Patent Publication Number: US-2007123891-A1

Title: Facet joint reamer

Description:
FIELD OF THE INVENTION  
      The invention relates to a facet joint reamer with a substantially cylindrical shank, with teeth provided at the distal shank end and with a handle at the proximal end.  
     BACKGROUND OF THE INVENTION  
      Such a facet joint reamer is known from DE 699 17 683 T2. The known reamer has a hollow cylindrical shank, a handle at its rear, proximal end and teeth at its front end. Such a reamer is used for cutting out vertebral components in the vicinity of a lateral process of a vertebral column vertebra in order to create a postero-lateral access to the strangulated nerve roots of the central nervous system. Through said access removal then takes place of the intervertebral disk pulp tissue and other tissue types (capsular, cicatricial and ring tissue), because they press on the nerve roots. The vertebral process in question forms with an adjacent process of an adjacent vertebra the so-called facet joint.  
      Microinvasive surgery for the decompression of strangulated nerve roots using the known facet joint reamer is highly successful. However, it has been found that in the vicinity of the teeth, also in the case of standard cleaning and disinfection, osseous tissue can be left behind, which at best could be carefully removed with considerable effort. In addition, since reamers of different thicknesses are used, it would be desirable to be able to use different reamers with a common operating handle.  
      Therefore the problem of the invention is to improve such a facet joint reamer in the above-indicated manner.  
     SUMMARY OF THE INVENTION  
      According to the invention this problem is solved by a facet joint reamer which is characterized in that the shank and handle are separable and in particular nondestructively. separable.  
      In a specific development the shank and handle are provided with a cooperating joining device, which is constructed in such a way that at its proximal end the shank has a lateral depression in which engages a ball seated on the handle and which in turn can be introduced into a recess on the reamer shank. The ball can be locked on the handle, so that as a result the reamer shank is held in securely seated manner in the handle. This results from the fact that a slider is movable between a release position for releasing the shank from the handle and a locking position in which the shank is reliably held in the handle.  
      According to a preferred development the slider is spring loaded, the slider being more particularly held in the locking position by a spring.  
      In a further development the slider has a widened, inner area into which the ball can retreat when the slider passes over the ball. This leads to a release position for the reamer shank and the latter can be removed from the handle in the indicated slider and ball positions.  
      Additionally, in a preferred development, the slider can be slid out of the locking position counter to the force of the spring by manual action into its release position and in accordance with the differing preferences of surgeons either the slider is slidable counter to the action of the spring in the proximal direction into its release position or the slider is slidable counter to the action of the spring in the distal direction into its release position.  
      Further developments of the invention are characterized in that the shank and handle are connectable to rotate with one another and in particular one connecting part of the shank is constructed as an external polygon, particularly trihedron and a reception area of the handle as an internal polygon, preferably an internal trihedron.  
      In a highly preferred development a connecting part of the shank is made from plastic, said connecting part being connected in a fixed, unreleasable (at least nondestructively release) manner with the reamer shank and is e.g. injection moulded around the same. This makes it possible to code different shank thicknesses, e.g. by differing colours of the plastic part, i.e. formation thereof with a reflection-absorption capacity in different wavelength ranges. In addition, on the plastic shank can be provided a marking, e.g. in the form of an elevation if the reamer shank is provided with a lateral protective lip projecting over the teeth for protection of nerves during working, said marking in the form of an elevation on the plastic part being aligned with the lip at the distal reamer end. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Further advantages and features of the invention can be gathered from the claims and the following description of two preferred embodiments of the inventive facet joint reamer and with reference to the attached drawings, wherein show:  
       FIG. 1 A  first development of the inventive facet joint reamer, partly in longitudinal section.  
       FIG. 2  Another development of an inventive facet joint reamer, also partly in longitudinal section.  
       FIG. 3 A  front view of the insertion opening of the handle of an inventive facet joint reamer.  
       FIG. 4 A  rear view of two adjacent lumbar vertebrae of the human vertebral column.  
       FIG. 5 A  part sectional view of the spinal intervertebral disks between two vertebrae according to  FIG. 4 . 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      The facet joint reamer  1  according to the invention has a substantially cylindrical steel shank  2 , which is provided with teeth  4  at its distal end  3 . At the proximal end  5  the shank has a fastening part  6  in the form of a polygon, here trihedron plastic sleeve injection moulded onto the same and whose side wall is provided with a depression  7 . Shank  2  is nondestructively releasably connectable to a handle  11 .  
      Handle  11  has a T-shaped handle part  12  with a longitudinal bar  13  and at its distal end a crossbar  14 . To the handle part  12 , more precisely the proximal end of longitudinal bar  13 , is connected in fixed manner a sleeve  15 , on whose end rests a seal  16 . Along the sleeve can be axially slid counter to the action of a spring  18  a slider  17 , said spring being placed in a recess  19  between sleeve  15  and slider  17  and its abutment in the represented embodiment of  FIG. 1  is on the one hand, proximally, on a frontal ring section  12 . 1  of handle part  12  and on the other on a ring-shoulder  17 . 1  of slider  17 , so that the spring preloads or presses it in the distal direction.  
      A recess of sleeve  15  contains a ball  20 , which is held on the radial inside by an annular flange  15 . 1  bounding the recess, so that it cannot drop out of the sleeve  15 . Slider  17  has an area  17 . 2  sliding on the sleeve  15  and by means of which, as shown in  FIG. 1 , the sleeve can be pressed into recess  7  of part  6 . Following onto the same on the side remote from the sleeve is provided a recess  17 . 3 , which has larger radial dimensions than wall  17 . 2  and consequently, if area  17 . 3  reaches the axial height of the ball, releases the latter, so that the shank  2  can be extracted from the handle  11 .  
      On the side of slider  17  remote from the cross-section  14  of handle  11  is provided a gripping trough  17 . 4 . Counter to the action of spring  18  and by action on gripping trough  17 . 4  and pulling the slider  4 , the latter can be moved counter to cross-section  14  and then the widened recess  17 . 3  of the slider arrives at the axial height of ball  20  and in this way releases the same for removing or inserting reamer  2 . On releasing the slider  17  again, under the influence of spring  18  its area  17 . 2  slides over ball  20 , presses the latter into recess  7  and in this way locks reamer  2  in the axial position represented here.  
      As a result of the polygonal construction of connecting. part  6  and the recess of handle  11 , the reamer is also connected to rotate in handle  11 .  
       FIG. 2  shows another development of the inventive reamer  1 , in which identical parts carry the same reference numerals. For a description thereof reference should be made to the preceding statements and only the differences are explained in detail hereinafter.  
      Also in the case of the development of  FIG. 2 a  sleeve  15 ′ as provided on handle  11  and is surrounded by a slider  17 ′ slidable axially along the same. At the rear, proximal end of sleeve  15 ′ is formed a shoulder  15 . 1 ′ and once again a helical spring  18  is provided with an inwardly projecting annular step  17 . 1  formed proximally on slider  17 ′. Said spring moves the slider  17 rearwards or in the proximal direction. The slider has an abutment by means of cooperating shoulders  15 . 2 ′ on sleeve  15 ′ and  17 . 2 ′ on the slider..  
      A ball  20  is seated in the described manner in a recess of sleeve  15 ′. Slider  17 ′ has an area  17 . 3 ′, whose internal diameter is aligned in this area with the external diameter of sleeve  15 . A widened slider area  17 . 4 ′ is provided proximally to area  17 . 3 ′.  
      Spring  18  presses the slider into the position shown in  FIG. 2 , in which area  17 . 3 ′ of slider  17 ′ is at the axial height of ball  20  and presses the latter into recess  7  of connecting part  6  and thus locks shank  2  in handle  11 .  
      On the slider is also formed a gripping part  17 . 5 ′ with which said slider can be moved in the distal direction.  
      If the surgeon grasps the gripping area  17 . 5  and slides slider  17 ′ in the distal direction, the widened area  17 . 4 ′ of slider  17 ′ arrives at the axial height of ball  20 , so that the latter can move radially outwards, passes out of recess  7  and consequently shank  2  can be removed from handle  7  and also in this slider position a shank  2  can be inserted in handle  11 .  
      The inventive reamer is used in the manner described hereinafter relative to  FIGS. 4 and 5 . In exemplified manner  FIG. 4  shows the fourth and fifth lumbar vertebrae L 4 , L 5  and between the same an intervertebral disk  30  with a strangulation  33  at the fibrous ring  31  immediately to the right of the central axis of the vertebral column with an extrusion  34  of intervertebral disk pulp tissue into the vertebral canal— FIG. 5 .  
      In the interior of the vertebral canal  22  are diagrammatically shown nerve structures  23 ,  24 ,  25 . Each vertebra L 4 , L 5  has a spinous process  40 ,and a left and right-hand. transverse process  42 , left and right-hand, lower; joint-forming processes  43  and left and right-hand, upper, joint-forming processes  44 , the left and right-hand joints between the upper and lower lumbar vertebrae L 4 , L 5 , referred to as the facet joint  46 , being formed by in each case the lower processes  43  of the upper vertebra L 4  and the upper processes  44  of the lower vertebra L 5 .  
      The reamer according to the invention is used in the following way:  
      Firstly a hollow needle or probe with an external diameter of approximately 1.25 mm is advanced into a position adjacent to the strangulation. A guide wire is then moved through the hollow probe lumen until its distal end projects somewhat over the probe end. The hollow probe is then removed, whereas the guide wire remains in place. A trocar shell is then advanced over the guide wire until the blunt trocar end is located on the facet joint  46 . Whilst holding the trocar in this position, a reamer according to the invention with a small diameter of approximately 4.5 mm is advanced over the trocar  54  until the distal reamer end engages on the surface of the facet joint  46 . The surgeon now e.g. manually rotates the handle provided at the reamer end close to him, so that a channel is produced in the protuberance  43  of vertebra L 4 . This step is repeated with larger diameter trocar shells and reamers until an adequate channel diameter is reached to permit the reception of a cannula with a lumen sufficiently large to permit the passage of not only forceps, but also an endoscope. The strangulation is then removed with the forceps, optionally under endoscopic observation.  
     REFERENCE NUMERALS LIST  
       1  Facet joint reamer  
       2  Shank  
       3  Distal end  
       4  Teeth  
       5  Proximal end  
       6  Fastening part  
       7  Depression  
       11  Handle  
       12  T-shaped handle part  
       12 . 1  Annular section  
       13  Longitudinal bar  
       14  Crossbar  
       15  Sleeve  
       15 . 1  Annular flange  
       15 ′ Sleeve  
       15 . 1 ′/ 15 . 2 ′ Shoulder  
       16  Seal  
       17  Slider  
       17 . 1  Annular shoulder  
       17 . 2  Wall  
       17 . 3  Recess  
       17 . 4  Gripping trough  
       17 . 5  Gripping area  
       17 ′ Slider  
       17 . 1 ′ Annular step  
       17 . 2 ′ Shoulder  
       17 . 3 ′ Area  
       17 . 4 ′ Widened area  
       17 . 5 ′ Gripping part  
       18  Helical spring  
       19  Recess  
       20  Ball  
       22  Vertebral canal  
       23 ,  24 ,  25  Nerve structures  
       30  Intervertebral disk  
       31  Fibrous ring  
       33  Strangulation  
       34  Extrusion  
       40  Spinous process  
       42  Transverse process  
       43 / 44  Processes  
       46  Facet joint  
       54  Trocar  
      L 4 , L 5  Lumbar vertebrae