Patent Application
20060206114
1. Field of the Invention
The present invention relates generally to a rod-coupling assembly for receiving, capturing, and/or securing at least one distraction rod that is used in a spinal operation, for example in an operation to internally correct and/or structurally support a number of vertebral bodies.
2. Description of the Related Art
Various systems 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, two rod-receiving devices, and a rod (commonly referred to as a distraction rod) secured at one end by a first rod-receiving device and secured at a second end by a second rod-receiving device.
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 the rod. For some surgeries, two such systems are inserted side-by-side 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.
The embodiments described herein are generally related to a bone fixation assembly that can be used to reinforce and/or augment a pedicle screw system for the internal fixation of vertebral bodies. The bone fixation assemblies described herein may be used to stiffen and strengthen a pedicle screw construct by joining one construct to another, to connect the rods of two pedicle screw systems to extend a fusion, for example during a re-operation or to transition rod sizes, or by providing one construct with another fixation point on the spine, for example using an extended hook to couple a rod to a posterior element of the spine. These bone fixation assemblies may be employed when minimally invasive surgery (MIS) techniques are used. The bone fixation assemblies described herein each generally include a rod-receiving body and a cam mechanism that operate together to capture and retain at least a distraction rod.
In one aspect, a rod-coupling assembly includes a rod-receiving body having a first channel positioned adjacent to a first opening. The first channel extends substantially parallel to a first wall and is configured to receive at least a portion of a distraction rod. In addition, the assembly includes a cam mechanism having a cam body with a contoured surface. The cam mechanism is rotatable in the first opening to urge the distraction rod into contact with a portion of the first wall.
In another aspect, a rod-coupling assembly includes a first rod-receiving body having a first channel positioned adjacent to a first opening. The first channel extends substantially parallel to a first wall and is configured to receive at least a portion of a first distraction rod. The assembly further includes a first cam mechanism having a first cam body with a contoured surface. The first cam mechanism is rotatable in the first opening to urge the first distraction rod into contact with a portion of the first wall. Further, the assembly includes a second rod-receiving body having a second channel, a second opening, and an elongated pocket. The second channel is positioned adjacent to the second opening, extends substantially parallel to a second wall, and is configured to receive at least a portion of a second distraction rod. The assembly also includes a pin, a lever, a second cam mechanism, and a transverse connector. The lever is received in the elongated pocket of the rod-receiving body and is rotatably coupled to the rod-receiving body via the pin. The second cam mechanism has a second cam body with a contoured surface. The second cam mechanism is rotatable in the second opening to urge the second distraction rod into contact with a portion of the lever. A transverse connector includes a first end, a second end, and an intermediate portion. The first end of the connector is coupled to the first rod-receiving body, the second end of the connector is received in the second rod-receiving body below the lever, and the intermediate portion is engageable with a portion of the lever.
In yet another aspect, a rod-coupling assembly includes a first rod-receiving body having a first channel positioned adjacent to a first opening. The first channel extends substantially parallel to a first wall and is configured to receive at least a portion of a first distraction rod. A first cam mechanism includes a first cam body with a contoured surface. The first cam mechanism is configured to be received in the first opening of the first rod-receiving body. A second rod-receiving body includes a second channel positioned adjacent to a second opening. The second channel extends substantially parallel to a second wall and is configured to receive at least a portion of a second distraction rod. In addition, a second cam mechanism includes a second cam body with a contoured surface. The second cam mechanism is configured to be received in the second opening of the second rod-receiving body. A connection rod extends between a first portion and a second portion, where the first portion includes an engagement surface to mate with the first cam mechanism and the second portion also includes an engagement surface to mate with the second cam mechanism. The first and second cam mechanisms are rotatable in the respective openings to secure the respective rods to the rod-coupling assembly.
In still yet another embodiment, a method of coupling a rod to a rod-receiving device includes receiving a rod in a channel of the rod-receiving device; and then rotating a cam mechanism by an amount sufficient to secure the rod between a helical cam surface of the cam mechanism and a portion of the rod-receiving device.
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.
In one embodiment, pedicle screw systems may be fixed in the spine, for example to perform spinal fixation and/or corrective surgeries, which surgeries may be performed 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 augment) 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 fix and/or correct a spine during surgery often necessitates that the pedicle screw systems be reinforced and/or augmented to achieve better stiffness and strength. Such reinforcement systems, once installed, permit the entire installation to be more robust when influenced by dynamic and static loads. In addition, the reinforcement assemblies permit at least two pedicle screw systems to work in tandem, which allows for equitable and efficient load distribution. For example, if a first pedicle screw system is placed on softer bone while an adjacent system is placed in healthier bone and then the systems are connected by a reinforcement assembly, the system in the healthier bone can take more of the operation forces and in turn reduce some of the stress from the other system (i.e., due to the relative stiffnesses of the healthier versus softer bone). Such an installation may be advantageous in allowing the softer bone to heal and harden quicker without being overly stressed in the interim.
The term “distraction,” 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.
Rod-to-Rod Coupling Assembly
The rod-receiving body 102 further includes a first opening 116 and a second opening 118. The first opening 116 is configured to receive the cam mechanism 104 and is located between the first and second rod slots 108, 110. The second opening 118 extends longitudinally from the first surface 112 to the second surface 114 and is configured to receive a retaining pin 120.
The tool engagement portion 124 is configured to receive a castellated torque device, according to the illustrated embodiment. It is understood, however, that the tool-engagement portion 124 may be configured to receive a variety of tools, such as a flat head screwdriver, a Philips head screwdriver, a hexagonal ratchet head, or some other type of tool capable of rotating the cam mechanism 104. The groove 126 is an arcuate and/or convex detent formed circumferentially around the body 122 and sized to be about the same diameter or larger than the diameter of the retaining pin 120. The groove 126 may have a shape other than an arc and/or convex shape, for example the groove 126 may be square or elliptical to receive a like retaining pin 120. The retaining pin 120 operates to transitionally couple the cam mechanism 104 to the rod-receiving body 102, while allowing the cam mechanism 104 to be rotated relative to the rod-receiving body 102. Alternatively stated, the insertion of the retaining pin 120 into the rod-receiving body 102 and the groove 126 of the cam mechanism 104 keeps the cam mechanism 104 from sliding out of the first opening 116 of the rod-receiving body 102.
During installation and after the pin 120 has been inserted to retain the cam mechanism 104 in the first opening 116 of the rod-receiving body 102, the cam mechanism 104 is rotated to capture and retain the distraction rods 106. In one embodiment, one distraction rod 106 is captured and retained between a first portion 137 (
Rod-to-Screw Coupling Assembly
The rod-receiving body 202 includes a rod slot 212, a first opening 214, and a second opening 216. The rod slot 212 is a U-shaped channel. The first opening 214 is configured to receive the cam mechanism 204, while the second opening 216 is configured to receive the head portion 208 of the pedicle screw 210. The rod slot 212 is located between the first opening 214 and the second opening 216.
The cam mechanism 204 includes a tool engagement portion 218, a truncated portion 220, and a helical cam surface 222. The tool engagement portion 218 is similar to the tool engagement portion 124 of the previous embodiment. The operation of the cam mechanism 204, in particular the function of the truncated portion 220 and the helical cam surface 222, is described below. In all other respects, the rod-coupling assembly 200 is generally structurally and functionally similar to the previously described embodiment.
Device for Coupling to a Vertebral Body
First Transverse Connector
The transverse connector 406 is coupled to and extends from the first rod-receiving body 402. In one embodiment, the transverse connector 406 is integrally formed with the first rod-receiving body 402 in that the body 402 and connector 406 comprise a monolithic part. The seat 408 includes a channel 432 configured to receive and support the transverse connector 406. In the illustrated embodiment, the channel 432 is U-shaped, however it is understood that the channel 432 and/or transverse connector 406 may have alternative configurations.
The lever 410 includes a first contact surface 434, a fulcrum point 436, and a second contact surface 438. The fulcrum point 436 is located between the first and second contact surfaces 434, 438, respectively. The pin 416 is used to couple the lever 410 with the second rod-receiving body 404, where the lever 416 is free to rotate relative to the second rod-receiving body 404.
The cam mechanism 414 is rotated by a first amount as indicated by arrow 454. This rotation 454 urges the rod 418b further into the rod slot 426 of the second rod-receiving body 404. The rod 418b contacts the second contact surface 438 of the lever 410, as indicated by the arrow 456. This contact force 456 causes the lever 410 to rotate about the fulcrum point 436 (i.e., pin 416). This rotation of the lever 410 results in an applied force 458 on the transverse connector 406, where the first contact surface 434 of the lever 410 contacts the transverse connector 406. The applied force 458 causing the contact between the first contact surface 434 of the lever 410 and the transverse connector 406 laterally fixes the first rod-receiving body 402 to the second rod-receiving body 404. Alternatively stated, the rotation of the lever 410 constrains the translational degree of freedom 420a, which is identified in
The rotation 454 of the cam mechanism 414 further captures and secures the rod 418b with the assembly 400. The helical cam surface 446 of the cam body 444 acts to frictionally urge and retain the rod 418b between the cam mechanism 414 and a portion 460 of the second rod-receiving body 404. In a similar manner, rotation of the cam mechanism 412 in the first opening 424 of the first rod-receiving body 402 captures and secures the rod 418a between the cam mechanism 412 and a portion 462 of the first rod-receiving body 402. In one embodiment, the rotation of the cam mechanism 412 does not impart any stress to the transverse connector 406, lever 410, and/or second rod-receiving body 404.
Second Transverse Connector
The connector 506 includes a two-force rod member 512 coupled between first and second end portions 514, 516. The first end portion 514, which is representative of the second end portion 516, includes an inner surface 518 that encompasses an oval or elliptical shaped opening 520, according to the illustrated embodiment. The inner surface 518 is contoured to mate with a portion of a helical cam surface (see
During installation, the first cam mechanism 508 is placed into the first rod-receiving body 502 through the opening 520 of the first end portion 514. Rotation of the first cam mechanism 508 permits the threaded helical cam surface of the cam mechanism 508 to work in cooperation with the first rod-receiving body 502 to capture and secure a first rod (not shown). Likewise, a second portion of the threaded helical cam surface engageably mates with the inner surface 518 of the first end portion 514 of the connector 506.
In a similar fashion, the second cam mechanism 510 is placed into the second rod-receiving body 504 through an opening 522 in the second end portion 516 of the connector 506. Rotation of the second mechanism 510 results in capturing and securing a second rod (not shown). This rotation further results in the engagement of the second cam mechanism 510 with the second end portion 516 of the connector 506.
The rod-coupling assembly 500 advantageously permits two rods to be quickly and easily coupled together. In addition, the rod-coupling assembly 500 has a low profile, which tends to minimize the impact and trauma on the tissue in the vicinity of the vertebral body.
The amount of compression can be adjusted by utilizing different length connectors 506. The induced residual compression (i.e., preload) in the assembly 500 may advantageously permit the assembly 500 to be more resistant to fatigue damage and/or failure. Because any applied tensile stress (e.g., bending, pulling, etc.) must first exceed the amount of residual compressive stress already present in the assembly 500, the net amount of potentially damaging tensile stress can be reduced, which means that fatigue damage in the assembly 500 may not accumulate as fast, thus resulting in a longer operational life of the assembly 500. In turn, the longer operational life may reduce a number of downstream surgeries to repair, correct, and/or re-align any internal spinal correction hardware. These advantages, as well as other advantages, will be apparent to those skilled in the art and are applicable to the present embodiment and other embodiments, or combinations thereof, described herein.
The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Although specific embodiments of and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the invention, as will be recognized by those skilled in the relevant art. The teachings provided herein of the invention can be applied to various screws and rods, not necessarily the exemplary pedicle screws and distraction rods generally described above.
The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, to include U.S. Provisional Patent Application Nos. 60/629,840 filed Nov. 19, 2004; 60/666,819 filed Mar. 30, 2005; 60/672,590 filed Apr. 18, 2005; 60/703,622 filed Jul. 29, 2005; and 60/703,684 filed Jul. 29, 2005, are incorporated herein by reference, in their entirety. Aspects of the invention can be modified, if necessary, to employ screws, materials and concepts of the various patents, applications and publications to provide yet further embodiments of the invention.
These and other changes can be made to the invention in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all spine anchoring devices that operated in accordance with the claims. Accordingly, the invention is not limited by the disclosure, but instead its scope is to be determined entirely by the following claims.
This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Nos. 60/629,840 filed Nov. 19, 2004; 60/666,819 filed Mar. 30, 2005; 60/672,590 filed Apr. 18, 2005; 60/703,622 filed Jul. 29, 2005; and 60/703,684 filed Jul. 29, 2005, where these provisional applications are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 60629840 | Nov 2004 | US | |
| 60666819 | Mar 2005 | US | |
| 60672590 | Apr 2005 | US | |
| 60703622 | Jul 2005 | US | |
| 60703684 | Jul 2005 | US |
