Abstract:
A guide sleeve with longitudinally offset bone engaging portions is provided for engagement with anterior-posterior offset vertebral bodies. In one aspect of the invention the guide tube has fixed bone engaging portions in a predetermined offset position. In another form of the invention, the guide sleeve is composed of at least two moveably connected portions adapted to permit adjustment of the offset between the bone engaging portions. Further, a method is provided for using a guide sleeve with offset bone engaging portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/081,206, filed Apr. 9, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to surgical procedures for spinal stabilization and more specifically to instrumentation adapted for inserting a spinal implant within the intervertebral disc space between adjacent vertebrae. More particularly, while there may be other applications, the present invention is especially suited for engaging two vertebral bodies that are offset in an anterior-posterior fashion, as in spondylolisthesis, with respect to each other and providing a protected passageway for the movement of instruments and implants therethrough. 
     Currently available systems utilize a hollow sleeve having a uniform bone engaging end with teeth extending therefrom to be driven into the vertebrae adjacent the disc space. However, a common condition in spinal abnormalities is that adjacent vertebral bodies have been displaced creating an anterior-posterior offset condition. While offset vertebral bodies may be encountered in any part of the spine as a result of trauma, disease, or degeneration, the condition of spondylolisthesis typically develops in the lumbar spine. With offset vertebral bodies, the uniform bone engaging end of the hollow sleeve in prior systems, adapted to engage anterior-posterior aligned vertebral bodies, fails to completely engage both offset vertebra bodies simultaneously. This incomplete engagement with the offset vertebral bodies creates an unprotected space between one of the vertebral bodies and the end of the hollow sleeve. This unprotected space may allow contact between instruments disposed within the sleeve, such as cutting instruments, and surrounding tissue. Such contact may damage the sensitive tissue adjacent to the vertebral body leading to potential injury or death for the patient. 
     While the more recent techniques and instrumentation represent an advance over earlier surgical procedures for protecting surrounding tissue during preparation of the disc space and insertion of a fusion device, the need for improvement still remains. The present invention is directed to this need and provides a more effective protective guide sleeve for engaging offset vertebral bodies. 
     SUMMARY OF THE INVENTION 
     The present invention provides a guide sleeve having offset bone engaging portions. In one aspect the sleeve comprises a first tube portion having a first bone engaging end and a second tube portion moveably connected to the first tube portion. The second tube portion includes a second bone engaging end disposed proximal to the first bone engaging end. The second tube portion is moveable in relation to the first bone engaging portion to create an offset between the second bone engaging surface in relation to the first bone engaging surface. Preferably, the bone engaging end will include a distraction portion extending distally therefrom. Optionally, the guide sleeve may define one or more windows for visualization. 
     In another aspect, the invention provides a sleeve composed of a tube having a longitudinal axis and a bone engaging end. The bone engaging end has a first bone engaging portion and a second bone engaging portion. The second bone engaging portion is offset with respect to the first bone engaging portion. Preferably, the offset bone engaging portions are adapted to engage offset vertebral bodies. 
     Still further, the present invention provides a method of positioning a guide sleeve against a first vertebral body offset from a second vertebral body. The method includes making a determination of the amount of offset between the first vertebral body and the second vertebral body. A guide sleeve is provided that includes a bone engaging portion with a first portion and a second portion longitudinally offset from the first portion, the offset between the first and second portions substantially corresponding to the offset between the first vertebral body and the second vertebral body. The guide sleeve is then positioned adjacent the spine with the first bone engaging portion engaging the first vertebral body and the second bone engaging portion engaging the second vertebral body. Optionally, the guide sleeve may be composed of a first portion slidably connected to a second portion. In this configuration, the amount of offset may be adjusted to correspond to the offset between adjacent vertebra. Additionally, it is contemplated that with a moveable first portion, the extent of offset between the bone engaging portion may be adjusted after insertion into the body. 
     One object of the present invention is to provide an improved guide sleeve for engaging offset bone segments. 
     Related objects and advantages of the present invention will be apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of an offset guide sleeve according to the present invention. 
     FIG. 2 is a side elevational view of the sleeve of FIG. 1 rotated 90° about the longitudinal axis. 
     FIG. 2 a  is an enlarged perspective view of the bone engaging end of FIG.  2 . 
     FIG. 3 is a side view of an alternative embodiment of an offset guide sleeve engaged in a vertebral column. 
     FIG. 4 is a perspective view of the guide sleeve of FIG. 3 engaged in a vertebral column. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated devices, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     The present invention provides a guide sleeve for guiding instruments to a surgical site and protecting surrounding tissue from injury as a result of contact with the instruments disposed within the sleeve. While the invention may have other applications, particularly in the spine, in one preferred embodiment the invention is specifically adapted to engage anterior-posterior offset vertebral bodies to define a protected access passage to the disc space between the offset vertebral bodies. Provisional application 60/081,206 filed Apr. 9, 1998 and related utility application 09/179,799 entitled METHOD AND INSTRUMENTATION FOR POSTERIOR INTERBODY FUSION, filed Oct. 27, 1998, are incorporated herein by reference. 
     FIGS. 1 and 2 illustrate a guide sleeve in accordance with a preferred embodiment of the invention. Specifically, guide sleeve  50  includes a tube body  52  defining a bone engaging end  58  and an opposite proximal end  59 . Tube body  52  defines a longitudinal axis  65  extending between bone engaging end  58  and proximal end  59 , as well as a longitudinally extending internal working channel  53  (FIG. 2 a ) adapted to receive surgical instruments. Preferably, tube body  52  defines windows  54  and  56  extending through the tube side walls. Windows  54  and  56  provide access through the tube for external visualization of instruments disposed within the tube, visualization of the disc space and instrument access for debridement. Smaller window  54  is offset along longitudinal axis  65  from bone engaging end  58  by side wall portion  76 . Similarly, larger window  56  is offset along longitudinal axis  65  from bone engaging end  58  by side wall portion  78 . Side wall portion  76  is longer than side wall portion  78  and thus provides greater protection against the intrusion of neural tissue into the working channel of guide sleeve  50 . 
     Referring now more specifically to FIG. 2 a  showing an enlarged view of bone engaging end  58 , in a preferred embodiment the bone engaging end includes a pair of opposing distraction extensions  60  and  61  having tapered leading tips to ease insertion into the disc space. Optionally, distraction extension  60  includes offset groove portions  62  and  64  to engage the adjacent vertebral bodies and resist expulsion from the disc space. Distraction extension  61  is similarly configured. Distraction extension  60  terminates on a first side adjacent bone engaging surface  72  and on a second side adjacent bone engaging surface  74 . Distraction extension  61  is similarly configured and terminates adjacent bone engaging surfaces  72  and  74 . Preferably, bone engaging surfaces  72  and  74  each have a substantially planar configuration interrupted by spikes  66  and  68 , respectively. While other geometries of guide tube  50  are contemplated, such as but without limitation square and rectangular, the end configuration in the preferred embodiment is substantially circular in cross section and defines a cylindrical internal working channel. Preferably, distraction extensions  60  and  61  are configured to have the same extent of longitudinal extension (FIG.  2 ). 
     As shown most clearly in FIG. 1, bone engaging surfaces  72  and  74  are longitudinally offset by a distance  70 . Preferably, each bone engaging surface  72  and  74  includes a spike  66  and  68 , respectively, for penetrating the vertebral bone. The tips of spikes  66  and  68  are likewise offset by a distance approximate to distance  70 . While spikes have been shown in a preferred embodiment, it is contemplated that spikes are not required to utilize the present invention. Moreover, although one spike has been shown on each surface, those skilled in the art will understand that more or less spikes or other bone engaging structures may be utilized on the bone engaging surfaces without deviating from the spirit and scope of the invention. 
     Bone engagement ends  72  and  74  are offset a distance  70  that is selected to approximate the amount of anterior-posterior displacement between adjacent vertebral bodies. It will be understood that a series of guide sleeves  50  may be provided, each having a different displacement  70 , such that the appropriate guide sleeve  50  may be selected depending upon the amount of anterior-posterior offset between adjacent vertebra determined during examination of the vertebral bodies. 
     Referring now to FIGS. 3 and 4, there is shown yet a further preferred embodiment of a guide sleeve according to the present invention. Guide sleeve  80  includes first end  81  and an opposite bone engaging end  89  and a longitudinal axis  85  extending therebetween. Guide sleeve  80  is divided into a fixed portion  82  and a movable portion  84 . In a preferred embodiment, fixed portion  82  and movable portion  84  are configured to define the side walls of a cylindrical tube to thereby form  360  degrees of protection. However, it is contemplated that one of the portions may form the complete guide tube with a segment thereof being movable to adjust the configuration of bone engaging end  89 . The proximal portion of fixed moveable portion  84  is maintained in alignment with fixed portion  82  by adjustment mechanism  83 . The distal portion of moveable portion  84  is maintained in alignment with fixed portion  82  by distal guide  86 . 
     Guide sleeve  80  also includes visualization windows  87  and  88  formed in movable portion  84  and an opposing visualization window formed in fixed portion  82 . The bone engaging end  89  is configured similar to the bone engaging end  58  of guide sleeve  50  previously described. Bone engaging end  89  includes a pair of distraction extensions  94 . In the illustrated embodiment, distraction extensions  94  do not include the tapered sections adjacent the distal tip as shown with respect to guide sleeve  50 . However, it is contemplated that such a configuration may be used if it is desirable to ease insertion of the distraction extensions into the disc space. Fixed portion  82  includes bone engaging surface  91  having a spike  90 . Moveable portion  84  includes bone engaging surface  93  having a spike  92 . 
     The position of moveable portion  84  relative to fixed portion  82  is adjusted by adjustment mechanism  83  disposed adjacent proximal end  81 . Adjustment mechanism  83  includes an internally threaded collar  95  rotatably mounted on sleeve  80  by several pins similar to pin  101  engaging an internal shoulder (not shown). Collar  95  is adapted to engage external threads  99  disposed on movable sleeve  84 . It will be understood that as internally threaded collar  95  is rotated about guide sleeve  80 , moveable portion  84  will move axially with respect to fixed portion  82  in relation to the thread pitch. In this manner the offset  102  between bone engaging surfaces  91  and  93  can be adjusted. The combination of mark  96  on fixed portion  82  and scale  97  on movable portion  82  provides an indication of the amount of displacement between fixed portion  82  and movable portion  84 , and the corresponding offset  102  between bone engaging surfaces  91  and  93 . Collar  95  may be prevented from rotation by use of lock  98  which consists of a threaded shaft (not shown) with an external knob. The threaded shaft is received in a threaded opening in collar  95  and may be advanced to prevent rotation of the collar and thereby securely lock the offset in the desired position. 
     Referring now to FIG. 4, an imaging system may be utilized to determine the anterior-posterior offset  102  between adjacent lower vertebral body V 1  and upper vertebral body V 2 . Once offset  102  has been determined, a fixed guide sleeve  50  having a longitudinal offset  70  between a lower bone engaging end  74  and an upper bone engaging end  72  approximating offset  102  may be selected or an adjustable guide sleeve  80  may be adjusted to provide a longitudinal offset  102 . While a guide sleeve according the embodiment shown in FIGS. 1 and 2 may be used in a similar manner, for the purposes of illustration the following description will be made with specific reference to the embodiment illustrated in FIGS. 3 and 4. 
     Surgical access to the spine is achieved by known methods. In FIG. 4, the surgical procedure is performed from the posterior side of the spine. Typically, as known in the art, a distractor with the desired distraction height will be inserted into the disc space D to accomplish distraction. Guide sleeve  80  having offset  102  and distraction extensions substantially matching the distractor height is then passed over the distractor and positioned adjacent the spine. Force is then applied to proximal end  81 , such as by mallet or other instrument if manual force is insufficient, to urge distraction extensions  94  into the disc space and spikes  90  and  92  into vertebral bodies V 1  and V 2 , respectively. Preferably, spikes  90  and  92  will be advanced into the vertebral bodies until at least a portion of bone engaging surfaces  91  and  93  are abuttingly engaged with vertebral bodies V 1  and V 2 , respectively. 
     In an alternative method, particularly where imaging of the disc space is inadequate, guide sleeve  80  may be adjusted once it is in position in the disc space. In this use, it is contemplated that movable portion  84  would be substantially advanced distally. Guide sleeve  80  would be advanced with distraction extensions  94  entering the disc space until contact between spike  92  and vertebra V 2  is achieved. Spike  90  would then be in contact with vertebra V 1 . The adjustment mechanism may then be locked and force applied to the proximal end  81  of guide sleeve  80  to fully seat the guide sleeve in position. 
     Guide sleeves according to the present invention are preferably made of biocompatible materials having sufficient strength to withstand the forces encountered during insertion and use. More preferably, the guide sleeves may be made of stainless steel, titanium, or aluminum. Further, while distraction extensions and spikes have been illustrated in the preferred embodiments, it will be understood that such features are not required and that guide sleeves according to the present invention may be formed without these features. Still further, the teaching of the present invention may be applied to double barrel guide sleeves, typically utilized in anterior procedures, to provide similar advantages for adjusting the bone engaging end of the guide sleeves to accommodate various configurations of the vertebral bodies. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.