Patent Publication Number: US-2021186565-A1

Title: Anti-Splay Head and Set Screw for Spinal Fixation

Description:
FIELD 
     The present technology is related generally to spinal fixation systems and processes and, more particularly, to an anti-splay head and set-screw arrangement. 
     BACKGROUND 
     Surgical screws and rods are used commonly in surgically correcting spinal abnormalities. Pedicle screw assemblies are used to facilitate placement and attachment of a spinal rod relative to the spine. Such pedicle screw assemblies include at least a bone screw section or anchor and at least one receiver portion attached to the bone screw. The bone screw sections are anchored to the vertebrae in the surgical procedure. 
     The receiver portions have arms between which portions of the spinal rod is received. The arms are often configured with internal threading corresponding to threading on a set screw. Following screw anchoring in the bone, and placement of the rod between the arms of the receiver, a set screw is threaded between the arms to secure the rod in the receiver. 
     The receiver portions of typical pedicle screws can be angularly or fixedly positionable with respect to the screw sections to facilitated desired attachment of the spinal rod between vertebrae. 
     Outward forces on the receiver arms over time following implantation try to splay the arms away from each other. One manner of limiting splay is by receiver and set-screw threads configured, such as with sloping thread faces, such that the set screw holds the arms inward, against the set screw. 
     Other attempted solutions for splaying include using a cap installable around at least a portion an exterior of the receiver arms, to hold the arms from moving away from each other. 
     These and other prior efforts to avoid splaying have various shortcomings. Shortcomings include undesirable cost, form factor (e.g., implant size or fit within the patient), and strength over time. 
     SUMMARY 
     The systems, process, and techniques of this disclosure relate generally to an anti-splay head and set-screw arrangement. 
     In one aspect, the present disclosure provides a system including an anti-splaying system including a receiver having a base, first and second arms, and first and second locking channels. The arms extend from the base forming a rod-receiving cavity, and arms have first and second inner threads formed in respective inner surfaces thereof. A first locking channel is formed in the inner surface of the first arm and a second locking channel being formed in the inner surface of the second arm. 
     The system also includes a set screw having a driving portion, such as approximal driving portion. The set screw also includes a body portion and an external thread extending form the body portion. The body is connected to the driving portion. The set screw also includes a distal locking component connected rotatably to the body portion. 
     The distal locking component of the set screw and the locking channel of the receiver are configured such that the locking component can, in operation of the system, slide into securing position within the locking channels. When in the secured position, the distal locking component fixes the two arms of the receiver from splaying away from each other. 
     In various embodiments, the locking component of the set screw has an anchor. The anchor is connected rotatably to the body portion by a slot of the body portion when the system is assembled. The anchor may be generally T-shaped, for instance. 
     Or, the body portion may include an anchor connected rotatably to a slot of the locking component of the set screw, in which case the anchor may be generally T-shaped. 
     In some cases, the locking component has opposing lateral ends having sizes and shapes corresponding to size and shape of the locking channel. Each lateral end may include opposing shoulders sized and shaped to engage opposing shoulders of respective ones of the locking channels, for instance. 
     In some cases, the first and second locking channels extend distally beyond a bottom of the first and second inner threads, respectively. The first and second locking channels may extend distally beyond a bottom of the first and second inner threads, respectively, by an amount equal generally to at least a height of the locking component, for example. 
     In some cases, the first locking channel extends between opposing sections of the first thread of the first receiver arm, from a first proximal opening to a first distal stop at or adjacent a distal end of the first inner thread, and the second locking channel extends between opposing sections of the second thread of the second receiver arm, from a second proximal opening to a second distal stop at or adjacent a distal end of the second inner thread. The set screw, including the locking component, has a height, and the first and second distal stops may be positioned, such that, in operation of the system, a distal surface of the locking component engages a spinal rod positioned in the cavity of the receiver, for instance. 
     In another aspect, the disclosure provides a system including an anti-splaying system having a bone anchor, a spinal rod, an anti-splay receiver, and an anti-splay set screw. The receiver and set screw of this aspect can in any way be like the receivers and set screws described above. 
     In yet another aspect, the disclosure provides a system includes a method for assembling an anti-splaying system, wherein the system includes any of the features described above. The method includes aligning an anti-splay set screw with an anti-splay receiver. 
     The aligning includes aligning opposing ends of a locking component of the set screw with opposing locking channels of the receiver. The method further includes sliding the opposing ends distally in the locking channels as outer threads of the set screw are threaded into inner threads of arms of the receiving component. 
     The method may include disposing the opposing ends of the locking component into the locking channels prior to engagement between the external threads and the internal threads, and moving the ends distally in the locking channels as the external threads of the set screw are threaded into the inner threads of the arms of the receiving component. 
     In some cases, the sliding is performed, with threading the locking-component into the receiver, until a distal surface of the locking component engages a rod positioned in the rod-receiving cavity of the receiver or stops of the locking channels of the receiver. 
     In still another aspect, the technology includes forming any aspects of the anti-splaying system described above. 
     Details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description, drawings, and claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows perspective views of an anti-splaying system partially disassembled, the system including an anti-splay receiver and an anti-splay set screw, according to embodiments of the present disclosure; 
         FIG. 2  is a cross section of the anti-splay set screw of  FIG. 1  taken along line F 2 -F 2  of  FIG. 1 ; 
         FIG. 3  is a side view of the anti-splaying system of  FIG. 1 ; 
         FIG. 4  is a perspective view of the anti-splay set screw being lowered for insertion to the receiver; 
         FIG. 5  is the perspective view of  FIG. 4  with the anti-splay set screw being threaded to final position within the anti-splay receiver; 
         FIG. 6  is a bottom view of the anti-splay set screw; 
         FIG. 7  is a top view of the anti-splay receiver; and 
         FIG. 8  is the top view of  FIG. 7 , with the anti-splay set screw inserted into the anti-splay receiver. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the drawings, and more particularly to the first figure,  FIG. 1  shows a perspective view of components of an anti-splay system, indicated generally by reference numeral  100 . 
     The system  100  includes an anti-splay head, or receiver  110 , and an anti-splay set screw  120 , according to embodiments of the present disclosure. 
     The receiver  110  has arms  112  extending up, or proximally, from a base  113 . The arms  112  define a rod cavity  114  between them, for receiving a spinal-fusion rod. A rod  300  is shown schematically, disposed in the cavity  114 , in  FIGS. 3 and 8 . 
     The set screw  120  extends from a driving, or proximal, end having a driving portion  122 , to an anti-splay, distal, end having a rotatable locking component  124 . In a contemplated embodiment, the driving portion  122  can be formed integrally or monolithically with or in the body  125  of the set screw  120 . The driving portion  122  includes a driving feature  123 , such as a cavity sized and shaped corresponding to any available set-screw driver (now shown). 
     The set-screw  120  further includes a primary body  125  extending between proximal and distal ends. The body  125  has a threaded exterior  126 . The threaded surface  126  corresponds in size and shape to a thread  116  of the receiver  110 , for being threaded into the receiver. 
     The locking component  124  is rotatably connected to the body  125 , as indicated by arrows in  FIG. 1 . While the arrows indicate a first direction of rotation, the connecting features are in various embodiments configured so that the locking component  124  can rotate in both direction, or in one direction or the other, only. 
     Reference numeral  128  indicates schematically in  FIG. 1  a portion of a rotatable connection between the locking component  124  and the set-screw body  125 . The connection is described further below in connection with  FIG. 2  and other figures. 
     Each arm  112  has an internal thread set  116 . And each thread set  116  is interrupted or separated by an anti-splay, or locking, channel  118 . The threads  116  oppose each other across the cavity  114 , and can be referred to as opposing threads or thread sections. 
     Each locking channel  118  extends distally from a proximal opening  117  (referenced in  FIG. 1 ) to a distal stop or bottom  119  ( FIG. 7 ). In operation of the system  100 , the locking component  124  is slid distally with respect to the locking channel  118 , as the external thread  126  of the set screw is threaded into the internal threads  116  of the receiver  110 , until a distal surface  230  ( FIG. 2 ) of the locking component  124  engages with the channel stop  119  ( FIG. 7 ) or the spinal rod  300  ( FIGS. 3 and 8 ). 
     The locking channel  118  in various embodiments extends down, or distally, by an amount sufficient to allow the set screw  120  to thread sufficiently into the receiver  110 . If the locking channel  118  is not long enough, the locking component  124  would bottom out before the set screw  120  is able to thread sufficiently into the receiver  110 . In various embodiments, each locking channel  118  extends distally beyond the internal thread  116  of the receiver arms  112 . Benefits of the locking channel  118  having sufficient height include avoiding having unused thread, and saving on manufacturing cost, at least by not having to make receiver thread  116  that is not used. 
     The amount of extension may be generally equivalent to at least a height of the locking component  124 , or at least generally a distance between a distal surface of the locking ends  400  and a distal-most portion of the set-screw thread  126 , so that the external thread  126  of the set screw  120  engages generally an entirety of the internal thread  116  of the arms  112  of the receiver  110  when the lateral ends  400  of the locking component  124  reach bottom  119  of the locking channel  118 , as the set screw  124  is threaded into the receiver  110 . 
     In contemplated embodiments, the system  100 , or a kit in which the system is provided, includes any of the components referenced. The system or kit can include any suitable components for performing the surgical procedures, including but not limited to implantable components and instruments for effecting the surgery. The system  100  can include, for instance, any of the anti-splay receiver  110 , the anti-splay set screw  120 , and the rod  300 . The system  100  or kit can include the driver referenced, but not shown. And the system  100  or kit can include any number and size of these parts, including multiple anti-splay set screws and receivers  120 ,  110 . 
     Turning to the second figure,  FIG. 2  illustrates a cross section of the set screw  120 , taken along line F 2 -F 2  of  FIG. 1 . The view shows more detail of the rotational connection  128  between the set-screw locking component  124  and the set-screw body  125 . 
     The connection  128  can be configured in any manner allowing the locking component  124  to rotate with respect to the body  125 . In the embodiment of  FIG. 2 , the connection  128  includes a generally T-shaped anchor  200 . 
     The body  125  has a generally T-shaped slot  210 . The slot  210  is sized and shaped to hold the anchor  200 . The components  200 ,  210  are sized to allow limited relative movement between the locking component  124  and set-screw body  125 . By the limited relative movement, the locking component  124  and body  125  are fixed generally from being moved away from each other, along a longitudinal (distal/proximal) direction (i. e., from moving away from each other). The anchor  200  can rotate in the slot, and thereby the locking component  124  with respect to the set-screw body  125 . 
     In a contemplated embodiment (not shown in detail), the slot is positioned instead in the locking component  124 , having a proximal opening, for holding a T-shaped anchor extending distally from the set-screw body  125 . This arrangement, including the T-shaped anchor and slot are considered shown inherently by the corresponding illustration of the T-shaped anchor and slot of  FIG. 2 . 
     The connection, while described in connection with at least one T-shape (e.g., a T-shaped anchor), can have any suitable configuration. 
     The connection can also include features facilitating the relative rotation, such as ball-bearings or a medical lubricant. 
     In operation of the system  100  ( FIG. 1 ), the locking component  124  is aligned into the locking channel  118  of the receiver  110 , by a surgeon or surgical robot. As the anti-splay set screw  120  is threaded into the receiver  110 , by the surgeon or robot turning a driver (or, driving instrument; not shown) against the driving feature  123  of the driving portion  122 , the locking component  124  slides down within the channel  118 . 
       FIG. 3  is a side view of the anti-splay receiver  110  and set screw  120  of  FIG. 1 . Rotatability of the locking component  124  relative to the set-screw body  125  is indicated again by arrow. 
       FIG. 3  also shows schematically an end view of the rod  300  positioned in the cavity  114  of the receiver  110 . 
       FIG. 4  is a perspective view of the anti-splay set screw  120  being lowered for insertion to the anti-splay receiver  110 . The movement is indicated generally by arrow in  FIG. 4 . 
     Prior to the movement of  FIG. 4 , the receiver  110  is secured to a patient vertebra, by a bone screw connected to the receiver  110 . The bone screw (not shown) can be any conventional or available type. The receiver  110  can be configured for top-loading or bottom-loading of the bone screw into the receiver  110 . The receiver  110  may in such ways be connected or connectable to the bone anchor readily—e.g., easily in the usual course of a surgery. 
     The anti-splay receiver  110  and anti-splay bone screw  120  can be further configured to allow desired relative motion, such as uniaxial or multiaxial motion. In some embodiments, the bone screw and the receiver  110  are fixed together, either by being formed integrally or monolithically, or by being fixedly connected to each other. 
     In operation of the anti-splaying system  100 , as the set-screw  120  is moved toward the receiver  110 , care is taken such that the locking ends  400  of the locking component  124  of the set screw  120  are aligned with the anti-splay channels  118  of the arms  112  of the receiver  110 . 
     The anti-splay channels  118  receive ends  400  of the locking component  124 . In various embodiments the locking component  124  is sized such that the ends extend further laterally than a maximum diameter of the screw body  125 , and in some cases farther than a maximum diameter than the thread  126 , as shown in the figures, and best seen in  FIG. 2 . 
       FIG. 5  shows the anti-splay set screw  120  having been threaded to a final position within the anti-splay receiver  110 . In this position, the locking component  124  would seat against the rod  300 , which is shown in  FIG. 3 , not  FIG. 4 . Motion of final threading, transitioning the set screw  120  to its final position, is indicated by arrow in  FIG. 5 . 
     As the set screw  120  is threaded into the receiver  110 , the locking component  124 , and particularly the ends  400  thereof, slide down in the anti-splay channels  118  of the receiver  110 . 
       FIG. 6  is a bottom view of the anti-splay set screw  120 . Relative rotatability between the set screw body  125  and the locking component  124  is indicated by arrow in  FIG. 6 , as in  FIG. 1 . 
     The ends  400  of the locking component  124  are configured such that, when engaged with the arms  112  of the receiver  110 , being slid into the anti-splay channels  118 , keep the arms  112  from moving away from each other. The connection keeps each arm  112  from moving away from the other arm—i.e., keeps the arms  118  from splaying. 
     The ends  400  of the locking component  124  include first engagement or locking features  600 , such as shoulders. The shoulders  600 , which may be referred to as external shoulders, engage second, corresponding, engagement or locking features  700  ( FIG. 7 ) of the receiver  110 . The shoulders  600  of the locking component  124  can be referred to as external shoulders, corresponding to internal shoulders  800  of the receiver  110 . 
     The locking component  124  can be referred to as dogbone for its general shape. The configuration of each end  400  can be referred to as a double-dovetail, corresponding to the opposing shoulders  600 . 
     In contemplated embodiments (not shown in detail), the locking or engaging features are configured in any of a variety of other ways. The features may include the locking component  124  having at each end  400  opposing internal shoulders. In this case, the internal shoulders of the locking component  124  form a locking-component void, for engaging with opposing external shoulders of a protrusion extending from or on an inner surface of each arm  112  of the receiver  110 , for instance. In this case, the locking component  124  is aligned so that the protrusion of the receiver  112  is received in the void of the locking component  124 , as the internal shoulder of the locking component  124  is slid down along the external shoulder of the protrusion of the receiver arms  112 . 
       FIG. 7  illustrates a plan view of the anti-splay receiver  110 . The view shows a top-down, or proximately looking, view of the receiver including anti-splay channels  118 . 
       FIG. 8  is the top view of  FIG. 7 , with the anti-splay set screw  120  inserted into the receiver  110 , yielding the anti-splaying system  100  assembled. Full assembly in some embodiments includes the anti-splay set screw and receiver  120 ,  110  being connected to the bone anchor (not shown). 
     The rod  300  is shown seated in the anti-splay receiver  110 . The rod  300  is secured in place there by the receiver  110  and the anti-splay set screw  120  threaded to the receiver  110 , with the ends  400  of the locking component  124  secured in the anti-splay channel  118  of the receiver  110 . 
     It should be understood that various aspects disclosed herein may be combined in combinations other than the combinations presented specifically in the description and the accompanying drawings. It should also be understood that, depending on the example, certain acts or events of any of the processes or methods described herein may be performed in other sequence, added, merged, or left out altogether (e.g., all described acts or events may not be necessary to carry out the techniques). 
     Any disclosure or claim herein referencing direction is not meant to limit interpretation of the disclosure, unless the disclosure or claim requires expressly such limitation. Reference, for instance, to movement up or down herein is not limited to movement in any certain direction during surgery or system assembly, as the surgery or assembly can be performed with any of a wide variety or orientations or in any suitable reference frame. 
     In addition, while certain aspects of this disclosure are described as being performed by a single module or unit for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of units or modules associated with, for example, a medical device. 
     Unless defined specifically otherwise herein, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc. It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless otherwise specified, and that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
     It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplification of the various embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.