Abstract:
An apparatus for cutting bone includes an elongate member ( 11 ) having a central axis. The elongate member includes a tubular portion ( 12 ) that extends between a proximal end portion and a distal end portion. The distal end portion includes an articulatable head section with a stop surface and a cutting edge ( 70 ) projecting from the stop surface. The head section is articulatable about a pivot axis ( 74 ) that extends transverse to the central axis. The apparatus further includes a mechanism ( 90, 100 ) for articulating the head section relative to the tubular portion. The apparatus is a form of an osteotome that is particularly useful for certain spine-related surgical procedures.

Description:
RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/436,867, entitled PERCUTANEOUS CONTROLLED VERTEBRAL OSTEOTOMY TOOL SET, filed Dec. 27, 2002. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to an articulatable apparatus for cutting bone and, in particular, is directed to a uniquely designed osteotome that is useful in cutting vertebrae.  
       BACKGROUND OF THE INVENTION  
       [0003]     A known procedure for treating vertebral compression fractures and other bone-related disorders is vertebral augmentation with bone cement. Vertebral augmentation can be performed by the direct injection of liquid cement into the collapsed vertebral body (commonly known as “vertebroplasty”). Vertebral augmentation can also be performed after the restoration of the vertebrae to near normal vertebral body anatomy and creation of an internal cavity with the use of an inflatable bone tamp. This minimally invasive procedure is commonly known as “kyphoplasty” (see, for example, U.S. Pat. Nos. 4,969,888 and 5,108,404). During the kyphoplasty procedure, the inflatable bone tamp is inserted through a small skin incision which accommodates a working tube passed into the vertebral body. Inflation of the bone tamp compresses the cancellous bone and desirably moves the fractured cortical bone to its pre-fractured orientation, creating a cavity within the vertebral body that can then be filled with a settable material such as a cement or any number of synthetic bone substitutes. In effect, the procedure “sets” the vertebra at or near its pre-fracture position and creates an internal “cast”, protecting the vertebra from further fracture and/or collapse.  
         [0004]     As compared to a traditional vertebroplasty procedure, kyphoplasty restores the vertebrae to a pre-fractured condition and the injected bone filler is less likely to leak out of the vertebral body during a kyphoplasty procedure. However, under some circumstances, it has been observed that unpredictable reductions can occur with the kyphoplasty technique in chronic or partially healed collapsed vertebral bodies. Under those circumstances, the surgeon would typically resort to a large open operation to re-align the post-traumatic kyphosis. Further, inadequate reductions can occur with certain other spinal deformities such as scoliosis and kyphosis using the known techniques and surgical tools. The large open operations do carry with them significant morbidity in an already physiologically compromised elderly population. The principle benefit of the percutaneous minimally invasive approach, which is the hallmark of the kyphoplasty procedure, is the minimal morbidity associated with the procedure. In this light, additional tools are required to further the technique, achieve better anatomic re-alignment of the spine, and maintain the minimally invasive nature of the surgery. The additional tools will be deployed through small working portals and be able to achieve the desired strategic vertebral osteotomies to move bone in three dimensional space. One such tool would provide a minimally invasive means to safely cut the side (or lateral) wall of a vertebral body, such as a lateral wall with a prior and at least partially healed compression fracture, from within the medullary cavity in the vertebral body. A tool with an articulatable cutting blade is particularly desirable so that aimed strategic osteotomies can be made across a broad path despite working within the confines of the medullary cavity in the vertebral body and the percutaneous cannula.  
       SUMMARY OF THE INVENTION The present invention is an  
       [0005]     apparatus for cutting bone comprising an elongate member having a central axis. The elongate member includes a tubular portion that extends between a proximal end portion and a distal end portion. The distal end portion includes an articulatable head section With at least one stop surface and a cutting edge projecting from the at least one stop surface. The head section is articulatable about a pivot axis that extends transverse to the central axis. The apparatus further includes means for articulating the head section relative to the tubular portion.  
         [0006]     The present invention further provides an apparatus for cutting through cortical bone in a vertebral body. The apparatus comprises an elongate member having a central axis. The elongate member includes a tubular portion that extends between a proximal end portion and a distal end portion. The distal end portion includes an articulatable head section with a cutting edge for cutting cortical bone and at least one stop surface for engaging the cortical bone after the cortical bone is cut by the cutting edge to stop further movement of the head section and prevent the cutting edge from undesirably engaging other tissue or bone. The head section of the distal end portion is pivotable between a plurality of predetermined angular positions about a pivot axis that extends transverse to the central axis. The apparatus further comprises a mechanism for pivoting the head section relative to the tubular portion.  
         [0007]     The present invention further provides a minimally invasive method for cutting through cortical bone in a vertebral body. In accordance with the inventive method, an elongate member having a central axis is provided. The elongate member includes a tubular portion that extends between a proximal end portion and a distal end portion. The distal end portion includes an articulatable head section with a cutting edge for cutting cortical bone. The head section is controllably pivotable between a plurality of predetermined angular positions about a pivot axis that extends transverse to the central axis. A cannula is placed through a pedicle of the vertebral body. The distal end portion of the elongate member is inserted into the cancellous bone in the vertebral through the cannula. The proximal end portion of the elongate member is then tapped on, by hand or hammer, to advance the elongate member and cut a first portion of the peripheral wall of the vertebral body with the cutting edge. The at least one stop surface engages the cortical bone after the cortical bone is cut by the cutting edge to stop further movement of the head section and prevent the cutting edge from undesirably engaging other tissue or bone. The head section is then pivoted to a different angular position while the distal end portion is located within the vertebral body. The proximal end portion of the elongate member is again manually impacted to advance the elongate member and cut a second portion of the peripheral wall of the vertebral body with the cutting edge. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which:  
         [0009]      FIG. 1  is a view of an articulatable apparatus for cutting bone constructed in accordance with the present invention;  
         [0010]      FIG. 2  is a view taken along line  2 - 2  in  FIG. 1 ;  
         [0011]      FIG. 3  is a view taken along line  3 - 3  in  FIG. 1 ;  
         [0012]      FIG. 4  is a sectional view taken along line  4 - 4  in  FIG. 3 ;  
         [0013]      FIG. 5  is a sectional view taken along line  5 - 5  in  FIG. 1 ;  
         [0014]      FIG. 6  is a sectional view similar to  FIG. 4  with an end portion of the apparatus in an axially displaced position;  
         [0015]      FIG. 7  is a sectional view similar to  FIG. 6  with the end portion of the apparatus in an angularly displaced position;  
         [0016]      FIG. 8  is a sectional view similar to  FIG. 7  with the end portion of the apparatus returned to its original axial position;  
         [0017]      FIG. 9  is a plan view illustrating the apparatus of  FIG. 1  being used to cut through cortical bone in a vertebral body; and  
         [0018]      FIG. 10  is a side view taken along line  10 - 10  in  FIG. 9 . 
     
    
     DESCRIPTION OF EMBODIMENTS  
       [0019]     The present invention relates to an articulatable apparatus for cutting bone and, in particular, is directed to a uniquely designed osteotome that is useful in cutting cortical bone in vertebrae. As representative of the present invention,  FIG. 1  illustrates an apparatus  10  comprising an elongate member  11  made of a medical grade metal such as stainless steel. The elongate member  11  includes a tubular portion  12  extending along a central axis  14  between a proximal end portion  16  and a distal end portion  18  of the apparatus  10 . The apparatus  10 , in particular the tubular portion  12  and the distal end portion  18 , are designed to fit through a 5 mm (inner diameter) cannula  20  ( FIG. 9 ) and thus have a maximum outer diameter of 4.8 mm. It should, however, be understood that the apparatus  10  and the cannula  20  could have correspondingly larger or smaller diameters.  
         [0020]     The tubular portion  12  of the apparatus  10  includes a cylindrical outer surface  30  and a central passage  32  ( FIG. 4 ) that extends along the axis  14  between a proximal end  34  and a distal end  36 . The tubular portion  12  further includes parallel first and second passages  38  and  40  that extend on opposite sides of the central passage  32 . The first passage  38  extends from the distal end  36  of the tubular portion  12  to a first slot  42  near the proximal end  34 . Similarly, the second passage  40  extends from the distal end  36  of the tubular portion  12  to a second slot  44  near the proximal end  34 . The first and second slots  42  and  44  in the tubular portion  12  extend from the first and second passages  38  and  40 , respectively, to oppositely disposed first and second openings  46  and  48 , respectively, in the cylindrical outer surface  30 . As best seen in  FIG. 6 , the distal end  36  of the tubular portion  12  includes a set of ratchet teeth  50  that extend in a concave manner along a hemispherical arc.  
         [0021]     The distal end portion  36  of the apparatus  10  includes an articulatable head section  60  ( FIG. 1 ) having a main body portion  62  extending between oppositely disposed first and second ends  64  and  66 . The cross-sectional shape of the head section  60  may be circular, oval, rectangular or other suitable shape. The first end  64  of the head section  60  has a planar stop surface  68  ( FIG. 2 ) that is perpendicular to the central axis  14 . A cutting edge  70  projects axially at a right angle from the stop surface  68 . In the illustrated embodiment, the cutting edge  70  is a smooth blade, however it is contemplated that the cutting edge could be serrated or spiked to produce perforations instead of osteotomies.  
         [0022]     The second end  66  of the head section  60  includes a ratchet wheel  72  fixed to the head section  60 . The ratchet wheel  72  has a pivot axis  74  that extends perpendicular to the central axis  14 . The head section  60  is pivotable about the pivot axis  74 . The ratchet wheel  72  includes a centrally located cylindrical section  76  ( FIG. 4 ) and a set of ratchet teeth  78  that extend in a convex manner along a hemispherical arc. The set of ratchet teeth  78  on the ratchet wheel  72  are complementary to, and adapted for meshing engagement with, the set of ratchet-teeth  50  on the distal end  36  of the tubular portion  12 .  
         [0023]     The apparatus  10  further includes a wire member  80  and first and second levers  90  and  100 . The wire member  80  is operatively coupled to the ratchet wheel  72  and includes a middle portion  82  and oppositely disposed first and second ends  84  and  86 . The middle portion  82  of the wire member  80  is fixedly attached to the cylindrical section  76  of the ratchet wheel  72 . The first and second ends  84  and  86  of the wire member  80  extend in parallel into the first and second passages  38  and  40 , respectively, in the tubular member  12  and are attached to the first and second levers  90  and  100 , respectively.  
         [0024]     The first and second levers  90  and  100  are housed and supported for relative axial movement within the first and second slots  42  and  44 , respectively, in the tubular portion  12  of the elongate member  11 . The first lever  90  includes a manually engageable flange  92  that projects radially outward through the first opening  46  in the tubular member  12 . Similarly, the second lever  100  includes a manually engageable flange  102  that projects radially outward through the second opening  48  in the tubular member  12 .  
         [0025]     The apparatus  10  also includes a shaft member  110  and a cap member  120 . One end of the shaft member  110  is attached to the head section  60  by a pin  111  at the pivot axis  74  so that the head section can pivot relative to the shaft member. The shaft member  110  extends into the central passage  32  in the tubular member  12  and is axially movable within the central passage. The opposite end of the shaft member  110  includes an external threaded portion  112  ( FIG. 4 ) that projects axially beyond an end  114  surface at the proximal end portion  34  of the tubular member  12 .  
         [0026]     The cap member  120  includes oppositely disposed first and second end surfaces  122  and  124  and cylindrical inner and outer surfaces  126  and  128 . The first end surface  122  faces toward and is engageable with the end surface  114  at the proximal end  34  of the tubular member  12 . The second end surface  124  of the cap member  120  is adapted to receive repetitive impacts. The outer surface  126  of the cap member is knurled (see  FIG. 1 ), while the inner surface  128  is threaded to mate with the threaded portion  112  of the shaft member  110 .  
         [0027]     As illustrated in  FIGS. 6-8 , the head section  60  of the apparatus  10  can be articulated from the position of  FIG. 4  to a number of predetermined angular positions (based on the number of ratchet teeth  50  and  78 ) to change the direction of the cutting edge  70 . The head section  60  is articulated by first unscrewing the cap member  120  from the end  112  of the shaft member  110 , which permits axial movement of the shaft member in the direction of arrow A in  FIG. 6 . The slotted openings  46  and  48  in the tubular member  12  allow for limited axial movement of the levers  90  and  100 . This axial movement of the shaft member  110  moves the ratchet teeth  78  on the ratchet wheel  72  out of engagement with the ratchet teeth  50  on the tubular member  12 .  
         [0028]     The head section  60  of the apparatus  10  is then pivoted about the pivot axis  74  by manually moving the first and second levers  90  and  100  in opposite axial directions, as shown by arrows B and C in  FIG. 7 . This relative axial movement of the first and second levers  90  and  100  causes the wire member  80  to rotate the ratchet wheel  72  about the pivot axis  74  as shown by arrow D in  FIG. 7 . It is contemplated that calibrated markings can be placed near the openings  46  and  48  in the tubular member  12  to indicate the amount of rotation of the head section  60  that results from a given amount of axial movement of the levers  90  and  100 .  
         [0029]     Once a desired amount of rotation is achieved (i.e. the cutting edge  70  is pointed in a desired direction), the cap member  120  is re-tightened on the end  112  of the shaft member  110 , which moves the shaft member in the direction of arrow E in  FIG. 8 . This axial movement of the shaft member  110  pulls the ratchet teeth  50  and  78 , respectively, into engagement and locks the head section  60  in the desired angular position.  
         [0030]      FIGS. 9 and 10  illustrate use of the apparatus  10  to cut bone. Specifically,  FIGS. 9 and 10  illustrate the apparatus  10  cutting through cortical bone  130  of a vertebral body  132 . The cortical bone  130  has an outer peripheral surface  134  and an inner surface  136  surrounding cancellous bone  138 . As best seen in  FIG. 10 , the vertebral body  132  has a partially healed compression fracture to be treated via a kyphoplasty procedure. In order to perform the kyphoplasty procedure, the partially healed cortical bone  130  in the anterior wall  140  and the lateral wall  142  of the vertebral body  132  must be cut to release the upper and lower end plates  144  and  146  of the vertebral body so that an inflatable bone tamp (not shown) inserted inside the vertebral body can, when inflated, move the upper and/or lower end plates back to their pre-fractured positions (illustrated in dashed lines).  
         [0031]     Access into the vertebral body  132  occurs in a minimally invasive manner via the cannula  20 . After creating a passage (not numbered) through a pedicle  150  of the vertebral body  132  and into the cancellous bone  138  via a drilling or reaming procedure, the cannula  20  is placed through the pedicle as shown in  FIG. 9 . The distal end portion  18  of the apparatus  10  is then inserted through the cannula  20  and into the cancellous bone  138  of the vertebral body. The cutting edge  70  on the head section  60  is then advanced through the cancellous bone  138  and into engagement with the cortical bone  130  of the anterior wall  140 . The apparatus  10  is advanced, via impact blows either by hand or by hammer (not shown) to the surface  124  on the cap member  120 , so that the cutting edge  70  itself creates a “pathway” through the cancellous bone  138  to the anterior wall  140 . Alternatively, another tool (not shown) may be used to create the aforementioned pathway through the cancellous bone  138  prior to the insertion of the apparatus  10  into the cannula  20 .  
         [0032]     Next, the cutting edge  70  is tapped through the cortical bone  130  of the anterior wall  140  of the vertebral body  132  through impact blows, either by hand or by hammer, to the cap member  120 . As the cutting edge  70  cuts through the anterior wall  140 , axial movement of the cutting edge is stopped when the stop surface  68  on the head section  60  engages the inner surface  136  of the cortical bone  130 . This prevents the cutting edge  70  from undesirably straying beyond the vertebral body  132  and cutting other tissues, such as blood vessels, nerves, and muscles, or bones.  
         [0033]     In order to fully release the end plates  144  and  146  of the vertebral body  132 , it is likely that additional cuts through the anterior wall  140  and through adjoining portions of the lateral walls  142  will be needed. The articulatable apparatus  10  is uniquely adapted to make these additional cuts by changing the angular position of the head section  60  (and thus the cutting edge  70 ), as shown schematically by the dashed lines in  FIG. 9 . Through a systematic adjustment of the angle of the cutting edge  70  and ensuing cuts through the anterior wall  140  and/or lateral wall  142 , the cortical bone  130  around the periphery of the vertebral body  132  can be sufficiently severed to release the end plates  144  and  146  for a kyphoplasty procedure. Thus, the apparatus  10  described above permits aimed strategic osteotomies along the periphery of a vertebral body  132  in a safe manner so that a minimally invasive kyphoplasty procedure can be used to treat the compression fracture of the vertebral body.  
         [0034]     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, it should be understood that, depending on the nature of the condition of a given vertebral body, the anterior and lateral walls nearer the opposite side of the vertebral body  132  shown in  FIG. 9 , or on both sides of the vertebral body, may need to be cut in order to release the end plates  144  and  146  of the vertebrae. In such situations, the apparatus  10  would be used in an identical fashion with access through a cannula placed through the other pedicle. Further, it should be understood that the apparatus  10  disclosed herein could be used to cut through other areas of cortical bone in vertebrae, as well as cortical bone in other bones in a mammalian body. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.