US20070129731A1 - Percutaneous Access Devices And Bone Anchor Assemblies - Google Patents

Abstract

A percutaneous access device includes an inner tube and an outer tube disposed about at least a portion of the inner tube. The outer tube may be sized to span from a skin incision in a patient to a site proximate the spine of the patient. The distal end of the outer tube may be adapted to releasably engage a bone anchor. The inner tube may be adjustable relative to the outer tube between a first position and a second position in which the distal end of the inner tube contacts the bone anchor. A bone anchor assembly includes a bone anchor having a distal bone engaging portion and a receiving member having a recess for receiving a spinal fixation element. The proximal end of the receiving member may have an arcuate groove formed on an exterior surface thereof to facilitate connection of an instrument to the receiving member.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. patent application Ser. No. 10/738,286, filed Dec. 16, 2003, which is incorporated herein by reference.
BACKGROUND
• For a number of known reasons, spinal fixation devices are used in orthopedic surgery to align and/or fix a desired relationship between adjacent vertebral bodies. Such devices typically include a spinal fixation element, such as a relatively rigid fixation rod or plate, that is coupled to adjacent vertebrae by attaching the element to various anchoring devices, such as hooks, bolts, wires, or screws. The fixation elements can have a predetermined contour that has been designed according to the properties of the target implantation site, and once installed, the fixation element holds the vertebrae in a desired spatial relationship, either until desired healing or spinal fusion has taken place, or for some longer period of time.
• Spinal fixation elements can be anchored to specific portions of the vertebrae. Since each vertebra varies in shape and size, a variety of anchoring devices have been developed to facilitate engagement of a particular portion of the bone. Pedicle screw assemblies, for example, have a shape and size that is configured to engage pedicle bone. Such screws typically include a threaded shank that is adapted to be threaded into a vertebra, and a head portion having a rod-receiving element, usually in the form of a U-shaped recess formed in the head. A set-screw, plug, or similar type of closure mechanism is used to lock the fixation element, e.g., a spinal rod, into the rod-receiving head of the pedicle screw. In use, the shank portion of each screw is threaded into a vertebra, and once properly positioned, a rod is seated through the rod-receiving member of each screw and the rod is locked in place by tightening a cap or other closure mechanism to securely interconnect each screw and the fixation rod.
• Recently, the trend in spinal surgery has been moving toward providing minimally invasive devices and methods for implanting bone anchors and spinal fixation devices.
SUMMARY
• Disclosed herein are percutaneous access devices that facilitate the delivery and implanting of bone anchors into bone, in particular, one or more vertebral bodies of the spine. In particular, the disclosed percutaneous access devices permit the delivery and implanting of one or more bone anchors in a minimally invasive manner thereby limiting trauma to surrounding tissue. Moreover, the percutaneous access devices disclosed herein can provide a percutaneous pathway between a skin incision and the bone anchor that may be used to deliver components of the bone anchor, such as the fastening mechanism, the fixation element, and/or instruments to the bone anchor. Also, disclosed herein are bone anchors that facilitate the connection of instruments, such as a percutaneous access device, to the bone anchor.
• In accordance with one exemplary embodiment, a percutaneous access device includes an inner tube and an outer tube disposed about at least a portion of the inner tube. The outer tube, in the exemplary embodiment, is sized to span from at least a skin incision in a patient to a predetermined site proximate the spine of the patient. The distal end of the outer tube may be adapted to releasably engage a bone anchor. The inner tube, in the exemplary embodiment, may be adjustable relative to the outer tube along the longitudinal axis of the outer tube between a first position and a second position in which the distal end of the inner tube contacts the bone anchor.
• In accordance with another exemplary embodiment, a bone anchor assembly includes a bone anchor having a proximal head and a distal bone engaging portion and a receiving member coupled to the bone anchor. The receiving member, in the exemplary embodiment, may have a proximal end, a distal end and a recess for receiving a spinal fixation element, such as a rod or a plate. The proximal end of the receiving member, in the exemplary embodiment, may have at least one arcuate groove formed on an exterior surface thereof to facilitate connection of an instrument, such as a percutaneous access device, to the receiving member.
BRIEF DESCRIPTION OF THE DRAWINGS
• These and other features and advantages of the percutaneous access devices and bone anchor assemblies disclosed herein will be more fully understood by reference to the following detailed description in conjunction with the attached drawings in which like reference numerals refer to like elements through the different views. The drawings illustrate principles of the percutaneous access devices and bone anchor assemblies disclosed herein and, although not to scale, show relative dimensions.
• FIG. 1 is a perspective view of an exemplary embodiment of a percutaneous access device;
• FIG. 2 is a perspective view of the components of the percutaneous access device ofFIG. 1;
• FIG. 3 is a perspective view of the distal end of the percutaneous access device ofFIG. 1;
• FIG. 4 is a perspective view of the distal end of the percutaneous access device ofFIG. 1 coupled to an exemplary embodiment of a bone anchor assembly;
• FIG. 5 is a side elevational view of the bone anchor assembly ofFIG. 4;
• FIG. 6 is a side elevational view of the receiving member of the bone anchor assembly ofFIG. 4;
• FIG. 7 is a side elevational view in cross-section of the distal end of the percutaneous access device ofFIG. 1 coupled to the receiving member of the bone anchor assembly ofFIG. 4;
• FIG. 8 is a side elevational view in cross-section of the distal end of the outer tube of the percutaneous access device ofFIG. 1 and the receiving member of the bone anchor assembly ofFIG. 4;
• FIGS. 9 and 10 are side elevational views in cross section of the distal end of the inner tube of the percutaneous access device ofFIG. 1 and the receiving member of the bone anchor assembly ofFIG. 4;
• FIGS. 11A-11D are perspective views of the distal end of the percutaneous access device ofFIG. 1 and the receiving member of the bone anchor assembly ofFIG. 4, illustrating exemplary steps for releasably coupling the distal end of the percutaneous access device to the receiving member of the bone anchor assembly;
• FIG. 12 is a side elevational view an another exemplary embodiment of a bone anchor assembly;
• FIG. 13 is a side elevational view of the receiving member of the bone anchor assembly ofFIG. 12;
• FIG. 14 is a side elevational view in cross section of the receiving member of the bone anchor assembly ofFIG. 12;
• FIG. 15 is a side elevational view in cross section of an arcuate groove of the receiving member of the bone anchor assembly ofFIG. 12;
• FIG. 16 is a side elevational view in cross-section of the distal end of the another exemplary embodiment of a percutaneous access device coupled to the receiving member of the bone anchor assembly ofFIG. 12;
• FIGS. 17A and 17B are perspective views of an alternative embodiment of a percutaneous access device and a bone anchor assembly, illustrating a threaded connecting between the percutaneous access device and the bone anchor assembly;
• FIGS. 18A and 18B are perspective views of an alternative embodiment of a percutaneous access device and a bone anchor assembly, illustrating a plurality of externally threaded removable tabs for releasable engagement with an instrument such as a percutaneous access device;
• FIGS. 19A-19D are perspective views of an alternative embodiment of a percutaneous access device and a bone anchor assembly, illustrating the percutaneous access device and the bone anchor assembly interconnected by one or more internal wires;
• FIGS. 20A-20D are perspective views of an alternative embodiment of a percutaneous access device and a bone anchor assembly, illustrating the percutaneous access device and the bone anchor assembly interconnected by one or more external wires;
• FIG. 21 is a perspective view of an alternative embodiment of a bone anchor assembly having a plurality of removable tabs for releasable engagement with an instrument such as a percutaneous access device;
• FIGS. 22A-22B are perspective views of an exemplary embodiment of a percutaneous access device, illustrating axial cut-outs provided in the outer tube of the percutaneous access device; and
• FIGS. 23A-23B are perspective views of an alternative embodiment of a percutaneous access device and a bone anchor assembly, illustrating flexible tabs provided on the distal end of the percutaneous access device for releasable engagement with the bone anchor assembly.
DETAILED DESCRIPTION
• Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the percutaneous access devices and bone anchor assemblies disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those of ordinary skill in the art will understand that the percutaneous access devices and bone anchor assemblies specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely be the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.
• The articles “a” and “an” are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.
• The term “distal” as used herein with respect to any component or structure will generally refer to a position or orientation that is proximate, relatively, to the bone surface to which a bone anchor is to be applied. Conversely, the term “proximal” as used herein with respect to any component or structure will generally refer to a position or orientation that is distant, relatively, to the bone surface to which a bone anchor is to be applied.
• The terms “comprise,” “include,” and “have,” and the derivatives thereof, are used herein interchangeably as comprehensive, open-ended terms. For example, use of “comprising,” “including,” or “having” means that whatever element is comprised, had, or included, is not the only element encompassed by the subject of the clause that contains the verb.
• FIGS. 1-5 illustrate an exemplary embodiment of apercutaneous access device10. The exemplarypercutaneous access device10 can facilitate the delivery and implanting of a bone anchor, such as the exemplarybone anchor assembly100 illustrated and described below, into bone, in particular, one or more vertebral bodies of the spine. In particular, the exemplarypercutaneous access device10 can facilitate the delivery and implanting of a bone anchor in a minimally invasive manner and can provide a percutaneous pathway between a skin incision in the patent and the bone anchor that may be used to deliver components of the bone anchor, such as the closure mechanism, one or more fixation elements, and/or instruments to the bone anchor. Thepercutaneous access device10 is preferably adapted to be introduced through a minimally invasive percutaneous incision, which is a relatively small incision that typically has a length less than the diameter or width of the device being inserted therethrough. Although the exemplarypercutaneous access device10 described below is designed primarily for use in spinal applications, one skilled in the art will appreciate that the exemplarypercutaneous access device10, as well as the other exemplary embodiments described below, may be used to facilitate the implantation of any type of bone anchor to any type of bone.
• The exemplarypercutaneous access device10 includes aninner tube12 and anouter tube14 disposed about at least a portion of theinner tube12. In the illustrated exemplary embodiment, theouter tube14 is coaxially disposed about theinner tube12 such that theinner tube12 and theouter tube14 share a commonlongitudinal axis16. One skilled in the art will appreciate, however, that theouter tube14 andinner tube12 need not be coaxially aligned. Theinner tube12 and theouter tube14, in the exemplary embodiment, are generally cylindrical in shape, having an approximately circular cross-section. One skilled in the art will appreciate, however, theinner tube12 and theouter tube14 may have other cross-sectional shapes, including, for example, elliptical or rectilinear. In the exemplary embodiment, theinner tube12 andouter tube14 have analogous cross-sections, however, one skilled in the art will appreciate theinner tube12 and theouter tube14 can have different cross-sectional shapes. The axial length of theinner tube12 andouter tube12 may vary depending on, for example, the patient anatomy, the procedures employed, and/or, that area of the spine in which thedevice10 is employed. Theinner tube12 and theouter tube14 may be linear, as in the exemplary embodiment, or may curved or angled along one or more sections or the entire length thereof. Theinner tube12 and theouter tube14 may be constructed from any suitable biocompatible material, including, for example, a metal, such as stainless steel, or a polymer, from any conventional method of manufacturing medical devices.
• Although the illustrated exemplary embodiment includes an inner tube and an outer tube, one skilled in the art will appreciate that any number of tubes, e.g., one or more tubes, may be employed depending on, for example, the type of bone anchor employed and the manner by which the device is releasably engaged to the bone anchor. For example, exemplary embodiments of a percutaneous access device having a single outer tube are described below.
• Continuing to refer toFIGS. 1-5, the inner tube orsleeve12 includes aproximal end20, adistal end22, and alumen24 extending between theproximal end20 and thedistal end22. Thelumen24 extends the length of theinner tube12 and defines alongitudinal axis26 of theinner tube12. The outer tube orsleeve14 includes aproximal end30, adistal end32, and alumen34 extending between theproximal end30 and thedistal end32. Thelumen34 may extend the length of theouter tube14 and defines alongitudinal axis36 of theouter tube14. Theinner tube12 in positionable within thelumen36 of theouter tube14. In the exemplarypercutaneous access device10, theinner tube12 is longitudinally adjustable with respect to theouter tube14. For example, theinner tube12 may adjustable from a first, proximal position, in which thedistal end22 of theinner tube12 is positioned proximal to thedistal end32 of theouter tube14 as illustrated inFIG. 3, and a second, distal position, in which thedistal end22 of theinner tube12 is positioned proximate to thedistal end32 of theouter tube14. In the exemplary embodiment, thedistal end22 of theinner tube12 preferably contacts at least a portion of the bone anchor assembly when theinner tube12 is in the second position, as illustrated inFIGS. 4 and 7 and as discussed in more detail below.
• The exemplarypercutaneous access device10 may include anadjustment mechanism40 that allows an operator to adjust the relative longitudinal position of theinner tube12 and theouter tube14. In the illustrated embodiment, for example, theadjustment mechanism40 is a hollow, tubular shapedcap41 havinginternal threads42 that engageexternal threads44 provided on theproximal end30 of theouter tube14. Thethreads42,44 allow thecap41 to be longitudinal adjusted relative to theouter tube14. In the exemplary embodiment, theinner tube12 is connected to thecap41 and, thus, can move withcap41 as thecap41 is advanced or withdrawn relative to theouter tube14. For example, theproximal end30 of theinner tube12 of the exemplary embodiment may include one or moreresilient tabs46, one or more of which may have aprojection48 that seats within an annular grove provided on the interior surface of thecap41 to thereby connect theproximal end30 of theinner tube12 to thecap41. In the illustrated embodiment, tworesilient tabs46 are provided on opposite sides of theouter tube14. Theprojection48, in the exemplary embodiment, is sized to rotate with in the groove provided in thecap41, thus allowing thecap41 to rotate relative to theinner tube12. Theresilient tabs46 are radially flexible to facilitate connection to and removal from thecap41. One skilled in the art will appreciate that other configurations for connecting theinner tube12 to thecap41 are possible and are within the scope of the present disclosure.
• Theinner tube12 may be inhibited from rotating with respect to theouter tube14, limiting the relative motion of theinner tube12 and theouter tube14 to along thelongitudinal axis16 of the percutaneous access device. For example, one or moreresilient tabs56 may be provided on theinner tube12 approximately midway between theproximal end20 and thedistal end22 of theinner tube12, although other positions are possible. In the illustrated embodiment, tworesilient tabs56 are provided on opposite sides of theouter tube14. One or more of theresilient tabs56 may include aprojection58 that is sized and shaped to seat within alongitudinal slot54 provided in theouter sleeve14. Theresilient tab56 can be radially flexible to facilitate insertion into and removal from theslot54. Theprojection58 can slide within theslot54 and, thereby can limit the relative motion between theinner tube12 and theouter tube14 to along thelongitudinal axis16 of thepercutaneous access device10. One skilled in the art will appreciate that other configurations for connecting theinner tube12 to theouter tube14 are possible and are within the scope of the present disclosure.
• Theinner tube12 may have one or more sidewall openings orslots60 formed therein. In the illustrated exemplary embodiment, theinner tube12 includes twoopposed slots60 that extend longitudinally from thedistal end22 of theinner tube12. Like theinner tube12, theouter tube14 may have one or more sidewall openings orslots62 formed therein. In the illustrated exemplary embodiment, theouter tube14 includes twoopposed slots62 that extend longitudinally from thedistal end32 of theinner tube12. Theslots60 and62 can be used to facilitate positioning of a spinal fixation device, such as a rod or a plate, relative to one or more bone anchors. Methods and devices for spinal fixation element placement are disclosed in commonly owned, co-pending U.S. patent application Ser. No. 10/737.537, filed Dec. 16, 2003, entitled Method and Devices for Spinal Fixation Element Placement (Attorney Docket No. 101896-210) and commonly owned co-pending U.S. patent application Ser. No. 10/738,130, filed Dec. 16, 2003, entitled Method and Devices for Minimally Invasive Spinal Fixation Element Placement, (Attorney Docket No. 101896-209), both of which are incorporated herein in by reference. To facilitate positioning of a spinal fixation element, theslots60 and theslots62 are preferably aligned with one another along at least a portion of the longitudinal axis of thepercutaneous access device10. The width and length of theslot60 andslot62 may be varied depending on the particular methods, instruments, and fixation elements being employed. In one exemplary embodiment, for example, the length of theslots60 and62 is selected to span at least from the skin incision to the distal end of theinner tube12 and theouter tube14, respectively. In such embodiments, theslots60 and62 may be accessible from outside of the patient. In another exemplary embodiment, the length of theslots60 and62 is selected to span from the distal end of theinner tube12 and theouter tube14, respectively, to a point distal to the skin incision. In such embodiments, theslots60 and62 may be accessible only from the lumens of the inner and outer tubes.
• In embodiments in which multiple slots are employed, theslots60,62 need not be similarly sized (width and/or length). For example, the one ormore slots60 may be sized differently than the one ormore slots62, the one or more of theslots60 on the inner tube may be sized differently thanother slots60, and/or one or more of theslots62 on the outer tube may be sized differently thanother slots62. Although the exemplary embodiment includes two opposing slots on theinner tube12 and theouter tube14, respectively, one skilled in the art will appreciate that any number of slots may be provided, e.g., no slots, one, two, three, etc. slots, may be provided depending on the method, instruments, and/or fixation element employed.
• One skilled in the art will appreciate that theslots60 and62 are optional and that in certain embodiments slots may not be provided.
• Referring toFIGS. 1-5 and7, thepercutaneous access device10 is preferably releasably engageable to a bone anchor. In the exemplary embodiment, theouter tube14 may be releasably engaged to a bone anchor, such asbone anchor assembly100. For example, theouter tube14 may be engaged to a bone anchor in a manner that allows thepercutaneous access device10 to be connected to thebone anchor100 during use, e.g., during implantation and/or delivery and/or fastening of a spinal fixation element to the bone anchor, and allows the percutaneous access device to be disconnected from thebone anchor100 at the conclusion of the procedure. Preferably, thepercutaneous access device10 can be disconnected remotely. For example, the exemplary embodiment, thepercutaneous access device10 can be disconnected from the bone anchor by manipulation of the proximal end of thepercutaneous access device10, as discussed in more detail below.
• Thedistal end32 of theouter tube14 includes a pair of opposed longitudinally extendingtabs70A and70B that may releaseable engage a bone anchor. In the exemplary embodiment, thetabs70A and70B are defined by the sidewalls of theouter tube14 and are separated by slots62A and62B. In certain exemplary embodiments, thetabs70A and70B may be flexible and resilient in the radial direction to facilitate connection to a bone anchor. For example, thetabs70A and70B may be flexed apart in the radial direction from a first, relaxed position to facilitate advancement of the tabs longitudinally over a portion of the bone anchor. Once positioned about a portion of the bone anchor, thetabs70A and70B may provide a radially compressive force on the bone anchor as thetabs70A and70B attempt to return to the first, relaxed position. In other exemplary embodiments, including the exemplarypercutaneous access device10, thetabs70A and70B need not be flexible and resilient.
• In the illustrated exemplary embodiment, eachtab70A and70B may include one or more radially inward facing projection72 that is sized and shaped to seat within an opening provided in a portion of the bone anchor. The size, shape and number of projections can be varied depending on, for example, the opening(s) provided on the bone anchor and type of connection desired. In the illustrated exemplary embodiment, for example, eachprojection72A,72B is generally arcuate in shape and has a cross section that is complementary to an arcuate groove130 provided in the spinal fixationelement receiving member108 of the exemplarybone anchor assembly100 described below. In particular, theprojection72A has adistal surface74, aproximal surface76, and a generally radially facing connectingsurface78 that spans between thedistal surface74 and theproximal surface76, as shown inFIG. 8. In the illustrated embodiment, thedistal surface74 is generally oriented perpendicular to the longitudinal axis of theouter tube14 and the connectingsurface78 is generally oriented parallel to the longitudinal axis of theouter tube14 and perpendicular to thedistal surface74. One or both of theproximal surface76 and thedistal surface74 may be oriented at an angle other than perpendicular to the longitudinal axis of theouter tube14. For example, theproximal surface76 may be oriented at an angle A to anorthogonal line80, which is oriented perpendicular to the longitudinal axis of theouter tube14. In the exemplary embodiment, the angle A may be approximately 5° to approximately 30° and is preferably approximately 20°. Thedistal surface74 and theproximal surface76 may be oriented at the same angle or, as in the exemplary embodiment, may be oriented at different angles.
• Referring toFIGS. 2, 3,4,7,9 and10, thedistal end22 of theinner tube12 may include acontact surface81 that contacts at least a portion of a bone anchor when theinner tube12 is in the second position. In the illustrated exemplary embodiment, for example, thedistal end22 of theinner tube12 may have two opposing generally arcuate contact surfaces81. The contact surfaces81, in the exemplary embodiment, are oriented approximately perpendicular to the longitudinal axis of theinner tube12. In the illustrated exemplary embodiment, the contact surfaces81 are configured to contact a generally arcuate contact surface provided on the proximal end of the receiving member of the exemplarybone anchor assembly100. Preferably, thecontact surface81 is complementary in size, shape, and orientation to the contact surface on the bone anchor. One skilled in the art will appreciate that the configuration of thecontact surface81, e.g., number, size, shape, and orientation of thecontact surface81, may be varied to, for example, suit the bone anchor being employed.
• Thedistal end22 of theinner tube12 and/or thedistal end32 of theouter tube14 may be configured to inhibit rotation of the bone anchor assembly relative to thepercutaneous access device10. For example, thedistal end22 of the inner tube may include one or more finger-like extensions82 that extend approximately axially from thedistal end22 of theinner tuber12 and engage a bone anchor to inhibit rotation of the bone relative to the percutaneous access device. For example, one or more of theextensions82 may seat within a groove, recess, slot, or similar structure provided in the bone anchor. Alternatively, one of more of theextensions82 may include acontact surface84 for contacting an axially extending surface of the bone anchor, as in the case of the exemplary embodiment and as discussed in detail below.
• FIGS. 5-6 illustrate an exemplary embodiment of abone anchor assembly100 that is particularly suited for use with the exemplarypercutaneous access device10 described. One skilled in the art will appreciate, however, that the percutaneous access devices disclosed herein are not limited to use with the exemplarybone anchor assembly100 but instead may be configured for use with any type of bone anchor, e.g., bone screw or hook; mono-axial or polyaxial. Exemplarybone anchor assembly100 includes abone screw102, such as a pedicle screw, having aproximal head104 and a distalbone engaging portion106, which in the illustrated exemplary embodiment is an externally threaded screw shank. The exemplarybone screw assembly100 also includes a receivingmember108 that is configured to receive and couple a spinal fixation element, such as a spinal rod or spinal plate, to thebone anchor assembly100.
• The receivingmember108 may be coupled to thebone anchor102 in any well-known conventional manner. For example, the bone anchor assembly may be poly-axial, as in the present exemplary embodiment in which thebone anchor102 may be adjustable to multiple angles relative to the receivingmember108, or the bone anchor assembly may be mono-axial, e.g., thebone anchor102 is fixed relative to the receivingmember108. An exemplary poly-axial bone screw is described U.S. Pat. No. 5,672,176, incorporated herein by reference. In mono-axial embodiments, thebone anchor102 and the receiving member may be coaxial or may be oriented at angle with respect to one another. In poly-axial embodiments, the bone anchor may biased to a particular angle or range of angles to provide a favored angle the bone anchor. Exemplary favored-angle bone screws are described in U.S. Patent Application Publication No. 2003/0055426 and U.S. Patent Application Publication No. 2002/0058942, both of which are incorporated herein by reference.
• The receivingmember108 of the illustrated exemplary embodiment includes aproximal end110, adistal end112, and a recess or slot114 for receiving a spinal fixation element such as a spinal rod. Theproximal end110 of the receivingmember108 has afirst bore116 defining afirst bore axis118. Therecess114 communicates with thefirst bore116 such that a spinal fixation element may be positioned through thefirst bore116 into therecess114. Thedistal end112 has asecond bore120 opposite thesecond bore116 and defining asecond bore axis122. Thesecond bore axis122 is designed to receive thehead104 of thebone anchor102 to couple thebone anchor102 to the receivingmember108. In the illustrated exemplary embodiment, thehead104 is seated within thesecond bore116. As the exemplary illustrated embodiment of the bone anchor assembly is poly-axial, thebone anchor102 is free to rotate relative to the receivingmember108 such that thelongitudinal axis124 of thebone anchor102 is positionable at an angle relative to thesecond bore axis120. Thesecond bore116 may be conically shaped to facilitate adjustment of thebone anchor102 relative to the receivingmember108. In favored-angled embodiments, thesecond bore axis122 may be positioned at an angle (other than 0°) to thefirst bore axis118. In the illustrated embodiment, thefirst bore axis118 andsecond bore axis122 are coaxial. In the exemplary embodiment, the receivingmember108 has a generally U-shaped cross-section defined by twolegs124A and124B separated byrecess114. Eachleg124A,124B is free at theproximal end110 of the receivingmember108.
• The receivingmember108 may be configured to receive a closure mechanism that locks a spinal fixation element within therecess114. The closure mechanism may be a cap that is advanceable through thefirst bore116 of the receivingmember108 and seats against the spinal fixation element. For example, the cap may have external threads that engageinternal threads148 provided in the receivingmember108, e.g., on thelegs124A,B, as in the exemplary embodiment. Any type of conventional closure mechanism may be employed, including, for example, non-threaded caps, multi-component closure mechanisms, and/or external caps.
• The receivingmember108 of the exemplarybone anchor assembly100 is configured to be releasably connected to an instrument such as the exemplarypercutaneous access device10 described above. For example, the receivingmember108 may include at least one groove130 that is configured to receive a portion of an instrument to releasably connect the instrument to the bone anchor assembly. The size, shape, position, and number of grooves can be varied depending on, for example, the instrument employed and the type of connection desired. In certain embodiments, for example, at least one arcuate groove130 may be provided on an exterior surface of theproximal end110 of the receivingmember108. In other exemplary embodiments, at least one arcuate groove may be provided on an interior surface of theproximal end110 of the receivingmember108. In the illustrated exemplary embodiment, eachleg124A and124B may be provided with anarcuate groove130A,130B, respectively, at the free, proximal end of theleg124A,124B. Thegrooves130A,130B may extend about a portion or all of the circumference of the proximal end of eachleg124A,124B. Eachgroove130A,130B may have size and shape that is complementary in size and shape to a projection provided on the instrument. For example, in the illustrated exemplary embodiment, the eachgroove130A,130B may be arcuate and may have a cross-section complementary to the cross-section of aprojection72A,72B provided on thetabs70A,70B of theouter sleeve14. In particular, groove130 may have adistal surface132, aproximal surface134 and an interconnectingsurface136 that spans between thedistal surface132 and theproximal surface134, as illustrated inFIG. 8. Thedistal surface132 and/or theproximal surface134 may be oriented to facilitate insertion of a projection into the grove130 and/or to inhibit undesirable separation of the projection from the groove130. In the illustrated exemplary embodiment, for example, thedistal surface132 may be generally oriented at an angle B to anorthogonal line140, which is oriented perpendicular to the longitudinal axis of the receivingmember108, to facilitate insertion of the projection into the groove. In the exemplary embodiment, the angle B may be approximately 0° to approximately 45° and preferably approximately 30° to 40°. In the illustrated exemplary embodiment, theproximal surface134 may be oriented at an angle other than perpendicular to longitudinal axis of the receivingmember108 to inhibit separation of the projection from the groove130, particularly in radial direction. For example, theproximal surface134 may be oriented at an angle C to anorthogonal line142, which is perpendicular to the longitudinal axis of the receivingmember108. In the exemplary embodiment, the angle C may be approximately 5° to approximately 30° and is preferably approximately 20°. Thedistal surface132 and theproximal surface76 may be oriented at the same angle or, as in the exemplary embodiment, may be oriented at different angles. Thegrooves130A and130B, as well as any additional grooves, may have similar cross-sectional geometries, as in the case of the illustrated exemplary embodiment, or may have distinct geometries.
• Referring toFIGS. 7 and 8, theproximal surface76 of each projection72 may be oriented at an angle A that is approximately equal to the angle C of theproximal surface134 of the corresponding groove. In one preferred embodiment, for example, angle A and angle C are each approximately 20°. One skilled in the art will appreciate that angle A and angle C need not be approximately equal but instead, may be separate, distinct angles.
• Theproximal end110 of the receivingmember108 may include one or more contact surfaces that may be contacted by an instrument such as thepercutaneous access device10. In the illustrated exemplary embodiment, for example, the proximal end of eachleg124A,124B may include one or more generally arcuate, proximally facing contact surfaces145.
• The outer diameter of the percutaneous access device may be selected to be approximately equal to the outer diameter of the bone anchor to facilitate insertion of the bone anchor into the body through a percutaneous pathway of minimal size. For example, in the illustrated exemplary embodiment, the outer diameter of theouter tube14, indicated by line D₁inFIG. 7, at at least thedistal end32 of theouter tube14, is approximately equal to, or less than, the outer diameter of the receivingmember108, indicated by line d₁inFIGS. 6 and 7. For example, the diameter of theouter tube14 may taper from a proximal diameter D₂to a distal diameter D₁at thedistal end32 of theouter tube14. Alternatively, the outer diameter of theouter tube14 may be approximately equal to, or less than, the outer diameter of the receivingmember108 along the entire length of theouter tube14. To accommodate theouter tube14, theproximal end110 of the receivingmember108 may have a diameter d₂that is less than the diameter d₁of a distal section of the receivingmember108, as illustrated inFIG. 6. For example, the diameter d₂proximal to thegrooves130A,B may be less than the diameter d₁of the receivingmember108 to provide a reduced diameter portion150 at he proximal end130 of the receiving member. The distance between the exterior surface of reduced diameter portion150 and the exterior surface of the receivingmember108, indicated by line E inFIG. 6 and8, is preferably greater than or approximately equal to the radial thickness of atab70A,70B, as indicated by line F inFIG. 8.
• To facilitate delivery of devices to the bone anchor assembly through thepercutaneous access device10, the inner diameter of thelumen24 of theinner tube12, indicated by line F inFIG. 7, at at least the distal end of theinner tube12, may be greater than or approximately equal to the inner diameter of at least a portion of the receiving member, indicated by line f inFIG. 7.
• Exemplary operation of thepercutaneous access device10 with the exemplary bone anchor assembly will be described with reference toFIGS. 11A-11D. To releasably connect thepercutaneous access device10, thedistal end32 of theouter tube14 is oriented such thattabs70A and70B are aligned withrecess114, as illustrated inFIG. 11A. Thepercutaneous access device10 is advanced distally until eachtab70A,70B is positioned between thelegs124A and124B, as illustrated inFIG. 11B. Thepercutaneous access device10 may be rotated about itslongitudinal axis16 to rotateprojections72A,72B intogrooves103B,130A, respectively, as illustrated inFIG. 11C. Theinner tube12 may be advanced distally along thelongitudinal axis16 of thepercutaneous access device10 from the first, proximal position, illustrated in FIGS.11A-C, to the second, distal position, illustrated inFIG. 11D, in which the contact surfaces81 of theinner tube12 contact the contact surfaces145A,145B provided on the proximal end of the receiving member of the exemplarybone anchor assembly100, to thereby releasably connect thepercutaneous access device10 to thebone anchor assembly100. Thecontact surface84 of one or more of theextensions82 may engage the axial extending contact surfaces152 (FIGS. 5 and 6) to inhibit rotation between the percutaneous access device and the bone anchor assembly.
• Thepercutaneous access device10 may be connected to the exemplarybone anchor assembly100, or another bone anchor assembly, before implantation of the bone anchor assembly or after the bone anchor assembly is implanted into the patient's body.
• Once thepercutaneous access device10 is releasably connected to thebone anchor assembly100 as illustrated inFIGS. 1 and 11D, thepercutaneous access device10 may provide a percutaneous pathway between the skin incision and thebone anchor100 that facilitates delivery of instruments, spinal fixation elements, and/or components of the bone anchor assembly, such as the closure mechanism, to thebone anchor assembly100. In the illustrated exemplary embodiment, for example, thelumen24 provides a pathway to thefirst bore116 of the receivingmember108 of thebone anchor assembly100, that may allow a closure mechanism, such as a threaded cap, to be delivered to the receivingmember108 of the bone anchor assembly and/or may allow a screw driver or the like to be advanced into engagement with thehead104 of thebone anchor102. Moreover, in the illustrated exemplary embodiment, theslots60 of the inner tube and theslots62 of theouter tube14 may be aligned with therecess114 provided in the receivingmember108. Alignment of theslots60 and62 with therecess114 facilitates the delivery of a spinal fixation element to the bone anchor assembly. Exemplary methods and devices for delivering a spinal fixation element to a bone anchor assembly are described in commonly owned, co-pending U.S. patent application Ser. No. 10/737,537, filed Dec. 16, 2003, entitled Method and Devices for Spinal Fixation Element Placement (Attorney Docket No. 101896-210) and commonly owned co-pending U.S. patent application Ser. No. 10/738,130, filed Dec. 16, 2003, entitled Method and Devices for Minimally Invasive Spinal Fixation Element Placement, (Attorney Docket No. 101896-209), each of which is incorporated herein in by reference.
• Thepercutaneous access device10 may be released from the bone anchor by rotating thepercutaneous access device10 about itslongitudinal axis16 and retracting thedevice10 distally.
• FIGS. 12-16 illustrate an alternative exemplary embodiment of abone anchor assembly200 and an exemplarypercutaneous access device300 that may be configured to releasably engage thebone anchor assembly200. The exemplarybone anchor assembly200 is analogous in construction to the exemplarybone anchor assembly10 described above, except that the receivingmember208 of thebone anchor assembly200 has a generally constant outer diameter d₁, as illustrated inFIGS. 14 and 16, at theproximal end110 thereof, and, thus, lacks the reduced diameter portion150 ofbone anchor assembly100. As a result, the outer diameter of thedistal end32 of theouter tube14 of the exemplarypercutaneous access device300, indicated by line D₂inFIG. 16, may be approximately equal to or, as in the illustrated embodiment, may be greater than the diameter d₁of theproximal end110 of the receivingmember208. The outer diameter of theouter tube14 may be constant, as in the illustrated exemplary embodiment, or may vary along the length of theouter tube14.
• FIGS. 17A and 17B illustrate an alternative embodiment of apercutaneous access device350 and abone anchor assembly400, in which the percutaneous access device and the bone anchor assembly are interconnected by threads. For example, thepercutaneous access device350 may have anouter tube352 having adistal end354 provided within internal threads that releasably engageexternal threads406 provided on theproximal end412 of the receivingmember408 of thebone anchor assembly400. Preferably, theexternal threads406 are clocked to facilitate alignment of thegrooves62, if any, provided on theouter tube14 with therecess414 provided in the receivingmember408. In the illustrated exemplary embodiment, thepercutaneous access device350 includes a single tube,outer tube352; an inner tube may be provided but is not necessary.
• FIGS. 18A and 18B illustrate an alternative embodiment abone anchor assembly500, in which the receivingmember508 includes one or more removable, externally threaded tabs502 that provide a threaded connecting between thepercutaneous access device350 and thebone anchor assembly500. In the illustrated exemplary embodiment, a pair of proximally extendingtabs502A and502B extend from the legs524A and524B, respectively. Each tab502, in the illustrated exemplary embodiment, is generally arcuate in shape and includes external threads for engagement with internal threads provided on the percutaneous access device. The tabs502 may includeinternal threads415 to facilitate advancement of a closure mechanism to the bone anchor assembly. Tabs502 may be sheared off thebone anchor assembly500 by over tightening of thepercutaneous access device350 or, alternatively, may be removed from thebone anchor assembly500 after withdrawal of thepercutaneous access device350 by a suitable instrument.
• FIGS. 19A-19D illustrate an alternative embodiment of apercutaneous access device550 and abone anchor assembly600, in which thepercutaneous access device500 and thebone anchor assembly600 are releasably interconnected by one or moreinternal wires551. In the illustrated exemplary embodiment, for example, a pair ofwires551, extend axially through opposing side walls of theouter tube552. Each wire extends through parallel axial holes provided in the side walls of theouter tube552. Eachwire551 may form aloop553 that can engage the receivingmember608 of the bone anchor assembly. The wires may be formed of any suitable biocompatible material including, for example a metal, such as a stainless, or a polymer. The receivingmember608, in the exemplary embodiment, includes two pairs of axially extendingholes611 for receivingwires551. Each pair ofholes611 may terminate in agroove613 oriented perpendicular to theholes611. The number of wires and holes provided in the outer tube and the receiving member may be varied depending on the application. Eachwire551 may be tensioned to couple thepercutaneous access device550 to the bone anchor assembly. Thewires551 may be tensioned by, for example, retracting thewires551 distally. Releasing the tension on thewires551 by, for example, cutting thewires551 or advancing thewires551 proximally, can release thepercutaneous access device550 from thebone anchor assembly600. In the illustrated exemplary embodiment, thepercutaneous access device550 includes a single tube,outer tube552; an inner tube may be provided but is not necessary.
• FIGS. 20A-20D illustrates an alternative embodiment of apercutaneous access device650 and abone anchor assembly700 in which thepercutaneous access device650 and thebone anchor assembly700 are releasably interconnected by one or more externally positionedwires551. The illustrated exemplary embodiment,wires551 extend axially along the exterior surface of theouter tube652 of thepercutaneous access device650 and extend axially along the exterior surface of the receivingmember708 of thebone anchor assembly700. Theouter tube652 may include one or more axially orientedgrooves653 in which thewires551 may be seated. Likewise, the receivingmember708 may include one ormore grooves707 in which the wires651 may be seated. The number of wires and/or grooves may be varied depending upon the particular application. In the illustrated embodiment, for example, a pair ofparallel grooves653 are provided in opposing sidewalls of theouter tube652 and a pair of parallel ofgrooves707 are provided in the opposinglegs724A,724B of the receivingmember708. Eachwire551 may be tensioned to couple thepercutaneous access device650 to thebone anchor assembly700. Thewires551 may be tensioned by, for example, retracting thewires551 distally. Releasing the tension on thewires551 by, for example, cutting thewires551 or advancing thewires551 proximally, can release thepercutaneous access device650 from thebone anchor assembly700. In the illustrated exemplary embodiment, thepercutaneous access device650 includes a single tube,outer tube652; an inner tube may be provided but is not necessary.
• FIG. 21 illustrates an alternative embodiment of abone anchor assembly800 having one or more removable tabs801 for releasable engagement with an instrument such as an embodiment of a percutaneous access device described above. In the illustrated exemplary embodiment, a pair of opposingtabs801A,801B extend proximally from the proximal end of the receivingmember808 of thebone anchor assembly800. Eachtab801A,801B, in the illustrated exemplary embodiment, is generally arcuate in shape and are positioned proximal to and extend from arespective leg824A,824B of the receivingmember808. The size, shape, and number of tabs801 may be varied without departing from the scope of the present invention. The tabs801 may include a mechanism for facilitating releasable engagement by an instrument. For example, the tabs may be provided with external threads, as in the case of the embodiment illustrated inFIGS. 17A, 17B described above, or may include one or more grooves. In the illustrated exemplary embodiment, eachtab801A,801B includes one or morearcuate grooves830A,830B that may be analogous in construction to thegrooves130A,130B described above. The tabs801 may includeinternal threads815 to facilitate advancement of a closure mechanism to the bone anchor assembly. Tabs801 may be sheared off thebone anchor assembly800 by the percutaneous access device or instrument or, alternatively, may be removed from thebone anchor assembly800 after withdrawal of the percutaneous access device or instrument using a suitable instrument.
• FIGS. 22A-22B illustrates an exemplary embodiment of apercutaneous access device850 having one or more axially extending cut-outs853 provided in theouter tube852 of the percutaneous access device. As illustrated inFIG. 22B, an axially extending cut-out853 may facilitate the use of multiple percutaneous access devices by minimizing interference between the devices. For example, in certain spinal applications, bone anchors placed on adjacent vertebrae may be closely spaced and/or angled in a manner that may cause interference between instruments, such as a percutaneous access device disclosed herein, used simultaneously with the adjacent bone anchors. By providing axial cut-outs853, two or morepercutaneous access devices850A,850B may be employed on adjacent bone anchors, or closely positioned anchors, by aligning the cut-outs853A,853B. The length and depth of a cut-out852 may be varied depending on the application. One or more cut-outs may be provided on any of the exemplary embodiments of the percutaneous access device described herein or with other instruments used with bone anchors, e.g., drills, drivers, cannulas, approximators, and the like. In embodiments including an inner tube or additional tubes, the additional tubes may also be provided with cut-outs853.
• FIGS. 23A-23B illustrates an alternative embodiment of apercutaneous access device950 and abone anchor assembly900 in which thedistal end956 of theinner tube954 of thepercutaneous access device950 includes one or more flexible bone anchor engaging tabs958 for releasable engagement with the receivingmember908 ofbone anchor assembly900. In the exemplary embodiment, a pair of opposingtabs958A,958B extend distally from thedistal end956 of theinner tube954. Each tab958, in the illustrated exemplary embodiment, is connected at a proximal end to theinner tube954 and has a freedistal end960. One or both of the tabs958 can flex from a first position, in which the tab958 is oriented approximately axially, e.g., parallel to the longitudinal axis of theinner tube954, to a second position, in which the tab958 is generally oriented at angle to the longitudinal axis of theinner tube954. In the exemplary embodiment, for example, eachtab958A,958B may flexed radially outward, e.g., away from each other, from a first position, in which thetabs958A,958B are approximately parallel, to a second, flexed positioned, in which thetabs958A,958B are oriented at an angle to one another. The tabs958 may be biased to the first position. For example, thetabs958A,958B may be biased to the first, parallel position, such that thetabs958A,958B may provide a radially compressive force on the receivingmember908 to releasably engage the receivingmember908. One or more of the tabs958 may be provided with a projection or the like for engaging a hole, groove, etc, that may be provided in the exterior surface of the receivingmember908. Although the exemplary embodiment includes twotabs958A,958B, any number (one or more) tabs958 may be provided.
• Thepercutaneous access device950 may include anouter tube952 that may be advanced about the tabs958 when the tabs958 releasably engage the receivingmember908. For example, in the illustrated exemplary embodiment, theouter tube952 may be advanced distally about thetabs958A,958B when the tabs are in the second, flexed position, to inhibit separation of thetabs958A,958B and/or provide a radially compressive force on the tabs.
• Non-limiting examples of applications of the bone fixation plates described herein include long bone fracture fixation/stabilization, small bone stabilization, lumbar spine as well as thoracic stabilization/fusion, cervical spine compression/fixation, and skull fracture/reconstruction plating.
• While the percutaneous access systems and bone anchor assemblies of the present invention have been particularly shown and described with reference to the exemplary embodiments thereof, those of ordinary skill in the art will understand that various changes may be made in the form and details herein without departing from the spirit and scope of the present invention. Those of ordinary skill in the art will recognize or be able to ascertain many equivalents to the exemplary embodiments described specifically herein by using no more than routine experimentation. Such equivalents are intended to be encompassed by the scope of the present invention and the appended claims.

Claims (46)

1. A percutaneous access device comprising:

an inner tube having a proximal end, a distal end, and a lumen extending between the proximal end; and

an outer tube disposed about at least a portion of the inner tube, the outer tube having a proximal end, a distal end, and a lumen extending between the proximal end and the distal end, the outer tube being sized to span from at least a skin incision in a patient to a predetermined site proximate the spine of the patient, the distal end of the outer tube being adapted to releasably engage a bone anchor, the inner tube being adjustable relative to the outer tube along the longitudinal axis of the outer tube between a first position and a second position in which the distal end of the inner tube contacts the bone anchor.

2. The percutaneous access device ofclaim 1, wherein the lumen of the inner tube has an inner diameter proximate the distal end of the inner tube that is greater than or equal to an inner diameter of a bore formed in a receiving portion of the bone anchor.

3. The percutaneous access device ofclaim 1, wherein the outer tube has an outer diameter proximate the distal end of the outer tube that is less than or equal to an outer diameter of a receiving portion of the bone anchor.

4. The percutaneous access device ofclaim 1, wherein the inner tube and the outer tube are coaxial.

5. The percutaneous access device ofclaim 1, wherein the inner tube has a first slot formed therein, the first slot having an opening at the distal end of the inner tube and extending a first slot length toward the proximal end of the inner tube.

6. The percutaneous access device ofclaim 5, wherein the outer tube has a second slot formed therein, the second slot having an opening at the distal end of the outer tube and extending a second slot length toward the proximal end of the outer tube.

7. The percutaneous access device ofclaim 6, wherein the first slot is aligned with the second slot.

8. The percutaneous access device ofclaim 6, wherein the first slot length is sized to be accessible external to the skin incision.

9. The percutaneous access device ofclaim 6, wherein the first slot and the second slot each has a width that is approximately equal to the width of a recess formed in the receiving member of the bone anchor.

10. The percutaneous access device ofclaim 1, wherein the distal end of the outer tube includes a pair of opposed tabs, each tab having a radially inward projection that is sized and shaped to seat within a groove formed in a receiving member of a bone anchor.

11. The percutaneous access device ofclaim 10, wherein each tab has a tab width that is less than or equal to the width of a slot formed in the receiving member of the bone anchor.

12. The percutaneous access device ofclaim 1, wherein the distal end of the inner tube defines a plurality of contact surfaces, each contact surface contacting a proximal surface of a receiving member of the bone anchor when the inner tube is in the second position.

13. The percutaneous access device ofclaim 12, wherein an extension extends axially from at least one of the contact surfaces, the extension engaging the bone anchor to inhibit rotation of the inner tube relative to the bone anchor when the inner tube is in the second position.

14. A bone anchor assembly, comprising:

a bone anchor having a proximal head and a distal bone engaging portion; and

a receiving member coupled to the bone anchor, the receiving member having a proximal end, a distal end and a recess for receiving a spinal fixation element, the proximal end of the receiving member having at least one arcuate groove formed on an exterior surface thereof to facilitate connection of an instrument to the receiving member.

15. The bone anchor assembly ofclaim 14, wherein the proximal end has a first bore defining a first bore axis, the recess is in communication with the first bore, the distal end has a second bore opposite the first bore and defining a second bore axis, and the second bore is sized to receive the head of the bone anchor.

16. The bone anchor assembly ofclaim 15, wherein the first bore axis and the second bore axis are coaxial.

17. The bone anchor assembly ofclaim 15, wherein the second bore axis is at an angle other than 0 degrees relative to the first bore axis.

18. The bone anchor assembly ofclaim 15, wherein the bone anchor is adjustable relative to the receiving member.

19. The bone anchor assembly ofclaim 15, wherein the receiving member has a substantially U-shaped cross-section defined by two legs separated by the recess, each leg being free at the proximal end of the receiving member.

20. The bone anchor assembly ofclaim 19, wherein the at least one arcuate groove is formed on an exterior surface of the proximal end of one of the legs.

21. The bone anchor assembly ofclaim 19, wherein a first arcuate groove is formed on an exterior surface of the proximal end of a first one of the legs and a second arcuate groove is formed on an exterior surface of the proximal end of a second one of the legs.

22. The bone anchor assembly ofclaim 14, wherein the arcuate groove has a proximal surface and a distal surface.

23. The bone anchor assembly ofclaim 22, wherein the proximal surface is oriented at angle greater than 0° relative to an orthogonal line that is oriented perpendicular to a longitudinal axis of the receiving member.

24. The bone anchor assembly ofclaim 22, wherein the proximal surface is oriented at angle between approximately 5° and approximately 30° relative to an orthogonal line that is oriented perpendicular to a longitudinal axis of the receiving member.

25. The bone anchor assembly ofclaim 22, wherein the proximal surface is oriented at angle of approximately 20° relative to an orthogonal line that is oriented perpendicular to a longitudinal axis of the receiving member.

26. The bone anchor assembly ofclaim 22, wherein the distal surface is oriented parallel to the groove plane.

27. The bone anchor assembly ofclaim 22, wherein the distal surface is oriented at angle greater than 0° relative to an orthogonal line that is oriented perpendicular to a longitudinal axis of the receiving member.

28. The bone anchor assembly ofclaim 14, wherein the bone anchor is fixed relative to the receiving member.

29. The bone anchor assembly ofclaim 14, wherein the bone anchor is at least one of a bone screw or a bone hook.

30. A bone anchor assembly, comprising:

a bone anchor having a proximal head and a distal bone engaging portion; and

a receiving member having a proximal end having a first bore, a distal end opposite the proximal end and having a second bore, and a recess for receiving a spinal fixation element in communication with the first bore, the second bore being sized to receive the head of the bone anchor, the receiving member having a substantially U-shaped cross-section defined by two legs separated by the recess, each leg being free at the proximal end of the receiving member,

wherein a first arcuate groove is formed on an exterior surface of the proximal end of a first one of the legs and a second arcuate groove is formed on an exterior surface of the proximal end of a second one of the legs.

31. The bone anchor assembly ofclaim 30, wherein the first arcuate groove has a proximal surface and a distal surface opposite the proximal surface and

the second arcuate groove has a proximal surface and a distal surface opposite the proximal surface.

32. The bone anchor assembly ofclaim 31, wherein the proximal surface of the first groove and the proximal surface of the second groove are co-planar.

33. The bone anchor assembly ofclaim 31, wherein the proximal surface of the first groove and the proximal surface of the second groove each are oriented at angle greater than 0° relative to an orthogonal line that is oriented perpendicular to a longitudinal axis of the receiving member.

34. The bone anchor assembly ofclaim 31, wherein the proximal surface of the first groove and the proximal surface of the second groove each are oriented at angle between approximately 5° and approximately 30° relative to an orthogonal line that is oriented perpendicular to a longitudinal axis of the receiving member.

35. The bone anchor assembly ofclaim 31, wherein the proximal surface of the first groove and the proximal surface of the second groove each are oriented at angle of approximately 20° relative to an orthogonal line that is oriented perpendicular to longitudinal axis of the receiving member.

36. The bone anchor assembly ofclaim 31, wherein the distal surface of the first groove and the distal surface of the second groove each are oriented at angle greater than 0° relative to an orthogonal line that is oriented perpendicular to a longitudinal axis of the receiving member.

37. A percutaneous access device comprising:

an inner tube having a proximal end, a distal end, and a lumen extending between the proximal end and the distal end, the inner tube having a first slot formed therein, the first slot having an opening at the distal end of the inner tube and extending a first slot length toward the proximal end of the inner tube; and

an outer tube coaxially disposed about at least a portion of the inner tube, the outer tube having a proximal end, a distal end, and a lumen extending between the proximal end and the distal end; the outer tube being sized to span from at least a skin incision in a patient to a predetermined site proximate the spine of the patient, the distal end of the outer tube being adapted to releasably engage a bone anchor, the outer tube having a second slot formed therein aligned with the first slot, the second slot having an opening at the distal end of the outer tube and extending a second slot length toward the proximal end of the outer tube.

38. The percutaneous access device ofclaim 37, wherein inner tube is movable along the longitudinal axis of the outer tube.

39. The percutaneous access device ofclaim 37, wherein the inner tube is movable between a between a first position and a second position in which the distal end of the inner tube contacts the bone anchor.

40. The percutaneous access device ofclaim 37, wherein the first slot length and the second slot length are approximately equal.

41. The percutaneous access device ofclaim 40, wherein the first and second slots lengths are selected to span from at least a skin incision in patient to the proximal end of the inner tube and the outer tube, respectively.

42. A medical device comprising:

a percutaneous access device comprising

an inner tube having a proximal end, a distal end, and a lumen extending between the proximal end and the distal end; and

an outer tube disposed about at least a portion of the inner tube, the outer tube having a proximal end, a distal end, and a lumen extending between the proximal end and the distal end; the outer tube being sized to span from at least a skin incision in a patient to a predetermined site proximate the spine of the patient; and

a bone anchor assembly comprising:

a bone anchor having a proximal head and a distal bone engaging portion; and

a receiving member coupled to the bone anchor, the receiving member having a proximal end, a distal end and a recess for receiving a spinal fixation element, the proximal end of the receiving member having at least one arcuate groove formed on an exterior surface thereof,

wherein the distal end of the outer tube is adapted to releasably engage the arcuate groove in the receiving member.

43. The medical device ofclaim 42, wherein the inner tube is adjustable relative to the outer tube along the longitudinal axis of the outer tube between a first position and a second position in which the distal end of the inner tube contacts the proximal end of the receiving member.

44. A medical device comprising:

a percutaneous access device comprising

an inner tube having a proximal end, a distal end, and a lumen extending between the proximal end and the distal end, the inner tube having a first slot formed therein, the first slot having an opening at the distal end of the inner tube and extending toward the proximal end of the inner tube, and

an outer tube coaxially disposed about at least a portion of the inner tube, the outer tube having a proximal end, a distal end, and a lumen extending between the proximal end and the distal end, the outer tube being sized to span from at least a skin incision in a patient to a predetermined site proximate the spine of the patient, the outer tube having a second slot formed therein aligned with the first slot, the second slot having an opening at the distal end of the outer tube and extending toward the proximal end of the outer tube; and

a bone anchor assembly comprising

a bone anchor having a proximal head and a distal bone engaging portion, and

a receiving member having a proximal end having a first bore, a distal end opposite the proximal end and having a second bore, and a recess for receiving a spinal fixation element and in communication with the first bore, the second bore being sized to receive the head of the bone anchor,

wherein the distal end of the outer tube is adapted to releasably engage the receiving member and the first and second slots are aligned with the recess in the receiving member when the outer tube is releasably engaged to the receiving member.

45. The medical device ofclaim 44, wherein the receiving member has a substantially U-shaped cross-section defined by two legs separated by the recess and each leg is free at the proximal end of the receiving member.

46. The medical device ofclaim 45, wherein a first arcuate groove is formed on an exterior surface of the proximal end of a first one of the legs and a second arcuate groove is formed on an exterior surface of the proximal end of a second one of the legs and the distal end of the outer tube is configured to releasably engage the first and second grooves.

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