AU2006202001A1 - Resection Guide Alignment Device - Google Patents

Description

I.

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Resection Guide Alignment Device Applicant: LUKEmedica Pty Ltd The following statement is a full description of this invention, including the best method of performing it known to me: RESECTION GUIDE ALIGNMENT DEVICE Field of the invention This invention relates to devices and methods for the surgical insertion of endoprosthetic joints.

Background to the invention The aims of prosthetic arthroplasty are to alleviate pain and restore function to an injured or diseased joint. While the nature of the prosthesis in itself replaces the damaged or diseased tissue which is surgically removed, the restoration of function relies significantly upon instrumentation or devices to insert the prosthetic components and attach them to the body in the correct anatomical and mechanical alignment.

The general process for insertion of a prosthetic component involves the surgical resection of the damaged cartilage on the joint surfaces together with an amount of underlying bone to provide a site for attachment of the prosthetic component. The amount of bone resection is determined by the thickness of the prosthesis and restores an appropriate amount of tension to the ligamentous structures surrounding the joint to ensure that the joint will function anatomically.

An important aim for the surgeon is to ensure that the ligament tension will be correct for the prosthesis which is to be inserted. This must be done before irreversible bone resection is carried out. Errors in attaining the correct tension can lead to ligament imbalance and misalignment of the prosthetic components, leading to poor function or premature failure of the prosthetic device.

Existing devices have attempted to address these issues by providing quantitative measurements of ligament tension which can be replicated between anatomic flexion and extension of the knee joint. Unfortunately, devices of the prior art have failed to resolve the intra-operative effects of 3 O external gravitational forces acting on the ligamentous structures due to the mass of the limb and the positioning of the limb required for surgical bone resection. For example, a force measuring unit inserted in the knee in flexion may measure the reaction force of the ligaments and muscles but also a component of the gravitational force acting on the femur and associated musculature. When the leg is placed in extension this component of force is removed and replaced mainly by frictional resistance of the leg on the (operating table or leg support. The mass effect cannot be resolved from structural tension while the limb is still attached to the patient. Further, shear and pivot forces exist across the joint due to the variability of limb position.

The result of ignoring intra-operative effects is inconsistency in ligament tension between flexion and extension.

Previous devices have also failed to provide optimal balance of the joint with only a limited number of predefined sizes of prosthetic components available to match the patient's anatomy. Previously, devices referenced femoral alignment in the transverse plane from an intramedullary rod which is invasive, increases morbidity, and produces potential adverse effects.

Adjustment of the flexion gap was at the expense of the height of the anterior resection, in other words, decreasing the flexion gap by moving the femoral component posteriorly, produced an increased patello-femoral gap which produces a lag effect in the quadriceps mechanism potentially affecting the patient's gait and function.

Many joint distraction devices exist that maintain a parallel distraction arrangement of the bone surfaces. These produce a rectilinear joint space for prosthesis insertion. Following insertion of the prosthesis, ligament imbalance may be accepted or surgically corrected. The latter generally resulting in reduction in ligament strength and integrity. Ligament release may also produce scaring and adhesion resulting in further pathological function.

Ligament release in one orientation will produce resulting effects in the other orientation and as such must be approached as a compromise between the two.

4 In United States Patent No: 5,649,929 a device directed to alignment of a knee joint prior to resection of the femur is disclosed. That device includes a rod which is inserted into the femur and a surface for resting on a tibial platform. The rod and platform are pivotally connected and application of a distraction force applies tension to the ligaments. Equalization of tension in the ligaments is achieved by the femur rotating on the rod. However, tension in the collateral ligaments is equalized by gravity. Furthermore, the device can only be used with the knee in flexion. Intramedullary alignment, as used by this device, is used in many knee instrument systems. It in itself does not provide mechanical axis alignment and also may provide inaccurate anatomical axis alignment. The size of the intramedullary rods used are approx 50% lower in diameter than the femoral canal and may produce considerable angular variation based on the entry point and the anterior bow of the femur. Also, drilling or reaming the intramedullary canal is associated with fat embolism and other thromboembolic events which are significant surgical risk factors. Other risks include haemarthrosis and fracture of the long bone concerned.

US5,540,696 discloses a device which allows a knee joint to be aligned with reference to collateral ligament tension. This device also allows alignment in both flexion and extension of the knee. However, the device has the drawback that equalization of ligament tension is performed manually. That is, tension in each ligament is adjusted individually. This results in the surgeon having to equalize tension multiple times during the arthroplasty.

Devices of this kind apply separate individually adjustable forces to each of the femoral condyles to tension the collateral ligaments. Due to a fulcrum effect on each condyle the force applied to one condyle will cause force to be applied to the opposite condyle increasing the tension the opposite collateral ligament so that the force cannot be properly equalized.

In US5,911,723 a device is disclosed which appears to align a knee joint with reference to ligament tension. This device allows the surgeon to tension the

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collateral ligaments of the knee, drill positioning holes and then use those holes to attach a resection guide. Following resection it is envisaged that the alignment of the knee can be checked and adjustments made by "soft tissue release operation".

US patent application 20040122441 describes a post resection measuring device to test resection accuracy. This measuring device is intended for checking alignment of a knee following femoral resection, using a device such as described in US5,911,723 (discussed above).

The problems associated with surgical prosthetic insertion are manyfold.

These include the inability of the surgeon to estimate the normal anatomical, mechanical alignment of the joint due to the disease process or injury.

Throughout the description and the claims of this specification the word "comprise" and variations of the word, such as "comprising" and "comprises" is not intended to exclude other additives, components, integers or steps.

The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of this application.

Summary of the invention In a first aspect, the present invention provides a method for positioning a resection guide during prosthetic arthroplasty including the steps of: applying a distraction force between major bones of a joint such that substantially equal tension is placed on ligaments surrounding the joint; and aligning a resection guide with a bone to be resected, wherein the distraction force is capable of being applied at any angle of normal flexion or extension of the joint. In preferred embodiments, the step of aligning the resection guide is performed while maintaining the distraction force. Preferably, the distraction force is substantially equivalent to the optimal tension on the ligaments surrounding the joint.

In further embodiments of the present invention, the step of applying the distraction force includes: contacting a first distraction surface with a first bone surface; and contacting a second distraction surface with a second bone surface, wherein the second distraction surface is rotatably connected to a pivot; wherein the distraction force is applied between the first distraction surface and the pivot thereby moving the distraction surfaces apart, and thereby applying substantially equal tension on ligaments surrounding the joint. Preferably, rotation of the second distraction surface occurs about an axis substantially parallel to the first distraction surface. More preferably, rotation of the second distraction surface about the axis serves to substantially equalize tension applied to the ligaments surrounding the joint.

The method is capable of applying a substantially equal tension to ligaments surrounding a joint at any angle of normal flexion or extension of the joint during prosthetic arthroplasty, by the application of a distraction force such that the joint is correctly aligned before resection of a bone of the joint.

In a second aspect, the present invention provides a resection guide alignment device for insertion into a joint including: a distractor incorporating a pivot which allows a distraction force to be applied between bones of the joint, to produce substantially equal tension in ligaments surrounding the joint at any angle of normal flexion or extension. In preferred embodiments, the distractor includes: a first distraction surface for contacting a first bone surface; and a second distraction surface for contacting a second bone surface, wherein the second distraction surface is rotatably connected to a pivot; wherein the first and second distraction surfaces are inserted between the first and second bone surfaces and the distraction force is applied between the first distraction surface and the pivot thereby moving the distraction surfaces apart, and thereby applying substantially equal tension on ligaments surrounding the joint.

In preferred embodiments, rotation of the second distraction surface occurs about an axis substantially parallel to the first distraction surface. More preferably, rotation of the second distraction surface about the axis serves to substantially equalize tension applied to the ligaments surrounding the joint.

In further preferred embodiments, the present invention provides a resection guide alignment device for being inserted into a knee joint including: a distractor incorporating a pivot whereby a distraction force applied between a tibia and a femur produces substantially equal tension in medial and lateral collateral ligaments of the knee at any angle of normal flexion or extension of the knee; and a resection guide removably attached thereto.

The device is capable of aligning a resection guide by applying a substantially equal tension to ligaments surrounding a joint at any angle of normal flexion or extension of the joint during prosthetic arthroplasty, by the application of a distraction force such that the joint is correctly aligned before resection of a bone of the joint.

Description of the figures Figure 1 shows an oblique view of an exemplary alignment device assembled with distal femoral bone resection guide and alignment rod.

Figure 2 shows a transverse view of an exemplary alignment device assembled with femoral bone resection guide and laser module.

Figure 3 shows a view of an exemplary femoral bone resection guide.

Figure 4 shows a medial-lateral view of femoral tibial endoprosthesis size and alignment geometries.

Figure 5 shows an anterior view of the relative anatomical alignment of femur and tibia.

Figure 6 shows an anterior view of correct anatomical prosthetic alignment in flexion.

Figure 7 shows a transverse view of an exemplary alignment device inserted into the knee joint in flexion.

Figure 8 shows a transverse view of an exemplary alignment device inserted into the knee joint in extension.

Figure 9 shows a femoral alignment tower attached to the femoral resection guide on the distal femur.

Figure 10 shows a transverse view of a femoral resection guide aligned on an anterior resection of the femur.

Detailed description of the invention The methods and devices of the present invention allow the surgeon to substantially equalize tension in opposing ligaments during prosthetic arthroplasty. Unlike previously available methods and devices, the present invention allows such equalization of tension to be maintained, by application of a distraction force, through various angles of flexion and extension of the joint. Such an arrangement allows the surgeon to correctly position a resection guide directly onto the bone and thereby resect the bone accurately prior to endoprosthesis attachment. Unlike previous devices, embodiments of the present invention provide a device which directly positions a resection guide on the bone while applying a distraction force to the joint at any angle of normal flexion or extension. Application of a distraction force to achieve substantially equalized tensions has the advantage of requiring the surgeon to make only one tension measurement for each angle of flexion and extension of the joint being operated upon.

As used herein, the term "distraction" refers to the moving apart of bones.

Accordingly, a "distraction force" is a force used to move bones apart and a "distractor" is a device used to move bones apart.

The devices of the present invention provide advantages over previously known joint distraction devices. One class of device (such as disclosed in US patent application 20040122441) is used for measuring the accuracy of bone resection prior to inserting a prosthesis. This type of device, however, requires at least one femoral osteotomy to be conducted on the femur before the device can be attached to measure force or movement in the joint. If this provisional resection is found to be incorrect after consideration of ligament tension and mechanical axis alignment the ability to fit the optimal prosthetic size may be lost due to the provisional bone resection.

Devices according to the present invention provide for final adjustment of the joint balance by flexion of the femoral component, to compensate for the situation where the ideal joint balance lies between the available prosthetic sizes, rather than anterior-posterior translation relative to intramedullary alignment. The present invention also seeks to address the alignment of a resection guide. As discussed below, resection guides have many forms or means of operation but they all seek to conform the bone to the interior dimensions of the endoprosthesis. The present invention concerns the correct alignment of the resection to ensure optimal functional alignment of the external geometries of the prosthetic joint components.

In certain embodiments, devices according to the present invention allow visual indication of the range of joint angulations or deviations from the normal mechanical axis alignment which is a relative and direct result of incorrect ligament tension, rather than a quantitative measurement of ligament tension itself, which cannot be resolved intra-operatively, from gravitational forces and the non-anatomical intra-operative positioning of the patient which is required to effect surgical access and insertion of the prosthetic components. The visual representation of joint stability based on the degree of possible varus valgus deviation of the joint is quantified and combined with simultaneous, automatic positioning of bone resection guides intra-operatively, to allow correct bone resection, ligament balance and therefore, functional prosthetic alignment.

While the present invention is exemplified for knee prostheses, it is envisaged that the methods and devices of the present invention could be equally applied to other joints where equalization of tension on opposing ligaments is desirable to ensure proper alignment during prosthetic arthroplasty. The skilled person is amply enabled, by the disclosures herein, to apply the methods and devices of the present invention to other applications, especially other examples of prosthetic arthroplasty.

During prosthetic arthroplasty, a surgeon cuts away bone from both sides of the joint. This allows the prosthetic joint to be inserted in such a way that the normal functioning of the joint is maintained.

In the case of knee surgery, the surgeon generally makes a single bone cut on the proximal tibia to accept a tibial component which usually includes a polyethylene seat mounted on a tibial plate. The tibial plate is often made of titanium alloy or a cobalt/chromium alloy. The femoral component of the knee usually has a unitary body having a highly polished distal surface for articulating within the polyethylene seat of the tibial component. Attachment of the femoral component to the femur often requires multiple bone cuts by the surgeon. It is generally accepted that it is the attachment of the femoral component which determines the success of the knee arthroplasty, in terms of movement of the knee post-surgery.

The precise cuts necessary for balancing the tension in the knee's ligaments and restoring the mechanical axis, are made with help of special templates.

These templates are generally known as "resection guides", "saw blade guide block" or "cutting blocks", these terms may be used interchangeably O throughout this specification. In principle, a resection guide is a plate for guiding a sawblade of a cutting machine. For example, the guide may have at least one opening through which the sawblade may be inserted. When the surgeon positions the sawblade in the openings of the resection guide he makes the cutting of the bone ends occur in the correct plane. Other types of resection guide may include a track for guiding a rotary cutting tool in addition Cto, or instead of, the openings described above. It is the positioning of the (N resection guide which determines the position of attachment of the N endoprosthesis and, ultimately, the success of the prosthetic arthroplasty.

Inappropriate attachment of the femoral component of a knee prosthesis can result in various problems such as incorrect leg length, incorrect articulation of the knee and incorrect and uneven tension applied to the collateral ligaments.

Such problems can result in adverse outcomes for the patient and can affect the longevity of the prosthesis.

The present invention provides a method for positioning a resection guide during prosthetic arthroplasty including the steps of: applying a distraction force between major bones of a joint such that substantially equal tension is placed on ligaments surrounding the joint; and aligning a resection guide with a bone to be resected, wherein the distraction force is capable of being applied at any angle of normal flexion or extension of the joint. In preferred embodiments, the step of aligning the resection guide is performed while maintaining the distraction force. Preferably, the distraction force is substantially equivalent to the optimal tension on the ligaments surrounding the joint.

The term "major bones" is intended to include the long bones of a limb which meet at the joint. For example, the tibia and femur meeting at the knee. In the case of the knee, the patella would not be considered a "major bone".

In further embodiments of the present invention, the step of applying the distraction force includes: contacting a first distraction surface with a first bone surface; and contacting a second distraction surface with a second bone surface, wherein the second distraction surface is rotatably connected to a pivot; wherein the distraction force is applied between the first distraction surface and the pivot thereby moving the distraction surfaces apart, and thereby applying substantially equal tension on ligaments surrounding the joint. In preferred embodiments, the pivot may be a multi-planar connection such as, but not limited to, a universal joint or a ball joint. Preferably, rotation of the second distraction surface serves to substantially equalize tension applied to the ligaments surrounding the joint.

In certain embodiments, the distraction force may be applied by use of a tool such as a handle, a torque wrench or torque screwdriver. However, it is envisaged that the distractor could incorporate a resilient member wherein the resilient member applies a distraction force substantially equivalent to the optimal tension in the ligaments surrounding the joint. The amount of distraction force applied may be determined by an indicator attached at or near the pivot. Whichever method of application of the distraction force is used, it is intended that the surgeon is able to apply a substantially constant distraction force to the joint at any angle of normal flexion or extension. Being able to apply a substantially constant distraction force means that tension in the ligaments may be maintained through all angles of movement of the joint undergoing arthroplasty. The indicator of distraction force may not necessarily measure a force per se, but rather give a visual indication of the amount of distraction of the joint as well as an indication of any deviation from parallel of the bone contacting surfaces.

The indicator allows visual indication of the range of joint angulations or deviations from the normal mechanical axis alignment which is a relative and direct result of incorrect ligament tension, rather than previous methods which rely on a quantitative measurement of ligament tension itself. The method of the present invention allows the surgeon to determine how much distraction is "sufficient distraction" by the indication of relative movement between the bones by the indicator attached to the pivot. The surgeon cannot know what the force is (for gravitational reasons as mentioned above), but he can know it is the correct force due to movement or lack of movement at the pivot, and this measurement can be duplicated where required at various angles of flexion or extension for the purpose of aligning the resection guide to ensure there is substantially equal ligament tension throughout the range of motion.

Embodiments of the present invention may be used in various joints of the body. Due to differences in joint anatomy, it is envisaged that different numbers of ligaments need to be tensioned in order for proper alignment of the joint. Equalization of ligament tension in, for example, a knee requires tensioning of only two ligaments, therefore the pivot of a device for use in a knee needs only to rotate in a single plane. More complex joints may require the use of a more complex pivot arrangement. As exemplified above, a universal joint or a ball joint may be used to provide a multi-planar tensioning means.

In particular embodiments, the method includes the step of using an alignment device having a distractor, incorporating a pivot, to apply a distraction force between the bones of the joint, to produce substantially equal tension in the medial and lateral collateral ligaments of the joint at any chosen angle of flexion or extension of the joint thereby reproducing the ligamentous anatomical alignment of the limb as a basis for positioning a bone resection guide to facilitate the bone removal required to inset an endoprosthesis, preferably a femoral endoprosthesis.

In another aspect, the invention provides a resection guide alignment device for insertion into a joint including: a distractor incorporating a pivot which allows a distraction force to be applied between bones of the joint, to produce substantially equal tension in ligaments surrounding the joint at any angle of normal flexion or extension. In preferred embodiments, the distractor includes: a first distraction surface for contacting a first bone surface; and a second distraction surface for contacting a second bone surface, wherein the second distraction surface is rotatably connected to a pivot; wherein the first and second distraction surfaces are inserted between the first and second bone surfaces and the distraction force is applied between the first distraction surface and the pivot thereby moving the distraction surfaces apart and the first and second bone surfaces apart, and thereby applying substantially equal tension on ligaments surrounding the joint.

As discussed above, the pivot of the device may be a multi-planar pivot such, but not limited to, a universal joint or a ball joint, thereby allowing substantial equalization of tension in all ligaments surrounding the joint.

Preferably the device includes an indicator, attached at or near the pivot, to provide the surgeon with an indication of the amount of distraction force being applied to the joint. The indicator of distraction force may not necessarily measure a force per se, but rather give a visual indication of the amount of distraction of the joint as well as an indication of any deviation from parallel of the bone contacting surfaces.

When a multi-planar pivot is used, the indicator attached at or near the pivot needs to be able to indicate the distraction force in more than one plane. This may be achieved, for example, by the use of two indicators mounted perpendicularly to each other. In other embodiments, more than two indicators may be used to provide a full indication of the distraction of the joint.

As discussed above, the indicator allows visual indication of the range of joint angulations or deviations from the normal mechanical axis alignment which is a relative and direct result of incorrect ligament tension, rather than previous methods which rely on a quantitative measurement of ligament tension itself.

The surgeon determines how much distraction is "sufficient distraction" by the indication of relative movement between the two bones by the indicator attached to the pivot. The surgeon cannot know what the force is (for gravitational reasons as mentioned), but he can know it is the correct force due to movement or lack of movement at the pivot, and this measurement can be duplicated where required at various angles of flexion or extension for the purpose of aligning the resection guide to ensure there is substantially equal ligament tension throughout the range of motion In preferred embodiments, rotation of the second distraction surface occurs about an axis substantially parallel to the first distraction surface. More preferably, rotation of the second distraction surface about the axis serves to substantially equalize tension applied to the ligaments surrounding the joint.

In further preferred embodiments, the present invention provides a resection guide alignment device for being inserted into a knee joint including: a distractor incorporating a pivot whereby a distraction force applied between a tibia and a femur produces substantially equal tension in medial and lateral collateral ligaments of the knee at any angle of normal flexion or extension of the knee; and a resection guide removably attached thereto.

In preferred embodiments at least one of the first and second distraction surfaces is a plate.

The device may further include a resection guide adapted to be positioned against a bone requiring resection by the device to permit proper resection of bones. Preferably, the resection guide includes one or more openings through which a saw blade may be inserted.

In preferred embodiments, the distraction force may be applied by use of a tool such as a torque wrench or torque screwdriver. However, it is envisaged that the distractor could incorporate a resilient member wherein the resilient member applies a distraction force substantially equivalent to the optimal tension in the ligaments surrounding the joint. The amount of distraction force applied may be determined by an indicator attached at or near the pivot.

Whichever method of application of the distraction force is used, it is intended that the surgeon is able to apply a substantially constant distraction force to the joint at any angle of normal flexion or extension. Being able to apply a substantially constant distraction force means that tension in the ligaments 16 O may be maintained through all angles of movement of the joint undergoing

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arthroplasty.

In preferred embodiments the joint is a knee. It is preferred that the first bone surface is a tibial platform. It is also preferred that the second bone surface comprises at least one femoral condyle. It is further preferred that the bone requiring resection is a femur.

Accordingly, for application to knee arthroplasty, the present invention also IND provides a resection guide alignment device for being inserted into a knee joint. The alignment device includes a distractor incorporating a pivot which allows a distraction force applied between the tibia and femur, to produce substantially equal tension in the medial and lateral collateral ligaments of the knee, at any chosen angle of flexion or extension of the knee thereby reproducing the ligamentous anatomical alignment of the leg as a basis for positioning a bone resection guide to facilitate the bone removal required to inset a femoral endoprosthesis.

Because the collateral ligaments of the knee may not be tensioned evenly throughout the range of movement of the joint, the device of the present invention allows the surgeon to correctly align the joint, with respect to ligament tension, at any angle of normal flexion and extension of the limb.

This allows the prosthesis to be inserted optimally.

By fixing a resection guide to the alignment device, the surgeon is able to determine the best position to resect bone of the joint in order to fit an endoprosthesis such the repaired joint will be correctly aligned with respect to substantially equal tension in the ligaments surrounding the joint.

Specific embodiments of the present invention will now be discussed in detail by reference to the accompanying figures. This discussion is in no way intended to limit the scope of the invention.

17 In one form of the invention (illustrated in Figure 1) the alignment device consists of a metallic plate 1 shaped to approximately match shape of the tibial plateau. The anterior portion of the plate is attached to a block 2 which houses a pinion gear 3 and ratchet mechanism 4. The pinion is driven by a removable handle inserted into a hexagonal socket in the centre of the pinion gear 5. A geared rack 6 insets into the block in such a manner as to engage the pinion. The rack is orientated at ninety degrees to the tibial plate and is attached to a femoral plate 7 by means of a pivot 8. The axis of the pivot 9 is orientated in the anterior posterior direction relative to the tibia and parallel to the tibial plate.

The pivot is constructed with a bearing in such a manner as to allow free movement of the femoral plate when load is applied by means of the rack and pinion mechanism.

The axle which is rigidly attached to the femoral plate extends through the rack and has attached to it a visual indicator in the form of needle 10 opposed to a scale 11 which enables visualization of any rotational movement of the femoral plate relative to the tibial plate. The superior surface of the femoral plate may be machined with fine groves in the anterior to posterior orientation to provide a high friction surface to engage cartilage or bone of the femoral condyles.

A calibrated alignment bar 12, preferably with a trapezoidal cross section, is attached to the tibial plate by means of a fenestration through the tibial plate 13, the fenestration being parallel to the path of the rack through the ratchet block and having a cross section to match with the cross section of the calibrated alignment bar. A screw 14 is used to lock the calibrated alignment bar in position by opposition of the preferably trapezoidal geometry thus providing a substantially ninety degree relationship with the tibial plate. The face of the calibrated alignment bar may be engraved with a series of markings 15 to reference the size of the femoral endoprosthesis to be used.

The markings are calibrated to align with the top of the tibial plate to indicate 18

IND

0 O the size being utilized. The position of the markings takes into consideration the size and type of endoprosthesis being used and may be manufactured accordingly. A fenestration 21 in the calibrated alignment bar aids visualization of the needle indicator The proximal portion of the calibrated alignment bar may include a preferably cylindrical bushing 16 fitted with a screw 17. The screw may be adapted with a conical point to engage a, preferably V-shaped, slot 19 in the resection guide coupling rod 20 thereby providing adjustment along the axis of the resection guide coupling rod but rigid alignment when the screw 17 is tightened preventing rotation of the resection guide coupling rod In this embodiment of the invention the resection guide coupling rod attaches to bone resection guides which consist of a metallic block with guiding surfaces 24 or slots to accept surgical cutting device such as an oscillating type surgical saw blade. The slots or guiding surfaces are placed to match the internal geometries of the various sized knee femoral prosthesis.

The preferred embodiment uses two types of saw blade guide block. The saw blade guide block 21 is used to resect the distal femur with the knee joint in extension and the saw blade guide block 40 (see Figure 2) is used to resect the anterior femur (as illustrated in Figure 4, F) posterior femoral condyles B and the anterior and posterior chamfers.

The distal femoral saw blade guide block 21 attaches to the resection guide coupling rod 20 by means of screw 22 which engages the preferably V-shaped slot 19 in the resection guide coupling rod 20 thus fixing the alignment of the guiding face of the saw blade guide block in a rigid, substantially parallel configuration with reference to the tibial plate 1.

In the embodiment illustrated in Figure 1, the anterior end of the resection guide coupling rod 20 may terminate in a hollow bush 26 the axis of which is ninety degrees to the axis of the resection guide coupling rod 20, and substantially parallel to the calibrated alignment bar 12. When the resection 19 guide coupling rod is locked into position by the screw 17 the axis of the bush 26 will be substantially perpendicular to the tibial plate and the cutting face of the distal femoral saw guide block.

The bush 26 may receive a visual alignment device to enable the surgeon to visualize the position of the distal femoral saw guide block relative to the mechanical axis of the limb. In its simplest form the alignment device may consist of a metallic or carbon fibre composite rod 27 having a diameter substantially the same as the internal diameter of the bush 26 and of sufficient length to reach from the distal tibia to the proximal femoral head. Alignment of the mechanical axis of the bones of the limb may therefore be compared to the alignment produced by the substantially equal tensioning of the collateral ligaments (see Figure 5, The location of the femoral head is determined by x-ray either intraoperatively or preoperatively and marked with palpable radiographic markers in the anterior-posterior and the medial-lateral alignments.

In other embodiments, such as shown in Figure 2, the bush 26 may be present and attached to the calibrated alignment bar 49, rather than the resection guide coupling rod (as shown in Figure The bush 26 may be used to house a laser module 30. Preferably, the laser 30 is of a low power, such as 0.5mW, and of 600-660nm wavelength classification. The module may be adapted to project a plane of visible light in the Sagital plane 53 (shown in Figure 6) from the knee joint to the proximal femur and simultaneously towards the distal tibia. Lasers have certain advantages over alignment rods. For example, the rod may sag or bend under its own weight resulting in incorrect alignment. The laser can be turned on and off with a switch 34 without the need to remove the module. The leg can be moved from flexion to extension without removal of the rod. The laser beam can extend beyond the sterile area of the surgical field to external reference markers without the risk of compromise of the sterile surgical area. The beam can indicate rotation of the femur relative to the tibia in flexion. The module may be keyed to the bush 26 by means of a screw surrounding the switch 34. The aperture at 33 may project light to the proximal femur with the leg in extension. The aperture at 32 may project light through the central fenestration 50 of the femoral cutting block 40 to reference femoral rotation against the alignment of the patellar-femoral trochlear. The aperture 31 may project light to the ankle and distal tibia.

The anterior-posterior femoral cutting block 40 may be connected to the alignment device by means of a coupling rod adapted with a cannulation to accept a long shaft screw which engages a screw hole 38 in the bone resection guide. Anterior to the screw thread a short pin may engage a second hole in the bone resection guide 37 which prevents rotation of the cutting block relative to the resection guide coupling rod.

An anterior femoral stylus 45 may be attached to the femoral bone resection guide 40 by means of a screw 44. The anterior femoral stylus 45 references the length of the anterior flange for each size of endoprosthesis (see Figure 4, the size may be indicated by one or more markings on the side of the stylus 43 as referenced against the mounting block 42 of the anterior femoral stylus. The tip of the stylus indicates the intersection of anterior femur with the alignment of the anterior femoral saw slot 46 of the femoral bone resection guide.

The illustrated embodiments of the device represent suitability for an endoprosthesis with parallel anterior and posterior femoral bone resection.

The femoral insertion angle is zero degrees relative to the distal anterior femoral cortex G (see Figure 4) and the tibial anterior posterior slope is zero degrees relative to the tibial mechanical axis E. The device may be adapted to variability of these parameters within the anatomical range as may be required for different endoprosthetic geometries. These adaptations include variation in the thickness and angle of the tibial plate 1 and variation of the calibrated scale 15 to adjust for increased posterior slope of the tibial component. They also indicate variation in the angle between the calibrated alignment bar 12 (Figure 1) or 49 (Figure 2) and the resection guide coupling O rod bush 16 or 48 to adjust for increased femoral flexion. The calibrated scale for each particular size of endoprosthesis may be adjusted to take into account the trigonometric effect of variation in flexion angle producing a change in the required bone resection for that particular size.

In addition to the above embodiments, it is envisaged that many variations of the methods and devices are encompassed by the present invention. For Nexample, the whole apparatus may be miniaturized to facilitate a minimally invasive surgical technique. The tibial plate 1 may be recessed to allow the femoral plate to descend into the recess, decreasing the thickness of the combined assembly. The AP length of the femoral plate 7 may also be reduced anteriorly and the axle extended to allow a greater range of varus valgus movement of the plate before impingement on the bone resection guide. Controls and the distraction mechanism may be moved by extension bars to orientate at ninety degrees to the pivot alignment, to emerge from a medial parapatellar incision of reduced length. This enables surgical access without the need to invert and deflect the patella. Similarly, the resection guides may be attached medially to cut from the medial to lateral orientation through the reduced incision rather than in the anterior to posterior aspect.

The pivot scale can be moved to be viewable from the medial position.

Alignment may be confirmed by fluoroscopic x-ray image intensification or by computer assisted triangulation from optical markers attached to the resection guides, as described in prior art.

In addition embodiments, the pivot movement indicator needle and scale may be adapted in several forms including but not limited to: an electronic transducer coupled to an electronic display device to amplify and indicate relative movement; (ii) a laser module to display amplified indication of movement by projected light; and (iii) an optical device to magnify movement by reflected light.

Furthermore, the geometry of the apparatus may be adapted for endoprosthesis differing geometric configurations. Type examples include (i) differing thickness medial and lateral posterior condyles designed to produce a rectangular joint space rather than a trapezoidal one, this may be accommodated by a change in medial to lateral thickness of the tibial plate 1; (ii) tibial resection with increased posterior slope is accommodated by increased anterior to posterior thickness of the tibial plate 1; and (iii) flexion of the femoral component (Figure 4 G) may be compensated for by increasing the angle between the calibrated alignment bar 49 and the coupling rod bush 48.

The alignment device may also locate the position of an intermediary device to which the resection guide is subsequently attached. This alternative method may be preferred in cases where the resection guide is large or requires the same surgical location as the alignment device or the resection guide requires assembly in multiple planes to resect a continuous radius or all linear resections sequentially for increased accuracy. Examples of this variation may include: the connection of a small drill guide to the alignment device in place of the resection guide which facilitates the placement of pins, drill bits, holes or screws in AP, ML and varus valgus planes in flexion and extension to which a resection guide is subsequently attached after the alignment device is removed from the joint. By this method the location of the resection guide may be virtually located in space by the intermediary alignment if required. (ii) The location and attachment to bone of a locating plate, block or fitting which remains in place in either flexion or extension to which the resection guide is attached when the alignment guide is removed for surgical access of the resecting device.

The alignment device may be adapted for use with endoprosthesis which requires preservation or resection of the posterior cruciate ligament. The device may also be adapted for use in mobile bearing or fixed bearing design endoprosthesis While a preferred embodiment of the present invention describes total knee arthroplasty, other exemplary embodiments may include hemi arthroplasty, I o 23

NO

O unicompartmental unicondylar arthroplasty, and bicompartmental unicondylar arthroplasty of the knee.

The device may also be adapted for revision arthroplasty by the adaptation of the femoral and tibial plates to accept trial bone augmentation blocks or wedges as are common to modular endoprosthetic designs the may be fixed or held in place by means of screws, holes, magnets and/or other fixation devices.

INO

The surface of the femoral plate may be adapted to receive a tibial articular insert trail prosthesis so that the actual prosthetic alignment and ligament tension may be determined with the endoprosthesis trial components in place.

In further embodiments, the device may be configured with a pivot on the tibial plate connecting it to the pinion block. This pivot axle is parallel to the axis of the femoral plate and incorporating a lock to prevent rotation when rotation is not required. This enables the device to be used in reverse mode. In the case of congenital deformity, tumour or traumatic injury causing total bone loss of the femoral condyles, the resection guide may be aligned by anatomical landmarks such as the patellar trochlear and fixed in place.

Distraction and alignment can now be visualized by the relative angle of rotation of the tibial pivot and surgical correction made.

Specific embodiments and applications of the present invention will now be discussed in detail by reference to the accompanying example. This discussion is in no way intended to limit the scope of the invention.

Example EXEMPLARY USE OF A RESECTION GUIDE ALIGNMENT DEVICE ACCORDING TO THE PRESENT INVENTION.

Preoperatively, the location of the head of the femur 72 (Figure the mid malleolar point 71 and trans-malleolar axis 70, are located by x-ray, or any other means of medical imaging which will enable visual observation of the required anatomical landmarks in the supine position. The positions are marked with palpable radiographic markers. Alternatively, fluoroscopic x-ray image intensification may be used intra-operatively to determine anatomical location.

The size of the prosthesis required is also determined preoperatively by magnification corrected radiographs, or any other means of medical imaging which will enable visual observation of the required anatomical landmarks, compared to templates of the prosthetic sizes available. In particular, a lateral radiograph of the femur is used to determine the most suitable size prosthesis to approximate the anatomical radius of the distal femoral condyles and the patellar trochlear, and any flexion of the femoral component required to do so.

Surgical access is typically via a medial Para-patella incision of sufficient length to accommodate prosthesis insertion. The patella is generally inverted and reflected laterally to gain access to the tibio-femoral joint space.

An extra-medullary tibial alignment guide is attached to the limb and the proximal tibia is resected at ninety degrees to the mechanical axis of the tibia in both the coronal and sagittal plains. Techniques of proximal tibial resection are well known to those of skill in the art, see for example US6,673,077 (Katz). For the present application, the amount of bone resected should match the minimum thickness of tibial prosthesis available for insertion as referenced from the tibial condyle representing the best approximation of the non-pathological anatomical joint line (Figure 5, The measurement of resection height must remain relative to the reference point regardless of the degree of posterior slope of the tibial resection.

The device is assembled with the appropriate size resection guide 40 (see Figure 2) and calibrated alignment bar 49. The size of the femoral endoprosthesis is set on the anterior stylus scale 43 via a screw 44 and also on the calibrated alignment bar 74. The limb should be positioned with the hip flexed to ninety degrees so that the femur is perpendicular to the body and the tibia parallel with it. This minimizes the component of gravitational force, due to the mass of the limb, producing a vector of shear force along the femoral articulated plate of the device. It also reduces the load on the distraction mechanism by limiting the reaction force to that of the ligaments and musculature of the knee.

The knee is flexed to approximately ninety degrees and the alignment device is inserted into the joint space as shown in Figure 7. The pinion driving handle is inserted into the pinion gear 5 (see Figure The handle is rotated to commence distraction of the joint. In the illustrated embodiment, each ratchet stop equates to 1 mm increments of the pitch of the rack. The pitch of the rack may be chosen and aligned by design to synchronize with the calibrated scale engraved there on. Travel of the rack may also be visualized by the surgeon via the calibrated scale 75. The scale is marked to demonstrate the distance of rack travel (distraction) relative to the sizes of prosthetic tibial articular insert thicknesses available to the surgeon for implantation.

The distraction is increased with the surgeon checking for joint stability at each increment. This is achieved by movement of the tibia in the medial-lateral plane, applying varus-valgus stress to the joint line, while observing the relative movement of the femur. The amount of load applied can be quantified using a spring type scale attached to the patient's lower tibia via a simple strap or other means. Ideally the test load should be relative to anatomical studies based on joint force loading relative to the patient's body mass. The relative movement between the tibia and femur can be visualized by the needle 10 of the pivot axle against the pivot scale 11. Sufficient distraction or joint stability is reached when the observable relative movement between the femur and tibia is within normal anatomical limits for the patient's body mass or as can be measured from the patient's contra-lateral nonpathological joint.

This quantification of relative tibial femoral movement is noted so that it may be duplicated in extension of the joint thus providing the same range of movement to varus-valgus stress in the full range of motion of the joint.

The distraction required to produce stability is transferred from the scale 75 to the calibrated alignment bar 49 by releasing and locking the screw 14.

Anatomical rotation of the femur 69 (see Figure 9) may now be confirmed by the observation of the patella-femoral trochlear 68, relative to the alignment guide and femoral bone resection guide 67. A parallel alignment should exist between the bone resection guide and a line representing the deepest aspect of the trochlear groove, over its length. Any mal-alignment can be surgically corrected at this point to produce correct mechanical alignment of the patella and quadriceps mechanism, before any bone resection.

Subsequently, the joint can be tensioned again in the same manner and, any increase in joint laxity due to surgical ligament correction can be compensated for in the adjustment of the scale 74 on the calibrated alignment bar.

When the appropriate distraction of the joint is achieved, the femoral bone resection guide is advanced by means of the coupling rod screw 36 (see Figure 2) to contact the distal femur. At this time, limb is extended slightly to engage the anterior stylus 60 (see Figure 7) with the anterior femoral cortex 61. Rotation of the alignment assembly relative to the tibial mechanical axis is now determined. The femoral alignment tower 77 is attached to the femoral resection guide by insertion into the anterior saw slots of the femoral cutting block and the laser module 30 (see Figure 2) is activated. The alignment beam is projected to the distal tibia and checked for intersection with the distal tibial radiographic marker. The alignment of the patella femoral trochlear 76 (see Figure 9) is similarly confirmed through the fenestration in the femoral cutting block 67. The alignment assembly should be rotated so that the beam projected through the femoral alignment tower via the prism 79, or alternatively an alignment rod inserted through 78 the femoral alignment tower to the proximal femur, intersects the radiographic marker situated over the femoral head 54 (see Figure 6) thus approximating the valgus angle of the distal femoral resection. This is relevant to prostheses having non-parallel anterior and posterior resection angles.

The bone resection guide is then fixed to the distal femur by means of 3.2mm bone pins inserted the through the fixation holes 40 (see Figure The anterior femur 61 (see Figure 7) is resected using a surgical oscillating saw through the anterior saw slot 46 (see Figure 3) of the femoral bone resection guide. Similarly, the femoral posterior condyles are resected 62.

After resection, the femoral bone pin fixation is removed and the femoral bone resection guide is removed by releasing the screw 14 (see Figure 1) and removing the calibrated alignment bar from the tibial plate 1.

The distal femoral bone resection guide 21 is assembled to the resection guide coupling rod 20 and secured by the screw 22 to the calibrated alignment bar 12. The assembly is inserted into the tibial plate setting the calibration to the level measured on the distraction scale when the joint was distracted in flexion. The distraction force is now released by depressing the ratchet release button 4 and the leg is placed in full extension (Figure 8).

Incremental distraction is again applied via the pinion gear mechanism until the relative movement between the tibia and femur is the same as that determined in flexion or a relative ratio thereof which may be visualized as in extension by the pivot needle 10 against the pivot scale 11.

Correct mechanical alignment of the limb is now confirmed by use of the laser module 30 or alignment rod 27. Correct alignment should extend from the radiographic marker centred over the femoral head 72 to the mid-malleolar 49 28

C>

O point of the distal tibia. Evident mal-alignment can be corrected before (-i resection of the bone surfaces and the joint re-tensioned to produce stability of the joint space.

(-i Having achieved correct alignment, the distal femoral cutting block is advanced by means of the coupling rod 20 and seated on the previously resected anterior surface of the femur Fixation of the distal femoral bone resection guide 21 is achieved by the insertion of headless 3.2mm bone pins through the fixation holes 24. Oblique fixation holes are also provided 23 for additional pins to prevent the block lifting during the cutting process. The distal femoral bone resection guide may also include holes 25 to engage a saw blade capture device to provide additional guidance to the saw blade during resection.

The alignment assembly may be detached from the resection guide by releasing the screw 22. The alignment assembly may then be withdrawn from the joint, leaving the distal femoral resection guide in place, to facilitate access for the surgical saw during resection.

Upon completion of the distal femoral resection, the bone pins are withdrawn and the resection guide removed from the distal femur.

Resection of the anterior and posterior chamfer resections of the femur are completed by the repositioning of the femoral bone resection guide 40 (see Figure 10) against the cut distal surface of the femur and aligned with the cut anterior surface by the insertion of an alignment plate 82 through the anterior saw slot 86. The block is fixed to the distal femur using bone pins 81 through the fixation holes and resection made through the anterior 84 and posterior 83 chamfer saw slots of the resection guide.

Claims (20)

1. A resection guide alignment device for insertion into a joint including: a distractor incorporating a pivot which allows a distraction force to be applied between bones of the joint, to produce substantially equal tension in ligaments surrounding the joint at any angle of normal flexion or extension.

2. A device according to claim 1, wherein the distractor includes: a first distraction surface for contacting a first bone surface; and a second distraction surface for contacting a second bone surface, wherein the second distraction surface is rotatably connected to a pivot; wherein the first and second distraction surfaces are inserted between the first and second bone surfaces and the distraction force is applied between the first distraction surface and the pivot thereby moving the distraction surfaces apart, and thereby applying substantially equal tension on ligaments surrounding the joint.

3. A device according to claim 2, wherein: the joint is a knee the first bone surface is a tibial platform; and the second bone surface includes at least one femoral condyle.

4. A device according to claim 2 or 3 wherein rotation of the second distraction surface occurs about an axis substantially parallel to the first distraction surface. A device according to claim 4, wherein rotation of the second distraction surface about the axis serves to substantially equalize tension applied to the ligaments surrounding the joint.

6. A method according to claim 2, wherein the pivot is a multi-planar pivot.

7. A device according to any one of claims 2 to 6, wherein at least one of the first and second distraction surfaces is a plate.

8. A device according to any one of claims 2 to 7, wherein the distraction force is measurable by an indicator, wherein the indicator is attached near the pivot.

9. A device according to any one of claims 1 to 8, further including a resection guide, wherein the resection guide is optionally removably attached to the device. A device according to any one of claims 1 to 9, further including a resilient member wherein the resilient member applies the distraction force.

11. A resection guide alignment device for being inserted into a knee joint including: a distractor incorporating a pivot whereby a distraction force applied between a tibia and a femur produces substantially equal tension in medial and lateral collateral ligaments of the knee at any normal angle of flexion or extension of the knee; and a resection guide removably attached thereto.

12. A resection guide alignment device for insertion into a joint, the device including a first distraction surface and a second distraction surface and a distractor, wherein the distractor movably connects the first and second distraction surfaces, and the first distraction surface is connected to the distractor through a pivot.

13. A device according to any one of claims 2 to 8, further including a pivot movement indicator, wherein the pivot movement indicator provides an indication of rotation of the first distraction surface relative to the second distraction surface.

14. A method for positioning a resection guide during prosthetic arthroplasty using the device of any one of claims 1 to 13. A method for positioning a resection guide during prosthetic arthroplasty including the steps of: applying a distraction force between major bones of a joint such that substantially equal tension is placed on ligaments surrounding the joint; and aligning a resection guide with a bone to be resected, wherein the distraction force is capable of being applied at any angle of normal flexion or extension of the joint.

16. A method according to claim 15, wherein the step of aligning the resection guide is performed while maintaining the distraction force.

17. A method according to claim 15 or 16, wherein the distraction force is substantially equivalent to the optimal tension on the ligaments surrounding the joint.

18. A method according to any one of claims 15 to 17, wherein the step of applying the distraction force includes: contacting a first distraction surface with a first bone surface; and contacting a second distraction surface with a second bone surface, wherein the second distraction surface is rotatably connected to a pivot; wherein the distraction force is applied between the first distraction surface and the pivot thereby moving the distraction surfaces apart, and thereby applying substantially equal tension on ligaments surrounding the joint.

19. A method according to claim 18, wherein rotation of the second distraction surface occurs about an axis substantially parallel to the first distraction surface.

20. A method according to claim 19, wherein rotation of the second distraction surface about the axis serves to substantially equalize tension applied to the ligaments surrounding the joint.

21. A method according to claim 18, wherein the pivot is a multi-planar pivot. 0

22. A method according to any one of claims 18 to 21, wherein at least one of the first and second distraction surfaces is a plate.

23. A method according to any one of claims 15 to 22, wherein the joint is a knee and the major bones are a tibia and a femur. DATED: 12 May 2006 Phillips Ormonde Fitzp, Attorneys for: LUKEmedica Pty Ltd Oc&4~0 -0~rt~