fig1 is a phantom view of a vertebral body showing a transverse cavity 18 and a coordinate system 16 . this figure shows a vertebral body 10 in isolation . two possible surgical entry points into the vertebral body contemplated within the scope of the invention are illustrated . one entry point is “ transpedicular .” this approach is indicated by the physical location of tube 12 , traveling through the pedicle into the vertebral body 10 . another approach is “ extra - pedicular .” this access approach is illustrated by tool 14 entering the vertebral body at a location lateral of the transpedicular approach on the posterolateral corner of the vertebral body . the typical surgery will include a small incision in the back adjacent to the vertebral body . next , a small gauge needle or guide - wire is introduced to confirm proper positioning under fluoroscopy . physicians typically utilize an 11 - gauge needle for the transpedicular approach and a larger needle or tube ( up to 6 mm id ) for the extra - pedicular approach . many physicians advance cannulated tools over a small gauge needle to successively increase the size of the working channel . other physicians may prefer to place a guide catheter at the site and to introduce tools though the lumen of the guide catheter . in general , the tools described herein can be used either over the wire or through a guide catheter or alone at the election of the physician . in this figure , a coordinate system 16 identifies a vertical direction z , which points along the spine . the y - direction is generally anterior . it is the purpose of the invention to create a cavity with a fixed and controlled vertical extent ( z - axis height ) and a controlled shape in the x - y plane . for the purposes of this disclosure , the term transverse cavity will be used interchangeably with a cavity created parallel to the surface that is to be reduced or restored to its normal anatomic position , and generally normal to the force applied . the surface that is reduced or displaced defines the x - y plane . this definition holds for other procedures performed with the invention . returning to the figure , the cavity 18 is typically ovaloid in shape as projected in the x - y plane . the ovaloid shape has an approximately uniform height in the z direction . this “ shape ” is referred to throughout the specification as a “ transverse cavity ” for the vertebral body application illustrated in these figures . therefore the x - y plane is defined as the “ transverse plane ” and the z - axis direction may be referred to as the “ vertical axis .” it is a characteristic of all the embodiments of the tools shown in the application that the cross sectional area of the tool at the entry point into the bone is smaller than the transverse cavity created with the tool . to facilitate description of the invention , the distal “ working ” structures of the cavity creation tools are illustrated in isolation while the proximal manipulation handles as contemplated are shown generically as handle 20 and finger loop 21 . in each embodiment , a handle structure 20 can be moved with respect to the tool sheath or tool body 14 . in each embodiment , the relative motion between handle 20 and sheath 14 activates the distal working surfaces of the device . the handle 20 or the finger loop 21 is indexed to the distal working surfaces to provide confirmation of the orientation of the working surfaces with respect to the bone structures . it is contemplated that in addition to direct manual manipulation , other power sources can be used to actuate the working surfaces , including hydraulic or pneumatic cylinders and electromechanical actuators shown generically in fig1 as power source 23 . in general , purely manual mechanical mechanisms are preferred because they improve tactile feedback to the physician . the tools may be made of conventional materials , with stainless steel preferred for “ blade ” embodiments and nitinol or other super elastic alloys adopted for the flexible arm embodiments . the tools may be reusable or disposable . materials choices do not appear critical for carrying out the invention . the overall length of the cavity creation tool from the handle structures 20 and 21 to the working distal tip may vary to facilitate the particular surgical procedure . for example , a length of 220 cm is useful for the vertebral application , while a length of 60 cm is a practical value for a tibial plateau procedure . fig2 shows an embodiment of the cavity creation tool 30 that includes a blade 38 mounted on the tool body 14 for rotational motion around the pivot 34 . the rod 32 is coupled to a proximal handle 20 ( fig1 ) and a push - pull motion between the handle and the finger loop 21 ( fig1 ) causes the blade to sweep out an arc 40 . the blade may be blunt or it may include a cutting surface 42 . in operation , the blade 38 laterally loads cancellous bone , breaking or cutting the bone in the x - y plane of the cavity . the pivot and blade are confined to a transverse plane so this action creates the transverse cavity . by advancing the tool along the axis 36 , the cavity may take an approximately oval shape in the x - y plane . fig3 shows a cavity creation tool 62 having a distal end that is positioned in a vertebral body . the distal end includes two arms . a first arm 52 is anchored to the tube 14 with a hinge point mechanism 56 at a first end . the second end of the arm 52 is coupled to the pull rod 64 . relative motion between the tube 14 and the pull rod 64 expands the first arm in a transverse plane . this particular embodiment of the tool is asymmetric and the tool includes a second arm 58 that is anchored to the tube 14 with a hinge mechanism 60 . the first and second arms define a plane for the operation of the device in the transverse plane . fig4 shows a cross section of the tool body 14 having a notch or groove 15 for locating and restraining a pull rod 32 . the tool body cross section defines the tool body area for the cavity creation tool . in general , the tool may be inserted into a bone through a hole of the size of the tool body area . this parameter or area is always smaller than the “ footprint ” of the transverse cavity in the x - y plane . the cross section of this portion of the tool defines the tool body area . fig5 shows a pull rod 32 is constrained in a groove in the tool body 14 . in this embodiment the pull rod actuates a blade or other structure . the cross section of this portion of the tool defines the tool body area . fig6 shows an embodiment of the tool that has two pull or push rods 100 and 106 . pull rod 106 operates a first arm 108 while the second arm 102 is activated by the independent pull rod 102 . the asymmetrical operation of the two independent arms can be used to control the shape of the cavity by directing expansion of the cavity to preferred areas within the vertebral body . fig7 shows an embodiment of the tool 70 where a container 72 surrounds a pair of arms 52 and 58 . the container interacts with the cancellous bone as the pull rod activates the arms and moves them against the cancellous bone . the container prevents debris from interfering with the retraction of the arms . the container 72 can be subsequently inflated to reduce the fracture and restore the natural anatomy . finally , the container may be detached and left behind . in this particular embodiments the first and second arms are identical , and will normally create a symmetric cavity . the container 72 is optional and the arms can be used alone in a fashion analogous to other versions of the tool . in this particular embodiment , the first and second arms have blunt dissection surfaces on the exterior of the arms to interact with cancellous bone . in this embodiment , the first and second arms may also have different mechanical properties for the creation of an asymmetric cavity . fig8 shows an embodiment of the cavity creation tool 80 that includes saw - like teeth on the first arm 88 and the second arm 82 . once again , traction on the pull rod 64 causes the teeth on the arms to cut through the cancellous bone . in a fashion similar to related embodiments , the arms lie in and define a cutting plane that creates a transverse cavity . the saw teeth typified by tooth 90 can be moved by manipulating both the pull rod and the tube . fig9 shows a cable - actuated device with a cable 200 wrapping a spindle or axle 202 mounted on the tool body 214 . cable motion results in sweeping out an arc 210 as seen in fig1 . fig1 shows the blade 38 can sweep through 360 degrees because of cable actuation . an arc of less than 360 degrees may be used when a non - circular cavity is required . fig1 is a cable - operated version with the pull rod 232 coupled to cable 200 . in this device , the pull on the cable forces the flex arms 202 and 208 in an outward direction to form the transverse cavity . fig1 shows the cable - operated version of fig9 with the arms deployed , creating a transverse cavity . fig1 which represents the prior art is a schematic of a balloon or other hydraulic lifting device as it is initially inserted into the vertebral body . fig1 is a schematic of the increased lifting force generated by a balloon or other hydraulic lifting device which immediately reaches a broad surface area because of the transverse cavity that has been prepared before deploying the balloon or hydraulic lifting device . although the invention has been illustrated in one context , it should be apparent that the device features maybe modified or combined in alternate configurations .
a surgical instrument and method is provided for creating and preparing a cavity in a bony intervertebral body . asymmetrical cutting structures selectively open a cavity which has a relatively large surface area in the vertical direction . one method pertains to the treatment of a vertebral compression fracture .