Patent Description:
The present disclosure relates generally to patient specific instrumentation (PSI) to suit a specific patient's anatomy used in orthopedic surgical applications, and more particularly to PSI devices and/or implants which are created based on patient specific bone models produced from X-rays.

Improvements in the design, creation and use of patient specific instrumentation and/or implants (PSI) continue to be sought. PSI devices are purpose designed to suit a specific patient's anatomy. In the context of orthopedic surgical applications, this is most commonly accomplished by first generating a digitized bone model of the specific patient's bone based on images produced from a Magnetic Resonance Imaging (MRI) scan of the patient's anatomy. MRI scans are most often used because they offer precise imaging of the anatomical features of the patient, including bone, cartilage and other soft tissue, which enables the creation of an accurate patient-specific digitized bone model. This bone model can then be used to create PSI devices. <CIT> describes an adjustable guide which is adjustable to the anatomy of many patients but is not a patient specific instrument which suits a specific patient's anatomy and is not created from a digital bone model.

In accordance with the present invention, there is provided a method of creating a patient specific instrument to suit a specific patient's anatomy for use in knee replacement surgery, the method comprising: performing at least two X-ray scans of one or more bones, each of the X-ray scans being taken from different angular positions; generating a digital bone model of said one or more bones based solely on the X-ray scans; planning the patient specific instrument based on the digital bone model, including determining locations for one or more anchor points on the patient specific instrument which are adapted to abut a surface of said one or more bones, the determined locations of the one or more anchor points being disposed on the patient specific instrument corresponding to areas of expected high accuracy on the digital bone model generated by the X-ray scans, said areas of expected high accuracy including at least a peripheral bone contour in at least one of said angular positions; and creating the planned patient specific instrument having said one or more anchor points thereon.

In accordance with the present invention, there is provided a patient specific instrument to suit a specific patient's anatomy for positioning a resection cutting block on a bone during orthopedic knee replacement surgery, the patient specific instrument being created based on a digital bone model generated solely using at least two X-ray scans taken from different angular positions, the patient specific instrument comprising: a body having a pair of pin guide holes extending therethrough, the pin guide holes adapted to receive bone pins used to fasten the resection cutting block to the bone; and one or more anchor elements on the body adapted to abut one or more surfaces of the bone, the anchor elements being disposed in locations on the body of the patient specific instrument overlying a peripheral bone contour of the bone in at least one of the X-ray scans, said locations and the peripheral bone contour corresponding to areas of expected high accuracy on the digital bone model generated by the two-dimensional X-ray scans.

There is also described a method of positioning bone pins for mounting a resection cutting block on a bone during orthopedic knee replacement surgery, including: obtaining at least two X-ray scans of the bone taken from different angular positions, and a digital bone model of the bone based solely on said X-ray scans; using a patient specific instrument designed based on the digital bone model, the patient specific instrument having one or more anchor points thereon which are adapted to abut a surface of the bone, the anchor points being disposed on the patient specific instrument at locations corresponding to areas of expected high accuracy on the digital bone model generated by the X-ray scans, said areas of expected high accuracy including at least a peripheral bone contour in at least one of said angular positions; engaging the patient specific instrument to the bone by abutting the anchor points against the bone; angularly adjusting the patient specific instrument in at least one of varus-valgus, flexion-extension, and rotation, in order to position the patient specific instrument in a predetermined position and orientation; and inserting the bone pins through corresponding pin holes extending the a body of the patient specific instrument.

Patient specific instrumentation/instruments/implants (collectively "PSI" as used herein) are purpose designed to suit a specific patient's anatomy, based on a digitized bone model of the anatomy in question. Such PSI devices are most commonly created based on digital bone models that are generated using Magnetic Resonance Imaging (MRI) images of the bone(s) and surrounding soft tissue (e.g. cartilage). MRI scans have to date been largely preferred for the creation of such PSI devices, due to the fact that the MRI scan images are capable of depicting cartilage as well as the bone, thereby ensuring the accuracy of the resulting surgery performed using the PSI device thus produced. However, such MRI scans are both costly and time consuming to conduct.

Accordingly, the present inventors have developed a suite of patient specific surgical implements particularly adapted for use in conducting knee replacement surgery (such as total knee replacement (TKR)), which are specifically designed to be created based on a digital bone model generated only using X-rays taken of the patient's bone(s).

Thus, the presently described system and method enables the creation and use of PSI components for knee surgery which are designed and created using a digital bone model generated using only two-dimensional (2D) X-ray images of the specific patient's bone(s). This enables the PSI components described herein to be created quickly and in a more cost effective manner than with known prior art systems and methods, which require the use of MRI scans to produce the digital bone models.

In accordance with a general aspect of the present disclosure, therefore, a patient specific digital bone model is first created using only X-ray scan images (i.e. no MRI scans are required), so as to digitally reconstruct the bone in a surgical planning computer program and/or a computer assisted surgery (CAS) system. At least two or more X-ray images are required of the patient's bone or bones, which must be taken from different angular positions (e.g. one lateral X-ray and one frontal or anterior X-ray). While one X-ray image may be insufficient, more than two X-ray images may alternately be used. Generally, the greater the number of X-ray scans taken from different angular positions (e.g. lateral, medial, anterior, posterior, etc.), the greater the resulting accuracy of the digital bone model created therefrom. However, the desired accuracy has been found to be obtainable when only two X-rays are taken from perpendicularly disposed angular positions (e.g. lateral and frontal/anterior).

Once a digital bone model is created using the surgical planning computer program and/or CAS system, using only the two or more X-ray images of the bone(s) of the specific patient, a PSI surgical component as described herein is then designed using the CAS system as will be described, and then subsequently created specifically for the patient, using the digital bone model of the patient's anatomy created based only on the X-ray images. The PSI components as described herein may therefore be created, once they have been planned/designed to fit with the digital bone model, out of any suitable material, but these may include plastics or metals which are suitable for use in surgical applications. Ideally, these PSI components are produced rapidly and on site, using an additive manufacturing process such as <NUM>-D printing.

While X-rays are typically perceived as being less precise than MRI images, the present method and system can nevertheless be used to create PSI components which are specially adapted to be formed based on a digitized patient bone model generated using only X-ray images. Thus PSI devices, tool and/or instruments described herein may accordingly be designed and created more time and cost effectively.

As will be seen, because an X-ray generated digital bone model is being used, standard surgical tools, and even previously developed standard patient-specific tools, cannot be readily used. This is because patient specific tools developed based on MRI-generated bone models can be designed knowing precisely where any cartilage and other soft tissue is located. As this is not the case for bone models generated using only X-rays images, any PSI component which is doing to be designed based on such X-ray bone models must be configured in such a way as to maximize the accuracy of the component and more specifically its mounting points with the actual bone, in order to ensure that the end surgical result when this component is used is acceptable.

The presently described PSI components, which are produced based solely on X-ray generated digital bone models, therefore include one or more anchor points thereon that are adapted to abut and/or otherwise engage a surface of the bone and that are disposed on the PSI component at one or more locations corresponding to areas of expected high accuracy on the digital bone model generated by the X-ray scans. These areas of expected high accuracy on the digital bone model will generally correspond to points on a peripheral bone contour in at least one of the angular positions from which an X-ray image is taken. For example, if a frontal, or anterior, X-ray has been taken of the bone, the medial, lateral and proximal outer peripheral contours of the bone will be very accurate in the X-ray image and thus in the resulting digital bone model created thereby. As a result, points on the bone model which are disposed along these medial, lateral and/or proximal peripheral contours of the digital bone model will be areas of expected high accuracy, even if the X-ray image is not capable of revealing any cartilage present. Similarly, if a lateral X-ray has been taken of the bone, the anterior, distal and/or proximal outer peripheral contours of the bone will be very accurate in the X-ray image, and thus in the resulting digital bone model created thereby. As a result, points on the bone model which are substantially disposed along these anterior, distal and proximal outer peripheral contours of the digital bone model will be areas of expected high accuracy, even if the X-ray image is not capable of revealing any cartilage present. Thus, by positioning any anchor or mounting elements of a PSI component in locations on the PSI component which correspond to these areas of expected high accuracy on the X-ray generated bone model, the PSI component so designed is particularly adapted for use without any appreciable loss in accuracy.

The term "anchor", "anchor elements" or "anchor points" as used herein is understood to mean points on the PSI component which engage the bone when the PSI component is mounted thereto, whether this be simply by abutting the bone without being directly fixed thereto (e.g. a bone spike, blade or jack screw which rests on the outer surface of the bone) or by being fastened (e.g. by a pin, bone screw, etc. which penetrates into the bone for rigid fastening thereto). The term "anchor" as used herein therefore does not necessarily imply rigid fastening by penetration of the bone, but rather such anchors fix the PSI component in place on the bone such that relative movement therebetween is not readily possible.

Referring now to the Figures, these general aspects of the present disclosure as outlined above are described and depicted in greater detail with reference to an exemplary orthopedic knee surgery system, and more particularly with respect to performing a total knee replacement (TKR) system involving components and methods specific to both tibia and femur resection and prosthetic reconstruction.

This may include, for example, providing PSI tools and/or implants, formed in order to correspond with the patient specific digital bone model created based on X-ray images. This may further include digitizing the tibial and/or femoral mechanical axis in order to be able to perform the TKR procedure on the patient using the PSI tools. This may be done in conjunction with a CAS system, for example one which employs inertial-based or micro-electromechanical sensor (MEMS) trackable members for use in orthopedic surgical applications. The presently described system, surgical tools and methods may therefore be used in conjunction with an inertial-based CAS system employing trackable members having inertial-based sensors, such as the MEMS-based system and method for tracking a reference frame disclosed in United States Patent Application Publication No. <CIT>, and the MEMS-based system and method for planning/guiding alterations to a bone disclosed in <CIT> and <CIT>, and in <CIT>.

However, it is to be understood that the tools and methods described herein may also be used with other CAS systems. The present systems and methods may also be used in conjunction with a tool for digitizing a mechanical axis of a tibia using a CAS system, as described in <CIT>.

The PSI components of the present disclosure are all particularly adapted for use during orthopedic knee surgery, such as TKR, and as such the surgical components of the present suite of surgical tools will now be described below generally as either tibial or femoral components, respectively adapted for use in the positioning of a resection cutting guide on either the tibia or the femur, for the purposes of preparing the bone for receipt of a prosthetic knee replacement implant. While the actual steps of the TKR surgery are as per those well known by those skilled in the art, the presently described PSI components differ in that they are specifically adapted for use in a system and method which has produced the digital bone model using only X-ray images.

In order to be able to resect a proximal end of the tibia T using a resection cutting guide <NUM>, as shown in <FIG>, locating pins <NUM> must first be accurately positioned at the desired position and orientation relative to the tibia T, such that the resulting resection cut will be made at the correct position and angle to accept the planned prosthetic tibial implant. Accordingly, several different embodiments will now be presented, each of which can be used to position these locating pins <NUM>.

In the embodiment of <FIG>, a PSI tibial pin guide <NUM> is shown which is produced based on at least two X-rays of the tibia, taken from two different angular positions as described above. The PSI tibial pin guide <NUM> includes generally a body <NUM> including a distally extending portion <NUM> and a pair of posteriorly extending arms <NUM>. The distally extending portion <NUM> of the body <NUM> has a slot <NUM> formed therein, which extends fully through the distally extending portion <NUM> and is adapted to receive therethrough an anterior bone pin <NUM>. The slot <NUM> has a transverse width, in the medial-lateral (M-L) direction, substantially similar although just slightly greater than the diameter of the anterior pin <NUM>. The slot <NUM> has a length, in the proximal-distal (P-D) direction, that is at least several times the diameter of the anterior pin <NUM>. As such, once the anterior pin is fastened in place in the anterior surface of the tibia T, the PSI tibial pin guide <NUM> can be mounted thereto by inserting the anterior pin <NUM> through the slot <NUM> in the body <NUM> of the PSI tibial pin guide <NUM>. Given the slot's length, the body <NUM> of the PSI tibial pin guide <NUM> can therefore be slid in the P-D direction relative to the fixed anterior pin <NUM> as required. Although only the anterior pin <NUM>, and not the body <NUM> of the PSI tibial pin guide <NUM>, is engaged to the bone, this pin-slot engagement nevertheless locates, or constrains, the rotation of the PSI tibial pin guide <NUM> (i.e. relative to longitudinal axis of the bone) while still permitting angular movement in the Varus-Valgus (V-V) and Flexion-Extension (F-E) orientations/directions.

At an upper end of the body <NUM> of the PSI tibial pin guide <NUM>, the pair of posteriorly extending arms <NUM> each have a proximal anchor element <NUM> disposed near the remote end thereof, the two proximal anchor elements <NUM> comprising bone spikes or nails. These bone spikes <NUM> are adapted to penetrate any cartilage on the tibial plateaus P and engage, but not substantially penetrate, the underlying bone surface of the tibial plateau P. These proximal bone anchors <NUM> accordingly locate, or constrain, the PSI tibial pin guide <NUM> in the V-V orientation relative thereto.

The remaining angular constraint required, and for which adjustment is provided, for the PSI tibial pin guide <NUM> is in the F-E direction. Accordingly, the PSI tibial pin guide <NUM> includes an adjustment jack screw <NUM> disposed at a remote end of the distally extending portion <NUM> of the body <NUM>, which has a bone abutting tip <NUM> thereon that forms another anchor point or anchor element for abutting the tibia T. By rotating the jack screw <NUM>, the position of the body <NUM> of the PSI tibial pin guide <NUM> relative to the tibia T can be adjusted in the F-E direction/orientation.

Accordingly, the PSI tibial pin guide <NUM> includes one or more anchor elements disposed at different anchor points. In this case, at least three anchor elements are provided, namely the two bone spikes <NUM> which abut medially-laterally opposite sides of the tibial plateau P and the distally located jack screw <NUM>. Importantly, each of these anchor elements is disposed at a location on the PSI tibial pin guide <NUM> which corresponds to, or more particularly overlies, point on the bone which correspond to areas of expected high accuracy on the X-ray generated bone model. More particularly, the two bone spikes <NUM> are located substantially along a proximal bone peripheral contour as defined in a frontal X-ray image taken of the tibia T, and the distal jack screw <NUM> is located substantially along an anterior bone peripheral contour as defined in a medial or a lateral X-ray image take of the tibia T.

The body <NUM> of the PSI tibial pin guide <NUM> also includes a pin guide element <NUM> disposed at a distal end of a portion of the body adjacent the distally extending portion <NUM>. A pair of pin guide holes <NUM> extend through the pin guide element <NUM>, and are configured to receive therethrough the bone pins <NUM> which are used to mount the resection cutting block <NUM> to the tibia (see <FIG>).

The PSI tibial pin guide <NUM> also includes an optical positioning element which is used to position the PSI tibial pin guide <NUM> in the desired location relative to the tibia T. This optical positioning element includes a laser <NUM> which is engaged to a laser mount <NUM> disposed on an extension bar <NUM> protruding from the body <NUM> of the PSI tibial pin guide <NUM>. The laser <NUM> produces a laser beam B, which may be either a point laser beam or a planar beam as shown in <FIG>. The laser <NUM> is positioned such that its laser beam B projects onto the ankle and/or foot of the patient. By aligning the laser beam B with either anatomical landmarks on the foot (such as the malleoli of the ankle, for example) or other reference points or markings on another object substantially fixed relative to the ankle (such as the ankle boot <NUM> as shown in <FIG>, for example), the user can position the PSI tibial pin guide <NUM>, and therefore the pin guide holes <NUM> of the pin guide element <NUM> in a predetermined location which will result in the pins <NUM>, when inserted through the pin guide holes <NUM> and fastened into the bone, to position the resection cutting block <NUM> mounted to these pins <NUM> in a selected position and orientation to perform the proximal resection cut of the tibia.

Referring more specifically to <FIG>, the boot <NUM> may optionally be used in order to serve as a reference guide for aligning the PSI tibial pin guide <NUM> using the laser <NUM> as described above. More particularly, the boot <NUM> may include markings or other visually identifiable demarcations, with which the laser beam B of the laser <NUM> can be aligned, thereby providing additional guidance to the user as the correct alignment of the laser, and thus the PSI tibial pin guide <NUM> to which it is fixed, in the F-E direction.

Because the tibial pin guide <NUM> is a PSI component, it is designed and configured to tailor to the specific anatomical features of the tibia T to which it is intended to be mounted. Therefore, while each tibial pin guide <NUM> will be slightly different to accommodate particularities of each patient's bone, they nevertheless include one or more anchor points thereon that are adapted to abut and/or otherwise engage a surface of the tibia T and that are disposed at one or more locations of the PSI tibial pin guide <NUM> which correspond to areas of expected high accuracy on a digital bone model generated only by X-ray scans.

Referring now to <FIG> in more detail, a PSI tibial resection cut guide <NUM> of the present system is shown which including a cutting block <NUM> having a saw slot <NUM> extending therethrough and a base block <NUM> that is itself fastened in place on the tibia T using the cut guide pins <NUM>. The pins <NUM> are positioned and fixed in place as described above using the PSI tibial pin guide <NUM>. The cutting block <NUM> is adjustable in one or more directions relative to the base block <NUM>, using a locking adjustment mechanism <NUM>. In the embodiment as shown in <FIG>, this locking adjustment mechanism <NUM> includes a stem <NUM> which forms part of the cutting block <NUM> and a mating opening in the base block <NUM> through which the stem extends. A locking screw <NUM> is used to fix the base block <NUM> to the stem <NUM> of the cutting block <NUM>, such as to prevent relative movement therebetween when the screw is tightened. As the stem <NUM> can slide within the opening in the base block, the cutting block <NUM> can accordingly be displaced in a proximal-distal direction, in order to increase or decrease the depth of the proximal resection cut as required. Accordingly, once the pins <NUM> are in place, the base block <NUM> is slid onto the pins <NUM>, whereupon the position of the cutting block <NUM> relative to the fixed base block <NUM> can be adjusted as required. Once the predetermined position for the cutting guide slot <NUM>, and therefore the cutting block <NUM>, is reached, the locking mechanism <NUM> is actuated to fix the cutting block <NUM> in the appropriate position.

<FIG> shows a PSI tibial pin guide jig <NUM> in accordance with an alternate embodiment of the present disclosure. This PSI jig <NUM> may be alternately used to align and position the mounting pins <NUM> for the PSI tibial resection cut guide <NUM>, however provides less adjustment features. The PSI tibial guide jig <NUM> is more akin to pin placement jigs used in conjunction with MRI-generated digital bone models. Nonetheless, however, the PSI tibia pin guide jig <NUM> is specifically designed to be used with digital bone model generated only using X-ray images. Accordingly, the PSI jig <NUM> also includes one or more anchor elements disposed at different anchor points, which in this embodiment includes two bone spikes <NUM> which abut medially-laterally opposite sides of the tibial plateau and an anterior abutting element <NUM> disposed on the distally extending body <NUM>. A pair of pin holes <NUM> also extend through the body <NUM>, and are used as described above to position the pins <NUM> used to mount the resection cutting block <NUM> to the tibia. Much as per the PSI tibial pin guide <NUM> described above, each of the anchor elements of the PSI jig <NUM> is disposed at a location on the PSI component which corresponds to, or more particularly overlies, a point on the bone which is disposed in areas of expected high accuracy on the X-ray generated digital bone model.

Referring now to <FIG>, an alternate PSI component of the presently proposed suite of surgical implements is shown, which could alternately be used instead of the PSI tibial pin guide <NUM> or the PSI jig <NUM>. In this embodiment, a PSI tibial extra-medullary (E-M) guide <NUM> (or simply "PSI E-M guide") is provided, which can be similarly used to accurately position the pins <NUM> to be used to mount the resection cutting guide <NUM> to the proximal end of the tibia T. The PSI E-M guide <NUM> differs from the previously described pin guides in that it includes an elongated rigid alignment rod <NUM> which extends distally from the upper mounting body <NUM>, and which has a malleoli clamping element <NUM> at its distal end. While the alignment rod <NUM> may be standardized across all, or at least a number of patient sub-populations, each of the opposed end portions, namely the proximal mounting body <NUM> and the distal malleoli clamping element <NUM>, is a PSI component that is purposed designed based on the anatomical features and needs of the individual patient. One of the possible benefits of the PSI E-M guide <NUM> is that it permits a less invasive surgical procedure (i.e. minimally invasive surgery), because no arms having spikes are included for contact with the tibial plateau. Accordingly, less of the bone needs to be accessed for engagement of the PSI E-M guide <NUM> thereto.

Much as per the PSI tibial pin guide <NUM> described above, however, the PSI EM guide <NUM> is first located relative to the tibia T by an anterior pin <NUM> which mates within a corresponding slot <NUM> formed, in this case, in the proximal body <NUM> of the PSI E-M guide <NUM>. This pin-slot engagement between the anterior pin <NUM> and the proximal body <NUM> of the PSI E-M guide <NUM> sets, or constrains, the rotation of the device. The proximal body <NUM> also includes a posteriorly extending finger <NUM> which includes a visual guide, such as an arrow marking or shape for example, which can be aligned with a known mechanical axis entry point on the tibia T so permit for the verification of the alignment with the mechanical axis of the tibia, thereby permitting the V-V alignment of the of the PSI E-M guide <NUM>.

A posterior abutting element <NUM> is disposed behind the proximal body <NUM> of the PSI E-M guide <NUM>, and provides an anchor element which abuts the anterior surface of the tibia T for positioning the component relative thereto. This abutting anchor element <NUM> is accordingly disposed at a location on the PSI component which corresponds to a point on the bone which is disposed in an area of expected high accuracy on the X-ray generated digital bone model (namely, along the anterior peripheral contour of the proximal tibia). The proximal body also includes a medially extending portion <NUM> having two pin holes <NUM> extending therethrough for receiving, and thus positioning, the pins <NUM> used to mount the resection cutting guide <NUM> thereto.

Although the relative orientation of the pins <NUM> can be varied somewhat when using the PSI E-M guide <NUM>, it is otherwise not readily adjustable (e.g. in height, etc). Rather, because both the distal malleoli clamp <NUM> and the proximal body <NUM> are both PSI components purposed design for the individual bone, the PSI E-M guide <NUM> can be designed such as to be accurately mounted to the tibia T to allow the pins <NUM> to be inserted through the guide holes <NUM> in their determined position and orientation.

Referring now to <FIG>, another alternate PSI component of the presently proposed suite of surgical implements is shown, which could alternately be used instead of the PSI tibial pin guide <NUM>, the PSI jig <NUM> or the PSI E-M guide <NUM>. In this embodiment, a PSI hip-knee-ankle (HKA) instrument <NUM> is provided, which can be similarly used to accurately position the pins <NUM> to be used to mount the resection cutting guide <NUM> to the proximal end of the tibia T. The PSI HKA instrument <NUM> includes an elongated rigid alignment rod <NUM>, of fixed length, which extends distally from an upper mounting body <NUM> and which has a malleoli clamping element <NUM> at its distal end, much as per the PSI E-M guide <NUM> described above. Accordingly, the PSI malleoli clamping element <NUM> is used to clamp the component onto the malleoli of the patient, thereby aligning the instrument with the mechanical axis of the tibia.

In contrast to the previously described instruments, however, the proximal end of PSI HKA instrument <NUM> engages both the tibia and the femur, as seen in <FIG>. More particularly, the PSI proximal mounting body <NUM> of the PSI HKA instrument <NUM> includes both a tibial portion <NUM> and a femoral portion <NUM>.

The tibial portion <NUM> is engaged in place relative to the tibia using an anterior pin <NUM> which is received within a corresponding slot <NUM>, in the same manner as described above with the previously tibial instruments. This pin-slot engagement between the anterior pin <NUM> and the slot <NUM> in the tibial portion <NUM> of the PSI proximal body <NUM> sets, or constrains, the rotation of the device.

A posterior abutting element <NUM> is disposed behind the tibial portion <NUM> of the PSI proximal body <NUM>, and provides an anchor element which abuts the anterior surface of the tibia T for positioning the component relative thereto. This abutting anchor element <NUM> is accordingly disposed at a location on the PSI component which corresponds to a point on the tibia which is disposed in an area of expected high accuracy on the X-ray generated digital bone model (namely, along the anterior peripheral contour of the proximal tibia). The tibial portion <NUM> of the PSI proximal body <NUM> also includes a medially extending portion <NUM> having two pin holes <NUM> extending therethrough for receiving, and thus positioning, the pins <NUM> used to mount the resection cutting guide <NUM> to the tibia T.

The femoral portion <NUM> of the PSI proximal mounting body <NUM> of the PSI HKA instrument <NUM> is interconnected with the tibial portion <NUM> by a sliding and/or pivoting joint connection which allows for one or more of relative P-D and F-E displacement between the two portions <NUM> and <NUM>, but does not allow for relative angular rotation therebetween. More particularly, the uppermost end of the tibial portion <NUM> forms a plate <NUM> which is received within a corresponding slot <NUM> formed in the lower end of the femoral portion <NUM>. The slot <NUM> therefore defines two spaced apart flanges <NUM> between which the plate <NUM> is received. Two holes <NUM> are provided in each of the flanges <NUM>, and two correspondingly sized holes (not visible) are also defined through the plate <NUM>. These holes may be aligned, such that a pivot pin is fed therethrough. Accordingly, without any such pivot pin in place, this joint between the tibial and femoral portions <NUM> and <NUM> allows for relative sliding displacement therebetween, substantially in the proximal-distal direction. However, when a single pin is disposed through one of the pin holes <NUM> and the corresponding hole in the plate <NUM>, a pivoting interconnection between the two portions <NUM>, <NUM> is thereby formed. This accordingly allows for relative rotation therebetween in the flexion-extension plane. Further, if a second pin is disposed through the other of the two pin holes <NUM> and the corresponding hole in the plate <NUM>, no further rotation is permitted between the tibial portion <NUM> and the femoral portion <NUM> of the PSI proximal mounting body <NUM>. This adjustment mechanism therefore provides adjustment flexibility in order to be able to selectively displace (e.g. translate or rotate), or lock, the tibial portion <NUM> and the femoral portion <NUM> of the PSI body <NUM> with respect to each other.

The femoral portion <NUM> of the PSI proximal mounting body <NUM> also includes a pair of pin holes <NUM> which extend through the body thereof and receive pins <NUM> therethrough for mounting a resection cutting guide to the femur, once the PSI HKA instrument <NUM> is positioned in place. The resection cutting guide may be the same PSI resection cutting guide <NUM> as described above (see <FIG>), or alternately a different one specific for the femur. In order to accurate locate the femoral portion <NUM> of the PSI proximal mounting body <NUM>, it also includes a proximally extending blade <NUM> having a femur abutting anchor element <NUM> thereon. In the same manner as those previously describe above, the femur abutting anchor element <NUM> is also disposed at a location on the PSI component which corresponds to a point on the bone (in this case the femur) which is disposed in an area of expected high accuracy on the X-ray generated digital bone model (namely, in this case, along the anterior peripheral contour of the distal femur).

When using the PSI HKA instrument <NUM>, the pins for the tibial resection are positioned, aligned and fixed in place in the same manner as per the PSI E-M guide <NUM> described above. However, in order to also correctly locate the PSI HKA instrument <NUM> to allow for pins for the femoral resection to be positioned in the desired position and orientation, both the tibia T and femur F are preferably positioned in the same relative orientation as when the X-ray scans were taken. Accordingly, in order to do so, a leg alignment jig <NUM> may be provided, as shown in <FIG>. The leg alignment jig <NUM> is thus configured such as to position the leg of the patient, and thus the tibia T and femur F thereof, in a substantially identical relative position as when the X-ray scans were taken of the bones. The leg alignment jig <NUM> therefore allows the surgeon to set the leg as it was taken during the X-ray, thereby providing the best positioning for reproducing the planning and therefore maximizing precision of the operation. While the use of such a leg alignment jig <NUM> is not necessary, it may be useful to use this additional component for the reasons above.

Given that the PSI HKA instrument <NUM> is also used to locate the pins for mounting to the femur, the PSI HKA instrument <NUM> can also be used in conjunction with the adjustable femoral resection cutting guide <NUM> of <FIG>, and the PSI A-P sizers <NUM> and <NUM> of <FIG>.

<FIG> depicts a final embodiment of a PSI tibial pin guide component, which is a hybrid PSI pin and E-M guide <NUM>. Essentially, this embodiment is a combination of the PSI tibial pin guide <NUM> and the PSI E-M guide <NUM>. However, the PSI pin and E-M guide <NUM> differs in that it does not use or require an anterior locating pin <NUM>, as per the devices of the above-mentioned embodiments. Accordingly, the proximal mounting body <NUM> has bone spikes <NUM> which form proximal anchor elements that engage the tibial plateau, which set the V-V angular position of the PSI guide <NUM>. Because these anchor elements <NUM> are offset from each other in the anterior-posterior direction, they also serve to set rotational position of the PSI guide <NUM>. The distal malleoli ankle clamps (not shown in <FIG>), located at the end of the alignment rod <NUM>, are used to set the F-E position. As per the embodiments above, the proximal mounting body <NUM> also includes a medially extending portion <NUM> through which a pair of pin holes <NUM> extend, which are used to guide the pins <NUM> of the resection cutting guide block <NUM>.

Much as per the tibial components described above, the present suite of PSI implement for TKR surgery also include a number of embodiments of components which can be used for positioning the locating pins <NUM> on the femur, which used to mount a resection cutting block, such as the resection cutting guide <NUM> as described above (<FIG>) which can also be used to resect the distal femur. Again, these PSI components are also specifically designed to be used when the digital bone model of the patient's femur is generated using only X-ray images.

Referring to <FIG>, a PSI femoral pin guide <NUM> is shown which adapted to be mounted to the distal femur and which is produced based on at least two X-rays of the femur, taken from two different angular positions. The PSI femoral pin guide <NUM> includes generally a body <NUM> including a proximally extending portion <NUM> and a pair of posteriorly extending arms <NUM>. The posteriorly extending arms <NUM> each have a distal anchor element <NUM> disposed near the remote ends thereof, the two distal anchor elements <NUM> comprising bone spikes or nails which are adapted to piece any cartilage, if necessary, and abut directly on the distal condylar surfaces of the femur. These distal bone anchors <NUM> accordingly locate, or constrain, the PSI femoral pin guide <NUM> in the V-V orientation. The proximally extending portion <NUM> includes an anteriorly extending blade <NUM> which acts abuts the anterior surface of the distal femur and thus serves as another anchor element for locating the PSI guide <NUM>. The anteriorly extending blade <NUM> provides constraint in the F-E orientation.

Accordingly, the PSI femoral pin guide <NUM> includes one or more anchor elements disposed at different anchor points. In this case, at least three anchor elements are provided, namely the two distal bone spikes <NUM> which abut medially-laterally opposite sides of the distal condylar surfaces and anteriorly extending blade <NUM>. Each of these anchor elements is disposed at a location on the PSI femoral pin guide <NUM> which corresponds to, or more particularly overlies, points on the bone which correspond to areas of expected high accuracy on the X-ray generated bone model. More particularly, the two distal bone spikes <NUM> are located substantially along a distal bone peripheral contour as defined in a frontal X-ray image taken of the femur F, and the anteriorly extending blade <NUM> is located substantially along an anterior bone peripheral contour as defined in a medial or a lateral X-ray image take of the femur F.

The body <NUM> of the PSI femoral pin guide <NUM> also includes a pin guide element <NUM> disposed in the proximally extending portion <NUM> of the body <NUM>. A pair of pin guide holes <NUM> extend through the pin guide element <NUM>, and are configured to receive therethrough the bone pins <NUM> which are used to mount the resection cutting block <NUM> to the femur.

The PSI femoral pin guide <NUM> may also include one or more visual alignment guides, including for example an alignment arrow <NUM> which may be used to visually align the guide <NUM> with a known anatomical landmark and a patient-specific shaped contour <NUM> (see <FIG>) which is formed on an interior surface of the guide <NUM> and is visible though the window opening <NUM> defined in the body <NUM>. The PSI contour <NUM> is specifically formed such as to correspond to the determined contour of the patient's bone on the anterior side of the distal femur, so that the surgeon can align this PSI contour <NUM> with the corresponding shape of the bone contour, thereby ensuring accurate alignment. Either of these visual alignment guides <NUM> and <NUM> may be used in order to align the PSI femoral pin guide <NUM> as required on the femur F.

The body <NUM> of the PSI femoral pin guide <NUM> may also include a medially extending arm <NUM> having a bone abutting element <NUM> at the end thereof, however this portion of the femur may be less accurately reproduced in the X-ray generated bone model, and therefore the medially extending arm <NUM> may be used for additional alignment guidance rather than primary location.

The PSI femoral pin guide <NUM> is designed to be used in conjunction with the adjustable femoral resection cutting guide <NUM> of <FIG>, and the PSI A-P sizers <NUM> and <NUM> of <FIG>, as will be seen.

<FIG> depicts an adjustable femoral resection cutting guide <NUM> which functions much like the resection cutting guide <NUM> as described above (<FIG>) with reference to the tibial resection. The femoral resection cutting guide <NUM> is particularly adapted to be used in conjunction with the PSI femoral pin guide <NUM>, which locates the pins in the femur to which the femoral resection cutting guide <NUM> is mounted. Similarly to the cutting guide <NUM>, the femoral resection cutting guide <NUM> is also adjustable such that the portion <NUM> having the cutting guide slot <NUM> therein can be adjusted in the proximal-distal direction relative to the fixed mounting base <NUM> so as to be able to adjust at least a resection depth.

Referring now to <FIG>, a PSI anterior-posterior (A-P) sizer is mounted to the distal end of the femur, and may be used in conjunction with both the PSI femoral pin guide <NUM> and the femoral resection cutting guide <NUM> as described above.

The PSI A-P sizer <NUM> includes a , which sets the rotational position relative to the femur F based on the posterior condyles by employing two bone anchors in the form of bone spikes.

The PSI A-P sizer <NUM> includes generally a body <NUM> which abuts the distal end of the condyles of the femur F, and includes a pair of proximally extending arms <NUM>. The posteriorly extending arms <NUM> each have a distal anchor element <NUM> disposed near the remote ends thereof, the two distal anchor elements <NUM> comprising bone spikes or nails which are adapted to piece any cartilage, if necessary, and abut directly on the posterior condylar surfaces of the distal femur. These bone anchors <NUM> accordingly set, or constrain, the PSI A-P sizer <NUM> in rotation.

Accordingly, the PSI A-P sizer <NUM> includes one or more anchor elements disposed at different anchor points. In this case, at least two anchor elements are provided, namely the two bone spikes <NUM> which abut posterior condyles. Each of these anchor elements is disposed at a location on the PSI A-P sizer <NUM> which corresponds to, or more particularly overlies, points on the bone which correspond to areas of expected high accuracy on the X-ray generated bone model. More particularly, the two bone spikes <NUM> are located substantially along a posterior bone peripheral contour as defined in a medial or lateral side X-ray image taken of the femur F.

The body <NUM> of the PSI A-P sizer <NUM> also includes a pin guide element <NUM> of the body <NUM>. A pair of pin guide holes <NUM> extend through the pin guide element <NUM>, and are configured to receive therethrough the bone pins which mount a posterior resection cutting block, such as the "<NUM>-in-<NUM>" cutting guide block <NUM> as shown in <FIG>, to the femur in order to perform the posterior resection cuts.

The PSI A-P sizer <NUM> may also include one or more visual alignment features, including for example the transverse marking lines <NUM> on the body <NUM> which define resection cut line positions and the central marking line <NUM> which defines the trans-epicondylar axis line.

In <FIG>, an alternate PSI A-P sizer <NUM> is shown, which is similar to the PSI A-P sizer <NUM> but having an additional attachment clip <NUM> for engaging the "<NUM>-in-<NUM>" posterior cutting guide block <NUM>.

<FIG> depicts simply an additional adjustment instrument <NUM> for use in repositioning the posterior cutting guide block <NUM> relative to its mounting pins and thus relative to the bone. For example, the adjustment instrument <NUM> permit the sliding displacement of the posterior cutting guide block <NUM> in the anterior posterior direction and/or rotating the posterior cutting guide block <NUM> internally or externally.

<FIG> shows a PSI femoral pin guide jig <NUM> in accordance with an alternate embodiment of the present disclosure. Much as per the PSI tibial pin guide jig <NUM> of <FIG>, the PSI femoral pin guide jig <NUM> may be alternately used to align and position the mounting pins for the femoral resection cut guides, however provides less adjustment features. The PSI femoral pin guide jig <NUM> is more akin to pin placement jigs used in conjunction with MRI-generated digital bone models. Nonetheless, however, the PSI femoral pin guide jig <NUM> is specifically designed to be used with digital bone model generated only using X-ray images. Accordingly, the PSI femoral pin guide jig <NUM> also includes one or more anchor elements disposed at different anchor points. Two different pairs of pin holes <NUM> and <NUM> also extend through the body <NUM>, and are used as described above to position the pins used to mount the resection cutting block to the femur. The anchor elements of the PSI femoral pin guide jig <NUM> which abut the femur are disposed at locations on the PSI component which correspond to, or more particularly overly, points on the bone which are disposed in areas of expected high accuracy on the X-ray generated digital bone model.

Claim 1:
A method of creating a patient specific instrument to suit a specific patient's anatomy (<NUM>,<NUM>,<NUM>,<NUM>) for use in knee replacement surgery, the method comprising:
performing at least two X-ray scans of one or more bones, each of the X-ray scans being taken from different angular positions;
generating a digital bone model of said one or more bones based solely on the X-ray scans;
planning the patient specific instrument based on the digital bone model, including determining locations for one or more anchor points on the patient specific instrument which are adapted to abut a surface of said one or more bones, the determined locations of the one or more anchor points being disposed on the patient specific instrument corresponding to areas of expected high accuracy on the digital bone model generated by the X-ray scans, said areas of expected high accuracy including at least a peripheral bone contour in at least one of said angular positions; and
creating the planned patient specific instrument having said one or more anchor points thereon.