SPINAL IMPLANT INSERTION INSTRUMENT FOR SPINAL INTERBODY PROSTHESES

Abstract: A spinal implant insertion instrument (10) for intervertebral implant surgery formed from a hollow first element (12) of various external diameters, including a channel to accommodate and incorporate a vertebral pedicle, and a second element (18) joined by a hinge (22) to the first element (12), allowing reduction of the external diameter of the leading edge of the spinal implant insertion element (10) sufficient to allow the passage of the spinal implant insertion instrument (10) into the intervertebral disc space in a safe fashion, as the first maneuver, to be followed by activation of the second element (12) upon the first, restoring the internal diameter of the spinal implant insertion instrument (10) to a sufficient radius to allow successive passage of cutting, reaming, tapping instruments, and subsequent implantation of a spinal interbody implant device. The design of this instrument (10) reduces traction upon sensitive neural elements, allows controlled removal of the medial portion of the vertebral pedicle, distracts the intervertebral disc space, and allows safe passage of reaming, tapping, and spinal implant insertion devices through the expanded bore of the spinal implant insertion instrument (10).

Description: DESCRIPTION SPINAL IMPLANT INSERTION INSTRUMENT FOR SPINAL INTERBODY PROSTHESES Cross-Reference to a Related Application This application claims the benefitof U.S. ProvisionalApplicationNo. 60/160,71 1, filed October 20, 1999. Field of the Invention The invention relates generally to a spinal implant instrument for use in intervertebral spinal fusions, and more specifically, to an improved method of protection for neural elements during intervertebral disc space distraction, disc space reaming and tapping, and placement of intervertebral disc space bone grafts and prosthetic devices. Background of the Invention The spinal column is formed from a number of vertebrae, which in their normal state, are separated from each other by cartilaginous intervertebral discs. These discs form a cushion between adjacent vertebrae, resisting compression along the support axis of the spinal column, but permitting limited movement between the vertebrae to provide the characteristic flexible movement of the healthy spine. Injury, disease, or other degenerative disorders may cause one or more of the intervertebral discs to shrink, collapse, deteriorate, or become displaced, herniated, or otherwise damaged. Intervertebral stabilization by fusion of adjacent vertebrae has proven successful in permanently preserving intervertebral spacing. However, a number of technical barriers exist, including, for example, the retraction of neural elements out of the normal anatomic position, to a temporarily disadvantageous position, to allow reaming, tapping, and insertion of various intervertebral disc space bone grafts and prostheses. The displacementof neural elements (nerve roots) in such fashion is not uncommonly followed by temporary, or even permanent injury to the nerve roots. This can present an unpleasant, nearly intolerable burning pain in the extremities. Also, traumatic openings in the nerve covering may occur, allowing the escape of cerebral spinal fluid, and requiring with subsequent repair, resulting scar and nerve restriction. There may also be disruption of motor and sensory nerve elements, potentially causing permanent numbness and weakness in the extremities, bladder, bowel, or genitalia. Attempts to minimize the disadvantageous effects of retraction of neural elements include various nerve root retractors, designed to facilitate placement of the insertion tools against the adjacent nerves, and are commercially available. One disadvantage of these hand held retractors is instability. This instability may be caused by movement of the retractors by the insertion tools or by the shifting attention of the surgical assistant responsible for holding the retractors. Also, the physical bulk of the retractors themselves requires additional space in the limited confines of the intervertebral disc space being prepared for the intervertebral body prosthesis. In view of this, a need exists for a spinal implant insertion instrument to eliminate the need for separate nerve root retractors, and to protect neural elements from injury by the sequence of insertion tools as outlined above. A need further exists for such a device designed for easy insertion, combining protection and nerve root retraction, at the same time speeding up the entire operative procedure in a safe and efficient manner. Still another need exists for a method of distraction of the intervertebral disc space prior to insertion of the improved spinal implant. It is to that provision, for a device and method meeting these and other needs, that the present invention is primarily directed. Brief Summary of the Invention The subject invention provides a means for the protection of the nerve root during the insertion of a spinal implant on bone graft into an intervertebral disc space. Briefly described, in a preferred form, the present invention comprises a spinal implant insertion instrument, generally comprising a hollow body with an outer surface and an open interior surface. A fixed conically shaped curved guide with straight concave or convex contours extends from the bottom end of the hollow body. Additionally, a handle element, with a retractable conically shaped curved guide, is pivotally attached to the bottom end of the hollow body with an adjustable articulating hinge. The handle element is attached to the hollow body such that the retractable curved guide is positioned on an opposite side of the hollow body as the fixed curved guide. The cross-sectional area of the hollow body can be rectangular, elliptical or other shape, so long as it is of sufficient size to allow passage of instruments for reaming, tapping, and placement of intervertebral bone grafts or prosthetic devices. In an alternative form, stringer elements are affixed to the outer surface of the fixed curved guides, where the stringer elements traverse the lengths of the curved guides. The stringer elements add additional strength to the curved guides. In a preferred form, the spinal instrument comprises a primary locking mechanism. The primary locking mechanism locks the curved guides in the fully extended position by securing the handle element to the hollow body. Preferably, the locking mechanism is a spring-loaded retraction ring, which locks and secures the handle element by engaging a locking tab, which extends from the handle proximal end. The spinal implant insertion instrument can be fabricated from biocompatible materials including, without limitation, titanium, surgical alloys, stainless steel, or any other material suitable for fabrication of surgical instruments. In a preferred method use, the curved guides are positioned between a first vertebra and a second vertebra, with the curved guides being in the un-retracted position. The outer surface of the fixed curved guide is positioned against the lumbar dural tube. The hinged joint allows simultaneous retraction of the nerve root by compressing the handle element into the hollow body. The simultaneous retraction of the nerve root away from the lumbar dural tube allows for a safe retraction of the neural elements, eliminating the need for an independent retraction means, which would add additional bulk in a confined space, which in the present art, contributes to inappropriate compression of neural elements. In the retracted position, the internal diameter of the hollow body is sufficient to allow passage of instruments for reaming, tapping, and placement of intervertebral bone grafts or prosthetic devices. These and other objects, features and advantages of the present invention will be more readily understood, with reference to the detailed description below, read in conjunction with the accompanying drawings. Brief Description of the Drawings Figure 1 shows a side view of a retracted spinal implant insertion instrument, according to one cylindrical form of the present invention. Figure la shows an end view of a retracted spinal implant insertion instrument, according to one cylindrical form of the present invention. Figure 2 shows a side view of an un-retracted spinal implant insertion instrument, according to one cylindrical form of the present invention. Figure 3 shows a top view of a retracted spinal implant insertion instrument, according to one cylindrical form of the present invention. Figure 4 shows a cross-sectional side view of a retracted spinal implant insertion instrument, according to one cylindrical form of the present invention. Figure 5 shows a side view of the spinal implant insertion instrument in situ according to the cylindrical form of the present invention. Figure 6 shows a front view of the un-retracted spinal implant in situ according to the cylindrical form of the present invention. Figure 7 shows a front view of the retracted spinal implant in situ according to the cylindrical form of the present invention. Figure 8 shows a perspective view of the plunger to assist in the retraction of the retractable curved guide. Figure 9 shows a perspective view of the hollow guide element. Figure 10 shows a cut away side view of the hollow element inserted into the spinal implant insertion instrument. Figure 11 shows a side view of the stringer elements on the fixed and retractable curved guides. Figure 12 shows a top view of the stringer elements on the retractable curved guide. Figure 13 shows a side view of a retracted spinal implant insertion instrument with two retractable curved guides. Figure 14 shows a side view of an un-retracted spinal implant insertion instrument with two retractable curved guides. Figure 15 shows a side view of a retracted spinal implant insertion instrument with a threaded locking means. Figure 16 shows a side view of an un-retracted spinal implant insertion instrument with a threaded locking means. Figure 17 shows a side view of a retracted spinal implant insertion instrument with vertically adjustable articulating hinges. Figure 18 shows a side view of a un-retracted spinal implant insertion instrument with vertically adjustable articulating hinges. Detailed Disclosure of the Invention Referring now in detail to the figures wherein like reference numbers represent like parts throughout, preferred forms of the present invention will now be described. As seen in Figures 1-3, one embodiment of the present invention comprises a spinal implant insertion instrument 10, generally comprising a hollow body 12 with an outer surface and an open interior surface 14. The insertion instrument 10 further comprises a distal end 17 and a proximal end 15 with a fixed conically shaped curved guide 16 extending from the distal end 17. Additionally, the insertion instrument 10 comprises a handle element 18 with a handle distal end 19 and a handle proximal end 21, with a retractable conically shaped curved guide 20 extending from the handle distal end 19. The handle element 18 is pivotally attached to the hollow body 12, such that the conically shaped curved guides 16 and 20 are positioned on opposite sides of the hollow body 12. In a preferred embodiment, the handle distal end 19 is attached to the hollow body 12 distal end 17 by an articulating hinge 22. The articulating hinge 22, allows relative pivotal movement between the hollow body 12 and the handle element 18. In an alternative embodiment, as shown in Figures 17 and 18, the articulating hinge 22 is vertically adjustable along the length of the hollow body 12 distal end 17. In an embodiment, the hollow body 12 distal end 17 comprises a plurality of articulating hinges 22. The handle 18 distal end 19 is removable attached to an articulating hinge 22 by an attachment pin. The insertion depth of the retractable curve guide 20 may be vertically adjusted by repositioning the handle 18 distal end 19 on to the desired articulating hinge 22. In an alternative embodiment, as shown in Figures 1 1 and 12, stringer elements 44 are affixed to the outer surface of the fixed curved guide 16 and to the outer surface of the retractable curved guide 20. The stringer elements 44 traverse the lengths of the curved guides 16 and 20, partially covering the distal end 17 of the hollow body 12 and the distal end 19 of the handle element 18, respectively. The outer surface of each stringer element 44 is sufficiently shaped so as not to cause trauma to the exposed nerves. In a preferred embodiment, the curved guides 16 and 20 are milled incorporating the stringer elements 44. In an alternative embodiment, the stringer elements 44 can be affixed to the curved guides 16 and 20 by welding, or other similar methods known in the art. In a further embodiment, as shown in Figures 13 and 14, the spinal implant insertion instrument 10 comprising a hollow body 12 with an outer surface, an open interior surface 14, a distal end 17, and a proximal end 15. The insertion instrument 10 further comprises a handle element 18 with a handle distal end 19 and a handle proximal end 21, with a retractable conically shaped curved guide 20 extending from the handle distal end 19. The handle element 18 is pivotally attached to the hollow body 12 at the distal end 17. The insertion instrument 10 comprises a second handle element 37, with a handle distal end 61 and a handle proximal end 62, with a second retractable conically shaped curved guide 35 extending from the handle distal end 61. The second handle element 37 is pivotally attached to the hollow body 12, such that the conically shaped curved guides 20 and 35 are positioned on opposite sides of the hollow body 12. In a preferred embodiment, the handle distal ends 19 and 61 are attached to the hollow body 12 distal end by articulating hinges 22 and 36. The articulating hinges 22 and 36 allow relative pivotal movement between the hollow body 12 and the handle elements 18 and 37. The inner diameter of the hollow body 12 is of sufficient size to allow passage of instruments for vertebral cutting, reaming and tapping, and subsequent placement of intervertebral bone grafts and prosthetic devices. Preferably, the inner diameter of the hollow body 12 is between from about 6 millimeters and 24 millimeters. In an alternative embodiment, the cross-sectional area of the hollow body 12 can be rectangular, elliptical or other shape, so long as it is of sufficient size to allow passage of instruments for reaming, tapping, and placement of intervertebral bone grafts and prosthetic devices. In a further embodiment, an end cap 24 and a primary locking mechanism 26 are located at the proximal end 15 of the hollow body 12. When engaged, the primary locking mechanism 26 secures the handle element 18 such that the guides 16 are in the fully extended position. In a preferred embodiment, as shown in Figure 4, the primary locking mechanism 26 is a spring- loaded retraction ring, which locks and secures the handle element 18 by engaging a locking tab 28, which extends from the handle proximal end 21. In an alternative embodiment, as shown in Figures 15 and 16, the handle element 18 is secured to the hollow body 12 by a threadably adjustable locking mechanism 60. The proximal end 15 of the hollow body 12 and the interior surface of the primary locking mechanism 26 are match threaded. The primary locking mechanism 26 secures the handle element 18 by threading the primary locking mechanism 26 onto the locking tab 28. The primary locking mechanism 26 releases the handle element 18 by threadingthe primary locking mechanism 26 off of the locking tab 28. The spinal implant insertion instrument 10 can be fabricated from biocompatible materials including, without limitation, titanium, surgical alloys, stainless steel, or any other material suitable for fabrication of surgical instruments. In a preferred method of use, as shown in Figures 5-7, the curved guides 16 and 20 of the insertion instrument 10 are positioned between a first vertebra 30 and a second vertebra 32, with the curved guides 16 and 20 being in the un-retracted position. As shown in Figure 6, the spinal implant 10 is inserted into the intervertebral space, in the un-retracted position, with the outer surface of the fixed curved guide 16 being positioned against the lumbar dural tube. The hinged joint 22 allows simultaneous retraction of the nerve root by compressing the handle element 18 into the hollow body 12. The simultaneous retraction of the nerve root away from the lumbar dural tube allows for a safe retraction of the neural elements, eliminating the need for an independentretraction means, which would add additional bulk in a confined space, which in the present art, contributes to inappropriate compression of neural elements. In the retracted position, the internal diameter of the hollow body 12 is sufficientto allow passage of instruments for cutting, reaming and tapping, and subsequent placement of intervertebral bone grafts and prosthetic devices. In a specific embodiment, a plunger 38, as shown in Figure 8, can be inserted into the spinal implant insertion instrument 10 to assist in retracting the curved guides 16 and 20. The plunger comprises a shaft 39 with a stop 40 located at one end and a wedge 40 located at the opposite end. Once the curved guides 16 and 20 of the spinal implant insertion instrument 10 are positioned between a first vertebra 30 and a second vertebra 32, with the curved guides 16 and 20 being in the un-retracted position, the wedge 41 is inserted into the proximal end 15 of the hollow body 12. The plunger 38 is pushed through the hollow body 12 until the wedge 41 engages the curved guides 16 and 20. The curved guide 16 is retracted by simultaneously pushing the wedge 41 through the curved guides 16 and 20 and compressing the handle element 18 into the hollow body 12. The stop 39 prevents the wedge 41 from being pushed passed the curved guides 16 and 20. Once the handle element 18 is in the locked position, the plunger 38 is removed from the hollow body 12. The curved guide 16 can be locked in the retracted position to the curved guide 20 with a minimally larger snap lock flange along it's longitudinal axis. In a further embodiment, as shown in Figures 9 and 10, a hollow guide element 46 is inserted into the hollow body 12. The hollow guide element 46 has an outer diameter 50 and an inner diameter 48, where the outer diameter 50 is slightly less than the inner diameter of the hollow body 12, such that the hollow guide element 46 can be inserted into the hollow body 12. The inner diameter 48 is of a size sufficient to allow passage of instruments for reaming, tapping, and subsequent placement of intervertebral bone grafts and prosthetic devices. A stop 56 is positioned at the top end 52 of the hollow guide element 46, limiting the hollow guide element's 46 travel distance. The length of the hollow guide element 46 is substantially equal to the length of the spinal insertion instrument 10. When the curved guides 16 and 20 are locked in the fully distracted position the bottom end 54 of the hollow guide element 46 is inserted into the proximal end 15 of the hollow body 12 . In the fully inserted position the bottom end 54 of the hollow guide element 46 is positioned between the curved guides 16 and 20. In an alternative embodiment, the cross-sectional area of the hollow guide element can be, for example, rectangularor elliptical in shape, matching the shape of the hollow body 12, and being any of a variety of sizes, sufficient to allow passage of instruments for reaming, tapping, and placement of intervertebral bone grafts and prosthetic devices. In another embodiment, the spinal implant insertion instrument 10 can be more efficiently inserted by first introduction of a distraction tool. The distraction tool comprises a rectangular working surface, presenting first, the lesser dimension into the intervertebral disc space, and second, rotating the instrument so that the rotational action of the greater dimension distracts and moves apart the opposing vertebral surfaces preparatory to placement of the spinal implant insertion instrument into the center of the intervertebral disc space in it's retracted form. The spinal insertion instrument 10 can be inserted into the confined intervertebral disc space without undue retraction of neural elements, preparatory to placing the spinal implant insertion instrument into the intervertebral disc space in its retracted form. Again, when fully deployed in the distracted state, the internal diameter of the insertion instrument 10 is restored to a sufficient radius to accommodate the previously-mentioned cutting, reaming, tapping, and spinal implant insertion instruments. It should be understood that the examples and embodiments described herein are for illustrative purposes only, and various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.

Claims: Claims 1 1.. A spinal implant insertion instrument comprising; a) a hollow body, wherein said hollow body comprises an outer surface, an inner surface, a proximal end, and a distal end; b) a first guide, wherein said first guide extends from said distal end of said hollow body c) at least one handle element, wherein said handle element comprises a handle proximal end and a handle distal end; and ) at least one retractable guide, wherein said retractable guide extends from said handle distal end; wherein said handle distal end is hingedly attached to said distal end of said hollow body, such that said retractable guide opposes said first guide. 2. The spinal implant insertion instrument according to claim 1 , wherein said first guide is a fixed guide. 3. The spinal implant insertion instrument according to claim 1 , wherein said first guide is a second retractable guide. 4. The spinal implant insertion instrument according to claim 1, further comprising a locking means for locking said retractable guide in a retracted position. 5. The spinal implant insertion instrument according to claim 4, wherein said locking means comprises a spring-loaded retraction ring attached to the proximal end of said hollow body and a locking tap extending from said handle proximal end, wherein said spring-loaded retraction ring engages said locking tab, such that said retractable guide is locked in a retracted position. 6. The spinal implant insertion instrument according to claim 4, wherein said locking means comprises a threadably adjustable retraction ring threaded on the proximal end of said hollow body and a locking tap extendingfrom said handle proximal end, wherein said threadably adjustable retraction ring engages said locking tab, such that said retractable guide is locked in a retracted position. 7. The spinal implant insertion instrument according to claim 1, further comprising an impact cap positioned on said proximal end of said hollow body. 8. The spinal implant insertion instrument according to claim 1, further comprising a hollow guide element comprising a top end, a bottom end, an inner diameter and an outer diameter, such that said hollow guide element can be inserted through said proximal end of said hollow body when said retractable guide is in a retracted position and said bottom end is positioned between said retractable guide and said first guide and said top end is positioned at said proximal end of said hollow body. 9. The spinal implant insertion instrument according to claim 8, wherein said outer diameter of said hollow guide element is slightly less than an inner diameter of said hollow body. 10. The spinal implant insertion instrument according to claim 1 , further comprising a first stringer element affixed to an outer surface of said retractable guide. 1 1. The spinal implant insertion instrument according to claim 1 , further comprising a second stringer element affixed to an outer surface of said first guide. 12. The spinal implant insertion instrument according to claim 1, further comprising an adjustment means for adjusting an insertion depth of said retractable guide. 13. The spinal implant insertion instrument according to claim 1, wherein the geometric shape of a cross-sectional area of said hollow body is selected from the group consisting of circular, elliptical, and rectangular forms. 14. The spinal implant insertion instrument according to claim 1, wherein said hollow body has an inner diameter between about 6 mm to 24 mm. 15. The spinal implant insertion instrument according to claim 1, wherein said spinal implant insertion instrument is made of a biocompatible material. 16. The spinal implant insertion instrument according to claim 1, wherein said spinal implant insertion instrument is made of a material selected from the group consisting of titanium, stainless steel, and surgical alloys. 17. A method of inserting a spinal implant comprising the steps of: a) inserting a spinal implant insertion instrument into the intervertebral space between a first vertebra and a second vertebra, wherein said spinal insertion instrument comprises a hollow body comprising an outer surface, an inner surface, a proximal end, a distal end, and a first guide, wherein said first guide extends from said distal end of said hollow body, and a handle element comprising a handle proximal end, a handle distal end, and a retractable guide, wherein said retractable guide extends from said handle distal end; and said handle distal end is hingedly attached to said distal end of said hollow body, such that said retractable guide opposes said first guide, wherein said first guide and said retractable guide are inserted, in an un-retracted position, into the intervertebral space between said first and said second vertebrae, wherein an outer surface of said first guide is positioned against a lumbar dural tube; b) retracting said spinal implant insertion instrument by compressing said handle element into said hollow body, wherein said retractable guide retracts a nerve root away from the lumbar dural tube; c) locking said retractable guide in the retracted position; d) inserting a spinal implant through said hollow body into the intervertebral disc space; e) positioning said spinal implant in the intervertebral space; and f) removing said spinal implant insertion instrument from the intervertebral space. 18. The method of inserting a spinal implant according to claim 17, further comprising the steps of: a) inserting a cutting, reaming and tapping instruments thru said hollow body into the intervertebral disc; b) cutting , reaming or tapping the intervertebral space; and c) removing said cutting, reaming and tapping instruments prior to the insertion of the spinal implant or bone graft. 19. The method of inserting a spinal implant according to claim 17, further comprising the step of preparing the intervertebral space by inserting a distractor into the intervertebral space prior to insertion of a spinal implant insertion instrument. 20. The method of inserting a spinal implant according to claim 17, further comprising the steps of: a) inserting a plunger, comprising a wedged end, into said hollow body until said wedged end comes into contact with said retractable guide; b) retracting said retractable guide by simultaneously compressing said handle element into said hollow body and pushing said plunger into said hollow body, wherein said retractable guide retracts the nerve root from the lumbar dural tube; c) locking said retractable guide in the retracted position; and d) removing said plunger from said hollow body prior to the insertion of the spinal implant. 21. The method of inserting a spinal implant according to claim 17, further comprising the step of securing said retractable guide in the retracted position by inserting a hollow guide element through said hollow body, wherein a bottom end of said hollow guide element is positioned between said first guide and said retractable guide.

Inventors: CAUTHEN JOSEPH C, CAUTHEN, JOSEPH, C.
Applicants: CAUTHEN JOSEPH C, CAUTHEN RES GROUP INC, CAUTHEN RESEARCH GROUP, INC., CAUTHEN, JOSEPH, C.
Application year: 2000
Main classification: A61F2
IPC codes: A61B17, A61B19, A61F2