Sacroiliac Screw

A sacroiliac screw includes a tip, a head, a shank, and at least one screw thread that are integrally formed as a one-piece, monolithic component by additive manufacturing. The sacroiliac screw is configured to be implanted into the ilium bone and through the sacroiliac joint. The head has a frustoconical shape having an outer annular surface tapering from a proximal end to a distal end of the head. A washer may be received on the head of the screw.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to a sacroiliac screw.

BACKGROUND OF THE DISCLOSURE

A sacroiliac screw is a medical device used for the stabilization of the sacroiliac joint. The screw is designed to be implanted into the ilium bone and through the sacroiliac joint to provide stability and support to the joint.

SUMMARY OF THE DISCLOSURE

Features of a sacroiliac screw are described and shown herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring toFIG.1, an illustrated embodiment of a sacroiliac (SI) screw designed and constructed according to one or more teachings of the present disclosure is generally indicated at reference numeral10. The screw10includes a shank12, a tip14, a head16, and one or more screw threads18, each indicated generally. Each of these components are integrally formed so that the screw10is formed as a one-piece, monolithically formed component. The screw10may be formed by additive manufacturing, such as by direct metal laser sintering or by electron beam melting processes as is generally known. The illustrated screw is designed and constructed for the stabilization and/or fusion of the sacroiliac joint.

The shank12includes a shank body20and exposed open-cell metal foam22integrally formed on the shank body. The shank body20extends from the tip14(or adjacent thereto) to the head16(or adjacent thereto). The shank body20has a generally rod shape having an outer diameter and a length. As a non-limiting example, the outer diameter of the shank body20may be from about 9 mm to about 15 mm, such as 9.5 mm or 11.5 mm or 14.5 mm. As a non-limiting example, the length of the shank body may be from about 30 mm to about 110 mm in 5 mm increments. The dimensions of the shank body20may be dependent on the patient and the specific surgical procedure. An outer surface of the shank body20may be relatively smooth compared to an outer surface of the open-cell metal foam22. As shown inFIG.6, the screw10may be cannulated, whereby the shank body20defines a longitudinal internal passage26for receiving a guidewire or k-wire or other device, as is generally known in the art. The shank body20provides desired structural support, including desired bending strength, for the screw.

The shank body20further defines openings30(e.g., fenestrations) extending through the outer surface to the internal passage26to enable bone growth therein. The openings30may be of suitable shapes and sizes. In the illustrated embodiment, the openings30are outside the boundaries of discrete areas of the open-cell metal foam22. In the illustrated embodiment, openings30at adjacent the tip14and the head16are generally slot-shaped having lengths extending at offset angles relative to the longitudinal axis of the shank12, such that the slot-shaped openings extending longitudinally and circumferentially. The number, size and shape of the openings30are such that there is at least one open area at every angle around the 360-degree circumference of the shank body20. In other words, around the circumference of the screw body20, there is at least one opening30at some longitudinal position enabling bone growth. In this way, the screw10enables bone growth around the entire 360-degrees circumference of the screw body20to facilitate and enhance screw retention in bone.

In the illustrated embodiment, the open-cell metal foam22comprises a plurality of open-cell foam portions at discrete areas on the shank12so that the outer surface of the shank12includes discrete areas of open-cell metal foam22and discrete areas of the shank body20. As used herein, “open-cell metal foam” is a porous structural component having a relatively roughened surface, an apparent randomized filament arrangement, and cell sizes and shapes forming an interconnected network or labyrinth to facilitate bone in-growth. From a sectional view, such as shown inFIGS.6and7, the open-cell metal foam22appears to be disposed in pockets or recesses38defined by the shank body20. As explained above, the screw10may be formed from additive manufacturing, such that the features of the screw are integrally formed. The open-cell metal foam22is not received in the pockets or recesses because the pockets or recesses are formed as the open-cell metal foam is formed according to additive manufacturing processes. Accordingly, the description of the open-cell metal foam22being disposed in pockets or recesses38defined by the shank body20should be understood in a broad sense. In the illustrated embodiment, the recesses or pockets38of the shank body20have a radially inward surface38aand side walls38bextending radially from the bottom surface such that the open-cell metal foam22is not in communication with the internal passage.

In the illustrated embodiment, the open-cell metal foam portions22are elongate having longitudinal axes that are angularly offset from the longitudinal axis of the shank12, so that the portions extend at least partially circumferentially in addition to longitudinally. The number, size and shape of the open-cell metal foam portions22are such that there is open-cell metal foam22at every angle around the 360-degree circumference of the shank body20. In other words, around the circumference of the shank body20, there is at least one open-cell metal foam portion22at one or more longitudinal position enabling bone ingrowth into the open-cell metal foam. In this way, the screw10enables bone growth around the entire 360-degrees circumference of the screw body20to facilitate and enhance screw retention in bone.

In the illustrated embodiment, the screw thread18comprises more than one screw thread. In particular, the screw thread18includes a lengthwise thread18a,a proximal screw thread18b,and a distal screw thread18c.The lengthwise thread extends from adjacent the tip14(i.e., adjacent the distal end of the shank body20) to adjacent the head16(i.e., adjacent the proximal end of the shaft bod). Thus, the lengthwise thread18aextends more than a majority, and in one embodiment more than 85%, of the length of the shank body20. The lengthwise thread18amay have a uniform pitch along its length or the thread may have a variable pitch. In the illustrated embodiment, the lengthwise thread has a variable pitch, as explained in more detail below.

The distal thread18cextends from adjacent the tip14to a longitudinal location that is distal of the mid-length of the shank body20. Accordingly, the distal thread is contained within a distal portion of the shank body20. The distal thread18cmay have a uniform pitch along its length or the distal thread may have a variable pitch. In the illustrated embodiment, the distal thread18chas a uniform pitch. The distal thread18cis intertwined with the lengthwise thread18aat a distal portion of the shank body20. In particular, a turn of the distal thread18cis disposed between adjacent turns of the lengthwise thread18a.In the illustrated embodiment, the pitch of the distal thread18cis equal to the pitch of the lengthwise thread18aat the distal portion of the shank body20, and the turns of the distal thread18care spaced mid-way between corresponding adjacent turns of the lengthwise body18a.Together, the distal thread18cand the lengthwise thread18aat the distal portion of the shank body20constitute a distal screw thread portion of the screw thread18.

In the illustrated embodiment, the distal screw thread portion defines serrations40to enable digging or cutting of the distal screw thread portion into bone. The serrations40are disposed in groupings around turns of the distal screw thread portion at suitable locations to define stripes of serrations extending longitudinally and circumferentially. In the illustrated example, the groupings of serrations40are disposed over and on or within the boundaries of the open-cell metal foam22.

The proximal thread18bextends from adjacent the head14to a longitudinal location that is proximal of the mid-length of the shank body20. Accordingly, the proximal thread is contained within a proximal portion of the shank body20. The proximal thread18bmay have a uniform pitch along its length or the thread may have a variable pitch. In the illustrated embodiment, the proximal thread18bhas a uniform pitch. The proximal thread18bis intertwined with the lengthwise thread18aat a proximal portion of the shank body20. In particular, a turn of the proximal thread18bis disposed between adjacent turns of the lengthwise thread18a.In the illustrated embodiment, the pitch of the proximal thread18bis equal to the pitch of the lengthwise thread18aat the proximal portion of the shank body20, and the turns of the proximal thread are spaced mid-way between corresponding adjacent turns of the lengthwise body. Together, the proximal thread18band the lengthwise thread18aat the proximal portion of the shank body20constitute a proximal screw thread portion of the screw thread18.

In the illustrated embodiment, a central screw thread portion of the screw thread18is disposed between the distal and proximal screw thread portions. The central thread portion consists of the lengthwise thread18aonly because the distal thread terminates18cadjacent a distal end of the central thread portion, and the proximal thread18bterminates adjacent a proximal end of the central thread portion.

The pitch of the distal screw thread portion is greater than the pitch of the proximal screw thread portion. The pitch of the central screw thread portion is greater than both the distal and proximal screw thread portions. Through this construction, the screw thread imparts and compressive load when screwed into the ilium and sacrum.

The screw thread18is integrally formed and directly connected to the shank body20. Referring toFIG.7, segments of the screw thread18are connected directly to the outer surface of the shank body20or the radially inner surface38aof the shank body that partially defines the pockets38. Thus, the radially inner end of the screw thread is connected directly the shank body20(e.g., radially inner surface38a), and the open-cell metal foam22is not disposed radially between the radially inner end of the screw thread and the radially inner surface of the shank body. This construction provides structural support to the thread18, including shear strength to inhibit shearing off of the thread from the shank. In the pockets38, the open-cell metal foam22is directly connected to and integrally formed the proximal and distal surfaces of the screw thread18and the radially inner surfaces38aof the shank body20.

In the illustrated embodiment, the tip14of the screw10is fluted or otherwise formed to enable cutting into bone. Also in the illustrated embodiment, the head16of the screw10defines a shoulder suitable for receiving a washer thereon. The head16has a frustoconical shape having an outer (or lateral) annular surface tapering from a proximal end to a distal end of the head. A distal end of the head16is has a generally planar surface extending radially outward from the shank body20. A proximal end of the head16has a generally planar surfaces and defines an opening leading to an internal passage through the head. The diameter of the head16at its proximal end of greater than the diameter of the head at its distal end. The entirety of the outer (or lateral) annular surface of the of the head16is disposed radially outward of the shank body20, and in one embodiment, radially outward of the thread(s)18a,18b,18c.The head16has rounded or radiused proximal and distal edges where the proximal end meets the outer (or lateral annular surface and the distal end meets the outer (or lateral) annular surface, respectively.

Referring toFIG.8, other embodiments of SI screws are generally indicated at reference numeral110. The SI screws110may be identical to the screw10described above, except as described below. Thus, the teachings set forth above, unless explicitly different than the description below, apply equally to the screws110.

The primary different between the screws110and screw10is that open-cell metal foam122is disposed on substantially the entirety (e.g., at least 85%, such as at least 85% or at least 90% or at least 95% or at least 98% or at least 99% or about 100%) of the outer surface area of the shank body120that is not occupied by the screw thread118or openings130. Thus, unlike the open-cell metal foam22of the screw10, the open cell metal foam122of this embodiment is not disposed in stripes or discrete areas of the shank body120, but covers substantially the entirety of the shank body120.

Also shown inFIG.8, are washers150configured to be received on the heads of the screws110. These washers150are described in more detail below with respect toFIGS.9and10.

Referring toFIG.9, one of the screws100ofFIG.8is shown in detail, including the washer150received on the head116. As shown inFIG.10, similar to the first embodiment, the head116screw110defines a shoulder suitable for receiving a washer thereon. The head116has a frustoconical shape having an outer (or lateral) annular surface tapering from a proximal end to a distal end of the head. A distal end of the head116is has a generally planar surface extending radially outward from the shank body120. A proximal end of the head116has a generally planar surfaces and defines an opening leading to an internal passage through the head. This internal passage is configured to receive a tool for inserting the screw110in bone of a patient. The diameter of the head116at its proximal end of greater than the diameter of the head at its distal end. The entirety of the outer (or lateral) annular surface of the of the head116extends radially outward of the shank body120, and in one embodiment, radially outward of the thread(s)118. The head116has rounded (or radiused) proximal and distal edges where the proximal end meets the outer (or lateral annular surface and the distal end meets the outer (or lateral) annular surface, respectively.

As shown inFIGS.9and10, the washer150has an annular shaped body with a proximal end margin defining a plurality of axially-extending slots152spaced apart circumferentially, and a distal end margin defining a plurality of teeth154spaced apart circumferentially. The slots152enable the proximal end margin to radially expand to enable the washer150to snap onto the head116as the washer slides proximally along the screw shank and over the head. The teeth154enable the distal end margin to dig into bone as the screw is into the bone. As shown inFIG.11, the interior of the washer150is rounded (i.e., concave) in cross section, and the proximal and distal edges of the head116engage the concave interior of the washer to enable the washer to pivot on the head. Moreover, as can be seen, the outer annular surface of the head116between the proximal and distal edges does not engage the interior of the washer150.

Modifications and variations of the disclosed embodiments are possible without departing from the scope of the invention defined in the appended claims.