Abstract:
A method and apparatus for determining the space between adjacent spinous process. A trial implant instrument contains a trial sizer and an elongated body. The trial sizer and elongated body are pivotally mounted so that as the trial sizer is urged between adjacent spinous process, a physician may rotate the elongated body through a range of motion and not place any torsional forces upon the trial sizer. The method comprises several steps whereby a physician inserts and removes trial implant instruments with sizers of varying diameters to determine the space between adjacent spinous process.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to a trial implant instrument. More particularly, the present invention relates to a trial implant instrument for determining the size of an implant location between adjacent spinous process.  
         BACKGROUND  
         [0002]    As the present society ages, it is anticipated that there will be an increase in adverse spinal conditions which are characteristic of older people. By way of example, with aging comes increases in spinal stenosis (including but not limited to central canal and lateral stenosis), the thickening of the bones which make up the spinal column, and facet arthropathy. Spinal stenosis is characterized by a reduction in the available space for the passage of blood vessels and nerves. Pain associated with such stenosis can be relieved by medication and/or surgery. Of course, it is desirable to eliminate the need for major surgery for all individuals and in particular for the elderly.  
           [0003]    Accordingly, there needs to be developed procedures and implants for alleviating such and other spine related condition, which are minimally invasive, which can be tolerated by the elderly and for that matter any individual, and which can be performed preferably on an outpatient basis.  
           [0004]    Therefore, there is a need for a trial implant apparatus to determine the size of the location where the device will be implanted prior to performing the procedure. Such an apparatus and procedure will assist the physician to accurately select the correct size of the device to be implanted in the patient while minimizing the damage to tissue.  
         SUMMARY OF THE INVENTION  
         [0005]    An object of the present invention is a trial implant device for determining the space between adj acent spinous process. Such a device has a sizer pivotally mounted with a handle so that the handle may rotate relative to the sizer.  
           [0006]    Another object of the present invention is a method for determining the size between adjacent spinous process prior to implanting a device in the same area.  
           [0007]    Other objects, aspects and features of the invention are evident from the description of the embodiments, the claims and the figures. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a perspective view of an embodiment of the present invention.  
         [0009]    [0009]FIG. 2 is a side view of an embodiment of the present invention.  
         [0010]    [0010]FIG. 3 is a front view of an embodiment of the present invention.  
         [0011]    [0011]FIG. 4 is a cut-away view of an embodiment of the present invention from the perspective of line A-A in FIG. 3.  
         [0012]    [0012]FIG. 5 is a rear view of an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    The trial implant instrument  100  is used for determining the space between adjacent spinous process. Referring now to FIGS.  1 - 3 , the trial implant instrument  100  contains a sizer  102  and an elongated body  108 .  
         [0014]    The sizer  102  has a front end  104 , flanges  106  and a track  118  (See FIG. 4). As illustrated by the embodiment of FIG. 3, the sizer  102  is generally cylindrical and substantially elliptical in cross-sectional shape. However, one of ordinary skill in the art will appreciate that the sizer  102  can comprise many different shapes and cross-sections, such as, but not limited to, circular, triangular, rectangular or egg-shaped.  
         [0015]    The front end  104  preferably can penetrate the body tissue between adjacent spinous process so that the sizer  102  can be urged between adjacent spinous process. To accomplish this, the front end  104  must have a small diameter at the tip. The diameter of the front end  104  then gradually increases to the full diameter of the body of the sizer  102 . Thus, once the front end  104  creates an opening, the front end  104  will distract the opening to the full diameter of the sizer  102 . As shown in FIG. 2, the front end  104  is cone-shaped. Other shapes such as elliptical shapes, oval shapes, pyramid shapes and egg-shapes are also within the scope of the invention. By way of example only, the full smallest diameters of typical elliptical or oval sizers  102  are 6 mm, 8 mm, 10 mm, 12 mm, and 14 mm. In FIG. 3 the full smallest diameter is a long line drawn between the apexes of flanges  106 .  
         [0016]    As indicated above the sizer in FIG. 3 has two flanges  106 . Both flanges  106  extend outward from the sizer  102 . The flanges  106  prevent the sizer  102  from penetrating deeper than the length of the sizer  102 . As illustrated by FIG. 3, the flanges  106  are triangular in shape with apexes and are located on opposite sides of the sizer  102 . However, the flanges  106  can comprise other shapes such as, but not limited to, circular, rectangular or pyramid. The flanges  106  may also be a continuous strip of material extending out from the sizer  102 , thus creating a rim around the sizer  102 .  
         [0017]    The track  118  is a curved cavity in the back surface of the sizer  102  (see FIG. 4). The track  118  preferably accepts a track pin  114  (described later) to limit the rotation of the sizer  104 .  
         [0018]    The handle  110  has a first cavity  111  for accepting the elongated body  108  and a second cavity  113  for accepting an insert  115  (FIG. 4). The handle  110  provides an area that a physician can grip to urge the sizer  102  between adjacent spinous process. The handle  110  is made of a convenient material, for example, Gray ULTEM™. Preferably, the insert  115  of the handle  110  has a color corresponding to the diameter of the sizer  102 . By color coding each handle  110 , a physician can differentiate between several trial implant instruments  100 . For example, a gold insert  115  corresponds to a 6 mm diameter sizer  102 . A green insert  115  corresponds to an 8 mm diameter sizer  102 . A purple insert  115  corresponds to a 10 mm diameter sizer  102 . A blue insert  115  corresponds to a 12 mm diameter sizer  102 . Lastly, a gray insert  115  corresponds to a 14 mm diameter sizer  102 . To further assist a physician to distinguish between several trial implant instruments  100 , a diameter size can also be indicated on the bottom of the insert  115 .  
         [0019]    The elongated body  108  has a track pin  116  and a mounting pin  114 . The sizer  102  is pivotally connected with the elongated body  108 . The mounting pin  114  and the track pin  116  extend substantially perpendicular from the elongated body  108 . The track pin  116  is parallel to the mounting pin  114 . The mounting pin  114  engages the cavity  105  of the sizer  102  such that the sizer  102  rotates about the axis of the mounting pin  114 . The mounting pin  114  can be threaded and the cavity can also be threaded in order to retain the sizer  102  on the mounting pin  114 . Preferably, the range of rotation for the sizer  102  is restricted by the track pin  116  which engages the curved track  118 . The range of rotation is limited because the track pin  116  extends into the curved track  118  and acts as a stopping mechanism when either end of the curved track  118  contacts the track pin  116 . The range of rotation is limited to approximately a 60° range of motion in a preferred embodiment. However, the range of motion for the sizer  102  could be larger or smaller. In other embodiments the track  118  and track pin  116  can be eliminated if desired. Accordingly a physician is able to rotate the handle  110  through a specific range of motion while urging the sizer  102  between adjacent spinous processes, without placing any torsional forces on the sizer  102 . Therefore, as the sizer  102  is being inserted between adjacent spinous process a physician can rotate the elongated body  108  and not cause additional damage to body tissue.  
         [0020]    Spinal implant surgery can be carried out by using specially designed instruments to determine the correct size of an implant to be used. Several trial implant instruments  100  can be used successively to size the implant location in preparation for inserting the implant device in the patient.  
         [0021]    A series of even larger instruments  100  can also be used to distract or separate apart the spinous process in order to ease the final implantation of the device that is left between the spinous process. After a surgical field is prepared, an incision or access port is made in the back of the patient. The intraspinous space is then accessed, and the trial implant instrument  100  can be used to determine the correct size of a spinal implant to be inserted into the patient between the spinous processes. Generally, the sizer  102  with the smallest diameter is inserted between the spinous processes first. If the sizer  102  is too loose in the interspinous process space, the sizer  102  is withdrawn from between the adjacent spinous process. The physician will then choose a trial implant instrument  100  with a larger diameter sizer  102 . Then, the physician will urge the new sizer  102  between adjacent spinous process. This process continues until a sizer  102  encounters resistance indicating that the diameter of the sizer  102  is substantially equal to the size of the device to be implanted into the patient. A physician can then select an implant with the same diameter as the sizer  102 , ensuring that the implant selected will properly fit between adjacent spinous process of the patient. Alternatively, the physician can select a larger diameter sizer to distract apart the spinous process an additional amount, if for example, there is a desire to place an implant with a larger diameter between the spinous process.  
         [0022]    The diameter of the sizer  102  is intended to accurately represent the size of the implant device that will be inserted into the patient. Therefore, a physician should find the sizer  102  which, when inserted between adjacent spinous process, encounters resistance indicating that the proper sizer  102  has been selected. Specifically, inserting a sizer  102  of a known diameter between adjacent spinous process of a patient allows the physician to determine the correct size of the device that will be implanted between the adjacent spinous process prior to the actual procedure.  
         [0023]    The foregoing description of preferred embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention with various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.