Abstract:
A surgical apparatus, the apparatus comprising: (a) a cutting tool comprising an axial member with a proximal end and a distal end, the axial member characterized by at least two adjacent axial sections, wherein differences between each of the sections are visually discernible when viewed in a projection x-ray image; and (b) a hollow tube adapted for parallel alignment with the cutting tool and selectively axially positionable to be adjacent at least a selective one of said axial sections and block x-ray radiation from at least one of passing through or passing adjacent said selected section so that said projection indicates a relative axial position of said hollow tube and said cutting tool.

Description:
RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. provisional patent application 60/720,725 filed Sep. 28, 2005 and entitled “Tools and Methods for Treating Bones” the disclosure of which is fully incorporated herein by reference. 
     This application is a continuation in part of PCT application IL2005/000812 filed Jul. 31, 2005, published as WO 2006/011152 and entitled “Materials, Devices and Methods for Treating Bones and Other Tissues” and of U.S. patent application Ser. No. 11/194,411 filed Aug. 1, 2005 and entitled “Materials, Devices and Methods for Treating Bones and Other Tissues” the disclosures of which are fully incorporated herein by reference. 
     This application is related to U.S. provisional patent application 60/646,539 filed Jan. 25, 2005 and entitled “Tools and Methods for Treating Bones” the disclosure of which is fully incorporated herein by reference. 
    
    
     FIELD OF INVENTION 
     The present invention relates to surgical tools characterized by markings which are visible under X-ray. 
     BACKGROUND OF THE INVENTION 
     Surgical treatment of fractured bones, osteoporotic bones, deformed bones and the like usually requires gaining an access into the interior of the bone as a first stage. When minimally invasive surgery is involved, such as percutaneous surgery, the step of accessing the bone is limited by dimensional requirements. The preferred tool should have minimal diameter and should provide safe and minimally invasive access into the bone in an uncomplicated manner. 
     Fixation of vertebral body fractures, for instance, may comprise fracture reduction and/or creation of a void in the cancellous bone, followed by injection of bone void filler/bone cement (PMMA), in order to reinforce the vertebral body. Exemplary fixation of this type is described in PCT/IL2004/000527; and U.S. Pat. Nos. 4,969,888 and 5,108,404 which are each fully incorporated herein by reference. The standard procedure includes gaining an access into the vertebral body optionally through the pedicle, using a needle and stylet assembly (such as Jamshidi needle), having a diameter of about 2.5-3.5 mm. The inner stylet is removed and replaced with a guide wire of about 1.5 mm diameter. Then, a small incision is made in the skin, and a trocar with a cone-shaped distal end is introduced over the guide wire, to enable passage through soft tissue. A cannula of about 4-6 mm diameter is introduced over the trocar, up to the pedicle, and the trocar is removed. Optionally, the trocar and cannula are assembled and introduced together. At this stage, a cannulated 3-6 mm diameter drill/reamer is advanced over the guide wire and via the cannula to enlarge the passage into the vertebral body. Optionally, the trocar and the drill are combined to one reamer. Normally, a manually operated drill/reamer is used. The guide wire and drill/reamer are removed, leaving the cannula inside the body. The rest of the procedure may proceed through the cannula. As can be seen, accessing the bone is a multiple-stage procedure, which is time consuming. 
     Lately a more shortened procedure is being used, during which a larger diameter Jamshidi needle is firstly introduced into the vertebral body. Following insertion, the stylet is withdrawn and the drilling stage and the rest of operation proceed via the needle, which serves as a working sleeve. Typically, positioning the Jamshidi needle into the pedicle may require several insertions (e.g., trial and error attempts) into the pedicle. 
     SUMMARY OF THE INVENTION 
     An aspect of some embodiments of the invention relates to detecting a less visible tool portion positioned adjacent a more visible tool portion when using X-ray based imaging. In an exemplary embodiment of the invention, the less visible tool portion is a thin outer portion of a surgical tool placed over an inner portion of a surgical tool, optionally in snug contact. In an exemplary embodiment of the invention, detection is made easier by presence of a gap (or other radio-visible feature, such as described below) between at least a portion of the thin outer portion and the inner portion. Optionally, the outer portion is provided as a sleeve which substantially contacts the inner portion of the tool at a widest portion thereof. In an exemplary embodiment of the invention, the inner tube has a generally cylindrical shape and is made of a radio-opaque material, for example, steel. In an exemplary embodiment of the invention, the tool is a bone access tool. 
     In an exemplary embodiment of the invention, the gap is formed near the distal end of the tool, for example, within 40 mm, 30 mm, 20 mm, 10 mm or intermediate or lesser amounts. In an exemplary embodiment of the invention, the positioning of the gap matches expected relative positioning of an outer cannula and a bone drill. Typically, the gap does not reach to the bone penetration section of such a drill or other tool. Optionally, the cannula and the drill are configured so that in usage the cannula cannot reach to the distal end of the drill in a mechanically locked position and/or have a locked position where it does not reach. 
     In an exemplary embodiment of the invention, absent the gap, it is difficult to distinguish presence of the outer portion over the inner portion due to its thinness and thus small increase in diameter. In an exemplary embodiment of the invention, the outer portion, for example, a tube, selectively blocks radiation that would otherwise pass through the gap. Alternatively or additionally, the gap is visible even when the outer portion is adjacent (albeit possibly less visible), and the contrast with the gap makes the outer portion more visible. 
     In an exemplary embodiment of the invention, the gap, when visualized under X-ray, indicates an amount of relative axial motion of the outer portion with respect to the inner portion. Optionally, the gap is marked so that a degree of coverage thereof can be assessed visually. 
     In an exemplary embodiment of the invention, the gap is formed by engraving, etching or otherwise modifying a cross section of the inner portion of the tool, optionally along a relatively short axial section thereof. Optionally, the gap is non-uniform in an axial and/or circumferential direction, for example, being in the form of a series of grooves, a series of indentations or bumps formed in a groove or a spiral shaped groove. In an exemplary embodiment of the invention, the gap comprises one or more circumferential indentations. In an exemplary embodiment of the invention, the tool has a same or similar diameter and/or radio-visible profile before and after the gap. Optionally, the gap itself has a relatively uniform profile/diameter. 
     Optionally, the gap is filled in so the surface of the inner portion is smooth. 
     In an exemplary embodiment of the invention, the outer portion of the tool comprises a cannula. Optionally, the cannula is provided as a sleeve adapted to fit over at least a portion of a reamer. In an exemplary embodiment of the invention, the cannula serves for injection of a bone filler and/or cement after removal of the reamer drill. 
     In an exemplary embodiment of the invention, the series of gaps are characterized by known axial dimensions with respect to reamer and are placed at known positions on the (e.g. at a known distance from a distal end of the reamer drill). Optionally, a user of the tool evaluates a position of an end of the cannula relative to the series of gaps. In an exemplary embodiment of the invention, this evaluation aids in inserting the cannula to a desired depth by helping to judge a distance from an anatomic landmark (e.g. cannula end is 12 mm from a distal side of a vertebra). Optionally, translational motion of the cannula with respect to the reamer can cover and/or uncover a portion of the gaps. In an exemplary embodiment of the invention, a number of exposed gaps is an indicator of relative axial position of the cannula with respect to the reamer drill. 
     In various exemplary embodiments of the invention, the tool is adapted for percutaneous spinal surgeries, such as fixation of vertebral body fractures or intervertebral disc surgeries (e.g. for gaining access into the disc). Optionally, a small difference in outer diameter between the reamer drill and the cannula makes it possible to insert the cannula and reamer drill together and/or minimize soft tissue and/or bone damage. 
     In other exemplary embodiments of the invention, the tool is used in treatment of non-vertebral bones. 
     An aspect of some embodiments of the invention relates to a device/kit, intended to gain an access into a body component, such as a bone or an intervertebral disc, comprising stylet/guide wire, reamer/drill and cannula. 
     In one embodiment of the invention, the device provides for a one-step access into, for example, a bone. 
     In another embodiment of the invention, the device components are assembled prior to use, and are inserted together into the bone. In an exemplary embodiment of the invention, the stylet/guide wire has a pointed distal end, and connection means to the reamer/drill at its proximal end. In another exemplary embodiment of the invention, the stylet/guide wire diameter is smaller than the internal diameter of the reamer/drill, and it is adapted to be introduced into the cannulated reamer/drill. Optionally, the stylet/guide wire is longer than the reamer/drill. In an exemplary embodiment of the invention, the reamer/drill comprises a distal section capable of reaming/drilling, respectively, the bone. At its proximal end, the reamer/drill may include a handle and connection means to the stylet/guide wire. In another embodiment of the invention, the cannula is assembled over the reamer/drill. In an exemplary embodiment of the invention, the cannula is shorter than the reamer/drill. Optionally, the cannula includes a handle at its proximal end. Optionally, the reamer/drill component has a section, located distally to the cannula while the cannula and reamer/drill are assembled, which is differentially visible on an x-ray image compared to the cannula. Optionally, said section is located partly distally to the cannula, while its proximal end is located within the distal portion of a cannula lumen. Thus, the distal end of the cannula can be easily distinguished from the reamer/drill body. This feature allows a minimal difference between cannula and reamer/drill diameters, and hence provides for a smaller total diameter of the device. Optionally, the reamer/drill is narrowed at said section. Optionally, the reamer/drill and/or cannula are made of radio-opaque material, for example stainless steel. Optionally, said reamer/drill small diameter section is covered by additional material, which is radiolucent and thus is visibly distinguished under fluoroscopy from the cannula. Optionally, said radiolucent material is a polymer, for example polypropylene or ABS. Optionally, said radiolucent material is mold injected onto the reamer/drill small diameter section. Optionally, the covered section of the reamer/drill has the same diameter as the nearby sections of the reamer/drill body. 
     In yet another embodiment of the invention, the bone access assembly is constructed from biocompatible materials. In an exemplary embodiment of the invention, the components of the bone access assembly are made of, for example, metal, such as stainless steel, and/or polymer material. Optionally, the handle is made of polymer. 
     An aspect of some embodiments of the invention relates to a method, intended to provide a one-step access into a body organ, such as a bone. In an exemplary embodiment of the invention, said method is used in minimally invasive procedures. In another exemplary embodiment of the invention, the method is used in percutaneous spinal surgeries, such as fixation of vertebral body fractures. Alternatively, said method is used in intervertebral disc surgeries, e.g., for gaining access into the disc. In additional exemplary embodiment of the invention, said method is used in treatment of other bones. 
     In another embodiment of the invention, the procedure for gaining access into the body organ, such as a bone, is monitored by CT scanning and/or fluoroscopy. 
     In an exemplary embodiment of the invention, there is provided a device for gaining one-step access into a bone, comprising a stylet, a reamer and a cannula. 
     In an exemplary embodiment of the invention, there is provided a device for gaining one-step access into an intervertebral disc, comprising a stylet, a reamer and a cannula. 
     Optionally, the bone is a vertebral body. 
     In an exemplary embodiment of the invention, there is provided a method for accessing a vertebral body, wherein positioning of the insertion tool into the pedicle is done using a small diameter tool over which a larger diameter tool is positioned to continue the dilatation once a smaller diameter tool is well positioned. 
     In an exemplary embodiment of the invention, there is provided a “gaining access” device into a bone, comprising a reamer having a retractable distal tip, capable of forming a passage in a bone, over which the reamer and cannula are positioned in one step. 
     Optionally, the device is used in vertebroplasty and/or kyphoplasty procedures. 
     Optionally, the reamer component comprises a section located distally or partly distally to the cannula component while at least reamer and cannula are assembled, and where said reamer section is visibly distinguished from the cannula under fluoroscopy or other imaging means. 
     In an exemplary embodiment of the invention, there is provided a surgical apparatus, the apparatus comprising: (a) a cutting tool comprising an axial member with a proximal end and a distal end, the axial member characterized by at least two adjacent axial sections which do not form a part of a cutting tip of said tool, wherein differences between each of the sections are visually discernible when viewed in a projection x-ray image; and (b) a hollow tube adapted for parallel alignment with the cutting tool and selectively axially positionable to be adjacent at least a selective one of said axial sections and block x-ray radiation from at least one of passing through or passing adjacent said selected section so that said projection indicates a relative axial position of said hollow tube and said cutting tool. 
     Optionally, the cutting tool is adapted for bone access. 
     Optionally, the cutting tool is adapted for vertebral access. 
     Optionally, the hollow tube comprises a sleeve adapted to contain at least an axial portion of the cutting tool. 
     Optionally, the hollow tube comprises a partial sleeve which does not circumferentially surround the cutting tool, adjacent said section. 
     Optionally, the sleeve has an inner diameter which is adapted to ensure substantial contact with said cutting tool. 
     Optionally, the hollow tube blocks said radiation from at least part of said selective section. 
     Optionally, the hollow tube blocks said radiation from an area adjacent said selected section. 
     Optionally, the visually discernible difference results from an outer radial section of reduced radio-opacity. 
     Optionally, the outer radial section comprises a filled-in groove. 
     Optionally, the cutting tool comprises at least one radially distal hollow. 
     Optionally, the radially distal hollow does not reach a distal end of said cutting tool. 
     Optionally, the visually discernible differences are rotationally symmetric, with respect to rotation of said cutting tool and said hollow tube with respect to said x-ray radiation. 
     Optionally, the visually discernible differences are each axially uniform. 
     Optionally, the at least one of the axial sections comprises an axially varying profile. 
     Optionally, the axially varying profile comprises a series of axially separated decreased radio-opaque diameter portions. 
     Optionally, at least one of said axial sections comprises an axially extending spiral of at least partly radio-opaque material. 
     Optionally, the cutting tool comprises an inner lumen. 
     Optionally, the cutting tool can operate with a guide element, optionally provided as part of the apparatus, adapted for insertion through the inner lumen. 
     Optionally, the cutting tool comprises a bone penetrating element and said hollow tube comprises a bone cannula. 
     Optionally, the bone cannula has a wall thickness of 0.4 mm or less. 
     Optionally, the bone cannula has a wall thickness of 0.3 mm or less. 
     In an exemplary embodiment of the invention, there is provided a method for discerning relative axial displacement of two tool portions under X-ray, the method comprising: (a) inserting a first tool portion having at least two sections with different X-ray silhouettes into a bone; (b) positioning a second tool portion adjacent a first one of said sections in a manner which does not alter an appearance of a silhouette of said first one of said section; and (c) axially relatively repositioning said second tool portion adjacent a second one of said sections in a manner which alter an appearance of a silhouette of said second one of said sections. 
     Optionally, the bone is a vertebra. 
     Optionally, the method comprises determining a relative axial location of said second tool portion relative to said first tool portion based on a change in a visualization of said second section. 
     Optionally, the determining comprises counting visually identifiable x-ray markers. 
     Optionally, the second tool comprises a cannula and the method comprises determining a correct placement of said cannula relative to a bone based on said determining. 
     Optionally, the determining comprises ascertaining a reduction in an axial extent of said second section. 
     In an exemplary embodiment of the invention, there is provided a method for locating a hollow radio-opaque tube adjacent or inside a bone, the method comprising: 
     (a) inserting a first element into a bone, said element comprising both radio-opaque and radiolucent portions; and 
     (b) positioning said radio-opaque hollow tube adjacent to the first element so that a relative position of the radio-opaque hollow tube and a radiolucent portion is visible in an image acquired using non-invasive imaging equipment. 
     Optionally, the non invasive imaging equipment employs X-ray. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Some exemplary embodiments of the invention will be further described with reference to the accompanied drawings, in which same number designations are maintained throughout the figures for each element and in which: 
         FIG. 1  is a perspective view of an exemplary stylet component of an exemplary bone access device, in accordance with some exemplary embodiments of the invention; 
         FIG. 2  is a perspective view of an exemplary reamer component of an exemplary bone access device, in accordance with some exemplary embodiments of the invention; 
         FIG. 3  is a perspective view of an exemplary cannula component of an exemplary bone access device, in accordance with some exemplary embodiments of the invention; 
         FIG. 4  is a perspective view of an exemplary bone access device, in accordance with some exemplary embodiments of the invention; 
         FIGS. 5A, 5B and 6  illustrate an exemplary assembly of an exemplary bone access device, in accordance with some exemplary embodiments of the invention; 
         FIGS. 7A and 7B  illustrate an alternative bone access device, in accordance with an exemplary embodiment of the present invention; 
         FIG. 8  is a simplified flow diagram illustrating an exemplary sequence of events associated with use of some embodiments of the invention; and 
         FIGS. 9A and 9B  are cross sectional side views of apparatus including a radiolucent and/or radio-transparent marking section according to exemplary embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  illustrates an exemplary stylet  10  suitable for an exemplary bone access device  40  ( FIG. 4 ), in accordance with some exemplary embodiments of the invention. Optionally, stylet  10  can be replaced by a guidewire. Stylet  10  is depicted as a tubular rod  12 , having a pointed distal end  14  adapted to puncture and penetrate skin, soft tissue and/or cortical bone. Distal end  14  may be, for example, of diamond type, bevel type or J-type. Exemplary embodiments of stylet  10  designed for use with fractured vertebral body are optionally characterized by a diameter of about 1.4-2.2 mm. These exemplary embodiments of stylet  10  can optionally be inserted into the vertebral pedicle (up to about 2 mm in the vertebral body). In an exemplary embodiment of the invention, a proximal end of stylet  10  includes a thread  16 . Optionally, thread  16  is compatible with matching threads on a reamer  20  ( FIG. 2 ). In an exemplary embodiment of the invention, thread  16  is operable during assembly of stylet  10  and reamer  20  components. Optionally, rotation of a head  18  of stylet  10  serves to rotate threads  16 . Alternative connecting/interlocking mechanisms may be used as well, for example as described below with respect to  FIGS. 7A and 7B . 
       FIG. 2  illustrates an exemplary reamer  20  suitable for exemplary bone access device  40  ( FIG. 4 ). In the depicted embodiment, reamer  20  comprises a tubular body  22 , a reamer-like distal end  24 , and a handle  26 . Optionally, distal end  24  is adapted for drilling. Optionally, a proximal section of reamer  20  includes a thread (not shown in  FIG. 2 ), for connection of reamer  20  and stylet  10 . In an exemplary embodiment of the invention, a lumen of reamer  20  is adapted to accommodate stylet  10 . Optionally, the lumen of reamer  20  has an inner diameter slightly larger than an outer diameter of stylet  10 . In some exemplary embodiments of apparatus  40  adapted for use in spinal surgery, the outer diameter of the reamer may be 3, 4, 5 or 6 mm or lesser or intermediate diameters. Optionally, reamer  20  is shorter than stylet  10  so that stylet  10  protrudes from distal end  24  of reamer  20  when head  18  of stylet  10  engages handle  26  of reamer drill  20 . 
       FIG. 3  illustrates an exemplary cannula  30  suitable for use as part of exemplary bone access device  40 . In an exemplary embodiment of the invention, cannula  30  comprises a tubular body  32  and a handle  34 . Optionally, reamer  20  is adapted for insertion into cannula  30  so that tubular body  32  of cannula  30  substantially conforms to axial member  22  of reamer drill  20 . In an exemplary embodiment of the invention, cannula  30  is shorter than reamer  20 . Optionally, when reamer  20  is inserted in cannula  30  so that handle  34  of cannula  30  is adjacent to handle  26  of reamer  20 , distal portion  24  of reamer  20  protrudes from cannula  30 . Optionally, the outer surface of cannula  30  slightly tapers at its distal portion to facilitate insertion of cannula  30  into bone. 
       FIG. 4  illustrates exemplary stylet  10 , exemplary reamer  20 , and exemplary cannula  30  assembled to form exemplary bone access device  40 . 
     Referring now to  FIGS. 5A, 5B and 6 , exemplary assembly of bone access device  40  is described in detail. As can be seen in  FIGS. 5A and 5B , stylet  10  can be inserted into reamer  20 , through a proximal end of the reamer  20 , in the arrow direction. Stylet  10  and reamer  20  are threaded and locked together, optionally by clockwise rotation of the stylet  10  and threads  16 . Optionally, stylet thread  16  can be made sufficiently long ( FIG. 5B ) to allow a user to control an amount of stylet  10  which protrudes from a distal end  24  of reamer  20  (optionally none, in some stages of use). 
     In an exemplary embodiment of the invention, device  40  is configured for vertebral body treatment and about 20 mm of stylet  20  protrudes from distal end  24  of reamer  20  after assembly ( FIG. 6 ). 
     In other exemplary embodiments of the invention, relative sizes of stylet  10 , reamer  20  and cannula  30  may differ. 
       FIG. 6  depicts connection of cannula  30  to already-assembled stylet  10  and reamer  20 . In the depicted embodiment, cannula  30  is assembled over reamer  20 , in the arrow direction, until cannula handle  34  is adjacent to reamer handle  26 . 
     In an exemplary embodiment of the invention, once assembly as described above is complete, accessing of a vertebral body is undertaken. Optionally, access is conducted under fluoroscopy. Initially, device  40  can be inserted into a vertebra so that pointed distal tip  14  of stylet  10  penetrates the skin, soft tissue and vertebra pedicle. Optionally, penetration at this stage is a few millimeters into the vertebral body. 
     In an exemplary embodiment of the invention, the accessing of the vertebral body is by a transpedicular approach. Optionally, stylet tip  14  passes through the entire pedicle, along its axial midline. At this stage, handle  26  of reamer  20  can optionally be slightly rotated in each direction. In an exemplary embodiment of the invention, this slight bidirectional rotation (or single-directional rotation) serves to ream and/or drill the bone, and/or to advance reamer  20  slightly into the vertebral body. 
     At this stage, stylet  10  can optionally be disconnected (e.g. by unthreading) or partly disconnected from reamer  20 . Disconnection of stylet  10  prior to reaming and/or drilling of the bone optionally prevents undesired advancement of stylet  10  beyond a desired depth. If stylet  10  has been previously partially disconnected, disconnection can be completed at this stage and stylet  10  can be removed. 
     In an exemplary embodiment of the invention, reamer  20  is employed for additional drilling at this stage. Optionally, the additional drilling proceeds until distal end  24  of reamer  20  is about 2-3 mm from an anterior cortex. Optionally, the distance is assessed by fluoroscopy. In an exemplary embodiment of the invention, cannula  30  is advanced over reamer  20  at this stage. Optionally, advancement of cannula  30  continues until cannula  30  penetrates the pedicle to a depth of about 2 mm. Optionally, the gap ( FIG. 9 ) is positioned to be at the entrance to the pedicle or in cortical bone thereof, to make this penetration depth more visible. Cannula  30  may optionally be gently hammered to achieve a desired penetration. At this time, the reamer is optionally removed. In an exemplary embodiment of the invention, the operation may proceed via the cannula. 
       FIGS. 7A and 7B  illustrate alternative exemplary embodiments  50  of a bone access device. 
       FIG. 7A  depicts an assembled device  50 , comprising a cannula  52 , a drill  54 , and a guide wire  56 . 
       FIG. 7B  is an exploded view of device  50  of  FIG. 7A . Optional guide wire  56  is depicted as a tubular rod with a pointed distal end  62  adapted to puncture and/or penetrate skin, soft tissue and cortical bone. Distal end  62  may be, for example, of diamond type, bevel type or J-type. In an exemplary embodiment of the invention, guide wire  56  fits into a lumen of drill  54 . 
     In an exemplary embodiment of the invention, configured for use in a fractured vertebral body, guide wire  56  may be characterized by a diameter of about 1.4-2.2 mm. Optionally, this configuration allows insertion of tip  62  of guidewire  56  into a vertebral pedicle (e.g., up to about 2 mm in the vertebral body). 
     Optionally, guidewire  56  includes a knob or other control  64  for selective advancing and/or retracting guide wire  56  relative to drill  54 . 
     Exemplary drill tool  54  of device  50  includes an elongate body with a distal end  66  adapted for drilling, and a handle  68 . The body of drill  54  fits in the lumen of cannula  52 . Optionally, the design of tips  62  and  66  are matched to provide a desirable bone penetrating behavior, optionally acting as a single bit. Optionally, the bone type and/or penetration desired determined the allowed extension of tip  62  past tip  66 . 
     In an exemplary embodiment of the invention, drill  54  has a section  60 , located distally to cannula  52  when device  50  is assembled, which contributes to distinguishing between drill  54  and cannula  52  in an x-ray image as cannula  52  advances towards distal tip  66  drill  54 . In an exemplary embodiment of the invention, covering a portion of section  60  by cannula  52  contributes to determining a position of a distal tip of cannula  52  (see  FIG. 9  below). 
     In an exemplary embodiment of the invention, drill  54  is characterized by an outer diameter of 2, 3, 4, 5 or 6 mm or lesser or greater or intermediate diameters. Optionally, cannula  52  is configured as a sleeve with a thickness of less than 0.5, optionally less than 0.4, optionally less than 0.3 mm. In an exemplary embodiment of the invention, the outer portion of the tool is provided as a cannula with an inner diameter of about 2.7 mm and an outer diameter of about 3 mm. 
     In an exemplary embodiment of the invention, use of section  60 , in which radio-opacity is reduced on an outside of drill  54 , contributes to detection of a minimal difference in change of outer diameter of device  50 . Optionally, an axial position at which a change in outer diameter of device  50  occurs is readily discernible in an X-ray image, by the change being relative to a reduced radio-opaque diameter at section  60 , rather than the regular radio-opaque diameter at other parts (see  FIG. 9 ). Optionally, reduction in reliance on cannula thickness to determine cannula position makes it possible to construct a cannula  52  with a smaller outer diameter, for example, 0.25 mm, 0.2 mm or less. 
     In an exemplary embodiment of the invention, drill  54  and/or cannula  52  are made of radio-opaque metal (e.g. stainless steel and/or aluminum). Optionally, section  60  includes radiolucent or radio-transparent material such as a polymer (e.g. polypropylene or ABS). 
     Optionally, drill section  60  comprises at least one small diameter metal region. Optionally, the small diameter metal region is covered by radiolucent or radio-transparent material. Optionally, radiolucent or radio-transparent material is mold injected onto relevant portions of section  60 . 
     In an exemplary embodiment of the invention, an outer diameter of drill section  60  is similar to an outer diameter of adjacent portions of drill  54 . Optionally, a drill  54  for spinal surgery, is characterized by an outer diameter of about 4-5 mm, or less. 
     In an exemplary embodiment of the invention, cannula  52  comprises a tubular body  70 , and a handle  72 . Optionally, the cannula  52  slightly tapers at its distal portion to facilitate its insertion into the bone. Optionally, cannula  52  comprises depth markings  58 . Optionally, drill handle  68  selectively rotationally locks to cannula handle  72 , for manipulation using a single hand, optionally using a snap-lock. Optionally, the snap-lock locks in one rotation direction and unlocks in another. Other interlocking mechanisms may be used. 
       FIG. 8  is a simplified flow diagram  800  of a method of employing apparatus  40  in a surgical procedure, in accordance with an exemplary embodiment of the invention. 
     At  810  a patient is prepared and positioned. 
     At  820  an exemplary bone access device  40  is assembled as described hereinabove. 
     At  830 , a visualization device (e.g. an X-ray camera or fluoroscopy device) is provided to monitor an approach of apparatus  40  to an operation site. 
     At  840 , apparatus  40  is inserted, optionally until stylet tip  14  reaches a desired location. Optionally, the visualization device indicates when the desired location has been reached. 
     At  850 , reamer drill  20  is advanced until penetration to a desired location is achieved. Optionally, the visualization device indicates when the desired penetration has been achieved. 
     At  860 , stylet  10  is retracted and removed from reamer drill  20 . 
     At  870 , reaming/drilling is optionally continued. 
     At  880 , cannula  30  is advanced over reamer/drill  20 , optionally into the pedicle. At this stage, a position of a distal end of cannula  30  is optionally ascertained and/or adjusted using the visualization device. Optionally, ascertaining a position indicates ascertaining a relative position of cannula  30  with respect to reamer drill  20  as described in greater detail below with reference to  FIGS. 9A and 9B . Optionally, reamer drill  20  is removed from cannula  30 . 
     At  890  cannula  30  is employed to conduct a desired surgical procedure. For example, injection of a bone filler and/or cement via cannula  30  may be undertaken to affect vertebroplasty. 
       FIGS. 9A and 9B  are cross sectional side views of exemplary embodiments  900  and  950 , respectively of apparatus  40  and in particular radiolucent and/or radio-transparent marking section  60  thereof. In each of these figures, a distal end  14  of stylet  10  is seen protruding beyond a reamer-like distal end  24  of body  22  of reamer  20 . Tubular body  32  of cannula  30  is shown assembled on body  22  of reamer drill  20 . 
       FIG. 9A  depicts an exemplary embodiment  900  of apparatus  40  in which a single groove  910 , pictured as a circumferential groove, is formed in body  22  of reamer drill  20 . Formation of groove  910  may be accomplished by any means known in the art including, but not limited to, etching, engraving, die casting, carving and lathe turning. Groove  910  represents one exemplary embodiment of section  60  as described hereinabove. 
     In an exemplary embodiment of the invention, the groove terminates, in a distal direction, in a diameter increasing section, so that two steps are visible in x-ray imaging, one when entering the groove at a first axial position and a second one when exiting the groove. Optionally, the diameter at the two steps is the same and matches the inner diameter of the cannula. 
     In  FIG. 9A  an optional radio-transparent or radiolucent filling  920  is shown filling groove  910 . In an exemplary embodiment of the invention, radiolucent filling  920  makes advancement of a leading edge  31  of body  32  of cannula  30  over groove  910  easier. In cases where the leading edge is not radio-opaque, a location of a radio-opaque section (e.g., ring or other marker) of cannula  30  may be detected. 
     In an exemplary embodiment of the invention, construction of body  22  of reamer  20  is conducted according to an engineering plan so that dimensions of groove  910  (e.g. axial length and depth) are known. In addition, the engineering plan specifies a distance between groove  910  and reamer-like distal end  24  of body  22  of reamer  20 . 
     As tubular body  32  of cannula  30  advances along body  22  of reamer  20 , leading edge  31  of tubular body  32  progressively covers an increasing portion of groove  910 . In an exemplary embodiment of the invention, an X-ray based imaging modality (e.g. fluoroscopy) is used to monitor progress of leading edge  31  of tubular body  32  with respect to groove  910 . 
     In some exemplary embodiments of the invention, at least a portion of tubular body  32  is radio-opaque with respect to the chosen imaging modality. According to these exemplary embodiments of the invention, as leading edge  31  advances, an increasing portion of groove  910  is obscured. As a result, a fluoroscopy image acquired laterally (or otherwise non-axially) will indicate an apparent decrease in an axial length of groove  910  as edge  31  advances towards distal end  24  of body  22  of reamer drill  20 . Optionally, a portion of tubular body  32  is substantially radio-transparent and the radio-opaque portion is used to determine relative axial position of tubular  32  with respect to reamer  20 . 
     In other exemplary embodiments of the invention, tubular body  32  is relatively radiolucent with respect to the chosen imaging modality. According to these exemplary embodiments of the invention, as leading edge  31  advances, an increasing portion of groove  910  is covered, but not completely obscured. As a result, a fluoroscopy image acquired laterally will indicate a division of groove  910  into two zones. A first zone inside tubular body  32  will be subject to decreased X-ray transmission and will appear lighter. A second zone, outside tubular body  32  will not be subject to decreased X-ray transmission and will appear darker. Optionally, even if body  32  is relatively radiolucent so that a regular thickness thereof does not hide the groove, it is noted that a portion of the tube has a greater thickness in the x-ray imaging direction, and that portion may be visible against the contrast with the groove and the nearby portion  24 . 
     Because details of the engineering plan of body  22  of reamer  20  are known, determination of a position of edge  31  of tubular body  32  of cannula  30  can optionally be translated into a determination of a distance from edge  31  to distal end  24  of body  22  of reamer  20 . Optionally, this translation is useful in determining a position of edge  31  relative to anatomic landmarks in a bone in which reamer drill  20  has been inserted. 
       FIG. 9B  shows an additional embodiment  950  of apparatus  40  in which a groove  908  formed in body  22  of reamer drill  20  is divided axially by protrusions  912 . According to various exemplary embodiments of the invention, protrusions  912  may comprise individual rings or a spiral extending axially along body  22  of reamer  20 . Optionally, protrusions  912  result from formation of groove  912  or are applied after groove  908  is applied. Filling with radio-lucent material is optionally provided. 
     In those exemplary embodiments of the invention in which protrusions  912  are provided as individual rings, groove  908  is divided into a plurality of grooves. 
     In those exemplary embodiments of the invention in which protrusions  912  are provided as a spiral extending axially along body  22  of reamer  20 , groove  908  can be a spiral groove extending axially along body  22  of reamer  20 . 
     In those exemplary embodiments of the invention which include protrusions  912 , advancement of edge  31  of tubular body  32  produces a series of covered portions  930  of groove  908 . In an exemplary embodiment of the invention, each space between adjacent protrusions  912  represents an axial length of body  22  of reamer drill  20 . As the number of covered portions  930  increases, the number of spaces between adjacent protrusions  912  in front of edge  31  decreases. In an exemplary embodiment of the invention, counting of spaces between adjacent protrusions  912  in front of edge  31  can be used to calculate a distance between edge  31  and distal end  24  of reamer  20 . Optionally, this counting is useful in determining a position of edge  31  relative to anatomic landmarks in a bone in which reamer drill  20  has been inserted. 
     The method described above is not limited to spinal procedures and to bones. In addition, other geometries than a sleeve on a cylinder may be used. For example, the inner-tool portion may be a rectangular in cross-section. In another example, the sleeve may not cover an entire circumference of the cylinder. In another example, the less visible tool section rides in a slot in the more visible tool portion and is made visible by the more visible tool portion including an area adjacent the slot which is radiolucent. 
     Components of apparatus  40  are not necessarily limited by exemplary dimensions recited above. Recited dimensions are exemplary only, and may vary and/or become part of a range of dimensions. 
     Various features of exemplary embodiments of the invention have been described in the context of a device, apparatus or a method. It should be appreciated that combinations of the above features are also considered to be within the scope of the invention. In addition, features described in the context of a device or apparatus may be employed to characterize exemplary methods according to the invention. Alternatively or additionally, features described in the context of a method may be employed to characterize exemplary devices or apparatus according to the invention. It should also be appreciated that some of the embodiments are described only as methods or only as apparatus, however the scope of the invention includes both methods for using apparatus and apparatus for applying methods. The scope of the invention also covers machines for creating the apparatus described herein. In addition, the scope of the invention also includes methods of using, constructing, calibrating and/or maintaining the apparatus described herein. When used in the following claims or in the text above, the terms “comprises”, “comprising”, “includes”, “including” or the like mean “including but not limited to”.