WO2015027288A1

WO2015027288A1 - Cutting guide including measurement indicia for verification of pre- planned resections

Info

Publication number: WO2015027288A1
Application number: PCT/AU2014/000867
Authority: WO
Inventors: Scott Fletcher
Original assignee: The Australian On-Line Prosthetic Company
Priority date: 2013-09-02
Filing date: 2014-09-02
Publication date: 2015-03-05
Also published as: WO2015027287A1

Abstract

A patient matched cutting guide which is arranged to guide a user to resect bone at predetermined positions during a surgical procedure., the guide including formations which engage bone parts to locate the guide such that other parts of the guide align with planned resection planes; characterised in that the cutting guide includes specifically placed, spatially orientated indicators which enable verification of resection locations intra-operatively based on measurements between at least one known reference on the cutting guide and the underlying bone to thereby allow verification of the planned resection planes.

Description

CUTTING GUIDE INCLUDING MEASUREMENT INDICIA FOR

VERIFICATION OF PRE- PLANNED RESECTIONS

BACKGROUND

[01 ] The present invention relates to improvements in surgical, equipment and more particularly relates to tmprovemeots in patient matched cutting guides used in surgery such as in knee arthro lasty. The invention further relates to a modified cutting guide used in surgery which allows a surgeon to make intraoperative measurements related to planned resections to enable verification of resections. The present invention also relates to a modified cutting guide which includes measurement indicia which is capable of use in intra operati ve validation of pre planned resections once the guide is placed on the patient's bone.

PRIOR AR

[02] Knee arthroplasty is a well-known surgical procedure by which a diseased and/or damaged natural knee joint, is replaced by a prosthetic knee joint. Typical knee prostheses include a tibial component, a femoral component, and a patellar component.

[03] Various knee prostheses are disclosed in the prior art. Examples are disclosed in US Patent 5,593,449 to Robertson Jr. US patent 5.782,921 to Colleran United States Patent 5,800,552 the contents of which are incorporated by reference herein. Examples of resurfacing types of total knee prosthetic devices are also disclosed in the following US patents also incorporated by reference herein. U,S,PatNo.3,?74,244 to Walker; US patent No.3,728,742 to Averill et a . U.S. Pat o.4,081 ,866 and U.S. Pat. No. 4,207,627 to Cloutier. [04] Modern total knee replacement involves the resurfacing of the femoral condyles with a metallic component, roughly approximating the shape of the anatomical femoral condyles, and resurfacing the tibial plateau with usually, but not exclusively, a polyethylene component having a metallic tibial base plate. Ideally the femoral component should be congruent with the top of the tibial component in order to minimise wear of a surface liner which is usually polyethylene. During normal movements of the knee, rotation of the femur, upon the tibia occurs with roll back of the femoral condyles upon the tibia, particularly when the knee is flexed. If the plane of the tibial plate when fitted to the tibia is misaligned with the resected proximal surface of the tibia, uneven wear will result between the articular surfaces. A patient may not notice the misalignment and uneven loading of the femoral component on the tibial component but where the loading is concentrated through one condyle wear is accelerated. This may lead to a reduction of up to 50% of the normal life of the prosthesis

[05] The femoral component generally includes a pair of spaced apart condylar portions, the surfaces of which articulate with a portion of the polyethylene tibial component. In known total knee prostheses the articular surface of th distal femur and proximal tibia are usually but not exclusively replaced with respective metal and plastics condylar-type articular bearing components. The knee prostheses provide adequate rotational and translational freedom and require minimal bone resection to accommodate the components within the boundaries of the available joint space. The patella-femoral joint may also be resurfaced by a third prosthetic component, as well. The femoral, tibial and patella prosthetic resurfacing components are affixed to respective, surgically prepared adjacent bone structure by cementing or by biological bone ingrowth. The femoral component is usually but not exclusively a metallic alloy construction such as cobalt-chrome alloy and provides medial and lateral condylar bearing surfaces of similar shape and geometry as the natural distal femur. The tibial component can be made entirely of ultra high molecular weight polyethylene or can be comprised of a metallic base and stem component distal! y and an interlocking plastic (UHMWFE) component., proximally. The plastic tibial plateau bearing surfaces are often of concave multi -radius geometry to more or less match tire artic ular geometry of the mating femoral condyles, depending upon the desired design mechanics of primary femoro-tibial motion, e.g. the flexion-extension, including posterior rollback and rotational and translational articular motions. [06] The femoral and tibial components are positioned on the respective side of the knee joint and are not mechanically connected or l inked together. The components are intended to be disposed such that it will allow more accurate simulation of anatomical geometry or dynamic action at an implant site in a patient. [07] Additionally, in resurfacing types of total knee prostheses the tibial plateau bearing surface geometry can assume a variety of configurations, depending upon the desired extent of articular contact and associated trans lational (medial-lateral and anterior-posterior) and rotational (axial and varus-valgus) secondary femora-tibia! motions. These various secondary motions allow the resurfaced knee to function in a natural-like hiomechamca!. manner in conjunction with the surrounding ligamentous and muscle structures about the knee joint. The viable soft tissue structures functionally maintain the femoral and tibial bearing surfaces in contact, provide the necessary levels of constraining force to achieve knee joint stability, and decelerate the principal motion in flexion-ex tension and secondary motions, such as axial rotation, etc. in a controlled manner.

[08] The objective in knee replacements is to simulate with a dynamic implant, natural knee function as closely as possible. Any improvement which allows a surgeon greater capacity in achieving this objective is desirable. The articulation of the femoral condyles with the tibial plateau bearing surfaces involves complex biomechanics allowing primar femoro-tibial flexion and extension, and secondary motions of axial and varus-valgus rotations and anterior-posterior and medial -lateral translations, all of which occur in the normal knee joint. The knee joint reaction forces during primary or secondary motion are principally supported by the tibial bearing surfaces, and are transferred to the underlying fixation interfaces and adjacent supportive bone structures. In a normal knee, physiological femoro-tibial rollback starts at the onset of knee flexion and is generally mostly completed by 40 degrees of flexion. This rollback is accompanied by a transitional motion of roiling and sliding. In the normal knee, these complex interactions are accompanied by complex active interaction of the anterior and posterior cruciate ligaments and other surrounding adjacent soft tissue structures. [09] The above is a description of known biomechanics of a knee joint prosthesis. As knee prostheses attempt to simulate as closely as possible the patient's biomechanics this required simulation necessitates extremely accurate fixation so any means which enables a. surgeon to meet this objective is desirable. Accurate placement of components in total, knee arthroplasty has become increasingly identified as an issue that affects both function of the knee replacement and how long the knee replacement is likely to survive. Methods to help the surgeon place components accurately include conventional methods, computer navigation and patient specific resection guides, ^'Navigation, by default, has provided an intraoperative method to validate the planned resections. To date, there has been no objective method of validating the planned resections when using Patient Matched Guides (PMG). On the basis that the patient matched guides may be inaccurate or alternatively, that the guides may be inaccurately placed on the bone, it is desirable to have a. method for validating the intra-operative resection positions on the tibia and femur, prior to the surgeon performing the actual resection.

[10] Proper rotation of the femoral component in total knee arthroplasty (T A) is critical, as improper rotation can lead to various adverse consequences including instabilities such as but not limited to patella/femoral instabilit ^'; anterior knee pain, arthrofibrosis, and flexion instability- Various methods are available for determining accurate femoral component rotation. One method is a measured resection technique favoured by many surgeons in which bone landmarks (femoral epicondyies, posterior femoral condyles, or the antero posterior axis) are the primary references for determination of femoral component rotation. Another method used is a gap balancing methodology in which the femoral component is positioned parallel to the resected proximal tibia with each collateral ligament equally tensioned. Each method used has some attendant disadvantages and relies on the surgeon to intra operatively accurately confirm angles and distances using bone landmarks (measured resection technique) or correct, soft tissue tensioning in the circumstance where gap-balancing methodology is used to determine femoral component rotation in a total knee arthroplasty (TKA).

[1 ί ] The use of a measured resection technique for determination of femoral component rotation relies o accurate intraoperative identification of numerous bone landmarks. Advocates of this technique recommend placement of the femoral component either parallel to the transepicondylar axis, perpendicular to the anteroposterior axis, or approximately 3° to 4° externally rotated relative to the posterior condylar axis. Use of each of these landmarks is associated with pitfalls that risk improper rotation of the femoral component. [1.2] The transepicondylar axis has been recognized as an acceptable axis to guide femoral implant rotation.. This is supported by kinematic analyses that have demonstrated better coronal plane stability (lowe incidence and magnitude of femoral condylar lift-off) if the femoral component is placed parallel to the transepicondylar axis. There are instances where accurate surgeon identification of the transepicondylar axis is not frequently accomplished, which can result in flexion gap asymmetry.

[1.3] Accuracy of ep.i condylar identification can be assessed post operative!)' to determine if there had been accurate epicondylar identification. One study performed showed that when 74 TKAs were assessed in which the femoral epicondyles were marked with pins mtraoperatively, and postoperative CT scans were performed to assess the accuracy, it was observed that the epicondyles were correctly identified to within ±3° in only 75% of the cases, with a wide range of error from 6° of external rotation to 11° of internal rotation. There are significant errors in intraoperative surgeon identification of the femoral epicondyles. The error can be as much as 2S° - 11 ° external rotation to 17° of internal rotation . Studies show that the ability of the surgeon to accurately and reproducibly identity the transepicondylar axis land mark which is a good landmark to determine femoral component rotation, can be quite poor. Many T A instalment systems have been developed that reference the posterior condylar axis to assist the surgeon in performing femoral bone resections that result in femoral component placement 3^C to 4° externally rotated to this axis.

[ 4] Although simple to use in the operating room, there are problems with using the posterior condylar axis to reference femoral component rotation. Investigations have shown wide anatomic variations in the relationship of the posterior condylar axis to the transepicondylar axis 1 °-10°. Therefore, if a patient's anatomical relationship of the posterior condylar axis is 7° of external rotation vs the transepicondylar axis and the instramentation used places the femoral component in 3° of external rotation, the femora! component will be internally rotated 4° relative to the transepicondylar axis. Hypoplasia or erosion of the posterior aspect of the lateral femoral condyl in knees with valgus deformity will lead to erroneous femoral component position if the posterior condylar axis is used as the primary determinant of femoral component rotation. [1.5] The anteroposterior axis, traversing from the deepest point of the trochlear groove to the center of the intercondylar notch, is an additional bone landmark used to determine femoral component rotation. Another method is to place the coronal plane position of the femoral component perpendicular to the anteroposterior axis and observed enhancement of both stability as well as patellar tracking. There can be a wide range of external rotation error when using the anteroposterior axis as a determinant of femoral, component rotation.

[16] Another technique currently used with femoral component rotation is a gap balancing methodology, in which the femoral component is positioned parallel to the resected proximal tibia with each collateral ligament equally tensioned. Comparisons have bee made in outcomes betwee use of ga balancing techniques and measured resection techniques using bone landmarks as the primary references to achieve femoral component rotation. There are studies which identified rotational errors of at least 3° occurring in. 45% of patients when rotation was determined from fixed bony landmarks. Anatomic bony landmarks (measured resection) are used in determining rotation of the femoral component. Gap balancing can also be used.

[17] Wide variations in femoral component position have been observed with use of both the posterior condylar axis and anteroposterior axis. When the posterior condylar axis was used, the femoral component was positioned at a mean, of 0.4° internally rotated as compared with gap balancing (range, 15° internal to 13° of external rotation). Gap-balancing methods when used demonstrate a significantly lower incidence and magnitude of femoral condylar lift-off. This indicates the superiority of the use of the gap-balancing technique in obtaining a balanced flexion gap. Statistically, the gap balancing technique provides a more accurate and reproducible way to obtai satisfactory flexion gap stability.

[18] Although there are multiple methods which currently may be used to determine correct femoral component rotation during T A, surgeons still experience difficulty in accurately determining correct femoral rotation and also in precise identification of critical bone landmarks when deciding correct femoral component rotation using a measured resection methodology. INVENTION

[1.9] The present invention provides improvements in Patient Matched Guides (PMG) used in surgery such as in knee arthroplasty. The invention further provides a modified PMG used i knee surgery which allows a surgeon to make intra -operative measurements and assessments related to planned resections and to enable verification of resections. The present invention also provides a modified PMG which is capable of use for measurements intra-operatively to allow validation of pre planned resections.

[20] Although the assembly will primarily be described with reference to its application to tools for accurate setting of knee prostheses, it will be appreciated by persons skilled in the art that the arrangements to be described may be applied in other circumstances where intra operative measurement verification of PMG placement is required. Such applications would include verification of PMG placement in Hip replacement and shoulder replacement and spine instrumentation. [21] In its broadest form the present, invention provides: a patient matched cutting guide which is arranged to guide a user to resect bone at predetermined positions during a surgical procedure, the guide including formations which engage bone parts to locate the guide such that othe parts of the guide align widi planned resection planes; characterised in that the cutting guide includes specifically placed, spatially orientated indicators which enable verification of resection locations intra- operatively based on measurements between at least one known reference on the cutting guide and the underlying bone to thereby allow verification of the planned resection planes. [22] In another broad form the present in ention comprises

a patient matched cutting guide which is arranged to guide a user to resect femoral bone at predetermined positions during a total knee replacement, the guide including formations which engage bone parts to locate the guide such that other parts of the guide align with planned resection planes; characterised in that the cuttin guide includes specifically placed, spatially orientated indicators which enable verification of resection locations intra- operatively based on measurements between at least one known reference on the cutting guide and the underlying bone to thereby allow verification of the planned resection planes.

[23] The known cutting guide includes free end formations which when placed in position o a patient's knee provide a guide to resectio locations on the condylar surfaces of the distal femur and proximal tibia. According to the present invention a known patient matched guide is specifically modified to enable its use as a measurement instrument or ruler to enable intra-op rative assessment and measurement between reference points to verify predetermined or planned resection locations. The measurements are conducted with reference to indicia included on the guide which are referable to fixed locations on the cutting guide.

[24] In another broad form the present invention comprises a patient matched guide for use i knee arthroplasty which allows determination of resection locations on bone: characterised in that the guide has indicia or formation located on the guide which allows a secondary function of verification of the accuracy of resection locations initially determined by the guid when the guide is placed in a predetermined location on the bone. According to one embodiment the modification to a patient matched guide comprises in the guide body any one of the following indicators; a hole, notch, marking, groove,, indent, V shape, slit, number, letter, alpha numeric combination, opening numeric gradations, additional formations.

[25] According to one embodiment, there is provided a patient matched cutting guide which allows assessment of the accuracy of placement of the cutting guide by assessing a fixed spatial relationship between a formation and an identifiable reference point on the bone. According to this embodiment, there is provided an additional instrument that interfaces between the cutting guide formation and a known bone reference point. The instrument demonstrates a correct relationship between this formation and the bone reference point (the assessment), enabling an assumption or assessment that the cutting guide was correctiy placed. This arrangement enables a detennination of a correct relationship between the cutting guide and the underlying patient bone. [26] According to a preferred embodiment the indicators enable validation of resectio position using the difference between a first distance from a fixed point on the cutting guide to a position of the distal femoral resection slot and a distance from the fixed point to a most distal part of the medial or lateral distal femoral condyles.

[27] According to a preferred embodiment a known resection guide is adapted with an indicator which relates to a fixed point and a distance from that fixed point to a resection slot. A measured distance from point P to a most distal part of the femur allows a determinatio of a resection distance. The modified guide is identified by an indicator or the like which identifies that they have been manufactured to allow for mtra-operative validation of the planned resections. Using a modified cutting guide a surgeon can elect to intra-operatively validate the pre operative, pre planned femoral and tibial resections. [28] In its broadest form the present invention comprises; a modified patient specific cutting guide used to determine bone resection planes in a tibia or femur characterised in that the guide includes indicators which allow measurements of a first distance between a known reference point o the cutting guide and a second location on the guide, a second distance between the first reference point and the difference between the first and second distance to verify a resection depth of cut in either the proximal tibia or distal femur.

[29] n another broad form the present invention comprises; a patient matched guide for verification of bone resection locations on a proximal tibia during a knee joint replacement, the guide including a designated first known reference point from which can be measured a .first known distance to either a second reference point on the guide or to an anatomical bone reference point, a second measurabl distance taken from the first known reference point to a tibial plateau; the first and second distances allowing a deduction of a third distance comprising tibia! resection plane depth from the tibial plateau. According to a preferred embodiment the above verification regime is applicable to different locations on the proximal tibia. [30] The present invention provides an alternative to the known prior art and the shortcomings identified. The foregoing and other objects and advantages will appear from the description to follow. In the description reference is made to the accompanying representations, which forms a part hereof, and in which is shown by way of iUusttation specific embodiments in which the invention may be practiced. These embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilised and that staictural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[31] The present invention will be now described according to a preferred but non limiting embodiment and with reference to the accompanying illustrations wherein:

Figure la,b,c shows a schematic view of the principle applied in calculation of a resection depth with reference to a distal femur.

Figure Id shows a schematic view of a three dimensional validation geometry for resection depths.

Figure le shows a lateral elevation view of a proximal tibia with a patient specific cutting guide applied to the front of the tibia.

Figure 2 shows the resection guide of figure 1 e with measurements included.

Figure 3 shows the resection guide of figure le misaligned according to one orientation.

Figure 4a shows the resection guide of figure le misaligned according to an

alternative orientation.

Figure 4b shows a lateral view of a proximal tibia with a Tibial Patient Specific

Guid instrument applied to the front of the tibia and the additional instrument is applied to interface between measurement point and superior aspect of tibia having narrow contact. Figure 4c shows a lateral view of a proximal tibia wit a Tibial Patient Specific Guide instrument applied to the front of the tibia and the additional instrument is applied to interface between measurement point and superior aspect of tibia having broader contact.

Figure 4d shows a coronal view of a right tibia with a tibial mstmment having a verification point applied to the distal tibia.

Figure 5 shows a side elevation of a resection guide for a distal femur indicating a first distance from a first known location on the guide to a second location on the guide.

Figure 6 shows the resection guide for a distal femur of figure 5 indicating a second distance from the first location to the distal femur.

Figure 7 shows the resection guide for a distal femur of figure 5 indicating a distance which is the difference between the first and second distances.

Figure 8 shows a side elevation of a resection guide for a distal femur indicating a first distance from a first known location on the guide to a second anatomical location on the femur.

Figure 9 shows the resection guide for a distal femur of figure 8 indicating a second distance from the fust location to a second location on the proxim l femur.

Figure 1 shows the resection guid for a distal femur of figure 8 indicating a third distance which is the difference between the first and second distances.

Figure Π shows a front elevation view of a distal femur and resection guide viewed ax tally to reveal the posterior femoral condyles to be resected.

Figure 12 shows a front elevation view of the distal femur and resection guide of figure 11 for the opposite condyle viewed axially to reveal the posterior femoral condyle to be resected.

Figure 12a shows an axial view of the distal femur. The femoral instrument is

placed incorrectly on femur to demonstrate the changed position {malposition) of the posterior measurement points on the posterior femur. Figure 13 shows an elevation view of a distal femur including a patient matched guide and an additional verification, instrument.

Figure 14 Shows a coronal view of the right hip. The figure demonstrates the applicability of this technology to validation of correct placement of a hip PMG -V. in this case, the SG captures the rim of the acetabulum.

Figure 15 shows a sagittal view of the spine. A Patient Matched Guide is seen placed between spinous processes.

DETAILED DESCRIPTION

[32] For any joint prosthesis replacement including the knee to function optimally 4 vectors need to be considered in the design to return the joint position in space to as normal as possible a natural position. The tour vectors are;

1 medial- lateral

2 anterior - posterior

3 rotational

4 vertical (height).

[33] in the known art of knee replacement one method for implanting employs a patient specific guide which is prepared by computer aided design once patient parameters are known from pre operative imaging. The guide is provided with a model of femoral bone anatomy for a particular patient. Once the guide is manufactured from imaging provided to the manufacturer, it has contours which enable it to locate in one correct position on the distal femur thereb allowing the surgeon to make the condyle cuts dictated by the guide. However, the guide is initially provided with a model of the patients distal femur but it must be placed on the patient's actual distal femur which may be different from the model due to such factors as soft tissue or bone changes during the period between initial imaging and the time the operation is done. The objective is to make sure that the resections occur in accordance with the pre operative plan. Once the guide is placed on the patient's knee in the required location the surgeon needs to be sure that the guide will in fact guide the surgeon to make the cuts in accord with the pre operative plan. A surgeon can elect to rely completely on the guide without an further verification or elect to rely on the verification regime described herein. Once the guide is in place the surgeon applies the verification with reference to indicators on the guide. With the guide located on a patient's bone and when the surgeon is satisfied that the guide is in its required position, the guide is stabilised to the bone with pins, screws or wires. The surgeon then uses the guide to makes the cuts.

[34] The present invention provides a further option for the surgeon to verify resection locations. More specifically it provides an intra operative method using the customised patient matched guides which enable verification of bone resections and soft tissue balance before the bone resections are performed to ensure as close as possible simulation of the planned resection levels for that patient's anatomy. The present invention according to a preferred embodiment provides a modified patient matched re section guide which includes indicating references which allows a user to validate the accuracy of a position of the guide on the tibia and femur, prior to any bone resection. [35] Despite measures that aim for the greatest degree of accuracy when manufacturing PMI resection guides, there is no guarantee the surgeon's actual femoral and tibial resections will be always aligned with a preoperative plan.

PMI accuracy is subject to

1. Image quality

2. Patient factors

3. MRI or CT quality factors

4. Technician interpretation of the 3D imagi ng

5. Software programming issues

6. Design of the PSI

7. Suitability of anatomy to accurately stabilise the PMI

8. Surgeon factors

[36] Accuracy of resection locations with planned resections can be improved by Intr-operative validation of bone resections prior to actual hone resection. Validation of soft tissue balance prior to definiti ve femoral resection allows for greater flexibility in surgical options, with the potential reduction i adverse outcome.

[37] Validation of bone re sectio establishes that hone cuts are made in the location planned pre operatively. In one form the present invention provides a kit comprising patient matched cutting guide with a location, indicator, formation or other guide part marked thereon to enable intra-operative measurements relative to known points and relative to patient anatomy. The primary function of the existing femoral and tibial instruments is to guide bone resections but there is currently no means to intra-operatively validate these planned PMI resections, unless a parallel verification system is simultaneously used (eg navigation). It is one object of the present invention to provide PM instruments with a measuring capacity which is ancillary to a primary alignment function and which allows intra -operative validation of the point of bone resections prior to resections performed.

PRINCIPLE OF OPERATION

[38] The us of the patient matched guide for verification of resection is based on the following principles which are described with reference to figures 1 (a), (b) and (c) which schematically depict a distal femur and Figure 1(d).

[39] Figures 1 (a), (b) and (c) shows the first principle of this IP (two dimensional validation). A lateral view of the distal femur. If AC is known (part of the manufacturing specifications of the instrument) and AB can be directly measured , then BC can be calculated. The distance AB can be measured directly (eg with a depth gauge). For example, the depth of resection of the distal femur may be calculated, if the distance between the measurement point and the manufacture depth of resection is 20mm, and the distance between the measurement point and the underlying distal femoral condyle is 12mm. then the calculated depth of resection is calculated as 8mm. This principle particularly applies to distal femoral resection and proximal tibial resection. This principle is used in most of the femoral and tibial resections. For example, when performing distal femoral resections, AC is the known distance from a fixed point on the cutting guide (the measurement point, "P") to the position of the distal femora! resection slot. AB is the distance measured between the measurement point "P" and the most distal part of the medial or lateral distal femoral condyles, BC is the difference between these two measurements (the actual depth of bone resection).

[40] Figure i(d ) shows the second principle of the three dimensional validation. If there is a known spatial, relationship between Points A and B and between points B and C, then the three dimensional spatial relationship between Points C and A can be inferred and is known. For example, if an identified point in the proximal tibia (Point A) has known A ^χ,γ,ζ co-ordinates, and the relationship to a fixed Point B (B χ.ν,ζ coordinates) on the distal tibia (eg medial malleolus) is known by preoperative three dimensional imaging and the relationship between Points B and Points C on tibial instrument applied to the proximal tibia is known and can be validated by intraoperative direct measurement, then the relationship between the instrument (Point C) and proximal tibial bone can be validated. The correct placement of the tibial instrument on the proximal tibia in all planes can be inferred. This means that the instrument placement on proximal tibia can be validated in the axial, coronal and sagittal planes. Changes to Tibial and Femoral Instruments

[41 ] In order to be able to validate the tibial and femoral resections, there is provided a modification of the Patient Matched Technology customised instruments. According to a preferred embodiment measurement points are manufactured at precise locations for both femora! and tibial instruments. The instruments are manufactured so a surgeon can use them as rulers or measurement devices (their "secondary function).

Posterior Tibial Slope

[42] Figure le shows an elevation view of a patient matched tibial resection guide 3 mounted on a proximal tibia 2, The posterior tibial slope 3 is usually assessed by comparing the projected PMI resection slope, to the native or constitutional posterior tibial (sagittal) slope. This comparison to native slope, allows only for a subjective assessment of accuracy of the planned posterior slope. The posterior tibial slope can be objectively assessed against the planned posterior tibial slope by using a customised tibial guide 1 and a standard depth gauge 4. The measurement points shown, (P i, P3) are a pan of the manufactured tibial instrument and are positioned over the anterior and posterior aspects 5, 6 respectively of the referenced tibi al pl ateau 7. Measurement points 1 and 3, are used to validate the posterior tibial slope. The distance from PI and P3 to the upper part of the existing (arthritic) tibial bone is planned to a specific distance. For convenience, this distance (Ml and M3) is be assigned to the depth of resection planned for this particular tibial plateau 7. Figure 2 shows with corresponding numbering the resection guide 1 of figure 1 with actual measurements (8mm) included for distances Ml and M3. 8mm is a planned resection from the medial tibial plateau then Ml and M3 can be manufactured to a distance of 8mm. If this distance has a measuremen that is the same as planned, then the assigned posterior slope is validated as accurate.

Proximal tibial resection depth

[43] Figure 1 is shown with marks A, B and C. The distance AC is known. This is the distance between the top of the instrument (to be known as measurement point , "P"), and the tibial resection slot 9 on the lower part of the tibial instrument 1. The distance AB, is a measured distance between the measurement point, P, and the actual tibial bone plateau 7. This AB distance is measured on both medial and lateral tibial plateaus. The amount of bone to be resected is reflected by the distance BC, This distance is the calculated difference in length between the total distance AC and the measured distance BC. For example, if AC = 30mm, and AB is measured as 20mm, then the calculated bone resection from proximal tibia is 10mm. Guide I includes locating formations 1 1 and 12 which when the guide is set in position, conform to patient bone anatomy for the purpose of setting the guide 1 and measurement "formation ' points PI and P3.

Tibial instrument

[44] Referring to figure 2 if the pre-surgical plan is to remove 8mm from the proximal medial tibial plateau and 10mm from the lateral tibial plateau, then the distance from measurement point MP2, to bone will be arbitrarily assigned distances of 8mm and 1.0mm respectively. This means that the medial MP2 measurement point will be 16 mm above the resection level and the lateral MP2 measurement point will be 20mm above the lateral resection level and that validation of the depth and coronal slope of proximal tibial resection will b made when the depth gauge measurements are confirmed as 8mm medially and lOmrn laterally. In addition to validating the tibia! resection depth, depth gauge measurement will also confirm correct posterior slope, because the instrument has been manufactured with, a 3° slope and measurement point @8mm from registered tibial bone at that point if both measurements are not concordant, the the assigned posterior slope is not validated and may be changed prior to definitive correction.

[45] if the tibial instrument 1 is not placed according to plan, there will not be concordance i measurement of M l and M3 distances. Figure 3 shows with corresponding numbering the resection guide of figure le misaligned according to one incorrect orientation where M3 is grater than ML Figure 4a shows the resection guide 1 of figure J e misaligned according to an alternative orientatio where Ml is greater than M3. Figure 4b shows a lateral view of proximal tibia 40. The Tibial Patient Specific Guide instrument 41 is applied to the front of the tibia 40 and the additional instrument is applied to interface between measurement point and superior aspect of tibia. This may have narrow contact at point 42 (see Figure 4b) or broader contact at point 43 (see Figure 4c). Figure 4d shows a coronal view of a right tibia 44 with a tibial instrument 45 having a verification point applied to the distal tibia. The pre-operative imaging will allow the construction of an interface between the subcutaneous medial (or lateral) malleolus and the tibial PSG instrument, if the tibial instrument is accurately placed on bone, then tibial instrument rotation, varus / valgus and posterior slope will be validated. If there is a known spatial relationshi between Points A and B and between points B and C, then the three dimensional spatial relationship between Points C and A can be interred and is known. [46] Tills figure highlights the practical approach to validation of depth of resection proximal tibia. Principle of the schematic of figure 1 is applied. A stylus or measurement tool interfaces between bone and tibia PMG. The measurement tool will allow a direct assessment of depth of resection from a known point on the tibial surface. When a broad interface to proximal tibial is applied (4c). then slope and varus valgus may be assessed. The coronal plane varus, valgus may also be assessed by independently measuring each tibial plateau. The preferred option for varus / valgus and posterior slope assessment is via the medial malleolus (see Fig 7 below) Proximal tibia varus / valgus

[47] An. accurate assessment of the proximal tibia varus / valgus is .important for overall coronal alignment and for flexion and extension stability. If the amount of bone to be resected from the proximal tibial plateaus is known (see above regime) and there has been a pre-operative assessment of proximal tibial coronal plane varus / valgus, then the coronal alignment of the proximal tibia is now known.

Distal Femoral Resection (incl. varus / valgus).

Femoral instrument

[48] The femoral instrument includes manufactured measurement points to validate distal femoral resection, (including distal femoral varus valgus) and posterior condylar resection (including femoral rotation). The measured distance between distal, femoral measurement points and bone are assigned the same measurement distance as the planned distal femoral bone resections. For example, if the planned distal femora medial bone resection is for 8mm and the distal femoral lateral bone resection is 10mm, then the manufactured distance between measurement points and level of resection is 16mm and 20mm respectively. If the amount of bone resected from the distal femur is known and the pre-operative distal femoral varus valgus has been assessed, then the post resection distal femoral slope is known.

[49] Figure 5 shows a side elevation of a resection guide 20 for a distal femur 21 indicating a first distance 22 from a first known location 23 on the guide to a second location 24 on the guide 20 designated as distance AC. Figure 6 shows the resection guide 20 for the distal femur 21 of figure 5 indicating a second distance 25 from the second location 24 to a distal femur location 26. Distance 25 is indicated as distance BC. Figure 1 shows the resection guide 20 of figure 5 indicating a distance 27 which is the difference between the first distance 22 and second distance 25. [50] The distance 22 (AC) is known as it is a manufacturing measurement). The distance 25 (BC) ca be measured for each of the distal femoral condyles. The amount of bone to be resected - distance 27 (AB) can be deduced, if the amount of bone to be resected from each distal femoral condyle is confirmed and the distal femoral angle is known pre-operati ely, then the distal femoral angle post resection will also be known,

Posterior Femoral Resection and Femoral Rotation [51 ] Referring to figures 8.-10, the distance BC is known (manufacturing measurement), and the distance AC can be measured. The amount of each posterior femoral condyle can be deduced. The amount of bone resected from each posterior femoral condyle will determine the amount of femoral rotation. The femoral resection depth, alignment, including femoral rotation have now been validated.

[52] Figure 8 shows a side elevation of a resection guide 30 for a distal femur 2.1 indicating a first distance 31 from a first known location 32 on the guide 30 to a second location 33 on the distal femur and specifically to posterior condyle 35. Figure 9 shows the resection guide 30 for a distal femur of figure 8 indicating a second distance 36 from the first known location 32 to an anatomical location 37 on the proximal femur 21. Figure 10 shows the resection guide 30 for a distal femur 21 of figure 8 indicating a third distance 38 taken from location 37 to location 39 which is the difference between the first distance 3 and second distance 36. Validation pads can be placed in situ.

Posterior condylar resectio

[53] Figure 11 shows a front elevation axial view of a distal femur and resection guide 30 of figure 8 viewed axially to reveal the posterior femoral condyles to be resected.

[54] Figur 12 shows a front elevation view of the distal femu and resection guide of figure 1 1 for the opposite condyle viewed axially to reveal the posterior femoral condyle to be resected. The femoral instrument guide 30 is placed o the distal femur with location pads (P5-P6) interfacing with specific bone points, Measurement points may be assigned distal !y and posteriorly (or at other points) to verify correct placement of instrument. The distal femoral resection may be validated through points P3, P4, the posterior resection and femoral rotation can be made through P5, P6. An assessmen of femoral component position may also be made through P 1 , P2,

[55] Figure 1.2a shows an axial view of the distal femur. The femoral instrument is placed incorrectly on femur to demonstrate the changed position (mal-position) of the posterior measurement points on the posterior femur. The femoral instrument is placed incorrectly on femur to demonstrate the changed position (mal-position) of the posterior measurement points on the posterior femur, in this view the posterior pads (P5, P6) are translated from the posterior femoral bone.

[56] The posterior condylar validation requires a measurement from the anterior measurement pomt(s) to the point on the most posterior part of the posterior femoral condyle, (see figures 8-10). This poin is identified on the femoral model and is usually symmetrically placed on the posterior aspec of the femoral condyle. The technique does require a 3.2mm drill hole to allow the passage of the depth gauge 40. The exit point of the drill should correspond with the identified point on the nylon femoral model. The posterior condylar resection equals the difference between the measured distance BC ( see figure 11) and the known distance AC between anterior measurement point and the level of resection, if the amount of bone resected from each posterior femoral condyle is known, then change in femoral rotation can be determined. This ca be validated against the pre-operative plan.

[57] Figure 13 shows an elevation view of a distal femur 50 including a patient matched guide 51 mounted thereon. Patient matched guide 51 is used as per earlier descriptions for verification of resections locations. According to a further embodiment, there is provided a patient matched cutting guide which allows assessment of the accuracy of placement of the cutting guide 51 by assessing a fixed spatial relationship between a formation and an identifiable reference point on. the bone. According to this embodiment, there is provided an additional instrument 52 that interfaces between the cutting guide formation 53 and a known bone reference point 54. The instrument 52 demonstrates a correct relationship between this formation S3 and the bone reference point 54 (the assessment), enabling an assumptio or assessment that the cutting guide 51 was correctly placed. This arrangement enables a determination of a correct relationship between the cutting guide 5 ] and the underlying patient bone.

[58] Figure 14 Shows a coronal view of the right hip. The drawing demonstrates the applicability of this technology to vahdation of correct placement of a hi PMG-V. In this ease, the SG captures the rim of the acetabulum. The validation host bone is the fovea of the acetabulum. Depth of acetabular reaming can be validated by distance reamed from the fixed acetabular PSG-V7

[59] Figure 15 shows a sagittal view of the spine. A Patient Matched Guide is seen placed between spinous processes. Accuracy of position of this PMG can be validated against adjacent bone (eg base of pedicles).

[60] it will be recognised by persons skilled in the art that numerous variations and modifications may be made to the invention broadly described herein without departing from the overall spirit and scope of the invention.

Claims

THE CLAIMS DEFINING THE IN VENTION ARE AS FOLLOWS:

1. A patient matched cutting guide which is arranged to guide a user to resect bone at predetermined positions during a surgical procedure, the guide including formations which engage bone parts to locate the guide such that other parts of the guide align with planned resection planes; characterised in that the cutting guide includes specifically placed, spatially orientated indicators which enable verification of resection locations intra- operatively based on measurements between at least one known reference on the cutting guide and the underlying bone to thereb allow verification of the planned resection planes.

2, A cutting guide according to claim 1 wherein the guide comprises a generally L shaped body.

3. A cutting guide according to claim 2 including a first leg which terminates in free ends each having formations arranged to conform to an adjacent bone contour .

4. A cutting guide according to claim 3 including a second leg which terminates in free ends each having formations arranged to conform to a bone contour adjacent one said free ends.

5. A cutting guide according to claim 4 wherein the second leg includes an integral cutting slot which aligns with a re section plane through said bone.

6. A cutting guide according to claim 5 furthe comprising a predetermined first distance AC measured from a first known proximal locatio on the guide to a second location on the guide which aligns with a cutting slot.

7. A cutting guide according to claim 6 further comprising a second distance BC measured from the first known proximal location on the guide to a second location at an extremity of the bone.

A cutting guide according to claim 7 further comprising third distance AB hich represents a difference between the first distance AC and second distance BC and which provides a cutting depth from the distal extremity of the femur and to a cutting plane.

9. A cutting guide according to claim 8 wherein the first distance measured from the first known proximal location on the guide to the second location is a manufacturing measurement provided on the guide.

I.0. A cutting guide according to claim 9 wherein a distance measured from a second free end of the first leg of the cu tting guide to the cutting slot provides a fourth distance.

I I. A cutting guide according to claim 10 wherein the free end formations are each retained on inwardly directed return members which extend between one of said legs of the guide and terminate in said formations.

12. A cutting guide according to claim 11 wherein there are four return members on the cutting guide which each engage via the free end formations bone locations which are specific to a particular patient cutting guide.

13. A cutting guide according to claim 12 wherein each said free end formations indi idually conform to a bone location at which each free end locates.

14, A cutting guide according to claim 13 wherein the cutting guide matched to a particular patient is specifically modified to enable its use as a measurement instrument or ruler to enable intra-operative assessment and measurement between reference points to verify predetermined or planned resection locations.

15. A cutting guide according to claim. 14 wherein the guide includes any one of the following indicators; a hole, notch, marking, groove, indent, V shape, slit, number, letter, alpha numeric combination, opening numeric gradations, formations.

16. A cutting guide according to claim 15 wherein the bone is a distal femur.

17. A cutting guide according to claim 16 wherein the free ends of one leg engage a distal end of the femur

18. A cutting guide according to claim 17 wherein the free ends of the second leg of the cutting guide engage a posterior bone contour of a the distal femur,

19. A cutting guide according to claim 18 wherein the second distance BC is measured from a distal end of a first of two femoral condyles.

20. A cutting guide according to claim 19 wherein the second distance BC is measured from a distal end of a secon d o f the two femoral condyles.

21. A cutting guide according to claim 20 wherein a first cutting distance for one of the femoral condyles taken from said first location on t!ie guide is different from the second cutting distance for second femoral condyle.

22. A cutting guide according to claim 21 wherein the free ends of the first leg of the cutting guide are spaced apart so that one end engages one said condyles and the other end engages the other condyle.

23. A cutting guide according to claim 22 wherein measurements are enabled with reference to indicia included on the guide are referable to fixed locations on the cutting guide.

24. A cutting guide according to claim 22 wherein the guide enables detemiination of the amount of bone to be resected from each distal femoral condyle .

25. A cutting guide according to claim 24 wherein the guide enables determination of a distal femoral, angle post resection for matching with a distal femoral angle known pre-operatively.

26. A patient matched cutting guide for use in bone surgery and which allows verification of resection locations on bone; characterised in that the guide has indicia or formations located on the guide which allows a secondary function of verification of the accuracy of resection locations initi all y determined by the guide when the guide is placed in a predetermined, location on the bone.

27. A patient matched cutting guide according to claim 26 wherein the guide includes any one of the following indicators; a hole, notch, marking, groove, indent,

V shape, slit, number, letter, alpha numeric combination, opening numeric gradations, formations .

28. A patient matched cutting guide according to claim 27 wherein the indicators enable validation of resection position using the difference between a first distance from a fixed point on the cutting guide to a position of the distal femoral resection slot and a distance from the fixed point to a most distal part of d e medial or lateral distal femoral condyles.

29. A patient matched cutting guide which allows assessment of the accuracy of placement of the cutting guide by assessing a fixed spatial relationship between a formation and at least one identifiable reference point on the bone.

30. A patient matched cutting guide according to claim 29 wherein there is provided an additional instrument that interfaces between the cutting guide formation and known bone reference point.

31. A patient matched cutting guide according to claim 30 wherein the instrument demonstrates a correct relationship between this formation and the bone reference point, enabling an assessment that tire cutting guide was correctly placed, thereby enabling a determination of a correct relationship between the cutting guide and the underlying patient bone.

32. A modified patient specific cutting guide used to determine bone resection planes in a bone during surgery; characterised in that the guide includes indicators which allow measurements of a first distance between a known reference point, on the cutting guide and a second location on the guide, a second distance between the first reference point and the difference between the first and second distance to verify a resection depth of cut in the bone.

33. A cutting guide according to claim 32 wherein the bone in which a cut is made is a femur, tibia, hip or spine.

34. A patient matched resection guide for verification of bone resection locations on a proximal tibia during a knee joint replacement, the guide including a designated first known reference point from which can be measured a first, known distance to either a second reference point o the guide or to an anatomical bone reference point, a second measurable distance taken from the first known reference point to a tibial plateau; the first and second distances allowing a deduction of a third distance comprising tibial resection plane depth from the tibial plateau. According to a preferred embodiment the above verification regime is applicable to different locations on the proximal tibia.

35. A patient matched resection guide according to claim 33 wherein the guide is adapted with an indicator which relates to a fixed point and a distance from that fixed point to a resection slot.

36, A patient matched resection guide according to claim 35 wherein a measured distance from point P to a most distal part of the tibia allows a determination of a resection distance.

37. A kit comprising a patient matched cutting guide with, a location marked thereon to enable intra-operative measurements relative to known points and relative to patient anatomy to determine cutting planes.