US20110054546A1 - Polyaxial Pedicle Screw Assembly - Google Patents

Abstract

A pedicle fixation assembly and method for assembly comprises a screw head comprising a male bulbous end; a bone fixator component comprising a female concave semi-spherical socket for receiving the screw head; a locking saddle pin for engaging the screw head and the bone fixator component; and a blocker for engaging the screw head and for securing the longitudinal member.

Description

CROSS REFERENCE TO RELATED APPLICATION
• This application is a continuation of U.S. Utility patent application Ser. No. 11/045,908 filed Jan. 28, 2005, which claims the benefit of U.S. Provisional Patent Application No. 60/548,543 filed on Feb. 27, 2004 and U.S. Provisional Patent Application No. 60/565,658 filed on Apr. 27, 2004, whereby the contents of all three applications, in their entireties, are herein incorporated by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The embodiments of the invention generally relate to medical devices and assemblies, and more particularly to an orthopedic surgical implant assembly used in the field of surgical lumbar, thoracic and cervical spine treatment.
• 2. Description of the Related Art
• Surgical procedures treating spinal injuries are one of the most complex and challenging surgeries for both the patient and the surgeon. When there are various deformities, trauma, or fractures of the vertebra, surgeons may attempt to “fuse” them together by attaching screw-like devices into the pedicles of the spine and thereby connecting several vertebrae (typically two or more) using a semi-rigid rod. However, due to the complexity of the human anatomy, most surgeons must bend the rod (causing notches thereby reducing fatigue resistance) before placing them into two or more non-aligned pedicle screws in order to properly stabilize the pedicle screw assembly within the patient's body.
• Depending on the purpose of the spine surgery, indications, and patient size, surgeons must pre-operatively choose between different spinal systems with differing rod sizes pre-operatively sometimes causing delays in surgery while waiting for more adequate systems to be sterilized. Some surgeons prefer monoaxial screws for rigidity, while some sacrifice rigidity for surgical flexibility in screw placement. Therefore, a system is needed to accommodate both theories. For example, during scoliosis surgery conventional polyaxial systems typically cannot lock into a desired position to persuade the spinal column into desired correction before final construct assembly.
• Most conventional top loading polyaxial spine screws do not do enough to address cantilever failure of the assembly components. Additionally, most polyaxial screws generally do not offer enough flexibility because the rod sits too closely on top of the center of rotation. Furthermore, most top loading screw systems generally do not accommodate different rod sizes. Thus, there remains a need for a new and improved pedicle screw assembly capable of overcoming the limitations of the conventional designs thereby providing the surgeon with improved intra-operative flexibility and the patient with an improved prognosis for better and complete rehabilitation.
SUMMARY OF THE INVENTION
• In view of the foregoing, an embodiment of the invention provides an assembly comprising a screw head comprising a bulbous end; a fixator component configured for receiving the bulbous end of the screw head; a pin mounted in the screw head; and a blocker adapted to engage the screw head. The screw head comprises a slot configured for receiving a longitudinal member. The fixator component comprises a concave socket configured for receiving the bulbous end of the screw head. In one embodiment, the fixator component comprises a threaded end opposite the concave socket and configured for attaching to a bone. Preferably, the pin engages the fixator component and a bottom portion of the longitudinal member. Preferably, the blocker secures a top portion of the longitudinal member.
• Preferably, the pin comprises an upper saddle portion and a lower tip portion. Additionally, according to one embodiment, the pin comprises a multi-part assembly. The pin may be made of one part that may be coated or it can be made of two parts (an upper and lower portion) comprising different materials, with the lower portion comprising a mechanically harder material than the upper portion. The screw head and the fixator component comprise a first material, and the lower tip portion of the pin comprises a material having a higher material hardness and compressive yield strength than the first material. The assembly may further comprise a wear resistant ceramic coating over the screw head and the fixator component.
• Preferably, the screw head further comprises two opposed upright ends separated by the slot, wherein each of the opposed upright ends comprise an inner wall and an outer wall, wherein the inner wall comprises wall threads, and wherein the outer wall comprises grooves. Preferably, the blocker comprises blocker threads configured around an outer perimeter of the blocker, the blocker threads being dimensioned and configured to mate with the wall threads. The upper saddle portion of the pin may comprise a slot or slots. The bulbous end of the screw head may comprise a plurality of slots terminating at an opening at a tip of the bulbous end. Moreover, the bulbous end of the screw head preferably comprises a gap configured to receive the pin. The concave socket of the fixator component comprises an inner portion adapted to receive the bulbous end of the screw head; and preferably a dimpled outer portion or other geometries. Preferably, the fixator component comprises any of a bone screw and a hook.
• Another aspect of the invention provides a pedicle fixation assembly comprising a screw head comprising a male bulbous end; a bone fixator component comprising a female concave semi-spherical socket for receiving the screw head; a locking saddle pin for engaging the screw head and the bone fixator component; and a blocker for engaging the screw head and for securing the longitudinal member.
• Still another aspect of the invention provides a method of assembling a pedicle fixation assembly, wherein the method comprises attaching a screw head to a bone fixator component; securing the bone fixator component in a bone; securing a locking pin in the screw head; engaging the locking pin with the bone fixator component; inserting a longitudinal member in the screw head; and inserting a blocker in the screw head, wherein the screw head comprises a male bulbous end and the bone fixator component comprises a female concave semi-spherical socket for receiving the screw head. Preferably, the method further comprises coating the screw head and the bone fixator component with a wear resistant ceramic coating. The bone fixator component may be configured as any of a bone screw and a hook.
• The embodiments of the invention provide a pedicle screw assembly implant device, which may be used anteriorly or posteriorly, and which is capable of being utilized in surgeries to achieve anterior lumbar interbody fusion, posterior lumbar interbody fusion, transverse lumbar interbody fusion, correct degenerative disc disease, adult and pediatric scoliosis as a fixation device, and posterior cervical fusion.
• The embodiments of the invention provide a polyaxial spinal screw that can become rigid similar to a monoaxial screw inter-operatively on demand. The embodiments of the invention also offer the surgeon more lateral range of motion than conventional products by utilizing the space under the screw head to provide a bigger arc of rotation. Moreover, the saddle pin component offers the flexibility to use a diametrical range of spinal rods instead of a fixed size rod.
• These and other aspects of the embodiments of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments of the invention and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments of the invention without departing from the spirit thereof, and the embodiments of the invention include all such modifications.
BRIEF DESCRIPTION OF THE DRAWINGS
• The embodiments of the invention will be better understood from the following detailed description with reference to the drawings, in which:
• FIG. 1 illustrates an exploded view of the screw assembly according to an embodiment of the invention;
• FIG. 2 illustrates an exploded view of the screw assembly during a step in the manufacturing according to an embodiment of the invention;
• FIG. 3 illustrates an exploded view of the screw assembly during a step in the manufacturing according to an embodiment of the invention;
• FIG. 4 illustrates an exploded view of the screw assembly during a step in the manufacturing according to an embodiment of the invention;
• FIG. 5 illustrates a perspective view of the fully assembled screw assembly in a monoaxial position according to an embodiment of the invention;
• FIG. 6 illustrates a perspective view of the fully assembled screw assembly in a polyaxial position according to an embodiment of the invention;
• FIG. 7 is a partial internal view of the screw assembly in a monoaxial position according to an embodiment of the invention;
• FIG. 8 is a partial internal view of the screw assembly in a polyaxial position according to an embodiment of the invention;
• FIGS. 9A through 9H are isolated views of the screw head according to an embodiment of the invention;
• FIG. 10A is a perspective view of a bone fixator assembly according to a second embodiment of the invention;
• FIG. 10B is a detailed view of the hook of the bone fixator assembly ofFIG. 10A according to the second embodiment of the invention;
• FIGS. 11A through 11B are detailed views of the saddle pin according to a first embodiment of the invention;
• FIGS. 12A through 12B are detailed views of the saddle pin according to a second embodiment of the invention;
• FIGS. 13 through 14aare detailed views of the saddle pin according to a third embodiment of the invention;
• FIGS. 15A through 15C are detailed views of the blocker according to an embodiment of the invention; and
• FIG. 16 is a flow diagram illustrating a preferred method according to an embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
• The embodiments of the invention and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. It should be noted that the features illustrated in the drawings are not necessarily drawn to scale. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments of the invention. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments of the invention may be practiced and to further enable those of skill in the art to practice the embodiments of the invention. Accordingly, the examples should not be construed as limiting the scope of the embodiments of the invention.
• As mentioned, there remains a need for a new and improved pedicle screw assembly capable of overcoming the limitations of the conventional designs thereby providing the surgeon with improved intra-operative flexibility and the patient with an improved prognosis for better and complete rehabilitation. The embodiments of the invention address this need by providing an improved polyaxial pedicle screw device and method of assembly capable of accommodating multiple rod diameters and withstanding higher failure strengths. Referring now to the drawings and more particularly toFIGS. 1 through 16 where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments of the invention.
• FIGS. 1 through 6 provide an exploded view of thepedicle screw assembly1 according to a first embodiment of the invention. Thescrew assembly1 comprises a bone screw (fixator component)10 having a threadedend11 for engaging a bone (not shown) and a concavefemale socket end12 for engaging and receiving thescrew head20.
• As implemented, thescrew head20 is first snapped into place in thebone screw10 as shown inFIG. 2. Then, as shown inFIGS. 3 and 9B, thesaddle pin30 snaps into place in thelower base portion25 of thescrew head20, which includes a groove26 (best seen inFIG. 7) for receiving thesaddle pin30. In the manufacturing process, once thesaddle pin30 snaps into place, thescrew assembly1 is prepared for ultra sonic cleaning to remove any impurities and subsequently may be shipped in this manufactured format (with thesaddle pin30 connected to thescrew head20, which is connected to the bone screw10).
• FIG. 7 shows that the femalespherical socket12 of thebone screw10 has an undercut7 to allow thescrew head20 to pivot freely but not to disassemble once thesaddle pin30 is inserted. Thethread11 of thebone screw10 may be a multiple lead thread to allow faster insertion into a bone. Thisthread11 may be tapered on the minor diameter while cylindrical on the major diameter to allow a new “bite” with every turn and to accommodate more thread depth towards the bottom of thebone screw10 for the cancellous bone.
• Once thebone screw10 is inserted into the bone, alongitudinal member50, which may be embodied as a rod, bar, etc. andblocker40 are inserted into thescrew assembly1, as illustrated inFIG. 4. Thescrew head20 can accommodate 5.5 mm as well as 6.0 mm rods, which is advantageous over conventional screw assemblies that are limited to accepting only rods of a uniform dimension.FIG. 5 illustrates the assembled view of thescrew assembly1 in the straight monoaxial direction. Thethreads11 of thebone screw10 are double lead, which provides greater surface contact with the bone, but drives at 4 mm/revolution.FIG. 6 illustrates thescrew assembly1 in a rotationally articulated position. The maximum angulation is 25 degrees/side, but the medial correction/travel of thelongitudinal member50 is 3.8 mm/side, which is nearly twice of what most conventional screws offer.
• InFIG. 7, the locking mechanism of thescrew assembly1 is illustrated. Here, a two step locking process is shown. The first position expands thescrew head20 into thebone screw10, and the second position permanently turns thepolyaxial screw assembly1 into amonoaxial screw assembly1 by using thesaddle pin30 to lock theassembly1. AsFIG. 8 demonstrates, thescrew assembly1 can be permanently locked in any desired position (within the 25 degree guideline) simply by sending thelongitudinal member50 “home” or by using a tool (not shown) to lock theassembly1 at the desired angle.
• FIG. 9A illustrates the overall configuration of thescrew head20.FIG. 9B illustrates a front view of thescrew head20.FIG. 9C is a cross-sectional view from cut-line “CC” ofFIG. 9D.FIG. 9E is a cross-sectional view from cut-line “BB” ofFIG. 9F and FIG.9G is a cross-sectional view from cut-line “AA” ofFIG. 9F. Additionally,FIG. 9H is an enlarged detailed view of the encircled area “A” ofFIG. 9G illustrating the threadedinner portion23 in more detail. As shown inFIGS. 9A through 9H, thescrew head20 includes a bulbous (spherical)male end21 for engaging the concavefemale socket12 of thebone screw10. Thescrew head20 also includes a pair of upright ends22 opposite the bulbousmale end21, wherein the upright ends22 comprise a threadedinner portion23 for engaging theblocker40. Furthermore, thescrew head20 includes a generally open U-shapedinner portion24 for receiving thesaddle pin30 and thelongitudinal member50. Themale end21 of thescrew head20 includes a plurality (for example, four or more)slots6 that allow themale end21 to expand into the femalespherical socket12 of thebone screw10 at any allowable angle once thesaddle pin30 is forced through.
• Since thescrew head20 is pivoting inside thefemale socket end12 of thebone screw10, theassembly1 is allowed to be inserted deeper into the bone without having the bone or anatomy prematurely limit the range of angulations of thescrew head20. Thescrew head20 further includes external features orcuts29 that assist in accommodating surgical instrumentation during manipulation and assembly during the surgical procedure. Thesecuts29 allow various instruments (not shown) to firmly and positively hold and manipulate thescrew head20 on one side or both sides ofscrew head20.
• FIG. 10A is a perspective view of a bone fixator assembly according to a second embodiment of the invention, wherein the bone fixator component is configured as ahook60. Thehook60 is further illustrated inFIG. 10B. Thehook60 includes aconcave socket12 having aninner portion9 adapted to receive thebulbous end21 of thescrew head20; and a dimpled outer portion8. Thehook60 further includes a pair ofarms61,62 connected by aconnection arm64. Aspace63 separates thearms61,62 from one another. Thearms61,62 are configured to receive an additional member (not shown) for subsequent attachment to the bone.
• The several embodiments of thesaddle pin30 are shown inFIGS. 11A through 14. Thesaddle pin30 provides a proper seat for thelongitudinal member50 and avoids notching a typical titanium longitudinal member50 (titanium is very notch sensitive). Furthermore, thesaddle pin30 allows one to accommodate multiple sizes oflongitudinal members50 in the samescrew assembly system1 which is a first for a titanium system because of the above-mentioned notching factors. Thesaddle pin30 is configured with aslot32 through the center to allow expansion of the upper portion (head)131 of thesaddle pin30. The bottom35 of thesaddle pin head131 is angled to allow thesaddle pin30 to accept a larger-sizedlongitudinal member50. Thesaddle pin30 initially expands themale sphere21 of thescrew head20 into the femalespherical socket12 in thebone screw10 causing thescrew assembly system1 to lock or start locking (i.e., causing themale sphere21 of thescrew head20 to lock in the femalespherical socket12 of the bone screw10). Thesaddle pin30 then “digs” into the femalespherical socket12 of thebone screw10 to provide a secondary locking force to avoid bending failure of theassembly1.
• FIGS. 11A through 11B illustrate a first embodiment of thesaddle pin30. Thesaddle pin30 generally includes anupper portion131 and alower portion132. The upper portion includes aslot32, which is configured from thelowest area33 of theupper portion131 into theupper area34 of thelower portion132 of thesaddle pin30. Asecondary locking mechanism36 may be configured on thelower portion132 of the saddle pin to further achieve locking of thesaddle pin30 once it is inserted in thescrew head20. Thelower portion132 of thesaddle pin30 terminates with apointed end37 to allow for digging into thefemale socket12 of thebone screw10.FIGS. 12A through 12B illustrate a second embodiment of thesaddle pin30. The difference between the first and second embodiments of thesaddle pin30 is that the upper portion of thesaddle pin131 in the second embodiment includes two generally flat upper opposed ends38 to more matingly configure with the geometry of thescrew head20 and thelongitudinal member50.
• FIGS. 13 through 14 illustrate a third embodiment of thesaddle pin30. In particular, in the third embodiment, thesaddle pin30 comprises two parts: anupper portion131 preferably comprising titanium and alower portion132 which is preferably ceramic. According to the third embodiment, the material of thelower portion132 of thesaddle pin30 is preferably ceramic and has a higher hardness and compressive yield strength than the comparative hardness and compressive yield strength of Ti₆Al₄V, which is the material which may be used in constructing thescrew head20 andbone screw10.
• As shown inFIG. 13, theupper portion131 of thesaddle pin30 includes aslot32 in theseat portion133 and tapered angled ends134. Preferably, thesaddle pin30; i.e., theupper portion131 and theceramic tip132 are assembled last in the overall process. Specifically, thescrew head20 snaps into thebone screw10. Then, theceramic tip132 slides into thescrew head20, and finally the titanium saddle (upper portion)131 is press fitted into thescrew head20 keeping everything in place and oriented in a relaxed state.
• As best seen inFIG. 14, thelower portion132 of the saddle pin terminates with a series of cascading walls137,138 having sloped angles, terminating with thepointed end37 for attachment into thescrew head20/bone screw10 assembly. The material properties of thesaddle pin tip132 are such that it prevents the deformation on thesaddle pin30 before thesaddle pin30 gives the proper bending and penetrating effects onto thescrew head20/bone screw10 assembly. Examples of the types of materials used for the saddle pin pointedend37 include Zyranox™ and HIP Vitox™, both of which are available from Morgan Advanced Ceramics, United Kingdom.
• Theblocker40, which is further illustrated inFIGS. 15A through 15C, includes a standard buttressthread41 configured along an outer perimeter of theblocker40. Theblocker40 helps to secure thelongitudinal member50 inside thescrew head40. Thethreads41 of theblocker40 are configured to engage thethreads23 of thescrew head20. Additionally, theblocker40 aids in preventing the expansion of thescrew head20 when torqued on thelongitudinal member50, directing the counterforce more vertically than horizontally. The top42 of theblocker40 has afastening feature43 such as a hex or square lock feature to allow high torque to be applied in locking theassembly1. Furthermore, theblocker40 may be configured with a free rotating saddle (not shown) to accommodate, via tangential contact, thelongitudinal member50 and help to further prevent notching of the titanium alloy used to construct thelongitudinal member50. Moreover, theblocker40 may have a “timed”thread41 that is consistently and precisely related to the blocker driving tool (not shown) to help calculate the torsional and vertical position of theblocker40 thereby assisting the torque measurement applied to theblocker40.
• Another aspect of the invention is illustrated in the flowchart ofFIG. 16, which includes descriptions which refer to components provided inFIGS. 1 through 15C.FIG. 16 illustrates a method of assembling apedicle screw assembly1, wherein the method comprises attaching (200) ascrew head20 to abone fixator component10; securing (210) thebone fixator component10 in the bone (not shown); securing (220) asaddle pin30 in thescrew head20; engaging (230) thesaddle pin30 with thebone fixator component10; inserting (240) alongitudinal member50 in thescrew head20; and inserting (250) ablocker40 in thescrew head20. As mentioned, the embodiments of the invention provide an axial movement of the screw head up to 25 degrees in any plane. Moreover, the embodiments of the invention allow for greater medial translation of the longitudinal member50 (nearly 4 mm compared to the conventional devices which are generally limited to 2 mm).
• Moreover, according to an aspect of the invention, theinventive assembly1 can be used as a dynamic rod system to complement artificial discs. According to this embodiment, the outside of the sphericaljoint part21 of thescrew head20 and the innerspherical surface9 of thebone screw cup12 are coated with a wear resistant ceramic coating. In this scenario, thesaddle pin30 is not digging into thebone screw10 and in fact is configured at a shorter length than some of the other embodiments. This system allows some motion instead of rigid fixation and shares the load with the artificial disc disallowing excessive forces being applied to the artificial disc and increasing its functional life. For example, this occurs as a result of the ceramic coating, which may be used in the embodiments of the invention. As such, the spherical joint21 of thescrew head20 and the innerspherical surface12 of thebone screw10 have lower friction and higher wear resistance characteristics, thus improving the overall characteristics of thescrew assembly1.
• Generally, as shown inFIG. 1 through 15C, the embodiments of the invention provide anassembly1 comprising ascrew head20 comprising abulbous end21; afixator component10 configured for receiving thebulbous end21 of thescrew head20; apin30 mounted in thescrew head20; and ablocker40 adapted to engage thescrew head20. Thescrew head20 comprises aslot24 configured for receiving alongitudinal member50. Thefixator component10 comprises aconcave socket12 configured for receiving thebulbous end21 of thescrew head20. In a first embodiment, thefixator component10 also comprises a threadedend11 opposite theconcave socket12 and configured for attaching to a bone. Thepin30 engages thefixator component10 and abottom portion51 of thelongitudinal member50. Theblocker40 secures atop portion52 of thelongitudinal member50. Thepin30 comprises anupper saddle portion131 and alower tip portion132.
• Additionally, thepin30 may comprise a multi-part assembly. Theupper saddle portion131 of thepin30 comprises titanium and thelower tip portion132 of thepin30 comprises a ceramic material. Moreover, thelower tip portion132 comprises a mechanically harder material than theupper saddle portion131. Thescrew head20 and thefixator component10 comprise a first material, and thelower tip portion132 of thepin30 comprises a material having a higher material hardness and compressive yield strength than the first material. Theassembly1 further comprises a wear resistant ceramic coating (not shown) over thescrew head20 and thefixator component10.
• Thescrew head20 further comprises two opposed upright ends22 separated by theslot24, wherein each of the opposed upright ends22 comprise aninner wall27 and anouter wall28, wherein theinner wall27 compriseswall threads23, and wherein theouter wall28 comprises grooves (cuts)29. Theblocker40 comprisesblocker threads41 configured around anouter perimeter42 of theblocker40, theblocker threads41 being dimensioned and configured to mate with thewall threads23. Theupper saddle portion131 of thepin30 comprises aslot32. Thebulbous end21 of thescrew head20 comprises a plurality ofslots6 terminating at anopening4 at a tip3 of thebulbous end21. Moreover, thebulbous end21 of thescrew head20 comprises agap19 configured to receive thepin30. Theconcave socket12 of thefixator component10 comprises aninner portion9 adapted to receive thebulbous end21 of thescrew head20; and a dimpled outer portion8. Thefixator component10 is configured as any of a threaded bone screw10 (as shown inFIGS. 1 through 8) and a hook60 (as shown inFIGS. 10A and 10B) according to the several embodiments of the invention.
• The embodiments of the invention provide a pedicle screwassembly implant device1, which may be used anteriorly or posteriorly, and which is capable of being utilized in surgeries to achieve anterior lumbar interbody fusion, posterior lumbar interbody fusion, transverse lumbar interbody fusion, correct degenerative disc disease, adult and pediatric scoliosis as a fixation device, and posterior cervical fusion.
• Moreover, the embodiments of the invention provide a polyaxialspinal screw assembly1 that can become rigid similar to a monoaxial screw inter-operatively on demand. The embodiments of the invention also offer the surgeon more lateral range of motion than conventional products by utilizing the space under thescrew head20 to provide a bigger arc of rotation. Moreover, thesaddle pin30 component offers the flexibility to use a diametrical range of spinallongitudinal members50 instead of a fixed size longitudinal member.
• The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments of the invention have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments of the invention can be practiced with modification within the spirit and scope of the appended claims.

Claims (20)

What is claimed is:

1. A pedicle screw assembly comprising:

a screw head comprising a slot and a bottom portion;

a connecting end operatively connected to said bottom portion of said screw head;

a bone fixator component comprising a socket that receives said connecting end;

means for causing engagement of said connecting end to said bone fixator component; and

a blocker that engages said screw head.

2. The pedicle screw assembly ofclaim 1, wherein a combination of said bottom portion of said screw head with said connecting end form a substantially bulbous body.

3. The pedicle screw assembly ofclaim 1, wherein said bone fixator component is located completely outside of said screw head.

4. The pedicle screw assembly ofclaim 1, wherein said bottom portion of said screw head and said connecting end are locked into said socket of said bone fixator component.

5. The pedicle screw assembly ofclaim 1, wherein said screw head comprises at least one upright end adjacent to said slot.

6. The pedicle screw assembly ofclaim 5, wherein said screw head comprises:

a lower base portion adjacent to said at least one upright end; and

an aperture extending from said lower base portion through said connecting end.

7. The pedicle screw assembly ofclaim 2, wherein substantially bulbous body is rotatable with respect to said socket.

8. An assembly comprising:

a slotted screw head comprising a substantially bulbous body extending away from a bottom portion of said slotted screw head;

a hole in said slotted screw head and extending through said substantially bulbous body;

a bone engaging component comprising a socket that cups said substantially bulbous body; and

means for causing outward expansion of said substantially bulbous body.

9. The assembly ofclaim 8, wherein said bone engaging component is located completely outside of said slotted screw head.

10. The assembly ofclaim 8, wherein said substantially bulbous body is locked into said socket of said bone engaging component.

11. The assembly ofclaim 8, wherein said slotted screw head comprises at least one upright end pointing away from said substantially bulbous body.

12. The assembly ofclaim 11, wherein said slotted screw head comprises:

a lower base portion adjacent to said at least one upright end; and

an aperture extending from said lower base portion through said substantially bulbous body.

13. The assembly ofclaim 8, wherein substantially bulbous body is rotatable with respect to said socket.

14. An assembly comprising:

a bone engaging component comprising a socket; and

a screw head comprising a stem portion extending from a bottom of said screw head and fits inside said socket.

15. The assembly ofclaim 14, further comprising means for locking said stem portion inside said socket.

16. The assembly ofclaim 14, wherein said stem portion is located completely outside of said screw head.

17. The assembly ofclaim 14, wherein said screw head is rotatable with respect to said bone engaging component.

18. The assembly ofclaim 14, wherein said screw head comprises:

at least one upright end positioned opposite to said stem portion;

a lower base portion adjacent to said at least one upright end; and

an aperture extending from said lower base portion through said stem portion.

19. The assembly ofclaim 18, further comprising a pin dimensioned and configured to fit in said aperture.

20. The assembly ofclaim 14, wherein said stem portion is expandable.

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