Patent Publication Number: US-10327919-B2

Title: Variable angle spinal surgery instrument

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 12/698,691, filed Feb. 2. 2010, now U.S. Pat. No. 9,345,586 which issued on May 24, 2016, which application is a continuation of U.S. patent application Ser. No. 11/257,745, filed Oct. 25, 2005, which claims the benefit of U.S. Provisional Patent No. 60/623,274, filed Oct. 29, 2004 and. U.S. Pat. No. 9,345,586, filed Feb. 2, 2010, is also a continuation-in- part of, U.S. Pat. No. 7,806,932, filed on Aug. 1, 2003, the entire contents of which are hereby expressly incorporated by reference for all purposes. 
    
    
     BACKGROUND 
     1. Field of Invention 
     The present invention generally relates to the field of medical devices. Some embodiments of the invention relate to instruments used during surgical procedures to install a spinal implant in a human spine. Some embodiments of the invention relate to instruments used in evaluating and/or preparing a disc space for a spinal implant. Some embodiments of the invention relate to an instrument used to manipulate and/or position a spinal implant between human vertebrae. 
     2. Description of Related Art 
     An intervertebral disc may degenerate. Degeneration may be caused by trauma, disease, and/or aging. An intervertebral disc that becomes degenerated may have to be partially or fully removed from a spinal column. Partial or full removal of an intervertebral disc may destabilize the spinal column. Destabilization of a spinal column may result in alteration of a natural separation distance between adjacent vertebrae. Maintaining the natural separation between vertebrae may prevent pressure from being applied to nerves that pass between vertebral bodies. Excessive pressure applied to the nerves may cause pain and/or nerve damage. During a spinal fixation procedure, a spinal implant may be inserted in a space created by the removal or partial removal of an intervertebral disc between adjacent vertebrae. The spinal implant may maintain the height of the spine and restore stability to the spine. Bone growth may fuse the implant to adjacent vertebrae. 
     A spinal implant may be inserted during a spinal fixation procedure using an anterior, lateral, posterior, or transverse spinal approach. A discectomy may be performed to remove or partially remove a defective or damaged intervertebral disc. The discectomy may create a space for one or more spinal implants. The amount of removed disc material may correspond to the size and type of the spinal implant or spinal implants to be inserted. 
     Spinal surgery may be complex due in part to the proximity of the spinal cord and/or the cauda equina. Preparation instruments and spinal implants may need to be carefully inserted to avoid damage to nerve tissue. Alignment and spacing of a spinal implant that is to be inserted into a patient may be determined before surgery. Achieving the predetermined alignment and spacing during surgery may be important to achieve optimal fusion of adjacent vertebrae. 
     U.S. Pat. No. 6,682,534 to Patel et al., which is incorporated by reference as if fully set forth herein, describes an endplate preparation instrument for preparing endplates of adjacent vertebral bodies. The instrument includes an elongated member that rotates in a housing member. The elongated member includes a cutting element that penetrates and removes bone from the endplates when the elongated member is rotated. 
     U.S. Pat. No. 6,599,294 to Fuss et al., which is incorporated by reference as if fully set forth herein, describes a surgical instrument for introducing a spinal implant between two vertebrae. The instrument includes two mutually opposing guide bodies. The guide bodies combine to form a guideway for lateral insertion of a spinal implant in the intervertebral space. 
     Some spinal implants may be inserted using a lateral (transverse) approach. U.S. patent application Ser. No. 10/633,371 to Mitchell at al., which is incorporated by reference as if fully set forth herein, describes spinal implants that may be inserted using a lateral (transverse) approach. 
     SUMMARY 
     An instrument may be used in a procedure to insert a spinal implant. In some embodiments, the spinal implant may be inserted into an intervertebral disc space. The spinal implant may provide stability and promote fusion of adjacent vertebrae. In an embodiment, an instrument may include a shaft assembly and an end member. The end member may rotate with respect to the shaft assembly. In some embodiments, an angle of the end member relative to the shaft assembly may be varied while the end member is in a disc space. The ability to rotate an end member relative to a shaft assembly may simplify and facilitate positioning of the end member at a desired location in the disc space. The ability to rotate the end member relative to the shaft assembly may decrease the size of an incision and opening needed to provide room for preparing a disc space and inserting a spinal implant in the disc space. 
     In certain embodiments, an instrument set for a spinal fusion procedure may include end members that are coupled to shaft assemblies such that separation of the end members from the shaft assemblies is inhibited. The end members may be coupled to the shaft assemblies by rivets, press fit connections, adhesives, or other fastening systems. An end member may be rotated and set in desired positions relative to a shaft assembly prior to insertion of the end member into a patient and during use of the end member. 
     In certain embodiments, an instrument set may include a shaft assembly and modular end members. Various end members may be removably coupled to the shaft assembly. The instrument set may include end members for various steps in a procedure for installing a spinal implant, such as disc preparation, disc space evaluation, and implantation. 
     In some instrument embodiments, an end member of an instrument may be separable from a shaft assembly of the instrument when the end member is placed in a selected orientation relative to the shaft assembly. An end member may include a slot. A portion of the shaft assembly may engage the slot to allow the end member to be selectively coupled to or separated from the shaft assembly. 
     In some instrument embodiments, a shaft assembly of an instrument may include a slide. The slide may engage an end member of the instrument to secure the end member at a selected angle with respect to the shaft assembly. The slide and the end member may include cooperative capture elements. The capture elements may engage to inhibit rotation of the end member with respect to the shaft assembly. In some embodiments, the capture elements may be frictional surfaces. In some embodiments, the capture elements include meshing teeth that form an interference fit to inhibit undesired rotation of the end member relative to the shaft assembly. The shaft assembly may include a locking member to lock a slide in position against an end member. In certain embodiments, a shaft assembly may include a biasing member to urge a slide into engagement with an end member. 
     In some embodiments, an end member of an instrument may be a rasp for abrading surfaces of vertebrae adjacent to a disc space. Upper and lower surfaces of the rasp may be textured to cut vertebral bone. In an embodiment, a surgeon may vary an angle of the rasp with respect to a shaft assembly while the rasp is in the disc space to selectively position the rasp relative to the vertebrae. 
     In certain embodiments, an end member of an instrument may be a trial member for evaluating a size and/or shape of a disc space. An instrument set may include trial members of various sizes that can be removably coupled to a shaft assembly. Sizes of the trial members may correspond to the sizes of implants available to a surgeon. In an embodiment, a surgeon may vary an angle of the trial member with respect to the shaft assembly to facilitate positioning of the trial member in the disc space. 
     In some embodiments, an end member of an instrument may be a tamp for positioning a spinal implant in a disc space. The tamp may include an end that engages the spinal implant to advance the spinal implant in the disc space. In an embodiment, a surgeon may vary an angle of the tamp with respect to a shaft assembly during insertion to facilitate positioning of the spinal implant in a desired location. 
     In certain embodiments, an angle of an end member relative to a shaft assembly may be controlled during a surgical procedure to allow a proximal end of a shaft assembly to be maintained in a relatively small range at an incision at a surface of the body. The angle of the end member relative to the shaft assembly may be adjusted at selected points of advancement of the instrument into a disc space. The angle of the end member relative to the shaft assembly may also be adjusted during removal of the end member from the disc space. 
     In some embodiments, an end member may be secured at a first angle relative to a shaft assembly. An end member may be moved to a first position along a path in a disc space while the end member is secured at the first angle. A capture element of the end member may be disengaged to allow the end member to rotate with respect to the shaft assembly. The angle of the end member with respect to the shaft assembly may be adjusted to a second angle. The end member may be secured to the shaft assembly at the second angle. The end member may be advanced to a second position on the path while the end member is secured at the second angle. The end member may be successively adjusted and advanced until the end member is in a desired position in the disc space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the present invention will become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings in which: 
         FIG. 1  depicts a perspective view of an embodiment of an instrument including a shaft assembly and a separable end member. 
         FIG. 2  depicts a perspective view of an embodiment of an instrument with a non-separable end member. 
         FIG. 3  depicts a front view of an embodiment of a shaft assembly. 
         FIG. 4  depicts a side view of an embodiment of a shaft assembly. 
         FIG. 5  depicts a cross-sectional view of the embodiment of the shaft assembly, taken substantially along line  5 - 5  of  FIG. 4 . 
         FIG. 6  depicts a detail view of the embodiment of the locking member shown in  FIG. 5 . 
         FIG. 7  depicts a detail view of an embodiment of a locking mechanism. 
         FIG. 8  depicts a detail view of an embodiment of a distal portion of a shaft assembly in a closed position. 
         FIG. 9  depicts a detail view of an embodiment of a distal portion of a shaft assembly in an open position. 
         FIG. 10  depicts a detail view of an embodiment of teeth on a collar of a shaft. 
         FIG. 11  depicts an end view of an embodiment of a collar of a shaft. 
         FIG. 12  depicts a perspective view an embodiment of a shaft assembly with a portion of a bias section of the shaft assembly shown in cut-away to show a biasing member of the shaft assembly. 
         FIG. 13  depicts a top view of an embodiment of a rasp. 
         FIG. 14  depicts a front view of an embodiment of a rasp. 
         FIG. 15  depicts a top view of an embodiment of a trial member. 
         FIG. 16  depicts a front view of an embodiment of a trial member. 
         FIG. 17  depicts a top view of an embodiment of a tamp. 
         FIG. 18  depicts a front view of an embodiment of a tamp. 
         FIGS. 19A-19D  depict schematic representations of installation of an end member onto a shaft assembly. 
         FIGS. 20A-20E  depict-schematic representations of use of a rasp to prepare a disc space. 
         FIGS. 21A-21D  depict schematic representations of use of a tamp to position a spinal implant in a disc space. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood that the drawings and detailed description are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     An instrument may be used in a procedure to insert a spinal implant between human vertebrae. In an embodiment, the instrument may include a shaft assembly and an end member. The end member may rotate (e.g., pivot or angulate) with respect to the shaft assembly. The shaft assembly may include a slide that engages the end member to secure the end member at a selected angle with respect to the shaft assembly. To facilitate use of the instrument, the angle of the end member relative to the shaft assembly may be adjusted while the end member is in use in a patient. 
     Components of instruments may be made of materials including, but not limited to, metals, ceramics, and/or polymers. The metals may include, but are not limited to, stainless steel, titanium, and titanium alloys. Some components of instruments may be autoclaved and/or chemically sterilized. Components that may not be autoclaved and/or chemically sterilized may be made of sterile materials. 
     In some embodiments, an instrument may include end members that are coupled to shaft assemblies such that separation of the end members from the shaft assemblies is inhibited. The end members may be coupled to the shaft assemblies by rivets, press fit connections, adhesives, threaded connectors or other fastening systems. An end member may be rotated and set in desired positions relative to a shaft assembly prior to insertion of the end member into a patient and during use of the end member. 
     In some embodiments, an instrument set may include a shaft assembly and modular end members. The end members may be removably coupled to the shaft assembly. An instrument set may include different end members for various steps of a procedure, including, but not limited to, distraction, disc preparation, disc space evaluation, and implantation. End members used for disc preparation may include, but are not limited to, rasps, trials, chisels, curettes, or distractors. End members used for implantation may include, but are not limited to, inserters, tamps, or guides. 
     An instrument including an adjustable end member may allow preparation of a disc space and insertion of a spinal implant between human vertebrae to be effected from above an incision in a patient through a relatively small opening in the patient. The instrument may allow simple, efficient, and safe preparation of a disc space for receiving a spinal implant, including preparation of the contralateral (opposite) side of the disc space. The instrument may allow spinal implant insertion through a relatively small opening in the patient while maintaining maneuverability and visibility of the surgical site, spinal implant, and instruments during the procedure. 
       FIG. 1  depicts a perspective view of an embodiment of instrument  50 . Instrument  50  may include shaft assembly  52  and end member  54 . End member  54  may be pivotably coupled to shaft assembly  52 . In some embodiments, end member  54  may be separable from shaft assembly  52 . Shaft assembly  52  may be included in a modular instrument set having one or more end members. 
     Shaft assembly  52  may include shaft  56 , slide  58 , handle  60 , locking member  62 , and connector  64 . Handle  60  may be coupled to shaft  56 . In some embodiments, slide  58  of shaft assembly  52  is able to move longitudinally relative to shaft  56 . A distal portion of slide  58  may engage an end member to inhibit undesired rotation of the end member relative to shaft  56 . Locking member  62  may limit movement of shaft  56  relative to slide  58  to fix an angular position of an end member coupled to shaft assembly  52 . As used herein, “slide” includes any element that moves (e.g., translates and/or rotates) with respect to another element. The slide may be positioned outside, inside, or along side the other element. A slide may be, but is not limited to, a shaft, a tube, a rod, a bar, a beam, or a combination thereof. In certain embodiments, a slide may threadably engage another element. 
     As shown in  FIG. 1 , slide  58  may be an outer shaft that surrounds a portion of shaft  56 . Distal end  66  of slide  58  may engage end member  54  to hold the end member at a desired angle relative to shaft  56 . Locking member  62  may be coupled to slide  58 . Locking member  62  may be operated to control axial position of slide  58  relative to shaft  56 . In some embodiments, locking member  62  may include a spring or other bias element that applies force to move slide  58  towards connector  64  of shaft  56 . 
     In some embodiments, shaft  56  of instrument  50  may be a single member. In certain embodiments, a shaft may include multiple members. Distal portion  68  of shaft  56  may include connector  64 . Connector  64  may be oriented perpendicular to a longitudinal axis of shaft  56 . Connector  64  may form a “tee” shape in distal portion  68  of shaft  56 . 
     End member  54  may include body opening  70 , and surfaces  72 ,  74 . End member  54  may be coupled to connector  64  of distal portion  68  of shaft  56 . Pivoting end member  54  relative to shaft  56  about connector  64  may allow the end member to be positioned at various angles relative to the shaft during use of instrument  50 . A rotational range of motion of end member  54  relative to shaft assembly  52  may be limited by a surface of the end member that defines opening  70 . In some embodiments, the surface of the end member that defines opening  70  is a planar surface so that the range of motion of end member  54  relative to shaft assembly  52  is 180°. In other embodiments, the surface of the end member that defines opening  70  may be angled or curved so that the range of motion of end member  54  relative to shaft assembly  52  is less than or greater than 180°. 
     In some embodiments, end member  54  may be separable from shaft assembly  52 . In certain embodiments, end member  54  may be separated from shaft assembly  52  when the end member is in a selected orientation with respect to the shaft assembly. For example, end member  54  may be separable from shaft assembly  52  when distal portion  68  of shaft  56  is aligned in slot  76 . To separate end member  54  from shaft assembly  52 , end member  54  may be rotated about connector  64  until distal portion  68  of shaft  56  is aligned in slot  76 . Slide  58  may be retracted from connector  64 , and end member  54  may be removed from distal portion  68 . 
     In some embodiments, slide  58  and end member  54  may include complementary capture elements. As used herein, “capture element” includes any element that directly or indirectly contacts or engages another element to at least partially inhibit relative motion (e.g., translation, rotation) of the elements. A capture element may include, but is not limited to, a detent, a spring, a groove, a ridge, a tab, a pin, a projection, a slot, a hole, a notch, roughened or textured surfaces or threading. For example, as shown in  FIG. 1 , slide  58  may include teeth  78  and end member  54  may include complementary teeth  80 . A capture element may be a separate component or may be a part of another element. In some embodiments, a capture element may automatically release when a predetermined amount of force is applied to the element that is captured. In other embodiments, release of a capture element may require a separate action by a user (e.g., user actuated movement of the slide relative to the shaft). 
     Capture elements may be positioned over a subset of the range that end member  54  is able to rotate relative to shaft assembly  52  to define an instrument use range of the end member relative to the shaft assembly. In some embodiments, teeth  80  may be formed on end member  54  so that the instrument use range of the end member relative to the shaft assembly is from about 20° to about 180°, where 0° is the angle formed between the shaft assembly and the end member when a shaft of the shaft assembly is positioned in slot  76  such that the shaft assembly can be removed from the end member. In other embodiments, the instrument use range of the end member relative to the shaft assembly may be less or greater than the range of 20° to 180° (e.g., 30° to 180°, 10° to 180°, 10° to 190°, 45° to 135°). 
     In some embodiments, a slide of a shaft assembly may include detents or pins that engage holes or slots in an end member. In other embodiments, a slide of a shaft assembly may include holes or slots that engage detents or pins on an end member. In some embodiments, engaging surfaces of a slide and/or end member may be textured to inhibit relative motion between a shaft assembly and an end member when the slide is biased against the end member. 
     In an embodiment, turning (e.g., clockwise rotation) locking member  62  in a first direction (e.g., clockwise) may move slide  58  toward end member  54 . Distal end  66  of slide  58  may engage end member  54 . Turning locking member  62  in an opposite direction (e.g., counterclockwise) may move slide  58  away from end member  54 . Distal end  66  of slide  58  may disengage from end member  54 . With distal end  66  disengaged from end member  54 , end member  54  may pivot with respect to shaft  56  about connector  64 . 
       FIG. 2  depicts an embodiment of instrument  50  that has end member  54  fixed to shaft assembly  52 . Connector  64  may be a pin that is press fit into end member  54 . A portion of the pin passes through shaft  56  so that end member is able to rotate relative to shaft assembly  52  about connector  64 . Locking member  62  may move slide  58  so that capture elements of the slide engage with, or disengage from, capture elements of end member  54 . 
       FIG. 3  and  FIG. 4  depict front and side views of an embodiment of shaft assembly  52 .  FIG. 5  depicts a cross-sectional view of an embodiment of shaft assembly  52 . Shaft  56  may include tip  82 , body  84 , and sleeve  86 . Tip  82 , body  84 , and sleeve  86  may be coupled by various methods including, but not limited to, application of an adhesive, welding, press-fitting, threading, pins, and/or rivets. Tip  82  may have an elongated section and connector  64 . A cross-sectional shape of the elongated section perpendicular to the longitudinal axis of the elongated section may be substantially square. Handle  60  may be coupled to sleeve  86  and shaft  56  by a pin. 
     Slide  58  may include tube  88  and collar  90 . In some embodiments, tube  88  may have a substantially cylindrical outer surface. An opening through collar  90  may have a substantially square shape that corresponds to a shape of the elongated section of tip  82 . The shape of the opening in collar  90  and the shape of the elongated section of tip  82  may inhibit rotation of slide  58  relative to shaft  56 . 
     Slide  58  may include indicia  92 . Indicia  92  may indicate insertion depth of an end member into a patient. 
     Handle  60  may be used to hold shaft assembly  52 . In some embodiments, locking member  62  may be rotated with fingers of the same hand with which a user is holding handle  60 . A top of handle  60  may be an impact surface. A mallet or other impact instrument may strike the impact surface to drive an end member coupled to the shaft assembly into a disc space. As shown in  FIG. 5 , some embodiments of handle  60  may include spring  94  and pin  96 . An end of a slap hammer may include a keyway that engages pin  96  to couple the slap hammer to shaft assembly  52 . Spring  94  may apply force to the slap hammer that holds the shaft assembly and the slap hammer together. The slap hammer may be used to remove an end member from a disc space. 
       FIG. 6  depicts a detail view of an embodiment of locking member  62 . Locking member  62  may include portions  62 A and  62 B. Portions  62 A and  62 B may be fixedly coupled (e.g., by adhesive, welding, threads, or soldering) after the portions are properly positioned relative to shaft  56  and slide  58 . Capture washer  98  may be coupled to a distal end of portion  62 A. Capture washer  98  may engage rim  100  of slide  58  when locking member  62  is rotated to move the slide away from a connector of the shaft assembly. Belleville washers  102  may be positioned between end face  104  of slide  58  and end face  106  of portion  62 B. When locking member  62  is rotated to move slide  58  towards connector  64  (depicted in  FIGS. 3-5 ), end face  106  may push against Belleville washers  102 . Belleville washers  102  may push against slide  58  to move the slide towards the connector. 
     Threading  108  on portion  62 B may mate with threading  110  of sleeve  86 . Locking member  62  may be rotated in a first direction to move slide  58  towards a connector of a shaft assembly. Teeth of the slide may engage teeth of an end member to fix the angular position of the end member relative to the shaft assembly. Locking member  62  may be rotated in an opposite direction to move slide  58  away from the connector. When the slide is moved away from the connector, teeth of the slide may disengage from teeth of the end member to allow the angular position of the end member relative to the shaft to be changed. 
     To assemble shaft assembly  52  (depicted in  FIGS. 3-5 ), collar  90  may be placed on tip  82 . Tip  82  may be welded to body  84 . Retainer washer  98  may be welded to portion  62 A. Portion  62 A may be placed on tube  88 . Tube  88  may be welded to collar  90 . 
     Sleeve  86  may be press-fit into handle  60 . Portion  62 B may be threaded onto thread  110  of sleeve  86 . Belleville washers may be placed about shaft  56 . An opening in sleeve  86  may be aligned with an opening in shaft  56  and a pin may be press fit into the openings to couple the sleeve and handle  60  to the shaft. Portion  62 A may be positioned against portion  62 B. Portion  62 A and portion  62 B may be welded together to form locking member  62  and the complete shaft assembly. 
       FIG. 7  depicts a cross-sectional view of a portion of an embodiment of a shaft assembly. Capture washer  98  may be positioned on slide  58 . A tip may be placed in a collar. The tip may be coupled to a body. The body may be positioned in slide  58 . The collar may be coupled to slide  58 . Locking member  62  may be positioned on slide  58 . An adhesive (e.g., Loctite Engineering Adhesive) may be applied to threading of capture washer  98 . Capture washer  98  may be threaded on locking member  62 . Sleeve  86  may be press fit in handle  60  so that an opening through the sleeve aligns with an opening through the handle. Sleeve  86  may be threaded in locking member  62  until an opening in body  84  aligns with the openings through the sleeve and handle  60 . Pin  111  may be positioned in handle to fix the position of body  84  relative to sleeve  86  and handle  60 . Rotating locking member  62  advances or retracts slide  58  relative to handle  60 . 
       FIG. 8  depicts a distal portion of a shaft assembly when a locking member of the shaft assembly is rotated to drive slide  58  towards connector  64  of shaft  56 .  FIG. 9  depicts a distal portion of an embodiment of a shaft assembly when the locking member of the shaft assembly is disengaged to drive slide  58  away from connector  64  of shaft  56 . 
       FIG. 10  depicts a detail view of an embodiment of teeth  78  of collar  90  of a slide. In some embodiments, collar  90  may include from 1 to about 8 teeth  78 . In an embodiment, collar  90  includes 4 teeth. In some embodiments, an angular spacing between teeth  78  may be from about 5 to about 30°. In an embodiment, the angular spacing between teeth is about 14°. In some embodiments, an angle between sides of tooth  78  may be from about 150° to about 5°. In an embodiment, the angle between sides of a tooth is about 60°. 
       FIG. 11  depicts an end view of an embodiment of a collar of a slide. Opening  112  may receive a tip of a shaft of a shaft assembly. In some embodiments, opening  112  may have a shape other than square or rectangular, such as, but not limited to, circular, diamond-shaped, or hexagonal. A slide of an instrument may translate on a shaft without rotation of the slide relative to the shaft. Engaging surfaces of the shaft and the collar may inhibit rotation of the shaft with respect to the collar. If a shape of an opening of the collar is circular, a shaft positioned in the collar may include a slot. A pin may be press fit into the slide through the slot so that rotation of the shaft relative to the slide is inhibited, while still allowing for axial movement of the slide relative to the shaft. 
     In an embodiment, a shaft assembly may include a biasing member that urges a slide toward a distal portion of a shaft assembly. A biasing member may include, but is not limited to, a coil spring, Belleville washers, or an elastomeric member.  FIG. 12  depicts shaft assembly  52  including shaft  56  and slide  58 . Shaft  56  may include a distal portion and a proximal portion. Distal portion  68  may include connector  64 . Proximal portion  114  may include knob  116 . Knob  116  may be an impact surface that allows an end member that is coupled to connector  64  to be driven into a disc space. Knob  116  may also be positioned against a user&#39;s palm or thumb during use to allow a user to move slide  58  relative to shaft  56 . 
     Shaft assembly  52  may include bias section  118 . A portion of bias section  118  of  FIG. 12  is shown in cut-away to reveal some of the inner features of the bias section. Bias section  118  may include biasing member  120 , and grips  122 . A first end of biasing member  120  may be positioned against a portion of bias section  118 . A second end of biasing member  120  may be positioned against ledge  124  of shaft  56 . In some embodiments, ledge  124  may be formed by reducing a diameter of a portion of shaft  56 . In some embodiments, a ledge may be formed by placing a weld bead or other obstruction on the shaft. In some embodiments, a ledge may be formed by a pin or washer coupled to the shaft. Biasing member  120  may provide a force to slide  58  that moves the slide towards connector  64  of shaft  56 . A user may grasp grips  122  with fingers while knob  116  is positioned against the user&#39;s palm or thumb. Grips  122  may be pulled away from connector  64  to move slide  58  away from the connector. When grips  122  are released, biasing member  120  may move slide  58  towards connector  64 . 
     An end member may be coupled to connector  64 . Teeth  78  may engage portions of the end member to set a desired angle of the end member relative to shaft assembly  52 . The angle of the end member relative to the shaft assembly may be adjusted during use by repositioning slide  58  relative to the end member. 
     In some embodiments, shaft assembly  52  may include lock  126 . Lock  126  may include thread that complements a threaded portion of shaft  56 . When an end member that is coupled to connector  64  is at a desired angle relative to shaft assembly  52 , lock  126  may be rotated to position an end of the locking member against bias section  118 . Positioning locking member  126  against biasing section  118  may inhibit movement of slide  58  relative to the end member, thus inhibiting rotation of the end member relative to shaft assembly  52 . When it is desired to change the angle of shaft assembly  52  relative to the end member, locking member  126  may be rotated to move the locking member away from bias section  118  so that slide  58  can be moved to allow the teeth of the slide to be repositioned with respect to the end member. 
     In an embodiment, an end member may be a rasp that is used to abrade surfaces of vertebrae.  FIGS. 13 and 14  depict top and front views, respectively, of rasp  128 . Rasp  128  may include opening  70 , slot  76 , and hole  130 . Rasp  128  may couple with a shaft of a shaft assembly. Hole  130  may receive a portion of a connector of the shaft. Opening  70  may allow rasp  128  to pivot relative to the shaft of the shaft assembly. 
     Rasp  128  may include posterior side  132  and anterior side  134 . Sides  132 ,  134  may be curved. Sides  132 ,  134  may have substantially the same curvature as a spinal implant to be inserted in a disc space formed using the rasp. In some embodiments, the curvature of posterior side  132  may be substantially the same as the curvature of anterior side  134 . In some embodiments, the curvature of posterior side  132  may be different than the curvature of anterior side  134 . In some embodiments, posterior side  132  may have a smaller radius of curvature than anterior side  134 . In some embodiments, posterior side  132  and/or anterior side  134  may include no significant curvature. 
     Distal end  136  of rasp  128  may be tapered and/or curved. Tapered and/or curved surfaces of distal end  136  may facilitate insertion of rasp  128  in a disc space. In some embodiments, the tapered and/or curved surfaces of distal end  136  may be textured. The textured surface may facilitate removal of intervertebral disc material during use. In some embodiments, distal end  136  may not be tapered and/or curved. Proximal end  138  of rasp  128  may be blunt and/or rounded. In some embodiments, upper surface  72  and lower surface  74  of rasp  128  may be angled relative to each other. Angled upper surface  72  and lower surface  74  may facilitate removal of intervertebral disc material during use. 
     Upper surface  72  and lower surface  74  of rasp  128  may be textured to abrade and/or cut vertebral bone. Texturing may be provided by methods including, but not limited to, sanding the surface, forming grooves in the surface, shot peening the surface, scoring the surface using an electrical discharge process, and/or embedding hard particles in the surface. 
     Rasp  128  may include teeth  80 . Teeth  80  may engage cooperating elements of a slide of a shaft assembly to secure a position of rasp  128  relative to the shaft. Teeth  80  may allow an angle of rasp  128  relative to a shaft to be selectively set in range R. In some embodiments, range R may be at least about 90°. In some embodiments, range R may be about 150°, about 120°, about 90°, or about 45°. Slot  76  may allow rasp  128  to be separated from the shaft assembly when a portion of the shaft is aligned with slot  76 . Slot  76  may be located on rasp  128  such that the portion of the shaft cannot be aligned with slot  76  when the rasp is positioned between vertebrae in a patient. 
     In an embodiment, an end member may be a trial member used to evaluate size and/or shape of a disc space.  FIGS. 15 and 16  depict top and front views, respectively, of trial member  140 . Trial member  140  may include various tapered, curved and/or flat outer surfaces. Trial member  140  may include opening  70 , slot  76 , and hole  130  that allow the trial member to be removably coupled to a shaft of a shaft assembly. Slot  76  may be located on trial member  140  such that the shaft of the shaft assembly cannot be aligned with slot  76  when the trial member is positioned between vertebrae in a patient. Trial member  140  may include teeth  80 . Teeth  80  may allow the trial member to be set at a desired angle relative to the shaft of the shaft assembly. Trial member  140  may include marker  142 . Marker  142  may be color coded or include indicia to indicate to which instrument set the trial belongs. 
     An instrument set may include trial members of various sizes. The instrument set may include a trial member for each spinal implant size included in the instrument set. In some embodiments, a trial member may have the same dimensions as the dimensions of a corresponding spinal implant. In some embodiments, one or more dimensions of a trial member may differ from those of a corresponding spinal implant. For example, a height of each trial member may be undersized relative to a height of a corresponding spinal implant for each trial. 
     In an embodiment, an end member may be a tamp used to position a spinal implant in a disc space.  FIGS. 17 and 18  depict top and front views, respectively, of tamp  144 . Tamp  144  may include opening  70 , slot  76 , and hole  130  that allow the tamp to be removably coupled to a shaft of a shaft assembly. Slot  76  may be located on tamp  144  such that the shaft of the shaft assembly cannot be aligned with slot  76  when the tamp is positioned between vertebrae in a patient. Tamp  144  may include teeth  80  that allow the tamp to be set at a desired angle relative to the shaft of the shaft assembly. Tamp  144  may include end face  146  and tips  148 . End face  146  may contact a spinal implant that is partially inserted into a disc space. An instrument formed of a shaft assembly and tamp  144  may be pushed or impacted with a mallet to advance the spinal implant into a desired position in a disc space. 
     End face  146  may include any of a variety of profiles, including, but not limited to, flat, convex, concave, arcuate, wedge-shaped, u-shaped, or yea-shaped. End face  146  may have various surface contours, including, but not limited to, smooth, textured, or padded. In certain embodiments, a tamp may include elements such as tabs, pins, or protrusions for engaging a portion of a spinal implant. Such elements may facilitate manipulation of the spinal implant with the tamp. For example, tips  148  (shown in  FIG. 17 ) on tamp  144  may engage a groove or notch on a spinal implant to facilitate placement of the spinal implant using the tamp. 
       FIGS. 19A-19D  depict coupling of end member  54  with shaft assembly  52 . Pin  64  may be aligned with hole  130  (shown in  FIGS. 13-18 ). As depicted in  FIG. 19A , distal portion  68  of shaft  56  may be aligned with slot  76 . Pin  64  and distal portion  68  may be placed in slot  76 .  FIG. 19B  depicts pin  64  may engaged with hole  130  (shown in  FIGS. 13-18 ). End member  54  may be pivoted about pin  64 . As depicted in  FIG. 19C , distal portion  68  of shaft  56  may be positioned in opening  70  away from slot  76 . Slide  58  may be translated toward end member  54 . As depicted in  FIG. 19D , teeth  78  on distal end  66  of slide  58  may engage teeth  80  of end member  54 . Engagement of teeth  78 ,  80  may inhibit rotation of end member  54  relative to shaft assembly  52 . 
     In an embodiment, an instrument may be used in a procedure to insert a spinal implant in a disc space between adjacent vertebrae. The spinal implant may replace all or a portion of an intervertebral disc that has degenerated due to wear, trauma, and/or disease. The spinal implant may restore a normal separation distance between adjacent vertebrae and promote fusion of the vertebrae. In certain embodiments, a spinal implant may be inserted in a space formed between two portions of a bone to extend the length of the bone. 
     A discectomy may be performed to remove disc material from a disc space. A distractor may be positioned in the disc space to establish a separation distance between the vertebrae. A disc space may be prepared using instruments such as, but not limited to, scalpels, drills, curettes, chisels, or rongeurs. A chisel may be used to remove portions of vertebral bone and form channels in the vertebral endplates adjacent to the disc space. 
     In some embodiments, an angle of an end member relative to a shaft assembly may be adjusted while the end member is in a disc space. Pivoting the end member may facilitate positioning of the end member in various regions of the disc space. The ability to pivot an end member may allow a user to maintain the shaft assembly of an instrument in a desired range without requiring a large working space. For example, an angle of the end member relative to the shaft assembly may be controlled such that a position of the shaft assembly is maintained in a relatively small range within a surgical opening in the patient at a surface of the body as the end member is advanced in the disc space. The angle may be adjusted at selected points of advancement of the instrument into and/or withdrawal of the instrument from a disc space. In one embodiment, an angle of an end member with respect to a shaft assembly is adjusted twice during advancement of the end member and twice during withdrawal of the end member. In other embodiments, an angle of the end member with respect to the shaft assembly is adjusted three or more times during advancement of the end member and three and/or more times during withdrawal of the end member. 
     In some embodiments, an end member may be allowed to pivot freely relative to the shaft assembly as the end member is withdrawn from an incision. The end member may deflect as the end member encounters tissue during withdrawal. Pivoting of an end member during withdrawal may reduce damage to tissue that might occur if the end member were locked at a fixed angle during withdrawal of the end member. 
     Vertebral surfaces may require preparation before insertion of a spinal implant in a disc space. A rasp may be inserted in an intervertebral disc space from a posterior or transverse approach to abrade vertebral surfaces. Vertebral surfaces may be abraded to remove osteophytes and/or to smooth rough surfaces. In some embodiments, an instrument with an end member that is a rasp may be used to roughen vertebral endplates. Roughening of vertebral endplates may initiate a healing response that promotes bone growth. The bone growth may promote fusion of adjacent vertebrae with an installed spinal implant. 
     In an embodiment, an instrument including a rasp may be used to prepare a disc space for a spinal implant. An angle of the rasp with respect to a shaft assembly of the instrument may be adjusted to facilitate positioning of the rasp in the disc space.  FIGS. 20A-20E  depict use of instrument  50  including rasp  128 . Rasp  128  may be placed in disc space  150  at various angles relative to shaft assembly  52  of instrument  50 . Vertebral surfaces may be abraded by moving shaft assembly  52  back and forth with rasp  128  in disc space  150 . 
     An angle of rasp  128  relative to shaft assembly  52  may be selected to allow rasp  128  to be inserted in disc space  150  during a transverse approach. After insertion, an angle of rasp  128  relative to shaft assembly  52  may be adjusted to allow instrument  50  to be positioned and used at different locations within disc space  150 , including but not limited to the area across midline of the vertebral body. Shaft assembly  52  may be pivoted relative to rasp  128  by moving a slide of the shaft assembly and angling the shaft assembly relative to rasp  128 . After a desired angle is obtained, the slide may be moved against rasp  128  to secure the position of the rasp relative to shaft assembly  52 . Rasp  128  may be forced against an endplate of a first vertebra. Rasp  128  may be moved to treat the vertebral surface of the first vertebra. Rasp  128  may be forced against the endplate of a second vertebra. Rasp  128  may be moved to treat the vertebral surface of the second vertebra. 
     A discectomy may be performed to remove a portion of an intervertebral disc. The discectomy may form an initial path between vertebrae. After formation of the initial path, rasp  128  may be used to extend the path in a desired trajectory. Referring to  FIG. 20A , rasp  128  may be initially secured in first orientation A relative to shaft assembly  52 . Rasp  128  may be advanced in disc space  150  in an initial space formed during a discectomy. With rasp  128  in disc space  150 , shaft assembly  52  may be adjusted from orientation A to orientation B. Frictional engagement of rasp  128  with adjacent disc  152  may stabilize rasp  128  sufficiently to allow shaft assembly  52  to be angled by moving a slide of the shaft assembly and angling the shaft assembly. After obtaining desired angle B, the slide may be moved so that the slide engages capture members of rasp  128 . Rasp  128  may be used to extend disc space  150  formed between vertebrae.  FIG. 20B  depicts a representation of disc  152  after rasp  128  has been used to extend disc space  150 . Shaft assembly  52  may be adjusted from orientation B to orientation C. Rasp  128  may be further advanced into disc into  152  to establish desired disc space  150 , as depicted in  FIG. 20C . 
     Instrument  50  may be removed from disc space  150  by reversing the steps used for insertion of the instrument. For example, with shaft assembly  52  at orientation C, rasp  128  may be partially withdrawn from disc space  150  ( FIG. 20D ). Shaft assembly  52  may be adjusted to orientation B. Rasp  128  may be further withdrawn from disc space  150  ( FIG. 20E ). Shaft assembly  52  may be adjusted to orientation A, and instrument  50  may be removed from the incision. 
     In an embodiment, an instrument including a trial member may be used to gauge a disc space before insertion of a spinal implant. In an insertion procedure that uses modular end members, a rasp may be removed from a shaft assembly after a disc space is prepared. A trial may be attached to the shaft assembly. The instrument with the trial attached may be inserted into the disc space. The trial may have the same outer shape as the shape of a spinal implant in an instrumentation set provided for the spinal implant insertion procedure. If the trial is easily inserted into the disc space, the corresponding spinal implant may not have sufficient height. If the trial cannot be inserted, the corresponding spinal implant may have too much height. Insertion of the trial should be achieved with some impact on an end of the shaft assembly. The trial may be fully inserted along the established disc space to ensure that the corresponding spinal implant will be able to follow the same path. The angle of the shaft assembly relative to the trial may be adjusted during insertion of the trial into the disc space. After complete insertion, the trial may be removed from the disc space. 
     In an embodiment, an instrument may be used to position, guide, and/or manipulate a spinal implant in a disc space.  FIGS. 21A-21D  depict positioning of spinal implant  156  in disc space  150 . In some embodiments, bone growth promoting material may be placed in the disc space and/or in openings in the spinal implant to minimize or eliminate gaps between the spinal implant and walls defining the disc space. The bone growth promoting material may be, but is not limited to, autologous bone, allograft bone, xenograft bone, calcium phosphates, collagen, calcium sulfates, demineralized bone matrix, bone morphogenetic proteins, platelet derived growth factors, bone marrow aspirate, and/or blood. Spinal implant  156  may be placed in an initial position in disc space  150  using a spinal implant inserter  158  ( FIG. 21A ). 
     As depicted in  FIG. 21B , instrument  50  with tamp  144  and shaft assembly  52  may be coupled to spinal implant  156 . Tamp  144  may be angled relative to shaft assembly  52  in orientation A. Shaft assembly  52  may be advanced to drive tamp  144  and spinal implant  156  in disc space  150  ( FIG. 21C ). In certain embodiments, a mallet may be used to strike shaft assembly  52  of instrument  50  to advance spinal implant  156  in disc space  150 . 
     Shaft assembly  52  may be changed from orientation A to orientation B while tamp  144  remains in place in disc space  150 . In some embodiments, instrument  50  may be withdrawn slightly from spinal implant  156  to facilitate angular adjustment. Tamp  144  may be secured to shaft assembly  52  when the tamp is positioned in orientation B. Instrument  50  may be used to further advance spinal implant  156  into disc space  150 . Tamp  144  may be used to push spinal implant  156  fully into disc space  150 . A position of spinal implant  156  may be monitored using radiological techniques. After full insertion of spinal implant  156 , instrument  50  may be withdrawn from the surgical site. 
     In this patent, certain U.S. patents have been incorporated by reference. The text of such U.S. patents is, however, only incorporated by reference to the extent that no conflict exists between such text and the other statements and drawings set forth herein. In the event of such conflict, then any such conflicting text in such incorporated by reference in such U.S. patents is specifically not incorporated by reference in this patent. 
     Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, ail as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.