The present invention relates to a method for manufacturing a device to be connected to a location associated with a defect on a bone of a patient, particularly a device for supporting defect-filling material, such as bone graft, on a bone. The invention further relates to a device for supporting defect-filling material on a bone. The invention further relates to a method for providing a volume of defect-filling material on a bone.

Bone loss and poor bone quality are two major challenges of joint revision surgery. Where there is a deficiency of bone stock, the defect can be prepared for implant placement, e.g. by filling it with defect-filling material such as adjunctive morselized bone-graft material, donor materials, bone- marrow-scaffold mixtures, or micro tissue cultures.

Next to defect preparation for implant placement, the same defect-filling material can be applied for re-establishing viable bone stock.

It is important to achieve good contact between the defect-filling material and both the host bone and the implant, in order to stimulate bone remodelling, ingrowth and ongrowth. The challenge is therefore to be able to form the layer of defect-filling material in such a way that it fills all the cavities and that its shape is appropriate for receiving an implant, in particular a cup implant.

One technique of preparing the defect is the impaction bone-grafting technique, in which morselized bone-graft material is impacted within the defect cavity. This ensures a mechanically stable base for supporting an implant, and allows for the formation and remodelling of bone tissue at the location of the former defect.

In particular for larger defects (e.g. Paprosky Type 2), it is hereby known to manufacture a device for supporting said defect-filling material, also referred to as bone cage, in situ to contain and support the defect-filling material. Such a bone cage can for instance be formed by a mesh-like sheet which is connected to the bone surrounding the defect using suitable connecting means, such as screws, pins or the like. The mesh is bent to form a suitable receptacle for the defect-filling material. Although these meshes can be used for treating larger defects, the meshes are typically too flimsy to allow a reliable and efficient connection to the bone in very large defects (e.g.

Paprosky Type 3). Moreover, the graft containment is crafted in situ, such that there is little control over implant location and orientation. This renders the method less suitable for use in combination with a patient-specific implant or pre-operative planning. An alternative for the meshes, particularly when treating very large defects, are large implants, for instance provided with a plurality of flanges, for instance triflanges. Larger implants however often give rise to stress shielding, thereby jeopardizing the chances of survival of bone grafts.

It is a goal of the present invention, amongst other goals, to provide an unproved device for supporting defect-filling material on a bone wherein at least one the above mentioned problems is at least partially solved. This goal, amongst other goals, is met by a method according to claim 1. More specifically, this goal, amongst other goals, is met by a method for manufacturing a device to be connected to a location associated with a defect on a bone of a patient, wherein the method comprises the steps of:

- providing a numerical three-dimensional patient model of at least a part of the patient

including the location on the bone with said defect;

- determining a correction volume in the patient model, wherein said correction volume is representative for a volume of defect-filling material;

- designing the device on the basis of the patient model and the determined correction volume; and

- manufacturing said device,

wherein the step of designing of the device comprises:

- designing at least one volume-contacting surface on the basis of the determined correction volume such that the correction volume is at least partially enclosed by the bone and said volume-contacting surface;

- designing at least one bone-contacting surface arranged to contact a surface of the bone, wherein the bone-contacting surface is formed to be substantially congruent to said bone surface to ensure a unique fit of the device on said bone.

According to the invention, the correction volume, i.e. the volume which is to be filled by the defect-filling material, is planned pre-operatively on the basis of a three-dimensional patient model. In accordance with this planned volume, a suitable device for supporting the defect-filling material can be designed. The device is thereto provided with at least one volume-contacting surface which is formed in accordance with the pre-planned volume. The volume-contacting surface is preferably shaped so as to form a volume of defect-filling material in the shape of the pre-planned correction volume in use. The device, and in particular the volume-contacting surface thereof, thereby functions to form a receptacle for the defect-filling material on the location of the bone. The device thereby forms, in connected state, a mould, wherein the mould is arranged to receive the defect-filling material.

A typical device according to the invention for supporting defect-filling material in a defect in a bone of a patient therefore preferably comprises:

at least one volume-contacting surface for at least partially enclosing a correction volume of defect-filling material, wherein said correction volume is representative for a volume of defect-filling material which at least partially fills said defect;

at least one bone-contacting surface arranged to contact a surface of the bone, wherein the bone-contacting surface is formed to be substantially congruent to said bone surface to ensure a unique fit of the device on said bone.

In order to ensure that the correction volume as pre-operatively planned will be located on the planned location, the device is further designed to have at least one bone-contacting surface which is preferably patient specifically designed. The bone-contacting surface is arranged to closely mate with a predetermined surface of the bone to ensure a unique fit between the device and the bone. This ensures that the device can only be placed on the bone in one pre-determined orientation such that upon correct placement of the device, the correction volume defined by the volume-contacting surface will be located on the location as pre-operatively planned. The surface of the bone- contacting surface is hereto preferably formed congruent to the surface of the bone onto which the bone-contacting surface is to rest in connected state. It is however also possible that the device comprises a plurality of connection points or a plurality of connection surfaces, wherein the combination of connection points or connection surfaces ensures a unique and stable fit of the device onto the bone. These connection points then together form a congruent bone-contacting surface.

The bone-contacting surface is preferably large enough to, next to a unique fit of the device as mentioned above, also provide a stable fit of the device on the bone. In particular because the defect-filling material is to be impacted after introduction in the correction volume, a stable fit of the device on the bone is important.

The planning of the correction volume and design of the device are preferably based on a three- dimensional patient model of at least the part of the bone to which the device is to be connected. Providing the three-dimensional patient model may comprise the step of obtaining an image of the bone to which the device is to be connected. Digital patient-specific image information can be provided by any suitable means known in the art, such as for example a computer tomography (CT) scanner, a magnetic resonance imaging (MRI) scanner, an ultrasound scanner, or a combination of Roentgenograms. A summary of medical imaging has been described in

"Fundamentals of Medical imaging", by P. Suetens, Cambridge University Press, 2002. For example, the step of obtaining an image of the bone and the defect therein may comprise the steps of obtaining 2D datasets of the bone and reconstructing a 3D virtual patient model from said 2D datasets. Indeed, the first step in a planning is the construction of a 3D virtual model of the bone. This reconstruction starts with sending a patient to a radiologist for scanning, e.g. for a scan that generates medical volumetric data, such as a CT scan, MRI scan or the like. The output of the scan can be a stack of two-dimensional (2D) slices forming a 3D data set. The output of the scan can be digitally imported into a computer program and may be converted using algorithms known in the field of image processing technology to produce a 3D computer model of a relevant bone. Preferably, a virtual 3D model is constructed from the dataset using a computer program such as Mimics(TM) as supplied by Materialise N.V., Leuven, Belgium. Computer algorithm parameters are based on accuracy studies, as for instance described by Gelaude at al. (2008; Accuracy assessment of CT-based outer surface femur meshes Comput. Aided Surg. 13(4): 188- 199). A more detailed description for making a perfected model is disclosed in U.S. Patent No. 5,768, 134 entitled Method for making a perfected medical model on the basis of digital image information of a part of the body'. The three-dimensional model of the bone is reconstructed for instance as disclosed in Gelaude et al. (2007; Computer-aided planning of reconstructive surgery of the innominate bone: automated correction proposals Comput. Aided Surg. 12(5): 286-94).

Planning of the correction volume can be based on reconstructing a surface of the bone, for instance corresponding to the surface in non-defected state. The correction volume can then be determined to fill the space between the bone surface of the defect and the reconstructed surface. With the bone seen as lower part, an upper surface, or correction surface, of the correction volume is then determined on the basis of the reconstructed surface of the bone. The lower surface of the correction volume can then be determined on the basis of for instance the defected bone, perhaps after suitable reaming as will be explained in greater detail later. The volume-contacting surface of the device can then for instance be planned so as to allow a suitable enclosure of the volume and to support the defect-filling material.

It is however preferred if the correction volume is planned on the basis of an implant to correct the defect. Therefore, according to a preferred embodiment, the method further comprises the step of planning the position of an implant for correcting said defect on the basis of the patient model, wherein the correction volume is determined on the basis of said implant. Such an implant may be a generic implant, for instance a cup for receiving another part of a joint, or may be a patient- customized implant which is for instance also planned on the basis of a three-dimensional patient model, preferably the same model as used for the planning and determination of the correction volume.

As will be explained in greater detail below, in the case of a generic implant, the correction volume may be designed to prepare the bone for said implant such the implant has a stable and predetermined fit on the bone, despite the implant being generic. A properly supported implant reduces the effects of stress shielding, thereby reducing further bone quality deterioration.

An implant typically comprises a correction surface, which in implanted situation forms the corrected surface of the bone. This correction surface may correspond to the surface in non- defected state or, as mentioned above, have a specific design, for instance to cooperate with another bone or implant implanted therein. The correction volume is preferably determined to support the implant in a stable manner. This reduces any effects of stress shielding. The correction volume is hereby preferably determined on the basis of a lower surface of the implant, i.e. the surface directed towards the bone. It is preferred if the correction volume is designed to have a correction surface, in particular the upper surface thereof, which is formed with a shape corresponding to the shape of the implant to be supported.

It is noted that the shape of the correction volume, in particular the correction surface thereof, need not to be formed to exactly match the surface of the implant. It is for instance possible that the correction volume is determined to be larger than the final volume of the defect-filling material between the bone and the implant. Placing the implant on said over-dimensioned correction volume will then result in compression or additional compaction of the defect-filling material upon fixation of the implant, which may be beneficial. It is then preferred if the correction volume, in particular the correction surface thereof, is formed to be geometrically similar to the implant, in particular the surface to contact the defect-filling material. It may further be possible to design the correction volume to be smaller than the actual volume between the implant and the bone in connected state. Under-dimensioning the correction volume allows for cement to be inserted between defect-filling material and the implant.

The correction volume is preferably determined so that in use, that is when the device is connected to the bone and defect-filling material is introduced in said volume, the defect is at least partially filled by said material. The defected bone is then at least partially filled or reconstructed, such that also the defected part of the bone can support the implant. This provides a more homogeneous support of the implant on the bone, also on the defected bone.

It is in particular important that the defected bone is sufficiently loaded after placement of the implant. In case the defected bone remains unloaded, for instance due to an implant bridging the defected bone, the quality of the defected bone may further diminish as unloaded bone tends to resorb. It is therefore preferred if the correction volume is determined to ensure sufficient loading on the defect bone in connected state of the implant to prevent bone resorption. Preferably, the defect is hereto substantially filled. It is hereby preferred if the correction volume is determined to be substantially congruent to the defect of the bone. The lower surface of the correction volume hereby preferably matches the surface of the bone. Correctly defining the lower surface of the correction volume allows an accurate determination of the correction volume and thereby also of the amount of defect-filling material to be used as will be explained in greater detail below.

It is however not necessary that the correction volume is located in the defect only. A correction volume may also be determined to be located on healthy bone surfaces to customize the surface thereof. It is for instance possible that the correction volume is designed on the basis of the implant, wherein the correction volume is designed to fill a volume between the bone and the implant. This for instance allows a custom fit of a generic implant on the bone, wherein the implant is at least partially supported by the defect-filling material in the correction volume. Instead of, or at least in addition to, reaming, i.e. removing bone to allow a fit between an implant and the bone, the bone surface may be customized to the implant using defect-filling material. It is further possible to provide a plurality of correction volumes.

It may however also be possible that the bone quality of the bone surrounding the defect is not suitable to support an implant and/or defect-filling material. In that case, it may be necessary to prepare or remove bone from the location on the bone. The removal or preparation of the bone may be planned pre-operatively, such that the determination of the correction volume may be based on the bone after preparation of the bone. For this case it is preferred if the method further comprises the step of planning bone preparation on the basis of the patient model and that the design of the device further comprises designing guiding features for guiding instrument for the preparation of bone in accordance with the planned preparation. The device can hereby function as guide for instrument to prepare the bone. The device may for instance be provided with suitable drill or saw guiding means, wherein the guiding means are positioned and oriented in accordance with the planned removal or preparation of the bone.

In particular when the defect-filling material is to be impacted as mentioned earlier, it is preferred that the device lies stably on the bone while the defect-filling material in the correction volume is being compacted. Therefore, a further preferred embodiment of the method according to the invention further comprises the step of planning fixation of said device, for instance using a screw, pin or wire, on the basis of the patient model, wherein the step of designing the device further comprises designing fixation means in accordance with the planned fixation. It is for instance possible to pre-operatively plan the trajectories and lengths of a plurality of screws or pins for connecting said device the bone to ensure that the device is reliably connected to said bone. The planning may for instance include determining the bone quality of the bone surrounding the device in connected state to ensure that for instance the screws or pins engage healthy bone. Preferably, the device according to the invention therefore further comprises fixation means for connecting the device to the bone, for instance using a screw, pin or wire, wherein the fixation means are designed on the basis of a pre-planned fixation of said device. The fixation means may for instance be formed as holes in said device, wherein the holes have an orientation in accordance with the planned trajectories. In order to ensure a stable fit of the device on the bone, it is preferred if the step of designing the bone-contacting surface comprises identifying a healthy bone surface and forming said bone- contacting surface substantially congruent to said identified bone surface. The bone surface is preferably identified to be remote from the defect such that the device does not rest on said defect to be corrected. Preferably the fixation means as mentioned above are then preferably arranged in said bone-contacting surface such that the device is connected to the healthy bone.

The device according to the invention preferably comprises an annular body arranged to surround the defect in the bone. Such a device is in particular suitable to correct an acetabular defect. The annular body is then designed to surround the acetabular region, which is typically defected. The annular body is then arranged to receive the defect-filling material to correct the defect or to allow fixation of an implant, such as a cup. It is then preferred if a volume-contacting surface is arranged on a radially inwardly surface of the annular body.

In order to ensure a reliable support of the device on the bone as mentioned above, it is then preferred if the bone-contacting surface is designed such that the bone-contacting surface engages a surface of the bone outside said cup. Preferably, a bone-contacting surface is arranged on a flange extending radially outwardly with respect to said annular body. It is hereby preferred if the radially outwardly bone-contacting surface is provided with fixations means. This ensures a reliable connection of the device to healthy bone. Some bones are defected to such an extent, that the bone is perforated. In order to be able to also correct perforated defect, a further preferred embodiment of the method comprises the step of identifying a perforation in the defect of the bone and wherein the step of designing the device includes designing a perforation-filling element such that the correction volume is at least partially enclosed by said perforation-filling element, the bone of the defect and the volume-contacting surface of the device. A preferred embodiment of a device according to the invention therefore comprises a perforation-filling element connected to said annular body for filling a perforation in the defect of the bone. This prevents the defect-filling material from leaking away trough the perforation. An efficient way of defining the correction volume with the device is obtained if according to a further preferred embodiment, the device is designed to substantially cover the defect, such that the correction volume is substantially enclosed by the volume-contacting surface and the bone, and possibly the perforation-filling element as described above, wherein the device is designed with at least one through hole extending between the exterior and the correction volume for introducing defect-filling material.

An efficient way of fixing an implant to the bone while using bone-reconstructing techniques using defect-filling material is obtained when the device is designed as an implant for correcting said defect. The device hereby not only functions to define and shape the defect-filling material, specifically in accordance with the predetermined correction volume, but also serves as implant itself. The device is then provided with a suitable implant surface which is shaped and defined in accordance with its function, for instance to receive another bone or an implant inserted therein. In order to provide a smooth surface for the implant, it is preferred if the method further comprises the step of designing and manufacturing at least one closing element for closing the through hole.

As an alternative, the device is arranged to align an implant according to a pre-operative planning. The method therefore preferably comprises the step of planning the position of an implant for correcting said defect on the basis of the patient model, wherein the step of designing the device further comprises designing implant connection means, wherein the implant connection means are arranged to align and connect the implant according to the planned position of the implant with respect to the device. As position and orientation of the device according to the invention is already uniquely defined using the bone-connecting surfaces, the device can also be used to correctly align an implant in accordance with a pre -operative planning. The connecting means may comprise alignment means which ensure a unique fit of the implant with respect to the device and thereby with the bone.

In order to ensure that the bone, in particular the defected bone, is sufficiently loaded, it is preferred that the implant-connection means be arranged to allow relative movement of the implant and the device along a predetermined direction. The movement of the implant with respect to the device, and thus with respect to the bone, will result in extra loads being transferred from the implant, preferably via the defect-filling material, to the bone. Preferably the direction is substantially parallel to the prevailing loading direction on the implant Joint loads are hereby transferred from the implant straight to the bone and defect-filling material, instead of to the device. This prevents stress shielding and promotes bone remodelling. The implant-connection means may for instance comprise cooperating guiding surfaces on the device and the implant which limit relative movement along a predetermined direction. Stops are then preferably arranged to limit said movement within a predetermined range. In order to allow an efficient and smooth movement between the implant and the device, a liner is preferably arranged between the implant and the device. The liner may for instance be formed from a suitable plastic. It is however also possible that the device according to the invention only serves to form the volume of defect-filling material, such that when the bone has been reconstructed, the device is replaced with an implant. According to a preferred embodiment, the device is then designed as a temporary device for providing the correction volume of defect-filling material on the bone to be replaced by a separate implant. The implant may for instance be a generic implant. In order to ensure a good fit of the implant on the bone, the method preferably further comprises the step of providing a design of the implant, wherein the correction volume is determined on the basis of the design of the implant and the patient model, such that the implant is at least partially supported by the defect-filling material in the correction volume and preferably has a unique fit on the bone and/or defect-filling material.

It is however also possible to use the device according to the invention in combination with a customized implant. A further preferred embodiment then further comprises the steps of:

planning the position of an implant for correcting said defect on the basis of the patient model;

- designing the implant on the basis of the planning and the patient model; and

manufacturing said implant, wherein the step of designing the implant comprises:

designing at least one volume-contacting surface on the basis of the determined correction volume such that the correction volume is at least partially enclosed by the bone and said volume-contacting surface;

- designing at least one bone-contacting surface arranged to contact a surface of the bone, wherein the bone-contacting surface is formed to be substantially congruent to said bone surface to ensure a unique fit of the implant on said bone.

The design of the implant may be based on the design of the device, in particular in terms of the bone-contacting surfaces and the volume-contacting surface. The latter further ensures a proper interconnection and fit of the implant and the defect-filling material.

The invention thus further relates to a combination, or a kit of parts, of a device according the invention and said implant, wherein the device is designed as a temporary device for providing the correction volume of defect-filling material on the bone to be replaced by the separate implant. A good fit between the applied defect-filling material and the implant is achieved when, according to a preferred embodiment, the implant and the device are provided with corresponding volume- contacting surfaces. An efficient design method is obtained if the implant and the device are provided with

corresponding bone-contacting surfaces. The bone surfaces identified for connecting the device to the bone are then also used for connecting the implant to the bone.

The device may further be provided with guiding means for guiding fixation means for fixing the implant to the bone, for instance in accordance with a pre -operative plan as mentioned above, wherein the implant is provided with corresponding fixation means. In this embodiment, the device may also function as drill guide which allows drilling screw holes in accordance with a pre- operatively determined plan. Next to guidance of fixation means, the device may further be used to guide means for bone preparation. The device is then preferably provided with tool-guiding means arranged to guide bone-preparing tools, such as saws, drills or the like. The device may for instance be provided with cutting slots or guides for reamers which are designed to guide the tools for preparation of the bone, in particular the bone defect. In order to be able to accurately reconstruct the bone according to plan, a further preferred embodiment of the method further comprises the step of determining an amount of defect-filling material for filling said correction volume and providing a container with said amount of defect- filling material. This ensures that the correct amount of material is available on site to fill the correction volume as planned.

A further preferred embodiment further comprises the step of providing an applicator device arranged for introducing defect-filling material in the correction volume, wherein the applicator device is provided with at least one engagement surface arranged for engaging said defect-filling material, wherein said engagement surface is designed in accordance with the determined correction volume. The applicator device is arranged to form the material introduced in accordance with the shape of the correction volume, in particular the surfaces of the volume which are not in contact with the bone, the volume-contacting surfaces or other shape-defining surfaces. The correction volume is then preferably enclosed by the engagement surface of the applicator device, the volume-contacting surface of the device, the bone and possibly the perforation-filling element as mentioned above. The engagement surface is preferably shaped in accordance with the correction surface.

The invention thus further relates to the combination, or a kit of parts, of a device according to the invention and an applicator as described. Specifically, the invention then also relates to combination of a device according to the invention and an applicator device arranged for introducing defect-filling material in the correction volume, wherein the applicator device is provided with at least one engagement surface arranged for engaging said defect-filling material, wherein said engagement surface is designed in accordance with the determined correction volume such that in combined situation on the bone, the correction volume is enclosed by the engagement surface of the applicator device, the volume-contacting surface of the device, the bone and possibly the perforation-filling element as described above.

Although the applicator may be generic impacting device, wherein the device is shaped in accordance with said applicator, it is preferred if the applicator device is customized to the device, in particular to ensure a unique fit between the applicator device and the device to ensure that the defect-filling material is applied according to the pre -operative plan. A further preferred embodiment therefore further comprises the steps of:

designing the applicator device wherein the applicator device is designed to be complementary to the device; and

manufacturing said applicator device. The applicator device may for instance be designed to mate with the device such that the applicator device is correctly aligned with any through holes which are provided in the device for introducing the material as mentioned above. The applicator device is hereby preferably provided with a member provided with an engagement surface fitting in said through hole. Also when using for instance an annularly shaped device, the applicator device is preferably designed to uniquely fit in the device, while still being movable for impacting the defect-filling material, to be able to accurately form the correction surface, on the basis of which the engagement surface of the applicator device is preferably shaped.

According to a further preferred embodiment, the applicator device comprises a plunger, wherein the plunger is movable between a first position such that the determined amount of defect-filling material can be contained in said applicator device and a second position such that the defect- filling material can be introduced in said determined correction volume. This ensures that the correct amount of material is introduced into the volume, while at the same time the material is correctly shaped in accordance with the correction volume as planned.

It is possible to use a single applicator device. It is however also possible to use a plurality of applicator devices, for instance one for each through hole provided in the device. The applicator devices are then preferably shaped in accordance with the location of said through holes, for instance in terms of volumes of material to be held and/or shape of the engagement surface. For that case, it is preferred if an applicator device and the associated hole are provided with unique alignment means to ensure that the correct applicator device is used for the correct hole. As an alternative, it is possible that the applicator device is formed integrally with said device. The device then functions as a defect-filling material shaping and introducing device. The device may then for instance be provided with one or more movable members as mentioned above.

To be able to reliably and accurately manufacture the device in accordance with the design thereof, according to a further preferred embodiment, the step of manufacturing preferably comprises using a three-dimensional printing technique, also referred to as rapid-manufacturing technique, layered- manufacturing technique, additive-manufacturing technique or material deposition manufacturing technique.

Rapid manufacturing includes all techniques whereby an object is built layer by layer or point per point by adding or hardening material (also called free-form manufacturing). The best known techniques of this type are stereo lithography and related techniques, whereby for example a basin with liquid synthetic material is selectively cured layer by layer by means of a computer-controlled electromagnetic beam; selective laser sintering, whereby powder particles are sintered by means of an electromagnetic beam or are welded together according to a specific pattern; fused deposition modelling, whereby a synthetic material is fused and is stacked according to a line pattern;

laminated object manufacturing, whereby layers of adhesive-coated paper, plastic, or metal laminates are successively glued together and cut to shape with a knife or laser cutter; or electron- beam melting, whereby metal powder is melted layer per layer with an electron beam in a high vacuum

In particular embodiments, Rapid Prototyping and Manufacturing (RP&M) techniques are used for manufacturing the device of the invention. Rapid Prototyping and Manufacturing (RP&M) can be defined as a group of techniques used to quickly fabricate a physical model of an object typically using three-dimensional (3-D) computer-aided design (CAD) data of the object. Currently, a multitude of Rapid Prototyping techniques is available, including stereo lithography (SLA),

Selective Laser Sintering (SLS), Fused Deposition Modeling (FDM), foil-based techniques, etc. A common feature of these techniques is that objects are typically built layer by layer.

Stereo lithography (SLA), a common RP&M technique, utilizes a vat of liquid photopolymer "resin" to build an object a layer at a time. On each layer, an electromagnetic ray, e.g. one or several laser beams which are computer-controlled, traces a specific pattern on the surface of the liquid resin that is defined by the two-dimensional cross-sections of the object to be formed. Exposure to the electromagnetic ray cures, or solidifies, the pattern traced on the resin and adheres it to the layer below. After a coat has been polymerized, the platform descends by a single layer thickness and a subsequent layer pattern is traced, adhering to the previous layer. A complete 3-D object is formed by this process.

Selective laser sintering (SLS) uses a high power laser or another focused heat source to sinter or weld small particles of plastic, metal, or ceramic powders into a mass representing the 3- dimensional object to be formed.

Fused deposition modeling (FDM) and related techniques make use of a temporary transition from a solid material to a liquid state, usually due to heating. The material is driven through an extrusion nozzle in a controlled way and deposited in the required place as described among others in U.S. Pat. No. 5.141.680. Foil-based techniques fix coats to one another by means of gluing or photo-polymerization or other techniques and cut the object from these coats or polymerize the object. Such a technique is described in U.S. Pat. No. 5.192.539. Typically RP&M techniques start from a digital representation of the 3-D object to be formed, in this case the design of the device. Generally, the digital representation is sliced into a series of cross-sectional layers which can be overlaid to form the object as a whole. The RP&M apparatus uses this data for building the object on a layer-by-layer basis. The cross-sectional data representing the layer data of the 3-D object may be generated using a computer system and computer-aided design and manufacturing (CAD/CAM) software.

The device of the invention may be manufactured in different materials. Typically, only materials that are biocompatible (e.g. USP class VI compatible) with the human body are taken into account. Preferably the device is formed from a heat-tolerable material allowing it to tolerate high- temperature sterilization. In the case SLS is used as an RP&M technique, the device may be fabricated from a polyamide such as PA 2200 as supplied by EOS, Munich, Germany or any other material known by those skilled in the art may also be used.

The invention further relates to a method for correcting a defect in a bone of a patient comprising the steps of:

providing a device according the invention, in particular as manufactured using the method according to the invention;

connecting the device to the bone;

inserting defect-filling material in the correction volume.

The present invention is further illustrated by the following Figures, which show preferred embodiments according to the invention, and are not intended to limit the scope of the invention in any way, wherein: figures 1 a-e show different steps of fixing an implant to a bone seen in cross section through the bone;

figures 2a-c show different ways of fixing the implant to a support device seen in cross section through the bone;

figures 3a-d show an alternative way of fixing an implant to a bone seen in cross section through the bone;

- figure 4 shows a top view of the device of figures 3a-d; figures 5a-d schematically show a further alternative way of fixing an implant to a bone seen in cross section through the bone;

figure 6a shows a top view of the applicator device of figures 5a-c;

figure 6b shows a top view of implant of figure 5d;

- figure 7 shows a device for filling a cavity in a defect seen in cross section through the bone; and

figures 8a and 8b show top views of devices for filling a cavity in a bone.

In figures la-e, a support device 2 is shown which is arranged to support and delimit a volume of defect-filling material 34 in a defect 12 in a bone 1. With further reference to figure 2a, it is shown that - in this example - the support device 2 has a substantially annular shape having an annular body 23 which surrounds the defect 12, which is in this case an acetabular defect.

In order to manufacture the device 2, a three-dimensional patient model of the bone 1 is obtained, on the basis of which the design of the support device 2 is made. More specifically, on the basis of the patient model which contains the three-dimensional bone morphology of at least the part of the bone containing the defect, a planning is made how to correct the defect 12 in the bone 1. In this example, it is planned to place a cup implant 4 in the defect 12, see figure Id. On the basis of the design of the implant 4, in particular the lower surface 41 thereof, a volume 3 is determined (see figure la) which is to be filled with defect-filling material 34 (see figure lb).

The upper or correction surface 33 of the correction volume 3 is planned to correspond to the shape of the lower surface 41 of the implant 4. As will be explained in greater detail below, the shape of the correction surface 33 is not determined to be exactly as the shape of the lower surface 41 of the implant 4. The lower surface 32 of the correction volume 3 is determined on the basis of the surface 13 of the defect 12 and the lower surface 32 is determined to be congruent to said surface 13 of the defect 12.

To support and delimit the defect-filling material 34 when inserted into the correction volume 3 (as shown in figure lb), the support device 2 is provided with a volume-contacting surface 21 which is provided along the inner surface of the annular body 23 of the support device 2. The bone surface 12 and the volume-contacting surface 21 thereby form a receptacle for the defect-filling material 34 to be inserted in a later step. In this example the correction volume 3 is enclosed on its lower surface 32 by the bone surface 12, on the upper surface 33 by a surface corresponding to the lower surface 41 of the implant 4 and at the sides 35 by the volume-contacting surface 21. It is however noted that determining the correction volume 3 is preferably based primarily on the lower surface 41 of the implant 4, or any other surface to be reconstructed. In a next step, the side boundaries 35 may be determined, for instance also based on the structural requirements of the support device 2. Dependent on the case, the amount of defect-filling material may vary. As a result, the correction volume 3 is at least partially enclosed and delimited by said volume- contacting surface 21.

As the correction volume 3 can be designed in great detail in relation to the bone 1, also the implant location can be planned accurately. It is therefore important that also the actual defect- filling material 34 ends up in the planned location. The support device 2 is thereto provided with in this example three bone-contacting surfaces 22 which are formed on flanges 24 of the support device 2, wherein specific reference is again made to figure 2a. The flanges 24 extend radially outwardly from the annular body 23. The bone-contacting surfaces 22 of the flanges 24 are formed congruent to the bone surface 11 onto which the bone-contacting surfaces 22 are designed to engage. The flanges 24 are furthermore provided with screw holes 25 arranged to receive bone screws to fixate the support device 2 to the bone 1. In this example, the support device 2 is to be permanently fixed to the bone 1. The screw holes 25 are positioned and aligned such that the screws to be inserted in the holes extend along pre-operatively planned screw trajectories. Also the annular body 23 is provided with flanges 26a provided with screw holes 26 to receive screws.

The bone-contacting surfaces 22 are formed to closely match the bone surfaces 11 such that the device 2 rests stably on the bone 1. The bone-contacting surfaces 22 on the other hand ensure that the support device 2 can only be placed on the bone 1 in a unique way, in this way ensuring the planned correction volume 3, which will also be defined by the volume-contacting surface 21, will be positioned on the bone 1 as planned.

After fixation of the device 2 to the bone 1, defect-filling material 34 can be inserted into the correction volume 3 using a suitable applicator. In figure lb this situation is shown. It can be seen that the top surface of the applied defect-filling material 34 does not yet correspond to the pre- planned correction surface 33 of the correction volume 3. In order to impact the defect-filling material 34 and to bring the material 34 into conformity with the correction volume 3 as planned, an applicator 6 is used.

In figure lc the applicator 6 is shown in inserted position. The applicator 6 is provided with an engagement surface 61 which has a shape corresponding to the correction surface 33 and therefore with the lower surface 41 of the implant 4. The applicator 6 is arranged to be received in the support device 2 in a predetermined way along a direction indicated with I such that the engagement surface 61 of the applicator 6 and the support device 2 are correctly aligned. This allows bringing the upper surface of the material 34 to conform to the pre-planned correction surface 33 of the correction volume 3.

In this example, the applicator 6 is provided with a flange 62 which is arranged to abut the upper surface of the support device 2, thereby limiting further movement of the applicator 4 with respect to the support device 2. As the applicator 6 is formed rotationally symmetrical in this example, the close fit of the applicator 6 in the support device 2 ensures a unique fit between the applicator 6 and the support device 2, thereby ensuring that the resulting upper surface of the material 34 corresponds to the correction surface 33 as planned. It is further possible to provide further alignment means, for instance in the form of a protrusion engaging in a slit to ensure proper alignment between the applicator 6 and the support device 2. After withdrawal of the applicator 6, the cup-shaped implant 4 can be inserted. The implant 4 is hereby arranged to closely fit the walls of a rim 21a arranged on the annular body 23 such that the position of the implant 4 (being also rotationally symmetrical) with respect to the support device 2 is uniquely defined. Other suitable means for ensuring a unique fit between the implant 4 and the support device 2 may be provided.

When comparing the thicknesses hi and h2 of the material layer above the bone surface 13 in figures lc and Id, it can be seen that the implant 4 even further compacts the defect-filling material 34 upon insertion. The pre-planned correction volume 3 therefore does not necessarily need to exactly match the lower surface 41 of the implant 4 as already mentioned above. Further compacting the material further facilitates retention as it promotes bone ingrowth from the bone surface into the defect-filling material 34.

In order to lock the implant 4 with respect to the support device 2, implant-connection means are provided which are formed as a locking ring 27b which fits in an annular groove 27a of the support device 2 in this example, see again figure 2a. As an alternative to the locking ring, discs 27d can be used which can be screwed in correspondingly shaped recesses 27c in the upper surface of the support device 2, see figure 2b. Figure 2c shows a further alternative, wherein the washers 27f that can be fixed to the support device in correspondingly shaped recesses 27e are shown. In the embodiment of figures 1 and 2, the device 2 serves to support the defect-filling material 34, in particular to shape the material upon insertion into the pre-planned correction volume 3. The support device 2 however only limits movement of the implant 4 transversely or radially, see arrows Π in figure Id and outwardly in the direction opposite to the direction indicated with I in figure lc. Loads in the direction indicated with I in figure lc, which are typical loads exerted on an acetabular cup implant 4, are directly transferred from the implant 4 to the defect-filling material 34 and then to the bone 1. It is hereby preferred that the correction volume 3, and thereby the design of the support device 2, is planned such that the exerted loads, or at least the majority thereof, are directly transferred from the implant to the defect-filling material.

It is hereby preferred if some movement in the direction indicated with I in figure le is allowed between the support device 2 and the implant 4. The locking ring 27b as shown in figure le, or any of the other connection means, may hereby delimit the movement. In the alternative embodiment of figure le, an annular liner 46 manufactured from a plastic having low friction coefficient is provided between the implant 4 and the support device 2 to prevent metal-on-metal friction. In the example shown, only movement parallel to the direction indicated with I is allowed, while other movements are blocked. Direction I is hereby parallel to the prevailing loading direction on the implant 4.

As an alternative as shown in figures 3 and 4, the device 2 can be designed as an implant 4, whereby the device 2 itself is provided with an upper implant surface 42 (see figure 3d). The device 2 is again provided with flanges 24 (see also figure 4) with bone-contacting surfaces 22 as used in the earlier embodiment. In this embodiment however, the device 2 is designed to substantially cover the defect 12. An implant-shaped part 23b is thereto provided inside the annular body 23a. The implant-shaped part 23b is cup shaped and has an upper surface 42 designed to function as an implant surface, for instance for receiving a liner, another bone or an implant provided therein. The lower surface 21 of the device 2 facing towards the bone 1 hereby again forms the volume-contacting surface 21. The volume-contacting surface 21 and the bone surface 13 hereby enclose the correction volume 3.

As is also visible in figure 4, the device 2 is provided with two through holes 28 which extend between the exterior (globally indicated with 100 in figure 3a) and the correction volume 3. These holes 28 are arranged to receive the defect-filling material 34 in order to fill the correction volume 3. In figure 4, also screw holes 26 are visible which are arranged to receive screws which are arranged to be inserted into the defect-filling material 34 and the bone 1, see the screw trajectories indicated in figure 3d. Figures 3b and 3c show two alternative ways of introducing the material 34 into the correction volume 3. In figure 3b, an applicator 6a is shown which is provided with a housing 65 wherein a plunger 64 is movably arranged. In the retracted position, the space defined in the housing 65 corresponds to a pre-determined volume corresponding to a pre-determined part of the correction volume 3. The total combination of applicators 6a (in this example two) are then arranged to contain the amount of defect-filling material 34 which corresponds to the volume of the correction volume 3. This ensures filling the correction volume 3 as planned and ensures that sufficient, but also not too much, defect-filling material 34 is inserted into the correction volume 3. Also this applicator 6a is designed to mate with the device 2 in a unique way. The housing 65 of the applicator 6a is on the outside thereto provided with flanges 62 which are received on the surface of the device 2. Other suitable alignment means can be used as mentioned earlier. In the extended position of the plunger 64, the material is injected into the correction volume 3 and the applicator 6a is designed such that the engagement surface 61 of the plunger 64 is then flush with the correction surface 33.

If the different applicators 6a to be used are mutually different in construction, for instance in terms of volumes or engagement surfaces 41, each of the applicators 6a is preferably provided with unique alignment means associated with its hole 28.

In the alternative of figure 3c, a single applicator 6b is used which is shaped to mate with the holes 28 of the device 2. Also in this embodiment, the applicator6 is preferably shaped to uniquely fit on the device 2. The applicator 6b is provided with protrusions 63 on which ends the engagement surfaces 61 are provided. The engagement surfaces 61 are again shaped to be flush with the correction surface 33, and thereby with the lower surface 21 of the device 2 in the final position of the applicator 6b. Also in this example, the applicator 6b is provided with a flange 62 to limit further movement.

In this example, a predetermined amount of material 34 can be inserted into the cup of the device 2 to be subsequently pressed into the correction volume 3 using the applicator 6b. The material 42 is preferably taken from a customized container shaped to contain the amount of the defect-filling material suitable for filling the predetermined correction volume 3.

In order to provide a smooth implant surface 42, inserts 29 are provided which are shaped to closely fit the holes 28 such that upon insertion of the inserts 29, a smooth surface 42 is formed. In the above embodiments, the device 2 remains fixed to the bone 1. In the first example the device acts as a support device for supporting an implant, whereas in the second example the device itself is formed as an implant. In the embodiment of figures 5 and 6 however, the device 2 is only temporarily connected to the bone to be subsequently replaced by an implant. This allows the use of different materials for the device 2 and the implant 4.

Although it is possible to use a device as shown in the second example for introducing the defect- filling material into the defect to subsequently replace the device 2 with an implant, this principle will be explained using a device 2 with integrally formed plungers 64.

The device 2 as shown in figure Sa is again provided with flanges 24 provided with bone- contacting surfaces. See also figure 6a. It can be seen that only a limited amount of screw holes 25 are provided, as the device 2 only needs to be fixed to the bone 1 temporarily. The device is again provided with a volume-contacting surface 21 which is shaped in accordance with the correction surface 33 of the correction volume 3. The correction surface 33 is again shaped in accordance with the lower surface 41 of an implant to be received, see figure Sd.

The device 2 is again provided with through holes 28, three in this example, see the top view of figure 6a. The device 2 is however provided with tubular guides 64a wherein plungers 64 are provided. The guides 64a only allow a linear movement of the plungers 64 held therein. The plungers 64 are again movable between a retracted position, wherein combined spaces 69 formed in the device 2 correspond to the correction volume 3 such that the amount of material 34 to be inserted into the correction volume 3 can be held in the device 2. Upon moving the plungers 64 to their extended position, see figure Sb, the held material will be injected into the space between the device 2 and the bone 1, thereby filling the correction volume 3. The movement of the plungers is limited (not shown) such that in their extended positions, the end surfaces forming the engagement surfaces 61 are flush with the correction surface 33 as planned. In the next step, the device 2 can be removed, see figure Sc, to be replaced by an implant 4, see figures Sd and 6b. The implant 4 is shaped similar to the device 2, with the difference that now an implant surface 42 is provided instead of the applicators in the form of plungers 64. The implant 4 is for instance provided with flanges 44 which correspond to the flanges 24 of the device 2. The implant 4 can be fixed to the bone 1 using the screw holes 45 and 26. In the above embodiments, the acetabulum is shown to be defected but still more or less cup shaped. It is however also possible that the bone contains a perforation 14 as shown in figure 7. In order to be able to use defect-filling materials in this kind of defects, a perforation-filling element 5 is designed on the basis of the patient model which is arranged to fill the perforation 14. The correction volume 3 is thus enclosed by the perforation- filling element S, the bone surface 13 (see the top view in figure 8a) and the volume-contacting surface 21 of the device 2. As the perforation is located at the bottom of the cup, a connecting structure 51 is provided to connect the perforation- filling element to the device 2. Also when the perforation is located elsewhere, see for instance figure 8b, it may be advantageous to provide a connecting structure 51 to ensure structural integrity. The present invention is not limited to the embodiments shown, but extends also to other embodiments falling within the scope of the appended claims.