Patent Publication Number: US-2022233218-A1

Title: Flexible Sleeve For Bone Fixation, And Related Systems And Methods

Description:
TECHNICAL FIELD 
     The present invention relates to a flexible sleeve for coupling to a bone anchor, particularly for extending from an implanted bone anchor to provide a guide channel through soft tissue between the bone anchor and an ex vivo location. 
     BACKGROUND 
     Traditional spine surgeries were conducted utilizing an open procedure resulting in a relatively large incision, disruption or resection of significant soft tissue and long recovery times for patients. Minimally invasive techniques have become increasingly popular, particularly for spine surgeries, wherein relatively small incisions and surgical pathways are utilized to perform surgical procedures on a patient, generally resulting in a smaller incision or several relatively small incisions, less retraction and resection of soft tissue and shorter recovery times for patients in comparison to open procedures. Minimally invasive procedures are, in certain circumstances, able to obtain comparable or improved long term surgical outcomes in comparison to open procedures and can provide short term benefits including reduced post-operative pain, reduced use of post-operative narcotics, reduced tissue disruption, thereby permitting reduced scar tissue and potential benefits if a revision is necessary, reduced blood loss, accelerated recovery time, shorter hospital stays and cosmetically appealing smaller incisions. However, the smaller incision or incisions diminish the line-of-sight for a surgeon to directly view a surgical site, because patient soft tissue often limits a surgeon&#39;s ability to view the surgical site. 
     A common procedure in spine surgeries involves fixing screws to several vertebra and securing the screws and vertebra relative to each other with a rod. Such spinal constructs are typically implanted by mounting enclosed or substantially enclosed rigid cannulae or sleeves to the screws such that the enclosed rigid cannulae or sleeves create a surgical pathway through soft tissue and provide access for the surgeon to the surgical site. Minimally invasive spine instruments utilized for such procedures, such as those employing K-wires, can be difficult to assemble, tend to be bulky and extend a significant distance out of a patient&#39;s skin, limit a surgeons ability to view the surgical site, and can also inhibit imaging utilizing a C-arm or Fluoroscope as a result of their size and material composition and may be difficult to detach from the screws at the conclusion of the procedure. In addition, current minimally invasive fixation of screws and placement of rods in spine surgery often result in undesirable levels of trauma to a patient&#39;s soft tissue in and around the surgical site, along the surgical pathway and proximate the incision. Once assembled for rod insertion, these conventional minimally invasive systems are typically locked into a predetermined position and inhibit a surgeon&#39;s options in adapting their surgical technique to a particular patient&#39;s anatomy or in adapting the instruments to implant the components in a manner that would benefit the patient. 
     SUMMARY 
     According to an embodiment of the present disclosure, a flexible tubular member for guiding insertion of instrumentation to a bone screw affixed within bone includes a tubular body that is flexible, constructed of textile material, and defines a longitudinal axis. The tubular body also defines a proximal end and a distal end opposite each other along the longitudinal axis. The tubular body further defines a guide channel that extends from a proximal opening at the proximal end to a distal opening at the distal end. An attachment member is located at the distal end of the tubular body and is configured to couple the distal end to a proximal portion of the bone screw. The attachment member has an annular shape around the guide channel and is configured to expand responsive to a predetermined tensile force applied to the tubular body for decoupling from the bone screw. 
     According to another embodiment of the present disclosure, a system for bone fixation includes a bone screw having a head and a shaft extending therefrom toward a distal end of the bone screw in a distal direction. The head also defines a tapered portion that narrows in the distal direction. The system includes a sleeve that is flexible and constructed of textile material. The sleeve defines a longitudinal axis and a proximal end and a distal end opposite each other along the longitudinal axis. The sleeve also defines a guide channel that extends from a proximal opening at the proximal end to a distal opening at the distal end. An attachment ring is located at the distal end of the sleeve and is configured to couple the distal end of the sleeve to the tapered portion of the bone screw. The attachment ring extends annularly around the guide channel and is configured to expand responsive to a predetermined tensile force applied to the sleeve for decoupling the sleeve from the bone screw. 
     According to an additional embodiment of the present disclosure, a method for securing a bone screw to bone includes attaching a flexible sleeve to a head of the bone screw such that the sleeve extends proximally from the bone screw. Attaching the sleeve involves advancing the bone screw through a guide channel defined by the sleeve until a distal surface of the head contacts an attachment ring located at a distal end of the sleeve. The attachment ring defines an inner diameter that is less than a maximum diameter of the head. The method includes inserting a driver into a socket defined by the head, advancing the bone screw through soft tissue to a fixation site of the bone; and rotating the driver about a central axis, thereby driving a shaft of the bone screw into the fixation site such that the sleeve extends through the soft tissue and a proximal end of the sleeve is located ex vivo. The method also includes applying a tensile force to the sleeve, thereby forcing expansion of the attachment ring for decoupling the sleeve from the bone screw. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of illustrative embodiments of the present application, will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the structures of the present application, there is shown in the drawings illustrative embodiments. It should be understood, however, that the application is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIG. 1  is a rear plan view of a spinal surgery system that includes a flexible sleeve extending from an implanted bone anchor to an ex vivo location, according to an embodiment of the present disclosure; 
         FIG. 2  is a perspective view of the flexible sleeve illustrated in  FIG. 1 , wherein the sleeve is depicted in a theoretical neutral configuration; 
         FIG. 3  is a perspective view of an ex vivo portion of the flexible sleeve illustrated in  FIG. 1 ; 
         FIG. 4  is an enlarged perspective view of the flexible sleeve illustrated in  FIG. 3 ; 
         FIG. 5  is a side view of a prior art bone anchor for use with the flexible sleeve illustrated in  FIGS. 1-4 ; 
         FIG. 6  is a perspective view of a distal portion of the flexible sleeve coupled to a head of the bone anchor illustrated in  FIG. 5 ; 
         FIG. 7  is an exploded perspective view of a spinal surgery system that employs the flexible sleeve illustrated in  FIGS. 1-4 ; 
         FIG. 8  is a plan elevation view of the sleeve coupled to a bone anchor and a drive tool of the spinal surgery system illustrated in  FIG. 7 ; 
         FIG. 9  is a plan elevation view of the sleeve guiding insertion of a second drive tool carrying an extension member of the spinal surgery system illustrated in  FIG. 7  toward the bone anchor; 
         FIG. 10  is a partial sectional side view of the extension member illustrated in  FIG. 9  coupled to the bone anchor, wherein the flexible sleeve is omitted for illustration purposes; 
         FIG. 11  is a plan elevation view of the extension member illustrated in  FIG. 9  coupled to the bone anchor with the second drive member removed from the flexible sleeve; 
         FIG. 12  is an enlarged perspective view of a distal portion of the extension member illustrated in  FIG. 11  shown residing in the sleeve and coupled to the bone anchor; 
         FIG. 13  is a perspective view of the distal portion of the flexible sleeve illustrated in  FIG. 12  coupled to the bone anchor; 
         FIG. 14  is a perspective view of the distal portion of the flexible sleeve illustrated in  FIG. 13 , wherein an attachment member of the sleeve is broken and the sleeve is partially withdrawn, exposing a distal portion of the extension member that is coupled to the bone anchor; 
         FIG. 15  is a perspective view of various components of the spinal surgery system illustrated in  FIG. 7  attached to adjacent vertebral bodies during an intermediate phase of a spinal surgery, according to an embodiment of the present disclosure; and 
         FIG. 16  is a perspective view of various of the components of the spinal surgery system illustrated in  FIG. 15  attached to adjacent vertebral bodies during a final phase of the spinal surgery, according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The present disclosure can be understood more readily by reference to the following detailed description taken in connection with the accompanying figures and examples, which form a part of this disclosure. It is to be understood that this disclosure is not limited to the specific devices, methods, applications, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the scope of the present disclosure. Also, as used in the specification including the appended claims, the singular forms “a,” “an,” and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. 
     The term “plurality”, as used herein, means more than one. When a range of values is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. All ranges are inclusive and combinable. 
     The terms “approximately” and “substantially”, as used herein with respect to dimensions, angles, and other geometries, takes into account manufacturing tolerances. Further, the terms “approximately” and “substantially” can include 10% greater than or less than the stated dimension or angle. Further, the terms “approximately” and “substantially” can equally apply to the specific value stated. 
     The embodiments described below pertain to flexible sleeves configured to couple to an implant member, such as a bone anchor, and provide a guide channel through soft tissue for guiding insertion of instrumentation and/or additional implant components through the soft tissue to the implant member. For example, current spinal fixation procedures, such as spinal fusion procedures, particularly minimally invasive spinal fusion procedures, tend to employ percutaneous pedicle screws for anchoring to pedicles of one or more vertebral bodies at the surgical treatment site. Such percutaneous pedicle screws commonly comprise a bone screw having a reduced-profile head and a separate extension member that can be coupled to the reduced-profile head of the bone screw. These extension members tend to define a distal anchor head that can be severed or otherwise decoupled form the remainder of the extension member. The anchor head commonly defines a U-shaped channel for receiving a spinal rod therein for affixing a relative position between adjacent vertebral bodies. Alternatively, the anchor head can define a C-shaped channel, such as for use in a screw system configured for side-loading of a spinal rod therein. The anchor head can be configured for polyaxial angulation relative to the bone screw for providing fine adjustability for the orientation of the spinal rod receivable therein. 
     The current state of the art favors mounting the extension member to the bone screw prior to implanting the bone screw. However, this technique can result in bulky components extending outwardly from the patient, particularly as the number of inserted pedicle screws and attached extension members increases, thereby providing physical obstructions at the surgical site and also obstructing the surgeon&#39;s direct line of site. This technique can also impose excessive forces on soft tissue, and can thus result in ischemia therein. Moreover, these components tend to be radiopaque, thus also obstructing electronic imaging of the surgical site, such as radiology and fluoroscopy. However, coupling the extension members to the bone screws in vivo also poses challenges, particularly in that it tends to be difficult to located the heads of the bone screws blindly in the patient, especially if the surgeon is limited to percutaneous access to the implanted bone screw. Furthermore, coupling the extension member to the head of the bone screw in vivo can be complicated by fluids and/or tissues that might become interposed between mating surfaces of the bone screw and the extension member. 
     The flexible sleeves disclosed herein provide a reliable guide channel through soft tissue, such as for inserting the extension member. In this manner, the bone screw can be implanted prior to coupling with the extension member, which reduces physical obstruction at the surgical site and provides the surgeon with greater ease of movement during the surgery. Additionally, the flexible material of the sleeve allows the ex vivo portion thereof to be laid substantially flat along the outer surface of the patient&#39;s skin, thereby also reducing visual obstruction of the surgical site, including electronic visualization, e.g., fluoroscopy. Furthermore, the flexible sleeve material is preferably constructed to allow the sleeve to expand radially (i.e., outwardly) without reducing the overall length of the sleeve, thereby reducing friction imposed on the surrounding soft tissue. 
     Referring now to  FIG. 1 , an exemplary embodiment of a bone fixation system  100  includes a flexible tubular body  2 , also referred to herein as a flexible sock or sleeve  2 , that is configured to couple to a bone anchor  4 , such as a bone screw, that is affixable to a target site in bone  102 . The sleeve  2  is configured to extend from a distal end  6  thereof attached to the bone anchor  4  and proximally through soft tissue  104  to a proximal end  8  positioned at an ex vivo location with respect to patient anatomy. The sleeve  2  is configured to guide insertion of implant components and/or instrumentation through the soft tissue  104  to the bone anchor  4 . In the illustrated example, the bone anchor  4  is a pedicle bone screw configured for insertion into a vertebral body  105  through a pedicle thereof, and the sleeve  2  extends from the pedicle screw  4  proximally through the soft tissue  104  along a trajectory axis  106  to an incision  108  at a skin line  110  of patient anatomy, and further extends from the incision  108  to the proximal end  8 . As shown, the sleeve  2  is preferably configured such that a proximal, ex vivo portion thereof can fold away from the trajectory axis  106  and lay along an outer surface of the patent&#39;s skin  110 . 
     Referring now to  FIG. 2 , the sleeve  2  is elongate along a longitudinal direction L and defines a longitudinal axis X oriented along the longitudinal direction L. The distal and proximal ends  6 ,  8  of the sleeve  2  are opposite each other along the longitudinal direction L, such that the distal end  6  is spaced from the proximal end  8  in a distal direction D along the longitudinal direction L, and the proximal end  8  is spaced from the distal end  6  in a proximal direction P along the longitudinal direction L. It should be appreciated that the proximal and distal direction P, D are opposite one other and are each mono-direction components of the longitudinal direction L, which is bi-directional. It should also be appreciated that  FIG. 2  depicts the sleeve  2  in a theoretical neutral configuration free of external forces (including gravity). 
     The sleeve  2  further defines a guide channel  10  that extends along the longitudinal axis X from a distal opening  12  at the distal end  6  to a proximal opening  14  at the proximal end  8 . The sleeve  2  also defines an exterior surface  16  and an interior surface  18  spaced from each other along a radial direction R that is perpendicular to the longitudinal axis X (and thus also perpendicular to the longitudinal direction L). A wall  20  of the sleeve  2  extends radially (i.e., along the radial direction R) between the exterior and interior surfaces  16 ,  18 . It should be appreciated that the interior surface  18  defines the guide channel  10 . 
     The sleeve  2  includes an attachment member  22  at or adjacent the distal end  6  for coupling the distal end  6  to a proximal portion of the bone anchor  4 , as described in more detail below. The proximal end  8  of the sleeve  2  preferably includes an introduction member  24  configured to facilitate insertion of instrumentation into the guide channel  10 . As shown, the introduction member  24  can be a ring that extends annularly around the guide channel  10  and defines the proximal opening  14 . The ring  24  is preferably configured to provide a funnel-like structure at the proximal opening  14 . The sleeve  2  defines a length L 1 , measured along the longitudinal direction L from the proximal end  8  to the distal end  6 . The sleeve  2  also defines a cross-sectional dimension R 1 , measured along the radial direction R. 
     The sleeve  2  is preferably constructed of a textile material, which can be a woven, braided, knitted, and/or electrospun construct. The textile material can be an implant grade biocompatible material, such as polyethylene terephthalate (PET), ultra-high-molecular-weight polyethylene (UHMWPE), polydioxanone (PDS), polypropylene (PP), polyester, and nylon, by way of non-limiting examples. However, it should be appreciated that because the sleeve  2  is configured for temporary use during a surgical procedure and not as a permanent or long-duration implant, the textile material need not be implant grade material, but can be a medical grade material and/or a bio-degradable material. 
     The sleeve  2  is also preferably configured to be radially compliant, particularly to be capable of expanding radially (i.e., along the radial direction R) and circumferentially while maintaining a substantially constant length. Stated differently, the sleeve  2  is preferably constructed such that the cross-sectional dimension R 1  is configured to expand while the length L 1  remains substantially constant. Such a configuration can be provided by the manner in which the sleeve  2  is constructed. By way of a non-limiting example, the textile material of the sleeve  2  can be constructed by knitting polyethylene terephthalate (PET) fibers in a weft knit pattern, which provides high radial compliance. Other materials and constructions can be employed to provide the sleeve  2  with high radial compliance. In this manner, the sleeve  2  can expand radially to accommodate passage of implant components and/or instrumentation through the guide channel  10 , substantially without lengthening or shortening the length L 1 , thereby avoiding or at least reducing friction between the exterior surface  16  of the sleeve  2  and the soft tissue  104  adjacent the sleeve  2 . The sleeve  2  is also preferably configured to collapse in a substantially flat manner (i.e., without folding in on itself) in the soft tissue  104 . In this manner, the sleeve  2  can be configured to avoid compressing the soft tissue  104  that surrounds the sleeve  2 . Additionally or alternatively, the sleeve  2  material can also be configured to prevent or at least reduce moisture seepage into the guide channel  10 , for example by employing a low porosity. In other embodiments, the sleeve  2  need not inhibit moisture within the guide channel  10 . Furthermore, the sleeve  2  is preferably configured to be substantially radiolucent, thereby avoiding obstructing fluoroscopy images. Additionally or alternatively, one or more portions of the sleeve  2  can be partially radiopaque so as to be visible in fluoroscopy or X-ray images. Moreover, the sleeve  2  can be configured to be at least partially visible in magnetic resonance imaging (MRI). This can be achieved, for example, by incorporating metallic filaments in the textile material, by way of a non-limiting example. Additionally or alternatively, the sleeve  2  can carry antibiotic and/or disinfecting liquids to provide therapeutic advantages for soft tissue in contact with or in close proximity to the sleeve  2 . Moreover, the textile material of the sleeve  2  can optionally include light emitting fibers, such as for providing illumination within the guide channel  10  and/or for emitting ultraviolet (UV) light for sterilizing soft tissue adjacent the sleeve  2 . 
     Referring now to  FIGS. 3 and 4 , the sleeve  2  can also be configured such than any portion thereof, or at least any portion between the attachment member  22  and the introduction member  24 , is configured to lay substantially flat when in a resting configuration and when the guide channel  10  thereof is unoccupied. Thus, the physician can lay the ex vivo portion of the sleeve  2  extending from the incision  108  substantially flat along the outer surface of the patient&#39;s skin  110 . In this manner, the sleeve  2  can advantageously provide access to the implanted bone anchor  4  while reducing obstruction to the surgical site. Stated differently, the ex vivo portion of the sleeve  2  can be folded out of the way until access to the bone anchor  4  is desired. If needed, the physician can manually flatten the ex vivo portion of the sleeve  2 , such as by running a finger or thumb along the exterior surface  16  thereof in a manner depressing the sleeve  2  against the skin  110 , or by pinching the sleeve  2  between the thumb and forefinger and running the thumb proximally toward the proximal end  8 , by way of non-limiting examples. 
     Referring now to  FIG. 5 , the bone anchor  4  can be a bone screw, such as a pedicle screw, having a head  30  and a shaft  32  extending from the head  30  in the distal direction D. A proximal surface  34  of the head  30  defines a proximal end of the bone screw  4 . Accordingly, the proximal surface  34  can be referred to as the proximal end of the bone screw  4 . The shaft  32  preferably defines external threads  36  for engaging bone material at the targeting site. The external threads  36  can be helical, as shown, and can extend toward a distal tip  38  that defines a distal end of the bone screw  4 . Accordingly, the distal tip  38  can be referred to as the distal end of the bone screw  4 . The bone screw  4  defines a central screw axis  40  along the longitudinal direction L. The bone screw  4  preferably defines a cannulation along the central screw axis  40  for receiving receive a guide wire, such as a Kirschner wire or “K-wire”, for guiding insertion of the bone screw  4  to the target site. 
     The head  30  of the bone screw  4  is preferably configured for attachment to an extension member that extends from the bone screw to an ex vivo location. Accordingly, the head  30  depicted throughout the illustrated embodiment does not include external threads, although it should be appreciated that the sleeve  2  can be employed with screw heads that are threaded. The head  30  defines an outer surface  42  that is preferably smooth and has a curvate or semi-spherical shape to facilitate rotation with respect to the extension member, as described in more detail below. Accordingly, the head  30  defines a maximum width W 1  and preferably defines a tapered portion  43  that narrows distally (i.e., in the distal direction D) to a neck  45  having a second width W 2  that is less than the maximum width W 1 . 
     The head  30  also preferably defines one or more sockets  44   a,b  for receiving one or more complimentary drive tools. As shown, the head  30  can define a first socket  44   a  configured to receive a first drive tool, such as a driver for driving the bone screw  4  into the target site in the bone  102 . The head  30  can also define a second socket  44   b  configured to receive a second drive tool, such as a driver for driving the extension member into engagement with the head  30 , as described in more detail below. Each socket  44   a,b  can define a drive surface configured to mate with a corresponding bit of the associated drive tool. For example, the drive surface of the first socket  44   a  can be a star-hex pattern configured to mate with a star-hex drive bit, and the drive surface of the second socket  44   b  can define internal threading configured to engage external threading on a threaded post drive bit, by way of non-limiting examples. It should be appreciated that other drive surface patterns are within the scope of the present disclosure. The bone screw  4  and the features thereof can be configured as more fully described in U.S. Pat. No. 8,262,662, issued Sep. 11, 2012, in the name of Beardsley et al. (hereinafter the “Beardsley Reference”); U.S. Pat. No. 10,136,923, issued Nov. 27, 2018, in the name of Keyer et al. (hereinafter the “Keyer Reference”); and U.S. Patent Publication No. 2019/0150989, published May 23, 2019, in the name of Biester et al. (hereinafter the “Biester Reference”), the entire disclosure of each of which is incorporated herein by reference. 
     Referring now to  FIG. 6 , the sleeve  2  is configured to couple to the bone anchor  4 , particularly at or adjacent the head  30  thereof. As shown, the attachment member  22  is preferably configured to couple to the bone screw  4  at a location distally spaced from the maximum width W 1  of the head  30 , such as the neck  45 , as shown, or the tapered portion  43  of the head  30 , by way of non-limiting examples. The attachment member  22  preferably defines an annular shape that extends around the guide channel  10  at or adjacent the distal end  6  of the sleeve  2 . For example, the attachment member  22  can be an annular ring or band, and can define the distal opening  12 , although in other embodiment the attachment member  22  can be proximally spaced from the distal opening  12 . The attachment member  22  can define an inner diameter D 1  that is equivalent to or slightly greater than the second width W 2  of the bone anchor  4 , such that an inner surface of the attachment member  22  preferably forms a snug fit with an exterior surface of the bone anchor  4 , such as at the neck  45  or the tapered portion  43  of the head  30 . 
     The attachment member  22  is also configured to expand, particularly by increasing its inner diameter D 1 , responsive to a decoupling force, such as a predetermined tensile force applied to the sleeve  2  along the longitudinal axis X. In this manner, the physician can apply the predetermined tensile force to the sleeve  2 , such as by pulling on the introduction member  24 , when it is desired to decouple the sleeve  2  from the bone anchor  4 . By way of a non-limiting example, the attachment member  22  can be defined by a glue, epoxy, or other material configured to be applied in a liquid or semi-liquid phase in a ring annularly around or at least partially around the guide channel  10  and further configured to harden into a solid phase. In other embodiments, the attachment member  22  can be defined by a portion of the sleeve  2  that is at least substantially melted and subsequently solidified into a ring annularly around or at least partially around the guide channel  10 . The foregoing example attachment members  22  can be configured to expand by breaking, ripping, tearing, or otherwise undergoing a mode of mechanical failure. In additional embodiments, the attachment member  22  can be a spring member, such an annular or semi-annular spring, such as a slotted or C-shaped ring, or a spiral spring, that is configured to open or otherwise by expand (such as by expanding the inner diameter D 1  thereof) responsive to the predetermined tensile force. These embodiments that employ a spring member as the attachment member  22  can be advantageous because they need not undergo a mode of mechanical failure to expand and de-couple from the bone screw  4 . It should be appreciated that other techniques for constructing the attachment member  22  are within the scope of the present disclosure. 
     With reference to  FIGS. 7-16 , further use of the spinal fixation system  100  will be described according to an example surgical procedure. In this example, the surgical procedure is a spinal fusion surgery, such as for providing spinal decompression, although it should be appreciated that the sleeve  2  can be employed with similar benefit for other types of surgical procedures. 
     Referring now to  FIG. 7 , the spinal fixation system  100  includes the sleeve  2  and the bone anchor  4 , as described above, and can further include a first drive member, such as a first drive bit  120  having a distal end  122  configured to engage the first socket  44   a  of the bone anchor  4  and a proximal end  124  configured to engage a drive tool. 
     The system  100  can further include an extension member  130  that is elongate along the longitudinal direction L and configured to couple to the head  30  of the bone anchor  4 . The extension member  130  defines a proximal end  132  and a distal end  134  spaced from each other along the longitudinal direction L. The extension member  130  can include a main portion  136  that extends distally from the proximal end  132 , an anchor head  138  that extends to and defines the distal end  134 , and a frangible portion  140  interposed between the main portion  136  and the anchor head  138 . The extension member  130  can also define a longitudinally elongate channel  142  that extends along the main portion  136 , such as from the proximal end  132 , and extends along a portion of the anchor head  138 . The elongate channel  142  also extends from opposed sides  144   a ,  144   b  of the main portion  136  and the anchor head  138 , respectively, along a transverse direction T that is substantially perpendicular to the longitudinal direction L. In this manner, the elongate channel  142  can define a pair of elongate tabs along the main portion  136 . Accordingly, the main portion  136  can also be referred to as “extension tabs”  136 . The elongate channel  142  is configured for guided insertion of a spinal rod into the anchor head  138 , as discussed in more detail below. 
     The anchor head  138  preferably defines a chamfer surface  146  that extends to the distal end  134  for facilitating advancement of the extension member  130  through the sleeve  2 . The anchor head  138  also defines a mounting formation, such as a receptacle  148 , configured to receive the head  30  of the bone anchor  4 . The frangible portion  140  is configured to break responsive to a predetermined force, such as a predetermined torsion force and/or pulling force, thereby separating the extension tabs  136  from the anchor head  138  after the anchor head  138  couples to the bone anchor  4 . The extension member  130 , including the extension tabs  136  and the anchor head  138 , are more fully described in the Biester and Beardsley References. 
     The system  100  can include a second drive member, such as a second drive tool  150 , configured to extend longitudinally within the elongate channel  142  of the extension member  130  for coupling with the extension member  130  and advancing it through the guide channel  10  of the sleeve  2  to the head  30  of the bone anchor  4 . The second drive tool  150  can include a handle  152  located at a proximal end thereof. The handle  152  can define a proximal mounting formation, such as an annular recess  154 , for mounting with the proximal end  132  of the extension member  130 . The second drive tool  150  can further define a cannulation  153  extending from the proximal to a distal end of the second drive tool  150 . The cannulation  153  can be sized to receive the first drive bit  120  therein. In this manner, the second drive tool  150  can advance the extension member  130  through the guide channel  10  of the sleeve  2  and along the first drive bit  120  while the distal end  122  thereof is engaged with the first socket  44   a  of the bone anchor  4 . 
     A distal end of the second drive tool  150  can define a distal mounting formation, such as a threaded mounting post  155  having external threads for engaging the internal threads of the second socket  44   b  of the bone anchor  4 , thereby locating the head  30  of the bone anchor  4  within the receptacle  148  of the anchor head  138 . Such threaded engagement between the threaded mounting post  155  and the internal threads of the second socket  44   b  effectively holds the bone anchor  4  in place and prevents it from angulating relative to the second drive tool  150  while additional coupling elements are attached to the anchor head  138 . 
     The second drive tool  150  can also include one or more additional formations for carrying one or more associated coupling elements for coupling the anchor head  138  to the head  30  of the bone anchor  4  in secure fashion. For example, the second drive tool  150  can include a first boss  156  for carrying a retention member  160 , such as a snap-on collar, for insertion over the head  30  in a manner to reside in the receptacle  148  between the anchor head  138  and the head  30  of the bone anchor  4 . The second drive tool  150  can also include a second boss  158  for carrying a locking member  170 , such as a locking cap, for engagement with a complimentary locking formation of the anchor head  138  in a manner retaining the spinal rod in the channel  142  of the anchor head  138 , as described in more detail below. It should be appreciated that the second driving tool  150  can also include a formation configured to engage a complimentary formation of the main portion  136  of the extension member  130  for applying the predetermined torsion force and/or pulling force thereto and decoupling the main portion  136  from the anchor head  138 . 
     Referring now to  FIG. 8 , the physician can engage the first drive bit  120  with the bone anchor  4 , particularly by inserting the distal end  122  of the bit into the first socket  44   a  of the head  30  of the bone anchor  4 . In the illustrated example, the bone anchor  4  is a pedicle screw  4 . The physician can subsequently insert the connected pedicle screw  4  and first drive bit  120  into the guide channel  10  of the sleeve  2  from the proximal opening  14  thereof and advance the pedicle screw  4  and first drive bit  120  distally through the guide channel  10  until the attachment member  22  engages the desired portion of the pedicle screw  4 , such as the neck  45  or the tapered portion  43  of the head  30  (shown more clearly in  FIG. 6 ). With the pedicle screw  4 , first drive bit  120 , and sleeve  2  coupled in this manner, the physician can employ the first drive bit  120  to advance the pedicle screw  4  and a distal portion of the sleeve  2  through an incision, such as a stab incision, through the soft tissue  104  along the trajectory axis  106  to the target site of a first vertebral body  105  and can drive the screw shaft  32  into bone material  102  at the target site. After the shaft  32  is inserted to the desired depth in the first vertebral body  105 , the first drive bit  120  can be withdrawn proximally from the guide channel  10 , leaving the distal portion of the sleeve  102  within the soft tissue  104  along the trajectory axis  106 . 
     With the first drive bit  120  removed from the sleeve  2 , the physician can lay the ex vivo portion of the sleeve  2  flat along the outer surface of the patient&#39;s skin and out of the way, as described above. The physician can then use a drive tool, such as the first drive bit  120 , to couple a second pedicle screw  4  to a second sleeve  2  and insert the second pedicle screw  4  into a second target site in bone  102 , such as into another pedicle, such as a pedicle of a second vertebral body  105  or the opposite pedicle of the first vertebral body  105 , with the sleeve extending proximally therefrom through the soft tissue  104  to a second ex vivo location in like manner to the first sleeve  2 . The physician can repeat the foregoing steps as needed to insert additional pedicle screws into additional target sites with associated sleeves  2  extending therefrom to respective ex vivo locations. The physician can lay the ex vivo portions of the sleeves  2  flat along the outer surface of the patient&#39;s skin to reduce obstruction of the surgical site and also to reduce imaging obstruction. 
     When it is desired to couple the extension member  130  to the pedicle screw  4 , the physician can ensure that the extension member  130  is properly coupled to the second drive tool  150 . The physician can manipulate the ex vivo portion of the sleeve  2  into alignment along the trajectory axis  106 , such as by lifting the introduction member  24 . Referring now to  FIG. 9 , with the ex vivo portion of the sleeve  2  aligned, the physician can manipulate the second drive tool  150  to insert the distal end  134  of the extension member  130  through the introduction member  24  and into the guide channel  10 . The physician can further advance the second drive tool  150  and the extension member  130  coupled thereto distally until the threaded mounting post  155  engages the second socket  44   b  of the screw head  30 . 
     Referring now to  FIG. 10 , the physician can rotate the second drive tool  150  to threadedly mate the threaded mounting post  155  to the internal threads of the second socket  44   b  until the threaded mounting post  155  is fully seated in the second socket  44   b , thereby causing the head  30  to reside in the receptacle  148  of the anchor head  138  at a desired depth. The collar  160  can be advanced distally along the outer surface  42  of the head  30  until the collar  160  is fully seated with respect to the head  30 . In its fully seated position, an inner surface  162  of the collar  160  can extend distally across the location of maximum width W 1  and along the tapered portion  43  of the head outer surface  42 , while an outer surface  164  of the collar  160  engages an interior surface  149  of the anchor head  138  that defines the receptacle  148  thereof. The collar  160  of the illustrated embodiment is configured to snap into place on the head  30  once the distal end of the collar  160  clears the location of maximum width W 1 , thereby providing the physician with tactile feedback and preferably also auditory feedback (e.g., a snapping or clicking sound) indicating when the collar  160  is fully seated with respect to the screw head  30  and the anchor head  138 . The collar  160  is further configured to provide the anchor head  138  with polyaxial angulation with respect to the screw head  30 , as described more fully, for example, in the Keyer and Biester References. 
     Referring now to  FIGS. 11 and 12 , with the anchor head  138  coupled to the pedicle screw  4 , the second drive tool  150  can be decoupled from the second socket  44   b  and withdrawn from the sleeve  2 , leaving the extension member  130  within the sleeve  2  and coupled to the pedicle screw  4 . The flexibility of sleeve  2  allows the physician to manipulate the extension member  130  through the sleeve  2 , such as by gripping around the ex vivo portion of the sleeve  2  that contains the extension member  130 , for angulating the extension member  130  polyaxially relative to the pedicle screw  4 , as needed, such as to place the elongate channel  146  at a desired orientation for receiving the spinal rod. 
     Referring now to  FIGS. 13 and 14 , when it is desired to remove the sleeve  2 , the physician can apply the predetermined tensile force F 1  thereto, thereby breaking the attachment member  22 . The physician can then withdraw the sleeve  2 , thereby exposing the extension tabs  136  and the elongate channel  142 . In this manner, the sleeve  2  can protect the screw head  30 , anchor head  138 , and extension tabs  136  in vivo until it is desired to insert the spinal rod in the channel  142 . 
     Referring now to  FIGS. 15 and 16 , the physician can repeat one or more of the foregoing steps as needed to insert pedicle screws  4  into a plurality of vertebral bodies, such as a pair of adjacent vertebral bodies  105 , and for coupling extension members  130  to the pedicle screws  4 . It should be appreciated that the physician can elect to remove a sleeve  2  entirely or only partially from the associated extension tabs  136  for inserting the spinal rod into the elongate channels  142 . For example,  FIG. 15  shows a first pair of extension members  130   a  from which the sleeves  2  have been entirely withdrawn. For these extension members  130   a , an associated spinal rod  180  can be inserted into the elongate channels  142 , such as from the proximal ends  132  of the extension members  130 , and the spinal rod  180  can be advanced distally along the channels  142  until the spinal rod  180  is seated in the channels  142  of the anchor heads  138 . 
     Also depicted is a second pair of extension members  130   b , one of which has had its associated sleeve  2  fully withdrawn, and the other of which has had its associated sleeve  2  partially withdrawn, exposing a distal portion of the elongate channels  142 . For these extension members  130   b , the physician can elect to insert the spinal rod  180 , such as with assistance of a rod carrying tool  182 , distally along the channel  142  of the extension member  130   b  having had the sleeve  2  fully withdrawn therefrom. The physician can use the tool  182  to insert a distal end of the rod  180  into the exposed anchor head  138  of the extension member  130   b  having the sleeve  2  only partially withdrawn therefrom. The physician can then seat the rod  180  as desired in both of the associated anchor heads  138 . In this manner, at least one of the sleeves  2  can continue to provide a barrier between the soft tissue  104  and the associated extension members  130 . Additionally, by distally advancing the spinal rod  180  along only one of the second pair of extension members  130   b , less compressive force can be applied to the soft tissue adjacent and particularly between these extension members  130   b . The remaining sleeve  2  can optionally remain in place over the associated extension tabs  136  for subsequent operation, thereby reducing entry of in vivo fluids into the associated channel  142 , thus providing a cleaner channel  142  for insertion of subsequent members therein, such as the locking cap  170  for locking the spinal rod  180  in the anchor head  128 , and also for a decoupling tool that applies the predetermined torsional force and/or pulling force to the frangible portion  140  for decoupling and removing the extension tabs  136 . In such embodiments, a portion of the extension tabs  136  can optionally remain within the sleeve  2  while the frangible portion  140  is broken, and the sleeve  2 , the extension tabs  136 , and the decoupling tool can optionally be removed from the patient in unison. In this manner, the sleeve  2  can be employed to reduce friction and/or abrasion between the extension members  130  and the associated instrumentation during the surgical procedure. 
     It should be appreciated that the sleeve  2  described herein can be employed with other types of bone fixation procedures or any procedure where it is advantageous to provide a guide channel through soft tissue to a bone anchor. 
     Although the disclosure has been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, features of the various embodiments described herein can be incorporated into one or more and up to all of the other embodiments described herein. Moreover, the scope of the present disclosure is not intended to be limited to the particular embodiments described in the specification. As one of ordinary skill in the art will readily appreciate from that processes, machines, manufacture, composition of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure.