to conventional approaches by using the same adjustable trial neck with different sized femoral parts.

Further benefits and advantages of the present invention will be apparent from the following description of the use of the trial neck 100 and assembly 120 or 160.

Figure 8 shows a flow chart 200 illustrating a hip replacement surgical procedure in which the trial neck may be used. Some of the steps may be largely conventional and so are not described herein in detail so as not to obscure the invention. Also, unless the context requires otherwise, some of the steps may be optional and/or the order of the steps may be changed as will be apparent to a person of ordinary skill in the art. At 202, the acetabulum of the patient is prepared in a generally conventional manner which may include removing soft tissues and reaming the acetabular cavity. Then a trial cup and any liner may be placed in the prepared acetabulum. At 204 the femur is prepared which may include resecting the femoral neck and forming an intramedullary cavity along the proximal axis of the femur using one or more rasps and broaches. When the cavity has been formed, then a final sized broach 130 may be left in the cavity. At 206, the surgeon may select a default or initial neck offset for the trial joint and then insert the trial neck 100 into the appropriate position in the femoral broach cavity 140. At 208, the surgeon may use the tool 180 to reduce the length of the trial neck so as to ease joint reduction. Then at 210 the surgeon may place a trial femoral head on the taper 106 and reduce the trial joint by introducing the femoral head into the acetabular cup. At 212, the surgeon may use tool 180 to increase the neck length of the trial neck to correspond to a previously planned neck length. At 214 the surgeon can assess the trial joint for the current neck length. This may include, in particular assessing the tension in the trial joint to see if any changes in neck offset or other properties of the hip joint may be appropriate.

After the initial assessment at 214, the surgeon may optionally use the tool 180 to adjust the neck length to assess the effect on joint tension for different neck length settings. Adjusting the neck length simulates the selection of different head offset options for different femoral heads. Also, if the implant system uses progressive neck sizing then adjusting the neck length can be used to simulate the effect of selecting a larger or smaller prosthetic stem, compared to the current broach size. After any adjustments and assessment of the trial joint at 216, the tool 180 can be used again to reduce the neck length at 218 to ease dislocation of the trial joint at 220. If the surgeon is not satisfied with the joint geometry during trialling, then at 222, the surgeon can change the neck offset by removing the trial neck form the broach and inserting the trial neck at a different position within the broach cavity 140 at 224 to simulate an alternate style of stem and neck. The reduction-trialling-dislocation steps described above can then be repeated for the new neck geometry. As well as changing just the neck offset, by altering the neck length, the effect of different overall neck sizes, head positions and neck angles can be simulated. When the surgeon has determined an acceptable neck geometry, then after 222, the trial components can be removed from the femur and acetabulum. At 226 the prosthetic femoral component having a geometry closely matching that determined previously in the method can either be selected from a range of femoral implants having different neck geometries, or can be assembled from a modular implant system, and implanted in the femur and the prosthetic cup can be implanted in the acetabulum. The method then generally finishes with any conventional end surgical steps.

Hence, the assembly of the trial neck and femoral part can be used to change neck offset in order to adjust the tension in the joint, but without changing leg length. The continuously adjustable neck length allows different neck geometries to be trialled and also eases reduction and dislocation of the trial joint, thereby helping to avoid or reduce any soft tissue damage and hence encouraging the surgeon to carry out more trialling. In this specification, an example embodiment has been presented as a particular combination of features. However, a person of ordinary skill in the art would understand that many other embodiments may be practiced which include a different combination of features, including fewer features or a greater number of features. It is intended that the following claims cover all possible embodiments.

Any instructions and/or flowchart steps may be carried out in any order, unless a specific order is explicitly stated or would be understood to be required from the context of the description. Also, those skilled in the art will recognize that while one example method has been discussed, a variety of other differing methods are possible based on other combinations and/or orders of method steps, and are to be understood within the context provided by this detailed description.

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

Claims

CLAIMS:

1. A kit of parts for trialling a hip joint, comprising:

a femoral part having a first attachment formation at a superior end; and a trial neck having a second attachment formation, wherein the second attachment formation is attachable to the first attachment formation at one of a plurality of attachment positions, and wherein the trial neck component includes a head attachment formation at a free end for releasably attaching a trial femoral head and an adjustment mechanism operable by a user to vary the separation between the head attachment formation and the second attachment formation to adjust the neck length and wherein each of the plurality of attachment positions corresponds to a different neck offset for an assembly of the femoral part and the trial neck.

2. The kit of parts of claim 1, wherein the first attachment formation is configured such that the plurality of attachment positions correspond to the same leg length for an assembly of the femoral part and the trial neck.

3. The kit of parts of claim 1 or 2, wherein the first attachment formation is a female formation and the second attachment formation is a male formation.

4. The kit of parts of claim 3, wherein the first attachment formation includes a first plurality of ribs and grooves and the second attachment formation includes a second plurality of ribs and grooves and wherein the first plurality of ribs and grooves are arranged to define the plurality of different attachment positions.

5. The kit of parts of claims 3 or 4, wherein the female formation is in the form of a cavity defined by a base wall which extends transversely to a longitudinal axis of the femoral part and arranged to act as a stop to control the depth of insertion of the second attachment formation.

6. The kit of parts of any of claims 1 to 5, wherein the adjustment mechanism is configured to be operable by a user to vary the separation continuously.

7. The kit of parts of any of claims 1 to 6, wherein the adjustment mechanism includes an external interface arranged to receive a tool to operate the adjustment mechanism.

5 8. The kit of parts of any of claims 1 to 7, wherein the trial neck includes a scale arranged to indicate the neck length.

9. The kit of parts of any of claims 1 to 8, wherein the trial neck comprises a first part and a second part, and wherein the first part is translatable relative to the second part

10 by the adjustment mechanism and wherein the head attachment formation is provided at a free end of the first part and the second attachment mechanism is provided toward a base of the second part.

10. The kit of parts of any of claims 1 to 9, and further comprising a further femoral 15 part having a third attachment formation at a superior end and wherein the second

attachment formation is attachable to the third attachment formation at one of a plurality of further attachment positions, and wherein each of the plurality of further attachment positions corresponds to a different neck offset for an assembly of the further femoral part and the trial neck.

20

1 1. The kit of parts of claim 10, wherein the first femoral part and the second femoral part are different sizes.

12. The kit of parts of any of claims 1 to 1 1, wherein the or each femoral part is a 25 femoral broach.

13. The kit of parts of any of claims 1 to 12 and further comprising a trial femoral head having a cavity arranged to receive the head attachment formation.

30 14. An assembly of the kit of parts of any of claims 1 to 13, wherein the trial neck is attached to the femoral part at a selected one of the plurality of attachment positions.

15. A method of trialling a hip joint during a hip replacement procedure being carried out on a patient, comprising:

attaching a trial neck to a femoral part at a selected one of a plurality of different positions each corresponding to a different neck offset;

5 reducing a trial hip joint including a trial femoral head mounted on the trial neck;

adjusting the length of the trial neck; and

assessing the tension of the trial hip joint.

16. The method of claim 15, and further comprising:

10 shortening the length of the trial neck before reducing the trial hip joint.

17. The method of claim 15 or 16, and further comprising:

shortening the length of the trial neck after assessing the tension of the trial hip joint; and

15 dislocating the trial hip joint.

18. The method of any of claims 15 to 17, and further comprising:

further adjusting the length of the trial neck after assessing the tension of the trial hip joint; and

20 further assessing the tension of the trial hip joint.

19. The method of any of claims 15 to 18, wherein a tool is used to adjust or shorten the length of the trial neck while the trial hip joint is reduced.

25 20. The method of any of claims 15 to 19, further comprising:

establishing a target geometry of the trial hip joint after assessing the tension; providing a femoral implant having a neck arranged to reproduce the target geometry; and

implanting the femoral implant after the trial neck has been removed.

30

21. The method of any of claims 15 to 20, wherein the femoral part is a femoral broach.