FIELD OF THE INVENTION

The invention is in the field of medical technology. It relates to a bone implant, in particular to 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.

BACKGROUND OF THE INVENTION Generally speaking, known methods for rendering bone implants suitable for being integrated in live bone tissue by bone growth after surgery are based on three principles: surface structures and/or coatings enhancing osseointegration, body structures such as suitable porosities enhancing ingrowth of bone tissue into the structures, and cavities (“graft windows”) filled with bone growth enhancing material such as e.g. bone graft material. The three approaches differ mainly in the depth to which new bone tissue growing after surgery is able to penetrate into the implant. Osseointegration enhancing surface structures are usually realized as roughness, preferably undercut roughness, und are known to have a depth in the micrometer range e.g. in the range of up to 50pm. Bone ingrowth enhancing body structures are usually realized as structures with a network of channels, e.g. open porosity, wherein suitable channel cross sections have a diameter in the range of tenths of a millimeter, e.g. 0.1 to 0.7 mm, which cross section size is inspired by the lamellar structure of natural bone tissue. Dimensions of cavities to be filled with bone growth enhancing material need to be large enough for enabling the filling process and are limited in size mainly by mechanical requirements on the implant. Such cavities may have largely differing forms and dimensions usually in a range of up to centimeters. In known interbody fusion implants such cavities are often designed to extend through the implant from a first implant surface to a second implant surface, wherein both first and second implant surfaces are, in the implanted state of the implant, face live bone tissue of the patient. Such cavities constitute e.g. in spinal cages up to 75% of the implant surfaces facing the live bone tissue and may have dimensions in the range of 10 - 30 mm for lumbar cages and correspondingly smaller for cervical cages. Often, due to the required dimensions, spinal cages having such through cavity are provided with one cavity per cage only.

Experience shows that rough and possibly undercut surface structures as sole integration enhancing measure is suitable mainly for implants having a relatively high ratio of implant surface to implant volume (relatively small implants). Known implants of a larger bulk often feature a combination of the named surface structures with the above-named bone ingrowth enhancing features or with further permanent mechanical implant retention means.

EP 3 607 914 discloses a spinal interbody device that comprises a solid wall at last partially defining a boundary of the device, and a porous body. The porous body forms at least a portion of the superior and interior bone interface side of the device. The device may comprise a plurality of elongate through-channels of diameters between 0.2 and 1 mm extending through the porous body from the superior bone interface side to the interior bone interface side.

SUMMARY OF THE INVENTION It is the object of the present invention to provide 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, wherein the bone implant according to the invention is to enable more complete and more rapid bone ingrowth into the implant than know such implants, such that the bone tissue grown after surgery and in particular already during a rehabilitation period, can bear at least a relevant part of or even the full load acting on the bones between which it is implanted, or such that the implant can be designed with a minimum of material and virtually without regard for long term functionality (limited e.g. by material fatigue or resorbability of the used material) respectively.

For achieving the above detailed object, the bone implant according to the invention 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, preferably about 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 implant according to the invention 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, at least over a part of their length, cross sections of any suitable form of which the smallest dimension is in the range of 1 to 3 mm or in the range of 1.2 to 3 mm. A mean supply channel diameter (i.e. the diameter of a circle having the same area as the cross sectional area of the supply channel if the cross section is constant; if it is not constant the definition refers to the such determined diameter averaged over the supply channel’s length) is between 1.5 mm and 3 mm, especially between 1.7 mm and 2.5 mm. In many embodiments, the cross section is constant along the supply channel’s length, with the possible exception of an enlarged mouth portion (see below), in which case the above definition of the mean diameter applies to the channel portions excluding the mouth portion.

Throughout the porous implant, the supply channels may have distances from each other and for example from the peripheral surface portions 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%).

Especially, the supply channels may be arranged to be capable of forming an arrangement of equidistant of supply of the porosity channels in that the largest distance (measured between their respective surfaces) between neighboring supply channels may, with the possible exception of a central region having a cavity of the above-mentioned kind, correspond to at most 6 mm or at most 5 mm or corresponds to at most 3.5 times or at most 3 times or at most 2.5 times their mean diameter (the ratios being a possible design criterion for all different kinds of implants described in this text and especially being a good measure for smaller implants, for example for cervical applications). In addition or as an alternative, a maximum distance between peripheral supply channels and the lateral surface may correspond to at most 3.5 times or at most 3 times or at most 2.5 times their mean diameter, whereby the arrangement of the channels follows the outer contour of the implant.

The design of the porous implant body of the bone implant according to the invention 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.

The dimensions of the supply channels are chosen in view of such findings about physiological relations. It has been found that especially, but not only, for implants having a thickness (extension perpendicular to the ingrowth surfaces) of more than 10 mm, especially around 20 mm - which is a characteristic dimension for spinal fusion implants especially for the lumbar and thoracic vertebrae - the vasculature and lymph structures will not grow sufficiently deep into the supply channels if their diameter is about 1 mm or lower. Thus, physiological relations yield a lower limit of about 1.2 mm, 1.5 mm, in examples even 1.8 mm for the supply channel diameter. An upper limit of typically 3 mm or 2.5 mm is set both, by mechanical/geometrical considerations (if the supply channels are too wide, there is not sufficient space for there also being load bearing structures and a sufficient number of supply channels as well as sufficient volume for the porosity channels) and by the above-explained findings on spontaneous bone growth. For smaller implants, for example for cervical applications, having a lateral width of for example not much more than 10 mm and having a height of only a few millimeters (for example just 4 mm), a diameter of the supply channels may be lower than 2 mm and for example in the range between 1 mm or 1.2 mm and 2 mm, and the above-mentioned considerations for the ratio between distances and channel diameters may apply.

Based on the above listed findings, therefore, the supply channels of the porous implant body of the implant according 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 locations thereof. Furthermore, it is found that supply channels longer than about 20 mm are preferably equipped with an enlarged mouth portion.

An aspect ratio of the supply channels (i.e. a ratio between their length across the implant and their mean diameter) may be chosen to be not higher than about 15 or not higher than about 10 or about 8. In embodiments with the enlarged mouth portion, the length of the supply channel for determining the aspect ratio in this is measured excluding the enlarged mouth portion. For larger aspect ratios than these values, ingrowth into the supply channels has been found to be sometimes incomplete. 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 possible arrangement, the supply channels extend substantially parallel to each other from one ingrowth surface towards, preferably reaching all the way to, the other one, where the above-discussed distances between the supply channels may apply. In embodiments, for being able to supply the largest porous volume with the smallest number of supply channels, the latter may be arranged in an approximately hexagonal system, wherein, in a cross section through the channel arrangement, each channel has six neighboring channels at an approximately same distance of for example 5-6 mm.

In addition or as an alternative to being arranged in an approximately hexagonal system, the channels may be arranged in a pattern that follows the outer contour and, if the implant comprises a cavity, a contour defined by the limits of the cavity. The pattern may therefore comprise a (first) row of outer, peripheral supply channels following the outer contour and at least one further, second row of supply channels parallel to the first row, the position of the supply channels of the second row for example being staggered with respect to the positions of the supply channels of the first row to yield an approximately hexagonal system. The implant may comprise further (third, for example fourth or even more) rows of supply channels successively increasing distances from the peripheral surface portions. The implant according to the invention 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 preferably 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 implant according to the invention 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 implant according to the invention 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 processes (e.g. etching) or non-galvanic processes (e.g. nano-deposition).

Preferably, the support frame and possibly also further elements and retention means of the implant according to the invention 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 implant according to the invention 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 according to the invention 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 WO20 10/096942, 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.

The interbody fusion device of the stand-alone type may, in addition to a bone implant according to the invention, further comprise at least one bone anchor designed for fixating the plate of the interbody fusion device to the neighboring vertebral bodies, wherein the at least one bone anchor is adapted to a through opening in the plate or implant respectively and wherein the system of bone anchor and plate or implant has e.g. the following features.

The system 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 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 cooperates in a per se known manner, 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. 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 comprises in a per se known manner 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 are designed in a per se known manner for a loose fit in the locked position.

The locking element of the system of bone anchor and through opening 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).

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.

The implant and/or the bone anchor 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.

Furthermore, the bone anchor being part of the intervertebral fusion device may be a fenestrated bone anchor and 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 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 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 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.

BRIEF DESCRIPTION OF THE DRAWINGS A plurality of exemplary embodiments of the bone implant according to the invention and parts thereof are described in further detail in connection with the appended Figs., wherein:

Figs. 1 and 2 illustrate the principle of the bone implant according to the invention, the bone implant being shown in section perpendicular to ingrowth surfaces of the porous implant body;

Figs. 3, 4, 5 are cross sections of exemplary embodiments of supply channel arrangements

Fig. 6 illustrates a further exemplary embodiment of the implant according to the invention;

Fig. 7 shows an interbody fusion device of the stand-alone type comprising an interbody implant in the form of a bone implant according to the invention and, preferably integrated therewith, a bone plate suitable for fixating the device to adjacent vertebral bodies with the aid of bone anchors;

Figs. 8A/B/C illustrate the principle of an exemplary locking element of the system comprising a bone anchor and an implant with a through opening, the illustrated locking element having the form of a resilient cantilever;

Figs. 9A/B/C illustrate the principle of an exemplary locking element of the system comprising a bone anchor and an implant with a through opening, the illustrated locking element having the form of a resilient bending beam; Figs. 10A/B/C shows an exemplary embodiment of a bone anchor, 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. 11A/B show an exemplary embodiment of a bone anchor, 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. 12A/B/C show an exemplary embodiment of a bone anchor, 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. 13A/B/C illustrate an exemplary embodiment of a fenestrated bone anchor, the embodiment comprising three lateral channels with pear-shaped cross sections;

Fig. 14 is a plan view of the fenestrated bone anchor Figs 13A/B/C (viewing direction towards the head of the anchor);

Figs. 15 and 16 are cross sections through further exemplary embodiments of bone anchors, the embodiments comprising an increase in wall thickness in a direction towards the lateral channels.

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 is a direction towards the surgeon and a distal direction a direction towards the patient or further into the patient. Each described 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, also referred to as longitudinal axis, wherein this axis on implantation coincides with or is 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.

Figs. 1 and 2 illustrate the principle of the structure of the porous implant body of the implant according to the invention, wherein Fig. 1 illustrates an implant example with two opposite substantially parallel ingrowth surfaces, e.g. an interbody fusion implant, and Fig. 2 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 surface portions of the implant that extend around the implant and extend between the two ingrowth surfaces are called “peripheral surface portions” in this text. If the implant is an interbody fusion implant, the peripheral surface portions include an anterior surface portion, a posterior surface portion, and two lateral surface portions.

In embodiments (this generally pertains to embodiments of the present invention, not only the structures shown in Figs. 1 and 2, the porous body extends to peripheral surface portions at least in areas, for example at least to the lateral surface portions, i.e. the non-porous support frame (see below) in these embodiments has at least one window in the peripheral surface. The implant 100 shown in Fig. 1 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, especially 1.5-2.5 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, the distances between the peripheral-most supply channels 105 and the peripheral surface may be in the range of 2 to 6 mm, for example 3 to 5 mm, for example at most 6 mm or at most 5 mm.

Also shown in Fig. 1 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. 1 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. 2 is a very schematic representation (again in a section perpendicular to the ingrowth surfaces 104) of an exemplary wedge-shaped implant 100 according to the invention, 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. 1, namely the porous implant body 102 with ingrowth surfaces 104 (in Fig. 2 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. 2 differs from the support frame of the implant according to Fig. 1 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. 2 may or may not comprise surface elements or struts (none shown) as described further above in connection with Fig. 1.

Any embodiment of the bone implant according to the invention may comprise in addition or alternatively to supply channels extending from one ingrowth surface to another one (as shown in Fig. 1), blind supply channels as illustrated in Fig. 2. Fig.3 further illustrates a preferred embodiment of the arrangement of supply channels 105 in a bone implant according to the invention, 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. 3 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 implant according to the invention 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 implant according to the invention. On the contrary, in all embodiments of the implant according to the invention, 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. 4 and 5 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. 4 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. 3, the volume of porous structure which can be supplied by each one of the supply channels 105.

The arrangement shown in Fig. 5 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 implant according to the invention, 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. 3 to 5.

Fig. 6 illustrates in a very schematic manner an exemplary bone implant according to the invention, 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. 6, 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 implants according to the invention, 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. 7 is a top view (viewed against one of the ingrowth surfaces 104) of a further exemplary embodiment of the implant according to the invention. 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 porous implant body 102, the support frame members 108, the bone plate 130, and, if applicable, surface elements 109 or struts can be made of the same material, as one piece, which is for example 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. As can be seen in Fig. 7, the supply channels (with the possible exception of a central region comprising the cavity 133 and adjacent sections) for a framework for equidistant supply. To this end, the distance between neighboring supply channels is smaller than about 2-3 times their mean diameter. Also, the distance between the peripheral-most supply channels and the peripheral surface portion of the implant - including the support frame - is also about 2 times their mean diameter or smaller. Therefore, the pattern of the supply channels follows the outer contour of the implant, i.e. the regular pattern of the supply channels is not a rectangular grid but a pattern following by anatomy. Especially, the peripheral supply channels are arranged along a bow that is parallel to the peripheral surface portion and has a similar curvature as the latter in cross section perpendicular to the longitudinal extension of the supply channels.

The supply channels in Fig. 7 are arranged in rows that follow the outer contour and the contour of the (optional) cavity 133, namely in four rows, four to six (five in the outermost row) supply channels on each of the two sides divided by the cavity 133. The outermost row follows the contour of the peripheral surface portion, and the other rows follow the same contour, with the arrangement of the supply channels between the rows being staggered so that the supply channels (except the ones along the periphery or along the cavity 133) each have six neighboring supply channel at an approximately same distance.

Interbody fusion devices such as the one illustrated in Fig 7 further comprise a plurality of bone anchors suitable for fixating the device to neighboring vertebral bodies and being adapted to the through openings of the implant or the plate respectively may have the features as below discussed in connection with Figs. 8 to 16. These features regard in particular locking elements for locking the bone anchor in the through opening or the implant. Figs. 8A/B/C and 9A/B/C illustrate each in a schematic manner the principle of exemplary embodiments of locking elements 200 of a system of bone anchor and through opening. 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. 8A, 8C, 9A and 9C 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. 8B and 9B 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 G. 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. 8A/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. 8A) or fully through the bulk underneath the locking element (Fig. 8C).

The locking elements illustrated in Figs 9A/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. 8C) or fully through the bulk underneath the locking element (Fig. 9C). 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. 8A and 9A, 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. 8C and 9C, for which the thickness of the locking element is given by the bulk thickness. Whereas the embodiments of Figs. 8A and 9A only require a minimum bulk thickness, the embodiments according to Figs. 8C and 9C can only be realized within a limited range of bulk thickness (substantially limited to cannulated bone anchor). Applicability of the embodiments according to Figs. 8C and 9C 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. 8A/B/C and 9A/B/C comprise cantilevers or bending beams with a length extending substantially parallel to the directions I and G 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. 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. 11A/B and 12A/B/C.

Figs. 10A/B/C illustrate an exemplary embodiment of a bone anchor comprising a locking element as described above. The bone anchor is shown viewed from a lateral side (Fig. 10A), sectioned along its axis (Fig. 10B), and in a three-dimensional representation (Fig. IOC). 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. 8A and 8B 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. 10A, have a width smaller than the width of the cantilever, and which, as seen best from Fig. 10B, 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.

Figs. 11A/B show a further exemplary embodiment of a bone anchor 210, which is shown in a three-dimensional representation (Fig. 11 A) and in a plan view viewed against its proximal surface (Fig. 1 IB). The bone anchor 210 comprises a head 211, a shaft 212 (only partially shown in Fig. 11B), and arranged on the head, two locking elements 200 in the form of cantilevers as illustrated and described in connection with Figs. 8A and 8B. Other than shown in Figs. 8A and 8B, 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 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. 12A/B/C show a further exemplary embodiment of a bone anchor 210 invention, which is shown in a three-dimensional representation (Fig. 12 A) and in two lateral views (Figs. 12B and 12C, 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. 9A and 9B. Other than in Figs. 9A and 9B, the beam length does not extend substantially parallel to the anchor axis but substantially perpendicular to it, i.e. circumferentially 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. 11 A/B. In all previous Figs., the bone anchor and therewith also the through opening of the implant 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. 10 to 12 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 of bone anchor and through opening. 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 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.

Figs 13A/B/C illustrate an exemplary embodiment of a fenestrated bone anchor applicable in the intervertebral fusion device as described further above, wherein Fig. 13A is a three-dimensional illustration of the anchor, and Figs. 13A and 13B 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. 14 is a plan view of the fenestrated bone anchor as shown in Figs. 13A/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. 14 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. 15 and 16 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 _m ax 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. 15 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. 16 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 may 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.