Alignment tool

An alignment tool (2) for a joint is provided comprising a reference member 4 that defines a reference plane R and a distraction member (6). The distraction member (6) comprises first and second distraction arms (70, 72), each of which is independently moveable with respect to the reference member (4) along a movement axis M. The movement axes M, M of the first and second distraction arms (70, 72) are substantially parallel. A kit of parts is also provided comprising an alignment tool (2), a drill guide (200) and a cutting guide (300).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage of International application No. PCT/GB2011/050846, filed on Apr. 28, 2011 and published in English as WO/2011/135372 on Nov. 3, 2011. This application claims the benefit of Great Britain Application No. 1007062.1, filed on Apr. 28, 2010. The disclosures of the above applications are incorporated herein by reference.

The present invention relates to an alignment tool and particularly but not exclusively to an alignment tool suitable for use in total ankle replacement surgery.

BACKGROUND TO THE INVENTION

It is known to replace diseased or damaged articulating surfaces of a joint with prosthetic components in total or partial joint replacement procedures. During such procedures, it is necessary to balance the tension in the soft tissue structures that support the joint, for example the ligaments and surrounding tissues. In certain cases, it is also desirable to correct for deformities. These deformities may be from a pre-existing injury or condition, or may have developed in the joint in parallel with, and usually as a consequence of, the degradation of the natural articulating surfaces. For example, it is common for an ankle requiring total joint replacement surgery to exhibit a certain degree of varus or valgus deformity. This is where the distal bone of the joint is angled either medially (varus) or laterally (valgus) with respect to the normal joint line. Such deformities can be corrected by placing the joint in the desired anatomical alignment before resecting the distal bone articulating surface in preparation for implantation of the prosthetic component. The bone surface will have worn away, or subsided as a result of trauma, to a greater degree in one compartment or the other (depending on the nature of the deformity). Placing the joint in correct alignment before resecting will therefore cause the removal of a non symmetrical piece of bone, removing less bone from the side that is worn away or subsided in order to restore normal alignment to the joint. In conventional surgical procedures, the joint is placed and held in alignment prior to a distal bone resection by a surgical assistant. The correction for varus or valgus deformities is therefore conducted by eye and the accuracy and repeatability of the resection is dependent upon the surgical assistant holding the limb steady in the correct place.

SUMMARY OF INVENTION

According to the present invention, there is provided an alignment tool for a joint comprising a reference member that defines a reference plane and a distraction member, the distraction member comprising first and second distraction arms, each of which is independently moveable with respect to the reference member along a movement axis, the movement axes of the first and second distraction arms being substantially parallel.

The substantially parallel movement axes of the independently moveable distraction arms enable the alignment tool to differentially distract a bone with respect to a reference plane, thus affording control of the angular alignment of the distracted bone. If used in an ankle joint for example, the alignment tool affords differential distraction of the talus, allowing for correct angular alignment in the coronal plane.

The movement axes of the first and second distraction arms may be substantially perpendicular to the reference plane, which may be particularly advantageous when dealing with a substantially rectangular joint space.

The alignment tool may further comprise a first adjustment means, operatively connecting the first distraction arm and the reference member, and a second adjustment means, operatively connecting the second distraction arm and the reference member.

The reference member may comprise a reference body on which the first and second adjustment means are mounted, and a reference element.

The adjustment means may be mounted on the reference body in an adjustment plane and the reference element may protrude from the adjustment plane along an engagement axis that is angled with respect to the adjustment plane. In this manner, the mechanism of adjustment may be separated spatially from the reference element. This may be particularly advantageous when operating in a small joint space, enabling maximum visibility to be maintained into the joint when the instrument is in place and also ensuring that only those elements of the tool that are required to be within the joint space actually protrude into that space.

The distraction arms may be mounted on the adjustment means in the adjustment plane and may extend from the adjustment plane along axes substantially parallel to the engagement axis of the reference element. In this manner, the distraction arms also protrude into the joint space in use while being mounted on adjustment means that are removed from the joint space and thus not cluttering the space or obscuring the view of the surgeon.

Each adjustment means may comprise an adjustment socket that is mounted on the reference member and receives an adjustment arm, on which a corresponding distraction arm is mounted.

Each adjustment arm may carry a rack and each adjustment socket may carry a pawl for cooperation with the rack. Such a rack and pawl arrangement allows fine control of relative displacement between the arm and socket in which it is received.

The distraction arms may be mounted on the adjustment arms via mounting members.

Each distraction arm may comprise an attachment feature, which may be operable to receive a drill guide. In this manner, the alignment tool may cooperate with further surgical tools to enable drilling and bone resection to be carried out with the joint held in alignment by the alignment tool.

Each attachment feature may comprise an alignment feature, which may be operable to align the drill guide in a plane parallel to the reference plane of the alignment tool. Correct alignment with the reference plane may thus be assured, even with the distraction arms differentially distracted with respect to the reference plane.

The reference element may comprise a trial prosthesis component, which may be a trial tibial component for a total ankle arthroplasty. The trial prosthesis component may be inserted into a joint space such that the reference plane of the alignment tool is the plane in which the articulating surface of an eventually implanted prosthesis component will rest.

According to another aspect of the present invention, there is provided a kit of parts comprising an alignment tool of the first aspect of the present invention and a drill guide, operable to be mounted on the alignment tool. The drill guide may be operable to be received in either one of the attachment features of the first and second distraction arms.

The drill guide may be operable to direct insertion of guide wires. The guide wires may be inserted via inner guide tubes which may be received within outer guide tubes of the drill guide.

The kit of parts may further comprise a cutting guide, operable to be mounted on guide wires directed by the drill guide.

According to another aspect of the present invention, there is provided a method of aligning a joint using a tool comprising a reference member and a distraction member, the distraction member comprising first and second arms, each of which is independently moveable with respect to the reference member, the method comprising:a) inserting the tool into a joint space;b) distracting one of the first and second distraction arms relative to the reference member;c) distracting the other of the first and second distraction arms relative to the reference member; andd) repeating steps (b) and (c) until the joint is in alignment.

DETAILED DESCRIPTION OF EMBODIMENTS

With reference toFIGS. 1 to 4, an alignment tool2suitable for use in a total ankle replacement procedure comprises a reference member4and a distraction member6. The reference member4comprises a T shaped reference body8and a reference element10in the form of a trial prosthesis component which may be a trial tibial prosthesis component. The T shaped reference body8comprises a base11, that defines an engagement axis E of the tool2, and a cross bar16that extends across the base11substantially perpendicularly to the base11. The base11and cross bar16are integrally formed. The cross bar16lies in an adjustment plane that extends above and below the cross bar16such that the engagement axis E of the tool is substantially normal to the adjustment plane.

The reference element10is mounted via a threaded rod12that extends from a central point of the cross bar16of the T shaped reference body8through the base11, such that the reference element10is mounted at an end15of the base11that is remote from the cross bar16. The reference element10comprises an engagement portion17and an articulating portion19which is integrally formed with the engagement portion17. The engagement portion17comprises a threaded blind bore21in which an end of the threaded rod12is received to fix the reference element10to the reference body8of the tool2. The articulating portion19of the reference element10comprises a distal planar surface14which extends across and defines a reference plane of the tool2.

At opposite ends of the cross bar16of the reference body8are adjustment sockets18,20, which are integrally formed with the cross bar16. In an alternative embodiment, the sockets18,20may be fixedly joined to the cross bar16in an appropriate manner. Housings22,24extend upwardly (as seen in the Figures) from the sockets18,20in the adjustment plane and spring loaded fingers or pawls26,28are mounted on the housings22,24. Rotary drives30,32are also mounted on the housings22,24, each drive comprising a handle34,36and a pinion38,40. Adjustment arms46,48are received, one in each combination of socket18,20and housing22,24. Each adjustment arm46,48comprises a first end54,56(uppermost in the Figures), that protrudes from the associated housing22,24, and a second end58,60, that protrudes from the associated socket18,20.

Each combination of pawl26,28and pinion38,40mounted on the housings22,24engages a respective toothed rack42,44carried on the adjacent adjustment arm46,48which is received within the relevant socket18,20and housing22,24. Each pawl26,28is angled to engage the corresponding toothed rack42,44through an opening50,52in the housing22,24. The pawls26,28are angled such that relative movement between the adjustment arms46,48and associated housings22,24in a first direction along a movement axis may take place under the action of the rotary drives30,32, while relative movement in the opposite direction is opposed. The first direction is a direction in which separation between the second ends58,60of the adjustment arms46,48and the sockets18,20is increased, the second direction being the reverse direction, in which the second ends58,60of the adjustment arms46,48are moved towards and increasingly received within the sockets18,20. The rotary drives30,32engage the racks42,44of the adjustment arms46,48via the pinions38,40. The pinions38,40mesh with the racks42,44and, under the action of the handles34,36, drive linear motion of the adjustment arms46,48in the first direction. If linear motion in the second direction is necessary, the locking action of the pawls26,28may be manually over ridden by depressing the pawls26,28at ends remote from the adjustment arms46,48, compressing the springs of the spring loaded pawls26,28and removing the engaging ends of the pawls26,28from engagement with the racks42,44. Relative motion between the adjustment arms46,48and the housings22,24may then take place freely in either direction.

Depth stops62,64extend from the first ends54,56of the adjustment arms46,48, to prevent the first ends54,56of the adjustment arms46,48being completely received within the housings22,24. The depth stops62,64may be in the form of screws that protrude from a face of the adjustment arms46,48. Additional depth stops66,68protrude from the second ends58,60of the adjustment arms46,48to prevent the second ends58,60of the adjustment arms46,48being completely received within the sockets18,20. The additional depth stops66,68may be in the form of annular shoulders that are operable to engage corresponding annular surfaces of the sockets18,20.

First and second distraction arms70,72are mounted one on each second end58,60of the adjustment arms46,48. The distraction arms70,72are mounted via mounting members74,76that extend from the additional depth stops66,68at the second ends58,60of the adjustment arms46,48. The mounting members74,76extend towards each other, substantially parallel with the cross bar16of the reference body8. The distraction arms70,72are thus mounted substantially below (as seen in the Figures) and in line with the base11of the reference body8and the reference element10. The distraction arms70,72extend out of the adjustment plane, in which they are mounted via the mounting members74,76, substantially parallel with the engagement axis E defined by the base11of the reference body8. Each distraction arm70,72comprises a lower (as seen in the Figures) engagement surface78,80, remote from the reference element11and operable to engage a bone surface when the tool2is in use. Each distraction arm70,72may be displaced independently relative to the reference body8and reference element11by turning the appropriate handle34,36and thus driving relative movement between the relevant adjustment arm46,48(on which the distraction arms70,72are mounted) and its associated socket18,20and housing22,24(which are integrally formed with, or at least fixedly joined to the reference body8).

Each distraction arm70,72carries an attachment feature92,94in the form of two protruding lugs96,98,100,102, between which a keyhole shaped opening104,106is defined. Each pair of lugs96,98,100,102protrudes downwards (as seen in the Figures) from the relevant engagement surface78,80of the associated distraction arm70,72in the region of the mounting members74,76and therefore substantially in the adjustment plane of the tool2. Each keyhole shaped opening104,106comprises an upper (as seen in the Figures) part cylindrical region that carries an internal thread and defines an approach axis. The two approach axes being substantially parallel to each other and to the engagement axis of the tool. Each of the attachment features92,94comprises an alignment feature in the form of protruding upper108,110and lower112,114lips that extend substantially rearward, away from the distraction members70,72. The lower lips112,114are in two parts, a first part on one lug96,100and a second part on the other lug98,102of the relevant pair. The upper108,110and lower112,114lips of each attachment feature92,94comprise facing engagement surfaces that are angled slightly away from one another so as to engage corresponding surfaces on a drill guide200, as explained in further detail below.

With reference also toFIG. 5, a drill guide200, suitable for use with the alignment tool,2comprises a guide body202and two substantially cylindrical outer guide tubes204,206extending though the guide body202along parallel axes that define a guide plane. The guide body comprises an alignment feature208in the form of a lug208that protrudes from an approach face210of the guide body, substantially in the region of a dominant one of the outer guide tubes206. The lug208is shaped to fit between and tightly engage the lips108,110,112,114of either of the attachment features92,94of the alignment tool2. The upper and lower regions (as seen in the Figures) of the alignment lug208of the drill guide200are symmetrical, such that the lug208may be received between the lips of either of the attachment features92,94of the alignment tool2, depending on the orientation of the grill guide200with respect to the alignment tool2. The dominant outer guide tube206is rotatable relative to the guide body202, alignment lug208and other outer guide tube204. The dominant outer guide tube206further comprises an attachment feature in the form of an external thread212and integral head214that is operable to rotate the dominant outer guide tube206relative to the guide body202. The threaded portion212of the dominant outer guide tube206is dimensioned to be received within the threaded part cylindrical region of the keyhole shaped opening104,106of either of the attachment features92,94. Engaging the thread212of the dominant outer guide tube206into the threaded cylindrical portion of either of the openings104,106brings the lug208into close engagement with the lips of the relevant attachment feature92,94, thus forcing the drill guide200into an alignment where the axis of the dominant outer guide tube206is substantially coincident with the approach axis of the attachment feature92,94to which the drill guide200is connected.

The outer guide tubes204,206of the drill guide200are operable closely to receive and to direct inner guide tubes205,207, which may be inserted down the outer guide tubes204,206using handles220,222until leading edges of the inner guide tubes205,207engage a bone surface. The inner guide tubes205,207are operable to guide a surgical drill in forming bone holes into which guide wires216,218may be inserted. With particular reference toFIGS. 3 and 4, a cutting guide300may be mounted on the guide wires216,218. The cutting guide comprises a body302that carries an upper (as seen in the Figures) cutting guide surface304, and two mounting lugs306,308, through which openings extend. The cutting guide300may be mounted on the guide wires216,218via the openings through the mounting lugs306,308.

Use of the alignment tool2, drill guide200and cutting guide300will now be described with reference to a total ankle replacement operation. It will be appreciated however, that these tools may also be employed in for example total knee replacement surgery or other procedures involving realignment of a joint.

In a total ankle replacement procedure, an incision is first made and soft tissues retracted to give access to the joint. An appropriate tool is then used to guide resection of the distal tibia, so as to prepare the bone surface for implantation of a tibial prosthesis component. Once the distal tibia it prepared, it is then necessary to resect the proximal talus, preferably correcting for any varus or valgus deformity in so doing.

First, the alignment tool2of the present invention is assembled with an appropriate trial tibial component10fixed to the reference body8via the threaded rod12. The alignment tool is substantially closed by depressing the pawls26,28at their remote ends and thus disengaging the pawls26,28from the racks42,44of the adjustment arms46,48to allow free movement to the adjustment arms46,48in the second direction. The alignment tool2is closed when the additional depth stops66,68engage the annular surfaces of the sockets18,20, thus bringing the distraction arms70,72into close proximity with the trial tibial prosthesis component10.

The alignment tool is then inserted into the joint along the engagement axis E. The trial tibial component10is substantially implanted into the recess formed in the distal tibia to accept a prosthesis component so that the trial component10is substantially in the position that will be occupied by the final prosthesis component once the surgery is complete. With the trial component10in place, the distal planar surface14of the articulating portion19of the trial component10defines the reference plane for the tool, the reference plane being the articulating plane of the eventually implanted tibial component. When the trial component is in place, the alignment tool2is correctly inserted into the joint, with the two distraction arms70,72symmetrically arranged over the medial and lateral sides of the joint.

Once the trial component10is in place, each distraction arm70,72is then moved independently in the first direction (so as to open the alignment tool2) by rotating the handles34,36of the rotary drives30,32. The distraction arms are moved in the first direction until each arm contacts an articulating surface of the talus. Movement of the distraction arms is then continued until the soft tissues of the joint are adequately engaged and the foot is in correct varus/valgus alignment. This will usually involve moving one distraction arm70,72further than the other distraction arm70,72, so as to distract the joint differentially and correct for varus/valgus deformities caused by a differentially worn or subsided articulating surface of the talus. This differential distraction effectively rotates the talus and the rest of the foot in the coronal plane, until the foot is correctly aligned with the rest of the lower limb. The locking action of the pawls26,28prevents movement in the second direction (closing the alignment tool2) and so prevents tension forces in the soft tissues returning the joint to its accustomed misaligned position. Once the soft tissues are engaged, the action of the tension forces in the soft tissues against the locking action of the pawls26,28ensures that the alignment tool2remains stably in place with the joint held in the correct varus/valgus alignment.

With the joint held in this position by the alignment tool2, the drill guide200is attached to the alignment tool2via one of the attachment features92,94. The drill guide200is oriented such that the dominant outer guide tube206, carrying the external thread212and surrounded by the alignment lug208is brought into engagement with the attachment feature of the lower, or more distracted of the two distraction arms70,72. This can be seen illustrated inFIG. 6. The thread212of the dominant outer guide tube206is screwed into engagement with the threaded cylindrical portion of the keyhole shaped opening104,106of the appropriate attachment feature92,94. The cooperation of the alignment lug208of the drill guide200and lips108,110or112,114of the attachment portion92,94ensures that the drill plane D, along which the axes of the outer guide tubes extend, is parallel to the reference plane R of the alignment tool2, as illustrated inFIG. 6. It will be appreciated that this is made possible, even when the distraction arms that carry the attachment features are no longer parallel following differential distraction of the joint, by the keyhole shaped openings104,106of the attachment features92,94. For example, as shown inFIG. 6, with the dominant outer guide tube206of the drill guide200attached to the lower94of the two attachment features92,94, the other outer guide tube204of the drill guide200extends through the lower, substantially rectangular region of the keyhole shaped opening104of the other attachment feature92.

With the drill guide200in place, inner guide tubes205,207are inserted into the outer guide tubes204,206until leading edges of the inner guide tubes205,207contact the talar bone surface. A surgical drill bit is then inserted down first one and then the other of the inner guide tubes205,207to drill holes in the talus. The inner guide tubes205,207ensure that the surgical drill bit is supported up to the point of contact with the bone surface. K wires216,218are then inserted down the inner guide tubes205,207and into the drilled holes, Once the K wires are in place, the alignment tool2and drill guide200, including inner guide tubes205,207, are removed from the joint, leaving the K wires in position.

The cutting guide300is then mounted onto the K wires216,218via the openings in the mounting lugs306,308and is brought into proximity with the talus. The cutting guide300is dimensioned such that the planar cutting surface304is parallel to the drill plane D in which the K wires216,218extend. As explained above, the drill plane D of the drill guide, through which the K wires are inserted, is parallel to the reference plane of the alignment tool2, owing to the interaction of the attachment features92,94and the alignment lug of the drill guide200. The resection guided by the cutting guide300is therefore parallel to the reference surface of the trial prosthesis when the foot is in correct varus/valgus alignment, ensuring a rectangular joint gap with the foot in correct alignment, regardless of any differential wear or subsidence on the resected articulating surface of the talus.

Once the talar resection has been made, the cutting guide300is removed and any additional cutting and or shaping of the talus may be conducting using appropriate guide tools. The additional tools may be mounted on the K wires216,218as necessary. Once the talus has been sufficiently shaped to receive a talar prosthesis component, the K wires216,218are removed. The tibial and talar prosthesis components, together with an appropriate bearing component may then be implanted in a largely known manner.

The present invention thus provides an alignment tool2that enables differential distraction of a joint to be conducted in a controlled and repeatable manner. The interaction of the alignment tool2, drill guide200and cutting guide300ensures resection resulting in a rectangular joint gap with the distal bone of the joint in correct alignment with the joint line. The adjustment mechanisms for the tool are removed from the referencing and distracting members, ensuring that the minimum amount of equipment is inserted into the joint space and that the frontal view of the joint is not impaired.

It will be appreciated that such controlled differential distraction may be of considerable assistance in performing surgery on other joints, notably the knee joint.

It will also be appreciated that the alignment tool may be adapted for particular applications. For example, the distraction arms may be curved convex or concave, in order to engage curved bone surfaces. Similarly, the dimensions of the tool may be matched to a particular joint or application as required.