FIELD OF THE INVENTION

The invention is in the field of medical technology. It relates to a surgical system comprising an implant and at least one bone anchor suitable for fixating the implant relative to bone tissue in a human or animal patient, wherein the implant comprises a through opening and the bone anchor comprises a head and a shaft, wherein the implant and the bone anchor are adapted to each other for the anchor shaft to be able to pass through the through opening and the anchor head to be retainable relative to the through opening in a final position. The invention further relates to the bone anchor and the implant of the system. BACKGROUND OF THE INVENTION

Implants fixated relative to bone tissue of a human or animal patient with the aid of at least one bone anchor cooperating with a through opening in the implant are widely used in all sorts of surgery procedures. For many of the applications, the implant is a bone plate and the bone anchor is elongated and possibly fenestrated. Examples of known applications of the named systems are e.g. stabilization of bone portions separated by fracture or osteotomy, stabilization of implants such as e.g. interbody fusion devices, intramedullary nails, fixation of endoprostheses replacing a joint or part thereof, or fixation of spine supporting instrumentation, such as e.g. rods and rod receiving elements. The implant of such systems comprises at least one through opening and the at least one bone anchor comprises a head and a shaft, wherein the shaft is driven through the through opening into the bone tissue and the head is retained on a proximal side of the opening or within the latter, for example in a shallow proximal indentation. The shaft of the anchor is equipped for being retained in the bone tissue in a press fit by corresponding dimensioning of the anchor and an opening provided for it in the bone tissue, and/or in a form fit with the aid of suitable retention means such as e.g. a thread, teeth, cutting edges, resilient retention elements, and/or by being equipped for augmentation when positioned in the bone tissue with the aid of e.g. a bone cement or a material having thermoplastic properties. For such augmentation the anchor comprises a longitudinal cavity and preferably lateral channels, wherein the cement, in a flow able form, is pressed into the longitudinal cavity and through the lateral channel into neighboring bone tissue, or wherein the material having thermoplastic properties is positioned in the longitudinal cavity, is liquefied therein by applying energy to it and is pressed, in a liquefied state, through the fenestration to re-solidify within the bone tissue surrounding the bone anchor or between such bone tissue and the bone anchor.

For safeguarding the long-term stability of systems of the above-named type, it is known to provide the system with a locking mechanism for preventing a backward movement (in a direction opposite to the implantation direction) of the bone anchor due to natural motion of the bone tissue in which the anchor is fixated and loosening of the anchor retention in the bone tissue. Locking of the anchor relative to the through opening of the implant is activated as soon as the anchor has reached its final position relative to the through opening, in which position, the anchor head usually abuts on a proximal surface of the implant or inside the through opening. Such locking may be designed to be actively reversible by e.g. a surgeon or it may be practically irreversible.

Known examples of locking mechanisms for the named purpose comprise locking elements arranged on the implant and/or on the anchor, wherein for the locking process, the locking element is moved into a locking position either actively by a surgeon or passively by e.g. relaxation of an elastic tension, or it is deformed, for which purpose it may have to be brought into a deformable configuration by e.g. being heated. Examples of known locking elements are e.g. resilient rings cooperating with grooves in implant and/or anchor, pivoting or slidable elements being locked in a locking position with e.g. the aid of a set screw, elements of a deformable, e.g. thermoplastic, material.

US 2016/0058480 discloses a fastener for a spinal interbody system, wherein the fastener is a screw. The screw has a collar with a plurality of petals with a free edge projecting towards proximally. The petals can flex relative to the shaft and the head of the screw. For fastening a plate to tissue, the collar is driven through an aperture of the plate, and the petals flex out distally of the plate, so that plate is sandwiched between a proximal lip (head) of the screw and the collar so as to lock the fastener relative to the plate. US 2015/0216573 discloses an implantable cervical plate assembly comprising a cervical plate and one or more bine fasteners being bone screws. The heads of the bone screws include one or more breakable structures configured to be broken when inserted into a groove of the bone plate and then unflex and remain captured in the groove so as to prevent disengagement of the crew after attachment to the vertebral elements. In case the bone screw after insertion is rotated counter-clockwise, the breakable components hit the sidewall and flex outward so as to increase the effective diameter of the screw head. This prevents the screw head from accidentally moving up and away from the plate.

The publication WO2010/096942 discloses systems of interbody fusion devices of the stand-alone type comprising an interbody implant and a bone plate cooperating with the interbody implant or forming an integral part therewith. The plate comprises a plurality of through openings, and the system further comprises a plurality of elongate fenestrated bone anchors suitably adapted to the through openings for fixating the plate to vertebral bodies. For locking the anchors in their final position relative to the through openings, it is suggested to provide a locking protrusion on the fenestrated anchor shaft cooperating with the distal plate surface or a groove in the through opening. On advancing the anchor shaft through the through opening, the locking protrusion is forced through the narrowest part of the through opening by at least locally elastically deforming at least a part of the wall of the fenestrated anchor shaft and, on arrival of the anchor in its final position, the deformed wall portion relaxes and the locking protrusion snaps back beyond the distal surface of the plate or into a suitable groove provided in the through opening. The named locking mechanism is very simple regarding manufacturing and operation. However, it restricts design and material choice for the bone anchor of the system considerably as it necessitates a relevant elastic deformability of the wall of the anchor shaft. For instance, it can hardly be adapted to function with a solid, i.e. non-cannulated anchor, or with a cannulated anchor having a rigid wall.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a system comprising an implant with at least one through opening and at least one bone anchor with a head and a shaft, wherein the through opening and the anchor are adapted to each other for the anchor shaft to be able to pass through the through opening and the anchor head to be retained by a proximal surface of the implant or in the through opening, thereby limiting movement of the anchor in a distal direction and defining a final position of the anchor relative to the implant. The system further comprises a locking mechanism for locking the anchor in the named final position for preventing it from moving in a proximal direction (backing out) away from its final position. The locking mechanism of the system according to the invention is to be operable without the necessity of a separate locking element and without a separate locking step, and it is to be manufacturable without a separate manufacturing step. Furthermore, the locking mechanism is to limit design and material choice of the implant or the bone anchor as little as possible. Preferable manufacturing processes suitable for manufacturing implant and/or bone anchor together with the locking mechanism are in particular additive manufacturing processes (3D-printing processes) as well as processes involving a material removal step, such as milling.

This object is achieved by the system of implant and bone anchor according to the invention, or by the bone anchor or the implant of the system.

The surgical system according to the invention comprises an implant with at least one through opening defining an opening axis and at least one bone anchor with a head and a shaft and an anchor axis, the through opening and the bone anchor being adapted to each other for the anchor shaft to be able to pass through the through opening and the anchor head to be retained by a proximal surface of the implant or in the through opening, for example in a shallow indentation in the proximally facing face of the implant, the shallow indentation belonging to the through opening, in a final position. For locking the anchor in said final position, the system further comprises at least one locking element being moveable between a relaxed position in which it protrudes from a general level of a surface portion of the anchor or the through opening and a resiliently tensioned position in which it protrudes less from or is substantially flush with said level. Therein the locking element is an integral part of the bone anchor or of the implant, constituting a part of the named surface portion and of a bulk of the anchor or the implant situated underneath this surface portion. A void delimits the locking element in the surface portion and further extends underneath the locking element or through the named bulk.

The locking element of the system according to the invention cooperates, if arranged on the bone anchor, with corresponding surface portions on the implant, preferably within the through opening, and, if arranged in the through opening, it cooperates with corresponding surface portions of the anchor, preferably of the anchor head. Such locking surfaces are in particular inner surfaces of grooves or depressions or portions of a distal surface of the implant or of a proximal surface of the anchor.

Especially, the locking element and the corresponding surface portion may be equipped to prevent a backing out movement independent on whether the bone anchor comprises a thread or not. To this end, in contrast for example to a system as taught in US 2015/0216573, they may be equipped to be suitable both, for an insertion of the bone anchor by an axial movement of the bone anchor relative to the implant without substantial rotation and for preventing a backing -out movement of the bone anchor into a proximal direction also without substantial rotation. Thereby, the locking mechanism may be configured for cooperating together to prevent the bone anchor from backing out independent of the structures and mechanism by which it is retained in the bone tissue. Especially, it is suitable for cannulated bone anchors anchored by bone cement pressed out from the cannulation into surrounding bone tissue, or by thermoplastic material using the approach as for example taught in WO 2011/054122 - independent on whether or not the bone anchor has an additional outer thread. The anchor may have a smooth outer surface, preferably over at least 20%, even more preferably over more than 50% of its length. Moreover, it may not have an outer screw thread in this area with a smooth outer surface.

The bone anchor may be a fenestrated bone anchor, wherein the shaft further comprises a longitudinal cavity extending in the direction of the axis from the proximal end towards the distal end and at least one lateral channel extending through a wall of the shaft from the axial cavity to the circumferential surface.

For guiding the movement and tensioning of the locking element on moving the bone anchor in a distal direction in the through opening, the locking element may to this end comprise a ramp leading parallel to the direction of this movement from a lower to a higher level, wherein, if the locking element is arranged on the bone anchor, the higher level is situated proximally of the lower level, and, if the locking element is arranged in the through opening, the higher level is arranged distally of the lower level. The locking element and the locking surfaces may be designed for a loose fit in the locked position.

The locking element of the system according to the invention is constituted as a resilient beam being supported on one beam end (resiliently pivoting cantilever) or on two opposite beam ends (resiliently bending beam), wherein the resilient beam is cut out of the bulk of the bone anchor or the implant, i.e. it is delimited by a void extending at least along a beam length and, in the case of a sufficiently thin bulk portion, extends right through this bulk portion (beam thickness substantially the same as local bulk thickness), or, in the case of a thicker bulk portion, extends additionally underneath the beam (beam thickness constituting part of local bulk thickness). The locking element may be such that no substantial plastic deformation or even disruption occurs. In the relaxed position, which corresponds to the locking position, the locking element may be in its initial position relative to the shaft and head, i.e., the position the locking element had before insertion in the through opening. In a relaxed position, the resilient locking element protrudes from a general level of a surface portion of the bone anchor or the through opening in which it is situated. On moving the bone anchor into its final position relative to the through opening, the resilient locking element is pivoted or bent out of the relaxed position to a resiliently tensioned position in which it does not protrude or protrudes less from the general level of the surface of the anchor or the through opening, and, when the final position is reached, it snaps back into its relaxed position.

In a special group of embodiments, the head forms a radial protrusion in a vicinity of the proximal end of the bone anchor, for example a ring-shaped protrusion. In this special group of embodiments, the resilient locking element forms part of this radial protrusion, and the corresponding surface portions of the implant are within the through opening. Especially, the resilient locking element may form an arc-shaped beam with a radius of curvature corresponding to the radial distance from the bone anchor axis. Such beam may be supported on both sides and thereby form part of the ring-shaped protrusion in a manner symmetrical with respect to twisting directions. A locking protrusion forming the ramp and, on a proximally facing side, the locking surface, may protrude radially from the beam, for example in a middle position between the sides on which the beam is supported.

This configuration has not only been found to have a very good ratio between used material and space on the one hand and stability provided on the other hand. It is also advantageous in terms of manufacturing, since the structure may be manufactured also by material removing processes, for example by a material removing tool that cuts the arc-shaped void radially-inwardly of the arc-shaped beam into the material of the ring- shaped radial protrusion that forms the head.

In a further group of embodiments, which includes embodiments of the mentioned special group of embodiments, the head of the bone anchor may form a proximally facing shoulder, whereby the portion with the greatest radial extension - for example including the arc-shaped beam in embodiments of the special group - is offset towards distally from the proximal end of the bone anchor. Such offset may be substantial, i.e. sufficient for the bone anchor portion proximally of the shoulder having a guiding function. For example, the offset may be by at least 0.3 mm or at least 0.5 mm or at least 0.7 mm. The portion proximally of the shoulder may form a substantially cylindrical or possibly slightly conical (taper angle for example at most 10°) guiding surface.

This structure with the proximally facing shoulder firstly brings about the potential advantage that the bone anchor may be inserted by a method that mechanically loads the proximal end of the bone anchor, for example by hammering. Secondly, a hollow guiding tool, such as a guiding tube or guiding sleeve, may be put over the bone anchor portion proximally of the shoulder, with its distal end resting against the shoulder and being supported thereby. Such hollow guiding tool may be used to insert material - such as a thermoplastic element in a solid state or also bone cement - into a longitudinal cavity of the bone anchor and/or may be used to guide a tool by which energy is coupled into material inserted at least partially into such cavity. Alternatively or in addition, such guiding tool may reach into the anchor resting on the bone anchor portion proximally of the shoulder. Therefore, the present invention also concerns a set of parts that comprises a system as described and claimed in the present text and in addition comprises a hollow guiding tool adapted to be put be put over the bone anchor portion proximally of the shoulder, with its distal end resting against the shoulder and being supported thereby. In embodiments, the bone anchor is capable of being inserted by a movement in essentially axial direction, without substantial rotation. Thus, in these embodiments the bone anchor is free from any outer threads or similar and does not need any structures for a subjecting the bone anchor to rotation.

The implant and/or the bone anchor of the system according to the invention are both made of a medically acceptable metal, polymer or ceramic material, wherein particularly the one of the bone anchor and the implant (or the part thereof comprising the through opening) which comprises the locking element is preferably manufactured using an additive manufacturing process (3D printing process). Bone anchor and/or implant (or part thereof) consist e.g. of a suitable titanium alloy, a CoCr-alloy or a molybdenum-rhenium alloy and are manufactured using a selective laser sintering a process, a selective laser melting process or an electron beam melting process.

One of a plurality of preferred embodiments of the bone anchor is part of a system constituting an interbody fusion device of the stand-alone type comprising an interbody fusion implant, a bone plate with a plurality of through openings and a plurality of bone anchors adapted to the through openings of the plate and suitable for fixating the plate relative to two neighboring vertebral bodies. Known such systems are e.g. disclosed in the publication WO2010/096942, which is enclosed herein in its entirety by reference. The plate of the system may constitute a fully separate element, may be fixed on the interbody implant or may form one integral part therewith. The interbody fusion implant is positioned between two neighboring vertebral bodies, the plate is arranged on the anterior or on a lateral side of the two vertebral bodies and is fixated thereto with the aid of the bone anchors. The bone anchors preferably used in the system are elongate fenestrated bone anchors with a head and a shaft, which bone anchors are driven into the bone tissue of the vertebral body through the through openings of the plate, and are anchored in the vertebral body e.g. with the aid of a material having thermoplastic properties and being liquefied by application of e.g. vibration energy within a central cavity of the fenestrated anchor and pressed to the outside of the anchor through lateral channels to re-solidify preferably within the trabecular structure of the bone tissue surrounding the anchor or between the bone tissue and the anchor.

The bone anchor of the system according to the invention may be a fenestrated bone anchor and further comprise the following features.

The fenestrated bone anchor comprises a shaft and possibly a head, the shaft having a proximal end, a distal end, and a longitudinal axis and a circumferential surface extending from the proximal end to the distal end, as well as a longitudinal cavity extending in the direction of the axis, if applicable, through the head and from the proximal shaft end towards the distal shaft end. Furthermore, the shaft comprises at least one lateral channel (e.g. two to four lateral channels) extending through a wall of the shaft from the longitudinal cavity to the circumferential surface. This wall has a wall thickness and the lateral channel has a cross section with an axial length and a width smaller than the axial length, wherein the width of the cross section of the lateral channel increases in a distal direction and/or the wall thickness increases gradually in selected ones of directions towards the lateral channel. This means that the cross section of the lateral channel or channels has a pear-shape and that in addition or alternatively the wall between the axial cavity and the circumferential surface has a thickness which is not the same around the longitudinal cavity but is largest at least partially where adjoining the lateral channel and is decreasing gradually in a direction away from the lateral channel.

The named design features make the fenestrated bone anchor particularly suitable for an anchoring process by augmentation with the aid of a material having thermoplastic properties as described briefly further above, for applications in which more proximal augmentation is desired, and for applications in which the proximal anchor end is more rigidly fixated (e.g. in a plate or in cortical bone) than the distal anchor end (e.g. in trabecular bone) and therewith bending load increases from the distal end towards the proximal end. The named mechanical conditions are in particular applicable for anchors used for fixating e.g. a plate on a vertebral body or in a meta- or epiphyseal region of a long bone or also for suture anchors, in which cases the preferred anchorage is as near as possible to the cortex where bone density is highest and where a body of augmenting material can lean on the cortex and so to speak extend the thickness of the cortex. In particular, the design measures of the pear-shaped cross section of the lateral channel and/or the wall thickness increasing towards the lateral channel make it possible to give the lateral channels a cross section guaranteeing satisfactory flow of the liquefied material with a minimum of quenching and still giving the anchor mechanical characteristics which allows it to bear the bending stress even if the lateral channel is arranged in a proximal portion of the anchor. The named design measures result in the anchor being homogeneously stressed over its length at a minimum of notch stress, which is particularly important for anchors subjected to cyclical stressing.

Preferably, the anchor is designed for the bending moment to vary less than about 20% at least along the anchor portion in which the at least one lateral channel is situated, preferably over half of the anchor length in which the lateral channel is situated and even more preferably over the entire anchor length.

The fenestrated bone anchor consists of a medically acceptable metal, polymer of ceramic material and it is preferably manufactured using an additive manufacturing method. The bone anchor consists e.g. of a suitable titanium alloy, a CoCr-alloy or a molybdenum-rhenium alloy and is manufactured using a selective laser sintering a process, a selective laser melting process or an electron beam melting process.

An exemplary embodiment of the fenestrated bone anchor which is made of a titanium alloy and is suitable for fixating a lumbar spinal fusion device as disclosed in the above-mentioned publication W02010/096942 has about the following dimensions: overall length (head and shaft) 25 mm, axial position of the lateral channels 3 to 4 mm below the plate, axial length, distal width and proximal width of cross section of lateral channels 3.8 mm, 1.8 mm, 1.4 mm, wall thickness of shaft below head and in the area of the lateral channels 0.7 mm and 0.6 mm. The above described system according to the invention is particularly applicable in an intervertebral fusion device or similar bone implant, wherein such intervertebral fusion device or similar bone implant may have the following features.

The bone implant comprising the system according to invention is a load-bearing bone implant suitable for being implanted in a human or animal patient between surfaces of live bones or bone fragments, suitable for bearing at least temporarily loads acting between these bones or bone fragments, and suitable for being integrated between the bones or bone fragments by bone growth after surgery. Such bone implants are applicable in surgical procedures such as e.g. spinal fusion, arthrodesis and osteotomy. The named bone implant comprises a porous implant body with an open porosity constituting throughout the porous implant body a three-dimensional network of porosity channels of dimensions suitable for bone ingrowth, which porous implant body constitutes two substantially opposite body surfaces (ingrowth surfaces) to be positioned against the live bone tissue on implantation. In addition to the porosity channels, the porous implant body comprises a plurality of supply channels, wherein each one of the supply channels has a mouth in at least one of the ingrowth surfaces and extends into or preferably through the porous implant body substantially parallel to the force lines of the force field acting on the implant in the implanted state. Therein the supply channels have cross sections larger than the cross sections of the porosity channels, but small enough for being bridgeable by spontaneous bone growth without bone growth enhancing material positioned in the channels.

The porosity channels of the porous implant body of the bone implant have cross sections with diameters in the range of 0.1 to 0.7 mm diameter, preferably in the range of 0.4 to 0.6 mm. The supply channels have cross sections of any suitable form of which the smallest dimension is in the range of 1 to 3 mm and, throughout the porous implant, they have distances from each other in the range of 2 to 6 mm, preferably in the range of 3 to 5 mm. The total volume of the porosity channels and the supply channels together constitute 40 - 80% of the volume of the porous implant body, preferably 60 - 80%).

The design of the porous implant body of the bone implant is based on the following findings. Bone ingrowth into porous implant body structures more or less mimicking the trabecular structure of natural bone tissue is successful only to a depth of 1 to about 3 mm (probably limited by the supply of the ingrown bone tissue by diffusion only). Spontaneous bone growth, i.e. bone growth within weeks after surgery, will bridge gaps of a width of not more than about 3 mm. In larger cavities (all dimensions larger than about 3 mm), bone growth will primarily cover the walls of the cavity, wherein in such cavities having a smallest dimension of not more than about 10 mm (7 to 10 mm), long term bone growth, i.e. bone growth within months, will be able to bridge the cavity, and wherein even larger cavities (all dimensions larger than 7 to 9 mm, critical size defect) do not fill with bone tissue at all, unless they are filled with a bone growth enhancing material such as e.g. bone graft material. No or hardly any ingrowth of bone tissue into the implant is found from implant surfaces other than the implant surfaces (ingrowth surfaces) being, in the implanted state, in direct contact with live bone tissue of the patient, i.e. ingrowth of bone tissue into the implant is highly anisotropic. Based on the above listed findings, the supply channels of the porous implant body of the bone implant to the invention originate from the ingrowth surfaces, have cross sections large enough for allowing ingrowth of bone tissue including supply means such as in particular vasculature and lymph channels and small enough for being bridged, i.e. completely filled with bone tissue, and, if suitably distanced from each other (and possibly from ingrowth surfaces) throughout the porous implant body enable bone growth in all location thereof. Furthermore, it is found that supply channels longer than about 20 mm are preferably equipped with an enlarged mouth portion.

The orientation of the supply channels along the force lines is advantageous from a mechanical point of view. In most considered cases, these force lines extend substantially parallel to each other from one of the ingrowth surfaces to the opposite other one. Therefore, in a preferred arrangement, the supply channels extend substantially parallel to each other from one ingrowth surface towards the other one, wherein, for being able to supply the largest porous volume with the smallest number of supply channels, the latter are arranged in a hexagonal system, wherein, in a cross section through the channel arrangement, each channel has six neighboring channels at a same distance. The bone implant comprises, in addition to the porous implant body, a support frame which partially surrounds and possibly also penetrates the porous implant body. The support frame is made of a suitable, preferably non-porous material. The support frame constitutes at least part of a proximal implant surface (trailing surface on implantation, usually not an ingrowth surface) and members e.g. running along edge regions of the porous implant body, which edge members e.g. surround ingrowth surfaces without protruding from the latter, extend in ingrowth surfaces, or penetrate the porous implant body. Outer surfaces of the support frame may be equipped with a per se known osseointegration enhancing surface structure or coating, at least where they are to be positioned against surfaces of live bone tissue and where osseointegration is desired.

The bone implant may comprise further elements of a substantially non-porous material. Such further elements are e.g. surface elements, which are arranged in the ingrowth surfaces and flush therewith and may serve for facilitating implantation by reducing friction between the ingrowth surface and the surface of the live bone tissue without impairing the direct contact between the porous implant body and the live bone tissue. The surface elements e.g. surround mouths of supply channels and therewith help to prevent mechanical damage of the mouth edges. Further such elements may also be struts extending along the wall of selected ones of the supply channels and serving as stiffening and supporting means. While the dimensions of the members of the support frame depend on the type and size of the implant and on the load the latter has to bear when implanted, the surface elements have dimensions which are as small as possible. In a medium interbody fusion implant, the members of the support frame have e.g. widths and depth (into the porous implant body) in the range of a few millimeters (2 to 5 mm) and the surface elements have widths and depths of about one millimeter (0.8 to 1.5 mm). The same applies to the struts. The bone implant may, in the same manner as known such implants, further comprise a larger cavity to be filled with bone growth enhancing material, wherein this cavity may, in a per se known manner, reach from one ingrowth surface to the other one. Furthermore, the bone implant may comprise per se known mechanical retention means.

The porous implant body is made of a suitable, medically approved metal, polymer or ceramic material, e.g. titanium (grade 1-4), titanium alloy (e.g. Ti-6A1-4V or Ή-7A1- 1 INb), resorbable magnesium alloys, PEEK, polylactide (resorbable), biocomposites, zirconium oxide, aluminum oxide or mixtures of the two oxides, or calcium phosphate (tri-calciumphosphate, hydroxyapatite, both resorbable). The porous implant body is preferably manufactured using an additive manufacturing method, e.g. selective laser sintering, e-beam melting, or fused deposition (in particular for polymer and ceramic material). For strengthening the porous structures manufactured e.g. with the named 3D-printing methods they may be compacted by HIP-processes. For rendering them more bio-active, they may be surface treated in galvanic or non-galvanic processes (e.g. etching or nano-deposition).

Preferably, the support frame and possibly also further elements and retention means of the bone implant are made of the same material as the porous implant body and are manufactured in the same additive process as the porous implant body such forming one integral part with the latter.

The bone implant is particularly suitable for applications in which the ratio between implant surface and implant volume is relatively small (relatively large implant bulk), in particular it is suitable for applications requiring an implant thickness (distance between opposite ingrowth surfaces) in the range of 4 to about 30 mm. Furthermore, it is particularly suitable for applications in which provision of permanent mechanical retention structures is limited, and for which long-term success of the corresponding surgical procedure is highly dependent on successful bone growth after surgery. This is e.g. the case for interbody fusion devices used in spine surgery, for various implants used in other arthrodesis methods, and for wedge-shaped implants used in various osteotomy procedures.

One of a plurality of preferred embodiments of the bone implant is an interbody fusion implant, which may be of the stand-alone type or of the type which is combined with further instrumentation such as e.g. systems of pedicle screws and spinal rods. Known such implants are e.g. disclosed in the publication WO2010/096942, which is enclosed herein in its entirety by reference. The devices as disclosed in the named publication comprise an interbody implant and, if of the stand-alone type, a plate which constitutes a separate element or is fixedly arranged on the interbody implant. The plate is fixated on the anterior or on a lateral side of the two vertebral bodies between which the interbody implant is positioned. For the fixation of the plate, in particular fenestrated headed bone anchors are proposed, which bone anchors are driven into the bone tissue of the vertebral body through through openings provided in the plate and are anchored in the vertebral body e.g. with the aid of a material having thermoplastic properties and being liquefied by application of e.g. vibration energy within a longitudinal cavity of the anchor and pressed to the outside of the anchor through lateral channels (fenestration) to re-solidify preferably within the trabecular structure of the bone tissue surrounding the anchor or between the bone tissue and the anchor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in further detail in connection with the appended Figs., wherein: Figs. 1A/B/C illustrate the principle of an exemplary locking element of the system according to the invention, the illustrated locking element having the form of a resilient cantilever;

Figs. 2A/B/C illustrate the principle of an exemplary locking element of the system according to the invention, the illustrated locking element having the form of a resilient bending beam;

Figs. 3A/B/C shows an exemplary embodiment of a bone anchor of the system according to the invention, the bone anchor comprising a locking element in the form of a resilient cantilever, the cantilever length extending substantially parallel to the movement of the bone anchor relative to the through opening;

Figs. 4A/B show an exemplary embodiment of a bone anchor of the system according to the invention, the bone anchor comprising a locking element in the form of a resilient cantilever, the cantilever length extending substantially perpendicular to the movement of the bone anchor relative to the through opening; Figs. 5A/B/C show an exemplary embodiment of a bone anchor of the system according to the invention, the bone anchor comprising a locking element in the form of a resilient bending beam, the beam length extending substantially perpendicular to the movement of the bone anchor relative to the through opening; Figs. 6A/B/C illustrate an exemplary embodiment of fenestrated bone anchor, the embodiment comprising three lateral channels with pear-shaped cross sections;

Fig. 7 is a plan view of the fenestrated bone anchor according to

Figs 6A/B/C (viewing direction towards the head of the anchor);

Figs. 8 and 9 are cross sections through further exemplary embodiments of fenestrated bone anchors, the embodiments comprising an increase in wall thickness in a direction towards the lateral channels;

Figs. 10 and 11 illustrate the principle of a bone implant, the bone implant being shown in section perpendicular to ingrowth surfaces of the porous implant body;

Figs. 12, 13, 14 are cross sections of exemplary embodiments of supply channel arrangements;

Fig. 15 illustrates a further exemplary embodiment of the bone implant;

Fig. 16 shows an interbody fusion device of the stand-alone type comprising a plate with through openings suitable for being fixated to vertebral bodies with the ais of bone anchors.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the whole of the present text the term proximal is used to designate a position nearer a surgeon and the term distal a position nearer the patient. Similarly, a proximal direction means a direction towards the surgeon and a distal direction a direction towards the patient or further into the patient. Each item has a proximal end and a distal end, the distal end being the leading end on implantation and the proximal end being the trailing end on implantation. Most described items have a proximal end and a distal end and an axis extending therebetween, wherein this axis, on implantation, substantially coincides with or is substantially parallel to the implantation direction, and wherein the length of this axis may or may not be the longest or main axis of the item.

Features of the system according to the invention which are described further above without restriction of their applicability are applicable for all exemplified embodiments of the system according to the invention and as illustrated in the appended figures. Similar elements or elements having same functions are designated with same reference numerals in all appended figures.

Figs. 1A/B/C and 2A/B/C illustrate each in a schematic manner the principle of exemplary embodiments of locking elements 200 of the system according to the invention. Each one of these Figs shows a surface portion 201 of a bone anchor or through opening of an implant belonging to the system, wherein the locking element 200 is arranged within this surface portion 201. Figs. 1A, 1C, 2A and 2C are sections through the surface portion 201 and the locking element 200, the section plane being oriented substantially parallel to the axis of the bone anchor or the through opening, or to the implantation direction respectively. These Figs show the locking element 200 in its relaxed position (uninterrupted lines), in which it protrudes from the general level of the surface portion 201, and in its resiliently tensioned position (interrupted lines) in which it protrudes less or not at all from the general level of the surface portion 201 (flush or countersunk). Figs. IB and 2B are plan views of surface portion 201 and locking element 200. The surface portions 201 are preferably portions of the circumferential surface of either the bone anchor head or the bone anchor shaft and are substantially convex. However, the illustrated surface portions 201 may also be portions of the inside surface of the through opening of the implant and, in such a case, are substantially concave. Locking elements arranged on the bone anchor (shaft or head) are moved relative to the through opening in a direction illustrated with an arrow I (implantation direction). Locking elements arranged in the through opening are moved relative to the bone anchor in an opposite direction indicated with the arrow G.

The locking element 200 comprises a protrusion with a guiding ramp 202 and a locking surface 203, wherein the guiding ramp 202 is situated upstream or downstream of the locking surface, depending on the moving direction I or F. The illustrated locking elements comprise protrusions with ramps 202 and locking surfaces 203 extending over the full width of the locking element. Alternatively, the protrusion may be narrower.

The locking elements illustrated in Figs. 1A/B/C have the form of a resilient cantilever pivoting in a plane substantially parallel to the directions I and G or to the axis of the bone anchor or the through opening respectively. The void 205 delimiting the cantilever extends along its length and on one side along its width also, and, depending on the thickness of the bulk beneath the surface portion 201 and on the bulk material, extends furthermore underneath the locking element (Fig. 1 A) or fully through the bulk underneath the locking element (Fig. 1C). The locking elements illustrated in Figs 2A/B/C have the form of a resilient bending beam with a bending movement in a plane substantially parallel to the directions I and G or to the axis of the bone anchor or the through opening respectively. The void 205 delimiting the bending beam extends along its length limiting its width, and, depending on the thickness of the bulk beneath the surface portion 201 and on the bulk material, extends furthermore underneath the locking element (Fig. 1C) or fully through the bulk underneath the locking element (Fig. 2C).

Dimensions of the cantilever or bending beam of the locking elements need to be adapted to the bulk material and bulk thickness in the region in which the locking element is situated. Generally speaking, deformation of the cantilever or bending beam needs to remain in the elastic range (less than 1%). For locking elements as shown in Figs. 1A and 2A, there is more design freedom regarding thickness and therewith length of the locking element than there is for the locking elements as shown in Figs. 1C and 2C, for which the thickness of the locking element is given by the bulk thickness. Whereas the embodiments of Figs. 1 A and 2A only require a minimum bulk thickness, the embodiments according to Figs. 1C and 2C can only be realized within a limited range of bulk thickness (substantially limited to cannulated bone anchor). Applicability of the embodiments according to Figs. 1C and 2C is further limited by the fact that these locking elements constitute through openings through e.g. a wall of a cannulated bone anchor which, in the location of the locking element may not be tolerable, in particular when the anchor is used e.g. for an augmentation process with the aid of a flowable material such as a bone cement.

The locking elements as illustrated in Figs. 1A/B/C and 2A/B/C comprise cantilevers or bending beams with a length extending substantially parallel to the directions I and F or to the axis of the bone anchor or the through opening on which they are arranged. This is not a necessary feature of the locking element of the system according to the invention. The lengths of such a cantilever or bending beam can also extend at an angle to the directions I and G or substantially perpendicular to them, wherein ramp and locking surface still have to be arranged following each other in the direction of the movement of bone anchor and through opening relative to each other. This means for a cantilever or bending beam length extending substantially perpendicular to the direction of this movement, that ramp and locking surface are arranged beside each other over the width of the cantilever or bending beam width. Two exemplary embodiments of locking elements in the forms of cantilever and bending beam having a length extending substantially perpendicular to the named moving direction or anchor axis respectively are illustrated in Figs. 4A/B and 5A/B/C. Figs. 3A/B/C illustrate an exemplary embodiment of a bone anchor of the system according to the invention. The bone anchor is shown viewed from a lateral side (Fig. 3A), sectioned along its axis (Fig. 3B), and in a three-dimensional representation (Fig. 3C). The bone anchor 210 comprises a head 211 and a shaft 212 on which two opposite integrated locking elements 200 of the type being illustrated in Figs. 1A and IB are provided. Each one of the locking elements 200 has the form of a resilient cantilever surrounded on three sides by a void 205 and having a length extending parallel to the anchor axis and the direction I. The locking element further comprises a ramp 202 and a locking surface 203 which, as best seen from Fig. 3A, have a width smaller than the width of the cantilever, and which, as seen best from Fig. 3B, are arranged adjacent to each over the cantilever length, wherein, in the direction I, the ramp 202 is arranged downstream of the locking surface 203.

The head of the bone anchor of Figures 3 A, 3B, and 3C is a first example of a head with a radial protrusion distally of the proximal end of the bone anchor, whereby a n outer shoulder is formed by the head, as explained hereinafter in more detail, referring to Figures 5A-5C. The bone anchor of Figures 3 A, 3B, and 3C as well as bone anchors shown in subsequent figures, have a longitudinal opening for anchoring material, as explained in more detail hereinbelow.

Figs. 4A/B show a further exemplary embodiment of the bone anchor 210 of the system according to the invention. The bone anchor 210 is shown in a three- dimensional representation (Fig. 4A) and in a plan view viewed against its proximal surface (Fig. 4B). The bone anchor 210 comprises a head 211, a shaft 212 (only partially shown in Fig. 4B), and arranged on the head, two locking elements 200 in the form of cantilevers as illustrated and described in connection with Figs. 1A and IB. Other than shown in Figs. 1A and IB, the cantilever length is not oriented parallel to the direction I or the anchor axis respectively, but it is oriented perpendicularly to the latter, i.e. the cantilever length extends circumferentially, in an arc shape, with a radius of curvature corresponding to the distance from the bone anchor axis and the ramp 202 and the locking surface 203 are arranged adjacent to each other over the cantilever width, with the ramp 202, relative to the direction I being arranged downstream of the locking surface 203.

Figs. 5A/B/C show a further exemplary embodiment of the bone anchor 210 of the system according to the invention. The bone anchor is shown in a three-dimensional representation (Fig. 5A) and in two lateral views (Figs. 5B and 5C, angle between the two viewing directions of 90°). The bone anchor 210 comprises again a head 211 and a proximally cannulated shaft 211 and, arranged on the head 211, two opposite locking elements 200 in the form of bending beams as illustrated in Figs. 2 A and 2B. Other than in Figs. 2A and 2B, the beam length does not extend substantially parallel to the anchor axis but substantially perpendicular to it, i.e. circumferentially in an arc shape, with a radius of curvature corresponding to the distance from the bone anchor axis, extending substantially perpendicular to the anchor axis or the direction I respectively. Therefore, the ramp 202 and the locking face 203 of the locking elements 200 are arranged adjacent to each other over the beam width as above further described in connection with Figs. 4A/B. The voids 260 underneath the beams (i.e., radially- inwardly of them) equally have an arc shape and extend around a substantial part of the circumference. In contrast to the embodiment of Figs. 4A/B, the beams are each supported on both sides, leading to a symmetrical arrangement. This support on both sides has the advantage of providing more stability, whereby the beams can be thinner compared to a support on one side only.

The embodiments of Figs. 5A-5C is another example of a bone anchor having a head 211 that defines a proximally facing shoulder 241, whereby the portion with the greatest radial extension - that has the locking elements 200 - is offset towards distally from the proximal end of the bone anchor. The offset, i.e. the height h _g of the guiding portion proximally of the shoulder, is sufficient for the guiding portion to have a guiding function, for example about 1 mm. The radially outer guiding surface of the guiding portion that is proximally of the shoulder 241 is cylindrical. Fig. 5B also illustrates, very schematically, a part of a plate-shaped implant 250. The thickness t of the implant around the through opening in which the bone anchor is locked is greater than an axial extension of the head 211, whereby the proximal end of the head 211 can be approximately flush with the proximal surface of the implant 250. A guiding groove 243 around the guiding portion may serve for receiving a hollow guiding tool (not shown in the figures).

The head is in a shallow indentation belonging to the through opening and is locked within the though opening implant with respect to both axial directions, by an implant portion distally of it and by the locking elements. In all previous Figs., the bone anchor and therewith also the through opening of the implant of the system according to the invention have substantially circular cross sections. Of course, these cross sections may have other forms, such as e.g. oval, rectangular, polygonal with sharp or blunt edges. This means that the surface portions in which the locking elements are provided are not necessarily curved surfaces.

All bone anchors shown in Figs. 3 to 5 are fenestrated bone anchors comprising a longitudinal cavity and lateral channels and are suitable for being retained in the bone tissue by being augmented using a bone cement or a material having thermoplastic properties. This is not a necessary feature of the system according to the invention. The bone anchor of this system may comprise any per se known retention means, i.e. the bone anchor can be a bone screw (solid, cannulated or fenestrated) or it can comprise retention means in the form of ribs, edges, resilient elements etc. The bone anchor of the system according to the invention may also be a simple headed pin with a possibly rough circumferential surface and being suitable to be retained in the bone tissue by a press fit.

The bone anchor of the system according to the invention may be a fenestrated bone anchor and further comprise the following features.

Figs 6A/B illustrate an exemplary embodiment of the fenestrated bone anchor invention, wherein Fig. 6A is a three-dimensional illustration of the anchor, and Figs. 6A and 6 are lateral views differing from each other by an angle of 90° between the corresponding viewing directions. The bone anchor 210 comprises a head 211 and a shaft 212. The longitudinal cavity 300 reaches through the head 211 into the shaft to a closed distal end and it is connected with the circumferential surface of the shaft by three lateral channels 301. As described further above, the lateral channels 301 have a pear-shaped cross section, i.e. an axial length greater than a circumferential width, the width decreasing in a proximal direction. The cross section has in a per se known manner no sharp corners such preventing load concentrations. The lateral channels 301 have outer mouths positioned all at the same axial position situated in the proximal half of the shaft axis, the closed distal end of the longitudinal cavity 300 is situated about half way between the proximal shaft end and the distal shaft end. The circumferential surface of the distal part of the shaft is equipped with circumferential ribs constituting exemplary means for retaining the anchor in a bone opening provided for its implantation.

Fig.7 is a plan view of the fenestrated bone anchor as shown in Figs. 6A/B/C (viewing direction from the head towards the tip of the anchor). It illustrates the distal end of the longitudinal cavity, which is equipped in a per se known manner with relatively sharp edges 306 or peaks serving as energy concentrators during the process of liquefaction of a material having thermoplastic properties being positioned in the longitudinal cavity and being pressed against the distal end of the longitudinal cavity, while ultrasonic vibration energy is applied to it. Also visible in Fig. 7 are the inner mouths of the lateral channels 301. Further exemplary embodiments of distal cavity ends suitable for the fenestrated bone anchor are e.g. disclosed in the publication WO201 1/054122, the disclosure of which is enclosed herein in its entirety by reference.

Figs. 8 and 9 are cross sections through the shaft 212 of further exemplary embodiments of the fenestrated bone anchor. The section plane of these cross sections is situated in the axial position of the lateral channels 301 and illustrate in particular the wall 310 between the longitudinal cavity 300 and the circumferential shaft surface. This wall has a wall thickness which increases in a circumferential direction towards each lateral channel 301 from a minimum wall thickness t _min in locations between the lateral channels 301 and a maximum wall thickness t _max where the wall meets the lateral channel 301. The increase of the wall thickness is e.g. in the range of 20%. This design measure renders the cross section of the anchor shaft 212 and the cross section of the longitudinal cavity 300 to be different, wherein in the illustrated case showing three lateral channels 301 the one cross section is circular and the other one is three - lobed having a circular envelope. Accordingly, for an anchor having two lateral channels, the lobed cross section is like an oval (two-lobed), for four channels it is four-lobed, and so on. The embodiment of wall 310 according to Fig. 8 for which the cross section of the shaft is lobed and the cross section of the longitudinal cavity is circular is advantageous when using the corresponding anchor for the above briefly described anchoring process with the aid of an element of a material having thermoplastic properties, as this element may be a simple pin having a circular cross section. On the other hand, it either necessitates a bone opening provided for the anchor having the trilobal cross section of the anchor shaft or a larger opening having a circular cross section substantially corresponding to the circular envelope or the trilobal shaft cross section. In an axial direction, in particular in a proximal direction, away from the lateral channels, the lobed cross section preferably changes gradually into a circular cross section such guaranteeing good guidance of the anchor in an also circular through opening of e.g. a bone plate. The embodiment of the wall 310 according to Fig. 9 is advantageous for an anchor of an overall circular cross section, e.g. a fenestrated screw, but for the above-mentioned anchoring process it necessitates an element of the material having thermoplastic properties in the form a pin with a non-circular cross section.

Further embodiments of the fenestrated bone anchor differ from the embodiments illustrated in the appended figures by not comprising a head or a head of a different form, by comprising instead of three lateral channels only one or e.g. 2 or 4 lateral channels, by the lateral channels not being situated further proximal but in the middle of the axial shaft length or further distal, by the longitudinal cavity reaching right through the shaft and having an open distal end, by not having a general circular shaft cross section but a shaft cross sections as e.g. listed in the introductory part of the present disclosure, by the lateral channels being situated not in a same axial position but in differing axial positions, and/or by comprising different or no retention means as e.g. listed in the introductory part of the present disclosure. All the named alternative features can be selectively used or combined for a plurality of further exemplary embodiments of the fenestrated bone anchor and designed for specific applications.

The implant of the system according to the invention may comprise a porous implant body, a support frame and retention means, e.g. in the form of a plate with through openings. In particular, the implant is an intervertebral fusion device. The bone implant or the intervertebral fusion device comprise the following features. Figs. 10 and 11 illustrate the principle of the structure of the porous implant body of the bone implant, wherein Fig. 10 illustrates an implant example with two opposite substantially parallel ingrowth surfaces, e.g. an interbody fusion implant, and Fig. 11 illustrates an implant example with two ingrowth surfaces extending at an angle relative to each other, e.g. a wedge-shaped implant as often used in osteotomy procedures.

The implant 100 shown in Fig. 10 in section perpendicular to the live bone surfaces 101 between which it is implanted is e.g. an interbody fusion implant, the live bone surfaces 101, in such a case, being suitably prepared lower and upper surfaces of neighboring vertebral bodies, wherein forces acting on the implanted implant are mainly compressing forces (arrows F) acting substantially perpendicular to the live bone surfaces 101 or the ingrowth surfaces 104 respectively. The implant 100 comprises a porous implant body 102 of an open porosity constituting a three- dimensional network of porosity channels 103. Ingrowth surfaces 104 are opposite surfaces of the porous implant body 102 which, in the implanted state of the implant, are in direct contact with the live bone surfaces 101. The implant body further comprises a plurality of supply channels 105 extending between the two ingrowth surfaces 104 substantially in the direction of the forces acting on the implanted implant. Whereas the porosity channels 103 have cross sections with diameters in the range of a few tenths of a millimeter, the supply channels 105 have cross sections of a diameter dl of a few millimeters (preferably 1 - 3 mm). The distances d2 between the supply channels 105 are in the range of 2 to 6 mm (preferably 3 to 5 mm). Preferably, but not necessarily, the distances d2 between the supply channels 105 are, throughout the porous implant body, about constant, and, in no case, are larger than about 5 to 6 mm. This means that the supply channels 105 preferably extend through the porous implant body 100 in a substantially regular pattern.

Also shown in Fig. 10 are substantially non -porous edge members 108 of a support frame surrounding at least partially the porous implant body 102, as well as substantially non-porous surface elements 109 arranged to extend flush in the ingrowth surfaces 104 and e.g. surrounding mouths of supply channels 105 and/or extending between such mouths. Also shown in Fig. 11 is a strut 110 extending along the wall of one of the supply channels 105, wherein more than one strut 110 may be provided in one and the same supply channel 105 and wherein distances between struts are to be in the range of 0.5 to 2 mm. Surface elements 109 and struts 110 may be provided for each one of the supply channels 105 or for selected ones only. Fig. 11 is a very schematic representation (again in a section perpendicular to the ingrowth surfaces 104) of an exemplary wedge-shaped implant 100, which implant is possibly suitable for use in an osteotomy operation. The main features of the implant are the same as the features of the implant as shown in Fig. 10, namely the porous implant body 102 with ingrowth surfaces 104 (in Fig. 11 two ingrowth surfaces at an angle relative to each other), supply channels 105 extending from one ingrowth surface 104 towards the other one, and members 108 of a support frame. In addition to the supply channels 105 extending from one ingrowth surface 104 to the other one and having a mouth in either one of the ingrowth surfaces 104, there are illustrated two blind supply channels 105’, which only have one mouth and a closed end opposite the mouth. For guaranteeing satisfactory supply for bone ingrowth beyond the closed end, the dead end is to be positioned not more than 5 to 6 mm (preferably between 3 to 5 mm) distanced from the neighboring ingrowth surface (same as distance between supply channels). The support frame of the implant according to Fig. 11 differs from the support frame of the implant according to Fig. 10 in that it comprises, in addition to an edge member 108 arranged at the distal end of the porous implant body 102, a member 120 constituting a proximal implant surface and at least one central member 121 extending through the implant body. The implant according to Fig. 11 may or may not comprise surface elements or struts (none shown) as described further above in connection with Fig. 10.

Any embodiment of the bone implant may comprise in addition or alternatively to supply channels extending from one ingrowth surface to another one (as shown in Fig. 10), blind supply channels as illustrated in Fig. 11.

Fig. 12 further illustrates a preferred embodiment of the arrangement of supply channels 105 in a bone implant, namely the above-mentioned hexagonal arrangement. The arrangement is shown in section substantially perpendicular to the supply channels. In this arrangement, every supply channel 105 has six nearest neighbor channels, wherein all positions between the channels can be safely supplied if the distance d3 (radius of circles marked with dash-dotted lines) corresponds to the given limit of 1 to 3 mm. With the hexagonal arrangement the largest volume of porous structure can be supplied with the smallest number of supply channels.

Also shown in Fig. 12 are exemplary supply channels bring equipped with surface elements 109 surrounding supply channel mouths or connecting them and supply channels comprising varying numbers of struts 110, wherein supply channels 105 in any supply channel arrangement and of any bone implant as above described may or may not be correspondingly equipped.

In all previous Figs the supply channels have a substantially circular cross section. This is not an obligatory feature of the bone implant. On the contrary, in all embodiments of the bone implant, the supply channels may have cross sections of any other form, as long as for these cross sections the smallest dimension is in the range of 1 to 3 mm. This means that the supply channels may have e.g. square, rectangular, slot-shaped, triangular, oval, lobed, pentagonal, hexagonal etc. cross sections, wherein in one implant all supply channels may have the same or different cross sections. Figs. 13 and 14 illustrate schematically two supply channel arrangements (sectioned again perpendicular to the supply channels), comprising supply channels having elongate, i.e. slot-shaped cross sections.

The arrangement shown in Fig. 13 is a staggered arrangement of supply channels 105 with slot-shaped cross sections having a width (smallest dimensions) in the range of 1 to 3 mm, and distances from each other in the given range of 2 to 6 mm, preferably 3 to 5 mm. Dash-dotted lines indicate, as in Fig. 12, the volume of porous structure which can be supplied by each one of the supply channels 105. The arrangement shown in Fig. 14 comprises supply channels 105 with slot-shaped and supply channels 105 with circular (or any other shape having a rotational symmetry) cross sections arranged in a regular pattern, and therewith constitutes an example of a supply channel arrangement comprising supply channels with differing cross sections. In any bone implant as above described, supply channels of other and possibly differing cross section shapes may be combined in varying numbers, wherein it is not necessary that the arrangement is as regular as shown in Figs. 12 to 14.

Fig. 15 illustrates in a very schematic manner an exemplary bone implant, wherein for this implant, the distance between the two ingrowth surfaces 104 is in a range (20 to 40 mm) for which it is preferable to design the supply channels 105 to have enlarged mouth portions 125. Such enlarged mouth portions preferably have dimensions in a range of 3 to 10 mm such that they are still able to be bridged by long-term bone growth without the necessity of bone growth enhancing material. Larger such enlarged mouth portions constituting critical size defects are not recommended because introduction of bone growth enhancing material is not really feasible. As shown in Fig.

15, the enlarged mouth portions 125 of the supply channels 105 are arranged alternatively in one and the other one of the ingrowth surfaces, which makes it possible to guarantee the given distances between the supply channels in the range of preferably 3 to 5 mm. Preferably the axial length of the enlarged mouth portions 125 of the supply channels 105 have a short axial length only, such maximizing spontaneous bone growth filling as much of the supply channels as possible.

All the above described features of bone implants, in particular regarding support frames and cross section shapes and supply channel arrangements are applicable also for embodiments comprising supply channels with enlarged mouth portions. Fig. 16 is a top view (viewed against one of the ingrowth surfaces 104) of a further exemplary embodiment of the bone implant. The implant 100 is an interbody fusion device of the stand-alone type and comprises, as described above, a porous implant body 102 with supply channels 105 and a support frame with members 108 to be positioned between adjacent vertebral bodies. The interbody fusion device further comprises a bone plate 130 (retention means) and a plurality of bone anchors (not shown) suitable for fixating the bone plate 130 to lateral or posterior wall portions of the vertebral bodies. In the shown embodiment, the bone plate 130 is reduced to a plurality of lobes 135 each comprising a through opening for receiving one of the bone anchors. The structures corresponding to the locking element and cooperating with the same to lock the bone anchor, for example a bone anchor of the kind illustrated in any one of Figs. 4A-7, may be within the through openings of the lobes 135.

The porous implant body 102, the support frame members 108, the bone plate 130, and, if applicable, surface elements 109 or struts are preferably made of the same material, as one piece, which is preferably manufactured in one single additive manufacturing process.

The porous implant body 102 comprises supply channels 105 as described above, mouths of the supply channels being at least partly surrounded by surface elements 109, possibly being connected to each other by connecting elements 111 (illustrated on left hand side of ingrowth surface). The support frame comprises edge members 108 and two central members 132, which extend through the porous implant body from the one ingrowth surface to the other one and which may or may not encircle a central cavity 133 suitable for being filled with bone growth enhancing graft material for which purpose this cavity 133 comprises a feed opening 134 connecting it with the proximal surface of the implant.