Patent Description:
Sacroiliac joint (SI-Joint) fusion is a surgical procedure that is performed to alleviate pain coming from the SI-Joint in patients who have failed to receive adequate pain relief with non-surgical treatments of the SI-Joint. Some conditions of the SI-Joint that may be treated with SI-Joint fusion (arthrodesis) are: degenerative sacroiliitis, inflammatory sacroiliitis, iatrogenic instability of the sacroiliac joint, osteitis condensans ilii, or traumatic fracture dislocation of the pelvis. Historically, screws and screws with plates were used as the standard instrumentation for sacro-iliac fusion. An SI-Joint fusion consisted of an open surgical approach to the SI-Joint from an anterior, a posterior, or a lateral direction. The surgeon would then debride (remove) the cartilage from the articular portion of the j oint and the interosseous ligament from the fibrous portion of the joint. These open approaches require a large incision and deep soft tissue dissection to approach the damaged, subluxed, dislocated, fractured, or degenerative SI-Joint.

With more recent advancements in SI-Joint surgery, a typical technique for placing implants involves placement of one or multiple implants from a lateral to medial direction across the SI-Joint. These implants are placed with a starting point on the lateral aspect of the ilium. The implants are then directed across the ilium, across the sacroiliac joint and into the sacrum.

Various styles of implants are available today for fusing the SI-Joint and other joints in the above minimally invasive surgeries. However, it would be desirable to provide improved implants and methods to promote even faster and stronger fusion of bone joints.

<CIT> discloses an intraosseous screw that includes at least one external thread, a receiving element extending into and parallel to the external thread, and connecting members connecting the individual screw threads of the external thread. The or each external thread has capillary through-channels that pass through the screw so as to end in the receiving element. The connecting members define a plurality of through-openings. The receiving element is shaped so as to be able to receive a cylindrical bone portion once the intraosseous screw has been screwed into the bone.

<CIT> discloses compression devices for joining tissue and methods for using and fabricating the same.

The present invention provides a threaded implant according to claim <NUM>.

A better understanding of the features and advantages of the present disclosure will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the disclosure are utilized, and the accompanying drawings of which:.

The threaded implant of the invention comprises an elongated main body having external threads configured to thread into bone, and an internal support structure located within the external threads. The internal support structure has a helical arrangement that extends in an opposite direction to the external threads. The threaded implant may further include a drive socket located on a proximal end of the main body and configured to receive a tip of a drive tool for rotationally driving the implant into bone. In some embodiments, a through bore is provided along a central longitudinal axis of the main body from a proximal end to a distal end. The external threads may have a single start and the internal support structure may have four starts. In some embodiments, the internal support structure has a pitch that is eight time the pitch of the external threads. The implant may further include fenestrations or interstices between the external threads and the internal support structure. The fenestrations or interstices may be filled with a porous infill which provides scaffolding with increased surface area for new bone growth. In some embodiments, the porous infill is at least <NUM>% more porous than the external threads and the internal support structure.

The threaded implant can be provided with an elongated main body, a first set of threads, a second set of threads and a sleeve. The main body has a proximal end, a mid-section and a distal end. The first set of threads is provided along the proximal end of the main body and the second set of threads is provided along the distal end. The sleeve is located on the mid-section of the main body such that it may rotate with respect to the main body while being constrained from axial movement. In some implants, the sleeve has a transverse cross-section that is rectilinear, has at least one apex and/or is triangular in shape. The second set of threads may have a pitch that is greater than a pitch of the first set of threads.

The threaded implant can be provided with an elongated main body, a head portion and a threaded portion. The elongated main body has a proximal end, a mid-section and a distal end. The head portion is located on the proximal end of the main body and configured to abut against an outer surface of a bone segment. The threaded portion is located on the distal end of the main body and has a transverse cross-section that is triangular in shape. The implant can be provided with a drive socket located on the proximal end of the main body and configured to receive a tip of a drive tool for rotationally driving the implant into bone.

The threaded implant can be provided with an elongated main body, a proximal screw, a proximal screw cap and at least one rotation stop. The elongated main body has a proximal end, a mid-section and a distal end.

A joint of a patient can be decorticated or selectively decorticated in order to promote bone regeneration and fusion at the implant site. Many types of hardware are available both for the fixation of bones that are fractured and for the fixation of bones that are to be fused (arthrodesed). While the following examples focus on the SI-Joint, the methods, instrumentation and implants disclosed herein may be used for decortication of other body joints as well.

Referring to <FIG>, the human hip girdle is made up of three large bones joined by three relatively immobile joints. One of the bones is called the sacrum and it lies at the bottom of the lumbar spine, where it connects with the L5 vertebra. The other two bones are commonly called "hip bones" and are technically referred to as the right ilium and-the left ilium. The sacrum connects with both hip bones at the sacroiliac joint (in shorthand, the SI-Joint).

The SI-Joint functions in the transmission of forces from the spine to the lower extremities, and vice-versa. The SI-Joint has been described as a pain generator for up to <NUM>% of lower back pain patients.

To relieve pain generated from the SI-Joint, sacroiliac joint fusion is typically indicated as surgical treatment, e.g., for degenerative sacroiliitis, inflammatory sacroiliitis, iatrogenic instability of the sacroiliac j oint, osteitis condensans ilii, or traumatic fracture dislocation of the pelvis. In some currently performed procedures, screws or screws with plates are used for sacro-iliac fusion. At the time of the procedure, articular cartilage may be removed from the "synovial joint" portion of the SI-Joint. This can require a large incision to approach the damaged, subluxed, dislocated, fractured, or degenerated joint. The large incision and removal of tissue can cause significant trauma to the patient, resulting in pain and increasing the time to heal after surgery.

In addition, screw type implants tend to be susceptible to rotation and loosening, especially in joints that are subjected to torsional forces, such as the SI-Joint. Excessive movement of the implant after implantation may result in the failure of the implant to incorporate and fuse with the bone, which may result in the need to remove and replace the failed implant.

<FIG> illustrate straight implants <NUM> and <NUM>, respectively, with a solid elongate body <NUM> or <NUM>' that can be used for the fixation or fusion of two bone segments. The implant <NUM> shown in <FIG> is cylindrical and can optionally have screw threads along the exterior of the implant body. As mentioned above, cylindrical screw type implants can suffer from excessive rotation. One solution to this problem is the implant <NUM> in <FIG>, which has a non-cylindrical cross-sectional area. For example, as shown, the implant <NUM> can have a triangular cross-sectional area, although other rectilinear cross-sectional profiles may be used as well, including rectangular, hexagonal and the like. Non-cylindrical implants need not have a strict rectilinear cross-sectional profile in order to resist rotation. A cross-sectional area that is non-circular will generally suffice. For example, a tear drop shaped cross-sectional area, or a cross-sectional area with at least one apex, can resist rotation. Other non-circular cross-sectional geometries that may not have a rectilinear component can also work, such as oval cross-sections.

<FIG> illustrates insertion of the implant <NUM> or <NUM> of <FIG> across the SI-Joint using a lateral approach that goes laterally through the ilium, across the SI-Joint, and into the sacrum. <FIG> illustrates insertion of the same implant across the SI-Joint using a postero-lateral approach entering from the posterior iliac spine of the ilium, angling through the SI-Joint, and terminating in the sacral alae. The implants and instrumentation described herein typically can be inserted across the SI-Joint according to one of these two approaches, or with a similar approach.

Referring to <FIG>, an exemplary method, not claimed, for fixation of the SI-Joint. Elongated, stem-like implant structures <NUM> or <NUM> like those shown in <FIG> make possible the fixation of the SI-Joint in a minimally invasive manner. These implant structures can be effectively implanted through the use a lateral surgical approach (as shown in <FIG>). The procedure may be aided by conventional lateral, inlet, and outlet visualization techniques, e.g., using X-ray image intensifiers such as a C-arms or fluoroscopes to produce a live image feed, which is displayed on a TV screen.

In this method, one or more implant structures <NUM> are introduced laterally through the ilium, the SI-Joint, and into the sacrum. This path and resulting placement of the implant structure(s) <NUM> are best shown in <FIG> and <FIG>. In the drawing, three implant structures <NUM> are placed in this manner. Also in the drawing, the implant structures <NUM> are rectilinear in cross section and triangular in this case, but it should be appreciated that implant structures <NUM> of other rectilinear cross sections can be used. Additionally, in some procedures (not discussed in further detail herein), implants may be introduced into the SI-Joint from an anterior direction. Further information on anterior techniques may be found in co-pending <CIT>. The decortication instruments and methods disclosed herein and variants thereof may also be utilized in these anterior procedures.

Before undertaking a lateral implantation procedure, the physician diagnoses the SI-Joint segments that are to be fixated or fused (arthrodesed) using, e.g., the Fortin finger test, thigh thrust, FABER, Gaenslen's, compression, distraction, and or diagnostic SI-Joint injection.

Aided by lateral, inlet, and outlet C-arm views, and with the patient lying in a prone position, the physician aligns the greater sciatic notches and then the alae (using lateral visualization) to provide a true lateral position. A <NUM> incision is made starting aligned with the posterior cortex of the sacral canal, followed by blunt tissue separation to the ilium. From the lateral view, the guide pin <NUM> (with pin sleeve (not shown)) (e.g., a Steinmann Pin) is started resting on the ilium at a position inferior to the sacrum end plate and just anterior to the sacral canal. In the outlet view, the guide pin <NUM> should be parallel to the sacrum end plate at a shallow angle anterior (e.g., <NUM> degree to <NUM> degree off the floor, as <FIG> shows). In a lateral view, the guide pin <NUM> should be posterior to the sacrum anterior wall. In the outlet view, the guide pin <NUM> should be superior to the first sacral foramen and lateral of mid-line. This corresponds generally to the sequence shown diagrammatically in <FIG>. A soft tissue protector (not shown), and a drill sleeve (not shown) within the soft tissue protector, may be slipped over the guide pin <NUM> and firmly against the ilium before removing the guide pin sleeve (not shown).

Over the guide pin <NUM> (and through the soft tissue protector and drill sleeve), a pilot bore <NUM> may be drilled with cannulated drill bit <NUM>, as is diagrammatically shown in <FIG>. The pilot bore <NUM> may extend through the ilium, through the SI-Joint, and into the sacrum. The drill bit <NUM> and drill sleeve (not shown) are then removed.

A shaped broach <NUM> may be tapped into the pilot bore <NUM> over the guide pin <NUM> (and through the soft tissue protector, not shown) to create a broached bore <NUM> with the desired profile for the implant structure <NUM>, which in the drawing is triangular. This generally corresponds to the sequence shown diagrammatically in <FIG>. The triangular profile of the broached bore <NUM> is also shown in <FIG>.

<FIG> illustrate the assembly of a soft tissue protector or dilator or delivery sleeve <NUM> with a drill sleeve <NUM>, a guide pin sleeve <NUM> and a handle <NUM>. In some procedures, the drill sleeve <NUM> and guide pin sleeve <NUM> can be inserted within the soft tissue protector <NUM> to form a soft tissue protector assembly <NUM> that can slide over the guide pin <NUM> until bony contact is achieved. The soft tissue protector <NUM> can be any one of the soft tissue protectors or dilators or delivery sleeves disclosed herein. In some procedures, an expandable dilator or delivery sleeve <NUM> can be used in place of a conventional soft tissue dilator. In the case of the expandable dilator, in some procedures, the expandable dilator can be slid over the guide pin and then expanded before the drill sleeve <NUM> and/or guide pin sleeve <NUM> are inserted within the expandable dilator. In other procedures, insertion of the drill sleeve <NUM> and/or guide pin sleeve <NUM> within the expandable dilator can be used to expand the expandable dilator.

In some procedures, a dilator can be used to open a channel though the tissue prior to sliding the soft tissue protector assembly <NUM> over the guide pin. The dilator(s) can be placed over the guide pin, using for example a plurality of sequentially larger dilators or using an expandable dilator. After the channel has been formed through the tissue, the dilator(s) can be removed and the soft tissue protector assembly can be slid over the guide pin. In some procedures, the expandable dilator can serve as a soft tissue protector after being expanded. For example, after expansion the drill sleeve and guide pin sleeve can be inserted into the expandable dilator.

As shown in <FIG>, a triangular implant structure <NUM> can be now tapped through the soft tissue protector over the guide pin <NUM> through the ilium, across the SI-Joint, and into the sacrum, until the proximal end of the implant structure <NUM> is flush against the lateral wall of the ilium (see also <FIG> and <FIG>). The guide pin <NUM> and soft tissue protector are withdrawn, leaving the implant structure <NUM> residing in the broached passageway, flush with the lateral wall of the ilium (see <FIG> and <FIG>). In the drawing, two additional implant structures <NUM> are implanted in this manner, as <FIG> best shows. In other procedures, the proximal ends of the implant structures <NUM> are left proud of the lateral wall of the ilium, such that they extend <NUM>, <NUM>, <NUM> or <NUM> outside of the ilium. This ensures that the implants <NUM> engage the hard cortical portion of the ilium rather than just the softer cancellous portion, through which they might migrate if there was no structural support from hard cortical bone. The hard cortical bone can also bear the loads or forces typically exerted on the bone by the implant <NUM>.

The implant structures <NUM> are sized according to the local anatomy. For the SI-Joint, representative implant structures <NUM> can range in size, depending upon the local anatomy, from about <NUM> to about <NUM> in length, and about a <NUM> inscribed diameter (i.e. a triangle having a height of about <NUM> and a base of about <NUM>). The morphology of the local structures can be generally understood by medical professionals using textbooks of human skeletal anatomy along with their knowledge of the site and its disease or injury. The physician is also able to ascertain the dimensions of the implant structure <NUM> based upon prior analysis of the morphology of the targeted bone using, for example, plain film x-ray, fluoroscopic x-ray, or MRI or CT scanning.

Using a lateral approach, one or more implant structures <NUM> can be individually inserted in a minimally invasive fashion across the SI-Joint, as has been described. Conventional tissue access tools, obturators, cannulas, and/or drills can be used for this purpose. Alternatively, the novel tissue access tools described above and in <CIT>, and in <CIT>, can also be used. No joint preparation, removal of cartilage, or scraping are required before formation of the insertion path or insertion of the implant structures <NUM>, so a minimally invasive insertion path sized approximately at or about the maximum outer diameter of the implant structures <NUM> can be formed.

The implant structures <NUM> can obviate the need for autologous bone graft material, additional pedicle screws and/or rods, hollow modular anchorage screws, cannulated compression screws, threaded cages within the joint, or fracture fixation screws. Still, in the physician's discretion, bone graft material and other fixation instrumentation can be used in combination with the implant structures <NUM>.

In a representative procedure, one to six, or perhaps up to eight, implant structures <NUM> can be used, depending on the size of the patient and the size of the implant structures <NUM>. After installation, the patient would be advised to prevent or reduce loading of the SI-Joint while fusion occurs. This could be about a six to twelve week period or more, depending on the health of the patient and his or her adherence to post-op protocol.

The implant structures <NUM> make possible surgical techniques that are less invasive than traditional open surgery with no extensive soft tissue stripping. The lateral approach to the SI-Joint provides a straightforward surgical approach that complements the minimally invasive surgical techniques. The profile and design of the implant structures <NUM> minimize or reduce rotation and micromotion. Rigid implant structures <NUM> made from titanium provide immediate post-op SI-Joint stability. A bony in-growth region <NUM> comprising a porous plasma spray coating with irregular surface supports stable bone fixation/fusion. The implant structures <NUM> and surgical approaches make possible the placement of larger fusion surface areas designed to maximize post-surgical weight bearing capacity and provide a biomechanically rigorous implant designed specifically to stabilize the heavily loaded SI-Joint. In some examples, a fenestrated matrix implant may be used, providing cavities in which to pack bone growth material, and or providing additional surface area for bone on-growth, in-growth and or through-growth.

To improve the stability and weight bearing capacity of the implant, the implant can be inserted across three or more cortical walls. For example, after insertion the implant can traverse two cortical walls of the ilium and at least one cortical wall of the sacrum. The cortical bone is much denser and stronger than cancellous bone and can better withstand the large stresses found in the SI-Joint. By crossing three or more cortical walls, the implant can spread the load across more load bearing structures, thereby reducing the amount of load borne by each structure. In addition, movement of the implant within the bone after implantation is reduced by providing structural support in three locations around the implant versus two locations.

Further details of bone joint implants and methods of use can be found in <CIT>, <CIT>, <CIT>, and <CIT>.

In the previously described methods, the implant(s) <NUM> or <NUM> (<FIG>) may be placed in the implant bore(s) <NUM> (<FIG>) using a generally medial or axial, non-rotational force, such as tapping an implant into place using a slide hammer. The external threads of the present implant may be threaded into place by applying a rotational force, as will now be described.

Referring to <FIG>, an embodiment of a threaded implant system constructed according to the present invention is shown. Implant <NUM> is provided with external threads <NUM> and an internal counter-rotating support structure <NUM>. As best seen in <FIG>, proximal end <NUM> may be provided with a hexagonally shaped socket <NUM> for receiving a drive tool (not shown) when implant <NUM> is being inserted or removed. A through bore <NUM> may be provided along the central axis from the proximal end <NUM> to the distal end <NUM>.

External threads <NUM> are used to engage bone when threading implant <NUM> across a bone joint. In some embodiments, external threads <NUM> are self-tapping. In this embodiment, internal counter-rotating support structure <NUM> extends helically in an opposite direction from external threads <NUM> as shown. Support structure <NUM> provides stiffness and torsional rigidity to implant <NUM> while permitting fenestrations between external threads <NUM> for promoting better bony on-growth, ingrowth and/or through-growth. In this embodiment, a single external thread <NUM> helically extends from near the proximal end <NUM> to the distal end <NUM> of implant <NUM>. In other embodiments (not shown), multiple starts of external threads <NUM> may be employed. In this embodiment, internal counter-rotating support structure <NUM> comprises four starts. In other embodiments (not shown), fewer or more starts may be employed. In this embodiment, internal counter-rotating support structure <NUM> has a pitch that is eight times the pitch of external threads <NUM>. In other embodiments (not shown), the pitch of structure <NUM> may be less or more than eight times that of threads <NUM>. Support structure <NUM> may comprise layers. In some embodiments, these layers alternate in direction.

In the embodiment of <FIG>, the fenestrations or interstices between external threads <NUM> and internal counter-rotating support structure <NUM> are filled with porous infill <NUM>. Infill <NUM> provides scaffolding with a large surface area for new bone growth. Infill <NUM> can also add additional strength to implant <NUM> in compression, tension, torsion, bending, shear, etc., but still allow for better bony on-growth, ingrowth and/or through-growth than if the fenestrations or interstices were completely filled with less porous material. The exploded view of <FIG> shows main portion <NUM> of implant <NUM> separately from the porous infill <NUM> for clarity, although in this embodiment infill <NUM> is a collection of many individual segments rather than an interconnected structure. In some embodiments, main portion <NUM> may also be porous, but having a different porosity than infill <NUM>. Infill <NUM> may be at least <NUM>% more porous than main portion <NUM>. Both may be made together in the same manufacturing process, such as 3D printing or other additive manufacturing process. In some embodiments, infill <NUM> is formed from the same material as main portion <NUM>, while in other embodiments a different material or materials may be used to form infill <NUM>.

In some embodiments, porous infill <NUM> has the same inner diameter as that of the main portion <NUM> of implant <NUM>, forming a continuous surface defining through bore <NUM>, as shown in <FIG>. The outer diameter of infill <NUM> may be the same diameter of the radially inward end of the tapered portions of threads <NUM>, thereby forming the root diameter of threads <NUM>. The inner and outer diameters of counter-rotating support structure <NUM> may also be the same as those of infill <NUM>, such that breaks <NUM> are formed in infill <NUM> (as seen in <FIG>) to accommodate structure <NUM>.

An implant bore may be formed across a bone segment before implant <NUM> is threaded into it. In some embodiments the diameter of the bore is approximately the same as the root diameter of threads <NUM>. In some embodiments, a tap may be used to create internal threads inside the bone before implant <NUM> is inserted. In other embodiments, self-boring and/or self-tapping features are provided on implant <NUM>. Implant <NUM> may be threaded into the bore until just the proximal head portion protrudes from the bone. In other implementations, proximal head portion may be partially or fully recessed into the bone, or flush with the outer surface of the bone.

Referring to <FIG>, a comparative threaded implant system is shown. Implant <NUM> comprises a main body <NUM> having a proximal end <NUM>, a mid-section <NUM> and a distal end <NUM>. Proximal end <NUM> is provided with a first set of threads <NUM> while distal end <NUM> is provided with a second set of threads <NUM>. As best seen in the exploded view of <FIG>, mid-section <NUM> has a constant diameter configured to receive triangle sleeve <NUM> (as shown in <FIG>) such that it may rotate with respect to main body <NUM> while being constrained from axial movement.

Referring to <FIG>, proximal end <NUM> of main body <NUM> may be provided with a hexagonally shaped socket <NUM> for receiving a drive tool (not shown) when implant <NUM> is being inserted or removed. A through bore <NUM> may be provided along the central axis from the proximal end <NUM> to the distal end <NUM>. As also shown in <FIG>, main body <NUM> may be provided with a constant root or minor diameter taper that extends from a smaller diameter <NUM> at distal end <NUM> to a larger diameter <NUM> closer to proximal end <NUM>, except for mid-section <NUM> which has a smaller diameter than the tapered root or minor diameter sections adjacent to it. The first set of threads <NUM> may have a constant outer or major diameter <NUM>, such that threads <NUM> protrude radially less from the root or minor diameter as they extend proximally along main body as shown in <FIG>. Similarly, the second set of threads <NUM> may have a constant outer or major diameter <NUM> (larger than the outer or major diameter <NUM> of the first set of threads <NUM>), such that threads <NUM> protrude radially less from the root or minor diameter as they extend proximally along main body as shown in <FIG>.

In some variations of this implant (not shown), the pitch of distal threads <NUM> is greater than the pitch of proximal threads <NUM>. This arrangement causes implant <NUM> to advance more rapidly in relation to a distal bone segment that it does relative to a more proximal bone segment, thereby drawing the two bone segments closer together (e.g. compressing a joint between the two bone segments) when the implant is tightened into place.

Referring to <FIG> and <FIG>, one or more fenestrations <NUM> may be provided in triangle sleeve <NUM> such that they communicate with a space around mid-section <NUM>. Fenestrations <NUM> provide additional area for on-growth, ingrowth and through-growth of new bone tissue after implantation of device <NUM>. During implantation, bone chips may be placed inside fenestrations <NUM> to aid in new bone growth. Chamfers <NUM> (also shown in <FIG>) may be provided along the apexes of triangle sleeve <NUM>. One advantage to providing chamfers <NUM> is that stress concentrations are avoided when creating a bore through the bone for implant <NUM> to reside in.

Device <NUM> may be implanted in bone in a manner similar to previously described devices. Triangle sleeve <NUM> may be provided with tapered leading edges (as shown in <FIG>), self-broaching features (not shown), and/or a separate broaching instrument (not shown) may be used to create a triangularly shaped bore before device <NUM> is implanted. In some arrangements, triangle sleeve <NUM> resides across a gap between two bone segments once device <NUM> is in place. A triangularly shaped bore may be broached just deep enough to accommodate triangle sleeve <NUM>, but not all the way to the distal tip of device <NUM>. In some arrangements, the full depth of threads <NUM> extends beyond the flats of triangle sleeve <NUM> and into the surrounding bone, as depicted in <FIG>. During implantation, triangle sleeve <NUM> may freely rotate with respect to main body <NUM> such that it travels axially into the triangularly shaped bore in the bone without rotating while main body <NUM> is rotated and advances with threads <NUM> and <NUM>. In some arrangements, bone in-growth and through-growth after implantation causes triangle sleeve <NUM> to become rigid with main body <NUM>. This mechanism inhibits implant <NUM> from backing out of the bone or migrating further into it, since triangle sleeve <NUM> is prevented from rotating by the surrounding triangularly shaped bore in the bone. In some arrangements (not shown), a mechanism such as a toggle, cam, or other feature can be activated immediately after implantation to lock triangle sleeve <NUM> to main body <NUM>, thereby providing immediate anti-rotation.

Referring to <FIG>, another embodiment of a threaded implant system constructed according to the present invention is shown. Implant <NUM> comprises a main body <NUM> having a proximal end <NUM>, a mid-section <NUM> and a distal end <NUM>. Proximal end <NUM> is provided with a head portion <NUM> configured to abut against an outer surface of a bone segment when implant <NUM> is implanted therein. Distal end <NUM> is provided with a threaded portion <NUM> having a triangular cross-section, as best seen in <FIG> and <FIG>. Mid-section <NUM> may have a constant diameter that extends radially to the same extent as the flat portions of the triangular cross-section. As shown in <FIG>, proximal end <NUM> may be provided with a hexagonally shaped socket <NUM> for receiving a drive tool (not shown) when implant <NUM> is being inserted or removed. A through bore <NUM> may be provided along the central axis from the proximal end <NUM> to the distal end <NUM>.

Similar to previously described implant <NUM> of <FIG>, threaded portion <NUM> of implant <NUM> is provided with external threads <NUM> and an internal counter-rotating support structure <NUM>. External threads <NUM> are used to engage bone when threading implant <NUM> across a bone joint. In some embodiments, external threads <NUM> are self-tapping. In this embodiment, internal counter-rotating support structure <NUM> extends helically in an opposite direction from external threads <NUM> as shown. Support structure <NUM> provides stiffness and torsional rigidity to implant <NUM> while permitting fenestrations between external threads <NUM> for promoting better bony on-growth, ingrowth and/or through-growth. In this embodiment, a single external thread <NUM> helically extends from near the distal end <NUM> to the mid-section <NUM> of implant <NUM>, although the thread is interrupted and has portions removed by the flat sides of the triangular cross-section. In other embodiments (not shown), multiple starts of external threads <NUM> may be employed. In this embodiment, internal counter-rotating support structure <NUM> comprises four starts. In other embodiments (not shown), fewer or more starts may be employed. In this embodiment, internal counter-rotating support structure <NUM> has a pitch that is eight times the pitch of external threads <NUM>. In other embodiments (not shown), the pitch of structure <NUM> may be less or more than eight times that of threads <NUM>, and or may form a shape other than helical.

Also similar to previously described implant <NUM> of <FIG>, the fenestrations or interstices of implant <NUM> between external threads <NUM> and internal counter-rotating support structure <NUM> are filled with porous infill <NUM>. Infill <NUM> provides scaffolding with a large surface area for new bone growth. Infill <NUM> can also add additional strength to implant <NUM> in compression, tension, torsion, bending, shear, etc., but still allow for better bony on-growth, ingrowth and/or through-growth than if the fenestrations or interstices were completely filled with less porous material. The exploded view of <FIG> shows threaded portion <NUM> of implant <NUM> separately from the porous infill <NUM> for clarity, although in this embodiment infill <NUM> is a collection of many individual segments rather than an interconnected structure. In some embodiments, threaded portion <NUM> may also be porous, but having a different porosity than infill <NUM>, as previously described. Both may be made together in the same manufacturing process, such as 3D printing or other additive manufacturing process.

In some embodiments, porous infill <NUM> has the same inner diameter as that of through bore <NUM>, forming a continuous inner surface as shown in <FIG>. The outer diameter of infill <NUM> may be the same diameter of the radially inward end of the tapered portions of threads <NUM>, thereby forming the root diameter of threads <NUM>. In this embodiment, these diameters are also equal to the outer diameter of mid-section <NUM>. The inner and outer diameters of counter-rotating support structure <NUM> may also be the same as those of infill <NUM>, such that breaks <NUM> are formed in infill <NUM> (as seen in <FIG>) to accommodate structure <NUM>.

The implant site may be prepared by forming a round bore into the bone having a diameter approximately equal to the root diameter of threads <NUM>. Implant <NUM> may be provided with self-boring and/or self-tapping features. Implant <NUM> may be implanted by inserting a hexagonal driver (not shown) into socket <NUM> and rotating implant <NUM> until head portion <NUM> contacts, becomes flush with or recessed within the outer bone surface. Bone chips may be packed into through bore <NUM> to aid in bone growth to further secure implant <NUM> as it heals in place.

Referring to <FIG>, another comparative threaded implant system. As best seen in <FIG>, implant <NUM> comprises a main body <NUM>, a proximal screw cap <NUM>, a proximal screw <NUM>, and a pair of rotation stops <NUM>. Proximal screw <NUM> comprises a head portion <NUM> and a shaft portion <NUM>. Shaft portion <NUM> may be provided with external threads (not shown) for threadably engaging with internal threads (not shown) located in the proximal end of central bore <NUM> which passes through main body <NUM>. When implant <NUM> is assembled (as best seen in <FIG> and <FIG>), proximal screw cap <NUM> is captivated between head portion <NUM> of proximal screw <NUM> and the proximal end of main body <NUM>. Rotation stops <NUM> are recessed within curved slots <NUM> in proximal screw cap <NUM> (as best seen in <FIG> and <FIG>) such that they prevent or inhibit counter-clockwise rotation of proximal screw head portion <NUM> relative to proximal screw cap <NUM>.

Referring to <FIG>, the distal end of implant <NUM> may be provided with threads <NUM> configured to engage with a bone segment. In this arrangement, as best seen in <FIG>, the threads <NUM> have a non-symmetrical longitudinal cross-section that has a saw-tooth pattern. More specifically, the proximal sides of the threads extend in a radial direction (perpendicular to the central axis of implant <NUM>) while the distal sides of the threads are angled relative to the central axis. One advantage to this configuration is that it provides a higher pullout force when implanted in bone. It can also be seen in <FIG> that threads <NUM> get progressively wider as they extend proximally (i.e. the thread peaks get wider and the roots or valleys get narrower. ) This arrangement allows for the more proximal threads to press against the adjacent bone grooves more than they otherwise would. The entire threaded area is constantly cutting into un-cut bone and allows the threads to create continuous compression into the bone during advancement.

As best seen in <FIG>, the threads <NUM> have a transverse cross-section that is generally triangular in shape. A scoop, divot or hook shape <NUM> may be provided on the leading edge (when rotating in an insertion direction) of each apex of the triangular-shaped threads. A lateral bore <NUM> may also be provided to connect each scoop <NUM> or leading edge with central bore <NUM>. The lateral bores <NUM>, in conjunction with the scoops <NUM> if provided, serve to harvest bone chips or fragments (not shown) as implant <NUM> is threaded into place. Bone chips may pass through lateral bores <NUM> and into central bore <NUM> where they may accumulate. The bone chips may then be removed through the proximal end of central bore <NUM> and manually reintroduced around the implant, may be forced out the distal end of the implant with a tamper, pushed back out of lateral bores <NUM> once implant <NUM> is in the desired position, and/or may be left in place to promote bony ingrowth into implant <NUM>.

Referring to <FIG>, the proximal side of head portion <NUM> of proximal screw <NUM> may be provided with a hexagonally shaped socket <NUM> for receiving a drive tool (not shown) when implant <NUM> is being inserted or removed. The distal side of head portion <NUM> may be provided with a curved, convex portion <NUM> configured to mate with a curved, concave portion <NUM> located on proximal screw cap <NUM>. The circumference of the distal side of proximal screw cap <NUM> may be provided with a series of teeth <NUM> configured to bite into bone. With this arrangement, proximal screw cap <NUM> may freely pivot in two dimensions relative to proximal screw <NUM> so that most or all of the teeth <NUM> of screw cap <NUM> can engage with an outer surface of a bone segment when implant <NUM> is implanted therein, particularly when implant <NUM> is implanted in an orientation that is not orthogonal to the outer surface of the bone.

In this exemplary arrangement, main body <NUM> is implanted first without proximal screw cap <NUM> or proximal screw cap <NUM>. The implant site may be prepared in a manner similar to that previously described. A three-lobed driver tool (not shown) may be inserted into a mating three-lobe receptacle <NUM> (shown in <FIG>) located at the proximal end of main body <NUM>. Main body <NUM> may then be threaded into the bone to a desired height, for example, such that the proximal end of main body <NUM> is just below the outer surface of the bone. The driver tool is then removed from main body <NUM>. Bone chips may then be packed into or moved inside central bore <NUM>. Proximal screw cap <NUM> may then be placed over the implant bore or over the proximal screw <NUM>, and the distal end of proximal screw <NUM> may be threaded into the proximal end of main body <NUM>. A hexagonal driver tool (not shown) may be used to tighten proximal screw cap <NUM> against the outer surface of the bone. Rotation stops <NUM> inhibit proximal screw <NUM> from backing out, as previously described. In some arrangements, rotation stops <NUM> may be removed from proximal screw cap <NUM> after implantation to allow proximal screw <NUM> to be rotated in the opposite direction to remove implant <NUM>.

In some arrangements (not shown), a compression spring may be provided between the proximal screw head or proximal screw cap and the proximal bone surface to maintain compression force on the joint and/or to inhibit the implant from backing out of the bone.

In any of the previously described embodiments, various thread profiles may be utilized. For example, a buttress, V, square, multi start, tapered (root and width), variable pitch, or other thread profile may be used. In some designs, the ISO <NUM> standard from the American National Standards Institute (ANSI) may be used for guidance. Thread profiles may be designed to reduce stress concentrations. Variable thread depths may be used.

Materials that may be used to form the implants include: titanium alloy, stainless steel, ceramic, other alloys, polymers, and bone. In some embodiments, the implant or portions of the implant are additively manufactured. Porosity, fenestrations, nano tubes, nano surface treatments, hydroxyapatite, drug elution, bioactive and anti-microbial (e.g. silver) materials, coatings and/or treatments may be used to encourage bone growth and/or deliver therapeutic benefits. Porosity may vary radially, longitudinally, and/or in other manners. The implants may include expandable sections and may include a modular design.

The implants disclosed herein may be provided in a various incremental lengths to match various anatomies. In some implementations, the lengths range from <NUM> to <NUM>. In some implementations, various incremental diameters may be provided, such as <NUM> to <NUM>. In some implementations, the thread pitch is <NUM> to <NUM>. In some implementations, the pore size of some or all of the implant is <NUM> to <NUM> microns. In some implementations, the porosity is <NUM> to <NUM>%.

In some implementations, a threaded proximal portion configured to engage the ilium is <NUM> to <NUM> long, a triangular middle portion without threads is <NUM>-<NUM> long, and a distal threaded portion configured to engage the sacrum is provided in various lengths, depending on the anatomy of the particular implant site.

In any of the previously described embodiments, the external threads may get progressively wider as they extend proximally. This arrangement allows for the more proximal threads to press against the adjacent bone grooves more than they otherwise would to provide a tighter fit of the implant against the bone.

In some embodiments, the implants disclosed herein are specifically designed to accommodate four or five zones of the sacroiliac joint. These zones can include: <NUM>) the lateral iliac wall; <NUM>) the ilium; <NUM>) the SI joint itself; <NUM>) the sacral ala; and <NUM>) sacral vertebral body. For example, the implant design may include <NUM>) a mechanism to lock against the lateral iliac wall (such as a series of teeth <NUM> on a proximal head as previously described), <NUM>) a finer thread configured to engage the ilium, <NUM>) fenestrations configured to be located inside the SI joint itself when the device is implanted to promote bone ingrowth and/or deliver biologics, <NUM>) a course thread for the ala, and <NUM>) possibly a fine thread for the sacral body. Other suitable features may also be provided and configured for each of the zones, particularly the first four zones.

Thus, a first feature/element discussed below could be termed a second feature/element, and similarly, a second feature/element discussed below could be termed a first feature/element without departing from the teachings of the present disclosure.

Claim 1:
A threaded implant (<NUM>, <NUM>) comprising:
An elongated main body (<NUM>, <NUM>) having external threads (<NUM>, <NUM>) configured to thread into bone;
an internal support structure (<NUM>, <NUM>) located within the external threads and having a helical arrangement that extends in an opposite direction to the external threads,
characterized in that the implant comprises a helical porous infill (<NUM>, <NUM>) between the external threads .