Patent Description:
The SI joint is composed of the ilium articulation to the sacrum to form a diarthrodial joint with <NUM> to <NUM> of multi planar motion. The iliac convex side of the SI joint is covered with fibrocartilage while the sacral side of the SI joint is concave and covered in articular cartilage. The SI joint can become a pain generator in an individual due to degenerative change in the joint and due to changes occasioned by injury. Sacroiliac pathology may be diagnosed with maneuvers that increase pressure or load to the SI joint to elicit buttock and low lateral sacral pain which is characteristic of sacroiliac pain. X-rays, MRI, and CT scan may also aid in the diagnosis of sacroiliac pathology.

Sacroiliac joint pain is commonly treated initially with anti-inflammatory injections, and/or radio frequency ablation. When these treatments fail, fusion of the joint is indicated. Prior methods of sacroiliac fusion include screw or other fixation devices placed from a lateral or oblique approach directly across the joint. Some of these techniques involve placing bone inductive and conductive material such as allograft, autogenous bone, stem cells, bone marrow aspiration, or other bone fusion materials such as a bone morphogenic protein in an effort to encourage bone growth across the SI joint to effect fusion of the j oint. These techniques of placing bone inductive and conductive materials in connection with screw or other fixation devices directly across the SI joint commonly fail to place sufficient material to facilitate fusion of the joint via inter articular surface bone growth in a desirable time frame.

<CIT> discloses an implant that is inserted into the articular region of the SI joint to facilitate fusion of the joint. Apertures are provided in the implant shown in this patent for receiving biologically active agents and biocompatible materials to encourage bone growth across the SIjoint. However, the structure of the implants shown in <CIT> allows little area for such materials relative to the overall area of the implant in the SI joint articular region.

It is an object of the invention to provide an implant for facilitating SI joint fusion via bone growth between the sacrum and ilium across the articular region of the SI joint. Implants according to the aspects of the invention provide relatively large areas for bone growth across the SI joint while maintaining sufficient structural integrity to withstand the forces required for implantation. Additionally, implants according to the present invention may be specifically designed to the details of the SI joint anatomy.

An implant according to the invention is defined in claim <NUM>.

Although a triangular shaped arrangement is a preferred form of the implant because it generally provides a good match to the details of the SI joint structure for most patients, the present invention is not limited to this triangular shaped arrangement. Thus an implant according to the invention may take other shapes. An implant according to the invention includes a base structure and an insertion end structure spaced apart from the base structure along an implant longitudinal axis. An elongated first side member extends along a first side longitudinal axis and defines a first lateral side of the implant, while an elongated second side member extends along a second side longitudinal axis and defines a second lateral side of the implant. These first and second lateral side of the implant are spaced apart along an implant width axis which lies perpendicular to the implant longitudinal axis and together with the implant longitudinal axis defines an implant plane. The implant further includes an internal support structure extending in the implant plane from the base structure to the insertion end structure. Two or more fusion passages are defined in an area between the first side member, second side member, base structure, and insertion end structure, each fusion passage extending along a thickness axis perpendicular to the implant plane and defining a respective open area through the implant.

An implant according to the invention may be formed from one or more biologically compatible materials and may be implanted in an implantation position within an SI joint generally with the thickness axis of the implant extending transversely across the joint from the sacrum to the ilium. In this implantation position, the implant stabilizes the SI joint against articulation while the areas defined by the fusion passages provide areas for bone growth from the sacrum to the ilium across the SI joint to effect or enhance fusion of the j oint. The configuration of the implant base and side members (or base structure, insertion end structure and side members) together with the internal support structure allows the open areas defined by the fusion passages to be maximized to thereby maximize the area of bone for fusion of the SI joint. In particular, the configuration of implants according to the first and second aspects of the invention provides a structure that may withstand the forces applied in the course of implantation while maximizing the area across the implant for fusion of the SI joint.

The areas defined by the fusion passages may be filled with bone fusion material which may encourage bone growth across the SI joint and thus fusion of the joint. As used in this disclosure and the accompanying claims, "bone fusion material" comprises one or more bone inductive materials or one or more bone conductive materials, or combinations of the two types of materials. These materials include allograft, autogenous bone, stem cells, bone narrow aspiration, bone morphogenic protein or any other material now known or developed in the future to help induce or support, or both induce and support, bone growth from one bone surface to another. "Biologically compatible material" as used in this disclosure and the accompanying claims comprises any material suitable for implantation in an SI joint. This includes various types of stainless steel and various types of plastic, and any other material now known or that may be developed in the future for use in forming implants which may be implanted in the SI joint.

In some implementations of an implant according to the invention, the internal support structure includes two or more beams extending transverse to the implant width axis in the implant plane. These two or more beams divide the area between the first side member, second side member, and base member into the fusion passages. The two or more beams may include a first lateral beam and a second lateral beam. In such implementations, the first lateral beam extends along a first lateral beam longitudinal axis from a first lateral beam base end connected to the base member to a first lateral beam forward end connected to the first side member. The second lateral beam extends along a second lateral beam longitudinal axis from a second lateral beam base end connected to the base member to a second lateral beam forward end connected to the second side member. The first and second lateral beams may converge in a direction along the implant longitudinal axis from a forward end of the implant to the base member. This beam arrangement and other beam arrangements which may be employed in the internal support structure of an implant according to the invention provide support for the first and second side members of the implant and help those members withstand the forces which may be encountered during implantation.

The first side member, second side member, and other elements of the implant according to the invention may define a first joint contact surface on one side of the implant plane and a second joint face contact surface on an opposite side of the implant plane. In some implementations of an implant according to this aspect of the invention, the two joint face contact surfaces extend at an angle of between approximately <NUM> and <NUM> degrees, and more preferably between approximately <NUM> and <NUM> degrees to each other in a direction between the base and forward end of the implant along the implant longitudinal axis, that is between the base member and forward end the implant.

Implants according to the invention may also include a retention feature formed on each of the joint face contact surfaces. Such retention features may help retain the implant in the implanted position once it has been placed in that position by the surgeon. These retention features may comprise a number of ridges spaced apart along the implant longitudinal axis and extending parallel to the width axis. Once the implant is impacted into the implanted position as will be discussed below, the ridges serve to catch on the prepared SI joint surface and help prevent the implant from sliding out of the desired implanted position along the implant longitudinal axis.

In some implementations of an implant according to the invention the elongated base member, elongated first side member, and elongated second side member may meet so that the members form a triangular shape in the implant plane. However, the present invention is not limited to such an arrangement. Other implementations may include a portion of one or more of the elongated first or second side members adjacent to the elongated base member that extend (for example) parallel to the implant longitudinal axis. In these implementations, the elongated base member may have a length dimension that is less that a dimension defined between a first point at which the first side longitudinal axis intersects the base member longitudinal axis in the implant plane and a second point at which the second side longitudinal axis intersects the base member longitudinal axis in the implant plane.

Implants according to the invention may also be adapted to receive a locking element once the implant is placed in the implanted position in the SI joint. Such a locking element may be configured to help secure the implant in the implanted position. A suitable connector arrangement may be used to connect the locking element to the base member (or base structure in the second aspect of the invention) in a locking position. The connector arrangement may include at least one fastener opening through the locking element and adapted to align with a threaded opening in the implant base member or base structure. In this aligned position a suitable threaded fastener may be placed in the fastener opening and driven into the threaded opening to connect the locking element to the implant. The base member (or base structure in the second aspect of the invention) may include an elongated channel and the locking element may include a projection configured to be received in the channel to help align the locking element in the desired position. Once connected to the implant, a fixation device such as a suitable bone screw may be driven into a receiver opening in the locking element and into adjacent bone of the sacrum or ilium to help secure the implant in the desired implanted position. A locking element may include two receiver openings, one aligned to place a fixation device in the sacrum and one to place a fixation device in the ilium.

The invention may be used in a method for effecting a fusion of the SI joint. This includes forming a sacral side implant receiving surface in the sacral side of the SI joint and forming an iliac side implant receiving surface in the iliac side of the SI joint opposite the sacral side implant receiving surface. These two implant receiving surfaces define an SI joint implant receiving volume for receiving an SI joint implant according to the invention as described above. The method then includes fixing the SI j oint implant in the SI j oint implant receiving volume in an implantation position in which the fusion passages extend transversely across the SI joint. As will be described below in connection with the drawings, fixing the implant in the implanted position may include driving the implant into the implant receiving volume with a suitable insertion or impacting tool. Fixing the implant in the implanted position may also include removing the insertion tool from the implant, attaching the locking element to the implant as described above, and then placing at least one surgical fastener through the receiver opening of the locking element so as to extend into the sacrum or ilium.

These and other advantages and features of the invention will be apparent from the following description of representative embodiments, considered along with the accompanying drawings.

In the following, <FIG> will be referenced to describe an example SI joint implant <NUM> embodying principles of the present invention and a locking element <NUM> which may be used with the implant <NUM>. <FIG> will be referenced in connection with describing procedures by which implant <NUM> may be implanted in an SI joint, and in connection with describing the installation and use of locking element <NUM>. <FIG> will be referenced to describe another example SI joint implant and locking element embodying the principles of the present invention.

Referring to <FIG>, the example SI joint implant <NUM> includes an elongated base member <NUM>, an elongated first side member <NUM>, and an elongated second side member <NUM>. Implant <NUM> also includes an internal support structure shown generally at reference number <NUM> in the figures. As shown in <FIG>, base member <NUM> has a longitudinal axis B extending parallel to an implant width axis W and perpendicular to an implant longitudinal axis L. These axes W and L define an implant plane, with a thickness axis T of the implant extending perpendicular to the implant plane. As shown in the plan view of <FIG>, first side member <NUM> extends along a first side longitudinal axis F while second side member <NUM> extends along a second side longitudinal axis S. <FIG> also shows that the longitudinal axis B of base member <NUM> forms a base of a triangle in the implant plane while first side longitudinal axis F and second side longitudinal axis S form the two lateral sides of the triangle. In this particular example implant <NUM>, longitudinal axis B forms the base of an isosceles triangle with the side longitudinal axes F and S forming the sides of the isosceles triangle.

Implant <NUM> also includes a number of fusion passages defined in the area between base member <NUM>, first side member <NUM>, and second side member <NUM>. This particular example implant, includes three fusion passages <NUM>, <NUM>, and <NUM>. Each of these fusion passages <NUM>, <NUM>, and <NUM> extend along the thickness axis T and define a respective open area through implant <NUM> in the direction of thickness axis T. As will be described further below, the fusion passages <NUM>, <NUM>, and <NUM> provide areas for bone growth across implant <NUM> when properly positioned in an SI joint to facilitate fusion of the joint.

Internal support structure <NUM> in example implant <NUM> includes two beams extending transverse to implant width the axis W. In particular, implant <NUM> includes a first lateral beam <NUM> extending along a first lateral beam longitudinal axis FB (<FIG>), and a second lateral beam <NUM> extending along a second lateral beam longitudinal axis SB (<FIG>). First lateral beam <NUM> has a base end connected to base member <NUM> and a forward end connected to first side member <NUM>. Second lateral beam <NUM> includes a base end connected to base member <NUM> and a forward end connected to second side member <NUM>. In this particular embodiment, first lateral beam <NUM> and second lateral beam <NUM> converge in a direction along the implant longitudinal axis L from a forward end of the implant shown generally at <NUM> to base member <NUM>. This convergence is particularly apparent in the plan view of <FIG>. Regardless of the particular arrangement of beams making up internal support structure <NUM>, such as beams <NUM> and <NUM> in the illustrated embodiment, these members divide the area of the implant between base member <NUM>, first side member <NUM>, and second side member <NUM> to define the fusion passages, in this example, passages <NUM>, <NUM>, and <NUM>.

The function of internal support structure <NUM>, which in this example is made of up of lateral beams <NUM> and <NUM>, is to provide support in the implant plane for the first and second sides members, <NUM> and <NUM> respectively. Support is desirable particularly for resisting forces applied to these side members in a direction along the longitudinal axis L from implant forward end <NUM> to the base member <NUM>. Forces in this direction are encountered in the course of placing the implant in an implanted position in an SI joint as will be described further below in connection with <FIG>. Numerous other beam arrangements may be used to provide suitable support for side members <NUM> and <NUM> against forces applied to the implant in the course of implantation. For example, rather than two discrete beams, the internal support structure may include an arrangement of elements forming generally a Y shape with an elongated member extending from a midpoint of base member <NUM> to form the bottom part of the Y shape, and then two diverging elements, each extending to a respective side member and forming the upper part of the Y shape. Additional alternative internal support structures may include elements defined between a number of circular or other shaped openings in the area of the implant defined between the base member and side members. These circular or other shaped openings in alternative embodiments define the fusion passages in those embodiments. Because the beams or other structures making up internal support structure <NUM> provide support for the first and second side members <NUM> and <NUM>, the fusion passages defined through the support structure will typically include at least three such passages. However, it is possible for an internal support structure to be configured within the scope of the invention to include only fusion passages or perhaps only one fusion passage. In any case the area of the fusion passage or passages according to the present invention is preferably maximized to provide the maximum area for bone growth across the implant when properly positioned in an SI joint.

In the illustrated example implant <NUM>, first side member <NUM>, second side member <NUM>, base member <NUM>, and internal support structure <NUM> define joint contact surfaces on either side of the implant plane. As shown in the side view of <FIG>, a first joint contact surface extends along a line C1 on a first side of the implant plane (the implant plane extending perpendicular to the plane of the drawing page in this view along longitudinal axis L). A second joint face contact surface extends along line C2 on the opposite side of the implant plane in <FIG>. In this embodiment, these two joint face contact surfaces extend at an angle A between approximately <NUM> and approximately <NUM> degrees, and more preferably between approximately <NUM> and approximately <NUM> degrees to each other in a direction along the implant longitudinal axis L from forward end <NUM> to base member <NUM>. As will be described further below particularly in describing the implantation process in connection with <FIG>, each of these two joint face contact surfaces faces a prepared surface in the articular region of the SI joint when the implant is placed in an implanted position in the SI joint. In particular, one joint face contact surface will face a prepared surface in the sacrum while the other joint face contact surface faces a prepared surface in the ilium.

In order to help facilitate retention of the implant in the implanted position, example implant <NUM> includes a respective retention feature formed on each joint face contact surface. The retention feature in each case comprises a number of ridges or teeth <NUM> spaced apart along implant longitudinal axis L and extending parallel to width axis W. As best shown in <FIG>, ridges <NUM> in the illustrated example implant <NUM> are angled rearwardly and in position to bite into the prepared bone surface on each side of the implant plane. As will be discussed below in connection with the implantation method, this contact helps prevent the implant from sliding rearwardly out of the desired implanted position.

As will be described further below in connection with the implantation method, locking element <NUM> provides an additional feature that may be used with implant <NUM> to help secure the implant in the desired implanted position. The illustrated locking element <NUM> includes two fixation device receivers <NUM> and <NUM> shown best by the phantom lines in <FIG>, and a connector arrangement for connecting the locking element to base member <NUM>. In this connected position a longitudinal axis of locking element <NUM> extends parallel to the longitudinal axis B of base member <NUM>. As shown in <FIG>, the example locking element <NUM> includes a projection <NUM> configured to be received in a channel <NUM> formed along base member <NUM> when the locking element is properly connected to base member <NUM>. Locking element <NUM> also includes two fastener openings <NUM> each with a fastener shoulder <NUM>. Each fastener opening <NUM> is adapted to align with a respective threaded opening <NUM> of base member <NUM> when locking element <NUM> is in the properly aligned position. In this position a respective fastener <NUM> may be inserted into each fastener opening <NUM> and threaded in to the respective threaded opening <NUM> to the position shown particularly in the section view of <FIG> to connect locking element <NUM> to implant <NUM>.

It will be appreciated particularly from <FIG> that when the locking element <NUM> is connected to base member <NUM> in the proper locking position, each fixation device receiver <NUM> and <NUM> formed in the locking element extends at an acute angle to implant longitudinal axis L in the direction from base member <NUM> to forward end <NUM> of the implant. Fixation device receiver <NUM> comprises a cylindrical bore extending along that acute angle from an opening <NUM> in a top surface <NUM> of locking element <NUM> to an opening <NUM> in a first side surface <NUM> of the locking element. Fixation device receiver <NUM> comprises a cylindrical bore extending at the acute angle on the opposite side of locking element <NUM> from an opening <NUM> in top surface <NUM> to an opening <NUM> in a second side surface <NUM> of the locking element. In these positions, fixation device receivers <NUM> and <NUM> are each in position to receive a device such as a suitable bone screw to secure the locking element <NUM> and connected implant <NUM> in the implanted position as will be described further below.

While the example implant <NUM> shown in the drawings has a generally triangular shape in the implant plane, implants within the scope of the present invention need not have such a triangular shape. For example, even where the implant includes a base member such as base member <NUM>, the side members of the implant may include portions that extend parallel to each other where they meet the base member. Still other embodiments of an implant according to the present invention may include an oval or circular shape in the implant plane, or other polygonal shape, or even an irregular shape in the implant plane.

Methods of effecting SI joint fusion using the present invention may be described with reference to the example implant <NUM> shown in <FIG> and with reference to the anatomical views of <FIG>. Although the following description will reference example implant <NUM>, it will be appreciated that the processes apply to any implant within the scope of the present invention.

Generally, methods of using the invention include forming implant receiving surfaces in the sacral side and iliac side of the SI joint in order to form an implant receiving volume between the sacrum and ilium for receiving implant <NUM>. The method then includes fixing implant <NUM> in the implant receiving volume in an orientation in which the fusion passages extend transversely across the SI joint in position to facilitate bone growth across the prepared surfaces of the sacrum and ilium to thereby fuse the joint. Implants placed in this fashion not only stabilize the SI joint against articulation so as to facilitate fusion, but also provide a large area (the implant fusion passages) for bone growth to effect fusion.

When implant <NUM> is implanted as a separate procedure, implantation requires first providing suitable access to the SI joint which is to be fused. The procedure may include first palpating and marking the super iliac crest, and making an oblique incision through the skin, taking the dissection through the subcutaneous tissue. The posterior superior iliac crest may then be palpated and the dissection carried down to the sacroiliac joint referencing the medial table of the posterior superior ilium. The concave depression on the iliac side of the SI joint (referenced here as the "posterior iliac fossa") may then be palpated and developed with further dissection. From this point electrocautery may be employed to take down a portion of the iliolumbar ligament to expose the short dorsal sacroiliac ligaments which may also be taken down with electrocautery. The sacroiliac interosseous ligaments are then encountered and taken down with electrocautery.

After the process described in the preceding paragraph, the SI joint is exposed and the procedure continues with forming the implant receiving surfaces. To form these surfaces the SI joint may be entered with curettes for curettaging the fibrocartilage on the iliac side of the joint until the decorticated and punctate bleeding is encountered. The sacral side may also be curettaged with curettes as well also until punctate bleeding is encountered. The dissection is taken deeply into the SI joint in this manner of dissection until an ample space is created. Cage rasps may then be used to form and even the curettaged surfaces of the joint to produce the sacral side implant receiving surface shown at <NUM> in <FIG> and the iliac side implant receiving surface shown at <NUM>, and to size the implant receiving volume <NUM> (comprising the space between the two surfaces) in preparation for implant trials. Once the correct implant size is selected, the procedure includes connecting the selected implant <NUM> to an inserter (not shown) with which the implant may be impacted into the implant receiving volume <NUM>. The inserter may be connected to implant <NUM> in any suitable fashion, such as by suitable fasteners to threaded openings <NUM> in base member <NUM> of the implant. Once implant <NUM> is connected to the inserter, the implant is aligned with implant receiving volume <NUM> so that the implant plane coincides generally with a plane of the implant receiving volume. This plane of implant receiving volume <NUM> is indicated in <FIG> (and <FIG>) as line R where the plane perpendicularly intersects the plane of the drawing sheet. With implant <NUM> properly aligned the inserter may be impacted to drive implant <NUM> into implant receiving volume <NUM> to the implanted position shown in <FIG>. Once implant <NUM> is in the desired implanted position, the inserter is detached from implant <NUM> and removed, leaving the implant in the implanted position. In this implanted position the fusion passages of implant <NUM> (passages <NUM>, <NUM>, and <NUM> shown in <FIG>) will extend transversely across the SI joint in position to allow bone growth between the prepared surfaces <NUM> and <NUM> of the joint to effect the desired fusion of the joint. Preferably the fusion passages <NUM>, <NUM>, and <NUM> of implant <NUM> are filled with one or more fusion materials prior to insertion and impaction into the implant receiving volume. When implant <NUM> is placed in the implanted position shown in <FIG>, the bone fusion material encourages and/or supports bone growth between surfaces <NUM> and <NUM> to effect the fusion of the SI joint.

A proper tight fit between implant <NUM> and implant receiving surfaces <NUM> and <NUM> and the impaction into SI joint implant receiving volume <NUM>, together with the ridges or teeth <NUM> provided on implant <NUM> may be sufficient for ensuring that the implant remains fixed in the implanted position shown in <FIG>. It may be desirable, however, to use locking element <NUM> to ensure that implant <NUM> is fixed in implant receiving volume <NUM>. Where locking element <NUM> is employed, it may be connected to implant <NUM> once the implant is placed in the desired implanted position and the inserter removed. It will be noted that in the orientation of the view in <FIG> (and <FIG>) locking element <NUM> mostly obscures implant <NUM> with only a small portion of implant <NUM> visible at either end of locking element <NUM>. The connection between implant <NUM> and locking element <NUM> is made using fasteners <NUM> shown in <FIG>, <FIG>, <FIG> and <FIG>. Once locking element <NUM> is connected to implant <NUM>, suitable fixation devices such as bone screws (not shown in <FIG>) may be placed through one or both fixation device receivers <NUM> and <NUM>. The angle of the receivers <NUM> and <NUM> allows the bone screw or other fixation device to penetrate into the adjacent bone structure, sacrum or ilium, on that side of implant <NUM> to further fix the implant in the implanted position. The larger scale view of <FIG> shows fixation devices comprising bone screws <NUM> and <NUM> in receivers <NUM> and <NUM>, respectively. Bone screws <NUM> and <NUM> are each shown in an installed position in the respective receiver, and may comprise any type of bone screw suitable for use in bone. Preferably, each bone screw <NUM> and <NUM> may have the same configuration as screws used in other procedures involving the ilium, such as hip joint replacement for example. Although implant <NUM> and locking element <NUM> are shown separately from the sacrum and ilium in <FIG>, the orientation of the implant <NUM> is essentially the same as that shown in <FIG>. Thus it will be appreciated from <FIG> and <FIG> that bone screw <NUM> would extend into the ilium when placed in the installed position in receiver <NUM> with implant <NUM> in the implanted position shown in <FIG>. Bone screw <NUM> would extend into the sacrum when placed in the installed position in receiver <NUM> with implant <NUM> in the implanted position shown in <FIG>.

Once implant <NUM> is fixed in the desired fashion in implant receiving volume <NUM>, the dissections are closed in any suitable fashion to complete the procedure. In particular, the lumbar fascia may be closed in any suitable technique and the subcutaneous tissues also closed in any suitable technique. The skin layers are then closed by any suitable technique such as with staples for example.

Referring to <FIG>, another example SI joint implant <NUM> is shown together with a locking element <NUM>. Implant <NUM> has a triangular configuration similar to implant <NUM> and includes an elongated base member <NUM>, an elongated first side member <NUM>, an elongated second side member <NUM>, and internal support structure including a first lateral beam <NUM> and second lateral beam <NUM>. Implant <NUM> also includes fusion passages <NUM>, <NUM>, and <NUM> defined in the area between base member <NUM>, first side member <NUM>, and second side member <NUM>. Locking element <NUM> is attached to implant <NUM> by suitable fasteners (not shown) similar to the embodiment shown in <FIG>. Although not shown in the figures, it will be appreciated that locking element <NUM> is adapted to receive suitable bone screws similar to screws <NUM> and <NUM> shown in <FIG> to help fix the locking element and implant in the desired position as described above in connection with implant <NUM>.

Unlike implant <NUM>, implant <NUM> includes a number of markers <NUM>, each located in a respective through hole <NUM> formed in the implant. These markers <NUM> may comprise Tantalum, Tantalum alloys, or other suitable materials which are readily apparent in x-ray images and thus facilitate radiographic identification of implant placement and fusion as is known in the art.

The various components of an implant according to the present invention may be formed from any suitable material or combination of materials. Some forms of the implant may be machined from a single block of suitable material such as a suitable stainless steel or titanium alloy. Alternatively, the various members of the implant, such as base member <NUM>, side members <NUM> and <NUM>, and beams <NUM> and <NUM> of example implant <NUM> may be separately formed and welded together or otherwise connected in a suitable fashion to form the implant. Any biologically compatible material that may withstand the forces required for implantation and withstand the normal forces expected in the implanted position may be used to form an implant according to the present invention.

Due to the structure of an implant embodying the principles of the present invention, the base member and side members from which it is formed together with the internal support structure may be made relatively small in the implant plane. This allows relatively larger fusion passages (such as passages <NUM>, <NUM>, and <NUM> in the illustrated example) as measured in the implant plane.

The dimensions of an implant embodying the principles of the invention and the various elements which make up the implant may be selected based on the sacrum and ilium bone structure of the patient to receive the implant. Generally, the overall length dimension of an implant such as implant <NUM> along the longitudinal axis L may be approximately <NUM> millimeters (mm) to approximately <NUM> for most patients, while the overall width dimension along width axis W may be approximately <NUM> to approximately <NUM> for most patients. The thickness of an implant such as implant <NUM> as measured at the widest part of base member <NUM> (in the direction perpendicular to the plane defined by axis L and axis W may be approximately <NUM> to approximately <NUM> for most patients. The angle A (<FIG>) may be approximately <NUM> degrees to <NUM> degrees and more preferably approximately <NUM> degrees to <NUM> degrees for most patients. The side members such as <NUM> and <NUM> in <FIG> and beams such as beams <NUM> and <NUM> (where such beams are included in the implant structure) may be approximately <NUM> wide for example in the width dimension (perpendicular to the member or beam longitudinal axis. While the above dimensions and ranges will hold for most patients, it should be appreciated that an implant according to the present invention may include one or more dimensions outside the above ranges and values while still falling within the scope of the invention as defined by the following claims.

As used herein, whether in the above description or the following claims, the terms "comprising," "including," "carrying," "having," "containing," "involving," and the like are to be understood to be open-ended, that is, to mean including but not limited to. Also, it should be understood that the terms "about," "substantially," "approximately," and like terms used herein when referring to a dimension or characteristic of a component indicate that the described dimension/characteristic is not a strict boundary or parameter and does not exclude variations therefrom that are functionally similar. At a minimum, such references that include a numerical parameter would include variations that, using mathematical and industrial principles accepted in the art (e.g., rounding, measurement or other systematic errors, manufacturing tolerances, etc.), would not vary the least significant digit.

Any use of ordinal terms such as "first," "second," "third," etc., in the following claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another, or the temporal order in which acts of a method are performed. Rather, unless specifically stated otherwise, such ordinal terms are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term).

In the above descriptions and the following claims, terms such as top, bottom, upper, lower, and the like with reference to a given feature are intended only to identify a given feature and distinguish that feature from other features. Unless specifically stated otherwise, such terms are not intended to convey any spatial or temporal relationship for the feature relative to any other feature.

The term "each" may be used in the following claims for convenience in describing characteristics or features of multiple elements, and any such use of the term "each" is in the inclusive sense unless specifically stated otherwise. For example, if a claim defines two or more elements as "each" having a characteristic or feature, the use of the term "each" is not intended to exclude from the claim scope a situation having a third one of the elements which does not have the defined characteristic or feature.

Claim 1:
An implant (<NUM>) for effecting a fusion of an SI joint, the implant (<NUM>) including:
an elongated base member (<NUM>) having a base member longitudinal axis (B) extending parallel to an implant width axis (W) and perpendicular to an implant longitudinal axis (L);
an elongated first side member (<NUM>) extending along a first side longitudinal axis (F);
an elongated second side member (<NUM>) extending along a second side longitudinal axis (S) wherein the base member (<NUM>), the first side member (<NUM>), and the second side member (<NUM>) are connected together and lie in an implant plane defined by the implant width axis (W) and the implant longitudinal axis (L);
an internal support structure (<NUM>); and
a plurality of fusion passages (<NUM>, <NUM>, <NUM>) defined by the internal support structure (<NUM>) in an area between the first side member (<NUM>), second side member (<NUM>), and base member (<NUM>), each fusion passage (<NUM>, <NUM>, <NUM>) extending along a thickness axis (T) perpendicular to the implant plane and defining a respective open area through the implant (<NUM>), characterised in that the internal support structure (<NUM>) extends in the implant plane from the base member (<NUM>) to the first side member (<NUM>) and from the base member (<NUM>) to the second side member (<NUM>).