BONE ANCHOR ASSEMBLY WITH PIVOTABLE RETAINER AND INDEPENDENTLY ROTATABLE SHANK

Abstract

A polyaxial bone screw includes a head member and a shank member. The shank has a capture end and an opposite threaded end for threaded insertion into a vertebra. The head has a U-shaped cradle for receiving a spinal fixation rod and a central bore for receiving the capture end of the shank. An expandible retainer ring with a radial split is snapped onto the capture end of the shank to retain it within the head. The retainer ring has a spherical outer surface which forms a ball joint with a spherical socket cavity within the head to enable the head to be angled relative to the shank. A threaded closure plug is tightened within the cradle to clamp the rod into engagement with a knurled dome on the capture end of the shank to secure the rod relative to the vertebra.

Description

BACKGROUND OF THE INVENTION

The present invention is directed to a bone screw of the type wherein a head of the bone screw is swingable or can swivel about the shank of the bone screw until the surgeon is satisfied with the relative placement of the two parts and thereafter the head can be locked in position relative to the shank. Such screws are also referred to as polyaxial head or swivel head bone screws, since the head can be positioned in any of a number of angular configurations relative to the shank.

Bone screws are advantageously utilized in many types of spinal surgery in order to secure various implants to vertebrae along the spinal column. Bone screws of this type typically have a shank that is threaded and adapted to be implanted into a vertebral body of a vertebra. The bone screw includes a head which is designed to extend beyond the vertebra and which has a channel to receive another implant. Typically the channel will receive a rod or a rod-like member. In bone screws of this type, the head may be open, in which case a closure must be used to close between opposite sides of the head once a rod-like implant is placed therein, or closed wherein a rod-like implant passes through the head of a bone screw. Open head screws are most often used, mainly because it is difficult to feed long rods through closed head screws.

Bone screws are also available with heads permanently fixed relative to a shank or with polyaxial heads that initially swivel to allow placement and are then lockable in a desired positional configuration. When the head and shank of the bone screw are fixed in position relative to each other, it is not always possible to insert a bone screw into the bone in such a manner that the head will be in the best position for receiving other implants. Consequently, the polyaxial head bone screws have been designed that allow the head of the bone screw to rotate or swivel about an upper end of the shank of the bone screw, while the surgeon is positioning other implants and finding the best position for the bone screw head. However, once the surgeon has determined that the head is in the best position, it is then necessary to lock or fix the head relative to the shank. Different types of structures have been previously developed for this purpose. Unfortunately, the prior art devices have a tendency to be bulky, slip under high loading or require many parts.

It is desirable to have a polyaxial head bone screw that can be captured by the shank prior to locking of the head, but that allows the head to freely swivel or pivot about a top of the shank prior to locking. It is then further desirable to have the head capable of being fixably locked in a configuration or position relative to the shank where the head best fits with other elements of the overall spinal implant.

As noted above, many prior art swivel type bone screws have a bulky and heavy structure. In spinal surgery, it is desirable to provide a light weight implant that impacts on the surrounding tissue as little as possible. Consequently, it is desirable to have a bone screw with a low profile with respect to both height and width. It is also preferable to limit the width profile of the bone screw to provide more room to work along a rod or other implant in which many elements may be required in a relatively small space.

Furthermore, it is desirable to maintain the number of parts of the device at a minimum. Also, it is desirable to secure the various parts together in such a way, so that, if parts become loose under use for some reason, the device will not totally disassemble.

SUMMARY OF THE INVENTION

The present invention provides an improved polyaxial head bone screw assembly for use in conjunction with spinal surgery and, in particular, for implanting into a bone and securing other medical implants to the bone. The polyaxial bone screw assembly includes a threaded shank member for threaded placement in a bone, a head member connecting to another implant such as a spinal fixation rod and capturing a capture end of the shank member, and a retainer sphere or retainer ring to capture and retain the capture end of the shank member within the head member. The shank member and head member may be set in a plurality of angular relationships with respect to each other within a range of obtuse angles.

The shank or shank member has an outer portion which is threaded, sized and shaped so as to be adapted to be operably screwed into a vertebral body in the spine of a patient. An end of the shank opposite the threaded lower portion includes a frusto-conical capture structure which diverges in diameter in a direction away from the threaded end of the shank. A top of the conical capture end is provided with apertures or formations for non-slip engagement by an installation tool to enable the shank to be threaded into a bone, such as a vertebra. Beyond the conical structure, a knurled dome is provided for positive interfering or cutting engagement by the surface of a rod which is to be clamped and supported by the bone screw assembly.

The head member is generally partially cylindrical in outer shape and has a central axial bore to receive the capture end of the threaded shank and a central U-shaped cradle opens in a direction opposite the axial bore to receive a spinal fixation rod and presents a pair of spaced apart arms. An interior of each of the arms includes threads to receive a threaded plug to secure the rod within the cradle and to clamp the rod into engagement with the knurled dome of the shank to fix the angular position of the head with respect to the shank. The head includes a lower partially spherical socket or seat at the lower end of the axial bore for receiving the ring and forms a neck for surrounding the shank during usage.

The retainer ring has an outer surface which is partially spherical and which is sized and shaped to fit within and swivel within the seat until locked in position, as noted below. The ring also has a central bore which is frusto-conical and of a shape which is compatible with the capture end of the shank to snugly receive the shank therein. The ring is sized to be too large in width to fit through the neck at the bottom of the head when in operable position and is either loaded from the top of the head or through other structure formed in the head. The ring is resiliently expandible to enable the ring to be snapped over the capture end of the shank to retain the capture end within the head member. The head has an assembly or orientation cavity therein which communicates with the U-shaped cradle and which is positioned and sized to enable proper orientation of the retainer ring and engagement of it with the capture end of the shank. The assembly cavity is spaced axially above the seat and neck and has a slightly larger partial spherical diameter than the seat so as to allow the ring to expand during insertion of the shank capture end and then return to a smaller diameter for snugly fitting in the seat. The spherical seat initially forms a pivot bearing with the retainer ring, when no axial downward force is applied to the shank and ring, to retain the capture end of the shank within the head and to enable pivoting the shank relative to the head throughout a limited range. The retainer ring is formed of a resilient or springy material and in a preferred embodiment has a radial split to enable expansion of the diameter of the ring and, particularly, to enable expansion of the diameter of the central bore to enable placement on the conical capture end of the shank.

Once the ring is on the shank and located in the seat in a position suitable to the surgeon with a rod received in the head channel, a closure plug is screwed into the threads between the arms so as to engage the rod and urge the rod under pressure into engagement with the dome on the shank. This in turn urges the spherical surface on the ring into frictional engagement with the spherical surface of the seat so as to lock the rotational position of the shank relative to the head. The dome of the shank is preferably radiused so that it engages the rod in the same manner no matter what alignment is formed between the head and the shank. The dome also preferably has a radius that is substantially less than the radius of the partial spherical surface of the ring. This reduces the required height of the head in comparison to the dome that is a continuation of the spherical surface.

Preferably, the shank feeds into the head from below through the neck of the head and has a smaller diameter in the region of the capture end than the diameter of the threads. This allows the shank to have a comparatively wide and normal thread for screwing into the bone that may be wider than the neck of the head, while also allowing the top of the shank to pass through the neck of the head to connect with the retainer ring.

In the present invention, because the retainer or retainer ring is wider than the width of the rod receiving channel in the head, the ring is preferentially less in height than the width of the channel such that the ring is turned sideways for loading and then turned again a quarter turn to reposition the ring in the head cavity to receive the shank. For a comparable head designed to receive a rod of a certain diameter this allows the retainer to have a greater width. This, in turn, allows the opening through which the shank passes to have a greater diameter and still block passage of the retainer. Because the diameter of the opening is greater, the diameter of the neck and capture end of the shank can also be sized greater allowing for greater strength and optionally allowing the shank to be cannulated or axially bored to provide for use of a guide wire.

In an alternative embodiment, the shank capture end is an axially aligned cylinder that is received through a lower opening in the head. A shank capture member or retainer is generally spherical in shape and has at least a lower partial spherical surface for rotatably engaging a mating surface in a cavity of a head of the bone screw. The spherical shaped retainer has a pair of diametrically opposed side bores that intersect with a bore that receives the shank capture end and which provide for the use of a crimping or deforming tool to pass through the retainer side bores so as to engage and deform the shank capture end.

The deformation of the shank capture ends interferes with removal of the retainer and locks or joins together the shank and retainer so that a main body of the shank protrudes outward from the opening in the bottom of the head and the retainer remains in inside the head on the opposite side of the head lower opening which has a smaller diameter than the portion of the retainer that engages the cavity at the head lower opening, swivelably rotatably securing both the retainer and shank to the head to allow a surgeon to position the head to receive the rod. A bore in the top of the retainer has faceted sides that produce a hex or other shaped opening for receiving a tool for driving the bone screw into a bone or removing the bone screw. The retainer and shank are further locked against rotation when a closure is used to apply pressure to a rod member received in the head which in turn applies pressure to the retainer and frictionally locks the position of the retainer in the cavity and the relative position of the shank to the head.

OBJECTS AND ADVANTAGES OF THE INVENTION

Therefore, the objects of the present invention include: providing an improved bone screw assembly for implantation into a vertebra of a patient wherein the head of the bone screw is swingable or swivelable about an end of a shank of the bone screw until a desired configuration is obtained after which the head is lockable in position relative to the shank; providing such a screw assembly including a threaded shank with a capture end, a head member with a shank receiving bore and a U-shaped rod cradle for receiving a spinal fixation rod, a resiliently expandible shank retainer or retainer ring to retain the capture end of the shank within the head, and a threaded plug receivable in the head to engage a cradled rod and urge it into securing engagement with the capture end of the shank to fix the angular position of the shank relative to the head; providing such a screw assembly wherein the head member includes an internal partial spherical cavity, socket or seat and the retainer ring includes at least a partial spherical outer surface to enable swiveling and universal positioning of the shank relative to the head member from side to side and front to rear within a limited range; providing such a screw assembly in which the head member includes an assembly or orientation cavity above the seat to enable expansion of the ring during joining with the shank and proper orientation of the retainer ring; providing such a screw assembly in which the retainer ring has a radial split to enable resilient expansion and retraction of the ring for snapping the ring onto the capture end of the shank; providing such a screw assembly in which the capture end of the shank is frusto-conical, diverging in diameter in a direction away from the threaded part of the shank and in which the retainer ring has a central bore which is compatibly frusto-conical in shape; providing such a screw assembly in which the capture end of the shank has a knurled dome for positive, interfering engagement by a spinal fixation rod clamped within the assembly and wherein the dome has a radius that is smaller than the radius of the ring partial spherical surface; and providing an alternative bone screw utilizing a generally spherical retainer with a bore for receiving a capture end of an associated shank after which the shank capture end is deformed so as to interferingly secure the shank to the retainer; and providing such a polyaxial head bone screw which is economical to manufacture, which is convenient and secure in use, and which is particularly well adapted for its intended purpose.

Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.

The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged cross sectional view of a polyaxial head screw with a split retainer ring which embodies the present invention, shown assembled with a rod to hold the rod and inserted in a vertebral bone.

FIG. 2 is an exploded perspective view of elements of the bone screw at a reduced scale and illustrates a threaded shank member, a head member, and a retainer ring.

FIG. 3 is an enlarged cross sectional view of the screw head and illustrates the orientation of the split retainer ring for insertion into the head.

FIG. 4 is a view of the screw head similar to FIG. 3 and shows the orientation of the retainer ring to prepare for insertion of a capture end of a threaded shank.

FIG. 5 is a view similar to FIG. 3 and shows the retainer ring about to be snapped onto the capture end of the threaded shank.

FIG. 6 is a view similar to FIG. 3 and shows the retainer ring positioned on the capture end of the threaded shank.

FIG. 7 is a view similar to FIG. 3 and shows the capture end of the shank with the installed retainer ring positioned in a spherical pivot seat of the screw head.

FIG. 8 is a view similar to FIG. 3 and shows the threaded shank with retainer ring pivoted to a selected angle relative to the screw head.

FIG. 9 is an exploded perspective view of a second embodiment of a polyaxial bone screw in accordance with the present invention, showing a shank, a head and a partial spherical retainer.

FIG. 10 is an enlarged cross-sectional view of the head of the second embodiment, taken along line 10-10 in FIG. 11.

FIG. 11 is an enlarged top plan view of the head of the second embodiment.

FIG. 12 is an enlarged cross-sectional view of the head of the second embodiment, taken along line 12-12 in FIG. 11.

FIG. 13 is an enlarged and fragmentary side elevational view of the shank, head and retainer of the second embodiment, showing the retainer being placed on the shank and raised relative to the head.

FIG. 14 is an enlarged and fragmentary cross-sectional view of the shank, head and retainer of the second embodiment with a crimping tool being utilized to deform the shank to interferingly secure the retainer and shank together.

FIG. 15 is a view similar to FIG. 14, but with the shank lowered relative to the head and with the retainer seated in a partial spherical chamber of the head allowing rotation of the shank and retainer relative to the head.

FIG. 16 is an enlarged and fragmentary view of the shank, head and retainer, taken along a line similar to line 10-10 of FIG. 11 and showing elements in the same position as FIG. 15.

FIG. 17 is an enlarged and fragmentary side elevational view of the shank, head and retainer, assembled as in FIG. 15.

FIG. 18 is an enlarged and fragmentary perspective view of the elements of the bone screw shown in FIG. 17 being driven into a vertebra that is shown in cross-section by a driving tool.

FIG. 19 is an enlarged, exploded and perspective view showing the elements of the bone screw, as seen in FIG. 15 along with a closure and closure set screw.

FIG. 20 is an enlarged front elevational view of the fully assembled bone screw of the second embodiment implanted in a vertebra shown in cross section and showing a break-off head of the set screw having been broken away from a remainder of the set screw.

DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.

Referring to the drawings in more detail, the reference numeral 1 generally designates a polyaxial bone screw arrangement which embodies the present invention. The arrangement 1 includes a threaded shank member 2 for threadably implanting into a bone 3, such as a vertebra, and a head member 4 which connects with the shank member 2 to engage and secure a rod member 5, such as a spinal fixation rod, relative to the bone 3. The arrangement 1 also includes a retainer or retainer ring 7 operably positioned within head 4 and engaging a capture end 9 of the shank 2 opposite a region having a thread 8 to retain the capture end 9 within the head 4. The arrangement 1 further includes a plug or closure member 10 which urges the rod 5 into engagement with the capture end 9 of the shank 2. The head 4 and shank 2 cooperate in such a manner that the head 4 and shank 2 can be secured at any of a plurality of obtuse angles, relative to one another and within a selected range of angles both side to side and front to rear, to enable flexible engagement of the arrangement 1 with a rod 5.

Referring to FIGS. 1, 2, and 5, the shank 2 is elongated and is sized and shaped to be screwed into one of the vertebra 3. The shank 2 includes the external helically wound thread 8 that extends from an outer tip 12 to near the capture end 9. On the illustrated shank 2, the capture end 9 includes a region that is frusto-conical in shape, diverging in diameter in a direction away from the outer tip 12 and that is coaxially aligned with an axis of the shank 2. The illustrated capture end 9 has a maximum radius that is substantially less than a radius associated with the shank thread 8 and further, preferably less than the radius of a body 13 of the shank 2 in the region whereupon the thread 8 is located.

The capture end 9 has a plurality of tool engageable grooves, apertures or the like 14 to enable positive engagement by an appropriately shaped installation tool (not shown) to thread and drive the shank 2 into the vertebra 3. An upper end surface 16 of the capture end 9 opposite the tip 12 is provided with a formation or dome 18 to be positively and interferingly engaged by the rod 5 when the assembly 1 is assembled into place. The illustrated shank 2 includes the dome 18 which is radiused and knurled and that centered on the upper end surface 16 of the shank capture end 9 so as to be coaxial with the remainder of the shank 2. The scoring or knurling of the dome 18 operably frictionally abuts against a cylindrical surface 20 of the rod 5, when the plug 10 is tightened to provide non-slip engagement of the shank 2 relative to the rod 5 and to thereby help maintain a desired angular relationship between the shank 2 and the head 4. In certain embodiments, the purpose of the dome 18 is simply to be engaged by the rod 5 during assembly and pushed in such a manner as to frictionally engage the ring 7 with the head 4 as described below. Preferably, the dome 18 is radiused so that the dome 18 engages the rod at the same location even as the head 4 is swivelled relative to the shank 2. However, in certain embodiments the dome 18 could have other shapes.

Referring to FIGS. 2-8, the head member 4 is generally cylindrical in external profile and has a central and axially aligned shank receiving bore 24 ending at an inner and lower neck 26. The neck 26 is radiused to receive the shank capture end 9 and preferably smaller than the radius of the shank body 13 and thread 8. The bore 24 is also preferably sized larger than the capture end 9 of the shank 2 to enable the shank 2 to be oriented through a range of angular dispositions relative to the head 4. The bore 24 may be conically counterbored or beveled in a region 28 to widen the angular range of the shank 2.

The head 4 is provided with a U-shaped rod cradle 30 which is sized to receive the rod 5 therethrough. The illustrated cradle 30 is rounded and radiused at an inner or lower portion 31 to snugly mate with the surface of the rod 5 and open at an outer end 33, with spaced apart parallel side surfaces 32 so as to form upstanding and spaced apart arms 35 with inwardly facing threading thereon. The side surfaces 32 have mating and guide structures 34 formed thereinto which are complementary to mating and guide structures 36 of the closure plug 10 (FIG. 1). The structures 34 and 36 may be helically wound flanges or threads which advance the plug 10 into the head 4, as the plug 10 is rotated about its axis. It is foreseen that structures 34 and 36 may be V-shaped threads, buttress threads, reverse angle threads, or other types of threads or flange forms. Preferably, the structures 34 and 36 are of such a nature as to resist splaying of the arms 35 when the plug 10 is advanced into the cradle 30.

As seen in FIGS. 3 and 4, the head 4 has an assembly cavity 38 formed therein which opens into the cradle 30. A partially spherical socket or seat 40 communicates between the assembly cavity 38 and the shank bore 24 and has a radius that is slightly less than the radius of the assembly cavity 38 that is located axially directly thereabove. The purposes for the cavity 38 and seat 40 will be detailed further below. The head 4 may include external, closed end grip bores 42 for positive engagement by a holding tool (not shown) to facilitate secure gripping of the head 4 during assembly of the arrangement 1. The seat 40 has a spherical radius and extends upward coaxially through the head 4 from the neck 26 to the cavity 38.

The closure plug 10 is generally cylindrical in shape and is provided with a break-off head 44 which is connected to the plug 10 by a weakened area such that the head 44 separates from the plug 10 at a predetermined torque applied to the head 44 during assembly. The illustrated break-off head 44 has a hexagonal cross section for engagement by a tool (not shown) of a complementary shape.

The retainer ring 7 is used to retain the capture end 9 of the shank member 2 within the head member 4. The retainer ring 7 resiliently expands and contracts to enable the ring 7 to be snapped over and seated on the capture end 9 of the shank 2. The ring 7, like the remainder of the arrangement 1, is preferably formed of a material such as a spring stainless steel, tantalum, titanium or other resilient implantable material. The illustrated ring 7 has a radial split 48 which allows the ring 7 to expand in circumference to fit over the capture end 9. Alternatively, other configurations of the ring 7 are envisioned to enable such expansion and retraction of the ring 7. The ring 7 has a central conical bore 50 which is conically shaped to be compatible with the conical shape of the capture end 9. The ring 7 has an outer surface 52 which is frusto-spherical, partially spherical, or a segment of a sphere, and which has a spherical radius approximately equivalent to the spherical radius of the spherical seat 40 within the head 4 and smaller than the radius of the cavity 38. The ring surface 52 also has a radius substantially greater than the dome 18.

FIGS. 3-8 illustrate step by step assembly of the components of the bone screw arrangement 1. In FIG. 3, the ring 7 is inserted into the head 4 through the interior of the U-shaped cradle 30. The ring 7 is oriented with its axis at a right angle to the axis of the bore 24 and to the side surfaces 32 of the cradle 30. FIG. 4 illustrates the ring 7 oriented with its axis parallel or coincident with the axis of the bore 24 and neck 26, by rotating the ring 7 within the assembly cavity 38. In FIGS. 5 and 6, the capture end 9 of the shank 2 is inserted through the bore 24 and engaged with the retainer ring 7 so as to snap the ring 7 over the capture end 9. This is accomplished by pressing the shank 2 into the head 4, causing the ring to engage a constriction at the top of the assembly cavity 38. The relative resistance encountered by the ring 7 allows the capture end 9 to expand the circumference of the retainer ring 7, by expansion of the split 48, so that the capture end 9 enters the central bore 50 of the ring 7. The capture end 9 includes a shoulder 56 which limits penetration of the capture end 9 into the retainer ring 7, as shown in FIG. 6.

FIG. 7 shows the arrangement 1 with the retainer ring 7 lowered from the assembly position and positioned in the spherical seat 40 and the central axis of the shank 2 coaxial with the central axis of the head 4. FIG. 8 shows the shank 2 angled relative to the head 4. The spherical seat 40 and spherical outer surface 52 of the retainer ring 7, when seated in the seat 40, allows universal angular positioning of the shank 2 relative to the head 4 within a limited range, as is shown in FIG. 8. The retainer ring 7, thus, performs the double functions of preventing the capture end 9 of the shank 2 from slipping through the neck 26 and, in conjunction with the seat 40, forms a ball joint for relative orientation of the shank 2 and head 4.

Under some circumstances, it may be desirable to assemble the shank 2 and head 4, prior to threading the shank 2 into the vertebra 3 or other bone. Thereafter, the shank 2 may be conveniently screwed into the vertebrae 3 by passing the installation tool through the cradle 30 to engage the grooves 14 of the capture end 9. The vertebra 3 may be predrilled with a pilot hole or the like (not shown) to minimize stressing the bone 3. Once the shank 2 has been threaded to its desired depth, the head 4 can be oriented as desired. The rod 5 is positioned in the cradle 30, engaging the knurled dome 18, and the closure plug 10 is advanced into the head 4 to clamp the rod 5 between the capture end 9 and the closure plug 10. When the preset torque limit of the plug 10 is reached, the break-off head 44 separates from the closure plug 10. The force transmitted by torquing of the closure plug 10 transmits through the rod 5 and through the dome 18 to the ring 7. The partial spherical surface 52 of the ring 7 is thereby urged into tight frictional relationship with the partial spherical surface 40 of the head 4, thereby locking the angular configuration of the head 4 relative to the shank 2.

The reference numeral 100 generally represents a second embodiment of a bone screw shown in FIGS. 9 through 20 in accordance with the present invention for implanting in a vertebra 101 or other bone.

The bone screw 100 includes a head 105, a shank 106, a retainer or capture sphere 107 and a closure 108. The bone screw 100 also operably receives a rod member 110 that is part of an implanted assembly.

The head 105 has a lower body 115 with a pair of upstanding and spaced arms 116 and 117. The arms 116 and 117 are spaced sufficiently to form a channel 120 that is sized and shaped to snugly receive and subsequently secure the rod member 110 to the bone screw 100. In this manner the channel 120 opens upward and sideways outwardly to opposed sides of the head 105. The head 105 has a central axis indicated by the reference letter A. The channel 120 has a pair of lower spaced curved surfaces 121 that preferably have substantially the same radius as the rod member 110.

An axially centered chamber 122 is located in the head 105 below the channel 120 and opens upwardly into the channel 120. The chamber 122 has a surface 125 that is sized and shaped to snugly but slidably receive the sphere 107. In particular, a lower portion or hemispherical seat 126 of the chamber surface 125 is curved or hemispherical so as to have substantially the same radius as the sphere 107.

An axially aligned bore 129 communicates between the chamber 122 and a lower exterior of the head 105. The bore 129 has a smaller diameter than the sphere 107, so as to prevent passage of the sphere 107 through the bore 129.

The arms 116 and 117 include inwardly facing flanges 131 with downward extending ears 132 at outer ends thereof. The flanges 131 and ears 132 collectively form curved channels 134 that receive the closure 108, as described below. Tool gripping indents 135 are formed on the exterior of the head 105.

The shank 106 is elongate and has a central axis of rotation indicated by the reference letter B. The shank 106 has a lower body 138 with a helically wound thread 139 wrapping thereabout. The shank body 138 is operably threaded into a vertebra 101 in the manner shown in FIG. 18.

The shank 106 has an axially aligned upper portion or capture end 144 with a cylindrically shaped surface 145 is connected to the shank body 138 by a neck 147 and extends upwardly therefrom.

The sphere 107 has an outer generally spherical or at least partially spherical shaped surface 150 that is sized and shaped to be snugly, but rotatably received in the hemispherical seat 126. The sphere 107 has a radial non passthrough bore 155 sized and shaped to snugly, but initially slidably receive the shank capture end 144.

The sphere 107 includes a pair of side opposed bores 157 and 158 which are diagonally aligned and which intersect with and open into the bore 155 so as to be perpendicular thereto. Furthermore, the sphere 107 has an upper drive bore 159 that is coaxial with the bore 155 and that has a polyhedral shaped interior surface 160 that is sized and shaped to receive an allen type driving tool or other suitably shaped tool for driving the shank 106 into the vertebra 101, as described below.

The closure 108 is seen in FIGS. 20 and 21 and is a “slide in” type device. The purpose of the closure 108 is to close the channel 120 and to secure the rod member 110 in the channel 120 and against movement relative to the head 105. The closure 108 includes a block or saddle 165 with a lower cylindrically shaped surface 166 that is sized and shaped to snugly mate with the rod member 100.

Located on opposite ends of the saddle 165 are a pair of upwardly extending ears 168 that are sized and shaped to be slidingly received in the head channels 134. The ears 168 are spaced from a body 169 of the saddle 165 by respective channels 170 that are curved and sized and shaped to slidingly receive the ears 132 of the head arms 116 and 117. In this manner the ears 132 and 168 overlap when the closure 108 is in the head 105 to resist outward splaying of the arms 116 and 117.

The central body 169 of the closure 108 includes an axially aligned pass through and threaded bore 180. The bore 180 receives a break-off set screw 183 that has a base 184 and a break-off head 185.

The bone screw 100 parts are assembled and used in the following manner. As is seen between FIGS. 9 and 14, the shank upper portion or capture end 144 is inserted through the lower side of the lower side of the head 105 and so as to extend into the chamber 122, while the sphere 107 is inserted or loaded through the channel 120 toward the cavity or chamber 122. The shank upper portion 144 is inserted into the sphere bore 155. While the sphere 107 is maintained raised or in the upper portion of the head 105, a crimping or deforming tool 190 is utilized to deform the shank 106 relative to the sphere 107, so as to lock or secure both to one another. In particular, the tool 190 has arms 191 that can be biased by a scissors action or the like toward one another and a pair of lower cylindrical shaped studs 192 ending in points. The studs 192 are sized and shaped to be inserted through opposed sides of the channel 120 and simultaneously through the side bores 157 and 158 respectively in the sphere 107 so as to engage the shank capture end 144. Pressure is then applied through the studs 192 against the shank 106 so as to produce a deformation 193 that frictionally engages and interferes with the sphere 107 and thereafter prevents removal of the sphere 107 from the shank 106. While deformation is used herein to secure the retainer sphere to the shank, it is also foreseen that the same could be accomplished by threading the parts and screwing them together, by inserting a pin through the parts, by using cleats interlocking with receivers, by welding, by adhering, or by any other suitable mechanism or composition.

After the sphere 107 is assembled onto the shank 106, a driving tool 197 with a driving head 198 that is sized and shaped to fit the sphere drive bore 159 is used to drive the assembled parts into a bone, such as the illustrated vertebra 102 shown in FIG. 18.

Thereafter, a rod member is inserted into the channel 120. An upper portion of the sphere 107 extends upwardly into the channel 120 such that it is engaged by the rod member 110. The closure 108 is then slid sideways while saddling over the rod member 110 so that the closure ears 168 seat in the head channels 134 inside the head ears 132 and thereby lock the arms 116 and 117 against outward splaying.

The set screw 183 is then inserted into the closure bore 180 and torqued until a preselected torque is reached at which time the set screw head 185 breaks from the body 184, as seen in FIG. 20.

At this time, the set screw 184 exerts pressure against the rod member 110 which in turn exerts pressure against the sphere 107 so that the sphere 107 and attached shank 106 are frictionally locked in place relative to the head 105. In particular, before the set screw 184 is tightened, the head 105 can be rotated or swivelled relative to the shank 106 and sphere 107 assemblage, so as to find an optimal position for insertion of the rod member 110. After the set screw 184 is tightened, the shank 106 and sphere 107 assemblage is locked in position relative to the head 105.

The bone screw 100 can be removed by removing the set screw base 184 after which the closure 108 can be taken from the head 105. The rod member 110 can then be removed from the head 105 and the shank 106 unscrewed from the vertebra 102.

It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.

Claims

1. A pivotal bone anchor assembly for securing an elongate rod to a bone via a closure top, the pivotal bone anchor assembly comprising:

a shank having longitudinal axis and a capture end opposite a threaded end, the capture end having a partial spherical outer surface;

a receiver having a top portion with a unitary base, the top portion configured to receive the elongate rod in an upper channel, the base including a cavity communicating with the upper channel and with a bottom of the receiver through a lower opening, the cavity at least partially defined by a partial spherical lower mating surface; and

a retainer positionable within the receiver cavity and having a partial spherical outer surface that is at least partially mateable with the receiver cavity partial spherical lower mating surface, the retainer configured to capture the shank capture end upon uploading of the shank capture end through the receiver lower opening, with at least a portion of the shank capture end partial spherical outer surface extending above a top surface of the retainer after capture by the retainer,

wherein after the shank capture end is captured by the retainer, the shank is independently rotatable around the shank longitudinal axis relative to the retainer and the retainer is pivotable in at least one plane with respect to the receiver prior to the closure being locked by the closure top.

2. The pivotal bone anchor assembly of claim 1, wherein the receiver cavity includes an upper larger portion sized and shaped to allow expansion of the retainer during the capture of the shank capture end.

3. The pivotal bone anchor assembly of claim 1,

wherein the receiver cavity further comprises a first region at least partially defined by the partial spherical lower mating surface and a second region being larger than the first region and located axially above the first region, and

wherein an uploading of the shank capture end through the receiver lower opening causes the retainer to resiliently expand around the shank capture end, with such expansion operably occurring in the second region to capture the shank capture end, thereafter the shank capture end and retainer being movable downward into the first region and configured for pivotal engagement between the retainer and the receiver cavity partial spherical lower mating surface.

4. The pivotal bone anchor assembly of claim 1, wherein the retainer is configured to snap on and capture the shank capture end during an upward movement of the shank capture end within the receiver cavity.

5. The pivotal bone anchor assembly of claim 1, wherein after the shank capture end is captured by the retainer, the retainer is configured to pivot in multiple planes relative to the receiver during positioning of the shank within the assembly.

6. The pivotal bone anchor assembly of claim 1, wherein the retainer is downloaded into the receiver cavity through the upper channel prior to uploading the shank capture end through the receiver lower opening.

7. The pivotal bone anchor assembly of claim 1, wherein the retainer further comprises a resilient retaining ring having a slit or slot.

8. The pivotal bone anchor assembly of claim 1, wherein the retainer further comprises an inner surface having a diameter between the top surface and a bottom surface of the retainer, the diameter of the inner surface decreasing toward the bottom surface of the retainer.

9. The pivotal bone anchor assembly of claim 1, wherein the retainer is spaced from the elongate rod when the elongate rod is received within the receiver upper channel.

10. The pivotal bone anchor assembly of claim 1, wherein the retainer is axially rotatable around a receiver longitudinal axis when the retainer is engage with the receiver partial spherical lower mating surface and prior to the assembly by the closure top.

11. The pivotal bone anchor assembly of claim 1, wherein the retainer further comprises an inner surface between the top surface and a bottom surface of the retainer devoid of horizontally extending ridges, recesses and edges, the inner surface configured to snap on and engage with a external surface of the shank capture end that is also devoid of horizontally extending ridges, recesses and edges.

12. The pivotal bone anchor assembly of claim 11, wherein the external surface of the shank capture end is spaced below the partial spherical outer surface.

13. The pivotal bone anchor assembly of claim 1, wherein the partial spherical outer surface of the shank capture end further comprises a dome surface centered about the shank longitudinal axis.

14. The pivotal bone anchor assembly of claim 1, wherein the shank capture end has a driving structure formed therein.

15. The pivotal bone anchor assembly of claim 1, wherein the shank includes a neck adjacent the capture end having an outer curvilinear circumferential surface.

16. The pivotal bone anchor assembly of claim 1, wherein the shank is cannulated along an entire length thereof.

17. The pivotal bone anchor assembly of claim 1, wherein when the shank capture end is capture by the retainer, the capture end is prevented from being moved up out of the retainer by an upward-facing surface on the capture end being in overlapping engagement with a surface on the retainer.

18. The pivotal bone anchor assembly of claim 1, further comprising the closure top, and wherein a downward force to lock a position of the shank relative to the receiver is provided by the closure top bearing down on a top surface of the elongate rod.

19. A pivotal bone anchor assembly for securing an elongate rod to a bone via a closure top, the pivotal bone anchor assembly comprising:

a shank comprising a threaded body adapted to be implanted into the bone and a capture end at an upper end of the threaded body;

a receiver having a longitudinal axis, an upper channel adapted to receive the elongate rod, a lower opening configured to receive the shank capture end therethrough, and a cavity communicating with the upper channel and the lower opening, the upper channel, the cavity, and the lower opening being in axial alignment centered on the longitudinal axis; and

a resilient retainer non-integral with the shank and sized and shaped to be located during use in the receiver cavity and having an outer radius that is larger than a radius of the lower opening, the retainer configured to resiliently expand around the shank capture end and thereafter capture the shank capture end in the receiver cavity, the shank capture end having an upwardly extending portion opposite the shank body that extends above the retainer, the upwardly extending portion configured for engagement by a driving tool,

wherein the retainer pivots with respect to the receiver after the shank capture end is captured by the retainer in the receiver cavity and prior to locking a position of the shank relative to the receiver via the closure top.

20. The pivotal bone anchor assembly of claim 19, wherein the shank capture end is axially rotatable in the retainer after the shank capture end is captured by the retainer in the receiver cavity and prior to locking a position of the shank relative to the receiver via the closure top.

21. The pivotal bone anchor assembly of claim 19, wherein the retainer is configured to snap on and capture the shank capture end during an upward movement of the shank capture end within the receiver cavity.

22. The pivotal bone anchor assembly of claim 19, wherein the receiver cavity includes an upper larger portion sized and shaped to allow expansion of the retainer during the capture of the shank capture end.

23. The pivotal bone anchor assembly of claim 19, wherein the retainer is downloaded into the receiver cavity through the upper channel prior to uploading the shank capture end through the receiver lower opening.

24. The pivotal bone anchor assembly of claim 19, wherein the retainer further comprises a resilient retaining ring having a slit or slot.

25. The pivotal bone anchor assembly of claim 19, wherein the retainer is spaced from the elongate rod when the elongate rod is received within the upper channel and secured via the closure top.

26. A pivotal bone anchor assembly for securing an elongate rod to a bone via a closure top, the pivotal bone anchor assembly comprising:

a receiver of unitary construction including a top portion and a base, the top portion configured to receive the elongate rod in an upper channel, the base including a cavity communicating with the upper channel and with a bottom of the receiver through a lower opening, the cavity at least partially defined by a radiused lower seating surface, with at least a portion of the radiused lower cavity seating surface adjacent to and surrounding the lower opening;

a shank having a threaded end opposite a capture end, the capture end being sized and shaped to be received into the receiver cavity through the receiver lower opening; and

a resiliently expandable retainer positionable within the receiver cavity separate from the shank, the retainer sized and shaped to resiliently receive and thereafter contractibly capture the shank capture end in the receiver cavity, the retainer having a radiused outer surface that is sized and shaped to be rotatably received on the radiused lower seating surface of the receiver cavity to provide pivotal motion between the retainer and the receiver cavity in at least one plane during positioning of the shank relative to the receiver,

wherein an upper portion of the shank capture end projects above the retainer when the capture end is captured in the receiver cavity by the retainer, and

wherein the shank is rotatable about a shank longitudinal axis with respect to and independent of the retainer after being captured in the receiver cavity by the retainer and prior to the assembly being locked via the closure top.

27. The pivotal bone anchor assembly of claim 26, wherein the retainer is configured to snap on and capture the shank capture end during an upward movement of the shank capture end within the receiver cavity.

28. The pivotal bone anchor assembly of claim 26, wherein the receiver cavity includes an upper larger portion sized and shaped to allow expansion of the retainer during the capture of the shank capture end.

29. The pivotal bone anchor assembly of claim 26, wherein the retainer is downloaded into the receiver cavity through the upper channel prior to uploading the shank capture end through the receiver lower opening.

30. The pivotal bone anchor assembly of claim 26, wherein the retainer further comprises a resilient retaining ring having a slit or slot.

31. The pivotal bone anchor assembly of claim 26, wherein the retainer is spaced from the elongate rod when the elongate rod is received within the receiver upper channel.

32. The pivotal bone anchor assembly of claim 26, further comprising the closure top, and wherein a downward force to lock a position of the shank relative to the receiver is provided by the closure top bearing down on a top surface of the elongate rod.

33. The pivotal bone anchor assembly of claim 26, wherein the shank capture end has a driving structure formed therein.

34. The pivotal bone anchor assembly of claim 26, wherein the shank is cannulated along an entire length thereof.