METHODS, IMPLANTS, AND TOOLS FOR FUSION OF SACROILIAC JOINTS

A method of fusing a sacroiliac joint includes inserting expandable implants into multiple implant-receiving holes in ilium and sacrum; expanding the implants to engage both bones; and permitting bone growth to fuse the bones. Alternatively, implants may be inserted into multiple non-round implant-receiving holes in ilium and sacrum formed using a power impact driver attached to a broach tool to prevent movement of the sacroiliac joint. The expandable implants have an outer shell with bone-engagement ridges in porous outer surface to permit ingrowth of bone; an inner expander screw with forcing cone and threads; the outer shell portion having threads engaged with threads of the inner expander screw and an inner conical mating surface for the forcing cone of the inner expander screw; the outer shell engaging an outer sleeve of an insertion tool; and the inner expansion screw engaging a rotatable bit of an insertion tool.

BACKGROUND

The sacroiliac joint, between the sacrum and the ilium bones of the pelvic girdle, is illustrated inFIGS. 1 and 2. Problems with this joint are involved in a significant percentage of people suffering from low back and/or sacroiliac joint pain.

A surgical relief procedure for sacroiliac pain involves stabilizing the sacroiliac joint by placing several implants, such as are illustrated inFIG. 3, across the sacroiliac joint as illustrated inFIG. 4. The implants prevent relative motion between sacrum and ilium at the sacroiliac joint. As the joint surfaces are disrupted and bone fragments enter the joint space during insertion of the implants, the sacrum and ilium fuse together after insertion of the implants as bone grows across the joint.

A prior procedure for insertion of the iFuse (trademark of SI-Bone, San Jose, Calif.) implant system is illustrated inFIG. 5. In this procedure, a surgeon opens a passage to a patient's ilium, inserts a tubular shield, and places a guide pin at a first location. The surgeon then drills a pilot hole over the guide pin through the ilium and into a first location in the sacroiliac joint into the sacrum using an electric drill. Since the pilot hole is round in cross-section, and the iFuse implant is triangular in cross section, and a tight fit of implant to hole is desired, the surgeon then inserts a triangular cutting tool, or broach, illustrated inFIG. 3A, and hammers this cutting tool through the ilium, sacroiliac joint space, and into the sacrum. The surgeon then pulls the cutting tool out of the resulting triangular hole in ilium and sacrum, and hammers an implant into the hole so the implant bridges the sacroiliac joint. The guide pin is then removed as is the tubular shield.

A hand-held hammer is typically used to hammer the cutting tool through the bone. Considerable force is required during the steps of hammering the cutting tool through the ilium, joint, and sacrum, the step of pulling the cutting tool out of the resulting hole, and the step of hammering the implant into the hole.

As a single implant is insufficient to stabilize the sacroiliac joint, the surgeon then removes the tubular shield and repeats the process to insert at least a second implant at a second location in the sacroiliac joint.

As shown inFIG. 3, the implants used in the iFuse system have a rough titanium surface that promotes the ingrowth of bone to ensure that, after a healing time, there is firm adhesion of the implant to both the sacrum and ilium as well as across the sacroiliac joint itself.

In an alternative sacroiliac joint stabilization system, several threaded screws, as illustrated inFIG. 6, are placed across the sacroiliac joint. While drilling a hole in sacrum and ilium is still necessary with this system, the holes remain round in cross section and there is no need for the broach of the iFuse system.

SUMMARY

In an embodiment, method of fusing a sacroiliac joint includes forming at least two implant-receiving holes in ilium and sacrum; inserting an expandable implant into each implant-receiving hole; expanding the implant to engage the implant into both ilium and sacrum; and permitting bone growth to fuse the sacrum and ilium.

In another embodiment, a method of fusing a sacroiliac joint includes forming a non-round implant-receiving hole in ilium and sacrum using a power impact driver attached to a broach tool; inserting an implant into the implant-receiving hole; and repeating the steps of forming an implant-receiving hole, and inserting an implant in at least one other location on ilium, sacroiliac joint, and sacrum to prevent rotation of the sacroiliac joint.

In another embodiment, an expandable implant for fusing a joint has an outer shell with ridges in a porous outer surface adapted to permit ingrowth of bone and adapted to engage a first and a second bone; an inner expander screw with a forcing cone and a threaded portion; the outer shell portion threads engaged with the inner expander screw and an inner conical mating surface for the forcing cone of the inner expander screw; the outer shell adapted to engage an outer sleeve of an insertion tool; and the inner expansion screw adapted to engage a rotatable bit of an insertion tool.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In an embodiment, instead of using a hand-held hammer to widen the pilot hole into the triangular hole, a power impact driver tool is used to drive the broach as illustrated inFIG. 7. The power tool is an electric or compressed air powered device providing successive impacts, in a manner similar to those provided by a small compressed-air chisel, miniaturized miner's drill, small electric chisel, or miniature electric jackhammer. For purposes of this document, the term impact driver includes compressed-air or electric powered devices that provide a series of small impacts when activated. In a particular embodiment, the power tool is used with the prior nonexpendable implant ofFIG. 3.

With this embodiment, a method of fusing the sacroiliac joint includes making an incision and inserting a tubular cannula extending from skin to an exposed spot on the ilium where the fusion device will be inserted. A first pilot hole is drilled into the ilium and sacrum, and a guide wire is inserted. Next, a larger pilot hole centered on the guide wire is drilled in ilium and sacrum using an electric drill inserted through the cannula. Then an impact driver attached to a broach tool is inserted through the cannula and used to enlarge the pilot hole to form an implant-receiving hole in ilium and sacrum. After removing the impact driver and broach, an implant is inserted into the implant-receiving hole using the impact driver. The cannula is then removed and the method is repeated in at least one other location to place another implant extending from ilium through sacroiliac joint into sacrum to prevent rotation of the sacroiliac joint around an axis of the implant.

In an alternative embodiment, where the broach tool serves as a punch, the drilling of the pilot hole is omitted and the broach tool is driven through the bones to create the implant-receiving hole.

In another embodiment, an expandable implant802is used to stabilize the sacroiliac joint (FIG. 8) after holes are drilled. The expandable implant has an outer, shield, portion804fabricated of a soft or springy metal, such as a titanium alloy. The shield portion804of the implant is formed of a biocompatible alloy, or alternatively coated with a biocompatible alloy. In an alternative embodiment, the shield portion is formed of a biocompatible plastic.

The expandable implant has an inner expander-screw806formed of a hard, biocompatible, metal such as cobalt-chromium alloy, certain hard titanium alloys or of a hard, strong, biocompatible ceramic such as zirconia. The inner expander-screw806has at least one threaded portion808that engages the shield portion804. The inner expander-screw806is formed with sacral810and ilial812forcing cones. The outer shield portion804has at least one threaded portion814that engages screw806threaded portion808, and conical portions816,818are configured to engage forcing expander-screw806forcing cones810,812. The shield portion has an engagement portion820, that in a particular embodiment is polygonal, configured to engage a stationary portion822of an insertion tool823. In an alternative embodiment, shield portion822has radial cuts (not shown) that engage mating radial ridges on an end of stationary portion822of insertion tool823, the radial ridges and cuts adapted to securely prevent rotation of shield portion822despite radial movement of segments of shield portion822. The insertion tool823also has a rotating portion824with a spring-loaded bit826. Insertion tool823may in various embodiments be manually or electrically operated.

The shield portion804of the implant, as seen in a side view (FIG. 9), has multiple ridges830configured to, upon expansion of the implant, lock the implant into holes in the ilium832sacrum834, or preferably both ilium832and sacrum834. In embodiments where shield portion804is fabricated from soft-metal or plastic, shield portion804may be fabricated in one piece, in embodiments where shield portion804is fabricated of springy metal, shield portion804has multiple segments840,842joined by slender bridges844, bridges844being sufficiently flexible to permit separation of segments840,842as expander-screw806is tightened into shield portion804. In a particular embodiment, bridges844serve as springs that, upon withdrawal of expander-screw806, retract segments840,842and permit withdrawal of the expandable implant from the bone.

The expandable implant may be round in cross section.

As illustrated inFIG. 10, in an alternative embodiment, the expandable implant shield portion is square in cross section with corners chamfered. As illustrated inFIG. 11, in another alternative embodiment the expandable implant shield portion is triangular in cross section with corners chamfered. In yet another alternative embodiment, the expandable implant shield has another shape such as a hexagonal cross section.

Insertion of the round expandable implant requires first exposing the ilium, then drilling holes through ilium832and into sacrum834of diameter such that implant802will fit into the holes. The implant is then inserted into the holes with the insertion tool stationary portion attached to the shield portion804, and central rotating portion attached to the expander-screw portion. The expander-screw portion806is then tightened into shield portion806, expanding the shield portion into firm contact with both the ilium and sacrum. To prevent rotation about an axis of the implant as could occur if a single implant were used, two or more implants are used for each sacroiliac joint, in a particular embodiment three implants are used for each sacroiliac joint being stabilized.

In embodiments using square (FIG. 10) or triangular (FIG. 11) implant cross sections, a pilot hole is drilled through ilium832into sacrum834. A square or triangular broach, similar to that ofFIG. 3A, but driven by an impact tool as illustrated inFIG. 7, is then used to widen the pilot hole into an implant engagement hole in both ilium and sacrum; the broach is then removed from the patient. Once the broach is removed, the expandable implant ofFIG. 8, attached to the insertion tool, is inserted into the holes in ilium and sacrum, bridging the iliosacral joint space. The shield portion804is prevented from rotating while the expander-screw portion806is tightened into the shield portion804, thereby forcing segments840,842,850,852,860,862(FIGS. 9, 10, 11) into intimate contact with bone. In particular embodiments, the shield portion804of the expandable implant has a porous titanium surface, and optionally holes in its surface leading to cavities within the implant, so that, as the bone of sacrum and ilium heals, the bone may grow into and osseointegrate with the implant. In particular embodiments, the expander-screw portion806of the implant also has a porous titanium surface so that, as the bone heals, the bone may grow into and osseointegrate with both portions of the implant.

In particular embodiments, the shield portion of the implant has a hydroxyapatite (HA) coating to encourage bonding with bone as the bone heals following implantation.

The expandable implant ofFIGS. 8-11has advantage over the nonexpendable implants ofFIG. 3because the implant ofFIGS. 8-11may be slightly smaller than a nonexpendable implant yet grip the bone with similar or greater firmness, while being easier to remove than the implant ofFIG. 3.

If removal of the implant is necessary before osseointegration occurs, implant removal is performed by exposing the implant, attaching the insertion tool823to the implant with its outer stationary portion822engaging the outer shield804of the implant to prevent rotation of the outer shield804while engaging the expander screw806with a rotatable spring-loaded bit826of the insertion tool823, and rotating the spring-loaded bit to unscrew the expander screw806, this allows the springy bridges844to withdraw segments840,842from contact with the bone. A retriever tool having a handle, (not shown) is then screwed into a threaded portion808of the shield portion of the implant804and the shield portion is then wiggled free of scrum and ilium.

The method900(FIG. 12) of fusing the sacroiliac joint includes insertion of the shield tube902and guide wire, followed by drilling904a hole through from illium through sacroiliac joint into sacrum. In embodiments using a non-round implant, such as the implants ofFIG. 10, or11, with triangular or square cross-section, a broach having similar non-round shape to the implant is used with a power impact tool as illustrated inFIG. 7to reshape906the hole to match and accept the implant. The implant is then attached to the insertion tool and inserted908into the hole bridging the sacroiliac joint and engaging with the hole in both ilium and sacrum. In embodiments using the expandable implants herein described, the implant is then expanded910. If912sufficient implants have been placed, generally at least two and in some embodiments three implants per sacroiliac joint, the procedure ends, otherwise the procedure of implant insertion is repeated beginning with inserting a shield and guidewire902and drilling a hole904for another implant.