Patent Description:
Pain and overuse disorders of the joints in the body is a common problem. The weight-bearing and articulate surfaces of the knees and other joints are covered with a layer of soft tissue that typically comprises a significant amount of hyaline cartilage. The friction between the cartilage and the surrounding parts of the joint is very low, which facilitates movement of the joints under high pressure. The cartilage is however prone to damage due to disease, injury or chronic wear. Moreover, it does not readily heal after damages, as opposed to other connective tissue, and if healed the durable hyaline cartilage is often replaced by less durable fibrocartilage. This means that damages of the cartilage gradually become worse. Along with injury/disease comes a problem with pain which results in handicap and loss of function. It is therefore important to have efficient means and methods for repairing damaged cartilage in knee joints.

The advantages of implants have stimulated a further development of smaller implants that can be implanted with less invasive surgery. In this development there has also been an effort to achieve small joint implants, suitable for repair of small cartilage injuries that have a minimal influence on the surrounding parts of the joint. In the surgical operation of implanting such small implants, it is critical that the implant is positioned in a precise manner. If the implant is offset from its intended position it may cause an increased wear or load on the joint. For example, if the implant is tilted, this may result in an edge that projects above the cartilage surface and causes wear on the opposing cartilage in the joint. Another example is the case that the implant is placed in a too shallow position, which may result in a too high top of the implant that causes the joint to articulate in an uneven manner and increase the load on an opposing point of the joint. For the patient, also small misplacements or deviations from an ideal position may result in pain, longer time for convalescence or even a surgical operation being done in vain and making it more difficult to repair the damage in the joint. A large burden is therefore placed on the surgeon not to misplace or misfit the implant. There is therefore a need for tools that are designed to relieve and support the surgeon in the implant surgery.

The design of the implant and the surgical tools, in other words, the design of the surgical kit, is crucial for the outcome of the implant's life-time in a joint. Also, the parameters for designing are of uttermost importance for the result in these operations. Small differences in the design can make a huge difference in fit and life-time of an implant in the body, convalescence time for the patient, economic values due or surgery time, and success of operations. Also, the number of successful operations will increase, and the working conditions for the surgeon will be improved, if the designing parameters are selected right.

There is a need for a design method for tools for use during repair of a cartilage damage which is more user friendly for the surgeon than the tools known from prior art. There is a need for tools which allow for small surgical cuts, and also a design method which allows for producing tools which are adapted to avoid problems with small misplacements or deviations from an ideal position, e.g. that the implant is tilted during insertion causing pain and longer convalescence time for the patient, and which are still stable and easy to use for the surgeon allowing for precise insertion of implants in a joint.

A prior art document that describes the design of an orthopedic implants and corresponding tools is for example <CIT>, which shows a design method for designing an individually designed surgical kit.

The general object of the invention is to solve the problem of designing an improved surgical kit for use during cartilage repair for replacing damaged cartilage and also an improved design method for designing a mandrel for hammering, pressing and/or pushing an implant into a recess made in a joint.

In aspects, the object of the invention is to design a mandrel which makes the surgical operation more accurate and safer, and which provides for less surgeon dependent operation procedures and faster recovery of the patients after surgery.

In certain aspects, the object of the invention is to design a mandrel for an implant which make the surgical operation safer and results in better fitting implants, less surgeon dependent operation procedures and faster recovery of the patients after surgery. It is a further object of the invention to provide a solution for making the surgical operation of rotationally positioning and inserting an implant in a recess safer and more accurate by providing a mandrel with at least one element and/or positioning mark which is adapted for rotationally positioning the mandrel in relation to at least one of an anatomic dependent direction, at least one element and/or positioning mark of the implant, and a mark to be made on side of a recess to be made at the determined implant position.

A method for designing a mandrel according to the invention is defined in claim <NUM>.

In embodiments, the method further comprises determining the position of the at least one element and/or positioning mark of the mandrel so that said at least one element and/or positioning mark is adapted for rotational positioning of the mandrel in relation to an element and/or a positioning mark of the implant. This enables a very exact positioning of the mandrel onto the implant to be implanted.

In embodiments, the method further comprises determining the position of the at least one element and/or positioning mark of the mandrel so that said at least one element and/or positioning mark is adapted for rotational positioning of the mandrel in relation to a mark on the side of the recess where the implant is to be inserted.

In embodiments, the method further comprises determining the position of the at least one element and/or positioning mark of the mandrel so that said at least one element and/or positioning mark is adapted for rotational positioning of the mandrel in relation to an anatomic dependent direction.

In embodiments, the method further comprises forming the contacting surface of the mandrel into a substantially circular shape, and designing the at least one element and/or positioning mark as a marking, such as e.g. a dot, or a groove in the circumference of the substantially circular shape.

In embodiments, the method further comprises forming the contacting surface of the mandrel from at least two substantially circular shapes, such that each of said substantially circular shapes is partly overlapping at least one other substantially circular shape, and designing the at least one element and/or positioning mark as a marking, such as e.g. a dot, or a groove in the circumference of at least one of said at least two substantially circular shapes.

In embodiments, the method further comprises designing at least a portion of the contacting surface of the mandrel to have an inverted surface, or essentially inverted surface, to the articulate surface of the implant to be inserted in the recess using the mandrel.

In embodiments, the method further comprises receiving image data representing a three-dimensional image of a joint; identifying cartilage damage in the image data; determining the position for the implant to be used for cartilage repair; simulating a healthy surface of the area of damaged cartilage; and designing the articulate surface of the implant to match the simulated healthy surface.

In embodiments, the method further comprises simulating said healthy surface based on image data representing a three-dimensional image of a joint and the curvature of the cartilage immediately surrounding the area of damaged cartilage.

In embodiments, the method further comprises designing the mandrel with a grip portion that has a smaller diameter close to the contacting surface than at the middle of the grip portion. It is an advantage to design the mandrel so that the point of gravity lies in the hand of the surgeon using the mandrel rather than close to the contacting surface. Further, if the grip portion has a larger diameter towards the middle, it may lie better in the hand of the surgeon.

A mandrel according to the invention is defined in claim <NUM>.

In embodiments, the at least one element and/or positioning mark of the mandrel is adapted for rotational positioning of the mandrel in relation to at least one of at least one element and/or positioning mark on the surface of the implant, a mark on the side of the recess where the implant is to be inserted, and an anatomic dependent direction.

In embodiments, the contacting surface of the mandrel has a substantially circular shape, and the at least one element and/or positioning mark is a marking, such as e.g. a dot, or a groove in the circumference of the substantially circular shape.

In embodiments, the contacting surface of the mandrel is formed from at least two substantially circular shapes, such that each of said substantially circular shapes is partly overlapping at least one other substantially circular shape, and the at least one element and/or positioning mark is a marking, such as e.g. a dot, or a groove in the circumference of at least one of said at least two substantially circular shapes.

In embodiments, at least a portion of the contacting surface of the mandrel has an inverted surface, or essentially inverted surface, to the articulate surface of the implant to be inserted into the recess using the mandrel.

In embodiments, the contacting surface of the mandrel has a cross-sectional profile that is designed to correspond to the cross-sectional profile of the implant to be inserted into the recess using the mandrel, with a tolerance preventing the mandrel from coming into contact with the surrounding cartilage during insertion of the implant into the recess.

In embodiments, the mandrel further comprises a grip portion that has a smaller diameter close to the contacting surface than at the middle of the grip portion. It is an advantage to design the mandrel so that the point of gravity lies in the hand of the surgeon using the mandrel rather than close to the contacting surface. Further, if the grip portion has a larger diameter towards the middle, it may lie better in the hand of the surgeon.

The technology disclosed relates to a design method for designing a mandrel for hammering, pressing and/or pushing an implant into position in a recess made in a joint and firmly attach the implant to the bone of a patient, comprising determining a contacting surface of the mandrel to be in contact with the articulate surface of the implant during the insertion of the implant to fit the articulate surface of the implant in that the contacting surface of the mandrel has a corresponding cross-sectional profile.

The implant which is hammered/pressed into a recess using the mandrel is an individually customized implant designed with an articulate surface having a shape and curvature which is simulating a healthy surface of the area of damaged cartilage at the determined implant position where the implant is to be inserted. The contacting surface of the mandrel to be in contact with the articulate surface of the implant (which is to be inserted into a joint using the mandrel) is then designed to have an inverted surface curvature to the surface curvature of the articulate surface of the implant.

A mandrel may according to the invention be any type of tool that may be used for tapping, hammering, pressing and/or pushing an implant into position into a recess made in a joint of a patient.

The invention will be further explained with reference to the accompanying drawings which are exemplified embodiments according to the invention and not limiting to the scope of the invention.

The technology disclosed relates to a design method for designing a mandrel for hammering, pressing and/or pushing an implant into position in a recess made in a joint and firmly attaching the implant to the bone of a patient, comprising determining a surface of the mandrel to be in contact with the articulate surface of the implant during the insertion of the implant to fit the articulate surface of the implant in that the contacting surface of the mandrel has a corresponding cross-sectional profile.

<FIG> shows an example of a surgical kit. This particular example of a surgical kit is especially adapted for cartilage replacement at the femur of a knee joint. The invention may however be applied for cartilage replacement in an articulate surface in any other joint in the body, e.g. elbow, ankle, finger, hip, toe and shoulder. The surgical kit may e.g. comprise a height adjustment device <NUM>, a hammer tool/mandrel <NUM>, a drill-bit or reamer-bit <NUM>, an implant dummy <NUM>, a guide tool <NUM>, and an implant <NUM>. A surgical kit may additionally comprise e.g. a cartilage cutting tool or cartilage cutter, a cartilage cut drill, a punch, a reamer guide, and/or a drill guide.

<FIG> show different embodiments of a mandrel <NUM> according to the invention having a grip portion <NUM> and a contacting surface <NUM> designed to be in contact with an articulate surface <NUM> of an implant <NUM> during insertion of the implant <NUM> by hammering, pressing and/or pushing the implant <NUM> into position in a recess made in a joint. The contacting surface <NUM> of the mandrel <NUM> is designed to have an inverted surface to the articulate surface <NUM> of the implant <NUM> to be implanted. The mandrel <NUM> preferably comprises an element and/or a positioning mark <NUM> for rotational positioning of the mandrel <NUM> in the recess. The element and/or positioning mark <NUM> is preferably arranged to allow the simultaneous rotational positioning of the implant <NUM> in the recess. The contacting surface <NUM> of the mandrel <NUM> is preferably the same size, or slightly smaller than, the surface <NUM> of the implant <NUM> to be implanted. If the contacting surface <NUM> of the mandrel <NUM> has a cross-sectional profile that has a tolerance with respect to the cross-sectional profile of the implant <NUM> to be inserted into the recess using the mandrel <NUM>, this may prevent the mandrel <NUM> from coming into contact with the surrounding cartilage during insertion of the implant <NUM> into the recess. The diameter of the surface <NUM> may be larger or smaller than the diameter of the grip portion <NUM> of the mandrel <NUM>. The mandrel <NUM> shown in <FIG> is intended for use with an implant <NUM> formed from two substantially circular shapes such that each of said substantially circular shapes is partly overlapping the other substantially circular shape.

The mandrel <NUM> shown in <FIG> further comprises a grip portion <NUM>, which is intended to provide a good grip for the surgeon using the mandrel <NUM>. The grip portion <NUM> is preferably shaped to be thicker in the middle, and have a smaller diameter close to the contacting surface <NUM> than at the middle of the grip portion <NUM>. It is an advantage to design the mandrel so that the point of gravity lies in the hand of the surgeon using the mandrel <NUM> rather than close to the contacting surface <NUM>. Further, if the grip portion <NUM> has a larger diameter towards the middle, it may lie better in the hand of the surgeon.

<FIG> shows an example of a medical implant <NUM> provided with a positioning mark <NUM>. The plate shaped implant body has an articulate surface (first surface) <NUM> configured to face the articulating part of the joint and a bone contact surface (second surface) configured to face bone structure in the joint. The plate shaped implant body has a cross-section that substantially corresponds to the area of the damaged cartilage and the articulate surface <NUM> has a curvature that substantially corresponds to the curvature of a healthy articulate surface at the site of diseased cartilage. The extending post extends from the bone contact surface. Since the implant <NUM> of the inventive concept is custom made for a specific patient, <FIG> is an exemplifying schematic picture displaying an embodiment of the implant <NUM>. Between the articulate surface <NUM> and the bone contact surface there is a cartilage contacting surface.

The implant is specially designed, depending on the knees appearance and the shape of the damage and in order to resemble the body's own parts, having a surface which preferably corresponds to a three dimensional (3D) image of a simulated healthy cartilage surface. The implant will be tailor-made to fit each patient's damaged part of the joint.

The implant body is substantially plate shaped, meaning that the shortest distance crossing the surface <NUM> of the implant body is substantially larger, e.g. at least <NUM> times larger than the thickness of the implant body. By substantially plate shaped is meant that the implant body may be substantially flat or may have some curvature, preferably a 3D curvature of the articulate surface <NUM>. The articulate surface <NUM> may for example have a curvature that corresponds to a simulated healthy cartilage reconstructed from an image taken e.g. with MRI or CT-scanning of the damaged cartilage surface of the joint. Once the implant <NUM> is placed in the joint there will be a surface with no parts of the implant pointing up from or down below the surrounding cartilage - the implant is incorporated to give a smooth surface.

The area and the shape of the implant surface <NUM> are individual depending on the size of cartilage damage and location of the cartilage damage. The area and shape of the implant can be decided by the surgeon himself or be chosen from predetermined shapes. For instance the cross-section of the implant body may have a circular or roughly circular, oval, triangular, square or irregular shape, preferably a shape without sharp edges.

In general, small implants are preferred since they have a smaller impact on the joint at the site of incision and are also more easily implanted using arthroscopy or smaller open surgical procedures. The primary factor for determining the size of the implant is however the nature of the lesion to be repaired.

The implant replaces an area of damaged cartilage in an articulate surface of a joint. Before the implant is placed in the desired position, the damaged cartilage is removed and also a part of the bone beneath, i.e. a recess fitting the implant is made in the bone. The recess can e.g. be drilled in the bone to fit the implant structure. The extending post or rod-part of the implant <NUM> is used for securing the implant <NUM> in the drilled hole of the bone. The length of the extending post, extending from the implant head, is adjusted to a length needed to secure the implant <NUM> in the bone. The extending post is intended to give a primary fixation of the implant <NUM>. It provides mechanical attachment of the implant <NUM> to the bone in immediate connection with the surgical operation.

<FIG> shows another example of a medical implant <NUM>, where the implant <NUM> comprises two substantially circular shapes <NUM>, where one of the circular shapes <NUM> is provided with a positioning mark <NUM> on its articulate surface <NUM>.

The positioning mark <NUM> on the articulate surface <NUM>, i.e. the top surface <NUM> facing the articulating part of the joint, of the medical implant <NUM> illustrated in <FIG>is designed to be used for determining the orientation in which the implant <NUM> is to be placed in a recess made in a damaged articulate surface of a joint.

The positioning mark <NUM> may be designed so that the direction of the positioning mark <NUM> is determining the placement orientation of the implant <NUM> in a recess, in that the placement orientation of the positioning mark <NUM> is also to be indicated by a mark made on the side of a recess made in the articulate surface of a joint in which the implant <NUM> is to be inserted, thereby providing for a correct or more accurate orientation of the implant when inserted in the recess made in a damaged articulate surface of a joint.

The positioning mark <NUM> on the articulate surface <NUM>, i.e. the top surface <NUM> facing the articulating part of the joint, of the implant <NUM> may be designed so that the direction of the positioning mark <NUM> is designed to be pointing in an anatomic dependent direction in relation to a recess made in the articulate surface of a joint in which the implant <NUM> is to be inserted, thereby providing for a correct or more accurate orientation of the implant <NUM> when inserted in the recess made in a damaged articulate surface of a joint.

<FIG> shows a guide tool <NUM> which may be used with embodiments of the invention. The guide tool <NUM> preferably has a cartilage contact surface that has a shape and contour that is designed to correspond to and to fit the contour of the cartilage or the subchondral bone in the joint in a predetermined area surrounding the site of diseased cartilage. The guide tool <NUM> aids with exact precision removal of a volume of cartilage and subchondral bone, and preferably has a guide channel <NUM>. The guide tool <NUM> preferably comprises a positioning mark <NUM>, comprised in the structure of the guide tool <NUM>, wherein the positioning mark <NUM> is aligned with the centre of the guide channel <NUM> in a joint axis direction. The guide tool <NUM> may also comprise an indentation <NUM> that enables marking of the cartilage surface in the position of the positioning mark <NUM>.

<FIG> shows a guide tool <NUM> comprising an implant dummy <NUM> placed inside the guide channel <NUM> of the guide tool <NUM>. The guide tool <NUM> may be placed in the joint using pins <NUM> for stabilization and fastening. The guide channel <NUM> is used for stabilizing tools that are to be inserted into the guide channel <NUM>, such as e.g. a drill bit <NUM> and/or an implant dummy <NUM>. The guide channel <NUM> therefore preferably has an inner cross-sectional profile that is designed to correspond to the cross-section of the drill bit <NUM> and/or the implant dummy <NUM>. In other words, the drill bit <NUM> and/or the implant dummy <NUM> fits the guide channel <NUM>, with a slight tolerance to allow a sliding movement of the drill bit <NUM> and/or the implant dummy <NUM> in the guide channel <NUM>.

The guide channel <NUM> has an opening on the cartilage contact surface, arranged to be placed in a position corresponding to the site of the diseased cartilage in a joint. The height of the guide channel <NUM> must be sufficiently long to give support to the tools used inside the guide channel <NUM>. The height of the guide channel <NUM> may e.g. be between <NUM> and <NUM>, preferably <NUM>-<NUM>, and always sufficiently high to ensure stabilization of the tools that are to be inserted into the guide channel <NUM>. In one example, the top of the guide channel <NUM> is designed to project above the tissue surrounding the surgery cut when the guide tool is placed on the cartilage in a joint during surgery.

The guide tool <NUM> is easy to place due to the precise fit of the cartilage contact surface on the cartilage surface. The size and shape of cartilage contact surface of the guide tool <NUM> is determined depending on the size and shape of the damaged cartilage and thus on the cross section of the implant body <NUM>, and also depending on the position of the cartilage area in a joint. The size, shape or spread of the cartilage contact surface of the guide tool <NUM> is a consideration between the following aspects; minimize surgery lesion, maximize stability for guide tool <NUM>, anatomic limitations on the site of the injury. Not all cartilage surfaces in a joint can be used for placement of the guide tool <NUM>. A large spread of the cartilage contact surface is preferable to get good stability of the guide tool <NUM>, however, a large surface area of the surface may also lead to a large surgical intervention which is undesired.

Thus the size of the guide tool <NUM> is determined by a balance between the desire to achieve good positioning stability and small surgical operations. Also, the cartilage contact surface need not have a continuous, regular shape, but may have an irregular shape, as long as it gives adequate support and stable positioning of the guide tool <NUM>. The cartilage contact surface may also consist of three separated points.

<FIG> shows the use of a mandrel <NUM> for for hammering, pressing and/or pushing an implant <NUM> into position in a recess made in a joint, according to one or more embodiments of the invention. <FIG> also shows a positioning mark indicated on the cartilage surface. The positioning mark is preferably added to the cartilage surface when the guide tool <NUM> is placed in the joint, e.g. by inserting a marking pen into the indentation <NUM> in the guide tool <NUM>. The implant <NUM> is placed in the recess, rotated so that the positioning mark <NUM> of the implant <NUM> corresponds to the positioning mark indicated on the cartilage surface. The element and/or positioning mark <NUM> on the mandrel <NUM> is then preferably aligned with the positioning mark <NUM> on the implant <NUM> and the positioning mark indicated on the cartilage surface.

The element and/or a positioning mark <NUM> on the mandrel <NUM> is preferably designed to allow the surgeon to view the the positioning mark <NUM> of the implant <NUM> when the mandrel <NUM> is used for hammering, pressing and/or pushing the implant <NUM> into position in a recess.

The method for inserting an implant <NUM> into a recess by use of a mandrel <NUM> further comprises: providing a guide tool <NUM> comprising a positioning feature/mark <NUM>; and making, by one of a surgeon and a mechanical arm such as a robot arm, a mark on the side of a recess made in an articulate surface of the joint in the direction of the positioning mark of said guide tool <NUM>, thereby determining the future placement orientation of the implant <NUM>. The surgical kit may also comprise a height adjustment device <NUM>, e.g. comprising a male part <NUM> and a female receiving part <NUM> which when used together allows for stepwise adjustment of drill depth.

The male part <NUM> is in the outermost position in a zero-mode and may from there be adjusted inwards allowing the surgeon to for example make stepwise deeper drill holes. When the height adjustment device <NUM> is in starting mode or outermost zero-mode, the position marking of the guide tool <NUM> and the positioning marking of the height adjustment device <NUM> are aligned.

Thus, by being able to adjust the length of the guide channel <NUM>, the surgeon is also able to adjust the depth of drilling and cutting into the bone. The length of the guide channel <NUM> may be varied since the guide tool <NUM> and the height adjustment device <NUM> are able to move in relation to one another. Further, the male part <NUM> and the female receiving part <NUM> of the height adjustment device <NUM> may be arranged such that the length of the guide channel <NUM> may be varied at certain stepwise intervals, e.g. at <NUM> or at <NUM>-<NUM> intervals or steps, or any other desired interval. For example, the height might be adjusted between for example <NUM>-<NUM>, in one or several steps. This may for instance be achieved by arranging the male part <NUM> inside the female receiving part <NUM> of the height adjustment device <NUM> such that the male part <NUM> insert tool to have a cross-sectional profile that corresponds to the cross-sectional profile of the guide channel of the female part <NUM> with a tolerance enabling the insert tool to slide within the guide channel of the female part <NUM>.

The insert tool may e.g. be placed in a starting position where both the positioning mark of the insert tool is aligned with the positioning mark <NUM> of the guide tool <NUM>.

According to the invention, the mandrel <NUM> has a contacting surface <NUM> that is designed to fit the articulate surface <NUM> of an implant <NUM>. In certain embodiments, the contacting surface <NUM> of the mandrel <NUM> according to the technology disclosed may have a cross-sectional profile that is designed to correspond to the cross-sectional profile of the implant <NUM>, with a tolerance preventing the mandrel <NUM> from coming into contact with the surrounding cartilage during insertion of the implant <NUM> into the recess. The contacting surface <NUM> of the mandrel <NUM> is thus preferably slightly smaller than the articulate surface <NUM> of the implant <NUM> all around the circumference.

The mandrel <NUM> according to the invention has a contacting surface <NUM> that is designed to fit the articulate surface <NUM> of the implant <NUM>, i.e. it has a corresponding cross-sectional profile and preferably also a corresponding, although inverted, curvature. The mandrel <NUM> is preferably used to hammer and/or press the implant <NUM> in place.

The mandrel or hammer tool <NUM> may also be accompanied by a hammer tool adapter, for facilitating the use of the mandrel <NUM> and minimizing the absorption of the shock caused by the mandrel <NUM> and/or minimizing the risk of scratching the surface of the implant while hammering/pressing/pushing. Such a hammer tool adapter may be made from a soft material that is gentle to the implant surface, e.g. a rubber or plastic material.

The implant <NUM> is an individually customized implant designed with an articulate surface <NUM> having a shape and curvature which is simulating a healthy surface of the area of damaged cartilage at the determined implant position where the implant <NUM> is to be inserted, and at least a portion of the contacting surface <NUM> of the mandrel <NUM> to be in contact with the articulate surface <NUM> of the implant <NUM> is designed to have a corresponding cross-sectional profile.

Claim 1:
A method for designing a mandrel (<NUM>) for hammering, pressing and/or pushing an implant (<NUM>) into position in a recess made in a joint, the mandrel (<NUM>) comprising a contacting surface (<NUM>) adapted to be in contact with an articulate surface (<NUM>) of the implant (<NUM>) to be inserted, the method comprising providing the mandrel (<NUM>) with at least one element and/or positioning mark (<NUM>) adapted to be used for determining the rotational orientation of the mandrel (<NUM>) in relation to the implant (<NUM>), in order to enable the mandrel (<NUM>) to be rotationally positioned so that the at least one element and/or positioning mark (<NUM>) on the mandrel (<NUM>) is aligned with a positioning mark (<NUM>) of the implant (<NUM>), and/or a mark on the side of the recess where the implant (<NUM>) is to be inserted, characterised by the method further comprising designing the contacting surface (<NUM>) of the mandrel (<NUM>) to be an inverted surface to a healthy surface of an area of damaged cartilage where the implant (<NUM>) is to be inserted, where the healthy surface is simulated based on image data representing a three-dimensional image of the joint and the curvature of the cartilage immediately surrounding the area where the implant (<NUM>) is to be inserted.