SACROILIAC, ANCHORING APPARATUS AND METHOD

A long-pitch, helical anchor (where long pitch is greater than length, itself greater than twice maximum diameter; and very long, extra-long, or hyper pitch exceeding several lengths of such anchor, typically at least 2 and usually 5 or 6) includes splines radially extending and helically progressing circumferentially around and axially along an elongate core. The center line or axis may be solid, all splines meeting near the center line. In other embodiments, the center line passes along the center of a lumen or channel of a hollow core, while the splines extend radially outward from, and axially along a length of the core. Installation may be from a posterior access or a lateral-posterior access, fixing two bones in two degrees of freedom, three degrees of freedom, or multiple anchors fixing the bones firmly in three degrees of freedom.

BACKGROUND

1. Field of the Invention

This invention relates to orthopedic surgery and, more particularly, to novel systems and methods for anchoring to and between bone structures.

2. Background Art

Orthopedic surgery has long depended on unique instruments and unique securement arrangements in order to encourage healing of fractures, regrowth of bone structures, and the like. Various securement mechanisms involve combinations of plates and screws, sometimes rods, and various other hardware.

Bones have a structure that is harder around the outside envelope (boundary) thereof, called cortical bone. Meanwhile, enclosed therewithin is medullar bone, sometimes called cancellous bone. Cancellous bone hosts the marrow and vasculature associated therewith. Consequently, the bone itself is quite porous and sparse, sometimes referred to as “spongey.” Cancellous or medullar bone material has less actual structural material forming around vacuoles containing soft tissues (marrow, vasculature, etc.). It has reduced ability to maintain embedded rigidly therein a conventional thread of a screw.

Meanwhile, thread pitch is of the same order of magnitude as the height of the threads from the shank (solid shaft) of a screw. Thus, the actual “purchase” (physical engagement or contact between the screw and the structural material of the bone) is much less in the cancellous bone than in the cortical bone. However, the cortical bone is comparatively thin, typically, or a comparatively small fraction of many bones or bone structures and length of screws anchored therein.

That is, just as in wood, threads on a screw or similar hardware may simply shear (core out) the corresponding threads they cut into the receiving bone. Thus, pull-out strength may be severely compromised by the spiraling threads with their intermediate bone material therebetween. It would be an advance in the art to provide a more secure form of anchoring. It would be an advance in the art to provide anchors capable of securing into cortical bone and cancellous bone with reduced risk of simply “coring” out.

Meanwhile, bone regrowth or “through growth” around and through foreign objects such as screws, plates, spacers, or the like is to be promoted. It would be an advance in the art to improve spaces for “through growth” through spacers or frames used with anchors in various types of surgery.

It would be an advance in the art to provide anchors capable of securing one bone structure to another in order to promote joinder therebetween. It would be an advance in the art likewise to provide both spacers and anchors having apertures, porosity, highly textured surfaces, and the like in order to provide more shear strength, as opposed to mere friction securing new bone growth to spacers, anchors, and so forth.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, in accordance with the invention as embodied and broadly described herein, a method and apparatus are disclosed in one embodiment of the present invention as including an anchor selected from several types that may be directly driven (malleted) rather than screwed with a driver. Anchors may include a central aperture or channel along a center line, where the center line is itself curved, such as on a radius or arc. In certain embodiments, the anchors may include splines. The splines may parallel the center line (center curve) as they extend radially away from a wall of a central channel or core. Splines may each progress helically in a comparatively long pitch, helical direction. By “long pitch” is meant that the pitch is typically multiple diameters, and even multiple lengths long. Pitch represents a distance traversed by a flute (where a flute may be a thread or a spline) per revolution of rotational progress. The twist (distance per revolution) in a conventional screw is typically sufficiently small that a full 360 degree rotation (two pi radians, or 2×π radians) occurs at a fraction of the diameter distance.

For example, a one quarter by 20 (¼×20) bolt or screw has a one quarter inch diameter in which 20 threads or 20 revolutions of the threads occur in every inch of length. This means an inch of axial progress occurs in 20 complete circles or complete spirals of the threads. In contrast, an anchor in accordance with the invention has a pitch that is typically several lengths (even up to dozens of diameters) of the fastener or anchor.

Splines are angled primarily to travel along their length, while progressing along a helical path that will typically not make a full revolution within the entire length, or even a few lengths, but many (e.g., four, six, eight, or more).

Thus, such splines will typically make less than one quarter (usually from one sixth to one tenth) of a revolution or progress about the circumference within the entire length. Meanwhile the aspect ratio of diameter to length is itself less than a fifth to a tenth (1:5 to 1:10). In fact, the progression or the amount of angle traversed circumferentially is typically on the order of only one eighth (⅛) of the circumference or less.

Thus, anchors in accordance with the invention may be malleted (driven axially by impact loading) into place. Spiraling and twisting by the splines moves the anchor through the cortical bone and along both an arcuate centerline and a helical path through the cancellous bone therewithin. The result is that only a small fraction of the spline surface area aligns parallel to the pull-out direction (back toward the head. Thus, the splines resist any force tending to pull out, while they themselves present a significantly greater surface area and less load (pressure, force per unit area) against the cancellous bone than does a conventional screw.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Herein, a number of unique terms are used, and others have unique definitions. Definitions of conventional structures are inadequate to describe certain features of embodiments of certain features in accordance with the invention. Moreover, certain terms will be necessarily terms of art specifically defined herein due to the lack of any suitable definition in prior art or in the art to which this invention pertains. Likewise, sometimes a definition or group of definitions may need to be narrowed down to the specific intent desired in order to adequately describe and claim the invention described herein.

An aperture is basically a hole. An aperture through a thin material may be virtually a two-dimensional plane. An orifice or an exit opening may be thought of as a plane past which a fluid flows. Other apertures may have to pass through a wall, or conduit, and therefore will not only have an area through which it passes but also a distance through which it passes. However, the point of the use of the word aperture is simply to show that a hole has been created for some purpose. The length of an aperture is insignificant. That is, if a significant distance is involved, then a channel or a path is spoken of. That is not typically defined as an aperture, but a line, path, channel, conduit, or the like, and may even have an entrance, exit (both of which are planes), or both identified.

Orthogonal means two items are oriented at right angles to each other. However, orthogonality applies in all kinds of reference systems. In polar coordinates a radius from an axis is based on circular, planar geometry, while the azimuth or the distance along that axis may be defined either by an angle from an axis or a distance from a reference plane. Similarly, spherical coordinates have a frame of reference in which an angle must be defined from three different axes or with respect at three different axes, and a radius to a location must be defined. Herein, orthogonal means that two items, axes, directions, forces, or anything else capable of being characterized by a directionality are oriented at right angles to one another.

However, effectively orthogonal is used to mean that the two items need not be at the exactly orthogonal angles but they are at an angular orientation that if they were connected rigidly, relative motion would be precluded outside the plan of their intersecting axes. In general, three dimensions can be defined in a set of any three coordinates using radii, axial distances, translating distances along Cartesian coordinate axes (rectangular three axis geometry), and so forth. Therefore, it may be necessary sometimes to refer to items that are effectively orthogonal, effectively parallel, or the like.

One reason for this “effective” adjective is the fact that bones are round not square. They tend to have rounded surfaces, edges, and ends, not sharp points. Thus, in running an anchor into a joint “effectively parallel” to the joint or to the two cortical surfaces that are to be fixed “rigidized” to one another will not necessarily be parallel. A straight object may be parallel to a tangent surface (plane instantaneously parallel at a point of contact) or pass along an undulating surface, and thus be called “effectively parallel.

Similarly, an anchor may pass primarily through a cortical surface of a bone, being “effectively” or “primarily” orthogonal thereto. Likewise, two bones may be spaced apart and extend so for some distance, even though they may be rounded conformally with one another or congruent with one another. Thus, the parallelism or the orthogonality may not be absolute. For that purpose, the term “effectively” may be used with the principal term parallel or orthogonal.

Likewise, principally parallel or principally orthogonal are used herein to mean that a device or a force or the like has an effect (typically its greatest effect) in a parallel direction or an orthogonal direction, even though the exact angle may not be precisely parallel or orthogonal. In general, one may rely on the fact that effectively parallel means that a tangent surface or tangent line may be approximately parallel to another even though both are curving. Likewise, principally orthogonal means that most of the orientation is in the orthogonal direction, notwithstanding it may also involve angular variation in other dimensions as well or even in the direction that was intended to be orthogonal but cannot be due to curvatures and so forth. One may typically regard principally parallel to mean less than forty five degrees off of parallel. One may consider principally orthogonal to mean less than forty five degrees off of orthogonal. Most typically, the angular discrepancy will be much less than forty five, much less than thirty.

An implant herein is anything that is embedded in the body of a subject by surgery, minor or major. The anchors used are considered to be implants, because they are intended to take a permanent place in the body, in this case between bones. An anchor as used herein may be relied upon to hold a bone in at least one degree, and typically at least two degrees, of freedom with respect to the anchor. It may anchor to another bone in more degrees of freedom.

Typically, an anchor will hold two bones with respect to one another in at least two degrees of freedom. For example, if an anchor has an axis, and that axis passes through two bones effectively orthogonally with respect to their cortical surfaces, then any plane perpendicular or orthogonal to that axis has two dimensions, and the axial orientation of the anchor fixes those two bones with respect to one another in those two degrees of freedom, the two degrees of freedom that can be used to define the plane perpendicular to the axis of the anchor.

However, in some embodiments, an additional degree of freedom or more may be fixed by virtue of the angles, or by virtue of additional anchors. Meanwhile, those anchors, in the case of multiples, may each fix two bones in two degrees of freedom, and yet duplicate restriction in certain of those degrees of freedom. The action of splines tends to fix anchors in a third degree of freedom.

By degrees of freedom is meant one of the six possible degrees of freedom in a three-dimensional, Cartesian space. In a Cartesian space, three axes, orthogonal to one another, and typically called an x, y, and z axis, define the space. Translation (linear motion) in any direction may be defined in terms of motion or displacement along each of those axes. However, in addition to translation, rotation may also occur. Rotation may similarly be defined according to degrees of rotation of any object or thing about any of those three axes.

The vector algebra may be somewhat complicated. Therefore, it is possible and often relied upon, to use a coordinate system centered, that is it has its origin in or on an object itself. This often simplifies the mathematics by fixing the axis system for translation and rotation to the object, rather than some arbitrary location in space, which might otherwise complicate the mathematics.

By fixing two objects or any object in a degree of freedom means that the freedom to move in that particular direction or degree of freedom has been restricted. Thus to restrict in degrees of freedom is to fix against movement in those particular degrees of freedom, where the degrees of freedom involve three axes of translation (linear movement in the directions of the axes) and any rotation about each of those three axes.

Various definitions used herein or terms needing definitions may include medical terms. For example, distract, means to move apart in tension, such as distracting two bones or distracting ligaments. Typically, in the SI joint (sacroiliac joint) the bones may need to be distracted or moved apart from one another resulting in tensioning or stretching ligaments. Both of these are considered distracting. Stretching or stressing a tissue is to distract it. Likewise, to move two items apart is to distract them.

The medical terms for direction may be used, as well as directional terms. Thus, posterior means rear, anterior means front, superior means above, inferior means below, lateral means a side, and typically means laterally from a center plane of the human body. Likewise, medial typically means at or near or toward a center plane of symmetry through the body, so one may speak of laterally or medially as far as positioning or motion. Pronation is rolling or rocking forward. This would be considered pitching in in aeronautic parlance. Pitching forward, that is nosing down is pronation. Pitching upward, nose up or pitching backward nose up is considered to be supination.

By access herein, is typically meant posterior access or a lateral-posterior access. Posterior access means access through tissues behind the sacroiliac joint whereas lateral-posterior means accessing at an angle that will give access from a side of the ilium but toward the rear, as opposed to from a frontal or anterior access.

Herein, anchoring means that the anchors or an anchor crosses both of the cortical surfaces that it is intended to fix with respect to one another. Parallel engagement or within-the-joint engagement means that an anchor is being installed along the two cortical surfaces sharing a joint, thus distracting the ligaments that hold those bones together. An anchor engages both the bones with at least splines on the anchor, thereby forming a stable fixation. The ligaments drawing the bones together and the anchor cutting into the bones with the splines and distracting the ligaments provide a stabilization.

Materials of the anchors may be inert metals, meaning that they will not react nor degenerate in the presence of materials naturally occurring in the body. However, polymers (plastics) and filled (reinforced) polymers, are improving all the time. Certain ones of these materials may be suitable for certain anchors in certain positions. Likewise, bone itself may be machined to form an anchor, and may thus eventually be subsumed within the bone growth fixing permanently a joint.

Typically, these types of grafts are called allografts, or homografts where the bone is from a same species, but not necessarily of a same blood type, and so forth. Meanwhile, it is conceivable that an autograft (from the subject) may be used, but this is less likely. An autograft involves using bone from the very subject of a surgery. Sacroiliac joint fusions or fixations are typically undertaken due to degeneration of the joint. This is typically a function of health and age. Accordingly, using an autograft is not a reliable process.

Force means force, a fundamental parameter of physics. It may be measured in any units of force. Stress means a force applied per unit area. Stress may occur in tension or compression or shear. The units of stress are force per unit of area. Any units of force and any units of area may be used to define a stress. Strain is a fraction having no dimensions (units) in that it is a measure of stretch in compression or tension of any material as divided by the unit length. Thus, strain is inches per inch, microns per micron, meters per meter, or any length over length, meaning it is a dimensionless (no units of measurement) value.

“Grow-through” means that a region has a porosity, an aperture, a window, a lattice, or some other vacancy through which bone may grow in order to strengthen the region and the attachment where an anchor or implant has been implanted (installed).

“Grow-on” identifies a characteristic of a material in which a texture includes shapes, convex, concave, some combination, or the like that do not pass through the wall onto which these textures are formed, and thus cannot allow bone to grow-through them, but bone may grow around them, and have strength due to the shear strength (shear being a technical engineering term meaning stress in a material orthogonal to the applied force). A coefficient of friction exists between any two materials.

The coefficient of friction is defined as the amount of force required to slide one material along another in a plane per unit of normal force forcing the two materials together at the plane. This is often defined as a Force equals Mu times N, where N is the normal force pushing the two materials together at their surfaces, Mu is the coefficient of friction (a property of those two materials in contact), and the force is the amount of force required to cause them to slip at that interface surface. Again, the coefficient of friction is dimensionless (unitless) because it is the ratio of two forces acting. One benefit of surface texturing is that it does not permanently rely on a coefficient of friction between surfaces, but rather provides small pillars extending up into the bone as it grows and to which the bone may attach itself.

“Pull-out” resistance or force represents a force required to withdraw a fastener once it has been inserted by pulling on that fastener from the direction in which it was forced into place. Screws are typically problematic in this type of testing. Because screws advance only a small fraction of their diameter with each rotation of the head, the threads act like blades or scrapers. Thus, as those threads thread into a material like bone, they are so close together (axially), and have so compromised the material penetrated, that drawing a screw out of the place where it has been threaded in will often “core out” the bone (literally shear out all the material engaged by the threads) where it had been originally threaded. This may happen intentionally or accidentally.

In an apparatus and method in accordance with the invention, threads are not used. Rather splines that extend helically at a very long pitch, where pitch is the distance between one revolution of a helix about a central axis, and the next revolution to the same circumferential point advanced along the helix. Thus with screws the pitch length is often a small fraction of a diameter of the screw. Certain types of screws in woodwork such as bugle-head screws or sheetrock screws, or the like have a larger pitch compared to machine screws, conventional threads, bolts, and the like with lesser pitch. Both are effectively wedges of a few degrees, about 3 degrees off a plane normal (perpendicular, at a right angle) to the longitudinal axis for a machine screw and about 10 degrees for a bugle head screw. In contrast, a helical spline in accordance with the invention typically has a wedge angle of over 90 degrees from that same plane.

One may think of any helical screw as a wedge that is simply coiled around itself so that the wedge may continue advancing longitudinally throughout multiple revolutions. Each revolution is a wedge having a length of Pi times the outer diameter of the screw. Each rotation of a screw advances axially by the distance of the pitch (crest to crest of each adjacent pair of threads). Even a very short, sheet metal screw must have one full turn of threads on a length of about one diameter.

In systems and methods in accordance with the invention, threads are not used. Instead, helical splines are used. Splines as used herein are helical walls that extend out from a central core or even a central axis. These splines extend radially outward but also extend longitudinally in a helical pattern that rotates around the core as they advance longitudinally along the length of the anchor. In accordance with the invention, the helices are not screw threads because their pitch is multiple lengths of the anchor. This means that a spline never completes a single rotation or a single 360 degree helical path around the core.

Typically, an odd number of splines is preferred, and that odd number of splines may be three, but is typically five, and may be more. Pitch does not depend on the number of splines. Three to seven splines may serve, but five splines have been found suitable in practice for both manufacturing and use. A typical pitch in accordance with the invention is greater than five lengths of the anchor, and may be more.

In general, herein, a long pitch means a pitch greater than the total length of the splined portion of an anchor, wherein the length of the anchor is greater than two of its greatest diameter around the splines, and typically about five diameters or more. Nothing sold as a “screw,” “bolt,” or other “threaded fastener” can qualify as having a “long pitch.” A very long pitch is at least two, and typically three to more than five times the splined length of an anchor of length greater than two diameters. Typical anchors are two to four and a half diameters long, and have a pitch of more than five lengths of the anchor. This translates to about three and a half degrees of angle from a longitudinal, axial line drawn at the outer surface of the core from which the splines extend. That is over 95 degrees of angle measured from a plane perpendicular to the longitudinal axis, when compared to screws, which have less than eight degrees for that angle, and typically closer to three degrees for that “wedge angle”.

Meanwhile, the term spline herein is used to mean a specific structure. Conventional splines typically involve connectors in which lands, extending radially outward as part of a shaft, alternate with grooves machined radially down into the shaft, alternating circumferentially between the lands. Typically, the circumferential distance across a land and an adjacent groove are essentially the same. Even when a spline has a triangular shape that comes to a single ridge, or if it is a “buttressed” trapezoidal shape adjacent a machined groove, the circumferential distance across the middle or the median radius of a land is the same as that of a groove.

Herein, the relative dimensions circumferentially are much more disproportionate. A spline is more like a thin blade compared to other splines and the grooves here. The groove occupies the great majority of the circumferential distance, and the spline occupies a relatively small fraction, typically about a fifth or less. This may be as little as one tenth of the circumference covered by splines, and ninety percent covered by grooves. However, this will depend on whether the spline and anchor are formed of a metal, a polymer, or bone.

Barbs, texturing, and grow-through regions may be used for resistance to sliding of bone with respect to an anchor along the longitudinal and axial direction of an anchor. Barbs and texturing may have an immediate effect against sliding, which is improved as bone growth continues. Grow-through areas initially provide insignificant resistance to axial displacement of bone along an anchor.

St. Venant's principle applies to most solid materials. Especially isotropic materials. Isotropic materials are materials in which the mechanical properties are the same in every direction. Cortical bone is typically isotropic. Cancellas bone, the central or marrow portion of bone is also typically isotropic. However, cancellas bone is much weaker and includes an almost sponge like hard structure filled in a mushy marrow, including vascular material. Thus, cancellas bone does not support force in any direction well. Cortical bone does support forces much better. Nevertheless, cortical bone, being essentially isotropic obeys the conventions of solid materials.

St. Venant's principle observes that stress or load (load being a force or a stress) begins distributing itself immediately from the point of application of the load out at a forty five degree angle. That forty five degree angle is a line, plane, or surface of principal shear stress. Maximum shear stress supportable is typically half the value of maximum compressive stress and maximum tensile stress supportable. Accordingly, driving screws into bone often has the effect of damaging the bone by forcing a shearing failure, flaking off chips of bone along the planes of principal shear. Accordingly, in accordance with the invention, drills, broaches, and the like are used to pilot and thereby reduce the stresses placed by anchors on cortical bone material.

Mohr's circle of stress defines maximum shear with respect to maximum compressive stress and maximum tensile stress. Mohr's circle of stress actually defines the principal stress line (in two dimensions), which moves away from the forty five degree plane depending on whether a second force other than a single direct compression or direction is being applied orthogonally to a first force.

A symmetric splining herein is used to define and indicate the fact that the grooves are a much larger portion of the circumference of an anchor than is a spline. Lands and grooves are not of similar dimensions.

Some terms used herein are not necessarily common. The term “pitch advance ratio” is a term coined herein to mean the circumferential distance (at maximum spline diameter) advanced by a single spline of an anchor divided by the overall length of an anchor. Thus, over the length of an anchor, a pitch advance will occur that is much less than the length, because the pitch is itself many times the length. It is typically less than Pi times the maximum diameter divided by five times the length. With fewer splines, it is not necessarily proper to use the number of splines to define pitch advance, because the issue is not dependent on number of splines, but the angle of progression circumferentially with advance axially.

The term “pitch length” means exactly the same as pitch length as pitch in screw threads. Pitch is the distance from one peak to the next peak along a threaded shaft, such as a screw or bolt. It is the distance that the screw or threaded rod travels for each rotation of 360 degrees by the head. Herein, the term “pitch advance angle” is a coined term meaning the angle that the helical spline makes with a plane that passes through the center line of an anchor, and the center line of the spline, at any point, measuring the angle that the ongoing helical path of that line makes with that plane at the outermost radius of the spline.

The term “pitch swept angle” is used to mean the total angular difference between a plane passing through the center line of the anchor and the center line of a spline closest to the head end or base of an anchor, and a plane through that center line of the anchor and the center line of the spline closest to the point end or leading end of the anchor. Thus, on a clock face, the pitch swept angle measures how much circumferential progress the spline makes over the length of that spline in an anchor.

Herein, the term plane will seldom apply to any physical part or location in a bone, other than an imaginary plane through certain points or lines. This is because bones are fundamentally rounded everywhere. They are not sharp and they are not angular. Accordingly, when two bones have curvature, one may pick a location on one bone and a corresponding location on another bone and one may draw a tangent plane to any surface. Any time the “plane” of a bone surface is spoken of, and it is not a plane, one may understand the plane to mean a tangent plane.

Referring toFIGS.1A-1H,1J-1K,1M-1N, and1P-1W, leaving the trailing letters “I,” “L,” and “O” unused to avoid confusion, a system10in accordance with the invention may be used to anchor one bone or bone structure (fragment, bone, or the like) to another. Various embodiments are shown, grouped asFIGS.1A through1Gdirected to cross-joint anchoring by multiple anchors,FIGS.1H,1J-1K,1M-1N, and1P-1Qdirected to cross-joint anchoring by a single anchor, andFIGS.1R through1Wdirected to anchoring by an implant (metallic anchor) within and along the direction of the sacroiliac (SI) joint requiring fixation by the presence of the implant.

Typically, the bones14may be defined by the body part to which they pertain. The body may be used to define directions11with respect thereto (e.g., a human or an animal, but typically a human). In the illustrated embodiment, the direction11ais a vertical direction11a, while a lateral direction11bmay be thought of as a left or right direction.

In medical parlance, lateral is an expression meaning toward the left or right side of a subject outward. Meanwhile, medial is used to mean toward a center plane or center of symmetry of a subject. Here, lateral and medial will be used as in medical technology. However, a lateral direction11bwill be either left or right without regard to whether it is traversing in a lateral direction, with respect to the subject, or a medial direction. Finally, a direction11ccovers any forward or backward (anterior or posterior) direction with respect to a subject. Thus, a direction11crefers to that front and rear, forward and backward, direction. Nevertheless, without a reference number, anterior and posterior maintain their same medical meanings, as do lateral and medial, as well as superior (up) and inferior (down).

An anchor12may be used in multiples with or without a frame30(see, e.g.,FIG.5). An anchor12may be of a pointed type12aor of a hollow type12b, also referred to as a cored type12b. The helical splines20of the anchors12, combined with an arcuate center line17(which is therefore not really a line17but a curve17or arc17) are configured to twist and spiral along an axis not necessarily within the actual material of an anchor12.

For example, in certain illustrated embodiment, bones14are exemplified by a sacrum14aand an ilium14b. These bones14may be referred to generally as bones14or by the trailing letters as14a,14b, designating specific instances14a,14bof particular items within the classification or type, here identified by the number14for bones14. Herein, a reference numeral will refer to a type or class of items, while that same reference numeral with a trailing letter refers to a particular instance or configuration thereof.

The bones14a,14bmay meet at a joint15or bone interface15. In certain illustrated embodiments, that joint15is known as the sacroiliac joint15. The joint15itself is actually formed of flexible, cartilaginous material. With age, deterioration, disease, inflammation, or the like, a particular joint15may become damaged, partially destroyed, and otherwise subject to excessive motion between the two individual bones14a,14binterfacing at the joint15. Accordingly, a “fixation” (growing rigidly together) as that term is understood in orthopedic surgery, may be required. When the flexible joint15becomes too flexible, movement may cause abrasion and other damage between the bones14a,14b. They may be fused to rigidize and literally grow together across the joint15. The joint15may be scraped to promote active bone healing and growth, and to remove ineffective cartilage and its debris remaining in the joint15.

In a sacroiliac joint15as illustrated, anchors12may be inserted in a medial direction11bthrough the ilium14binto the sacrum14astopped only by the head16of the anchor12at the cortical type bone14near the outer surface of the bones14a,14b. A center line17of each anchor12is arcuate in shape in certain embodiments, straight in others. It may be or lie within a single plane, or may itself be helical in shape having a curvature circumferentially as well as radial along its length. Such an embodiment would reflect an extremely long pitch (several lengths of the anchor12per 360 degrees of revolution or progression of a spline20proceeding therealong and therearound). A very long-pitch, centerless screw (or any thread external to a central portion) may be thought of as a coil or wedge in operation. It does not necessarily have to include any actual matter along its center line, yet spirals about a central axis whether that axis is straight, curved, or helical.

Each anchor12regardless of its particular type12a,12bwill typically have a point18or a leading edge18as its point, respectively. A pointed anchor12amay have all splines coming together to form a specific point18. Meanwhile, a hollow (cored) anchor12b, having a tubular shape inside the splines20, thereby leaves either a sharpened cutting edge18as a leading edge18to promote its progress through bone, or a hollow core to follow a K-wire as explained below. A pilot hole may be drilled for starting an anchor12and typically need only extend a short distance (typically about three diameters). Inasmuch as the helical splines20extend away from the center line17(curve17), each anchor12rotates into position following its point18or leading edge18and the path dictated by the splines20.

The splines20extend radially, and progress axially as well as angling circumferentially about the center line17of an anchor12. In the pointed embodiment12a, virtually the entire anchor12ais formed of splines20extending radially and axially from and along, respectively, the center line17. In contrast, the hollow anchor12bhas splines extending away from a lumen22or channel22defined by a wall23spaced from and traversing along the arcuate center line17. From that wall23around the lumen22, the splines20extend radially. Splines20have at least one of three possible mechanisms (texture, porosity, apertures) for encouraging securement thereto by the surrounding bone material.

For example, the lumen22may actually be accessible by elongated, somewhat rounded, oblong apertures60. For example, apertures60athrough the splines20may permit bone grow-through individual splines20. Likewise, apertures60bthrough the wall23may permit bone growth inside and through the lumen22and connecting through those apertures60bto bone growth between adjacent splines20.

In addition, the splines20, the wall23, or both may be formed of a porous material (e.g., sintered metal) provided with a rough texture. Sintering provides particles of a metal that are partially melted at their interfaces in order to provide an atomic bond between adjacent particles, while still leaving small, often microscopic interstices therebetween. Accordingly, fluids, gases, and cellular structures inherent in bone14may actually grow into, through, or both, with respect to such splines60aor walls60b. Bone will typically grow-through the porosity itself as well as through any larger apertures60. Thus, one may think of a grow-through-aperture60(GTA60) as a comparatively larger aperture60, although a porosity of much smaller effective diameter (defined as 4×area+perimeter) through the solid material itself may also exist.

The texturing on any given component such as a spline20or wall23may provide resistance against shear. That is, a texturing provides concavities and convexities at the surface itself of a solid, thereby resisting the physical shearing that might otherwise occur between a hard, slick, slippery, smooth, and non-bonded surface of a solid with respect to adjacent material of a bone14.

Referring toFIGS.2through4, an alternative embodiment of anchoring is illustrated. For example, inFIG.2is shown an ilium bone14b. Also shown is a sacrum14a. The demarcation between them is identified as a joint15or interface15between the two bones14identified as sacrum14aand ilium14b. The interface15or joint15is referred to as the sacroiliac joint15. In this illustration are shown the several anchors12.

The individual anchors12a,12b,12c,12dare instantiations of anchors12, generally. In the illustrated embodiment of an installation of a plurality of anchors, various options are illustrated. For example, the anchor12ais positioned high (superior) and posterior from the main hip joint. It may be located by identifying the posterior superior iliac spine (PSIS) which provides not only a navigation aid, but a positive location for positioning an anchor12athat crosses the SI joint15.

In order to provide resistance to relative rotation in anything like a vertical plane defining a joint between the sacrum14aand the ilium14b, additional anchors12b,12c, meaning either one or both, may provide restrictions against rotation about the anchor12aby either of the bones14a,14bbeing anchored together by the anchor12a. In certain alternative embodiments, one or more anchors12dmay be placed actually within the joint15, thereby distracting the ligaments holding the sacrum14aand ilium14btogether, inducing tension in the connecting ligaments and providing compressive pressure against each of the bones14a,14b. These anchors may be discussed in further detail hereinbelow.

Referring toFIG.5, while continuing to refer generally to all figures, an apparatus40and method40are illustrated. That is, one may think of the illustration ofFIG.5as representing both a method40of insertion and retraction as well as a set of hardware40for so doing.

A surgeon may use a mallet42to drive an anchor12into bone14with or without a frame30. The mallet42provides an impact loading (momentum, impulse, time and force). Impact is a comparatively short event. The mallet42transfers momentum of its motion and mass into a handle46, a cutting edge18or leading edge18, such as a point18. It will cut into both cortical bone and cancellous bone, subject to circumferential loading on the surfaces of the splines20.

Momentum has “units” of mass times velocity. Impulse has units of force times time. Energy has units of mass times the square of velocity. The mallet42transfers energy and momentum into the handle46upon striking. The handle43is held by a surgeon to position and optionally to provide a certain rotational (circumferential) force urging the handle46. The tool44will typically be rigidly secure between the handle46and shaft48. The shaft48extends from inside the handle46to a point50that operates as an interface50with the head16of the anchor12. The splines20are oriented to pass circumferentially70csimultaneously. They present a much larger surface area (the sides or surfaces of the splines20). That spline surface area will tend to urge the point18(regardless of whether actually pointed or hollow in the direction of the helical path of the splines20.

The front or leading edge of each spline20must effectively cut through bone, but presents comparatively much less surface area. Accordingly, even cancellous bone will tend to rotate the anchor12by moving the splines20circumferentially as they move axially along their direction of travel.

A surgeon may apply a moderate force in a circumferential direction70caround the handle46, in the same direction that the splines20angle or drift as they progress from the head16toward the point18. This will assist the slow rotation into local bone that may otherwise tend to absorb more momentum from the splines20in rotating the splines20moving along their trajectory.

Urging circumferential70crotation of the handle46is not required, but may result in less trauma to the bone14responsible to provide circumferential force rotating the anchor12along its path. Of course, the point18, terminating at the end of the arc that represents the center line17(center curve17) through the anchor12, will tend to arc along that path. Whether circular or spiral in and of itself, the path is followed by the splines20. Possible rotational70curging of the handle46by a surgeon may help.

Again, a frame30, of any suitable shape for the space to be accommodated, may be used or not. In certain embodiments, the distractors49a,49bmay be used to move tendon, muscles, or other tissue layers from an area into which a frame30is to be placed. Distractors are well known in the surgical art and need not be described in detail here. Suffice it to say that they operate in an opposite direction from forceps to spread tissues apart clearing space for a procedure to take place. Such a procedure inserting a frame30past tissues into a joint15between bones14. Thus, the illustration ofFIG.5shows various options, not all of which would be extant in a particular procedure.

The points50or interfaces50may be made in various configurations. For example, the point50ahas a slot51afor receiving a crossbar52flanked on each side by a key51b(slot51a, key51b, crossbar52a, and the relief52bin the illustrated embodiment of a head16). For installation or insertion of an anchor12, the point50amay be suitable. In other embodiments, a square point50bmay be used to fit into the head16. Alternatively, a hexagonal or other commercially available point50cmay be relied upon. The function of each of the heads50is to apply the impact load from the mallet42through the tool44and into anchor12along its axial direction70aand, optionally apply a slight torque circumferentially70c.

The engagement by a key51bin a key way52bor relief52bmay engage to provide a certain circumferential70ctorque. Torque is a force at a distance and therefore has units of force times distance. Axial force plus torque are suitable for progressing the anchor12both axially70aalong the arc of the center line17(center curve17) and circumferentially70calong the helical path described by the splines20.

The points50d,50emay be used for insertion, but may provide additional features including a threaded stud53aand a hook53b. The threaded stud53amay actually rotate with respect to the hexagonal point50cin the device50d, thereby permitting engagement of the female thread inside the head16, for extraction. The hexagonal head50cmay penetrate into the head16, after which turning a knurled handle, a T-handle, or another mechanism allows the threaded stud53ato advance forward with respect thereto out of the hexagonal head50c.

A polygonal (e.g., hexagonal) head50cmay provide secure engagement for rotation in a circumferential direction70c. The threaded stud53aprovides secure axial70aengagement with the head16in order to draw back along the center line17(center curve17). The handle46may be rotated in an opposite circumferential direction70cfrom that of insertion. Accordingly, the anchor12may be removed by pulling and rotating. This will be on the same trajectory on which it passes into bone14to which it anchors. The significance of the threaded stud53aand the hooks5d,50eis that axial tension is not employed during the insertion process. Insertion needs only force or impact applied in an axial direction70a, although some torque may assist.

Removal or loosening of the anchor12by the bone14does not occur readily because the axis17is curved not straight and the splines20are not aligned with it. That curve17has been modified in a helical path driven or guided by the splines20. Accordingly, a force near the head16trying to force apart adjacent bones14a,14bis resisted by every spline20at its angle. That angle is not aligned with the axial direction70aat the head16itself. Rather, along the entire length of the splines20the direction of force is continually changing.

The orientation of each spline20surface changes along its entire length to secure the splines20and thereby the entire anchor12in bone14, even cancellous bone. Pitch is pitch. Long pitch is a pitch longer than a length, where length is more than twice maximum diameter. Very long pitch or extra-long pitch means pitch is several lengths, typically greater than two and more typically greater than five, with the same or lower ratio of diameter to length. One will note that due to the extra-long (multiple anchor12lengths) pitch, the mallet42and tool44may drive the anchor12into the bone14. After that, the splines20provide a comparatively large surface area engaged at a comparatively modest force exactly the opposite effect as a conventional screw which tends to shear any cancellous bone into which it is anchored.

In fact, many conventional screws operate more like a sheet metal screw. A sheet metal screw passes through a single thin layer that is typically considerably less than one inch in thickness. One pitch is the difference in length between the crest of one thread and an adjacent thread. Not only do the splines20in accordance with the invention put less pressure on the cancellous bone, that pressure is distributed over a substantially larger area. There is not a location where the shear of a few threads can accumulate in close proximity to one another and at the exact same diameter as one another, in that nearly the same axially70alocation can be pulled through cancellous bones. Thus the coring out by simply stripping the threads cut into the cancellous bone is avoided.

Similarly, the hook type point50e, similarly to the stud type point50d, may engage the head16, this time by a crossbar52a. Meanwhile, the shaft48fits into the head16of the anchor12. For example, the hook point54bmay pass into the head16, past a crossbar (as inFIG.6H) then may be drawn backward in the axial direction70a. It may thus engage the anchor12to urge rotation in a circumferential direction70c, as well as drawing backward in an axial direction70a.

Referring toFIGS.6A through6G, as well asFIGS.7A-7H and7J-7K(again not using I, L, or O, in order to avoid confusion), an anchor12in accordance with the invention may have a pointed configuration12aor a hollow (tube-like core, or coring) configuration12b. In the illustrated embodiments, one will see that the proximal end is formed into a head16for engaging a tool44for insertion or installation.

The tool44may have any of the engagement mechanisms50athrough50efor driving, drawing, or both against the head16. It may urge the point18or cutting edge18axially along the center curve17or center line17. Progress along the center curve17necessarily drives the distal end of the anchor12at the leading edge18or cutting edge18(also called the point18) along the axial direction70a, where directions70are all with respect to the axis17or center line17through the anchor12along a curve17.

Like the frames30, the anchors12may be formed of a sintered material providing a porosity that can be penetrated in a straightforward manner by cellular material within a bone14. Following insertion of the anchor12, with the leading edge18or point18advancing first into the bone, and typically terminating when the head16abuts the cortical bone14or as shoulder countersunk therein. That is, the head16may be countersunk into cortical bone14. There is substantial benefit to leaving the head16outside the cortical bone14material in order that the splines20may be stabilized by the cortical bone14, and so that the head16may secure one portion of bone14to another.

To that end, a grow-through-aperture60or GTA60may be provided in any suitable portion of an anchor12. For example, in the illustrated embodiments, a GTA60aprovides an opening60athrough a spline20. It may be dressed or shaped to promote engagement with bone growth therethrough. Similarly, the wall23of the spline20, surrounding the lumen22or channel22, may likewise be perforated with GTA's60bat some suitable length and width, spaced apart at an effective, intermediate spacing therebetween.

One will note that the helical trajectory of an anchor12upon entry into bone14is guided by the splines20, which may in turn be guided or not by apertures32in the posterior wall36aof a frame30. Regardless, a suitable amount of urging in a circumferential direction70cwhile driving or malleting an anchor12into place, the point18and splines20will move the distal end in accordance with the forces applied in a circumferential direction70cby the splines20themselves. Thus, a combination of the splines20moving against already penetrated cancellous bone14, as well as the outer cortical bone14, will urge the rotation about the center curve17, even as the arcuate shape of that center curve17within the anchor12imposes its own arcuate direction on those helical splines20. That is, moving forward, the arcuate shape of the center curve17and consequently the anchor12will tend to move in an arc from a point of insertion. Meanwhile, the splines20and optional urging on the handle46in a circumferential direction70cwill also move that point18on a helical path combining the arcuate shape along the center curve17, and helical shape (and resulting orientation) of the several splines20.

To a certain extent, the angle64between adjacent splines20may be selected according to engineering principles. Likewise, the overall radial70bdimension or height in a radial direction70bof each spline20may be balanced against the diameter across the lumen22. For example, the embodiments ofFIGS.7A through7H and7J through7K, include no lumen22and no wall or core (e.g., cylindrical or circular tube-like structure) from which the splines20extend. However, in certain embodiments, a comparatively large fraction of the overall dimension across an anchor12in a radial direction70bmay be balanced between the diameter of the lumen wall23, against the altitude or radial70bextension of those splines20away from that lumen wall23.

In practice, the curvature of the path of leading edge18or point18is a combination of the center line17or center curve17and the helical disposition of the splines20. This results in the adjacent bones14a,14bacross a joint15being held firmly. The force direction across the joint (perpendicular to) a plane of the joint15is almost never aligned with the majority of area of the splines20, especially following installation.

Referring toFIGS.7J and7K, almost all of the foregoing information with respect toFIGS.7A-7Hmay be applied in a more-or-less “headless” variety of anchor12. In the illustrated embodiment, a tool may simply fit the splines20(in any embodiment of spline20discussed hereinabove) at a proximal end thereof. The tool may serve as the only “stop” for insertion of the anchor12. In fact, a tool may be contemplated that would not present enough cross-sectional area perpendicular to the direction of motion to even operate as a stop.

For example, a tool may fit between the splines20like pieces of a pie divided by the splines. Alternatively, a tool may simply engage a few splines with thin clips leaving the space largely open between splines. All the features and function of this description ofFIGS.7J and7Kmay be properly applied to almost all hollowed anchors12bas well as anchors12aby suitable engineering modifications. Therefore an insertion tool may fit into the central aperture22at the proximal or “head16” end, even without a solid head16other than what the splines20and wall23provide. Alternatively, note that trimming the outer diameter of the splines20may provide space to fit an insertion tool over the reduced diameter of splines, leaving a completely hollow center in the insertion tool.

In other embodiments, a distal end of an insertion tool may fit inside the aperture22, with small fingers or simple interfering stubs extending outside the wall23and aperture22. Those may engage splines to support rotational forces without presenting substantial resistance against the insertion tool following the anchor20as the anchor moves a distance longer than its length into or across a joint. Even the insertion tool may be cored (hollow), having a mere rim fitting inside and outside the aperture22, and having slots to receive splines20. Such a tool presents little more resistance to movement forward, permitting insertion along a path much longer than the anchor20itself. Thus longitudinal positioning of an anchor20need not be limited by a head16at a proximal end of the anchor20.

Thus, for example, certain SI joint fusions relying on an anchor12passing somewhat parallel to the adjacent faces of the sacrum and the ilium may rely on an insertion path longer than the anchor12itself. Neither the cortical bone nor the tool need stop the anchor, lacking a “bulkhead-like” face to stop forward progress of the distal (point18) end.

In all of the foregoing discussion of surface roughness or “texturing,” one should remember that shear forces along a slick, smooth, hard surface of a spline are going to be comparatively weak (compared to a textured surface having mechanical engagement of interfering projections “sticking out” from the nominal surface). On the contrary, just as apertures60engage tissues for through growth, texture provides concavities and convexities for “on growth.” However, the surface shear forces (slip of any bone tissue with respect to a hard, artificial surface of an anchor12) are augmented by local compressive and tensile forces on the bone material, supported by mechanical tension, compression, and shear forces in the texturing features themselves. The presence of texturing provides immediate “purchase” or grip. Nevertheless, the adhesion and filling in by “on-growth” tissues engages the structure of the bone and projects or transfers true shear stress away from the anchor12and out into the tissues farther away but mechanical bound to the tissues grown onto the concavities and convexities of the texturing features.

Thus, in general, it is contemplated in a system and method in accordance with the invention that sintering, sputtering, casting, forging, printing, or other manufacturing techniques may be relied upon to provide not only through-apertures of any type (through tortuous paths of sintered grains of metal, for example, or formed as large open apertures60in splines), but surface texturing along any surface (inside, outside, etc.) of an anchor. The healing by macrophages in the first days after a surgery (and implant) will thus provide additional resistance to pull out, in addition to such compressive loading provided by the nature of the helical splines radiating outward from an arcuate “centerline” of an anchor12.

In addition to tensioning of the anchor12providing compression in the tissue, the anchor provides a friction lock and a fast developing shear-engagement lock of the anchor12in place. That is, the tension in the anchor12due to its committing to a curvature of its centerline, and then being forced to rotate along the path of its helical splines, results in a compression of tissues behind (considering insertion path direction to be forward) the anchoring splines20. Meanwhile, those splines20, or rather their texturing will shear and smear tissues forward, which then engage immediately by friction against pull out. Healing then immediately begins to engage and lock in all that texturing, splines, and (apertures of every type) by intimate contact and growth filling concavities.

Referring toFIGS.8A through8C, one will see end views of an alternative embodiment of an anchor, this having a hollow core or hollow tube structure from which extend the individual splines20. The core23which may be thought of as a wall23surrounding a channel22or lumen22constitutes a tubular structure from which the splines20extend radially from a center line17and extend axially (longitudinally) and circumferentially along an outer “surface” of the wall23or core23. InFIG.8Ais seen the point end or leading end of the anchor12that will effectively be first to penetrate either the bones14a,14bor the joint15. If the joint15is penetrated along its own direction (effectively parallel, although the joint15is not planar nor flat) the splines20will still cut into and fix themselves within the cortical bone of the sacrum14aand ilium14b. However, when an anchor12is used to penetrate across the joint15as illustrated by the anchors12a,12b,12c, then the anchor12will be piloted in by drilling, broaching, and so forth as needed to reduce the trauma caused by penetration of the anchor12and particularly its splines20.

One will note that the illustration ofFIG.8Bshows the head end or base end of the anchor12. In this view, the engagement74is shown internally to the wall23or core23from which the splines20extend. Thus, the head16stands opposite to the leading end18or leading edge18, which may also be considered a point18, although no actual point exists at the center line thereof.

InFIG.8A, a dimension76ais matched by a symmetrical dimension76e. Meanwhile, the dimension76bprovides the distance between two adjacent splines20as measured at any point, and here shown as measured at the base or head end. Meanwhile, the dimensions76crepresents the outermost diameter of the core23or wall73from which the splines20extend. The dimension76drepresents the overall outer diameter of the entire anchor12at the outermost diameter of the splines20. The lumen22in this illustrated embodiment is sized to fit around and slide along a K-wire guide as described hereinbelow.

Thus, the cross section taken between the two ends, the point end18and the head end16, shows the effective cross ends of the material in the splines29, themselves, and the wall23.

Referring toFIGS.9A through9C, an alternative embodiment providing grow-through areas24formed in a porous wall23or core23. In these illustrations, the point end18operates exactly as the point end18ofFIG.8A. Similarly, the engagement at the head end16also may operate in exactly the same way as that ofFIG.8B. However, the embodiment ofFIGS.8A-8Cmay be formed of any material, including a non-reactive metal, a polymer, a filled polymer, or actual bone. A small porosity or lattice work24of apertures24as grow-through areas24are largely impractical if the anchor12is machined from actual bone capable of promoting growth through and around by the subject or patient.

Referring toFIGS.10A and10B, one may see that in the former embodiment, a single large aperture24forms effectively a window24as a grow-through area24. It has been found that such large windows24may affect the dimensional stability and the structural strength of an anchor12. Accordingly, such windows24as illustrated inFIG.10Ashould be kept to a length that provides for support between adjacent portions of the wall23between splines20. Engagement74, here shown as threads74, may be fabricated in a process such as centering, casting, molding, forging, or 3-D printing, even as metals, polymers, filled polymers, structurally reinforced polymers, and the like.

Comparing now the embodiment ofFIG.10Bof that of10A, a lattice work24of apertures24held together by the same material as the remainder of the wall23or core23supporting the splines20is illustrated. This lattice work24of apertures24may be formed in any suitable manner, including centered solid pieces that have a porosity through them, or specific patterns of lattice work providing apertures of a regular size or multiple sizes. One may note that the head16may include a transition73that thickens the wall23toward the head end16in order to support and provide clearance sufficient to form threads74as an engagement mechanics74to connect the anchor12to suitable tools for insertion.

Referring toFIGS.11through15, various lengths of anchors12are illustrated. In general, it is proper to speak of an aspect ratio when discussing the relative dimensions of any physical object. Accordingly, each of the illustrated anchors12includes a length, an outermost diameter around the outside of all splines20and outside diameter of the wall23or core23as well as an inside diameter of the wall23constituting the diameter of the lumen22or channel22.

An aspect ratio is simply the ratio of two dimensions. Accordingly, since an aspect ratio is one distance divided by another distance the aspect ratio has no units, that is, no dimensional name. An aspect ratio is a “dimensionless” number as well understood in the engineering arts and the technical arts of manufacturing and fabrication. In the illustrated embodiments, each of the anchors12includes or may be characterized by aspect ratios.

For example, the diameter of the lumen22compared to the diameter or outer diameter of the wall23is an aspect ratio of two diameters. Similarly, the diameter of the lumen22or the diameter of the wall23may be divided by the outer diameter around the splines20to determine yet another aspect ratio of comparative diameters. Similarly, lengths may be compared. For example, any of the foregoing diameters may be compared to the length of a particular anchor12thus defining an aspect ratio of diameter to length.

One will note that the aspect ratios may be reversed, such that length is divided by a particular diameter. One use of aspect ratios is to characterize a distance or a proportionality between dimensions of an object in the abstract, rather than specifying any particular set of measurements. In the physical arts of engineering, manufacturing, fabrication, and the like, these aspect ratios may be very useful. Moreover, performance is often related to aspect ratios, “dimensionless” numbers characterizing an object. It is typically beneficial to define or characterize an object by an aspect ratio that effectively equals a smaller dimension divided by a larger dimension. In this way, the aspect ratio will vary between zero and one. It cannot exceed one where the longest dimension in the object is the deviser.

InFIGS.11through15, one will note that the aspect ratio of all diameters with respect to lengths is considerably larger inFIG.11, is less inFIG.12, and is less still inFIGS.13through15. It is typically required to consider the anatomical distances or dimensions into, through, between, and the like with respect to bones14that are to be fused or fixed. Fusion typically occurs after a surgery, when the bones have been fixed by an anchor12in order that bone growth may occur around the anchor12in order to permanently fuse the two bones14together. Specifically, in the illustrated embodiments hereafter, where the bones14are a sacrum14aand ilium14b, dimensions and aspect ratios may have significance to the successful selection and implantation of an anchor12.

One will also note that certain embodiments illustrate apertures24or grow-through areas24. For the sake of clarity, the lattice work24or porosity24is not illustrated in any of theFIGS.11through15. This is not because they will not include those lattices24as illustrated in10B, but because such cannot be illustrated in this scale of the instant presentation. Thus, the illustrations ofFIGS.13through15represent the same physical object, including some walls23that have no grow-through apertures24, and other walls23that do include such. Accordingly,FIGS.13through15illustrate a single embodiment rotated to provide illustrations of the growth apertures24at different angles of rotation of the anchors12about their central axes (center line extending longitudinally through the center of the lumen22).

It has been found that support of the wall23or core23of an anchor12militates in favor of a lattice work24rather than comparatively larger (of the same order of magnitude as the distance circumferentially between splines), are less mechanically stable. Collapse, twisting closed, and the like may be problematic, depending on other dimensions. It has been found that grow-through areas24of the type illustrated inFIG.10Bprovides sufficient structural integrity to support the loads required to maintain the dimensional stability of the entire wall23, the splines20, and so forth.

Referring toFIG.16and includedFIGS.16A-16Hor images16A-16H, while continuing to refer generally to all figures, one embodiment of a growth engagement mechanism26or surface treatment surface26, also referred as texturing26is to provide various surface roughness26to which bone growth may adhere. Simply growing cortical bone into concavities represented by a particular texturing26is effective to resist any shearing of bone growth along the surface directions (in two dimensions, of the walls23).

For example,FIG.16includes several insets16A through16H. For example, the image16A suggests a somewhat scalloped appearance. This provides both convex and concave surfaces. It may be created on any surface, whether the surface of the wall23or the surface of the individual splines20. It may typically be provided by etching, additive manufacture (3-D printing), or the like. It may typically be regular, and thereby be provided in mass production.

The image16B shows a surface roughness that is quite irregular. In this embodiment, the edges tend to still be rounded, but the heights, the widths, and so forth (all dimensions) of the surface roughness26or texturing26are random. This is typically provided by a manufacturing technique known as sputtering. That is, random globules of molten metal may be attached to a base metal by a throwing by “sputtering” in which the material for texturing26is thrown as a liquid toward a heated surface and will secure, after splashing, and cooling. Likewise, such surface texturing may also be provided by sintering. Sintering is a process whereby a granular material may be packed into a mold, as distinct particles. The particles may then be heated until they partially melt, sufficiently to adhere to one another, but yet leaving porosity therebetween.

The image16C is an alternative embodiment in which larger spaces or gaps may be left along the surface of a wall23by one of the foregoing methods, such as centering or sputtering. Typically, these processes result in a somewhat random distribution of texturing26of random dimensions.

Referring toFIG.16, and its includedFIGS.16A-16Hor images16A-16H, and image16D in particular, this inset illustrates a surface texturing somewhat sharply pointed, suitable for creation by machining, molding, casting, forging, or the like. One benefit of such a mechanism is uniformity. Nevertheless, other manufacturing methods may provide randomness which has its own benefits, such as a random growth and therefore somewhat self-securing bone growth around the various, randomly sized, and randomly distributed texturing26.

The image for16E illustrates a smaller dimensionality, similar to the texturing26of the image16A. Similarly,FIG.16Fillustrates a more dense texturing26of a similar type toFIG.16D.FIG.16G, another somewhat reduced in height but random texturing. This relates very much to the same processes that may be employed forFIGS.16B and16C. However, images16B and16C indicate undercuts wherein bone growth on a surface23or wall23may actually have undercuts that are filled in with bone growth causing adherence to the wall23and further eliminating or reducing the probability that the bone growth can later be drawn away from the anchor12.

One may note that the anchor12in general, does not necessary need an undercut texturing26. This is because being surrounded by bone, typically cortical bone, the anchor12becomes encased and completely circumnavigated or circumscribed by the bone growth. Thus, any texturing26whatsoever becomes sufficient to prevent dislodgement or movement of the anchor12with respect to the subsequently grown bone growth.

Referring to image16H orFIG.16HinFIG.16, a barb78may be formed as a means of texturing26on a spline20. For example, barbs78as a form of texturing26on an edge of a spline20may provide immediate “purchase” or engagement with the native bone into which an anchor12has been installed or penetrated.

For example, the splines20will typically have an “interference fit” as that term is used in the engineering, manufacturing, assembly, fabrication, and other technical arts. An interference fit means that the dimension of an outer or receiving cavity, surface, slot, path, or the like is less than the outermost dimensions of the item (e.g., a spline20or core23of an anchor12), thus not an actual fit with a tolerance for clearance. Instead, one or both of the materials must provide a certain amount of “give.”

By the word give, is meant that either elastically, plastically, or by abrasion, one of the surfaces must displace in order to make the fit. Again, abrasion means wear, while elastically means still capable of full recovery of dimensions when any distorting force is removed. Plastically means that the material has “yielded.” Yielding means that the molecular structure or atomic structure of a material has permanently shifted, never to return to its former position. The term ‘yielding’ is a term of art that should be understood by any technician in mechanical or manufacturing arts.

Barbs78tend to move along a path during insertion or installation of an anchor12but will not return out of that path with the same amount of force applied. This is because the barbs78are slanted to glide forward in response to force axially applied to an anchor12, but will immediately dig in to the surrounding material upon application of a force in an opposite direction. Thus, such anchors12with splines20having barbs78become immediately fixative and will not remove or move opposite to their direction of insertion with the same amount of applied force required to insert them. Barbs78may be used in other embodiments of surface texturing, but creating undercuts such as barbs78is difficult and therefore may limit the utility or availability of barbs78generally.

One will note various mechanisms combine to stabilize anchors12. Texturing26may be applied to any particular surface. Those surfaces may be corrugated, shaped, convex, concave, undercut, through holes, blind holes, heavily (deeply) textured, roughened surfaces, regions perforated with grow-through areas60(GTA60), splining, helical splining with very long pitch, and so forth.

Referring toFIG.17, a trocar79includes a point79afixed to a handle79bacting as an extractor79b. This trocar79is placed inside a Jamshidi needle80. The actual penetrator81or needle81is typically used to connect to a syringe in place of the handle79bor interfacing therewith in order to draw a biopsy from tissue, bone marrow, or the like. Thus, a Jamshidi needle80is typically implemented by using the handle83to which a mount82secures the needle81or the needle portion81of a Jamshidi needle80.

In accordance with the invention, a trocar79extends beyond the needle portion81to be the vanguard or phalanx of the Jamshidi needle80. Thus, in this configuration, the Jamshidi needle80does not draw a biopsy, but simply forms an initial penetration for entry of the K-wire84ofFIG.18A. Upon withdrawal of the trocar79by means of drawing back the handle79b, the main penetrator81is left hollow and open to receive a length of K-wire84. The point86moves down through the penetrator81, anchoring into bone by applying force or impact on the base end88. The K-wire84is used in the role of a guide for subsequent instrumentation. Once the K-wire84has been anchored at its point86into bone, the Jamshidi needle80may be withdrawn.

Referring toFIGS.18A and18B, the K-wire84will be selected to have a certain, known length. The diameter of the K-wire84will fit not only inside the penetrator81of the Jamshidi needle80, but also in the lumen22of an anchor12. The gauge90is oriented according to the indicator92identifying the direction of the K-wire84. Thus, the graduations94on the gauge90allow a user, such as a surgeon, to measure the length of a K-wire84remaining exterior to a surgical site.

By laying the groove96or bed96of the gauge90against the K-wire84, one effectively lays the K-wire84into the bed96leaving the blunt end88or base end88of the K-wire84lying at some point along the gauge94. By reading the measurement of the gauge90, one may then determine how much of the K-wire length is still outside the surgical subject, and how much has been inserted within. This provides an indication of the exact location along the path of the K-wire84and originally the Jamshidi needle80from the surface of the subject or skin of the subject. At this point, the gauge90may be set aside and the K-wire84may be relied upon as a guide84in subsequent procedural steps.

Referring toFIGS.19A through19C, various dilators100are illustrated. InFIG.19A, the dilator100includes a lumen98or channel98fitted to slide along the K-wire84. A leading edge102or point102fits closely around the K-wire84, thus urging the soft tissue outward toward the main or outer diameter of the dilator100a. The dilator100ais considered a small (relatively speaking with respect to the larger or large) dilator100bofFIG.19B. As the barrel104of the small dilator100is urged axially along its length toward the point102, or following the point102, the dilator100awill cause stretching and a certain amount of trauma to the surrounding soft tissue.

However, as tissue stretches around the circumference and outer diameter of the small dilator100a, although there may be trauma, incisions will not be required to cut through the tissue, unnecessarily severing neighboring tissue. Eventually, any tooling, mallet, or other device used on the shank106to drive the small dilator100forward will be removed and a large dilator100bwill be slipped over the shank106of the small dilator100a. At this point, by force, pressure, or impact, the shank106of the large dilator100bwill be urged along the path now defined by the outer diameter of the small dilator100a. Again, gauge marks105on the barrel104of the large dilator100bprovide a direct reading of the depth of penetration by the large dilator100b. More is explained hereinbelow regarding the use and structure of the large dilator100b.

Referring toFIG.19C, in certain embodiments, it may be desired to place two anchors12exactly parallel to one another. This may be done with two anchors12placed parallel within a joint15or across a joint15. Typically, it is preferable to place parallel anchors12within a joint15, ostensibly parallel to the cortical surfaces of the bones14making up the joint15or joined by the joint15. In such a circumstance, the foregoing procedure regarding an installation of a small dilator100amay be done, but the small dilator100amay then be immediately removed, while a small dilator100cis passed down along the K-wire84and the path previously formed by the small dilator100a.

Thus, another small dilator100dfixed through a mount108securing the shanks106of both the small dilator100cand the small dilator100dwill require that the small dilator100cpenetrate parallel to the small dilator100c, which is following the path already dilated by the small dilator100athat was subsequently removed. It may be that a second K-wire84may be passed down through the second dilator100d, but this need not be necessary. In some respects, a K-wire84may be used as a trocar79inside the lumen98of the small dilator100din order to assist the small dilator100din penetrating tissues that were not addressed by the Jamshidi needle80.

It is a principal function of the twin dilator100ofFIG.19Cto provide a second, and parallel, path. Those parallel paths may both be provided with K-wire84as guides84. Eventually, the small dilators100c,100dmay be withdrawn and replaced with small dilators100adown both paths, down two K-wires84, one in each path, and thereafter the use of a large dilator100bover each may be accomplished. Nevertheless, use of dilators100becomes a function of the size of the path required in order to pass an anchor12into a securement site between two bones14.

Referring toFIG.20, a working portal110is typically a barrel104like those ofFIGS.19A through19C, but substantially thinner in its wall thickness. The function of the working portal110is not to further dilate a path for insertion of an anchor12but rather provide a stable passageway98or channel98through which to pass surgical instruments. To that end, the leading edge102of the working portal barrel104is suitable for sliding along the outer diameter of the barrel104of the large dilator100bofFIG.19B. Accordingly, a head111or mount111serves to strengthen and support and connect the barrel104of the working portal110. Thus, the lug106or shank106of the working portal110is provided with one or more apertures114suitable for receiving a shaft113applying force from a handle115or grip115.

Thus, as the working portal110is moved axially along the length of the large dilator100b, the handle115or grip115applies axial and circumferential force to the shank106or lug106of the working portal110. Points116are typically engineered to penetrate into cortical bone in order to secure or fix the working portal110to the bone that is the subject of the installation or insertion of an implant12, also called an anchor12.

Upon contacting bone14of some type, according to the specific surgery, a working portal110may advance under a mallet providing an impact load on the shank106of the working portal110to fix the points110and into local bone14thereby stabilizing the working portal110in all dimensions of consequence. Axially, it abuts the bone14. Radially, it is held by tissue, as well as by the points116against lateral motion in any radial direction. Similarly, the points116secure the barrel114of the working portal110against rotation with respect to the bone14.

At this point in a procedure in accordance with the invention, the user, medical professional, is prepared to pass various tools120,130,134,140, and so forth into the working portal110, and along the guide84that is the K-wire84still embedded in bone14at the center of the working portal110.

Referring toFIGS.21and22, a drill120is mounted to a shaft121. The shaft121may be provided with gauging marks105thus providing immediate feedback as to the depth at which the drill bit122has penetrated. Again, the drill120includes a point123having a lumen98or channel98guiding along the K-wire84. In the illustrated embodiment, a shank124may connect to a hand operated brace such as is used in a brace-and-bit combination. Alternatively, the shank124of the drill120may connect to a motorized unit for rotating the bit122.

In the illustrated embodiment, the shank124is provided with a securement125, here embodied as a groove such as may be used for a quick-connect mechanism for securing the drill120in an axial direction to a driver mechanism, well known and not shown. Meanwhile, a flat125bmay provide for engagement by a driver thereby assuring rotary motion by the driver. Thus, the engagement mechanism125aor securement125aacts to secure the drill120axially, while the flat125bacts to provide rotary motion driven by a drive mechanism. The drive mechanism is not shown because such are available in the art as hand cranks, electrical motors, and the like.

Of note, are riders126on the shaft121of the drill120. These riders126act as carriers126to center the drill bit122within the working portal110. Meanwhile, the lumen98passing axially through the center of the bit122and shaft121also guides down a K-wire84in place for that purpose. The flutes128on the bit122are designed to cut and carry back any materials drilled out by the bit122.

Likewise, the drill120may be withdrawn from a path, in order that saline or typical flush solution may be injected or introduced to irrigate the opening made by the drill bit122and wash away any resulting debris. One will note that the drill bit122is sufficiently long that it may drill through both bones in any crossing implementation and may drill along a cartilaginous joint in a parallel implementation. Thus, the flutes128may cut into soft tissue, marrow, cartilage, as well as cortical bone as required to establish the path that will eventually be followed by insertion of an anchor12.

Referring toFIG.22, in certain situations, a reamer130may be used. Inasmuch as cortical bone is comparatively brittle, meaning that it will typically fracture, chip, cut, abrade, or otherwise remove in response to a hard instrument like the flutes128of a drill bit122, softer tissues may not. Accordingly, it may be required to remove a drill120and insert the guiding K-wire84into the lumen98of a reamer130. Again, the reamer130has flutes128that include cutting edges132. The shaft121operates as other shafts121, passing down into the working portal110, and rotating about the K-wire84down the center lumen98of the tool130. The shank124may operate similarly to that of the drill120inFIG.21.

The reamer130in the illustrated embodiment is sometimes referred to as a paddle reamer130. It may have two, three, or more flutes128extending from it. Its function is to rotate to thereby clean out cartilaginous material soft tissue that may otherwise impede insertion of an anchor12. Also, the reamer130may also tend to scrape against cortical bone in a parallel insertion configuration in order to provide “bleeding bone” for enabling bone growth around an inserted anchor12thus permanently fixing the anchor12and creating a solid, fixed relationship between the two bones14a,14bbeing anchored together.

Referring toFIG.23, a broach134may not always be required, but may relieve somewhat a desired interference fit between an anchor12and the bones14a,14binto which it is placed. In the illustrated embodiment, the broach134may include a shaft121and riders126for maintaining the shaft121centered within the working portal110. Likewise, a head end136or head136opposite the shank124will serve as a cutting tool to cut paths for the splines20. That is, the head136of the broach134included splines20that will effectively cut spaces for the splines20of the anchor12. In the illustrated embodiment, cutting surfaces132are provided. However, these are not rotary cutting surfaces, but rather cut in order to provide entry for the broach head138to expand the space available in the hole or aperture drilled by the bit122.

One will note that the angle or the circumferential progression of the splines20on the head136exactly match those of an anchor12. Accordingly, the splines20of the head136may initially penetrate the diameter of the hole left by the bit122passing into or through bone14. The broach may be instantiated in multiple versions, each broaching slightly more material out of the cortical bone14. Alternatively, the various diameters of the head136may increase such that the cutting edges132and the head138may cut initially at one diameter, then subsequently at larger diameters until approaching, but typically not meeting the outer diameter of an anchor12.

Meanwhile, the thickness of each spline20in the head136is best served by being slightly less than a thickness of a spline20in an anchor12. In this way, an anchor12is inserted against the frictional clamping force of the interference fit in which the pathway formed by the broach head136is slightly undersized to fit the radial dimensions and circumferential dimensions of the anchor12and its splines20.

Threads137, along the shaft121may provide for adjustment by a grip139that acts as a contact surface138preventing further axial movement of the shaft121and broach134into the access portal110or working portal110. Of course the riders126maintain centering, as does the K-wire84in the lumen98of the broach134. Gauge marks105provide an immediate feedback as to the positioning of the contact surface138that will eventually contact the shank106of the working portal110, limiting the penetration of the broach134and head136into the surgical path.

In certain embodiments, the handle139may be engaged with an internal spiraling path that instead rotates and advances the shaft121at exactly the rate required by the splines20of the broach head136. The broach134may typically be operated by a hand tool secured to the shank124. Thus, a user can work the broach134, much as a rasp in order to provide forward axial force on the head136, as well as urging a rotational force along the direction of the splines20in order to cut through the bone14in a path suitable for receiving the anchor12later. Following broaching, the broach134is removed, and the path or cavity may be flushed to remove any debris, in preparation for insertion of an anchor12.

Referring toFIG.24, the insertion device140operates much like the broach134. Rather than a broach136, the actual anchor12is implemented. Again, the anchor12fits over a K-wire84, while riders126may rotate and slide within the working portal110. Similarly, the handle139or grip139may be threaded along the shaft121in order to gauge by the contact surface138the distance of penetration by the shaft121into the working portal110. A tool140or inserter140may provide relief apertures142along the shaft121, in order to allow free movement of a shank124connected directly to an anchor12as an inner shaft, inside the outer shaft121. In this way, direct movement, orientation, or the like may be felt in order to assure that the splines20find the suitable openings created by the splines20of the broach head136. An actuator144may operate to rotate the shank124, the outer shaft121, as needed for relative movement.

Referring toFIG.25, a process150is provided illustrating multiple embodiments of insertion techniques, depending upon the particular location and specific orientation of an anchor12in a joint15. Initially, the procedural preparations151may need to be conducted, including providing all the proper tools properly laid out, sized, measured, setting measured to the extent that they can be, and so forth. Likewise, patient preparation152may require conventional protections for the patient and for the medical personnel as well as the site. This may involve x-rays, antiseptic sterilization of areas or spaces, draping with coverings, and so forth. Preparation152may actually include an initial incision through skin, fat layers, fascia, or the like in order to gain access to muscular tissue, as well as any other common patient preparation152.

Insertion153of a Jamshidi needle80then occurs, followed by removal154of the trocar79. This is followed by inserting155a K-wire84through the shaft81of the Jamshidi needle80, ultimately securing the point86or other portion of the K-wire84into bone14. The K-wire84may actually penetrate through and beyond the anchoring site. For example, the K-wire84may move past cortical bone, cancellous bone, more cortical bone, and on into soft tissue. The K-wire84may define a path that extends beyond the insertion of the point18or leading edge18of the actual anchor12inserted. One reason for this is that bone graft material may be added.

Once the K-wire84is properly inserted155, removal156of the Jamshidi needle80can be done. Next, inserting157the small dilator100ais done, followed by a decision167as to whether a new second, parallel, path is to be created, as described hereinbelow. If not, then insertion158of the large dilator100bfollows. The working portal110is next inserted159, sliding over the outer diameter of the shaft105of the large dilator100b. Once the working portal110is inserted159and anchored as discussed hereinabove, a user may remove160both the dilators100a,100band gauge161for drilling162. The gauge90with the K-wire84laid into the bed96may provide a gauging mechanism94for determining exactly how deeply into the path the drilling162needs to progress.

At this point, the next alternative in the procedure depends on the decision163, whether the anchoring is across the bones14a,14b, or between the bones14a,14b(that is, along and inside the joint15). If the anchoring is to be into the joint15(what we will call parallel to cortical surfaces, not parallel anchor paths, although the cortical surfaces are more tangential, not planar). Reaming164occurs, in the “inside joint” or “parallel to cortical surfaces” case. In either the cross or the parallel configuration, broaching165occurs, both as described hereinabove. Inserting166the anchor12using the insertion tool140results in the anchor12being fixed into place. Installation is thereby completed158

In other words, if the decision163indicates a cross orientation across the joint15between, that is from one bone14ato another bone14b, then broaching165may proceed directly after drilling152, and followed by anchoring166or inserting166an anchor12. Note that the anchor12rotates as it moves forward into place, as a result of the helical path of the splines passing through the cortical bone as broached165. The insertion tool may be urged rotationally in order to relieve the load on cortical bone carrying the splines20as they helically progress into, through, across, or along the bones14a,14b.

Going back now to the decision167, if a new anchor, 12 parallel to the original K-wire84and small dilator1001, is desired, then one may need to remove169the initial small dilator100aand insert170the twin dilators100c,100d. Inserting170the twin dilators100c,100d, a second K-wire84may be inserted171, followed by withdrawing172the dilator, and returning to the process150at the step of inserting151two small dilators100adown those two parallel paths before proceeding.

Referring toFIGS.26and27, the two different types of orientations, alignments, or installation configurations of anchors (the cross configuration and the along inside configuration) are illustrated to show which, and in what order different instruments are implemented.FIG.26refers to an insertion in which the materials14a,14bstraddle a joint15. Typically, at some outer extremity of a joint15will be ligaments securing the bone14ato the bone14b. In this instance, the Jamshidi needle80is used followed by the K-wire84, small dilator100a, large dilator100bas described hereinabove. At this point, the path is ready for an access portal110shown on the left in the step wise instrument flow, and shown on the right as inserted through the skin, fat, fascia, and other soft tissues to get to the joint15between the two bones14a,14b.

Subsequently, the drill120is employed to drill through the bone14, followed by a reamer130in order to clear out loose cartilage, any other loose materials, as well as scoring or abrading part of the cortical bone if necessary. That is, for example, the reamer130may be as important as the drill120, since the reamer130makes the path for the anchor12to pass. A broach134may be employed to cut a path into cortical bone for passage of the splines20of the anchor12. Ultimately, the insertion tool140is employed in the working portal110to insert the anchor12.

At any point before, after, or during insertion of the anchor12, any significant spaces remaining may be filled with bone graft material, typically allograft, also called homograft. This typically includes small particles of bone to aid in the early healing and growth through any available spaces by natural bone. Following insertion of all anchors12, the working portal110may be withdrawn, and proper suturing may be done to close the wound.

When inserting anchors12across through one bone14into another bone14, the Jamshidi needle80begins the process, followed by insertion of a K-wire84. A small dilator100amay be implemented, but the twin may also be used at this point. However, it is more common that following insertion of the small dilator100ain the process ofFIG.26that a parallel path may be set up by twin dilators100bfollowing the path of a withdrawn small dilator100a, while establishing the path of the twin small dilator100din parallel to the dilator100c.

The large dilator100bis thus passed over the small dilator100a, followed by the working portal110being fitted over and forced into place. Again, the working portal110anchors to the bone14and the dilators100a,100bmay be removed.

Accordingly, the drill120may be implemented as described hereinabove, followed by the broach134. It is worth noting that broaching is optional, it is not always required. Nevertheless, due to the comparatively brittle cortical bone, meaning that cortical bone will fracture in response to force much more quickly than will cancellous bone or soft tissues, which may displace and even damage traumatically, but do not necessarily chip away as the conventional fracturing of cortical bone. Thus, the broach134has a very useful function, but in some instances may be unnecessary.

Of course the processes150may be repeated for multiple anchors12in multiple locations in an SI-joint fixation. Herein, a diameter of an anchor or any other article or component means the diameter of a circle circumscribing the anchor, other article, or component. Effective diameter means “hydraulic diameter,” which is four times the cross-sectional area divided by the perimeter (typically called “wetted perimeter,” the fluid contact perimeter when applied to a solid-fluid interface, interior or exterior to the solid). One will see that effective diameter becomes the regular diameter for a circular shape, and the length of a side for a square shape. For other shapes, especially irregular shapes, the effective diameter is some other value, but useful in various fluid-related calculations.

The present invention may be embodied in other specific forms without departing from its purposes, functions, structures, or operational characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.