Patent Publication Number: US-2003236506-A1

Title: Dual outside diameter cannula for insertion into bone

Description:
BACKGROUND OF THE INVENTION  
       [0001] Various medical procedures require a physician to obtain a sample of a patient&#39;s bone or penetrate to the bone marrow cavity to extract bone, bone marrow or bone marrow cavity fluids. Examples include diagnostic tests and determining the suitability of the patient as a transplant donor.  
       [0002] The procedures require the physician to use a sharpened instrument to penetrate the hard, outer layer of the bone. One type of sharpened instrument includes a stylet fitted within a cannula. The procedures require the instrument to have a combination of attributes including rigidity to prevent bending and breaking while being inserted into the bone, and be of a minimum size to prevent unnecessary damage to the bone and surrounding tissue.  
       [0003] Prior art instruments have been designed to be constructed of a flexible material to be inserted within soft tissue, veins, and arteries to access specific areas within the patient. These devices are not applicable to penetrating bone because the flexible construction does not have the necessary rigidity to penetrate through the hard outer layer of the bone.  
       [0004] Other biopsy needles are constructed of a rigid material for penetrating into the bone. These needles have a tapered tip to facilitate insertion into the bone and a constant outer diameter extending along the length. The outer diameter is sized such that the device has adequate rigidity and strength to be inserted into the bone without bending or flexing. However, the enlarged size may result in unnecessary damage to the bone and the surrounding tissue.  
       SUMMARY  
       [0005] The present invention is directed to a cannula for insertion into bone. In one embodiment, the cannula includes a distal section having a first outer diameter and a proximal section having an enlarged outer diameter. The sizing is important because the reduced size of the distal section allows for penetrating into the bone without causing unnecessary damage. The enlarged proximal section allows for support to prevent bending when the distal end is inserted into the bone.  
       [0006] In another or the same embodiment, the distal section has a first wall thickness. The proximal section has a larger wall thickness to further prevent the cannula from bending when in use.  
       [0007] An intermediate section may be positioned between the distal section and the proximal section. The intermediate section may have a tapered configuration such that the outer diameter tapers from the size of the proximal outer diameter to the size of the distal outer diameter. In another embodiment, a tip is positioned on the end of the distal section to facilitate penetration into the bone. The tip may be tapered, and may include a sharpened edge.  
       [0008] In use, the cannula is handled such that the distal end penetrates into the bone. The sections of the cannula having the larger diameter do not penetrate the bone. The distal section includes a length with a constant diameter. Increased penetration into the bone results in a longer opening, without an increase in the diameter of the opening within the bone. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009]FIG. 1 is a perspective view illustrating one embodiment of a cannula constructed in accordance with the present invention;  
     [0010]FIG. 2 is a partial perspective view of one embodiment of a cannula with a stylet extending outward from the distal end in accordance with the present invention;  
     [0011]FIG. 3 is a cross-sectional view of the cannula of FIG. 1 cut along line  3 - 3 ; and  
     [0012]FIG. 4 is a cross-sectional view of the distal section of FIG. 3 cut along line  4 - 4 ;  
     [0013]FIG. 5 is a cross-sectional view of the proximal section of FIG. 3 cut along line  5 - 5 ;  
     [0014]FIG. 6 is a cross-sectional view of an alternative embodiment of the present invention illustrating the cannula constructed of different materials;  
     [0015]FIG. 7 is a side view illustrating the cannula nearing insertion into the patient in accordance with one embodiment of the present invention;  
     [0016]FIG. 8 is a side view illustrating the cannula nearing insertion into the bone in accordance with one embodiment of the present invention; and  
     [0017]FIG. 9 is a side view illustrating the distal section of the cannula inserted within the bone with the intermediate section and the proximal section to the exterior of the bone in accordance with one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0018] The present invention is directed to a cannula, generally illustrated  10  in FIG. 1, and a method of inserting the cannula into a bone within a patient. Cannula  10  comprises a distal section  20 , a proximal section  40 , and an intermediate section  30  positioned there between. The distal section  20  has a smaller outer diameter than the proximal section  40 . The smaller outer diameter assists in inserting the distal section  20  into the bone. The proximal section  40  has a larger wall thickness than the distal section  20  to give rigidity and strength to prevent bending or flexing during insertion.  
     [0019] The distal section  20  includes a distal end  26  having an opening  28  through which a stylet  60  extends. The distal section  20  has a length L which may have a variety of sizes depending upon the application. In one embodiment, the length L of the distal section  20  is about 1.0 inch. The outer diameter d d  (FIG. 4) over the length L is substantially constant. In one embodiment, the distal end is 11 gauge and has an outer diameter d d  of about 0.120 inches. The wall thickness t d  of the distal section  20  is illustrated in FIG. 4. Wall thickness t d  may vary depending upon the application. In one embodiment, wall thickness t d  is about 0.027 inches. The wall thickness t d  may be constant over the length L, or may vary. In one embodiment illustrated in FIG. 3, wall thickness t d  is substantially constant over the length L. In another embodiment (not illustrated), wall thickness t d  gradually increases over the length L with the smallest thickness adjacent the distal end  26  and the largest thickness adjacent the intermediate section  30 .  
     [0020] An inwardly tapered tip  22  may be positioned at the end of the distal section  20  adjacent to the opening  28 . Tapered tip  22  may include a sharpened edge to facilitate insertion of the cannula  10  into the patient.  
     [0021] Intermediate section  30  is positioned between the distal section  20  and proximal section  40 . Intermediate section  30  has a tapering outer diameter that ranges in size between the outer diameter of the proximal section  40  to the outer diameter of the distal section  20 . In one embodiment, the intermediate section tapers from an outer diameter of about 0.165 inches to about 0.120 inches. The amount of taper and length may vary depending upon the application. In one embodiment as illustrated in FIG. 2, the taper angle α is about 10°. The wall thickness of the intermediate section varies across the length in a gradual manner from the smallest wall thickness adjacent to the distal section  20  and the largest adjacent to the proximal section  40 .  
     [0022] In one embodiment, the proximal section  40  has a larger wall thickness than the distal section  20 . The additional thickness increases the rigidity of the proximal section  40  to reduce flexing and bending during insertion of the cannula  10  into the bone. The wall thickness t p  of the proximal section  40  may be within a wide range depending upon the application. In one embodiment, the wall thickness t p  is about 0.072 inches. The wall thickness t p  may be constant over the length of the proximal section  40  as illustrated in FIG. 3. In another embodiment, the wall thickness t p  may vary along the length. In one embodiment, the wall thickness is constant over the distal, intermediate, and proximal sections.  
     [0023] Proximal section  40  has a larger outer diameter d p  (FIG. 5) than the outer diameter d d  of the distal section  20 . In one embodiment, the outer diameter d p  is about 0.165 inches. The outer diameter d p  may be constant over the length of the proximal section  40  as illustrated in FIG. 3. In another embodiment, the outer diameter d p  varies over the length.  
     [0024] The cannula  10  includes a lumen  50  extending the length. The lumen  50  is sized to receive a stylet  60  that extends the length of the cannula  10  and through the opening  28  in the distal end  26 . In one embodiment as illustrated in FIG. 4, an inner diameter d i  of the lumen  50  is substantially constant the entire length of the cannula  10 . In one specific embodiment, the inner diameter is about 0.093 throughout the length of the cannula  10 . In another embodiment, the inner diameter d i  may vary over the length. The inner diameter d i  may have a variety of sizes depending upon the application.  
     [0025] Cannula  10  may be constructed in a number of different manners. In one embodiment, cannula  10  is constructed from a single piece of material, such as stainless steel. The cannula  10  may further be constructed of any metal that offers rigidity for inserting the cannula  10  into the bone. In one embodiment, cannula  10  is constructed of titanium to be compatible with MRI equipment. In an alternative embodiment as illustrated in FIG. 6, cannula  10  is constructed of outer and inner materials  70 ,  72 . In one embodiment, the outer material  70  forms an outer shell around the inner material  72 . The outer material  70  has a rigid construction to prevent bending or flexing of the cannula  10  during insertion into the bone. Inner material  72  may further be constructed to add rigidity.  
     [0026] A stylet  60  may be inserted within the lumen  50  as illustrated in FIG. 2. The elongated stylet  60  extends the length of and is slideably received within the lumen  50 . The stylet  60  extends through the opening  28  at the distal end  26  and provides a smooth external profile between the cannula  10  and stylet  60  to facilitate penetration into the bone. Stylet  60  includes a cutting edge  62  at the distal end. Cutting edge  62  that may have a variety of orientations and dimensions to facilitate bone penetration.  
     [0027]FIGS. 7, 8, and  9  illustrate the use of the cannula  10 . FIG. 7 illustrates the cannula  10  positioned adjacent to the patients skin  100 , tissue  110 , and bone  120 . In this embodiment, the cannula  10  is inserted through the skin  100  and tissue  110 . In other embodiments, the skin  100  and tissue  110  may be resected prior to the use of the cannula  10  such that only the bone  120  is contacted. Stylet  60  is inserted within the cannula  10  with the cutting edge  62  protruding through the opening  28  for facilitating insertion.  
     [0028]FIG. 8 illustrates a stage during the insertion process. The distal section  20  has penetrated through the skin  100  and into the tissue  110 . The intermediate section  30  and proximal section  40  have yet to enter into skin  100 . FIG. 9 illustrates the cannula  10  with stylet with cutting edge  62  inserted into the bone  120 . The cannula  10  has been inserted a distance into the patient such that the distal section  20  is the only portion of the cannula  10  penetrating into the bone  120 . Neither the intermediate portion  30  nor proximal section  40  penetrate the bone  120 . The intermediate portion  30  and proximal section  40  penetrate through the skin  100  and into the tissue  110 . The smaller outer diameter d d  of the distal section  20  prevents unnecessary damage to the bone that could occur if the intermediate section  30  or proximal section  40  were inserted. The increased wall thickness t p  of the proximal section  40  prevents the cannula  10  from bending such that the force applied to the cannula  10  is directed to penetration into the bone  120 .  
     [0029] In the embodiment illustrated in FIGS. 7, 8, and  9 , stylet  60  also penetrates into the bone  120  as it extends from the opening  28  in the distal end  26 . In another embodiment, there is no stylet  60  and only the cannula  10  is inserted into the bone  120 .  
     [0030] The cross-section shape of the distal  20 , intermediate  30 , and proximal  40  sections may have a variety of different configurations. In one embodiment, each section is substantially circular. In one embodiment, the sections are rectangular. In another embodiment, sections are oval. In another embodiment, sections are triangular. The different sections may have different cross-sectional shapes. In one embodiment, distal  20  and proximal  40  sections have a first cross-sectional shape, and the intermediate section  30  has a second, different cross-sectional shape. The term “diameter” is used herein to mean the size of the device by a straight line passing through a center of the cross-sectional shape. The term “diameter” is used to include circles, as well as other shapes.  
     [0031] One embodiment of a cannula  10  includes a distal section  20  having a length of about 1.0 inches, an outer diameter of about 0.120 inches, and an inner diameter of about 0.093 inches. The proximal section  40  has an outer diameter of about 0.165 inches, an inner diameter of about 0.093 inches. The intermediate section has a tapered outer diameter that ranges from a first edge of about 0.165 inches to a second edge of about 0.120 inches. The intermediate section  30  tapers at about a 10° angle relative to the proximal section  40 . A constant inner diameter lumen  50  of about 0.093 inches extend the entire length of the cannula. The distal section  20 , intermediate section  30 , and proximal section  40  have a combined length of about 5.0 inches.  
     [0032] The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. Proximal section  40  may have a variety of lengths depending upon the application. A handle or other type of holding device may be mounted to the proximal section  40  for handling by the physician. The handles are well known in the art and are not considered part of this invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.