A femoral sizing jig for use in total arthroplasty of left and right knees, comprises a femoral body, an external-rotation-angle arm which is, preferably pivotable, relative to the femoral body for setting an external angular rotation of a left or right femur, at least one of a cutting-jig guide and a cutting jig which is, preferably slidable, relative to the femoral body and in unison with movement of the external rotation-angle arm, and a medial posterior-condylar locator which is movable in unison with the movement of the external-rotation-angle arm, so as to maintain a fixed or substantially fixed relative distance with a medial side of the at least one of a cutting-jig guide and a cutting jig. A posterior-referencing femur resecting system using said femoral sizing jig and a method of resecting a femur at a knee joint relative to the medial posterior condyle are also provided.

The present invention relates to a femoral sizing jig for use in total arthroplasty of left and right knees, a femur resecting system using the said femoral sizing jig, and to a method of resecting a femur at a knee joint using the medial posterior condyle as a datum.

Total knee replacement (TKR) surgery is a common orthopaedic procedure conducted to reduce joint pain and restore mobility, particularly in arthritic patients. Relative to patient satisfaction after total hip replacement surgery, knee functionality is in general not as satisfactory and patient outcome scores are reported as poor in many cases. A suggestion is that knee kinematics maybe improved by a better understanding of relationship of joint-line preservation and co-lateral isometry.

One common surgical approach is the conventional ‘measured resection’ technique in TKR that aims to restore the original surface geometry of the knee. It is common within such measured resection systems to size the knee and set external rotation via a centrally pivoting sizing guide which may be connected to an intramedullary rod extending longitudinally within the femur from the distal end. However, as arthritic knees are often deformed by cartilage or bone wear, dysplasia or ligament attrition and contracture, this technique can result in ligament imbalance and instability as the restoration of joint line is altered by the degree of external rotation of the femoral component chosen by the surgeon.

Another technique is a ‘ligament balancing’ technique where the surgeon aims to restore balance in the soft tissue structures of the knee post TKR by the position of bony cuts used to set the position of the femur. An instrument known as a tensioner is used with a central pivot point that relies on a tibio-femoral separation (set by the ligament length) to determine the position of the femoral component. In using a central pivot point, resection depth relative to the posterior femoral condyle is variable and often therefore results in a different centre of rotation of the femur after surgery compared to the natural pre-operated knee during flexion. This will further thus affect ligament isometry and can lead to instability at different flexion angles.

The present invention discloses a new method and instrumentation for a ‘ligament balancing’ technique and setting of external rotation for conventional TKR techniques.

The described instrument aims to blend both measured resection and ligament balancing techniques by providing tibio-femoral dependant positioning in combination with a measured resection about the centre of the medial femoral condyle in the sagittal plane.

As the medial side of the femur is the generally less worn, more stable and congruent side of the knee, TKR performed with this technique will produce more normal postoperative kinematics by ensuring that knee flexion is restored after surgery.

A novel aspect of the present invention is the provision of an instrument which allows tibio-femoral separation, tensioning both medial and lateral collateral ligaments, whilst allowing rotation about the medial condyle of the knee. The concept will maintain the resection depth of the medial condyle at a constant value, independent of external rotation value, therefore maintaining the pre-operative rotation of the knee joint.

A further aspect of the invention is the provision of shims to locate on the posterior feet of the instrument in cases where there is severe wear of the posterior femoral condyles to ensure preservation of the natural joint line.

The invention seeks to provide a solution to these problems.

According to a first aspect of the invention, there is provided a femoral sizing jig for use in total arthroplasty of left and right knees, the jig comprising a femoral body, an external-rotation-angle arm which is movable relative to the femoral body for setting an external angular rotation of a left or right femur, at least one of a cutting-jig guide and a cutting jig which is movable relative to the femoral body and in unison with movement of the external-rotation-angle arm, and a medial posterior-condylar locator which is movable in unison with movement of the external-rotation-angle arm, so as to maintain a fixed or substantially fixed relative distance with a medial side of the at least one of a cutting-jig guide and a cutting jig.

According to a second aspect of the invention, there is provided a posterior-referencing femur resecting system comprising a varus valgus alignment guide, a distal femoral resection jig, a femoral sizing jig in accordance with the first aspect of the invention, and a multi-plane femoral resection jig for posterior femoral resection, anterior femoral resection, posterior chamfer cutting and anterior chamfer cutting.

According to a third aspect of the invention, there is provided a method of resecting a femur at a knee joint relative to the medial posterior condyle, the method comprising the steps of: a] setting a femoral external rotation angle relative to a medial posterior condyle by pivoting an external-rotation-angle arm of a femoral sizing jig; b] applying a femoral sizing jig to a distal face of the femur, whereby the medial posterior condyle is directly or indirectly seated on a posterior-condylar locator; and c] using a cutting-jig guide and/or cutting jig to facilitate resection of a femoral face of the femur relative to the medial posterior condyle.

Referring to the drawings, there is shown one embodiment of a femoral sizing jig10, preferably formed of a suitable surgical material such as stainless steel or titanium, which comprises a femoral body12, an external-rotation-angle arm14, a cutting-jig location guide16and a posterior-condylar locator18. The femoral body12in this case is a generally flat housing20dimensioned to be compatible with a distal end22of a femur24. The housing20comprises preferably flat front and rear major walls26,28and minor side walls30which all together define an interior cavity32.

The external-rotation-angle arm14in this case is elongate having a substantially uniform lateral extent along at least a majority of its longitudinal extent. The arm14is pivotably mounted within the interior cavity32at or adjacent to its lower end34and at or adjacent to the lower end36of the housing20. The arm14is a close fit to at least one major wall26,28within the housing20such that the interior surface of the front and/or rear major walls26,28act as supporting and guiding surfaces.

A rotational-angle scale38is fixedly provided at the upper end40of the arm14, exterior of the housing20and adjacent to the upper end42thereof. An indicator44is preferably provided on the upper end42of the housing20, which in this case is a pointer, and indicates a rotational angle on the scale38.

A locking device46is provided on the femoral body12to hold the external-rotation angle arm14in a set position relative to the femoral body12. In this case, the locking device46extends through a slot48in the upper portion of the femoral body12. A plurality of femoral-body teeth50is provided adjacent to the slot48, in parallel or substantially parallel with each longitudinal edge of the slot48on the front major wall26. A locking tooth52is provided on a preferably spring-biased knob or grip54which passes through the lateral extent of the slot48. The knob or grip54is preferably spring biased towards the slot48so that the locking tooth52tends towards an engaged condition. However, the locking knob or grip54can also be axially rotated so that the locking tooth52aligns with the longitudinal extent of the slot48. This allows free sliding movement of the knob or grip54over the femoral-body teeth50. Once an angular rotation of the femur24is decided, the knob or grip54is pulled outwards and turned, and the spring force is then allowed to draw the locking tooth52into engagement between the femoral-body teeth50.

Also provided within the housing20is the cutting-jig location guide16. This may conveniently include a rigid plate body55which is linearly slidable within the cavity32, guided by a plurality of spaced apart guide pins56engaging in respective guide slots58formed in the front and rear major walls26,28of the femoral body12. Additionally, it is preferred that the external-rotation-angle arm14extends through the location-guide body55, and is slidable generally side-to-side therein.

The location guide16is connected to the external-rotation-angle arm14so that the two elements are movable in unison. To provide for this interengagement, a pin and guide channel60,62are provided on the arm14and the location-guide body55, respectively.

The pin60is provided partway along the longitudinal extent of the arm14, and the guide channel62is provided symmetrically about the vertical central axis of the location guide16. However, the location of the pin60and the guide channel62could conceivably be reversed.

The guide channel62includes an angled longitudinal extent, in this case defining a V15 shape pointing towards the lower end36of the housing20. The guide channel62preferably comprises two rectilinear channel portions which intersect at or substantially at the longitudinal line of symmetry of the femoral body12. The guide channel62is also open along both longitudinal sides, defining an open sided slot for receiving the pin60. However, the distal longitudinal side remote from the arm14may be closed, if necessary.

The pin60is thus slidable in the guide channel62as the arm14is pivoted, whereby the location guide16is urged upwardly or downwardly in the in use housing20.

The guide channel62may be arcuate rather than straight sided.

The location guide16also includes lateral and medial locator elements64,66. In this case, the locator elements64,66are apertures through the location-guide body55. The apertures are preferably cylindrical, and thereby provide a surgical drill guide. To enable access to the locator elements64,66, the front and rear major walls26,28of the femoral body12include elongate slots68aligned with the path of movement of the apertures66,68.

Beneficially, the location guide16also includes a width-checker connector70for releasably connecting a femoral width-checker device72. SeeFIG. 5e. In this case, the width-checker connector70includes two laterally spaced apart openings74adjacent to a lower edge of the location-guide body55. Two further elongate slots76are again included in the front major wall26of the femoral body12, and these are aligned with the path of movement of the openings74so that the femoral width-checker device72can slide relative to the femoral body12whilst remaining engaged in the openings74of the location-guide body55.

The posterior-condylar locator18is in this case integrally formed as one piece with the external-rotation-angle arm14. The posterior-condylar locator18comprises two legs78which extend at least substantially coplanar from a lower end portion80of the arm14, but above the pivot point82, and laterally from the femoral body12. A foot84extends at or substantially at right angles to the plane of the legs78and from a distal end thereof.

Each foot84preferably includes a substantially planar plate, tab, tongue or platform86for location on the posterior of the medial condyle. As such, the posterior-condylar locator18is pivotable in unison with the arm14, and also relative to the femoral body12. The said platform86may be angled relative to the plane of longitudinal symmetry of the femoral body12, so as to project away therefrom. This enables the femoral body12to be as small and compact as possible whilst still allowing location of the foot84on the posterior medial condyle.

The location guide16also advantageously includes a stylus-holder connector88for receiving a stylus holder90. In this case, the stylus holder90is a post, as shown inFIG. 2, and the stylus92is attached thereto. The post and/or stylus92may include gradations and/or measurements for use during sizing.

The stylus holder90is a releasable push-fit into the connector88, formed as an opening formed in a side of the location-guide body55, and as such the femoral body12is open to allow the stylus holder90to project unhindered therefrom. Since the stylus holder90is connectable to the location-guide body55, it is movable in unison with the location guide body55and thus also the arm14.

Referring now toFIGS. 5ato 5h, the use of the femoral sizing jig10as part of posterior-referencing femur resecting system will now be described. In general surgery, the proximal end94of the tibia96has already been prepared and resected to take a tibial plate of the prosthesis. However, the tibia can be prepared after the femoral bone cuts. The tibial preparation generally takes into account neutral varus/valgus alignment and the resection typically includes a 3 degree posterior (or other) slope.

A distal end22of the femur24is then prepared by using an intramedullary canal drill98to penetrate the cortex. The drill bit is inserted into the medullary canal, medial to the mid-point between the lateral and medial condyles100,102, and approximately 10 mm anterior to the origin of the posterior cruciate ligament.

An intramedullary rod104is then inserted and varus/valgus alignment along with distal face resection depth is set via a femoral distal alignment jig106located on the intramedullary rod104. A femoral resection jig108is located on the anterior cortex110of the distal end22of the femur24via the femoral distal alignment jig106, and is then pinned in place at the selected proximal/distal position to suit the amount of bone desired to be removed. With the intramedullary rod104and femoral distal alignment jig106removed, a first resection across the distal face112of the femur24is conducted, as shown inFIG. 5d.

The external-rotation-angle arm14of the femoral sizing jig10is then set to its required offset angle, and locked in place using the above-described locking device46. This offset angle causes effective counter-rotation of the femoral body12, and therefore also of the cutting-jig location guide16, relative to the medial-side foot84of the posterior condylar locator18, due to the medial-side foot84aand the medial-side locator element66having a fixed spatial relationship. In other words, as the arm14is moved angularly, the location-guide body55moves upwardly or downwardly within the femoral body12.

The medial-side foot84therefore moves in unison with the medial-side locator element66through the location-guide body55, maintaining the separation therebetween, but imparting effective rotation of the femoral body12and thus also of the lateral-side locator element64.

With the femoral sizing jig10then located on the resected distal face112, both rotational alignment and femoral sizing in conjunction with the femoral stylus92is possible. The femoral sizing jig10is a posterior referencer allowing for, in this case, 9 mm of bone resection from the medial posterior femoral condyles102at all angular settings of the femoral sizing jig10.

The medial-side foot84is located on the medial posterior femoral condyle102, and the rear major wall28positioned against the resected distal face112. The femoral width checker device72can be attached to the openings74in the location-guide body55to confirm rotational alignment of the femoral component and to conduct a secondary medial/lateral sizing check once the anterior/posterior size is confirmed.

With the stylus92connected to the stylus holder90, and the stylus holder90engaged with the medial and/or lateral stylus-holder connectors88, an optimal femoral size is determined. A surgical drill114is then used to form two peg holes in the resected distal face112utilising the positioned lateral and medial locator elements64,66. SeeFIG. 5f.

With the femoral sizing jig10removed, a multi-plane femoral resection jig116is positioned onto the resected distal face112and held in position with locator pins118which are inserted into the medial and lateral pin holes formed using the femoral sizing jig10. Further pins can also be used to hold the multi-plane femoral resection jig116more firmly to the resected distal face112, if necessary.

Posterior femoral resection120and anterior femoral resection122are undertaken, and a posterior chamfer124and an anterior chamfer126are now formed, all being guided by the multi-plane femoral resection jig116. SeeFIG. 5h.

Following these steps, an initial femoral trial is undertaken. Balancing of the flexion and extension gaps is performed, rotational adjustment is restored, final tibial and femoral preparation is undertaken, and patella resection, sizing and trial is implemented. Trial reduction in flexion and extension is then performed, and finally insertion of the definitive components of the prosthesis is undertaken.

Since the medial posterior condyle forms the datum for external rotation angle of the femur, it is feasible that the distal end face does not need to be resected initially.

Furthermore, it is possible that the medial locator element could be dispensed with, if any further cutting jig includes a reference element based on the medial posterior condyle. For example, this could be similar to the foot of the posterior-condylar locator of the femoral sizing jig.

Although the external-rotation-angle arm of the femoral sizing jig is set to its required offset angle, and locked in place using the locking device to achieve the predetermined offset angle, the locking device may be unlocked allowing the external-rotation-angle arm to initially freely move. In this case, with the femoral sizing jig applied to the distal end of the femur, the offset angle can be intra-operatively set to achieve optimum ligament balancing between flexion and extension checking of the knee. Once the ligament balance has been decided, the locking device can be locked.

It may also be advantageous to utilise one or more shims on or adjacent to the or each posterior-condylar locator. A shim is beneficial in reconstructing the patient's natural joint line which may be necessary if the posterior condyles of the femur are worn. A plurality of shims of different thicknesses is typically provided for appropriate selection therefrom. The or each shim may be mountable via mounting means on one or both posterior-condylar locators.

Additionally or alternatively, the femoral sizing jig could include one or more cutting jig guides and/or a cutting jig. For example, it would be feasible to include at least an anterior and/or posterior femoral resection cutting jig or guide in the femoral sizing jig to establish a rotational setting relative to the medial condyle. This may be in the form of a slot extending laterally across the top and/or bottom portion of the femoral body to allow for an initial anterior and/or posterior femoral resection, instead of forming medial and lateral pin holes, as described above. Additionally or alternatively, anterior and/or posterior chamfer cuts could be performed that would establish the rotational setting relative to the medial condyle.

It is thus possible to provide a femoral sizing jig which, as part of at least a posterior30referencing femur resecting system, ensures maintenance of a natural joint line of a patient's leg and facilitates co-lateral isometry post total knee replacement. It is intended that the use of the femoral sizing jig of the present invention during total knee arthroplasty places the prosthetic components in an anatomical position with respect to the physiological axis of the knee joint, whilst maintaining stability throughout the full range of knee flexion. The femoral sizing jig provides for setting of external rotation when using standard or conventional total knee replacement techniques. The femoral sizing jig facilitates measured resection and ligament balancing techniques following femoral dependant positioning utilising a datum taken from the medial posterior femoral condyle. As the medial side of the femur is the more stable compartment of the knee, total knee replacement performed with this technique will product more normal postoperative kinematics by ensuring that knee flexion is restored. The femoral sizing jig of the present invention is additionally highly advantageous in that it provides for a single jig being used in total arthroplasty of both left and right knees.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the art without departing from the scope of the invention as defined by the appended claims.