Polyaxial Pedicle Screw Assembly

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

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 of FIG. 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 14 a are 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 to FIGS. 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 the pedicle screw assembly 1 according to a first embodiment of the invention. The screw assembly 1 comprises a bone screw (fixator component) 10 having a threaded end 11 for engaging a bone (not shown) and a concave female socket end 12 for engaging and receiving the screw head 20.

As implemented, the screw head 20 is first snapped into place in the bone screw 10 as shown in FIG. 2. Then, as shown in FIGS. 3 and 9B, the saddle pin 30 snaps into place in the lower base portion 25 of the screw head 20, which includes a groove 26 (best seen in FIG. 7) for receiving the saddle pin 30. In the manufacturing process, once the saddle pin 30 snaps into place, the screw assembly 1 is prepared for ultra sonic cleaning to remove any impurities and subsequently may be shipped in this manufactured format (with the saddle pin 30 connected to the screw head 20, which is connected to the bone screw 10).

FIG. 7 shows that the female spherical socket 12 of the bone screw 10 has an undercut 7 to allow the screw head 20 to pivot freely but not to disassemble once the saddle pin 30 is inserted. The thread 11 of the bone screw 10 may be a multiple lead thread to allow faster insertion into a bone. This thread 11 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 the bone screw 10 for the cancellous bone.

Once the bone screw 10 is inserted into the bone, a longitudinal member 50, which may be embodied as a rod, bar, etc. and blocker 40 are inserted into the screw assembly 1, as illustrated in FIG. 4. The screw head 20 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 the screw assembly 1 in the straight monoaxial direction. The threads 11 of the bone screw 10 are double lead, which provides greater surface contact with the bone, but drives at 4 mm/revolution. FIG. 6 illustrates the screw assembly 1 in a rotationally articulated position. The maximum angulation is 25 degrees/side, but the medial correction/travel of the longitudinal member 50 is 3.8 mm/side, which is nearly twice of what most conventional screws offer.

In FIG. 7, the locking mechanism of the screw assembly 1 is illustrated. Here, a two step locking process is shown. The first position expands the screw head 20 into the bone screw 10, and the second position permanently turns the polyaxial screw assembly 1 into a monoaxial screw assembly 1 by using the saddle pin 30 to lock the assembly 1. As FIG. 8 demonstrates, the screw assembly 1 can be permanently locked in any desired position (within the 25 degree guideline) simply by sending the longitudinal member 50 “home” or by using a tool (not shown) to lock the assembly 1 at the desired angle.

FIG. 9A illustrates the overall configuration of the screw head 20. FIG. 9B illustrates a front view of the screw head 20. FIG. 9C is a cross-sectional view from cut-line “CC” of FIG. 9D. FIG. 9E is a cross-sectional view from cut-line “BB” of FIG. 9F and FIG. 9G is a cross-sectional view from cut-line “AA” of FIG. 9F. Additionally, FIG. 9H is an enlarged detailed view of the encircled area “A” of FIG. 9G illustrating the threaded inner portion 23 in more detail. As shown in FIGS. 9A through 9H, the screw head 20 includes a bulbous (spherical) male end 21 for engaging the concave female socket 12 of the bone screw 10. The screw head 20 also includes a pair of upright ends 22 opposite the bulbous male end 21, wherein the upright ends 22 comprise a threaded inner portion 23 for engaging the blocker 40. Furthermore, the screw head 20 includes a generally open U-shaped inner portion 24 for receiving the saddle pin 30 and the longitudinal member 50. The male end 21 of the screw head 20 includes a plurality (for example, four or more) slots 6 that allow the male end 21 to expand into the female spherical socket 12 of the bone screw 10 at any allowable angle once the saddle pin 30 is forced through.

Since the screw head 20 is pivoting inside the female socket end 12 of the bone screw 10, the assembly 1 is allowed to be inserted deeper into the bone without having the bone or anatomy prematurely limit the range of angulations of the screw head 20. The screw head 20 further includes external features or cuts 29 that assist in accommodating surgical instrumentation during manipulation and assembly during the surgical procedure. These cuts 29 allow various instruments (not shown) to firmly and positively hold and manipulate the screw head 20 on one side or both sides of screw head 20.

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 a hook 60. The hook 60 is further illustrated in FIG. 10B. The hook 60 includes a concave socket 12 having an inner portion 9 adapted to receive the bulbous end 21 of the screw head 20; and a dimpled outer portion 8. The hook 60 further includes a pair of arms 61, 62 connected by a connection arm 64. A space 63 separates the arms 61, 62 from one another. The arms 61, 62 are configured to receive an additional member (not shown) for subsequent attachment to the bone.

The several embodiments of the saddle pin 30 are shown in FIGS. 11A through 14. The saddle pin 30 provides a proper seat for the longitudinal member 50 and avoids notching a typical titanium longitudinal member 50 (titanium is very notch sensitive). Furthermore, the saddle pin 30 allows one to accommodate multiple sizes of longitudinal members 50 in the same screw assembly system 1 which is a first for a titanium system because of the above-mentioned notching factors. The saddle pin 30 is configured with a slot 32 through the center to allow expansion of the upper portion (head) 131 of the saddle pin 30. The bottom 35 of the saddle pin head 131 is angled to allow the saddle pin 30 to accept a larger-sized longitudinal member 50. The saddle pin 30 initially expands the male sphere 21 of the screw head 20 into the female spherical socket 12 in the bone screw 10 causing the screw assembly system 1 to lock or start locking (i.e., causing the male sphere 21 of the screw head 20 to lock in the female spherical socket 12 of the bone screw 10). The saddle pin 30 then “digs” into the female spherical socket 12 of the bone screw 10 to provide a secondary locking force to avoid bending failure of the assembly 1.

FIGS. 11A through 11B illustrate a first embodiment of the saddle pin 30. The saddle pin 30 generally includes an upper portion 131 and a lower portion 132. The upper portion includes a slot 32, which is configured from the lowest area 33 of the upper portion 131 into the upper area 34 of the lower portion 132 of the saddle pin 30. A secondary locking mechanism 36 may be configured on the lower portion 132 of the saddle pin to further achieve locking of the saddle pin 30 once it is inserted in the screw head 20. The lower portion 132 of the saddle pin 30 terminates with a pointed end 37 to allow for digging into the female socket 12 of the bone screw 10. FIGS. 12A through 12B illustrate a second embodiment of the saddle pin 30. The difference between the first and second embodiments of the saddle pin 30 is that the upper portion of the saddle pin 131 in the second embodiment includes two generally flat upper opposed ends 38 to more matingly configure with the geometry of the screw head 20 and the longitudinal member 50.

FIGS. 13 through 14 illustrate a third embodiment of the saddle pin 30. In particular, in the third embodiment, the saddle pin 30 comprises two parts: an upper portion 131 preferably comprising titanium and a lower portion 132 which is preferably ceramic. According to the third embodiment, the material of the lower portion 132 of the saddle pin 30 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 the screw head 20 and bone screw 10.

As shown in FIG. 13, the upper portion 131 of the saddle pin 30 includes a slot 32 in the seat portion 133 and tapered angled ends 134. Preferably, the saddle pin 30; i.e., the upper portion 131 and the ceramic tip 132 are assembled last in the overall process. Specifically, the screw head 20 snaps into the bone screw 10. Then, the ceramic tip 132 slides into the screw head 20, and finally the titanium saddle (upper portion) 131 is press fitted into the screw head 20 keeping everything in place and oriented in a relaxed state.

As best seen in FIG. 14, the lower portion 132 of the saddle pin terminates with a series of cascading walls 137, 138 having sloped angles, terminating with the pointed end 37 for attachment into the screw head 20/bone screw 10 assembly. The material properties of the saddle pin tip 132 are such that it prevents the deformation on the saddle pin 30 before the saddle pin 30 gives the proper bending and penetrating effects onto the screw head 20/bone screw 10 assembly. Examples of the types of materials used for the saddle pin pointed end 37 include Zyranox™ and HIP Vitox™, both of which are available from Morgan Advanced Ceramics, United Kingdom.

The blocker 40, which is further illustrated in FIGS. 15A through 15C, includes a standard buttress thread 41 configured along an outer perimeter of the blocker 40. The blocker 40 helps to secure the longitudinal member 50 inside the screw head 40. The threads 41 of the blocker 40 are configured to engage the threads 23 of the screw head 20. Additionally, the blocker 40 aids in preventing the expansion of the screw head 20 when torqued on the longitudinal member 50, directing the counterforce more vertically than horizontally. The top 42 of the blocker 40 has a fastening feature 43 such as a hex or square lock feature to allow high torque to be applied in locking the assembly 1. Furthermore, the blocker 40 may be configured with a free rotating saddle (not shown) to accommodate, via tangential contact, the longitudinal member 50 and help to further prevent notching of the titanium alloy used to construct the longitudinal member 50. Moreover, the blocker 40 may have a “timed” thread 41 that is consistently and precisely related to the blocker driving tool (not shown) to help calculate the torsional and vertical position of the blocker 40 thereby assisting the torque measurement applied to the blocker 40.

Another aspect of the invention is illustrated in the flowchart of FIG. 16, which includes descriptions which refer to components provided in FIGS. 1 through 15C. FIG. 16 illustrates a method of assembling a pedicle screw assembly 1, wherein the method comprises attaching (200) a screw head 20 to a bone fixator component 10; securing (210) the bone fixator component 10 in the bone (not shown); securing (220) a saddle pin 30 in the screw head 20; engaging (230) the saddle pin 30 with the bone fixator component 10; inserting (240) a longitudinal member 50 in the screw head 20; and inserting (250) a blocker 40 in the screw head 20. 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 member 50 (nearly 4 mm compared to the conventional devices which are generally limited to 2 mm).

Moreover, according to an aspect of the invention, the inventive assembly 1 can be used as a dynamic rod system to complement artificial discs. According to this embodiment, the outside of the spherical joint part 21 of the screw head 20 and the inner spherical surface 9 of the bone screw cup 12 are coated with a wear resistant ceramic coating. In this scenario, the saddle pin 30 is not digging into the bone screw 10 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 joint 21 of the screw head 20 and the inner spherical surface 12 of the bone screw 10 have lower friction and higher wear resistance characteristics, thus improving the overall characteristics of the screw assembly 1.

Generally, as shown in FIG. 1 through 15C, the embodiments of the invention provide an assembly 1 comprising a screw head 20 comprising a bulbous end 21; a fixator component 10 configured for receiving the bulbous end 21 of the screw head 20; a pin 30 mounted in the screw head 20; and a blocker 40 adapted to engage the screw head 20. The screw head 20 comprises a slot 24 configured for receiving a longitudinal member 50. The fixator component 10 comprises a concave socket 12 configured for receiving the bulbous end 21 of the screw head 20. In a first embodiment, the fixator component 10 also comprises a threaded end 11 opposite the concave socket 12 and configured for attaching to a bone. The pin 30 engages the fixator component 10 and a bottom portion 51 of the longitudinal member 50. The blocker 40 secures a top portion 52 of the longitudinal member 50. The pin 30 comprises an upper saddle portion 131 and a lower tip portion 132.

Additionally, the pin 30 may comprise a multi-part assembly. The upper saddle portion 131 of the pin 30 comprises titanium and the lower tip portion 132 of the pin 30 comprises a ceramic material. Moreover, the lower tip portion 132 comprises a mechanically harder material than the upper saddle portion 131. The screw head 20 and the fixator component 10 comprise a first material, and the lower tip portion 132 of the pin 30 comprises a material having a higher material hardness and compressive yield strength than the first material. The assembly 1 further comprises a wear resistant ceramic coating (not shown) over the screw head 20 and the fixator component 10.

The screw head 20 further comprises two opposed upright ends 22 separated by the slot 24, wherein each of the opposed upright ends 22 comprise an inner wall 27 and an outer wall 28, wherein the inner wall 27 comprises wall threads 23, and wherein the outer wall 28 comprises grooves (cuts) 29. The blocker 40 comprises blocker threads 41 configured around an outer perimeter 42 of the blocker 40, the blocker threads 41 being dimensioned and configured to mate with the wall threads 23. The upper saddle portion 131 of the pin 30 comprises a slot 32. The bulbous end 21 of the screw head 20 comprises a plurality of slots 6 terminating at an opening 4 at a tip 3 of the bulbous end 21. Moreover, the bulbous end 21 of the screw head 20 comprises a gap 19 configured to receive the pin 30. The concave socket 12 of the fixator component 10 comprises an inner portion 9 adapted to receive the bulbous end 21 of the screw head 20; and a dimpled outer portion 8. The fixator component 10 is configured as any of a threaded bone screw 10 (as shown in FIGS. 1 through 8) and a hook 60 (as shown in FIGS. 10A and 10B) according to the several embodiments of the invention.

The embodiments of the invention provide a pedicle screw assembly implant device 1, 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 polyaxial spinal screw assembly 1 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 20 to provide a bigger arc of rotation. Moreover, the saddle pin 30 component offers the flexibility to use a diametrical range of spinal longitudinal members 50 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

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; anda blocker that engages said screw head.

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

4. The pedicle screw assembly of claim 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 of claim 1, wherein said screw head comprises at least one upright end adjacent to said slot.

6. The pedicle screw assembly of claim 5, wherein said screw head comprises: a lower base portion adjacent to said at least one upright end; andan aperture extending from said lower base portion through said connecting end.

7. The pedicle screw assembly of claim 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; andmeans for causing outward expansion of said substantially bulbous body.

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

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

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

12. The assembly of claim 11, wherein said slotted screw head comprises: a lower base portion adjacent to said at least one upright end; andan aperture extending from said lower base portion through said substantially bulbous body.

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

14. An assembly comprising: a bone engaging component comprising a socket; anda screw head comprising a stem portion extending from a bottom of said screw head and fits inside said socket.

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

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

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

18. The assembly of claim 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; andan aperture extending from said lower base portion through said stem portion.

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

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