Polyaxial Pedicle Screw Assembly
A fastener and a bone fixation assembly for the internal fixation of vertebral bodies such as a pedicle screw is provided which allows a detachable tulip to be provisionally locked to a pedicle screw, while separately, the rod securely locks to the tulip. According to one exemplary embodiment, the tulip assembly includes a tulip body and an inner tulip member, the tulip body having a non-circular surface disposed on an outer surface. Additionally, a fastener is coupled to the tulip assembly and positionable to retain the tulip assembly on the head of a screw. Further, a cap having an outer surface and a plurality of inner protrusions is provided, wherein the plurality of inner protrusions are configured to mateably connect to the non-circular surface on the tulip body to compress the tulip assembly and secure a rod.
This application is a Continuation Application of U.S. application Ser. No. 11/342,420, filed Jan. 30, 2006, which application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Nos. 60/648,796 filed Jan. 31, 2005; 60/658,972 filed Mar. 4, 2005; and 60/701,543 filed Jul. 22, 2005 each titled “Oval Twist Polyaxial Pedicle Screw Assembly”, which applications are incorporated herein by reference in their entireties.
FIELDThe present system and method relate to bone fixation devices. More particularly, the present system and method provide for a screw assembly configured to facilitate the internal fixation of vertebral bodies.
BACKGROUNDVarious devices for internal fixation of bone segments in the human or animal body are known in the art. One type of system is a pedicle screw system, which is sometimes used as an adjunct to spinal fusion surgery, and which provides a means of gripping a spinal segment. A conventional pedicle screw system comprises a pedicle screw, a rod-receiving device, and a rod. The pedicle screw includes an externally threaded stem and a head portion. The rod-receiving device couples to the head portion of the pedicle screw and receives a rod (commonly referred to as a distraction rod). Two such systems are inserted into respective vertebrae and adjusted to distract and/or stabilize a spinal column, for instance during an operation to correct a herniated disk. The pedicle screw does not, by itself, fixate the spinal segment, but instead operates as an anchor point to receive the rod-receiving device, which in turn receives the rod. One goal of such a system is to substantially reduce and/or prevent relative motion between the spinal segments that are being fused.
Although conventional prior art pedicle screw systems exist, they lack features that enhance and/or benefit newer, minimally invasive surgery (MIS) techniques that are more commonly being used for spinal surgeries. It has been suggested that one possible advantage of an MIS approach is that it can decrease a patient's recovery time.
Conventional pedicle screw systems and even more recently designed pedicle screw systems have several drawbacks. Some of these pedicle screw systems are rather large and bulky, which may result in more tissue damage in and around the surgical site when the pedicle screw system is installed during surgery. The prior art pedicle screw systems have a rod-receiving device that is pre-operatively coupled or attached to the pedicle screw. In addition, some of the prior art pedicle screw systems include numerous components that must all be carefully assembled together. Further, traditional pedicle screw systems are pre-operatively assembled, which makes these systems more difficult to install and maneuver in a spinal operation where MIS techniques are used.
SUMMARYAccording to one exemplary embodiment, the tulip assembly includes a tulip body, an inner tulip member, and a cap, wherein one or more protruding compression features exist at the interface between the cap and the tulip body to compress the tulip body when the cap is engaged. Additionally, according to one exemplary embodiment, a fastener is coupled to the tulip assembly and positionable to retain the tulip assembly on the head of a screw.
The accompanying drawings illustrate various exemplary embodiments of the present system and method and are a part of the specification. Together with the following description, the drawings demonstrate and explain the principles of the present system and method. The illustrated embodiments are examples of the present system and method and do not limit the scope thereof.
In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, and have been solely selected for ease of recognition in the drawings. Throughout the drawings, identical reference numbers designate similar but not necessarily identical elements.
DETAILED DESCRIPTIONThe present specification describes a system and a method for separately locking the orientation of a tulip assembly relative to a pedicle screw and locking a positional location of a rod in the tulip assembly. Further, according to one exemplary embodiment, the present specification describes the structure of a tulip assembly configured to be placed on the head of a pedicle screw after placement of the pedicle screw in a patient's body and configured to receive and positionally secure a top loaded rod. Further details of the present exemplary system and method will be provided below.
By way of example, pedicle screw systems may be fixed in the spine in a posterior lumbar fusion process via minimally invasive surgery (MIS) techniques. The systems are inserted into the pedicles of the spine and then interconnected with rods to manipulate (e.g., correct the curvature, compress or expand, and/or structurally reinforce) at least portions of the spine. Using the MIS approach to spinal fixation and/or correction surgery has been shown to decrease a patient's recovery time and reduce the risks of follow-up surgeries.
The ability to efficiently perform spinal fixation and/or correction surgeries using MIS techniques is enhanced by the use of pedicle screw systems provided in accordance with the present exemplary systems and methods, which systems and methods provide a number of advantages over conventional systems. For example, a pedicle screw system in accordance with one embodiment of the present exemplary system and method provides the advantage that the pedicle screw may be inserted into the bone without being pre-operatively coupled with the rod-coupling assembly (hereinafter referred to as a tulip assembly). This is advantageous because the surgeon often needs to do other inter-body work after inserting the pedicle screw, but before attaching the larger and bulkier tulip assembly. Such an advantageous pedicle screw system may be even more crucial when using MIS techniques because the inter-body spatial boundaries in which the surgeon must work may be quite limited.
In addition to accommodating the new MIS approach to lumbar fusion, poly-axial pedicle screw systems in accordance with several embodiments of the present system and method remedy problems common to existing art. First, ‘tulip splaying’; which is a post-operative problem of a stressed rod forcing open the tulip and thus disassembling the implanted polyaxial pedicle screw construct is eliminated. Second, pain due to soft-tissue irritation from bulky or high profiled systems is reduced or eliminated.
Further, pedicle screw systems in accordance with several embodiments of the present system and method advantageously allow a user to initially fix (e.g., lock) the tulip assembly to the pedicle screw at a desired angle before fully locking the rod, thereby facilitating compression and distraction of the spinal segments. Initially locking the tulip assembly to the pedicle screw means that at least one of the components of the tulip assembly is manipulated to grip and/or clamp onto the pedicle screw to reduce and/or prevent any translational and/or rotational movement of the tulip assembly relative to the pedicle screw. The ability to initially lock the tulip assembly to the pedicle screw may facilitate the surgeon in performing compression and/or distraction of various spinal and/or bone sections.
The term “distraction,” when used herein and when used in a medical sense, generally relates to joint surfaces and suggests that the joint surfaces move perpendicular to one another. However when “traction” and/or “distraction” is performed, for example on spinal sections, the spinal sections may move relative to one another through a combination of distraction and gliding, and/or other degrees of freedom.
Additionally, as used herein, and in the appended claims, the term “non-circular” shall be meant to be understood as any surface profile that has a varying radius when measured from a single point. Consequently, any oval, helical cam, ellipsoid, or other non-circular graduated surface shall be considered, for purposes of the present application, as a non-circular surface.
Another advantageous feature of at least one embodiment of the present exemplary system and method is that an all-inclusive tulip assembly that can be coupled to the head portion of the pedicle screw intra-operatively is disclosed. This advantageous tulip assembly may include the aspects or features that enable the tulip assembly to be initially locked onto the head portion of the pedicle screw and then to further finally lock the rod into the tulip assembly. In one exemplary embodiment, the tulip assembly is initially locked onto the head portion of the pedicle screw after the rod has been received in the tulip assembly. This advantageous tulip assembly may decrease the complexity of the pedicle screw system installation by reducing the installation to essentially a seven-step process including, inserting the pedicle screw into bone, initially snapping the tulip assembly onto the pedicle screw, inserting the rod into the tulip assembly, placing the cap on the tulip assembly to capture the rod in the tulip assembly, rotating the cap to a first position to positionally lock the tulip assembly to the head of the pedicle screw, compressing and/or distracting spinal segments, and then rotating the cap to a second position to finally lock the rod to the tulip assembly. In addition to accommodating the new MIS approach to spinal correction and/or fusion, the present exemplary system and method are configured to eliminate instances of cross-threading and/or post-operative tulip splaying, which occurs when the amount of stress/strain in rod, which may be caused by post-operative back flexion forces open the tulip assembly and eventually leads to the disassembly and/or the failure of the pedicle screw system.
In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the present polyaxial pedicle screw system. However, one skilled in the relevant art will recognize that the present exemplary system and method may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with pedicle screws have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments of the invention.
Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.”
Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearance of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
Exemplary StructureIn one exemplary embodiment, the pedicle screw (12) is cannulated, which means a channel (130) (shown in dashed lines and extending axially through the pedicle screw (12)) extends through the entire length of the pedicle screw (12). The channel (130) allows the pedicle screw (12) to be maneuvered over and receive a Kirschner wire, commonly referred to as a K-wire. The K-wire is typically pre-positioned using imaging techniques, for example, fluoroscopy imaging, and then used to provide precise placement of the pedicle screw (12). While the pedicle screw (12) illustrated in
As mentioned, the pedicle screw and tulip assembly (10;
As illustrated in the assembled view of
In addition to the rod receiving channel (30), the upper portion (28) of the tulip body (20) can include a number of features that aid in the coupling of the cap (40) and the final locking of the rod (26;
According to the present exemplary embodiment, any number of non-circular compression surfaces (36) may be formed in the groove (38) to interact with one or more graduated compression tabs (46;
Additionally, according to one exemplary embodiment, one or more compression relief(s) (410) may be formed in the tulip body. The compression relief(s) (410) reduces the amount of material that is typically present in the sidewall of the tulip body (20). Consequently, the force required to induce bending in the sidewall of the tulip body (20) during compression of the upper portion (28) of the tulip body (20) is reduced, facilitating a lock of the rod (26;
In addition to the features described above, the present exemplary tulip body (20) also includes a number of features in the lower portion (29) that facilitate reception of a pedicle screw head portion (16;
According to one exemplary embodiment, the bore (402) is configured to facilitate assembly of the tulip assembly (18) before being placed onto the head portion (16;
Moreover, as is described below, the tulip body (20) includes a ring expansion channel (405) and a tapered retention bore (415) configured to interact with the split ring fastener (22) during reception and fixation of the head portion (16;
Further, the tapered retention bore (415) is configured to interact with a seating taper (470) of the split ring fastener. According to one exemplary embodiment, the tulip assembly (18) may be positionally fixed relative to the pedicle screw (12), at least partially, by forcing the split ring fastener (22) along the tapered retention bore (415). According to one exemplary embodiment, interaction between the tapered retention bore (415) and the seating taper (470) constricts the split ring fastener (22) about the head portion (16) of the pedicle screw (12), positionally fixing the tulip assembly (18) relative to the pedicle screw.
The exploded views of
As shown in
Further, as illustrated in
Additionally, as illustrated in
Turning to
While the above-mentioned tulip assembly (18) has been described in detail, any number of modifications in shape and feature combination may be made while still adhering to the teachings of the present exemplary system and method. For example, an alternative tulip housing (600) is illustrated in
As illustrated in
With the one or more pedicle screws inserted into a patient's spinal system (step 700), the tulip assembly may be snapped over the head of a previously inserted pedicle screw (step 710), as illustrated in
According to one exemplary embodiment, when the tulip assembly (18) is snapped onto the head portion (16) of the pedicle screw (12), the lower head interfacing surface (465;
As illustrated in
During the reduction step, the inner tulip member (24) remains positioned against an inner wall of the tulip body (20). Alternatively, the inner tulip member (24) may also be inserted at this time into the bore (402;
Once the tulip assembly (18) is disposed on the pedicle screw (12), the tulip assembly may then be rotated to achieve a desired orientation with respect to the pedicle screw so that the tulip assembly (18) may receive a rod (26;
Once the tulip assembly (18) is positioned, the rod can be snapped into the rod slot of the tulip (step 720;
With the rod (26) inserted in the rod receiving channel (30), the cap is placed over the rod and tulip assembly (step 730;
After the cap (40) is placed on the tulip assembly (18), the cap can be partially rotated to lock the angular position of the tulip assembly relative to the pedicle screw (step 740;
Next, the cap is further rotated to engage the graduated compression tabs (46) of the cap (40) with the non-circular compression surface (36) of the tulip body (step 750;
As shown in
Additionally, as the rod (26) and the inner tulip member (24) are pressed down into the tulip body (20), the extensions (440) are compressed, further increasing the compression on the head portion (16) of the pedicle screw (12). Consequently, completing the rotation of the cap (40) securely locks the rod (26) in the tulip assembly (18), while finally locking the relative position of the tulip assembly relative to the pedicle screw (12).
The preceding description has been presented only to illustrate and describe the present method and system. It is not intended to be exhaustive or to limit the present system and method to any precise form disclosed. Many modifications and variations are possible in light of the above teaching.
The foregoing embodiments were chosen and described in order to illustrate principles of the system and method as well as some practical applications. The preceding description enables others skilled in the art to utilize the method and system in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the present exemplary system and method be defined by the following claims.
Claims
1. A pedicle screw assembly comprising:
- a threaded screw, the screw having a threaded portion, a spherical head and an interface for driving the screw;
- a tulip assembly including a tulip body and an inner tulip member, the tulip body having non-circular surface disposed on an outer surface;
- a fastener coupled to the tulip assembly and positionable to retain the tulip assembly on the head of the screw; and
- a cap having an outer surface and a plurality of inner protrusions, wherein said plurality of inner protrusions are configured to mateably connect to said non-circular surface to compress said tulip assembly.
2. The pedicle screw assembly of claim 1 wherein said fastener comprises a compression ring configured to receive and be positioned around at least a part of the head portion of said threaded screw.
3. The pedicle screw assembly of claim 2 wherein said compression ring comprises a split in the ring that permits the diameter of the ring to vary from a first, larger diameter to a second, smaller diameter.
4. The pedicle screw assembly of claim 1, wherein said tulip body comprises an internal wall region defining a bore;
- said bore being configured to receive said fastener and said inner tulip member.
5. The pedicle screw assembly of claim 4, wherein:
- said bore extends from a top region of the tulip to a lower region of the tulip;
- said bore is sized to receive said spherical head of said screw; and
- said bore includes an expansion channel shaped to facilitate coupling of said fastener to said spherical head of said screw when inserted in said bore.
6. The pedicle screw assembly of claim 5, wherein said expansion channel further comprises a seating taper disposed on a lower portion of said expansion channel; and
- a taper disposed on a lower portion of said fastener corresponding to said seating taper;
- wherein said seating taper and said taper on said fastener are configured to constrict said fastener about said spherical head of said screw.
7. The pedicle screw assembly of claim 1, wherein said cap further comprises a plurality of protruding members on an inner surface of said cap;
- wherein said protruding members are configured to selectively engage said inner tulip member and impart a translating force on said inner tulip member.
8. The pedicle screw assembly of claim 7, wherein said protruding members comprise inclined planes.
9. The pedicle screw assembly of claim 7, wherein said inner tulip member is coupled in said tulip body adjacent to said fastener such that downward translation of said inner tulip member translates said fastener into a seating taper.
10. The pedicle screw assembly of claim 9, wherein said protruding members are configured to impart a translating force on said inner tulip member sufficient to seat said fastener in said seating taper lock an angular position of said tulip assembly relative to said threaded screw.
11. The pedicle screw assembly of claim 7, wherein said cap has a first position and a second retained position;
- wherein said first position engages said protruding members and said inner tulip member to lock a relative angle between said tulip assembly and said threaded screw; and
- wherein said second retained position engages said inner protrusions with said non-circular surface to compress said tulip assembly to lock a rod within said tulip assembly.
12. The pedicle screw assembly of claim 1, wherein said tulip body further comprises at least one compression relief
13. The pedicle screw assembly of claim 1, further comprising a coupling member formed on said tulip body;
- wherein said coupling member defines a single channel, said non-circular surface being disposed in said channel; and
- wherein said inner protrusions in said cap connect to and are rotated in said channel.
14. The pedicle screw assembly of claim 1, wherein said cap further comprises a tool receiving driving feature.
15. A tulip assembly configured to be coupled to a head of a bone fixation device comprising:
- an outer member including a non-circular surface;
- at least one inner member disposed in said outer member, said at least one inner member being configured to fix said tulip assembly to said head of a bone fixation device;
- a channel formed in said tulip assembly to receive a rod; and
- a cap having an outer surface and a plurality of inner protrusions, wherein a first set of said plurality of inner protrusions is configured to mateably connect to said non-circular surface to compress said channel.
16. The tulip assembly of claim 15, wherein said at least one inner member further comprises:
- a first inner member disposed in a lower portion of said outer member;
- a second inner member disposed in an upper portion of said outer member;
- wherein said first inner member is elastically expandable to receive said head of a bone fixation device; and
- wherein said second inner member is configured to interact with said rod when said channel is compressed.
17. The tulip assembly of claim 16, wherein said second inner member comprises:
- a main body;
- at least one extension proximally protruding from said main body;
- an inner bore formed in a distal end of said main body; and
- a compression surface formed on a distal end of said main body;
- wherein said compression surface is configured to contact said first inner member and selectively seat said first inner member in a seating taper, said seating taper being configured to constrict said first inner member about said head of a bone fixation device to fix a position of said tulip assembly relative to said bone fixation device.
18. The tulip assembly of claim 17, wherein said cap has a first position and a second retained position;
- wherein said first position is configured to engage a second set of said plurality of inner protrusions with said first inner member to seat said first inner member and to lock a relative angle between said tulip assembly and said threaded screw; and
- wherein said second retained position engages said first set of said plurality of inner protrusions with said non-circular surface to compress said channel to lock a rod within said tulip assembly.
19. A pedicle screw assembly comprising:
- a threaded screw, the screw having a threaded portion, a spherical head and an interface for driving the screw;
- a tulip assembly including a tulip body and an inner tulip member, the tulip body including an inner surface and an outer surface, said inner surface defining a bore for receiving said inner tulip member, and a non-circular surface disposed on said outer surface;
- a split ring fastener coupled to the tulip assembly and positionable to retain the tulip assembly on the head of the screw; and
- a cap having an outer surface and a plurality of inner protrusions, wherein said cap has a first position and a second retained position, wherein said first position engages a first group of said inner protrusions with said inner tulip member to lock a relative angle between said tulip assembly and said threaded screw, and wherein said second retained position engages a second group of said inner protrusions with said non-circular surface to compress said tulip assembly to lock a rod within said tulip assembly.
20. The pedicle screw assembly of claim 19, wherein:
- said bore extends from a top region of the tulip to a lower region of the tulip;
- said bore is sized to receive said spherical head of said screw; and
- said bore includes an expansion channel shaped to facilitate coupling of said fastener to said spherical head of said screw when inserted in said bore;
- wherein said expansion channel further comprises a seating taper disposed on a lower portion of said expansion channel, and a taper disposed on a lower portion of said fastener corresponding to said seating taper, wherein said seating taper and said taper on said fastener are configured to constrict said fastener about said spherical head of said screw.
21. The pedicle screw assembly of claim 19, wherein said first group of said inner protrusions comprise inclined planes.
22. The pedicle screw assembly of claim 19, wherein said inner tulip member is coupled in said tulip body adjacent to said split ring fastener such that downward translation of said inner tulip member translates said split ring fastener into a seating taper.
23. The pedicle screw assembly of claim 19, wherein said tulip body further comprises at least one compression relief.
24. The pedicle screw assembly of claim 19, further comprising a coupling member formed on said tulip body;
- wherein said coupling member defines a single channel, said non-circular surface being disposed in said channel; and
- wherein said second group of inner protrusions in said cap connect to and are rotated in said channel.
25. A method of fixing a tulip assembly to a pedicle screw comprising:
- inserting said pedicle screw into a bone, said pedicle screw including a head portion;
- expanding a first inner member of said tulip assembly over a head portion of said pedicle screw after said pedicle screw is inserted into a bone;
- inserting a rod in said tulip assembly;
- coupling a cap to a single channel of said tulip assembly;
- rotating said cap to a first position to fix an angle of said tulip assembly; and
- rotating said cap to a second position to compress an outer housing of said tulip assembly to lock said rod in said tulip assembly.
26. The method of claim 25, wherein rotating said cap to a first position to fix an angle of said tulip assembly comprises:
- engaging a protrusion on said cap with a first inner member of said tulip assembly to generate a compressive force on said inner member;
- transmitting said compressive force through said inner member to a second inner member, wherein said compressive force seats said second inner member in a seating taper.
27. The method of claim 26, wherein rotating said cap to a second position to compress an outer housing of said tulip assembly to lock said rod in said tulip assembly comprises:
- engaging a compression tab of said cap with a non-circular surface of said outer housing to create interference;
- wherein said interference compresses said outer housing to frictionally secure said rod in said tulip.
28. The method of claim 27, wherein said interference further compresses said first inner member about said rod.
29. A cap for compressing a tulip assembly comprising:
- an inner bore; and
- a plurality of graduated tabs configured to compress said tulip assembly.
30. A tulip assembly comprising:
- a tulip body; and
- an inner tulip member;
- wherein said tulip body includes a non-circular surface disposed on an outer surface, said non-circular surface being configured to interact with a cap to compress said tulip body about a rod, securely coupling said rod.
Type: Application
Filed: Sep 25, 2008
Publication Date: Jan 15, 2009
Inventors: David T. Hawkes (Pleasant Grove, UT), David R. Warnick (Spanish Fork, UT), Michael D. Ensign (Salt Lake City, UT)
Application Number: 12/237,992
International Classification: A61B 17/04 (20060101);