Patent Publication Number: US-2009222011-A1

Title: Targeting surgical instrument for use in spinal disc replacement and methods for use in spinal disc replacement

Description:
TECHNICAL FIELD 
     The present invention relates generally to the field of surgery and medical implants, and more particularly, to surgical tools and methods for use in positioning an intervertebral device between vertebral members of a patient. 
     BACKGROUND OF THE INVENTION 
     The human spine is a biomechanical structure with thirty-three vertebral members, and is responsible for protecting the spinal cord, nerve roots and internal organs of the thorax and abdomen. The spine also provides structure support for the body while permitting flexibility of motion. A significant portion of the population will experience back pain at some point in their lives resulting from a spinal condition. The pain may range from general discomfort to disabling pain that immobilizes the individual. Back pain may result from a trauma to the spine, be caused by the natural aging process, or may be the result of a degenerative disease or condition. 
     Procedures to remedy back problems sometimes require correcting the distance between vertebral members by inserting an intervertebral device (e.g., spacer) between the members. The spacer, which is carefully positioned within the disc space and aligned relative to the vertebral members, is sized to position the vertebral members in a manner to alleviate the patient&#39;s back pain. 
     Further, the intervertebral device is preferably designed to facilitate insertion into a patient. That is, the shape and size of the device are designed to provide for minimal intrusion to a patient during insertion, but still be effective post-insertion to alleviate the pain and provide maximum mobility to the patient. 
     Major blood vessels are located at an anterior aspect of the spine and often the intervertebral device is designed to be inserted in the spinal cavity at the mid-line of the spine from an anterior aspect. Such an approach requires particular care relative to the blood vessels and/or other sensitive objects located at the spine mid-line when approaching the spinal cavity from the anterior direction. 
     Thus, a need exists for instruments and methods for inserting an intervertebral device into a spinal cavity which minimizes the opportunities for injuring blood vessels and/or other sensitive bodies in the vicinity of a mid-line of a spine. 
     SUMMARY OF THE INVENTION 
     The present invention provides, in an aspect, a targeting surgical instrument for use in spinal disc replacement which includes a first arm, a second arm, and a body portion. The first arm is configured to be longitudinally aligned with a mid-line of a spine and to be at least partially received on an endplate of a lower vertebra of spinal cavity. The spinal cavity is defined by the lower vertebra and upper vertebra of the spinal cavity. The second arm is positioned at an angle relative to the first arm. The second arm defines an insertion angle. The body portion connects the first arm and the second arm. The body portion includes a plurality of radiopaque markers, which may be located to allow alignment of the first arm on the mid-line of the spine. 
     The present invention provides, in another aspect, a method for use in spinal disc replacement which includes aligning a first arm of a targeting instrument with a mid-line of a spine and placing the first arm on an endplate of a lower vertebra of a spinal cavity. The spinal cavity is defined by the lower vertebra and an upper vertebra of the spinal cavity. The targeting instrument includes a second arm aligned at an angle relative to the first arm and a body portion connecting the first arm and the second arm. The second arm defines an insertion angle for a spinal implant. The body portion includes a plurality of radiopaque markers, which may be located to allow alignment of the first arm on the mid-line of the spine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention will be apparent from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a perspective view of one embodiment of a targeting surgical instrument located on an endplate of a spinal cavity, in accordance with an aspect of the present invention; 
         FIG. 2  is a top elevational view of the targeting surgical instrument of  FIG. 1 , in accordance with an aspect of the present invention; 
         FIG. 3  is a side elevational view of the targeting surgical instrument of  FIG. 1 , in accordance with an aspect of the present invention; 
         FIG. 4  is a side elevational view of another embodiment of a targeting surgical instrument, in accordance with an aspect of the present invention; 
         FIG. 5  is a perspective view of the targeting surgical instrument and spinal cavity of  FIG. 1  along with blood vessels near the spinal cavity, in accordance with an aspect of the present invention; 
         FIG. 6  is a side elevational view of the targeting surgical instrument and spinal cavity of  FIG. 1 , in accordance with an aspect of the present invention; and 
         FIG. 7  is a side elevational view of the targeting surgical instrument of  FIG. 4  located in the spinal cavity of  FIG. 1 , in accordance with an aspect of the present invention; 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     In accordance with the principles of the present invention, a targeting surgical instrument for use in spinal disc replacement, and methods for use in implanting a prosthetic disc in a spinal cavity, are provided. 
     As depicted in  FIG. 1 , a targeting surgical instrument or tool  10  may be received on an endplate  110  of a lower (i.e., inferior) vertebra  100  defining a lower extent of a spinal cavity  120  into which it is desired to insert a spinal implant (not shown), e.g., a prosthetic disc. Such cavity may be created by a previous descectomy, i.e. the removal of a diseased or otherwise nonfunctional disc of a spinal column. 
     Tool  10  includes a first arm  200  and a second arm  300 , which may be separated from, and positioned at an angle  320  relative to, each other. Angle  320  may be an acute angle, for example, an angle between about 10 degrees and about 45 degrees, such as about 35 degrees. First arm  200  and second arm  300  may be connected at a connecting body  250 . Connecting body  250  may be rounded except for portions of an outer radial portion where first arm  200  and second arm  300  intersect connecting body  250  as depicted in  FIG. 1 . An intersection point of the longitudinal axis of first arm  200  (i.e., a first longitudinal axis  225 ) and second arm  300  (i.e., a second arm longitudinal axis  325 ) at a radial center  255  of connecting body  250  may be a rotation center (not shown) for a prosthesis (not shown) desired to be inserted in the spinal cavity. Tool  10  is particularly suited for inserting a prosthesis that is sensitive to the positioning accuracy of the rotation center on a mid-line of the spine. Connecting body  250  may include radiopaque markers  260  which may be located equidistant from a longitudinal axis  225  of first arm  200 . Connecting body  250  may also include a radiopaque probe  270  located at a distal extent of connecting body  250  opposite an intersection point between first arm  200  and connecting body  250 . Tool  10  may be formed of biocompatible plastic material (e.g., DELRINE). Also, as noted above, markers  260  and probe  270  may be made of radiopaque material, and the remainder of tool  10  may be formed of radio transparent material. Further, markers  260  and probe  270  may be formed integral to, or connected to, the remainder of connecting body  250 . Markers  260  and/or probe  270  may be metal portions press fit into pre-cut grooves in the remainder of connecting body  250 . Alternatively, markers  260  and/or probe  270  may be metal or other radiopaque portions, which are connected to, and/or extend from, connecting body  250 . 
     After a disc (not shown) has been removed from a spine of a patient to form spinal cavity  120 , first arm  200  may be aligned with a mid-line  310  of a spine or endplate (e.g., endplate  110 ) thereof as depicted in  FIG. 1 . More particularly, first arm  200  may be attached to a mid-line pin  130  previously attached (e.g., via impaction of the pin  130  into the endplate) to lower vertebra  100 . As depicted in  FIG. 5 , first arm  200  may be attached to the mid-line pin by receiving the mid-line pin in a slot  202  of two extending portions  205  which extend from first arm  200  outside of the spinal cavity along an outer surface  105  of lower vertebra  100 . These two extending portions  205  may be similar to some extent to the arms of a fork between which pin  130  is inserted. Alternatively, first arm  200  may be attached, or aligned with, mid-line  310  by a variety of other means. For example, an opening for receiving the pin surrounded on all sides by a descending (e.g., orthogonal to endplate  110 ) portion of arm  200  could be substituted for the slot. 
     Mid-line  310  of the spine may be identified intra-operatively using an anterior-posterior X-ray image. Mid-line pin  130  then may be attached (e.g, via impaction) to an outer surface  105  of lower vertebra  100 . Also, a lateral X-ray image may be taken of the spinal cavity with tool  10  inserted therein (i.e., after first arm  200  is attached to mid-line pin  130 ). The lateral X-ray image may allow markers  260  and probe  270  to be visible relative to the remainder of tool  10 . Thus, a distal extent of probe  270  may be adjusted by the user (e.g., a surgeon) such that probe  270  extends to, or near, a distal end  103  of endplate  100  without extending past such distal end. Markers  260  may be aligned such that an imaginary line connecting them is substantially orthogonal to mid-line  310  of the spinal column and contained in the plane defined by the two arms of the tool  10 . More particularly, the markers may be aligned with one another (i.e., one behind the other) when viewed via the lateral X-ray image of the spinal cavity with tool  10  inserted therein. Such alignment may thereby locate longitudinal axis  225  of first arm  200  on mid-line  310  of the spine. 
     In another example, probe  270  may include a hook  280  extending distally from connecting body  250  and being curved to a position substantially orthogonal to a longitudinal axis of first arm  200  as depicted in  FIG. 7 . The hook may extend over the posterior edge of the endplate and may be manipulated to contact a distal side  107  of the lower vertebra and/or a posterior ligament (not shown). For example, hook  280  may be configured (e.g., shaped or dimensioned) to conform to a shape of endplate  110 , distal side  107  of lower vertebra  100  and/or an intersection between endplate  110  and distal side  107 . 
     After longitudinal axis  225  of first arm  200  is aligned on the mid-line  310  of the spinal column, as depicted in  FIG. 1 , tool  10  may be held in place by a spreader (distraction tool) or other surgical tool (e.g., the tool which is the subject of co-owned U.S. patent application Ser. No. 11/344,946, filed Jan. 31, 2006, and entitled “A Spinal Disc Replacement Surgical Instrument And Methods For Use In Spinal Disc Replacement” (Attorney Docket No. P23436.00), and/or the tool which is the subject of co-owned U.S. patent application Ser. No. 10/768,354, filed Jan. 30, 2004 and entitled “Instrumentation and Methods for Preparation of an Intervertebral Space”, U.S. Publication No. US 2005/0113842A1, the entities of which are incorporated herein by reference). A targeting pin  400  ( FIG. 1 ) may be placed (e.g., by impaction) along longitudinal axis  325  of second arm  300  on outer surface  105  of lower vertebra  100  as depicted in  FIGS. 1-2 . The second arm  300  may be longer than the first arm  200  because it is intended to be partially outside of the patient body. Targeting pin  400  may then be used as an indicator for a direction when inserting a surgical tool or marking the vertebra with a marker to allow preparation of the spinal cavity for receiving a spinal implant at an angle offset (e.g., at the angle of second arm  300 ) from mid-line  310  of the spine. For example, a keel cutter (not shown) may be utilized to cut channels or keels in an upper (not shown) and lower vertebra  100  as described for example in the co-owned patent applications indicated above. Such keels or channels are utilized to receive protruding portions (not shown) of a spinal implant (not shown). For example, an upper channel may be cut in the upper vertebra while tool  10  is located on endplate  110 . Tool  10  may then be removed and the upper channel and targeting pin  400  may be utilized to align and cut a lower channel in endplate  110  of lower vertebra  100 . Comers of the vertebra may also be cut to facilitate the insertion of the implant. 
     The channels may be aligned relative to a longitudinal axis of first arm  200  and therefore the mid-line  310  of the spine such that a central rotation point of an implant is located at the mid-line  310  of the spine, and at a location defined by radial center  255  of contacting body  250  of tool  10 , when the implant is inserted in spinal cavity  120  with top and bottom protruding portions (not shown) of the implant being received in the channels (not shown) previously cut and a leading edge of the implant reaches the posterior wall (e.g., a radial end or edge of endplate  110 ) of the vertebra. As noted above, the insertion of the implant along the direction defined by targeting pin  400  and second arm  300  allows the implant and the tools used to facilitate the preparation of spinal cavity  120  for the implant to avoid contacting and/or damaging sensitive blood vessels  600  ( FIG. 5 ) located at or near mid-line  310 , and at the anterior side of the spine. 
     As will be understood by one skilled in the art, a surgical targeting instrument (e.g., tool  10 ) could be formed of a variety of materials and formed in a variety of shapes which are configured to be received in a spinal cavity and be aligned with a mid-line of a spine and provide an arm at an off set angle relative to the mid-line of the spine, which may provide a entry angle for a variety of surgical instruments which avoid contacting blood vessels  600  ( FIG. 5 ) or other sensitive objects in the vicinity of the mid-line of the spine, and which prepare the spinal cavity for the implantation of an intervertebral device, e.g., a spinal implant or prosthetic. Further, such a surgical targeting instrument (e.g., tool  10 ) could include a variety of means for being aligned with a mid-line of a spine. For example, radial opaque markers and/or probes may be located at various locations to allow an appropriate aligning of the instrument within the spinal cavity. 
     Although preferred embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.