Patent Application
20120130436
The present invention relates generally to bone fixation assemblies and more specifically to a reinforcing cross-connector assembly and method for placing a reinforcing cross-connector assembly between bone fixation elements.
When performing posterior cervical stabilization, a surgeon may place screws into the lateral mass of the cervical vertebral body, followed by a fixation element, such as a titanium rod. The titanium rod may be received in openings that pass through the heads of the screws, and may be secured in the openings with set screws. A pair of rods may be secured to the spine in a longitudinal arrangement, each rod extending generally parallel to one another. This construct stabilizes the cervical spine to aid in fusion of one or more levels. Occasionally, the condition of the spine requires a more rigid construct to stabilize the spine. In these situations, a transverse connecting element may be used to interconnect the two rods, like a bridge, to add stability to the construct. The transverse connecting element may be attached directly to the rod extending on one side of the spine and spanned to connect directly to the rod on the opposing side. This connecting element is sometimes referred to as a “rod-to-rod connector”, insofar as it interconnects two rods to one another.
U.S. Pat. No. 7,628,799 and U.S. Pat. No. 7,744,632 to Richelsoph et al. show a number of rod-to-rod connectors that clamp directly onto spinal fixation rods. Although these rod-to-rod connectors increase the overall rigidity of construct, they pose the risk of creating stress points along the fixation rods that can affect the integrity of the rods over time.
U.S. Pat. No. 7,645,294 to Kalfas et al. shows another type of transverse connecting element that attaches directly to the heads of bone screws, instead of the rods. This type of transverse connector is sometimes called a “head-to-head connector”, insofar as it interconnects the heads of two pedicle screw assemblies. Although head-to-head connectors reduce the concern for placing stress on the rods, head-to-head connectors create other concerns. The ability to use head-to-head connectors depends in large part on the location of the bone screws. Bone screws can be positioned relative to one another with different spacings and angular orientations. Head-to-head connectors often have fixed geometries that cannot be used unless they fit precisely over the bone screws. In addition, head-to-head connectors require separate set screws, caps, or other hardware to connect them with bone screw assemblies. This extra hardware adds to the number of small components that must be sterilized and handled. Moreover, head-to-head connectors often require at least two locking steps on each bone screw, for a total of at least four steps. In U.S. Pat. No. 7,645,294, for example, a set screw must be secured to the bone screw in a first step, and a cap must be secured over a plate and the set screw in a second step. Each of these steps requires the surgeon to precisely thread a very small component to another small component. These threading steps increase the difficulty of the procedure, and if done improperly, can lead to jammed threads and damage to the plates, set screws and caps.
There are multiple competing needs that must be addressed when designing an apparatus to reinforce spinal fixation assemblies, as demonstrated by the drawbacks observed with known rod-to-rod connectors and known head-to-head connectors. Rod-to-rod connectors raise the concern of putting excessive stress on the rods. Head-to-head connectors can reduce this concern, but raise new challenges. To connect to bone screws, the head-to-head connector must accommodate the components used in the bone screw assembly, and be able to adapt to different bone screw arrangements. As a result, known head-to-head connectors can satisfy the need to reduce stress on rods, but sacrifice other equally important needs. Therefore, there is a need for improved transverse connectors that address competing needs without sacrificing one need for another.
The drawbacks of known transverse connectors, and the competing needs they serve, are addressed by apparatuses and methods in accordance with the invention.
In a first aspect, a cross connector apparatus for reinforcing a bone fixation assembly may include a first connector element for coupling to a first bone screw assembly and a second connector element for coupling to a second bone screw assembly. The apparatus may also include an elongated connecting element for interconnecting the first connector element and second connector element. The first and second connector elements may each have an end, the end of the first connector element adapted to engage an elongated fixation element in a first bone screw assembly, and the end of the second connector element adapted to engage an elongated fixation element in a second bone screw assembly.
In a second embodiment, a cross connector apparatus for a bone fixation assembly includes a first connector element for coupling to a bone screw assembly. The first connector element may include a first tubular body having a bore with a longitudinal axis, and a first locking element retained in the bore of the first tubular body. The apparatus may also include a second connector element for coupling to a bone screw assembly. The second connector element may include a second tubular body having a bore with a longitudinal axis and a second locking element retained in the bore of the second tubular body. The apparatus may further include an elongated connecting element for interconnecting the first connector element and second connector element. The first and second tubular bodies may each include a first end for receiving the elongated connecting element and a second end opposite the first end comprising a socket. Each socket may be adapted for placement over a bone screw assembly.
In a third embodiment, a reinforced bone fixation assembly may include a first connector element. The first connector element may include a first tubular body having a bore with a longitudinal axis and a first link portion extending outwardly from the first tubular body. A first locking element may be retained in the bore of the first tubular body. The assembly may also include a second connector element. The second connector element may include a second tubular body having a bore with a longitudinal axis and a second link portion extending radially outwardly from the second tubular body. A second locking element may be retained in the bore of the second tubular body. The assembly may further include a fastener for connecting the first link portion of the first connector element to the second link portion of the second connector element, the fastener operable in a first condition to adjust the spacing between the first and second connector elements, and a second condition to fix the spacing between the first and second connector elements.
In a fourth embodiment, a method for locking fixation rods to bone screws may include placing a first fixation rod into a first bone screw head having an opening to receive the first fixation rod. A second fixation rod may be placed into a second bone screw head having an opening to receive the second fixation rod. A head-to-head cross-connector may be positioned in proximity to the first and second bone screw heads, the head-to-head cross-connector featuring a first cap, a second cap and a transverse connecting element extending between the first and second caps. The first cap may be attached over the first bone screw head, and the second cap may be attached over the second bone screw head. A single-step locking mechanism in the first cap may be operated to advance the first cap downwardly over the first bone screw head and lock down the first rod in the first bone screw head. A single-step locking mechanism in the second cap may be operated to advance the second cap downwardly over the second bone screw head and lock down the second rod in the second bone screw head.
The foregoing summary and the following description will be better understood in conjunction with the drawing figures, of which:
Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.
When used in reference to cylindrical or generally cylindrical objects, the term “longitudinal axis” as used herein means an axis connecting the center point of each cross section taken through the object, where the axis passes through the object parallel to the length of the object and perpendicular to the diameter of the object.
In a first embodiment, a cross connector apparatus for reinforcing a bone fixation assembly may include a first connector element for coupling to a first bone screw assembly and a second connector element for coupling to a second bone screw assembly. The apparatus may also include an elongated connecting element for interconnecting the first connector element and second connector element. The first and second connector elements may each have an end, the end of the first connector element adapted to engage an elongated fixation element in a first bone screw assembly, and the end of the second connector element adapted to engage an elongated fixation element in a second pedicle screw assembly.
In a second embodiment, a cross connector apparatus for a bone fixation assembly includes a first connector element for coupling to a bone screw assembly. The first connector element may include a first tubular body having a bore with a longitudinal axis, and a first locking element retained in the bore of the first tubular body. The apparatus may also include a second connector element for coupling to a bone screw assembly. The second connector element may include a second tubular body having a bore with a longitudinal axis and a second locking element retained in the bore of the second tubular body. The apparatus may further include an elongated connecting element for interconnecting the first connector element and second connector element. The first and second tubular bodies may each include a first end for receiving the elongated connecting element and a second end opposite the first end comprising a socket. Each socket may be adapted for placement over a bone screw assembly.
In a third embodiment, a reinforced bone fixation assembly may include a first connector element. The first connector element may include a first tubular body having a bore with a longitudinal axis and a first link portion extending outwardly from the first tubular body. A first locking element may be retained in the bore of the first tubular body. The assembly may also include a second connector element. The second connector element may include a second tubular body having a bore with a longitudinal axis and a second link portion extending radially outwardly from the second tubular body. A second locking element may be retained in the bore of the second tubular body. The assembly may further include a fastener for connecting the first link portion of the first connector element to the second link portion of the second connector element, the fastener operable in a first condition to adjust the spacing between the first and second connector elements, and a second condition to fix the spacing between the first and second connector elements.
The assembly may also include a first bone screw assembly with a first bone screw head, and a second bone screw assembly with a second bone screw head. The first connector element may extend over the first bone screw head and the second connector element may extend over the second bone screw head. The first and second connector elements may enclose a substantial portion of the first and second bone screw heads to prevent the first and second bone screw heads from radially expanding.
The first and second tubular bodies may be coaxially aligned with the first and second bone screw heads to center the first and second locking elements, respectively, in the first and second bone screw heads. The first and second tubular bodies may also be configured to apply pressure to a rod in response to screwing the first and second locking mechanisms into the first and second bone screw heads. One or both of the first and second link portions may include a pivoting joint.
In a fourth embodiment, a method for locking fixation rods to bone screws includes placing a first fixation rod into a first bone screw head having an opening to receive the first fixation rod. A second fixation rod is placed into a second bone screw head having an opening to receive the second fixation rod. A head-to-head cross-connector is positioned in proximity to the first and second bone screw heads, the head-to-head cross-connector featuring a first cap, a second cap and a transverse connecting element extending between the first and second caps. The first cap is attached over the first bone screw head, and the second cap is attached over the second bone screw head. A single-step locking mechanism in the first cap is operated to advance the first cap downwardly over the first bone screw head and lock down the first rod in the first bone screw head. A single-step locking mechanism in the second cap is operated to advance the second cap downwardly over the second bone screw head and lock down the second rod in the second bone screw head.
The method may include the step of adjusting the transverse connecting element to alter the relative positions of the first and second caps. The step of adjusting the transverse connecting element to alter the relative positions of the first and second caps may include the step of adjusting the distance between the first and second caps, and/or adjusting the angular orientation of the first cap relative to the second cap.
The transverse connecting element used in the method may include a first link portion extending from the first cap and a second link portion extending from the second cap. The step of adjusting the transverse connecting element may include the step of sliding the first link portion relative to the second link portion to adjust an area of overlap between the first link portion and second link portion. The step of adjusting the transverse connecting element may also include the step of locking the position of the first link portion relative to the position of the second link portion with a fastener. The step of adjusting the transverse connecting element may further include the step of pivoting a section of the first link portion relative to the first cap and/or pivoting a section of the second link portion relative to the second cap.
The step of operating a single-step locking mechanism in the first cap may include screwing a threaded locking element in the first cap into the opening in the first bone screw head to connect the first cap to the first bone screw head. The step of operating a single-step locking mechanism in the first cap may include the additional step of rotating the threaded locking element in the first bone screw to advance the first cap down over the first bone screw head and push the first rod downwardly into a seated position in the first bone screw head. The step of screwing the threaded locking element in the first cap into the opening in the first bone screw head and the step of rotating the threaded locking element in the first bone screw head to advance the first cap down over the first bone screw head may both be performed by a single continuous rotation of the threaded locking element.
The embodiments described in this section and illustrated in the drawings refer to assemblies that are specifically used in spinal fixation. It will be understood, however, that apparatuses and methods in accordance with the invention may be used in connection with many types of procedures, and need not be limited to spinal fixation.
Referring to
The rigidity of assembly 100 is reinforced with a head-to-head cross connector assembly 200 that bridges two pedicle screw assemblies 120. Connector assembly 200, which is shown in more detail in
Each cap 210 has a generally cylindrical body 220 that is hollow, forming a longitudinal bore 222. Bore 222 extends along the longitudinal axis L of the body 220. Each body 220 has a first end 230 adapted to receive one section of transverse connecting element 280 and one of the locking elements 290. Each first end 230 includes a pair of U-shaped channels 232 that are diametrically opposed to one another, with respect to longitudinal axis L. Each U-shaped channel 232 is positioned to receive one section of transverse connecting element 280, and orient the transverse connecting element transversely with respect to the orientation of fixation rods 110. Each body 220 has a second end 240 opposite first end 230. Each second end 240 has a pair of inverted U-shaped channels 242 that fit over the contours of rods 110.
In
Connector assembly 200 may be secured to occipitocervical fixation assembly 100 in the following manner. After rods 110 are secured in the two rows of pedicle screw assemblies 120, one or more locations along the construct are selected for placement of a connector assembly 200. The number of transverse connector assemblies that are used may vary depending on the amount of reinforcement that is desired. For this example, it is assumed that only one transverse connector assembly is needed to reinforce the entire construct.
To select a location for transverse connector assembly 200, an opposing pair of pedicle screw assemblies is selected that will support the transverse connector assembly. The location may be chosen based on the number and arrangement of pedicle screws, the condition of the bones, and other factors. In
Once a location for transverse connector assembly 200 is selected, the securing elements 150 inside the chosen pedicle screw assemblies 120 can be removed and replaced with locking elements 250. Alternatively, securing elements 150 can be left in place. A cap 210 is placed over the rod receiver 140 of each of the selected pedicle screw assemblies 120. The locking element 250 in each cap 210 is then threaded into the rod receiver 140 and driven downwardly by a driver to securely connect the cap to the rod receiver. The internal thread 224 in each cap matches an internal thread configuration 142 inside the corresponding rod receiver 140. When a cap 210 is placed over a rod receiver 140, the internal threads 142 and 224 align to form a continuous thread pattern with a smooth transition 213. Securing elements 250 are driven downwardly until they straddle the adjoining thread configurations 142 and 224 and overlap the transition 213. In this arrangement, securing elements 250 securely connect the caps 210 to their corresponding rod receivers 140. The internal thread configurations 142 and 224 and dimensions of the components are chosen so that each securing element 250 is completely advanced, or “bottoms out”, at a position in the rod receiver where it straddles the internal thread configurations and contacts the associated rod 110. Each securing element 250 bottoms out and secures the cap 210 in a condition where the perimeter edge inside each inverted U-shaped channel 242 firmly engages the contour of the associated rod 110.
Once the caps 210 are secured over the rod receivers 140, rod 280 is placed into the U-shaped channels 232 of each cap to bridge the two rod receivers. A locking element 290 is then inserted into the bore 222 of each cap 210 and driven downwardly with a driver until the locking element contacts rod 280. Each locking element 290 is driven against the rod 280 to urge the rod downwardly into a firmly seated position in the U-shaped channels 232 of the cap 210. At this stage, transverse connector assembly 200 is secured in place and reinforces the construct.
Referring to
Caps 320a and 320b each include a generally cylindrical body 322 having a hollow bore 323 that extends along the longitudinal axis L of the body. Caps 320a and 320b also include a link portion 324 that extends from the cap in a direction generally perpendicular to the longitudinal axis L of the body. The axial length of cap 320b is greater than the axial length of cap 320a, as shown in
The single-step locking mechanisms 350 are configured to lock spinal fixation rods 110 to pedicle screw assemblies 120, and lock connector assembly 300 to the pedicle screw assemblies 120, in a single turning operation. That is, the single-step locking mechanism 350 can “lock down” rods 110 in rod receivers 140, and also lock connector assembly 300 to the rod receivers, in one singular motion characterized by a continuous and uninterrupted rotation of the locking element 352. This singular motion has advantages over other head-to-head connector assemblies because it reduces the number of locking steps. In addition, it avoids the tedious steps of threading small components together. After the connector assembly 300 is placed over a pair of pedicle screw assemblies 120, each locking mechanism 350 is driven into a rod receiver 140 to lock down the fixation rod 110 in the rod receiver and lock the connector assembly 300 to the corresponding pedicle screw assembly. This results in only two tightening steps to secure the connector assembly 300. In contrast, the head-to-head connector in FIG. 1A of U.S. Pat. No. 7,645,294 requires at least four tightening steps. By reducing the number of tightening steps, connector assemblies in accordance with the invention, like connector assembly 300, shorten the time required to install and reinforce a fixation rod assembly, and reduce the number of complications that may occur.
Each single-step locking mechanism 350 includes a threaded locking element 352 that is generally cylindrical. Locking element 352 has a first end 354 and a second end 356. First end 354 has an external thread 355 configured to engage an internal thread 142 on the interior of a rod receiver 140. In addition, first end 354 includes an end face 358. End face 358 may or may not bear against fixation rod 110 and hold the fixation rod in a locked position in the rod receiver 140. As explained in more detail below, end face 358 need not contact rod 110 because other parts of the caps may contact and secure the rod. End face 358 has a slightly cone-shaped profile. Nevertheless, locking mechanisms in accordance with the invention may include end faces with various geometries, including convexly curved, concavely-curved, cone-shaped or flat geometries.
The second end 356 of each locking mechanism 350 includes a flange 351 that extends radially outwardly. Flanges 351 are held captive in annular grooves 321 in the interior of caps 320a and 320b, so that locking mechanisms 350 cannot move axially in the caps, but are free to rotate in the caps. Flanges in accordance with the invention preferably have a circular cross-section, but may have other cross-sectional configurations that extend into annular grooves.
Connector assembly 300 may be secured to an occipitocervical fixation assembly in the following manner. First, fastener 328 is inserted through elongated slot 326 of cap 320b and screwed partially into threaded hole 327 of cap 320a. The threaded shaft 329 of fastener 328 is screwed partially into hole 327, but not tightened completely, so that link portions 324 are coupled in the loosened condition. In this condition, the link portions 324 can translate and rotate relative to one another to adjust the spacing between the caps, until the spacing between the caps matches the spacing between the pedicle screw assemblies on which the connecting assembly 300 is to be placed. The caps 320a and 320b are adjusted until they align more or less with rod receivers 140. Then, any securing elements in the rod receivers 140 are removed (as they will be replaced by the single-step locking mechanisms 350). Caps 320a and 320b are then placed onto the rod receivers 140. Link portions 324 are left in the loosened condition so that the caps 320a and 320b can continue to adjust to the spacing and relative positions of the rod receivers 140. Once the caps 320a and 320b are placed on the rod receivers 140, they are advanced down over the rod receivers by rotating the single-step locking mechanisms 350. Caps 320a and 320b preferably have inverted U-shaped channels 325 to fit over the contours of the rods 110. Each U-shaped channel 325 has a rounded end 335 that engages the circumference of each rod after the cap is advanced down over the rod receiver. Once the caps 320a and 320b are completely advanced over the rod receivers, fastener 328 is tightened to lock the link portions 324 together in a fixed condition. As fastener 328 is tightened, the fastener pulls link portion 324 on cap 320a upwardly and into engagement with the underside of link portion 324 on cap 320b. This holds the two link portions 324 together in a tight frictional engagement, fixing the spacing between caps 320a and 320b.
At this stage, the fixation rods 110 rest inside rod receivers 140 but may or may not be locked in place in a fixed condition. In addition, connector assembly 300 rests on the pedicle screw assemblies 120 and interconnects the fixation rods 110 indirectly, but is not locked down onto the rod receivers 140. To lock down the fixation rods 110, and lock down connector assembly to the rod receivers 140, the locking mechanism 350 in each cap 320a and 320b is rotated so that the external thread 355 on each locking mechanism engages the internal thread 142 inside each rod receiver 140. Once the external threads 355 on locking mechanisms 350 engage the internal threads 142 in the rod receivers 140, the locking mechanisms are rotated in their respective caps. Each locking mechanism 350 is held captive in its respective cap by its flange 351, and cannot move axially in the cap. As each locking mechanism 350 is driven into a rod receiver 140, the flange 351 pulls the cap downwardly over the rod receiver and forces the rod downwardly into a seated position in the rod receiver. Once seated, the fixation rod 110 is locked in the rod receiver 140, and the connector assembly 300 is locked onto the pedicle screw assemblies 120.
In the embodiments described thus far, the caps play a number of important roles. The cylindrical geometry of the caps allows the caps to be placed over cylindrical rod receivers in a coaxial relationship. That is, the longitudinal axis passing through a cap is coextensive with the longitudinal axis of the rod receiver, when the cap is placed over the rod receiver. The section of each cap that receives the rod receiver has an inner diameter that is equal to or slightly greater than the outer diameter of each rod receiver. In this arrangement, the cap is centered over the rod receiver and can slide axially over the rod receiver in a telescoping relationship when the cap is placed over the rod receiver. Caps 320a and 320b circumscribe the rod receivers 140 and prevent the rod receivers from radially expanding or splaying when locking mechanisms 350 are advanced into the rod receivers.
Caps 320a and 320b are automatically centered in coaxial alignment with rod receivers 140 upon placing the caps over the rod receivers. As such, caps 320a and 320b further serve as centering guides to position the locking mechanisms 350 in proper alignment with inner threads 142 within rod receivers 140. This automatic centering ensures that the single-step locking mechanisms 350 readily engage inner threads 142 when the cross-connector assembly is to be locked.
Referring to
The end face 358 of single-step locking mechanism 350 need not engage the rod 110 in those situations where the rounded ends 335 of U-shaped channels 325 contact the rod. The rounded ends 335 provide two points of contact to advance the rod 110. The end face 358 can provide a third point of contact on the rod 110, if desired, but it is not necessary to have this third point of contact if the rod is contacted by the rounded ends 335. Likewise, if end face 358 contacts the rod 110, the rounded ends 335 of channels 325 need not contact the rod. More contact points on the rod 110 are preferred, however, as they distribute forces over a larger area of the rod.
In many instances, the pedicle screws to be bridged with a cross connector assembly will not be parallel to one another. Moreover, the two rods being bridged may not be parallel to one another. In such cases, the rod receivers will not be parallel to one another, and the orientations of the caps must be adjusted accordingly. Cross connector assemblies in accordance with the invention may include any number of mechanisms to adjust the relative orientation between the caps, so as to accommodate the relative orientations of pedicle screws and rods being bridged.
Referring now to
Although
While preferred embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions, including substitutions of elements between the embodiments shown, will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the scope of the invention.
This application claims priority to U.S. Provisional Application Ser. No. 61/416,460, filed Nov. 23, 2010, the contents of which are incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61416460 | Nov 2010 | US |
