Abstract:
A process is described for insertion of a prosthesis within an intradiscal space during a posterior laminectomy. The process insures proper orientation and alignment of prostheses inserted in the intradiscal space. The process also involves minimal removal of bone from the facet joint, which assures retention of the major portion of a patient&#39;s spinal column weight bearing capability.

Description:
SUMMARY OF THE INVENTION 
     The invention disclosed herein is a posterior approach laminectomy procedure for placing a prosthesis within the intradiscal space between adjacent vertebrae. The procedure includes the steps of retracting the nerve root and the dural and inserting a disc space spreader within the intradiscal space. The direction of the disc space spreader insertion is recorded and a single tang retractor is inserted within the intradiscal space in a direction substantially parallel to the disc space spreader recorded direction. Further, the steps of forming the surfaces on the adjacent vertebrae to receive the prosthesis and positioning the prosthesis in contact with the formed surfaces using the single tang retractor as a guide are included. 
     A further aspect of the invention relates to a posterior approach laminectomy procedure for placing a prosthesis into the space between adjacent vertebrae which includes the steps of retracting the dural to an out of the way position and spreading the adjacent vertebrae. A single tang retractor is inserted into the space between the adjacent vertebrae and the direction of insertion of the single tang retractor is recorded. Opposing surfaces on the adjacent vertebrae are formed to receive the prosthesis using the single tang retractor as a guide. The prosthesis is positioned between the opposing surfaces along the single tang insertion direction. 
     In yet another aspect of the invention a posterior approach laminectomy procedure for placing a split prosthesis having a first half and a second half within the intradiscal space between adjacent vertebrae is disclosed. The halves of the split prosthesis are placed in positions on one side of and an opposite side of the spinal column center line. The procedure includes the steps of retracting the nerve root and dural and inserting a disc space spreader within the intradiscal space on the one side. The direction of the disc space spreader insertion is recorded and a single tang retractor is inserted within the intradiscal space on the opposite side in a direction substantially parallel to the disc space spreader recorded direction. Surfaces on the adjacent vertebrae are formed on the opposite side to receive the prosthesis second half The prosthesis second half is positioned in contact with the formed surfaces on the opposite side using the single tang retractor as a guide. The single tang retractor is removed from the opposite side and the disc space spreader is removed from the one side. The single tang retractor is inserted within the intradiscal space on the one side in the position vacated by the disc space spreader and substantially parallel with the disc space spreader recorded direction. The surfaces on the adjacent vertebrae on the one side are formed to receive the prosthesis first half. The prosthesis first half is positioned in contact with the formed surfaces on the one side using the single tang retractor as a guide. Thereafter, the single tang retractor is removed from the one side. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a posterior view of the operating area surrounded by drapes. 
     FIG. 2 is a view along the line  2 — 2  of FIG. 1 wherein the view follows the lower surfaces of the superior vertebrae of FIG.  1 . 
     FIG. 3 is a view along the line  3 — 3  of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     This procedure relates to laminectomy procedures in humans primarily in the lumbar region. The spinal column is the bony structure that runs along the back, represented in FIG. 1 by a pair of adjacent vertebrae, a superior vertebrae  11  and an inferior vertebrae  12 . The dural is a column containing the nerve paths and for the sake of simplicity herein will include the nerve roots when reference is made to retraction of the dural. The dural runs within a channel seen as item  13  in FIG. 2 of the drawings and is not shown in the drawings for purposes of clarity. The back of the spinal column is seen in FIG.  1  and is that portion of the spinal column which provides the primary weight bearing structure. The front of the spinal column or that portion which is toward the abdomen, is seen in the lower portion of FIG. 2 providing the shock absorbing portion of the structure. The shock absorbing function is performed by discs which are situated between adjacent vertebrae bearing upon the relatively broad surfaces seen as item  14  in FIG.  2 . The bony structure near the back of the spinal column has a facet joint  16  on each side of a center line  17  through the spinal column that joins an inferior vertebrae with a superior vertebrae through cartilage tissues. The facet joint contains an inferior facet  19  and a superior facet  18  as seen in FIG.  1 . When it is necessary to reach the region of the surfaces  14  on the vertebrae during a posterior approach laminectomy procedure instruments and prostheses must pass the facet joints as can be seen with reference to FIGS. 1 and 2. One of the purposes of the procedure disclosed herein is to remove less bone and cartilage from the facet joint during laminectomies and another purpose is to provide greater freedom for the surgeon to orient the prostheses adjacent the surfaces  14  with greater accuracy. 
     Pre- and post-operative procedures during laminectomies are not subjects of the procedure disclosed herein. Usual procedures are used for opening the tissues and controlling bleeding by using bipolar coagulation, insertion of gel foam where necessary and protection of nerve roots and axilla using gel foam. Post-operative procedures involving packing, suturing the various layers of tissue, etc. are also usual and will not be discussed further herein. 
     Upon arrival at the operating site the dural and associated nerve roots are moved out of the way with known retractors. A bone chisel is used to cut a small groove in the superior and inferior surfaces  14  on adjacent vertebrae  11  and  12  on one side of the center line  17 . A disc space spreader  21 , such as that disclosed in U.S. patent application Ser. No. 09/329,096, Mehdizadeh, incorporated herein by reference, is inserted into the cut grooves with the spline  22  on the disc space spreader entering the grooves. As disclosed in the aforesaid disc space spreader application, the spreader is tapped into place by tapping on the free end of a detachable rod  23  until the spreader is positioned substantially as shown in FIG. 2 of the drawings. The splines  22  on the disc space spreader further cut and define the grooves in the surfaces  14  on adjacent vertebrae and the direction of the rod  23  is recorded. The direction of the rod  23  may be recorded by marking two coordinates  24  and  26  on drapes  27  lying on the patient and surrounding the operating site as seen in FIG.  1 . Alternatively, the direction of the rod  23  may be recorded by means of marks placed with a sterile pen on surrounding tissue or bone structure. Representative marks are seen by the marks carrying the items numbers  28  and  29  in FIG.  1 . The axis of the rod  23  is aligned so that it is substantially perpendicular to a line from each mark  28  and  29 . With adjacent vertebrae  11  and  12  now being spread, the rod  23  is detached from the disc space spreader  21  as described in the disc space spreader application and removed from the operating site. Nerve root and dural are now moved out of the way on the opposite side of the spinal column center line  17 . The beginning of grooves in both the superior and inferior surfaces  14  of adjacent vertabrae are cut with a chisel. The grooves on the opposite side are spaced slightly from the center line  17 . A single tang nerve root retractor and protector  31  (hereinafter referred to as a Hamid retractor) is inserted into the intradiscal space with a single tang  32  entering the chiseled grooves on the opposite side. The Hamid retractor  31  is tapped into place as seen in FIG.  2 . The Hamid retractor is described in full in U.S. Pat. No. 5,803,904, Mehdizadeh, and such disclosure is incorporated herein by reference. The Hamid retractor is inserted in a direction parallel to that detected and recorded for the disc space spreader rod  23 . Note that the Hamid retractor single tang  32  is positioned toward the center line  17  of the spinal column and that the nerve root and dural are outside or positioned to the left of the Hamid retractor  31  as seen in FIG. 2. A reamer of known configuration is inserted through the Hamid retractor into the disc space surrounded by the adjacent surfaces  14  to remove damaged disc material and any other debris. 
     The prosthesis to be placed within the disc space will usually have some means thereon to retain the prosthesis temporarily until tissue is allowed to grow around and retain it in a permanent fashion. The prosthesis may have outside threads, as in the case of the Ray threaded fusion cage(TM), or it may be non-threaded having surface pins to contact the surfaces  14 . Alternatively, it may be a plastic member carrying some means for temporary retention within the disc space. In the case of the threaded prosthesis, a tap is inserted into the disc space through the Hamid retractor and, as the tap passes the facet joint  16 , the inner edge of the facet joint is threaded thereby. With reference to FIG. 2, it may be seen that as the tap is moved through the Hamid retractor  31  toward the intradiscal space surrounded by the surfaces  14 , it will touch the inner edge of the inferior facet  18 . Following formation of the opposing surfaces  14  surrounding the disc space, the tap is removed through the Hamid retractor  31  and a threaded cage  33  is inserted into the disc space through the Hamid retractor and turned while engaged with the threads on the surfaces  14  to assume the position shown in FIG.  3 . The threaded cage is guided into position by the threaded inner edge of the facet joint  16  and by the Hamid retractor  31 . The Hamid retractor is aligned in a direction substantially parallel with the recorded direction for the disc space spreader rod  23  as described hereinbefore. The entry for the threaded cage  33  may be counter sunk about 2 mm. as seen at  34  to avoid any post-operative contact between the proximate end of the threaded cage  33  and the dural or nerve roots. The cage insertion handle is removed along with the Hamid retractor following positioning of the threaded cage  33 . 
     Rod  23  is once again engaged with the disc space spreader  21  and the disc space spreader is removed from the position seen in FIG.  2 . The Hamid retractor  31  is positioned in place of the disc space spreader on the one side so that the edges of the single tang  32  on the Hamid retractor enter the grooves formed by the splines  22  in the opposing surfaces  14 . The Hamid retractor  31  therefore assumes a mirror image position to that seen in FIG. 2 with respect to the center line  17 . With the Hamid retractor positioned as described, the nerve root and dural are again outside the retractor, in this instance to the right of the retractor in mirror image position to that seen in FIG. 2. A known reamer is inserted through the Hamid retractor into the disc space surrounded by the surfaces  14  to remove damaged disc material and any other debris. A tap is inserted through the Hamid retractor to form the surfaces  14  on opposite sides of the disc space. Upon removal of the tap a threaded cage is inserted through the Hamid retractor into the disc space to contact the threads formed therein. The threaded cage is guided by the threaded inner surface of the facet joint  16  and the Hamid retractor to assume a position represented by item  37  in FIG.  1 . Again, the entry for threaded cage  37  into the intradiscal space may be countersunk about 2 mm. for purposes hereinbefore described. The direction of insertion of the threaded cage  37  is substantially parallel to the insertion direction of threaded cage  33  by aligning the Hamid retractor  31  with the recorded alignment marks  24  and  26  or  28  and  29 . As a result, the two threaded cages  33  and  37  are inserted in parallel orientation within the intradiscal space surrounded by the surfaces  14  quite close to the center line  17  and separated only by about the width of the single tang  32  on the Hamid retractor. The laminectomy procedure is concluded in routine fashion by the operating surgeon. 
     The foregoing described laminectomy procedure is intended to be used for surgery performed inside the disc space surrounded by the surfaces  14  on the vertebrae and for placement of prostheses in the intadiscal space and spinal channel. 
     Although the best mode contemplated for carrying out the present invention has been shown and described herein, it will be understood that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.