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`Smith & Nephew Ex. 1034
`IPR Petition - USP 8,377,129
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`Smith & Nephew Ex. 1034
`IPR Petition - USP 8,377,129
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`W0 01/66021 A1
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`patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), European
`patent (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE,
`IT, LU, MC, NL, PT, SE, TR), OAPI patent (BF, BJ, CF,
`CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG).
`
`For two-letter codes and other abbreviations, refer to the "Guid-
`once Notes on Codes and Abbreviations ” appearing at the begin-
`ning ofeach regular issue of the PCT Gazette.
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`'
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`Published:
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`— with international search report
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`WO 01/66021
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`PCT/AU01/00258
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`A METHOD OF ARTHROPLASTLY ON A KNEE JOINT
`AND APPARATUS FOR USE IN SAME
`
`Field Of The Invention
`
`The present invention relates to a method of arthroplasty on a knee joint of a
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`patient. The method extends to both unicondylar knee arthroplasty and knee joint
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`arthroplasty involving resection of both the lateral and medial condyles of the tibia and
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`femur. There is also provided apparatus for use in the method.
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`Background Of The Invention
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`Various methods and apparatus for performing knee arthroplasty and unicondylar
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`knee arthroplasty in particular, are known in the art. The known methods involve
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`resection of the tibia and femur for fitting of trial tibial and femoral implants,
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`respectively. Once the bone has been resected and the trial implants are secured in place,
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`the surgeon then assesses the kinematics of the knee joint. At this stage, the surgeon
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`may transect, elevate and/or release ligaments and other soft tissue structures to achieve
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`the desired level of deformity correction, balance in the tension of relevant ones of the
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`ligaments and other stabilising soft tissue structures, and an acceptable range of motion
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`of the knee joint. Additional bone resection may also be required to achieve the desired
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`outcome. This leads to an increase in operation time with an associated increase in the
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`risk of surgery related complications. Moreover, such additional surgical intervention
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`following fitting of the trial implants potentially leads to subsequent increased
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`discomfort for the patient and increased healing times. Methods and apparatus for use in
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`arthroplasty of a knee joint are exemplified in United States Patent No. 5,171,244 and
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`United States Patent No. 5,520,695.
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`Summm Of The Invention
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`It is an aim of the present invention to ameliorate one or more problems of the
`
`prior art or at least provide an alternative to the prior art.
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`In one aspect of the invention there is provided a method of arthroplasty on a
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`knee joint, comprising the steps of:
`
`(a)
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`obtaining a desired spacing of the femur from the tibia;
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`(b)
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`determining depth of bone to be resected from at least one of the tibia and
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`the femur on the basis of the desired spacing of the femur from the tibia to enable fitting
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`of at least one prosthesis selected from tibial and femoral prostheses;
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`(c)
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`resecting bone from one or both of the tibia and the femur substantially to
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`the determined depth in the or each one, respectively; and
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`(d)
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`fitting the or each said prosthesis.
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`The method is particularly suitable for use in unicondylar knee arthroplasty but
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`may also be used in bicondylar knee arthroplasty involving resection of the lateral and
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`medial condyles of both the tibia and the femur. By unicondylar knee arthroplasty is
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`meant arthroplasty involving resection of either the lateral or medial condyles of the tibia
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`and the femur.
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`The resection of the bone may comprise cutting at least one of the tibia and the
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`femur substantially at the appropriate determined depth in the or each one of the tibia
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`and the femur to remove a segment of bone from the or each one.
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`Preferably, the resection of the bone from the tibia may comprise forming a
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`recess in the uppermost end of the tibia adjacent to the femur for receiving the tibial
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`prosthesis.
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`Accordingly, in another aspect of the present invention there is provided a
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`method of arthroplasty on a knee joint, comprising the steps of:
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`(a) surgically providing access to the knee joint;
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`(b) obtaining a desired spacing of the femur from the tibia;
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`(c) determining depth of bone to be resected from an end of the tibia to form a
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`recess for receiving a tibial prosthesis on the basis of the desired spacing of the femur
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`from the tibia;
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`(d) resecting the bone from the tibia to the determined depth to form the recess;
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`(e) positioning the tibial prosthesis in the recess.
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`The method may further comprise locating a guide jig in position about the knee
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`joint for guiding the resection of the bone. Preferably, the guide jig will be adapted for
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`guiding movement of a cutter device relative to the tibia for shaping the recess to a
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`desired profile. Most preferably, the jig will incorporate a template for guiding the
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`15 movement of the cutter device relative to the tibia.
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`Preferably, bone will be resected from both the tibia and the femur to enable the
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`fitting of both the tibial and the femoral prostheses.
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`Preferably, the desired spacing of the femur from the tibia will be obtained using
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`at least one spacer inserted into the knee joint between the femur and the tibia to thereby
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`provide the spacing.
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`In unicondylar knee arthroplasty only a single spacer will usually be used to
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`obtain the desired spacing of the femur from the tibia. In contrast, in bicondylar knee
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`arthroplasty a pair of spacers will usually be utilised, one being located between each of
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`the lateral and medial condyles of the femur and the tibia, respectively. In this instance,
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`the spacers may have the same thickness or a different thickness to each other.
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`Most preferably, the or each spacer will be adapted for being positioned between
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`corresponding ones of the condyles of the femur and the tibia.
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`In another aspect of the present invention there is provided a method of
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`arthroplasty on a knee joint, comprising the steps of:
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`(a)
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`surgically providing access to the knee joint;
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`(b)
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`selecting at least one spacer for providing desired spacing of the femur from
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`the tibia;
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`(c)
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`positioning the selected spacer in the knee joint to obtain the desired spacing
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`of the femur from the tibia;
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`(d)
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`using the spacer as a reference to determine a location on each one of the
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`tibia and the femur indicating depth of bone to be resected from each for fitting of
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`chosen tibial and femoral prostheses;
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`(e)
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`cutting the tibia and the femur substantially at the determined location on
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`each for resection of the bone from each one to the required said depth; and
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`(f)
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`fitting the chosen tibial and the femoral prostheses.
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`Typically, the knee joint will be placed in a position of flexion whereby the tibia is
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`arranged at an angle with respect to the femur for the resection of the bone. Generally,
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`bone will be resected from a posterior side of the femur and the uppermost end of the
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`tibia.
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`Preferably, a method of the invention will comprise selecting the at least one
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`spacer from a range of spacers for providing different spacings of the femur from the
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`tibia. Accordingly, the selecting of the or each spacer may comprise;
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`(1)
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`Choosing the spacer from a range of spacers for providing a different spacing
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`of the femur from the tibia, respectively; and
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`(ii) moving the tibia about the femur through an arc of motion between
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`backward and forward positions to evaluate movement of the knee joint while the chosen
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`spacer is in position in the knee joint between the femur and the tibia.
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`The selecting may further comprise repeating steps (i) and (ii) as necessary to
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`obtain the desired spacing of the femur from the tibia using a different spacer chosen
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`from the range of spacers each time.
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`The selected spacer will usually be of a thickness for providing appropriate tension
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`and optimising balance in the action of various ligaments and other soft tissue structures
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`of the knee joint during the movement of the tibia about the femur. Preferably, the
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`tension in the knee joint obtained by the spacing of the femur from the tibia with the use
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`of the selected spacer will be substantially retained upon the fitting of the or each
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`prosthesis.
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`Preferably, the guide jig will be adapted for guiding resection of bone from each of
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`the tibia and the femur. The securing of the guide jig may comprise arranging the jig
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`with the spacer to facilitate the positioning of the jig about the knee joint.
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`Knowing the relevant dimensions of the chosen tibial and femoral prostheses
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`allows the guide jig to be adapted such that when arranged with the spacer, the guide jig
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`is positioned relative to the tibia and the femur for guiding the cutting of the one or both
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`of them at the depth in the resection of bone therefrom for accommodating the tibial and
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`femoral prostheses. Accordingly, the selected spacer has two roles in unicondylar knee
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`arthroplasty, firstly to space the femur from the tibia and secondly, to act as a reference
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`for resection of bone from one or both of the tibia and the femur to the correct depth.
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`Therefore, in a further aspect of the invention there is provided a method of
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`determining the position of a guide jig about a knee joint for subsequently guiding
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`resection of one or both of the tibia and the femur to a desired depth in the or each one,
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`respectively, the method comprising:
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`(a) locating a selected spacer in the knee joint to obtain a desired spacing of the
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`femur from the tibia; and
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`(b) arranging the guide jig and the spacer together to thereby determine the
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`position of the guide jig for guiding the resection of the one or both of the tibia and the
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`femur.
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`In addition, a combination approach for resecting bone from the femur to the
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`desired depth may be employed. This may involve resecting a segment of bone from the
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`femur to the desired depth in that bone utilising a guide jig as herein described, and
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`inserting an appropriate cutter device into the knee joint between the tibia and the femur
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`in the absence of the guide jig, for resecting bone from the femur with operation of the
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`device and upon movement of the tibia in an arc of motion about the femur to thereby
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`resect further bone from the femur to the desired depth in that bone for fitting of a
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`femoral prosthesis. If desired, only the latter one of those steps may be employed in the
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`resection of the bone from the femur.
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`Accordingly, in another aspect of the present invention there is provided a method
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`of arthroplasty on a knee joint, comprising the steps of locating a cutter device in
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`position in the knee joint between the tibia and the femur, and moving the tibia through
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`an arc of motion about the femur between backward and forward positions while the
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`cutting device is being operated and is in position between the tibia and the femur, to
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`thereby remove bone substantially to a desired depth from the femur in a direction of
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`travel of the tibia relative to the femur.
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`There is also provided apparatus for use in the methods of the invention.
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`Apparatus as described herein may be provided in kit form or as an assembled
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`arrangement.
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`Hence, in a still further aspect of the present invention there is provided apparatus
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`for use in a method of arthroplasty on a knee joint of a patient, comprising:
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`a guide jig for guiding cutting of at least one of the tibia and the femur in resection
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`of bone therefrom for enabling fitting of one or both of a tibial and a femoral prosthesis,
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`wherein the guide jig is adapted for being arranged with at least one selected spacer for
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`spacing the femur from the tibia, and for being secured about the knee joint in a position
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`determined by the spacer to guide cutting of the at least one of the tibia and the femur
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`substantially at a desired depth in the or each one, respectively.
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`Typically, the guide jig will be adapted for guiding cutting of the tibia at a fixed
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`predetermined distance below the spacer. Preferably, the guide jig will be adapted for
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`guiding cutting of both the tibia and the femur when the guide jig is secured about the
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`knee joint in said position.
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`Accordingly, in yet another aspect of the invention there is provided apparatus for
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`use in a method of arthroplasty on a knee joint of a patient, comprising:
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`a guide jig for guiding cutting of the tibia and the femur in resection of bone
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`therefrom for enabling fitting of chosen tibial and femoral prostheses, and being adapted
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`for being secured about the knee joint in a position determined by at least one spacer for
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`providing a desired spacing of the femur from the tibia, to guide the cutting of the tibia
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`and the femur at a desired depth in each one, respectively.
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`In still another aspect of the invention there is provided apparatus for use in a
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`method of arthroplasty on a knee joint of a patient, comprising:
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`(a)
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`at least one spacer having a predetermined thickness for providing a desired
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`spacing of the femur from the tibia; and
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`(b)
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`at least one guide jig for guiding cutting of the tibia and the femur for
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`resection of bone to a desired depth from the or each one respectively, to enable fitting of
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`chosen tibial and femoral prostheses;
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`wherein the guide jig is adapted for being secured about the knee joint in a
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`position determined by the spacer to guide the cutting of the or each one of tibia and the
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`femur substantially at the desired depth in the or each one.
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`The spacer will normally be provided as one of a set of spacers for providing
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`different spacings of the femur from the tibia respectively, thereby allowing the selection
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`of different ones of the spacers as needed.
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`Hence, in yet another aspect of the present invention there is provided apparatus
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`for use in a method of arthroplasty on a knee joint of a patient, comprising;
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`(a)
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`a set of spacers for allowing selection of at least one said spacer for insertion
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`into the knee joint for providing a desired spacing of the femur from the tibia; and
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`(b)
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`at least one guide jig for guiding cutting of one or both of the tibia and the
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`femur for resection of bone to a desired depth from the or each one respectively, to
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`enable fitting of chosen tibial and femoral prostheses;
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`wherein the guide jig is adapted for being secured about the knee joint in a
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`position determined by the spacer to guide the cutting of the one or both of tibia and the
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`femur substantially at the desired said depth in the or each one, and wherein the spacers
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`have a different thickness to one another for providing different spacings of the femur
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`from the tibia.
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`The guide jig may be adapted for guiding the cutting of the femur and the tibia at
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`the same depth in each one or at a different depth in the tibia compared to the femur.
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`Preferably, the guide jig will be adapted for guiding the cutting of the tibia and the
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`femur at a predetermined fixed spacing. The guide jig will normally be adapted for
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`being coupled with one or more said spacers. The term “coupled” is to be taken in the
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`broadest sense and includes within its scope reception of the spacer(s) by the jig whether
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`the or each spacer is fixed to the guide jig or not.
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`Preferably, the guide jig will comprise a cutting block adapted for receiving the or
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`each selected spacer and most preferably, will have a through passageway for guiding the
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`cutting of one of the condyles of tibia and the femur. More preferably, the guide jig will
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`have another through passageway for guiding the cutting of the other of the condyles.
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`Most preferably, the cutting block will be adapted for being secured to the tibia.
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`Generally, the guide jig will be adapted for guiding cutting of one or both of the
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`tibia and the femur in a medial to lateral or lateral to medial direction with respect to the
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`knee joint.
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`Preferably, the guide jig will be adapted for being secured about the knee joint in a
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`position determined by the thickness of the spacer or spacers used.
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`In another aspect of the present invention there is provided a spacer for being
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`inserted into a knee joint for spacing the femur from the tibia, comprising an elongate
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`member with a leading end region adapted for being positioned between the tibia and the
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`femur to space the femur from the tibia, and an opposite end region for protruding from
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`the knee joint.
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`In a further aspect of the present invention there is provided a spacer for being
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`inserted into a knee joint to provide a desired spacing of the femur from the tibia in
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`arthroplasty on the knee joint, comprising an elongate member with a leading end region
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`adapted for being inserted between the tibia and the femur to thereby obtain the desired
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`spacing of the femur from the tibia and being retained in the knee joint during resection
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`of bone to a desired depth from one or both of the tibia and the femur respectively, and
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`an opposite end region adapted for protruding from the knee joint and coupling with a
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`guide jig for guiding the cutting of the or each one of the tibia and the femur in the
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`resection of the bone.
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`Preferably, the leading end region of the spacer will be adapted for retaining the
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`spacer in the knee joint. Most preferably, the leading end region of the spacer will be
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`adapted for receiving the medial or lateral condyle of the femur for retaining the spacer
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`in the knee joint.
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`In yet another aspect of the present invention there is provided a set of spacers for
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`allowing selection of at least one of the spacers for insertion into a knee joint to provide
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`a desired spacing of the femur from the tibia in arthroplasty on the knee joint, each said
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`spacer respectively comprising an elongate member with a leading end region adapted
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`for being inserted between the tibia and the femur to thereby space the femur from the
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`tibia and being retained in the knee joint during resection of bone from one or both of the
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`tibia and the femur respectively, and an opposite end region adapted for protruding from
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`the knee joint and coupling with a guide jig for guiding cutting of the or each one of the
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`tibia and the femur in the resection of the bone, wherein the spacers have a different
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`thickness to one another for providing different spacings of the femur from the tibia.
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`Usually, it is desirably to resect the tibia at an angle sloping downwardly in the
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`anterior to posterior direction of the knee joint for location of the tibial prosthesis on the
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`resulting sloping surface of the tibia. Typically, the angle of slope is about 3° although
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`this may vary from patient to patient.
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`Accordingly, in another aspect of the present invention there is provided an
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`alignment device for aligning a guide jig in position about a knee joint for guiding
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`cutting of at least one of the tibia and the femur at a desired location on the or each one
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`respectively during arthroplasty on the knee joint, and comprising:
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`a body for receiving the guide jig and coupling the guide jig with an alignment
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`guide for aligning the guide jig in a desired medial to lateral orientation with respect to
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`the knee joint;
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`and wherein the body is adapted for aligning the guide jig at a desired angle in an
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`anterior to posterior direction of the knee joint for securing of the guide jig at the desired
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`angle prior to removal of the body from about the knee joint for allowing cutting of the
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`one or both of tibia and the femur to be guided by the guide jig.
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`In still another aspect of the present invention there is provided an alignment
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`device for supporting a cutting device for resecting bone from the tibia to a desired depth
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`to from a recess in the tibia during arthroplasty on a knee joint, and comprising:
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`a body for receiving a guide jig for guiding cutting of the femur and coupling the
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`guide jig with an alignment guide for aligning the guide jig in a desired medial to lateral
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`orientation with respect to the knee joint;
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`and wherein the body is adapted for aligning the guide jig at a desired angle in an
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`anterior to posterior direction of the knee joint and for being secured about the knee joint
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`in a position determined by the guide jig for supporting the cutting device for the
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`resection of the bone from the tibia following removal of the guide jig from the body.
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`Accordingly, there is also provided an alignment guide for supporting the guide jig
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`and aligning the guide jig in a desired medial to lateral orientation with respect to the
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`knee joint to allow for varus and valgus adjustment.
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`The alignment guide will typically incorporate a mounting platform which is
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`angularly displaceable for allowing orientation of the guide jig in the medial to lateral
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`direction. Desirably, the mounting platform will be adapted for supporting the guide jig
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`adjacent to the medial condyles of the tibia and femur or the lateral condyles of the bones
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`as may be required. The alignment guide will generally be a tibial alignment guide for
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`being secured along the leg of the patient in alignment with the tibia.
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`Alternatively, the guide jig itself may be adapted for guiding the cutting of one or
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`both of the tibia and the femur at the desired angle in the medial to lateral direction of
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`the knee joint. Similarly, the guide jig may be adapted for guiding cutting of the one or
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`both of the tibia and femur at the downward angle in the anterior to posterior direction of
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`the knee joint, in which case the alignment component described above for this purpose
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`may not be utilised and the cutting block may be mounted directly on the alignment
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`guide.
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`In still another aspect there is provided the use of a guide jig of the invention in the
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`assembly of a medical device for arthroplasty of the knee, wherein the medical device
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`comprises the guide jig and at least one spacer for spacing the femur from the tibia.
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`In still another aspect there is provided the use of at least one spacer of the
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`invention in the assembly of a medical device for guiding resection of bone from at least
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`one of the tibia and the femur in arthroplasty of the knee.
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`In a further aspect there is provided the use of at least one spacer of the invention
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`in the assembly of a medical device for knee arthroplasty, wherein the medical device
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`comprises the or each spacer and a guide jig of the present invention.
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`Advantageously, the method of the invention may allow balancing of tension in
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`ligaments and other soft tissue structures of the knee joint to be optimised prior to
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`resection of bone for the fitting of the prostheses. Moreover, ligament and soft tissue
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`release to obtain adequate balancing of tension in the ligaments and soft tissue of the
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`knee joint during flexion and extension of the knee joint as is required for optimum knee
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`joint kinematics prior to or following fitting of trial tibial and femoral implants may be
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`eliminated or reduced.
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`In addition, the risk of incorrect alignment and orientation of the tibial and femoral
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`prostheses relative to one another with reference to the action of the ligaments and soft
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`tissue structures may be reduced.
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`It is another advantage that as the use of a spacer or spacers as herein described
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`may facilitate both positioning of the guide jig and appropriate tensioning of ligaments
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`and other soft tissue structures of the knee joint, decreased operating times may be
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`provided thereby potentially reducing the incidence of various time related surgical
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`complications such as wound infection, complications associated with the risk of
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`anaesthetic, and thrombosis associated with tourniquet application which can lead to
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`pulmonary embolus and other serious problems. Furthermore, by reducing the need to
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`transect, elevate, or release ligaments and other soft tissue structures of the knee joint,
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`post-operative recovery time may be reduced with consequential reductions in overall
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`health care costs associated with knee arthroplasty.
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`Unless the context clearly requires otherwise, throughout the description and the
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`claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an
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`inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense
`
`of “including, but not limited to”.
`
`The features and advantages of the present invention will become further apparent
`
`from the following detailed description of a number of preferred embodiments illustrated
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`in the accompanying drawings.
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`Brief Description Of The Accompanying Drawings
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`Figure l is a side schematic view illustrating a knee joint with tibial and femoral
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`prostheses fitted;
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`Figure 2 is an anterior view of the fitted tibial and femoral prostheses shown in fig.
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`Figure 3 is a perspective view of the femoral prostheses shown in fig. 1 prior to
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`being fitted;
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`Figure 4 is a perspective view of the tibial prostheses shown in fig. 1 prior to being
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`fitted;
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`Figure 5 is a diagrammatic front view of a knee joint;
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`Figure 6 is a diagrammatic front view showing a spacer in position between a
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`femur and a tibia of the knee joint illustrated in fig. 5;
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`Figure 7 is a diagrammatic side view of a set of different spacers, for providing
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`different spacing of the femur from the tibia;
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`Figure 8 is a perspective exploded View of apparatus for performing arthroplasty
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`on a knee joint;
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`Figure 9(a) is a perspective View of the apparatus of fig. 8 when assembled;
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`Figure 9(b) is a diagrammatic front view of the apparatus of fig. 8 fitted to the leg
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`of a patient;
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`Figure 10(a) is a rear perspective view of a guide jig of the apparatus shown in fig.
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`Figure 10(b) is a side view of the guide jig of fig. 10(a);
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`Figure 11 is a view of an alignment component of the apparatus shown in fig. 8.
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`Figure 12 is a schematic plan view of the guide jig of fig. 10 indicating the
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`orientation of channels defined in the jig for reception of pins for securing the jig in
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`position about the knee joint;
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`Figure 13 is a diagrammatic partial view of a tibial shaft;
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`Figure 14 is a diagrammatic front View of the guide jig fitted in position about the
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`knee joint;
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`Figure 15 is a front diagrammatic view showing the medial condyles of the femur
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`and the tibia following resection thereof;
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`Figure 16 is a diagrammatic View illustrating the use of a tibial sizing device for
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`determination of an appropriate size of tibial implant;
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`Figure 17 is a perspective view of a tibial trial;
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`Figure 18 is a diagrannnatic view of the tibial trial of fig. 17;
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`Figure 19 is a diagrammatic anterior view of the tibial implant of fig. 16 fixed in
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`position on the tibia of the knee joint;
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`Figures 20 and 21 are diagrammatic views illustrating marking of a femoral
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`condyle of the knee joint for further resection of the femur to enable fitting of the
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`femoral prosthesis of fig. 3;
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`Figure 22 is a diagrammatic View illustrating the use of a femoral sizer for
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`determination of the appropriate sized femoral prosthesis;
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`Figure 23 is a diagrammatic view illustrating the use of a femoral shaping rasp for
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`shaving bone from the relevant condyle of the femur to enable fitting of the femoral
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`prosthesis;
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`Figure 24 is a diagrammatic View illustrating the use of a femoral peg drill guide to
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`drill a bore into the femur for reception of the femoral peg of the femoral prosthesis
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`shown in fig. 3;
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`Figure 25 is a perspective View of a tibial implant of the invention;
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`Figure 26 is a diagrammatic view of the tibial implant of fig. 25 fixed in position
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`on the tibia;
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`Figure 27(a) is an elevated side View of a cutting device for resecting bone from
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`the femur;
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`Figure 27(b) is a perspective view of the cutter blade disk of the cutting device of
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`fig. 27(a);
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`Figure 28 is an end View of the cutting device of fig. 27(a);
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`Figure 29 is a side view of the cutting device of fig. 27(a);
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`Figure 30(a) is a longitudinal cross-sectional View of the cutting device of fig.
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`27(a);
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`Figure 30(b) is a diagrammatic partial view of a coupling arrangement used for
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`coupling the head and body of the cutter device of fig. 27(a) together;
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`Figures 31 and 32 illustrate reception of the cutting device of fig. 27(a) the tibial
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`implant of fig. 25 in unicondylar arthroplasty;
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`Figures 33(a) to 33(c) illustrate the resection of bone to a desired depth from the
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`femur;
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`Figure 34 is an exploded perspective view of an assembly for forming a recess in
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`the tibia for receiving a tibial implant;
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`Figure 35 is an exploded perspective view of the apparatus of fig. 8 when arranged
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`for removal of bone from the tibia for inset placement of a tibial implant;
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`Figure 36 is a perspective View of the apparatus arranged as shown in fig. 35 when
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`assembled;
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`Figure 37 illustrates removal of bone from the tibia for inset tibial implant
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`placement utilising apparatus of the invention; and
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`Figure 38 illustrates a further cutting device for resecting bone to a desired depth
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`from the femur.
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`Detailed Description Of Preferred Embodiments Of The Present Invention
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`The femoral prosthesis 2 shown in fig. 1 is fitted to the medial condyle 4 of the
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`femur 6 and abuts articulating surface 8 of the tibial prosthesis 10 fitted on the
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`corresponding medial condyle 12 of the tibia 14, for articulation thereon as the tibia
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`undergoes flexion and extension about the knee joint 15. The positioning of the femoral
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`prosthesis 2 and the tibial prosthesis 10 is more clearly shown in fig. 2.
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`As shown in fig. 3, the femoral prosthesis 2 is provided with a centrally orientated
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`upstanding fin 16 incorporating a peg l8 projecting from an interior face 20 of the
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`prosthesis.
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`The opposite outer face 22 has a curved contour for facilitating movement of the
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`tibia about the femur. The interior face 20 of the femoral prosthesis is textured to
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`enhance binding of bonding cement used to fix the prosthesis to the femur. The
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`prosthesis itself is formed from a cast cobalt chromium molybdenum alloy
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`conventionally used in the manufacture of such prostheses.
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`The tibial prosthesis 10 shown more clearly in fig. 4 is manufactured from ultra
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`high molecular weight polyethylene and has a dove tailed base 24 to again enhance
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`bonding of cement to the prosthesis for fixing the prosthesis to the tibia. The articulating
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`surface 8 of the tibial prosthesis is sightly concaved to substantially match curvature of
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`the outer face 22 of the femoral prosthesis.
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`An example of unicondylar arthroplasty will now be described. As a first step, a
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`longitudinal incision is made in the knee from just medial to the medial edge of the
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`patella 26 to just below the medial tibial plateau adjacent to the attachment of the
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`iliotibial tract, as indicated by the dotted line in fig. 5. The incision avoids transecting
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`any of the ligamentous structures that contribute to the kinematics of the knee. The
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`patella is not everted, but gently retracted laterally to expose the medial compartment of
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`the knee. All femoral and tibial osteophytes which are accessible are then removed.
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`In order to balance tension in ligaments and other soft tissue structures of the knee
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`joint as well as to correct deformity, a spacer 28 is located in position between the
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`condyle of the femur and the corresponding condyle of the tibia as shown in fig. 6. The
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`spacer effectively spaces the femur from the tibia.
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`To check for adequate tension of the soft tissue structures and kinematics of the
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`knee joint, the tibia is moved through an arc of flexion of between 0° to about 130°. If
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`the knee joint is unstable or has inadequate tension, the spacer may be removed and a
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`spacer having a greater thickness for spacing the tibia and the femur further apart may be
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`located in the joint. Conversely, if the knee feels over tensioned or adequate range of
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`movement through the arc of flexion cannot be achieved, the spacer may be replaced
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`with a spacer having a reduced thickness to decrease the spacing between the femur and
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`the tibia. This process may be repeated a number of times using a spacer having a
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`different thickness each time until adequate tension and kinematics of the knee joint is
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`achieved.
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`Importantly, the met
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