US20060058788A1 - Multi-axial connection system - Google Patents

Abstract

In one embodiment of the present invention a system for connecting a fastener element (e.g., a pedicle screw) relative to a rod for the purposes of vertebral fixation is provided. The system may permit multi-axial movement between the fastener element and the rod. Further, the system may permit the angular relationship between the fastener element and the rod to be held in a desired orientation. For the purposes of describing and claiming the present invention, the term “rod” is intended to refer to any elongated structure. Such an elongated structure may be solid or hollow and may have any desired cross-section (e.g., circular, oval, square, rectangular). Further, for the purposes of describing and claiming the present invention, the term “interference fit” is intended to refer to physical contact between two or more components.

Description

FIELD OF THE INVENTION
• In one embodiment of the present invention a system for connecting a fastener element (e.g., a pedicle screw) relative to a rod for the purposes of vertebral fixation is provided. The system may permit multi-axial movement between the fastener element and the rod. Further, the system may permit the angular relationship between the fastener element and the rod to be held in a desired orientation.
• For the purposes of describing and claiming the present invention, the term “rod” is intended to refer to any elongated structure. Such an elongated structure may be solid or hollow and may have any desired cross-section (e.g., circular, oval, square, rectangular).
• Further, for the purposes of describing and claiming the present invention, the term “interference fit” is intended to refer to physical contact between two or more components.
BACKGROUND OF THE INVENTION
• Various systems for connecting fastener elements (e.g., pedicle screws) to elongated supports (e.g., rods) for the purposes of vertebral fixation have been proposed. Examples include the systems described in the following U.S. Patents.
• U.S. Pat. No. 5,466,237 relates to a variable locking stabilizer anchor seat and screw. More particularly, this patent relates to a bone interface anchor provided for use with a stabilizer rod for the internal fixation of a spine. The anchor has a seat which accommodates the stabilizer rod and which receives a bone screw for the fixation of the seat to the bone. A compression member cooperates with the seat external to the stabilizer rod and can be tightened to cause a compressive force on the stabilizer rod. The stabilizer rod bears on a rounded surface of the bone screw so as to cause a mating interface between the seat and the bone screw. Subsequently, the position of the seat relative to the bone screw can be locked.
• U.S. Pat. No. 5,474,555 relates to a spinal implant system. More particularly, this patent relates to an apparatus for the internal fixation of the spine. The apparatus comprises an assembly having at least two anchors and an elongated stabilizer. The anchors each have means to hold the anchor to the bone, and include receiving means which receive the stabilizer as well as securing means which cooperate with the receiving means by means of the interaction of mating threads to cause the application of compression on the stabilizer into the receiving means.
• U.S. Pat. No. 5,669,911 relates to a polyaxial pedicle screw. More particularly, this patent relates to a polyaxial orthopedic device for use with rod implant apparatus. The device includes a screw having a curvate head, a locking collar disposed therearound, and a receiving member having a linearly tapered socket in which the screw and the collar are nested. The locking collar is slotted and tapered, and has a semi-spherical interior volume into which the screw head is initially polyaxially held. The receiving member has a transverse channel formed in it for receiving a rod, and an axial bore having a linearly tapered chamber in the bottom portion thereof. The collar is inserted down the bore from the top to seat in the chamber, and the screw is subsequently inserted up through the bottom of the bore and into the collar. The linear taper of the chamber provides a radially inward force on the locking collar when the collar is forced downward therein. This radially inward force causes the locking collar to crush lock against the head of the screw, therein locking the two at the given angulation. It is the placement of the rod in the transverse channel, against the top of the collar, and the subsequent locking down of the rod in the channel which provides the downward force against the locking collar, which in turn locks the screw in its given angulation.
• U.S. Pat. No. 5,879,350 relates to a multi-axial bone screw assembly. More particularly, this patent relates to a multi-axial bone screw assembly including a bone screw having a partially spherical head. The bone screw head is truncated at an upper surface in which a tool receiving recess is defined. The assembly includes a receiver member including a central bore that defines a tapered recess to receive a contracting collet carrying the head of the bone screw. The bore of the receiver member also defines a channel communicating with the recess and configured to receive a spinal rod therein. A portion of the channel is threaded to receive a set screw above the rod. The assembly also includes a contracting collet disposed between the rod and the head of the bone screw. The collet defines a partially spherical recess to receive the head of the bone screw, and includes deflectable fingers that substantially surround the screw head. As the set screw is tightened into the receiver member, the set screw compresses the rod against the collet, which presses the collet into the tapered recess of the receiver member, thereby deflecting the fingers of the collet against the bone screw head.
• U.S. Pat. No. 6,063,090 relates to a device for connecting a longitudinal support to a pedicle screw. More particularly, this patent relates to a device used to connect a longitudinal support to a pedicle screw by an accommodating head having a channel to accommodate the longitudinal support, wherein it is possible to freely choose from or mix laterally open, top open or closed accommodating heads. A top open accommodating head facilitates, for example, insertion of the longitudinal support, whereas a lateral opening enables lateral corrections. The pedicle screw and the accommodating head are connected via a conical collet chuck in the accommodating head and by a spherical head on the pedicle screw. The present invention allows engagement of the pedicle screw in the accommodating head after the pedicle screw has been inserted into bone.
• U.S. Pat. No. 6,582,436 relates to a device for connecting a longitudinal support to a bone anchor. More particularly, this patent relates to a device for connecting a longitudinal support to a bone anchor having a rounded head. The device includes a body defining a chamber for receiving the rounded head of the bone anchor and a first channel for receiving the longitudinal support. Further, a first sleeve is slidable over the body for compressing the chamber, a second sleeve is slidable over the body for biasing the longitudinal support against the first sleeve, and a fastener is operatively associated with the body for biasing the second sleeve toward the first sleeve. The forces exerted on the second sleeve by the fastener are transferred to the first sleeve in a plane perpendicular to the central axis. Preferably, the longitudinal support contacts the first sleeve at first and second contact points or zones and one of the sleeves includes at least one extended portion for contacting the other sleeve at least one additional contact point or zone.
• U.S. Pat. No. 6,660,004 relates to a multi-axial bone screw assembly. More particularly, this patent relates to a bottom-loading multi-axial bone anchor apparatus. The apparatus includes a receiver member, a crown member, a bone anchor and a retaining member. The receiver member defines an upper opening and a lower opening, which may form part of the same opening, a channel, and a groove. The crown member and bone anchor are loaded into the lower opening of the receiver member, and the retaining member fits around the bone anchor and into the groove in the receiver member. The bone anchor is capable of multi-axial positioning with respect to the receiver member. An elongated member is placed in the channel of the receiver member, contacting the crown member, and a compression member is applied via the upper opening. The compression member presses down on the elongated member, which presses down on the crown member and locks the bone anchor between the crown member and the retaining member.
• U.S. Pat. No. 6,740,086 relates to a screw and rod fixation assembly and device. More particularly, this patent relates to a screw and rod fixation assembly for fixing a screw and, optionally, a rod. The screw and rod fixation assembly includes a screw, fixing mechanism, a substantially annular ring, rod seating mechanism, and locking mechanism. The present invention also provides for a fixing mechanism for fixing a screw, wherein the fixing mechanism further includes an inner surface wall having a gripping portion and a non-gripping portion. Further, the present invention provides for a substantially annular ring for guiding and providing mechanical and frictional force to a screw head. Additionally, the present invention provides for a rod seating mechanism operatively engaged to the screw head and including at least one flexible portion capable of being compressed against a portion of a rod therein. Finally, the present invention provides for a locking mechanism for engaging the rod and the rod seating mechanism. The locking mechanism includes a deflecting mechanism for deflecting the at least one flexible portion of the rod seating mechanism against and around the rod as the locking mechanism further engages the at least one flexible portion of the rod seating mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 shows an exploded perspective view of a fastener assembly according to an embodiment of the present invention;
• FIG. 2 shows a cross-sectional view of a partially assembled fastener assembly according to the embodiment ofFIG. 1 (for clarity, this Fig. does not include the rod or compression member ofFIG. 1);
• FIG. 3 shows an exploded perspective view of a fastener assembly according to another embodiment of the present invention;
• FIG. 4 shows a cross-sectional view of a partially assembled fastener assembly according to the embodiment ofFIG. 3 (for clarity, this Fig. does not include the rod or compression member ofFIG. 3).
• FIG. 5 shows a side view of a fastener assembly according to another embodiment of the present invention;
• FIG. 6 shows a side view of a fastener assembly according to another embodiment of the present invention; and
• FIG. 7 shows a side view of a fastener according to an embodiment of the present invention.
• Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. The figures constitute a part of this specification and include illustrative embodiments of the present invention and illustrate various objects and features thereof.
DETAILED DESCRIPTION OF THE INVENTION
• Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention are intended to be illustrative, and not restrictive. Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.
• Referring now toFIGS. 1 and 2, a first embodiment of the present invention is shown. As seen in these Figs.,Fastener Assembly100 may be used in connection with mountingRod101 relative to a spine of a patient (of course, one or more such Fastener Assemblies may be used with one or more Rods). More particularly,Fastener Assembly100 may includeFastener103 havingHead103A at a first end andBone Connection Element103B at a second end (Bone Connection Element103B may be adapted for attachment on, in and/or to the spine). Further,Head103A may include at least one Deformation Element103C thereon.
• In one example (which example is intended to be illustrative and not restrictive), at least a portion ofHead103A may be spherical. In another example (which example is intended to be illustrative and not restrictive),Fastener103 may be a bone screw andBone Connection Element103B may comprise threads. In another example (which example is intended to be illustrative and not restrictive),Fastener103 may be a cannulated bone screw (see Cannulation103D ofFIG. 2). In another example (which example is intended to be illustrative and not restrictive), Deformation Element103C may substantially surround Cannulation103D (e.g., where Cannulation103D exitsHead103A). In another example (which example is intended to be illustrative and not restrictive), Deformation Element103C may be a substantially circular ring protruding fromHead103A. In another example (which example is intended to be illustrative and not restrictive), Deformation Element103C (and/or any other portion of Fastener103 (e.g.,Head103A or the entire Fastener103)) may include a material which is: (a) softer than a material from whichRod101 is formed; (b) harder than a material from whichRod101 is formed; or (c) of essentially the same hardness as a material from whichRod101 is formed (e.g., the same material from whichRod101 is formed).
• Still referring toFIGS. 1 and 2, it is seen thatFastener Assembly100 may includeBody105.
• Body105 may have a first end and a second end, whereinRod Receiving Channel105A for receivingRod101 is disposed adjacent the first end ofBody105 and FastenerHead Receiving Chamber105B is disposed adjacent the second end of Body105 (as seen in these Figs., FastenerHead Receiving Chamber105B may be tapered towards the second end ofBody105 andRod Receiving Channel105A and FastenerHead Receiving Chamber105B may be operatively connected (e.g., a hole inBody105 may connectRod Receiving Channel105A and FastenerHead Receiving Chamber105B)).
• Further,Fastener Assembly100 may includeRetention Ring107. ThisRetention Ring107 may be sized to fit at least partially aroundHead103A whenHead103A is disposed within FastenerHead Receiving Chamber105B. In one example (which example is intended to be illustrative and not restrictive),Retention Ring107 may be, as shown in the Figs., of a “split-ring” design.
• Further still,Compression Element109 may cooperate withBody105 to pushRod101, whenRod101 is disposed withinRod Receiving Channel105A, into contact with at least part of Deformation Element103C. Such contact betweenRod101 and Deformation Element103C will deform Deformation Element103C while pressingHead103A towards the tapered end (i.e., narrower end) of FastenerHead Receiving Chamber105B. This action will serve to fix the angular relationship ofFastener103 relative toRod101.
• More particularly, the angular relationship ofFastener103 relative toRod101 may be fixed at least in part due to: (a) an interference fit (caused by radial compression) between at least a portion of an outside surface ofHead103A and at least a portion of an inside surface ofRetention Ring107; (b) an interference fit (caused by radial compression) between at least a portion of an outside surface ofRetention Ring107 and at least a portion of an inside surface of FastenerHead Receiving Chamber105B; and/or (c) an interference fit between at least a portion of an outside surface ofRod101 and Deformation Element103C.
• In one example (which example is intended to be illustrative and not restrictive),Compression Element109 may have threads which cooperate with complementary threads ofBody105. In another example (which example is intended to be illustrative and not restrictive),Compression Element109 may have external threads which cooperate with complementary internal threads of Body105 (e.g.,Compression Element109 may be a set screw). In another example (which example is intended to be illustrative and not restrictive),Compression Element109 may have internal threads which cooperate with complementary external threads of Body105 (e.g.,Compression Element109 may be a nut). In another example (which example is intended to be illustrative and not restrictive),Compression Element109 may have one or more indentations, protrusions and/or drive faces for receiving torque from a drive tool (see, e.g., the female hex feature ofFIG. 1).
• Reference will now be made to the elements shown inFIGS. 1 and 2 in connection with the description of an example installation procedure. Such an example installation procedure is applicable to this embodiment of the fastener assembly of the present invention and, of course, is intended to be illustrative and not restrictive.
• More particularly, a guide wire may first be attached to a pedicle of the spine. The free end of the guide wire may then be passed through Fastener103 (via Cannulation103D). Fastener103 (e.g., a pedicle screw) may then be inserted (e.g., screwed into) the pedicle of the spine. Of note, such a pedicle screw may be self-tapping into a hole bored into the pedicle or the hole bored into the pedicle may be pre-tapped. Of further note, such a pedicle screw may be driven into bone with any desired tool (e.g., a hand or power driver applying torque throughRod Receiving Channel105A and FastenerHead Receiving Chamber105B).
• In one example (which example is intended to be illustrative and not restrictive), such a pedicle screw may be driven into bone with a torque applying tool that engages one or more indentations, protrusions and/or drive faces onHead103A (see, e.g., the four scallops ofHead103A inFIG. 1).
• In one example (which example is intended to be illustrative and not restrictive),Fastener103 may be driven into bone by itself. Next, a body/retention ring assembly (e.g., includingBody105 havingRetention Ring107 already disposed within FastenerHead Receiving Chamber105B) may be placed (or “snapped”) ontoFastener103.
• In this regard, asBody105 is subsequently pushed ontoHead103A,Retention Ring107 is pushed against the back wall of FastenerHead Receiving Chamber105B (see105C ofFIG. 2) andRetention Ring107 is free to expand outward enablingHead103A to pass through. OnceHead103A pushes through the bottom ofRetention Ring107,Head103A remains captured (sinceRetention Ring107 would have no room to expand as it was pulled forward byHead103A towards the tapered (i.e., narrowed) end of FastenerHead Receiving Chamber105B.
• Next,Rod101 may be placed inRod Receiving Channel105A (withRod101 coming into contact with Deformation Element103C.
• Finally, as Compression Element109 (e.g., a set screw) is threaded intoBody105,Compression Element109 clamps the components in a set position (that is,Compression Element109 pushesRod101 against Deformation Element103C (and, depending upon the size and shape ofRod101, Deformation Element103C andHead103A, against a portion ofHead103A)). Of note, during this clamping process Deformation Element103C is deformed (e.g., to form a surface complementary to the portion ofRod101 causing the deformation) and the result is improved locking (e.g., of the angular relationship betweenRod101 and Fastener103). Of further note, it is believed that Deformation Element103C is particularly useful in enabling secure locking of canulated fasteners, such as cannulated pedicle screws (it is believed that a cannulation (without the use of a deformation element according to the present invention) may tend to compromise the ability to lock the multi-axial adjustability).
• In another example (which example is intended to be illustrative and not restrictive), rather than drivingFastener103 into bone by itself and then placing a body/retention ring assembly thereon,Fastener103 may be captured within body/retention ring assembly as discussed above and then the entire body/retention ring/fastener assembly may be attached to the bone (e.g., by using a driving tool such as a hand or power driver to drive the pedicle screw through the hole provided inBody105 betweenRod Receiving Channel105A and FastenerHead Receiving Chamber105B).
• Referring now toFIGS. 3 and 4, another embodiment of the present invention is shown. This embodiment is similar to the embodiment shown inFIGS. 1 and 2 and, in this regard, the same elements will be identified by the same reference numerals (such similar elements will not be described again in detail). Of note, the main difference between the embodiment of theseFIGS. 3 and 4 and the embodiment ofFIGS. 1 and 2 is that in thisembodiment Fastener Assembly200 does not utilizeRetention Ring107.
• More particularly,Fastener Assembly200 may again be used in connection with mountingRod101 relative to a spine of a patient (of course, one or more such Fastener Assemblies may be used with one or more Rods). Further,Fastener Assembly200 may include Fastener103 (havingHead103A,Bone Connection Element103B and at least one Deformation Element103C).
• Still referring toFIGS. 3 and 4, it is seen thatFastener Assembly200 may further includeBody105′ (Body105′ may have a first end and a second end, whereinRod Receiving Channel105A′ for receivingRod101 is disposed adjacent the first end ofBody105′ and FastenerHead Receiving Chamber105B′ is disposed adjacent the second end ofBody105′). As seen in these Figs., FastenerHead Receiving Chamber105B′ may be tapered towards the second end ofBody105′ and a hole may be disposed throughBody105′ to connectRod Receiving Channel105A′ and FastenerHead Receiving Chamber105B′.
• Of note, the tapered (i.e., narrow) end of FastenerHead Receiving Chamber105B′ may be made sufficiently small so as to prohibitHead103A from passing therethrough (whileRod Receiving Channel105A′ and the hole inBody105′connectingRod Receiving Channel105A′ to FastenerHead Receiving Chamber105B′ may be made sufficiently large so as to allowHead103A to pass therethrough).
• In this regard,Fastener Assembly200 may be installed by insertingFastener103 throughBody105′ such thatHead103A comes to rest in FastenerHead Receiving Chamber105B′ (seeFIG. 4).Fastener103 may then be inserted (e.g., into the pedicle of the spine) as discussed above (e.g., a guide wire may be used to guideFastener103 and either a self-tapping bone screw may be driven into a hole in the bone or a pre-tapped hole in the bone may be provided).
• Finally,Compression Element109 may cooperate withBody105′ to pushRod101, whenRod101 is disposed withinRod Receiving Channel105A′, into contact with at least part of Deformation Element103C to deform Deformation Element103C while pressingHead103A towards the tapered end (i.e., narrower end) of FastenerHead Receiving Chamber105B. This action will fix the angular relationship ofFastener103 relative to Rod101 (the angular relationship ofFastener103 relative toRod101 may be fixed at least in part due to: (a) an interference fit (caused by radial compression) between at least a portion of an outside surface ofHead103A and at least a portion of an inside surface of FastenerHead Receiving Chamber105B′; and/or (b) an interference fit between at least a portion of an outside surface ofRod101 and Deformation Element103C.
• Referring now toFIGS. 5 and 6, two other embodiments of a fastener assembly body are shown. In this regard, it is noted thatBody105 ofFIGS. 1 and 2 has an upward facingRod Receiving Channel105A for receivingRod101. Likewise,Body105′ ofFIGS. 3 and 4 has an upward facingRod Receiving Channel105A′ for receivingRod101. In contrast, it is seen inFIG. 5 thatBody500 includes a sideward facingRod Receiving Channel501 for receiving Rod101 (Rod101,Fastener103,Compression Element109 andRetention Ring107 are shown in phantom and are essentially the same elements as described in detail above). Further, it is seen inFIG. 6 thatBody600 includes a “tunnel-type”Rod Receiving Channel601 for receiving Rod101 (Rod101,Fastener103,Compression Element109 andRetention Ring107 are shown in phantom and are essentially the same elements as described in detail above). Of note, the embodiments of theseFIGS. 5 and 6 may operate as discussed above (e.g., the body may include a tapered chamber for facilitating an interference fit between the components disposed therein).
• Referring now toFIG. 7, another embodiment of a fastener for use with the present invention is shown. Of note,Fastener700 is depicted here as a bone screw, although other types of bone attaching mechanisms may, of course, be utilized (e.g., a shaft having a hook on the end). In any case, it is seen that in this embodiment Undercut701 is provided (Undercut701 may be formed, for example, by a flattening of the bottom of the head of the bone screw (see701A) and/or by a narrowing of a portion of the shaft of the bone screw (see701B)). By using such Undercut701,Fastener700 may provide increased clearance in the area whereFastener700 extends from the body of the fastener assembly (wherein such increased clearance may translate into an increase in a maximum angle thatFastener700 may obtain in relation to the fastener body and/or the rod.
• While a number of embodiments of the present invention have been described, it is understood that these embodiments are illustrative only, and not restrictive, and that many modifications may become apparent to those of ordinary skill in the art. For example, the present invention may be placed at any desired level of the spine. Further, the present invention may be used in conjunction with a posterior spinal rod implantation. Further still, the controllable angulation provided by the present invention may be in any desired number of planes. Further still, the rod may be fixed axially and rotationally. Further still, any element described herein may be provided in any desired size (e.g., any element described herein may be provided in any desired custom size or any element described herein may be provided in any desired size selected from a “family” of sizes, such as small, medium, large. To give a more specific example (which example is intended to be illustrative and not restrictive), a bone screw may be provided in a desired thread pitch, thread outer diameter, shaft outer diameter, shaft outer diameter to thread outer diameter ratio and/or length and a body element may be provided in any desired inner diameter, outer diameter and/or length. Further still, the compression element may have a “break-off” feature for separating from the installed portion of the compression element when a desired amount of torque has been applied. Further still, one or more of the components of the fastener assembly may be made from any of the following materials: (a) any biocompatible material (which biocompatible material may be treated to permit bone ingrowth or prohibit bone ingrowth—depending upon the desire of the surgeon); (b) a plastic; (c) a fiber; (d) a polymer; (e) a metal (a pure metal such as titanium and/or an alloy such as Ti—Al—Nb, Ti-6Al-4V, stainless steel); (f) any combination thereof. Further still, use of the guide wire for guiding the fastener via the cannulation may be useful during a minimally invasive procedure, for example. Further still, the bone screw may be adapted for placement in cancellous bone. Further still, rather than a thread, the fastener may employ a hook for attachment to bone. Further still, an outer surface of the head of the fastener, an outer surface of the rod, an outer surface of the retention ring, an inner surface of the retention ring and/or an inner surface of the body (e.g., at any interface area between the aforementioned components) may have one or more features for increasing friction at the interface. For example, any of the aforementioned components may have: a roughened or treated surface (e.g., via sandblasting or knurling), a threaded surface, a grooved surface, a ridged surface, a surface with protrusions, and/or a surface with indentations. Further still, the deformation element may deform in dependence upon: (a) the material utilized for the deformation element; (b) the material utilized for the rod; (c) a geometry of the rod in the area where the rod contacts the deformation element; (d) a geometry of the deformation element; (e) a direction of a load applied to the deformation element by the rod; and/or (f) a magnitude of a load applied to the deformation element by the rod. Further still, a minimum of two fastener assemblies for each rod may be used (e.g., for stabilization purposes). Further still, any steps described herein may be carried out in any desired order.

Claims (40)

1. A spinal fixation system, comprising:

at least one rod;

at least one screw having a head at a first end, wherein the head of the screw includes at least one deformation element thereon;

at least one body, wherein the body has a first end and a second end, wherein a rod receiving channel is disposed adjacent the first end of the body, wherein a screw head receiving chamber is disposed adjacent the second end of the body, wherein the screw head receiving chamber is tapered towards the second end of the body, and wherein the rod receiving channel and the screw head receiving chamber are operatively connected; and

a compression element which cooperates with the body to push the rod, when the rod is disposed within the rod receiving channel, into contact with at least part of the deformation element of the head of the screw to deform the deformation element while pressing the head of the screw towards the tapered end of the screw head receiving chamber to fix the angular relationship of the screw relative to the rod.

2. The spinal fixation system ofclaim 1, wherein the angular relationship of the screw relative to the rod is fixed at least in part due to: (a) an interference fit between at least a portion of an outside surface of the head of the screw and at least a portion of an inside surface of the screw head receiving chamber; and (b) an interference fit between at least a portion of an outside surface of the rod and the deformation element.

3. The spinal fixation system ofclaim 1, further comprising a retention ring sized to fit at least partially around the head of the screw when the head of the screw is disposed within the screw head receiving chamber.

4. The spinal fixation system ofclaim 3, wherein the angular relationship of the screw relative to the rod is fixed at least in part due to: (a) an interference fit between at least a portion of an outside surface of the head of the screw and at least a portion of an inside surface of the retention ring; (b) an interference fit between at least a portion of an outside surface of the retention ring and at least a portion of an inside surface of the screw head receiving chamber; and (c) an interference fit between at least a portion of an outside surface of the rod and the deformation element.

5. The spinal fixation system ofclaim 1, wherein the screw is a bone screw.

6. The spinal fixation system ofclaim 5, wherein the bone screw is configured to be screwed into a pedicle portion of a spine.

7. The spinal fixation system ofclaim 5, wherein the bone screw is a cannulated bone screw.

8. The spinal fixation system ofclaim 7, wherein the deformation element substantially surrounds the cannulation in the bone screw.

9. The spinal fixation system ofclaim 8, wherein the deformation element is a substantially circular ring protruding from the head of the bone screw.

10. The spinal fixation system ofclaim 1, wherein the deformation element comprises a material which is selected from the group including: (a) a material which is softer than a material from which the rod is formed; (b) a material which is harder than a material from which the rod is formed; and (c) a material which is of essentially the same hardness as a material from which the rod is formed.

11. The spinal fixation system ofclaim 1, wherein the rod receiving channel and the screw head receiving chamber are operatively connected to allow a tool to be inserted therethrough to apply torque to the screw.

12. The spinal fixation system ofclaim 11, wherein the head of the screw is at least partially spherical.

13. The spinal fixation system ofclaim 11, wherein the head of the screw includes at least one torque receiving feature for receiving torque from the tool.

14. The spinal fixation system ofclaim 13, wherein the torque receiving feature is selected from the group including: (a) at least one indentation; (b) at least one protrusion; and (c) at least one drive face.

15. The spinal fixation system ofclaim 1, wherein the rod has a substantially circular cross section.

16. The spinal fixation system ofclaim 1, wherein the compression element has threads which cooperate with complementary threads of the body.

17. The spinal fixation system ofclaim 16, wherein the compression element has external threads which cooperate with complementary internal threads of the body.

18. A fastener assembly used in connection with fixing a rod relative to a spine of a patient, comprising:

at least one fastener having a head at a first end and a bone connection element at a second end, wherein the head of the fastener includes at least one deformation element thereon and the bone connection element of the fastener is adapted for connection to the spine of the patient;

at least one body, wherein the body has a first end and a second end, wherein a rod receiving channel for receiving the rod is disposed adjacent the first end of the body, wherein a fastener head receiving chamber is disposed adjacent the second end of the body, wherein the fastener head receiving chamber is tapered towards the second end of the body, and wherein the rod receiving channel and the fastener head receiving chamber are operatively connected; and

a compression element which cooperates with the body to push the rod, when the rod is disposed within the rod receiving channel, into contact with at least part of the deformation element of the head of the fastener to deform the deformation element while pressing the head of the fastener towards the tapered end of the fastener head receiving chamber to fix the angular relationship of the fastener relative to the rod.

19. The fastener assembly ofclaim 18, wherein the angular relationship of the fastener relative to the rod is fixed at least in part due to: (a) an interference fit between at least a portion of an outside surface of the head of the fastener and at least a portion of an inside surface of the fastener head receiving chamber; and (b) an interference fit between at least a portion of an outside surface of the rod and the deformation element.

20. The fastener assembly ofclaim 18, further comprising a retention ring sized to fit at least partially around the head of the fastener when the head of the fastener is disposed within the fastener head receiving chamber.

21. The fastener assembly ofclaim 20, wherein the angular relationship of the fastener relative to the rod is fixed at least in part due to: (a) an interference fit between at least a portion of an outside surface of the head of the fastener and at least a portion of an inside surface of the retention ring; (b) an interference fit between at least a portion of an outside surface of the retention ring and at least a portion of an inside surface of the fastener head receiving chamber; and (c) an interference fit between at least a portion of an outside surface of the rod and the deformation element.

22. The fastener assembly ofclaim 18, wherein the bone connection element of the fastener is selected from the group including: (a) threads; and (b) a hook.

23. The fastener assembly ofclaim 22, wherein the fastener is configured to be connected to a pedicle portion of the spine.

24. The fastener assembly ofclaim 23, wherein the fastener is a cannulated bone screw.

25. The fastener assembly ofclaim 24, wherein the deformation element substantially surrounds the cannulation in the bone screw.

26. The fastener assembly ofclaim 25, wherein the deformation element is a substantially circular ring protruding from the head of the bone screw.

27. The fastener assembly ofclaim 18, wherein the deformation element comprises a material which is selected from the group including: (a) a material which is softer than a material from which the rod is formed; (b) a material which is harder than a material from which the rod is formed; and (c) a material which is of essentially the same hardness as a material from which the rod is formed.

28. The fastener assembly ofclaim 18, wherein the rod receiving channel and the fastener head receiving chamber are operatively connected to allow a tool to be inserted therethrough to apply torque to the fastener.

29. The fastener assembly ofclaim 28, wherein the head of the fastener is at least partially spherical.

30. The fastener assembly ofclaim 28, wherein the head of the fastener includes at least one torque receiving feature for receiving torque from the tool.

31. The fastener assembly ofclaim 30, wherein the torque receiving feature is selected from the group including: (a) at least one indentation; (b) at least one protrusion; and (c) at least one drive face.

32. The fastener assembly ofclaim 18, wherein the rod has a substantially circular cross section.

33. The fastener assembly ofclaim 18, wherein the compression element has threads which cooperate with complementary threads of the body.

34. The fastener assembly ofclaim 33, wherein the compression element has external threads which cooperate with complementary internal threads of the body.

35. A cannulated fastener used in connection with fixing a rod in a body member relative to a spine of a patient, comprising:

a head at a first end and a bone connection element at a second end, wherein the head includes at least one deformation element thereon and the bone connection element is adapted for connection to the spine of the patient;

wherein the deformation element substantially surrounds the cannulation in the fastener; and

wherein the deformation element deforms under pressure applied thereto by the rod.

36. The fastener ofclaim 35, wherein the bone connection element of the fastener is selected from the group including: (a) threads; and (b) a hook.

37. The fastener ofclaim 36, wherein the fastener is configured to be connected to a pedicle portion of the spine.

38. The fastener ofclaim 37, wherein the fastener is a bone screw.

39. The fastener ofclaim 35, wherein the deformation element is a substantially circular ring protruding from the head of the fastener.

40. The fastener ofclaim 39, wherein the deformation element comprises a material which is selected from the group including: (a) a material which is softer than a material from which the rod is formed; (b) a material which is harder than a material from which the rod is formed; and (c) a material which is of essentially the same hardness as a material from which the rod is formed.

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