Abstract:
An endoscopic rotary abrader allowing for increased burr size while maintaining the required minimum clearance between the burr and the hood. This is accomplished either by an offset configuration of non-concentric inner and outer tubes, where the inner tube is shifted laterally away from the hood, or by employing an enlarged hood.

Description:
This application is a continuation of U.S. application Ser. No. 11/365,939, filed Mar. 2, 2006, now U.S. Pat. No. 7,618,428 which in turn claims priority to U.S. Provisional Application No. 60/657,418, filed Mar. 2, 2005, the disclosures of which are incorporated herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to rotary abraders used in surgery and, more particularly, to an abrader which gives the surgeon an improved view of the surgical site during endoscopic surgery. 
     BACKGROUND OF THE INVENTION 
     Least invasive surgical techniques have gained significant popularity because of their ability to accomplish outcomes with reduced patient pain and accelerated return of the patient to normal activities. Arthroscopic surgery, in which the intra-aticular space is filled with fluid, allows orthopedists to efficiently perform procedures using special purpose instruments designed specifically for arthroscopists. Among these special purpose tools are various manual graspers and biters, electrosurgical devices, and powered shaver blades and rotary abraders. Shaver blades having hollow bores are typically removably coupled to a shaver handpiece and are used for cutting, resecting, boring and abrading both soft and hard tissue at the surgical site. An arthroscopic abrader (also known as a burr) generally includes a rotatable inner tube having an abrading head at its distal end and a fixed outer tube for rotatably receiving the inner tube. Abraders are used for abrading or shaping both soft and hard tissue such as bone, cartilage, ligaments, etc. by use of the rotating abrading head. As the tissue is being abraded, debris and fluid are generally drawn or sucked through the rotatable inner tube. 
     Requirements for a rotary abrader for arthroscopy include a compact size so as to fit through small cannulae, a means for removal of debris, and a configuration which allows the surgeon to access structures within a joint, while retaining good visibility. One requirement for good visibility is the effective removal of debris as it is generated. Another is that the instrument be configured so that the view of the active portion of the abrader in contact with the tissue and the view of the tissue being abraded are not obscured by the instrument. 
     Rotary abraders for arthroscopy generally have a shield, also called a “hood,” on one side of the distal end of the outer tube to prevent inadvertent injury to tissue in close proximity to the tissue being abraded. The distal end of this hood is angled with respect to the tube axis so as to expose only one side of the burr head. During use, the burr head (the abrading element at the distal end of the rotating inner member) is subjected to significant lateral forces. Although all rotary abraders have a bearing near the distal end of the instrument to support the inner member, lateral deflection of the burr head occurs. Contact between the burr head and the hood is undesirable since the burr will abrade metal from the hood and deposit metallic debris in the joint. Accordingly, it is necessary to leave adequate clearance between the hood and the burr head. The amount of clearance necessary is largely determined by the rigidity of the inner tube and the placement of the distal bearing between the inner and outer tubes. It is desirable to place the distal bearing as close as practical to the burr head to minimize deflection. It is also desirable to make the distal portion of the inner tube as rigid as practical. On currently available rotary abraders, the outer, stationery tube and inner, rotating tube are concentric. Because of this, the diameter of the distal portion of the outer, stationery tube in proximity to the burr head is significantly larger than the diameter of the burr head, so as to have adequate clearance. The required diameter of this portion of the outer tube is determined by the resistance of the burr head to deflection, which in turn is determined by the bearing placement and inner tube distal end construction. While this increased diameter prevents contact between the burr head and the hood, it also restricts the surgeon&#39;s access to some structures, and often obscures the surgeon&#39;s view of the site being abraded. 
     Removal of debris from the field is accomplished by aspirating the material from the joint via a lumen in the inner, rotating member which is connected through a means in the handpiece to an external vacuum source. The aspiration of material through the inner member is desirable as this allows easy transfer of the materials from the proximal end of the instrument to the aspiration passage of the handpiece. The manner in which material and fluid enter the lumen at the distal end of the instrument has a large effect on the volume of flow through the instrument and on the frequency with which the instrument clogs. Insufficient flow causes decreased visibility because of residual debris suspended in the intra-articular fluid. Clogging requires that the instrument be removed from the joint and “de-clogged”. The degree of difficulty of clog removal is determined by the instrument design. Even if clog removal is easily accomplished, removing, de-clogging and reinserting the instrument is a nuisance and causes increased procedure times. Aspiration effectiveness, and therefore instrument design, have a large effect on burr efficiency. 
     Referring to  FIGS. 1 through 5 , prior art burr  10  has an inner assembly  12  rotatably positioned within an outer assembly  14 . Inner assembly  12  has an proximal end  16  forming a hub assembly  18  for engaging the drive element of a powered handpiece, and an elongated tubular portion  20  having an abrading element  22  at its distal end  24 . Bearing  26  is positioned near distal end  24  of tubular portion  20  slightly proximal to aspiration port  28  which provides a means of material flow to the lumen  21  of portion  20 . Outer assembly  14  has a proximal end  30  forming a hub assembly  32  for removably mounting in a powered handpiece, and an elongated tubular portion  34  having a distal end  36  forming a beveled surface  38 . As best seen in  FIG. 4 , bearing  26  centers distal end  24  of inner assembly  12  within distal end  36  of outer tubular portion  34  so as to maintain clearance  40  between abrading element  22  and shield (hood)  42  formed by distal end  36  and beveled surface  38 . Clearance  40  is determined by the diameter  46  of burr head (abrading element)  22 , and the inner diameter  47  and wall thickness  48  of outer tubular portion  34 . Debris and liquid are aspirated from the region of abrading element  22  along path  44  to lumen  21  via aspiration port  28 . 
     In U.S. Pat. No. 4,842,578, Johnson et al. teach an aspiration method in which material is drawn into the lumen of the inner tube via slots in the inner assembly distal to the bearing—the bearing is moved quite far proximal, thereby increasing the lateral deflection of the burr head during use. This, in turn, necessitates larger clearance between the burr head and the hood, and thus a large hood diameter, which obscures the surgeon&#39;s view and access. The relatively small slots in this design would make the instrument prone to clogging. 
     In U.S. Pat. No. 5,913,867, Dion teaches a rotary abrader with improved aspiration. As with the Johnson device, material is drawn into the lumen of the inner tube via an opening distal to the bearing between the inner and outer tubes. At least a portion of the opening is distal to the proximal end of the angled distal opening in the hood. This allows greater flow volumes and decreased clogging. However, the bearing is still proximal to the opening in the inner tube which allows for greater deflection of the abrading element during use. This necessitates that the hood diameter be significantly greater than the diameter of the burr head. 
     Vaca et al., in U.S. Pat. No. 6,053,923, teach a rotary abrader construction in which material is drawn into the lumen of the inner tube through axially aligned openings in the inner and outer tubes proximal to the distal end bearing. The inner and outer tubes may have a single opening or multiple openings. The openings admit liquid and tissue when angularly aligned and have a geometry designed to cooperatively cut tissue in the same manner as an arthroscopic shaver blade. The cutting action of the openings is intended to decrease clogging. The design is likely quite effective when the instrument is fully inserted into the joint, however, there will likely be instances in which the openings are obstructed because the burr is not fully inserted into a joint, or the joint is small. In these cases, it will be impossible to aspirate tissue through the instrument. 
     Grinberg, in U.S. Pat. No. 5,759,185, teaches a rotary abrader in which a lumen within the burr head extends distally such that openings in the troughs between the cutting flutes of the burr intersect the lumen. Debris is sucked into the openings while the burr is cutting tissue and removed from the site. A potential problem with this method is that the burr is rotating at high speed and the centrifugal force would tend to move material away from the openings. Also, it is likely that cavitation would tend to disrupt the flow of material into the openings, and proximally from the openings to the lumen in the inner tube. 
     Moutafis, in U.S. Patent Publication No. 2003/0055404, teaches a second stationary tube concentrically positioned about the standard stationery tube with a space between the tubes used to aspirate debris. It is likely that this passage would be prone to clogging unless it was made quite large, in which case the instrument diameter would be very large compared to that of the rotating abrading element. This, in turn, requires the use of large cannulae and generally obstructs the surgeon&#39;s view. 
     Moutafis, in U.S. Patent Publication No. 2003/0083681, teaches a distal bearing which does not have continual contact with the inner tube, but rather has contact regions separated by passages through which liquid and debris are aspirated. This allows the bearing to be placed quite close to the burr head as to minimize deflection, however, the decreased bearing surface will likely lead to higher forces between the bearing and the rotating member making galling and the generation of metallic debris more likely. Also, because of size constraints of the outer tube, the passages would be quite small and prone to clogging. Clearing clogs would be problematic since access to the passages is limited by the burr head, and the burr could not be readily disassembled for clearing as the burr head is larger in size than the bearing surfaces thereby preventing the inner portion from being withdrawn proximally. 
     U.S. Patent Publication No. 2004/0181251 by Hacker et al. describes a rotary abrader with multiple slots in the stationary outer tube proximal to the burr head and proximal to the distal bearing. A burr so constructed has excellent rigidity since the bearing is close axially to the burr head. It has good flow volume because of the number and size of the slots. If one or more slots become clogged by tissue the other slots still pass enough flow to allow the procedure to continue without having to remove and clear the instrument. A drawback of this construction, however, as in the case of the Vaca et al. device, is that the slots may be obstructed by tissue when the instrument is initially inserted into the joint, or when it is used on a small joint. 
     The rotary abraders previously herein considered may be generally divided into two categories: those which can be disassembled by withdrawing the inner tube proximally from the outer tube, and those which cannot be so dissembled. Most commercially available arthroscopy burrs fit into the first category. A burr which may be disassembled in this manner must of necessity have a bearing which is affixed to the inner member and is larger in diameter than the burr head, or alternatively have a portion of the rotating member proximal to the burr head with a larger diameter than the burr head to engage a bearing of the stationary outer member. The bearing is generally a thin polymeric or metallic layer applied to the inner which prevents galling between the inner and outer members. The inner member diameter is maximized to maximize the inner lumen size so as to increase flow volume and prevent clogging. Clogging, however, generally occurs at the distal end of the instrument, at the opening of the passage proximal to the burr head. The clogging most frequently occurs because soft tissue wraps around the inner member proximal to the burr. On burrs with a single opening, or with multiple openings in close proximity, a clog stops all aspiration of debris from the site and necessitates removal and clearing of the instrument for the surgical procedure to continue. 
     There is a need for an improved rotary abrader having rigidity, an aspiration means which effectively removes debris without clogging and which can be readily cleared of clogs without disassembly, and enhanced surgeon visibility. 
     It is accordingly an object of this invention to provide a rotary abrader with high resistance to deflection of the burr head. 
     It is also an object of this invention to provide a rotary abrader with improved visibility for the surgeon. 
     It is also an object of this invention to provide a rotary abrader able to produce high aspiration flow rates regardless of the insertion position of the instrument in the joint or the size of the joint. 
     It is further an object of this invention to provide a rotary abrader which has multiple aspiration openings so as to allow the instrument to be used with one or more openings partially for fully clogged. 
     SUMMARY OF THE INVENTION 
     The present invention achieves the foregoing objectives by providing, in one embodiment, a rotary abrader in which the inner member and outer member are not concentrically positioned. In this embodiment, the proximal end of the stationary outer member forms a hub for mounting to a handpiece, and the distal end has a generally laterally facing opening for exposing the burr head. A bearing is affixed to the tube inner lumen proximal to the opening. The inner surface of the bearing is not concentric with the outer tube, but rather is displaced laterally toward the laterally facing opening. Slightly proximal to the bearing are one or more elongated passages between the inner and outer surfaces of the tube. The bearing and outer tube together form axial passages which allow the flow of material from the distal side of the bearing to the proximal side. The passages are generally on the portion of the bearing that is away from the generally lateral facing opening. The rotating inner member has a proximal end forming a hub which engages a driving mechanism within a handpiece and an elongated portion, the distal end of which forms an abrading element. Proximal to the abrading element is a portion having a diameter less than that of the abrading member. Proximal to this portion is a tubular portion which extends proximally to the proximal end of the inner member. This tubular portion has an opening forming an aspiration port near its distal end which allows the flow of materials into the lumen of the tubular portion. 
     During use, liquid and debris are aspirated from the joint along two paths which join at the aspiration port in the inner tube. The first path, taken by debris and liquid in close proximity to the abrading element, is through the axial passages formed in the bearing to the aspiration port. The second path, taken by debris and liquid in the region adjacent to the instrument&#39;s distal end, is through the elongated passages between the outer and inner surfaces of the outer tube proximal to the bearing, going to the aspiration port in the inner tube. Material then flows via the lumen in the inner tube to the handpiece from which it is removed by an external vacuum source. This two-path aspiration is advantageous in that debris is removed through multiple external openings. If one or more openings get partially or completely clogged, aspiration continues through the remaining clear openings. Some clogging can be tolerated without removal of the instrument from the joint. Aspiration via the elongated slots in the outer tube increases the flow volume when the instrument has been inserted to sufficiently remove obstruction of the slots by tissue. Until these slots are unobstructed, debris is removed through the axial end of the outer tube via passages formed by the slots in the bearing. Clogs are easily removed. Clogs at the elongated slots are easily accessible while clogs in the passages formed by grooves in the bearing are accessible through the instrument&#39;s distal end. Access to these passages is not prevented by the burr head. Because the aspiration port in the inner assembly distal region is much larger than the elongated openings in the outer tube or the passages in the bearing, clogging of the aspiration port does not occur. 
     In one embodiment, the inner assembly is formed of two subassemblies. The first, distal subassembly has a burr head (abrading element) at its distal end, a cylindrical portion adjacent to the burr head, and an elongated tubular portion with a fastening means at its proximal end. The second, proximal subassembly had a hub with a driving means and a fastening means for affixing the proximal subassembly to the distal assembly. The diameter of the cylindrical portion proximally adjacent to the burr head has a smaller diameter than the burr head. The tubular, proximal portion has a smaller diameter than the cylindrical portion. The distal subassembly of the inner assembly is inserted into the distal end of the outer assembly. The proximal subassembly is affixed to the proximal end of the tubular portion by the fastening means to produce the complete instrument. The cylindrical portion of the inner assembly is rotatably positioned within the distal bearing. 
     The resistance of the burr head to lateral deflection is enhanced by the placement of the bearing in close proximity to the burr head. The burr head is shifted away from the hood by the offset in the bearing. This combination of enhanced rigidity and eccentricity of the inner assembly and outer tube allows the diameter of the outer tube to be decreased, or the diameter of the abrading element to be increased, thereby minimizing obstruction of the surgeon&#39;s view and improving access to structures within a joint. 
     In another embodiment, the distal and proximal portions of the inner assembly are permanently affixed. The inner assembly has a burr head at its distal end, a cylindrical portion proximally adjacent to the burr head, and an elongated tubular portion with a hub with a drive means at its proximal end. The diameter of the cylindrical portion is less than the diameter of the burr head and, in contrast with the previous embodiment, smaller than the diameter of the tubular portion. The outer assembly, which has a tubular portion and a proximal portion forming a hub, is composed of two subassemblies. The distal bearing is split axially to form two portions with a bearing portion attached to each of the outer subassemblies. The distal portion of the tubular portion is divided into an upper portion and a lower portion. The lower portion, with a fastening means for removal attaching it to the upper portion, forms the first subassembly. A first bearing portion is mounted to the upper (lumen) side of the subassembly near its distal end. The proximal end of the first subassembly forms a hub for removably mounting the abrader to a handpiece. The upper portion, with a fastening means for removal attaching it to the lower portion forms the second subassembly, a second bearing portion being mounted to the lower (lumen) side of the portion near its distal end. The distal end of this second subassembly forms a hood. 
     The abrader is assembled in two steps. The inner assembly is inserted into the first outer subassembly so that the cylindrical portion of the inner assembly is rotatably positioned in the first portion of the distal bearing. The second outer subassembly is then removably mounted to the first subassembly so as to form a complete outer assembly with the inner assembly rotatably positioned within it. The cylindrical portion of the inner assembly is positioned within the bearing formed by the first and second bearing portions. 
     The unique construction of this second embodiment provides advantages for certain applications. In the first embodiment, the diameter of the cylindrical portion of the inner assembly is greater than the diameter of the tubular portion, so as to allow the inner assembly to be inserted proximally into the bearing of the outer assembly. The tubular portion must be of sufficient diameter to transmit required torque to the abrading element, and have a lumen of sufficient size for effective aspiration. The minimum diameter for the tube determines the minimum diameter of the cylindrical element, which, in turn, determines the bearing configuration and the distance that the burr head can be shifted laterally away from the hood. 
     In the second embodiment, the cylindrical portion of the inner assembly can be smaller than the tubular portion since the inner assembly is not inserted into the bearing axially but rather is positioned between two halves of a split bearing. This allows the displacement between the center of the outer tube and the center of the inner assembly to be increased, allowing further increase in the clearance between the burr head and the hood for a given tube size. This, in turn, gives improved visibility for the surgeon and enhanced access to structures within a joint. Another advantage of the second embodiment is the ease of disassembly and reassembly for cleaning. This is essential for a reusable instrument. 
     In a third embodiment of the present invention, the inner and outer assemblies are concentric, rather than offset, but the inner assembly is provided with an enlarged burr head at the distal end. To maintain the required clearance between the enlarged burr head and the hood, the hood is positioned at an angle and enlarged. 
     In the various embodiments of the present invention, the enlarged burr is preferably configured so that its cutting edge is aligned with the outer surface of the outer tube to provide a “flush cut.” 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above described features of the invention will be more clearly understood from the following detailed description, which is provided with reference to the accompanying drawings. 
         FIG. 1  is a side elevational view of a prior art abrader with the inner assembly disassembled from the outer assembly. 
         FIG. 2  is a plan view of the prior art rotary abrader of  FIG. 1  assembled. 
         FIG. 3  is a side elevational view of the objects of  FIG. 2 . 
         FIG. 4  is an expanded side elevational sectional view of the distal end of the objects at location A-A of  FIG. 2 . 
         FIG. 5  is a plan view of the outer tube of a rotary abrader in accordance with a first embodiment of the invention. 
         FIG. 6  is a side elevational view of the objects of  FIG. 5 . 
         FIG. 7  is an expanded side sectional view of the distal portion of the objects at location A-A of  FIG. 5 . 
         FIG. 8  is a side elevational view of the distal bearing of a rotary abrader constructed in accordance with a first embodiment of the invention. 
         FIG. 9  is an axial view of the objects of  FIG. 8 . 
         FIG. 10  is a plan view of the outer assembly of a rotary abrader constructed in accordance with a first embodiment of the invention. 
         FIG. 11  is a side elevational view of the objects of  FIG. 10 . 
         FIG. 12  is an expanded side sectional view of the distal portion of the objects at location A-A of  FIG. 10 . 
         FIG. 13  is a plan view of the distal subassembly of the inner assembly of a rotary abrader constructed in accordance with a first embodiment of the invention. 
         FIG. 14  is a side elevational view of the objects of  FIG. 13 . 
         FIG. 15  is an expanded side elevational sectional view of the distal portion of the objects at location B-B of  FIG. 13 . 
         FIG. 16  is an expanded side elevational view of the proximal portion of the objects at location C-C of  FIG. 13 . 
         FIG. 17  is an expanded plan view of the objects of  FIG. 16 . 
         FIG. 18  is an expanded axial sectional view of the objects of  FIG. 16  at location D-D of  FIG. 17 . 
         FIG. 19  is a plan view of the proximal hub subassembly of the inner assembly of a rotary abrader constructed in accordance with a first embodiment of the invention. 
         FIG. 20  is a side elevational view of the objects at location A-A of  FIG. 19 . 
         FIG. 21  is an axial sectional view of the retaining slot portion of the objects at location B-B of  FIG. 19 . 
         FIG. 22  is a side elevational view of the retainer for affixing the inner hub to the inner tube of a rotary abrader constructed in accordance with a first embodiment of the invention. 
         FIG. 23  is a plan view of the object of  FIG. 22 . 
         FIG. 24  is an exploded view of a rotary abrader constructed in accordance with a first embodiment of the invention showing the method of assembly. 
         FIG. 25  is a plan view of the objects of  FIG. 24  when assembled. 
         FIG. 26  is a side elevational sectional view of the objects at location M-M of  FIG. 25 . 
         FIG. 27  is an expanded axial sectional view of the objects at location N-N of  FIG. 25  showing the position of the retainer in the inner hub. 
         FIG. 28  is an expanded side sectional view of the distal end of the objects of  FIG. 25 , showing the aspiration paths. 
         FIG. 29  is an exploded disassembled view of a rotary abrader constructed in accordance with a second embodiment of the invention. 
         FIG. 30  is a perspective view of a first outer assembly of a rotary abrader constructed in accordance with a second embodiment of the invention. 
         FIG. 31  is a plan view of the objects of  FIG. 30 . 
         FIG. 32  is a side elevational view of the objects of  FIG. 30 . 
         FIG. 33  is an expanded axial sectional view of the objects at location C-C of  FIG. 31 . 
         FIG. 34  is an expanded side elevational sectional view of the objects at location B-B of  FIG. 31 . 
         FIG. 35  is a plan view of a second outer assembly of a rotary abrader constructed in accordance with a second embodiment of the invention. 
         FIG. 36  is a side elevational view of the objects of  FIG. 35 . 
         FIG. 37  is a bottom view of the objects of  FIG. 35 . 
         FIG. 38  is an expanded axial view of the objects at location D-D of  FIG. 35 . 
         FIG. 39  is an expanded side elevational sectional view of the objects at location E-E of  FIG. 35 . 
         FIG. 40  is a plan view of the inner assembly of the embodiment of  FIG. 29 . 
         FIG. 41  is a side elevational view of the objects of  FIG. 40 . 
         FIG. 42  is an expanded side elevational sectional view of the distal portion of the objects at location H-H of  FIG. 40 . 
         FIG. 43  is an expanded side elevational sectional view of the proximal portion of the objects at location J-J of  FIG. 40 . 
         FIG. 44  is a side elevational view of the retainer of a rotary abrader constructed in accordance with a second embodiment of the invention. 
         FIG. 45  is a perspective view of the object of  FIG. 44 . 
         FIG. 46  is a side elevational sectional view of the object at location F-F of  FIG. 44 . 
         FIG. 47  is an axial end view of the object of  FIG. 44 . 
         FIG. 48  is a plan view of the spring washer of a rotary abrader constructed in accordance with a second embodiment of the invention. 
         FIG. 49  is a side elevational sectional view of the object of  FIG. 48 . 
         FIG. 50  is a perspective view of a partially assembled rotary abrader constructed in accordance with a second embodiment of the invention. 
         FIG. 51  is an expanded perspective view of the distal portion of the objects of  FIG. 50 . 
         FIG. 52  is a plan view of the assembled a rotary abrader constructed in accordance with a second embodiment of the invention. 
         FIG. 53  is a side elevational view of the objects at location A-A of  FIG. 52 . 
         FIG. 54  is an expanded view of the distal portion of the objects of  FIG. 53 . 
         FIG. 55  is a side elevational sectional view of the objects of  FIG. 52  along the axis of the abrader. 
         FIG. 56  is a plan view of the objects of  FIG. 52 . 
         FIG. 57  is an expanded side elevational view of the distal portion of the objects at location C-C of  FIG. 56 . 
         FIG. 58  is an expanded side elevational sectional view of the proximal portion of the objects at location C-C of  FIG. 56 . 
         FIG. 59  is an expanded axial sectional view of the objects at location D-D of  FIG. 56 . 
         FIG. 60  is a plan view of the outer tube of a rotary abrader in accordance with a third embodiment of the invention. 
         FIG. 61  is a plan view of the outer tube of a rotary abrader in accordance with a third embodiment of the invention. 
         FIG. 62  is a side elevational sectional view of the objects at location Z-Z of  FIG. 60 . 
         FIG. 63  is an expanded side elevational sectional view of the objects at location A of  FIG. 62 . 
         FIG. 64  is an expanded axial sectional view of the objects at location Y-Y of  FIG. 61 . 
         FIG. 65  is a plan view of the inner tube of a rotary abrader in accordance with a third embodiment of the invention. 
         FIG. 66  is an expanded plan view of the distal end of the inner tube of a rotary abrader in accordance with a third embodiment of the invention. 
         FIG. 67  is a perspective view of the distal end of the inner tube of a rotary abrader in accordance with a third embodiment of the invention. 
         FIG. 68  is a plan sectional view of the proximal hub subassembly of the inner assembly of a rotary abrader constructed in accordance with a third embodiment of the invention. 
         FIG. 69  is a side elevational view of the objects at location A-A of  FIG. 19 . 
         FIG. 70  is a side elevational sectional view of the rotary abrader of the third embodiment of the invention along the axis of  FIG. 71 . 
         FIG. 71  is a plan view of the rotary abrader of the third embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a first embodiment of the present invention, an inner assembly is rotatably positioned within an outer assembly. The proximal ends of the assemblies form hubs as in the prior art device of  FIGS. 1 through 4 . The elongated tubular portions of the inner and outer assemblies are not concentric, but rather have the inner tubular portion laterally positioned away from the hood so that required clearance can be maintained between the burr head and the hood while increasing the diameter of the burr head, or decreasing the diameter of the outer tube. 
     Referring now to  FIGS. 5 through 7 , showing the outer tubular portion (outer tube)  52  of the outer assembly  50  ( FIG. 10 ) of a rotary abrader formed in accordance with the first embodiment of the invention, outer tube  52  has a proximal end  54  and a distal end  56 . Tube  52  has a lumen  53  of diameter  60  and an outer diameter  62 . Distal end  56  has a first portion  64  with an inner diameter  66  formed therein, and a second portion  68  of length  70  with a diameter  72  formed therein. Diameter  72  is slightly larger than diameter  60 . Diameter  66  is slightly larger than diameter  72 . Elongated slots  73  extended from the lumen  53  to tube outer surface  55 . Beveled surfaces  75  and  77  together with outer surface  55  define a hood (or guard)  79 . 
       FIGS. 8 and 9  show the distal bearing  74  of a rotary abrader formed in accordance with the principles of this invention. Bearing  74  has a cylindrical outer surface  76  of radius  78  and an inner bore  80  of diameter  82 , the center of outer surface  76  and bore  80  being displaced a distance  84 . Radius  78  is slightly larger than half of diameter  66  of first portion  64  of outer tube  52  ( FIG. 7 ). Grooves  90  extended axially from distal surface  92  to proximal surface  94 . Bearing  74  is made from a suitable polymeric or metallic material. Thickness  93  is approximately equal to length  70  of second portion  68  of outer tube  52  ( FIG. 8 ). 
     Referring now to  FIGS. 10 through 12 , outer assembly  50  has a proximal end  96  with a hub  98  affixed to proximal end  54  of tube  52 . Bearing  74  is pressed into second portion  68  ( FIG. 7 ) of outer tube  52  ( FIGS. 5 and 6 ). 
     Referring now to  FIGS. 13 through 17 , inner tube assembly  102  of inner assembly  100  of a rotary abrader constructed in accordance with the principles of the invention has an elongated tubular portion  104  with a proximal end  106  and a distal end  108 . Distal end  108  has affixed thereto portion  110  having a proximal portion  112  of diameter  114 , and a distal portion  116  forming an abrading element (or burr head) of diameter  117 . Diameter  114  is slightly less than diameter  82  of bore  80  of bearing  74  ( FIG. 9 ). Near distal end  108  of tubular portion  104  aspiration port  111  extends from lumen  115  to outer surface  113 . As best seen in  FIGS. 16 through 18 , proximal end  106  of tube  102  has formed therein slots  116  of width  118  so as to form flats  119  displaced a distance  120  from the center of tube  102 . 
     Referring now to  FIGS. 19 through 21 , showing inner hub assembly  122  of inner assembly  100 , assembly  122  includes inner drive hub  124 , spring  125 , spring retainer  126  and thrust washer  127 . Hub  124  has formed therein slots  128  of width  130  and depth  132  joined by portion  134  also of depth  132 . Depth  132  is approximately equal to width  118  of slots  116  of tube  102  ( FIG. 16 ). Slots  128  are separated by a distance  131  which is slightly greater than twice distance  120  that flats  119  are displaced from the center of tube  102  ( FIGS. 17 and 18 ). Lateral aspiration passage  123  intersects bore  121 . 
     Retainer  140 , shown in  FIGS. 22 and 23 , is part of inner assembly  100 . The retainer is generally “U” shaped, with two leg portions  142  of width  144  and length  146  spaced a distance  148  apart and joined by a portion  150 . Retainer  140  has a thickness  152 , and is formed to a radius  154 . Thickness  152  is slightly smaller than depth  132  of slots  128  in inner hub  124  ( FIGS. 19 and 20 ) and width  118  of slots  116  of tube  102  ( FIG. 16 ). Width  144  is approximately equal to width  130  of slots  128  of inner hub  124  ( FIG. 21 ). Distance  148  is approximately equal to distance  131  between slots  128  of inner hub  124  ( FIG. 21 ) and slightly greater than twice distance  120  that flats  119  are displaced from the center of tube  102  ( FIGS. 16 and 18 ). Retainer  140  is made from a suitable metallic or polymeric material. 
     Referring now to  FIG. 24 , rotary abrader  160 , constructed in accordance with the principles of this invention, is assembled in the following manner. Tubular portion  104  of inner tube assembly  102  is inserted into distal end  56  of outer tube  52  of outer assembly  50 . Hub assembly  122  of inner assembly  100  is inserted into proximal end  96  of outer assembly  50  such that proximal end  106  of tubular portion  104  of inner tube assembly  102  is positioned within inner hub  124  and slots  116  of tube  104  align axially and angularly with slots  128  of inner hub  124 . Referring now also to  FIGS. 25 through 27 , retainer  140  is inserted into slots  128  thereby engaging slots  116  ( FIGS. 16 through 18 ) so as to establish and maintain the axial and angular positioning of tubular portion  102  and hub  124 . Deflection of the curved retainer  140  (radius  154 ,  FIG. 18 ) by the straight slots  128  of inner hub  124  causes high frictional forces between retainer  140  and hub  124  thereby retaining retainer  140  within hub  124 . While the axis of the inner assembly  102  is coplanar with the axis of the outer assembly  50  when viewed in a plan view, as best seen in the side elevational section view of  FIG. 26 , inner assembly  102  is offset angularly by angle  166  from outer assembly  50 . Angle  166  is determined by distance  84  between the center of the radial outer surface  76  and the center of bore  80  of bearing  74  ( FIGS. 9 and 10 ), and the distance between bearing  174  and the proximal end of inner assembly  102  which is centered in the handpiece. 
     As best seen in  FIG. 28  showing an expanded section view of the distal portion of abrader  160 , bearing  74  is positioned at proximal portion  112  of portion  110  ( FIG. 15 ) distal to aspiration port  111  of inner tube  104 , near the abrading element  116 . This position minimizes deflection of element  116  (the burr head) when it is subjected to lateral forces. Clearance  162  is equal to the difference between inner diameter  66  of outer tube  52  ( FIG. 7 ) and diameter  117  of abrading element  116 , plus distance  84  between the center of the radial outer surface  76  and the center of bore  80  of bearing  74  ( FIGS. 9 and 10 ). Distance  164  is equal to the difference between outer diameter  62  of outer tube  52  and outer diameter  117  of element  116 , less distance  84  between the center of the radial outer surface  76  and the center of bore  80  of bearing  74  ( FIGS. 9 and 10 ). Decreasing distance  164  increases the surgeon&#39;s view of the burr during use, and increases the ability of the burr to access structures during use. 
     Referring further to  FIG. 28 , during use, debris is aspirated from the site along two paths which join in lumen  115  of inner tube  104 , from which the debris is removed via aspiration passage  123  in inner hub  124  (see  FIG. 26 ) by suction supplied by the handpiece. Debris in close proximity to burr head  116  follows path  170  through passage  168  formed by groves  90  in bearing  74  ( FIGS. 9 and 10 ) to aspiration port  111  in inner tube  104 . Debris in the liquid in proximity to distal end  56  of outer tube  52  is aspirated along path  172  via slots  73  to aspiration port  111  in inner tube  104 . 
     Because the abrading element of abrader  160  is not concentrically positioned within the outer tube, but is displaced away from the hood, the diameter of the abrading element can be increased and still maintain the minimum clearance required between the element and the hood. This allows the use of a larger abrading element for a given outer tube diameter than would be possible if the inner and outer members were concentric. This larger diameter burr allows more rapid removal of bone than the smaller diameter burr of a conventional burr having the same outer tube diameter. The larger diameter burr can also advantageously be configured so that its cutting edge is aligned with the outer surface of the outer tube to provide a “flush cut.” 
     The material from which retainer  140  is made is determined by the intended life of the instrument, since reusable instruments must be disassembled for cleaning. In embodiments designed for disposal after a single use, retainer  140  may be made from a material which will degrade if the instrument is sterilized in an autoclave. In embodiments designed for reuse, retainer  140  is made from a durable material so that retainer  140  can be removed, the instrument cleaned and sterilized, and the instrument re-assembled using retainer  140 . In some embodiments retainer  140  has features which facilitate removal and reinsertion of the retainer for instrument disassembly, cleaning and reassembly. 
     Changes may be made to the form of retainer  140  and inner hub  124  without violating the principles of this invention. For instance, inner tubular portion  104  may have the diameter of the proximal portion which assembles into hub  124  reduced so that retainer  140  must only prevent tubular portion  104  from moving distally out of the hub, the proximal movement of  104  being prevented by the shoulder created by the reduced diameter. Retainer  140  may also take other forms. For instance, tubular portion  104  may be retained in hub  124  by various threaded, locking, or interfering means without violating the principles of this invention. 
     The construction of abrader  160  requires that the diameter  114  of portion  112  of the inner member  102  at the distal bearing  74  be greater than the outer diameter of the inner portion tubular member  104  so that the inner assembly  102  can be inserted into the outer assembly  50  from the distal end. The minimum diameter of the inner tubular member is determined by the level of torque which must be supplied to the abrading element and by the lumen size required for adequate removal of debris from the site. 
     A second embodiment of the present invention avoids this limitation. The distal bearing has a first portion mounted to a first, fixed portion of the outer tube assembly, and a second portion mounted to a second, demountable portion of the outer tube assembly. To assemble the rotary abrader, the demountable portion of the outer tube is removed, the inner assembly with hub permanently attached is positioned within the fixed portion of the outer tube assembly, and the demountable portion of the outer assembly is remounted to the outer assembly. This construction has two advantages: the instrument can be easily disassembled for cleaning between uses, and the tubular portion of the inner assembly can have a larger diameter than the bearing so as to allow better transmission of torque and better aspiration of debris from the site. 
     Referring now to  FIG. 29  showing an embodiment of the disclosed invention having a two-piece outer tubular assembly, rotary abrader  200  has an inner assembly  350 , an outer assembly first portion  240 , an outer assembly second portion  290 , and a retainer  390  with spring washer  420 . 
     As best seen in  FIGS. 30 through 34 , outer assembly first portion  240  has a proximal end forming a hub  242  suitable for removably mounting in a powered handpiece, and a tubular portion  244 , hub  242  having a distal portion  245  of diameter  253 . Distal end  245  has a first channel  241  of width  243  formed therein, the bottom surface of channel  241  being formed by tubular portion  244 . Hub  242  also has in its distal end  245  second and third channels  247  and  249  of width  251  which have axial portions and circumferential portions. Tubular portion  244  has a distal end  246  with a first bearing portion  248  mounted to inner surface  250  of tubular portion  244  by pins  252 . Elongated slots  254  extend from inner surface  250  to outer surface  256  of tubular portion  244 . First bearing portion  248  has formed therein a first axial channel  260  having a semicircular cross-section of radius  262 , and a second axial channel  264  of width  266  and depth  267 . Surface  268  of bearing portion  248  is approximately coplanar with axis  270  of tubular portion  244 . Surface  272  of bearing portion  248  forms the bottom of channel  264 . Axis  274  of semicircular channel  260  is coplanar with surface  272 . Depth  267  is approximately equal to the distance  276  between the axis of inner surface  250  of tubular portion  244 , and the axis of first axial channel  260 . As best seen in  FIGS. 32 and 34 , distal end  246  has formed therein a first slot  280  and a second slot  282 , slot  282  being of a constant width  284 . Slot  280  has an upper surface  286  inclined angle  288  from axis  270  of tubular portion  244 . 
     Referring now to  FIGS. 35 through 39 , outer assembly second portion  290  has an elongated proximal portion  292  of width  293  having a flange  294  at its proximal end, width  293  being slightly less than width  243  of first slot  241  ( FIG. 33 ), and a distal portion  296  formed to a cylindrical radius  297  with a second bearing portion  298  mounted to its inner surface  300  by pins  302 , and elongated slots  304  extending from inner surface  300  to outer surface  306 . Second bearing portion  298  has a channel  308  therein, channel  308  having a semicircular cross-section with a radius  310 . Passage  312  of diameter  314  extends axially through bearing portion  298  from distal surface  316  to axial surface  318 . Surfaces  320  of bearing portion  298  are coplanar with axis  323  of distal portion  296 . Surface  324  is coplanar with the axis  326  of channel  308  and is parallel to surface  320  and displaced a distance  328 . Parallel surfaces  330  are symmetrical about the plane containing axes  323  and  326 , and are separated by distance  332  which is equal to distance  266  of first bearing portion  248  ( FIG. 33 ). Distance  328  between surfaces  320  and  324  is equal to distance  267  between surfaces  268  and  272  of first bearing portion  248  ( FIG. 33 ). Radius  310  of channel  308  is equal to radius  262  of channel  260  ( FIG. 33 ). Distance  334  between axis  326  of channel  308  and axis  323  of distal portion  296  is equal to distance  276  between the axis of inner surface  250  of tubular portion  244  and the axis of axial channel  260  of first bearing portion  248  ( FIG. 34 ). As best seen in  FIG. 29 , distal portion  296  has formed therein protrusions  334  and  336  which are in form complementary to slots  280  and  282  respectively. 
     Inner assembly  350  (shown in  FIGS. 40 through 43 ) has a proximal end assembly  352  having an inner hub  354 , spring  356 , spring retainer  358 , and thrust washer  359 , together forming a means for transmitting rotary motion from a handpiece, and an elongated distal assembly  360  having a tubular portion  362  with a distal end member  364  affixed to distal end  363  by welding or another suitable means. Member  364  has a distal portion  366  forming an abrading element, and a cylindrical proximal portion  368 , the diameter  370  of portion  368  being less than the outer diameter  372  of tubular portion  362 . Aspiration port  374  extends from the outer surface  376  of tubular portion  362  to the inner lumen  378  near distal end  363 . 
     Retainer  390  ( FIGS. 44 through 47 ) forms a closed end tube having an outer cylindrical surface  392  with a plurality of grooves  394  formed therein, a cylindrical inner surface  396  of diameter  398  from which protrude radially cylindrical protrusions  400  of diameter  402 . Diameter  402  is slightly less than width  250  of second channel  247  and third channel  249  of distal portion  245  of hub  242  ( FIGS. 30 through 33 ). End wall  404  has formed therein axial cylindrical opening  406  of diameter  408 , diameter  408  being slightly greater than diameter  253  of distal portion  245  of outer hub  242  ( FIG. 33 ). 
     Spring washer  420  ( FIGS. 48 and 49 ) has a conical cross section with included angle  422 , an outer diameter  424  and an inner diameter  426 . Washer  420  is made from a high-yield strength spring material such as stainless steel. Outer diameter  424  is slightly less than diameter  398  of retainer  390 , and inner diameter  426  is slightly greater than diameter  408  of retainer  390  ( FIG. 46 ). 
     Referring to  FIGS. 50 and 51  showing a partially assembled abrader  200 , inner assembly  350  is inserted into outer assembly first portion  240  from the proximal end. As best seen in  FIG. 51 , cylindrical portion  368  of member  364  is rotatably positioned within first channel  260  of first bearing portion  248  ( FIG. 33 ). 
     When assembled, rotary abrader  200 , shown in  FIGS. 52 through 59 , has second outer assembly  290  mounted to first outer assembly  240 , with protrusions  334  and  336  engaging slots  280  and  282  respectively ( FIG. 54 ). Distal end  500  of distal portion  296  of second outer assembly  290  forms a hood (guard) adjacent to abrading element  366 . As best seen in  FIG. 59 , lateral alignment between the distal portions of first outer assembly  240  and second outer assembly  290  is established by surfaces  330  of second bearing portion  298  and channel  264  of first bearing portion  248 . First channel  264  of first bearing portion  248  and first channel  308  of second bearing portion  298  together form a cylindrical bore in which cylindrical portion  368  of inner assembly  350  is rotatably positioned. As best seen in  FIGS. 55 and 58 , flange  294  of proximal portion  292  of second outer assembly  290  is constrained by retainer  390  so as to apply via spring washer  400  a proximal axial force to distal portion  296  of second outer assembly  290 . Retainer  390  is removably attached to distal end  245  of hub  242  by engagement of protrusions  400  of retainer  390  ( FIGS. 45 through 47 ) in second and third channels  247  and  249  of distal end  245  ( FIGS. 30 through 32 ). As best seen in  FIG. 55 , axis  502  of inner assembly  350  is not parallel to axis  504  of the outer assembly, but is offset by angle  506 . As best seen in  FIG. 57 , the clearance  508  between abrading element  366  and inner surface  300  of distal end  500  of second outer assembly  290  is equal to the difference between the inside diameter  510  of the outer assembly and the diameter  512  of abrading element  366  plus the distance  514  between the axis  516  of abrading element  366  and axis  504  of the outer assembly at the distal end. 
     The aspiration of debris from the site follows two paths. The first path  520  aspirates material from the region surrounding abrading element  366 , through passage  312  in second bearing portion  298 , and through aspiration port  311  to inner lumen  378  of tubular portion  362  of inner assembly  350 . The second path  522  aspirates material from the region surrounding the distal end of abrader  200 , through elongated slots  304 , via aspiration port  311  to inner lumen  378  of tubular portion  362  of inner assembly  350 . 
     Rotary abrader  200  is easily disassembled for cleaning. Because the distal bearing is split, the diameter of the mating surface on the inner member can be smaller than that of the proximal portion of the inner member or the abrading element. This allows the burr to be offset a greater distance than is possible in the previous embodiment. This greater offset provides enhanced visibility for the surgeon, and allows the use of a larger abrading element relative to the outer tube size while maintaining required minimum clearance between burr head and the hood. 
     In a third embodiment of the present invention, the elongated tubular portions of the inner and outer assemblies are concentric, rather than offset, but the burr head is enlarged. The hood is positioned at an angle and enlarged so that the required clearance can be maintained between the enlarged burr head and the hood. As in the previous embodiments, the larger diameter burr is preferably configured so that its cutting edge is aligned with the outer surface of the outer tube to provide a “flush cut.” 
     Referring now to  FIGS. 60 through 64 , showing the outer tubular portion (outer tube)  552  of the outer assembly  550  of a rotary abrader formed in accordance with the third embodiment of the invention, outer tube  552  has a proximal end  554  and a distal end  556 . Tube  552  has a lumen  553  of diameter  560  and an outer diameter  562 . Distal end  56  has a first portion  564  of length  556  and a second portion  568  of length  570 . Three elongated aspiration slots  573 , at 120° apart, extend from the lumen  553  to tube outer surface  555 . Beveled surfaces  575  and  577  together with outer surface  555  define a flared hood (or guard)  579 . 
     Referring now to  FIGS. 65 through 67 , inner tube assembly  602  of a rotary abrader  660  constructed in accordance with the principles of the invention has an elongated tubular portion  604  with a proximal end  606  and a distal end  608 . Distal end  608  has affixed thereto portion  610  having a proximal portion  612  of diameter  614  and a distal portion  616  forming an abrading element (or burr head) of diameter  617 . Near distal end  608  of tubular portion  604  aspiration port  611  extends from lumen  612  to outer surface  613 . A second aspiration port  619  is provided proximally on the inner tube  604 , aligned with the three elongated aspiration slots  573  in the outer tube  552 . Another variation is to have two aspiration ports  611  near the burr tip, 180° apart. Shrink tubing  618  is provided along the entire longitudinal length of the inner tube  604  and serves as a bearing between inner tube  604  and outer tube  552 . 
     Referring now to  FIGS. 68 through 69 , showing inner hub assembly  622  as connected to abrader  660 . Assembly  622  includes inner drive hub  624 , spring  625 , spring retainer  626  and thrust washer  627 . Lateral passage  623  intersects bore  121 . 
     Referring to  FIGS. 70 and 71 , rotary abrader  660 , constructed in accordance with the principles of this invention, is assembled in the following manner. Tubular portion  604  of inner tube assembly  602  is inserted into distal end  556  of outer tube  552  of outer assembly  550 . Hub assembly  622  of inner assembly  600  is inserted into proximal end  596  of outer assembly  550  such that proximal end  606  of tubular portion  604  of inner tube assembly  602  is positioned within inner hub  624  and slots  616  of tube  604  align axially and angularly with slots  628  of inner hub  624 . The axis of the inner assembly  602  is coplanar with the axis of the outer assembly  550  while the radius of the hood  579  is enlarged as compared to the radius of the outer assembly  550  in order to accommodate a larger burr  616  while still maintaining the required minimum clearance and not obstructing the surgeon&#39;s view. 
     Debris is aspirated from the site along two paths which join in lumen  612  of inner tube  604 , from which the debris is removed via opening  623  in inner hub  624  (see  FIG. 26 ) by suction supplied by the handpiece. Debris in close proximity to burr head  616  follows a path along the hood  579  to aspiration port  611  in inner tube  604 . Debris in the liquid in proximity to distal end  556  of outer tube  552  is aspirated via slots  573  to aspiration port  611  in inner tube  604 . 
     Because the hood is enlarged as compared to the diameter of the outer assembly, the diameter of the abrading element can be increased and still maintain the minimum clearance required between the element and the hood. This allows the use of a larger abrading element for a given outer tube diameter than would be possible if the hood maintained the same radius. This larger diameter burr allows more rapid removal of bone than the smaller diameter burr of a conventional burr having the same outer tube diameter.