Abstract:
Bone anchors and bone anchor implantation devices can be used to maintain or improve urinary continence by suspending or stabilizing the bladder neck of a patient. The bone anchors have a generally cone-shaped head with two or more cutting edges which reduce the amount of force required to implant the bone anchor into bone.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 60/072,639 filed Jan. 27, 1998. The entirety of this priority document is hereby incorporated by reference. This application is a continuation of U.S. Ser. No. 09/238,663, filed Jan. 26, 1999, now U.S. Pat. No. 6,096,041, the disclosure of which is incorporated herein by reference in its entirety. 

   TECHNICAL FIELD 
   This invention relates to various bone anchor designs for use in a bone anchor implantation device. 
   BACKGROUND INFORMATION 
   Urinary incontinence, the inability to control urination from the bladder, is a widespread problem that affects people of all ages. Urinary incontinence is more prevalent in women than in men. Urinary incontinence in women is typically causes by intrinsic spincter deficiency (I SD), a condition in which the valve of the urethral spincter do not properly coapt, or by hypermobillity, a condition in which the muscles around the bladder relax, causing the bladder neck and proximal urethra to rotate and descend in response to increases in intraabdominal pressure. Hypermobilty may be the result of pregnancy or other conditions which weaken the muscles. Urinary incontinence in men can be caused by post radical prostatectomy, which destroys the valves of the urethral spincter. Urinary incontinence can also be caused by birth defects, disease injury, aging and urinary tract infection. 
   Numerous approaches for treating urinary incontinence are available. One treatment is a surgical operation to return the bladder and proximal urethra to their normal anatomical positions by elevating them in order to reduce intraabdominal pressure. There are also noninvasive procedures for stabilizing and/or slightly compressing the urethra so as to prevent the leakage of urine. For example, a stabilizing or compressive force may be applied by sutures passing through the soft tissue surrounding the urethra or, alternatively, may be applied by means of a sling suspended by sutures. In some procedures bone anchors are inserted in the pubic bone or symphysis pubis in order to anchor the suture to the bone. Often an anchor receiving hole is drilled into the bone prior to inserting the anchor. Other bone anchor devices incorporate a drill for predrilling an opening in the bone thus eliminate the need for a predrilling step. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a bone anchor implantation device for driving a bone anchor into the bone by the application of a retrograde force. More particularly, the present invention relates to improved bone anchors. Bone anchor configurations according to the invention reduce the amount of force required to secure the bone anchor into a bone anchor implantation site. 
   Bone anchors are often attached to bones in order to provide support for a “sling” useful in improving or maintaining a patient&#39;s urinary incontinence. In one procedure, a suture carrying anchor is driven through the vaginal wall and into the posterior portion of the pubic bone or symphysis pubic, and the suture(s) attached to the bone anchor(s) extend through the vaginal wall and may be attached to the endopelvic fascia, the vaginal wall, a sling, or other material to stabilize and/or slightly compress the urethra thereby improving the patient&#39;s urinary incontinence. The present invention effectively addresses concerns in affixing an anchor to bone or tissue. 
   The present invention is directed to a bone anchor which implants into the bone and supports a suture. The bone anchor, which releasable engages to a bone anchor implantation device, comprises a generally cone-shaped head with at least two, preferably three, cutting edges which come together to form a pointed tip at the end of the anchor that first contacts the target site. The cutting edges on the generally cone-shaped head can be defined by flat planar surfaces or outward curved surfaces. These bone anchor configurations reduce the amount of force and pressure that a user (i.e. a surgeon) of a bone anchor implantation device must apply to implant the bone anchor into the bone. 
   In general, one aspect of the present invention involves a bone anchor for use with a bone anchor implantation device. The bone anchor comprises a generally cone-shaped head which has a wide end, a narrow end, and at least two cutting edges. At the narrow end of the generally cone-shaped head, the cutting edges come together to form a pointed tip. The wide end of the head can releasably engage to a bone anchor implantation device. 
   Embodiments of this aspect of the invention can include the following features. The cutting edges can be defined by flat surfaces or curved surfaces. The cutting edges can be formed in various ways such as by cutting or scalloping the surface of the bone anchor. Also, the cutting edges can be sharp edges. In a preferred embodiment, there are three cutting edges which come together to form the pointed tip at the narrow end. 
   In an alternative embodiment, the bone anchor further comprises a collar member for retaining the bone anchor in place. The collar member is coupled to the wide end of the generally cone-shaped head. The bone anchor can also comprise a shaft with an eyelet for receiving a suture. The shaft is coupled to the wide end of the generally cone-shaped head. 
   In general, another aspect of the invention relates to a bone anchor implantation device comprising a handle having a proximal and a distal end, a hooked-shaped shaft, a bone anchor mount attached at the distal end of the shaft and a bone anchor releasably engaged to the bone anchor mount. The bone anchor comprises a generally cone-shaped head with a wide end which engages to the bone anchor mount, a narrow end, and at least two cutting edges which come together to form a pointed tip at the narrow end. The bone anchor can have various configurations, such as cutting edges defined by flat or curved surfaces. The bone anchor is inserted into a bone by applying a retrograde force to the bone anchor implantation device. 
   The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 
       FIG. 1  is a side view of a bone anchor according to the invention with curved surfaces defining the cutting edges. 
       FIG. 2  is another view of the bone anchor according to the invention of  FIG. 1 . 
       FIG. 3  is a side view of a bone anchor according to the invention with flat cutting edges. 
       FIG. 4  is another view of the bone anchor of  FIG. 3 . 
       FIG. 5  is a side view of a bone anchor according to the invention having a generally cone-shaped head with cutting edges and a collar member. 
       FIG. 6  is a side view of a bone anchor implantation device with a hook-shaped shaft. 
   

   DESCRIPTION 
   A bone anchor according to the invention has a generally cone-shaped head with a wide end, a narrow end, and at least two cutting edges which come together to form a pointed tip at the narrow end of the head. The bone anchor is utilized in a bone anchor implantation device. The various bone anchor configurations of the present invention reduce the amount of force required to drive the bone anchor into the bone. 
   Representative bone anchors are illustrated in  FIGS. 1–4 . The bone anchors  22  comprise a generally cone-shaped head  14  which is able to pierce and securely engage the bone, and the bone anchors  22  generally require less force than conventional bone anchors to drive them into bone. The generally cone-shaped head  14  has a wide end  18 , a narrow end  19 , and at least two cutting edges  26  which come together to form a pointed tip  24  at the narrow end  19 . The generally cone-shaped head  14  is coupled to a shaft portion  16 . The shaft portion  16  of the bone anchor  22 , which is generally cylindrical in shape, can be releasably engaged to a bone anchor implantation device  28 . Only a portion of the device  28  is shown in  FIGS. 1–5 . 
   The generally cone-shaped head  14  of the bone anchor  22  is located at an end of the shaft portion  16  opposite the end which attaches to the bone anchor implantation device  28 . The apex of the generally cone-shaped head is a point  24  which is suitable for piercing and being driven into bone. The diameter of the generally cone-shaped head  14  increases in the longitudinal direction from the point  24  towards the shaft portion  16 . 
   As shown if  FIGS. 1–4 , the generally cone-shaped head  14  of the bone anchor  22  has at least two, preferably three or more, cutting edges  26 . The cutting edges  26  can extend the length of the generally cone-shaped head  14 , and they come together at the point  24 . Preferably, the cutting edges are sharp. The cutting edges reduce the amount of force that is necessary to implant the bone anchor into the bone. 
   In some embodiments, such as that shown in  FIGS. 1 and 2 , the cutting edges  26  on the bone anchor  22  are defined by curved or scalloped surfaces  25  formed in the anchor  22 . These surfaces  25  are cut into the generally cone-shaped head  14 . These arcuate surfaces  25  form and define the cutting edges  26  and they generally extend from the wide end  18  of the generally cone-shaped head  14  to the narrow end  19  of the generally cone-shaped head  14 . 
   In other embodiments such as that shown in  FIGS. 3 and 4 , the cutting edges  26  on the bone anchor  22  are defined by flat surfaces  23  formed in the anchor  22 . The flat surfaces  23  are cut into the generally cone-shaped head  14 . The flat surfaces  23  extend generally from the wide end  18  to the narrow end  19  of the generally cone-shaped head  14 . 
   Preferably, the generally cone-shaped head  14  is formed integrally with the shaft portion  16  of the bone anchor  22 . Alternatively, the generally cone-shaped head  14  and the shaft portion  16  may initially be formed separately and then subsequently attached to one another. 
   Any known materials suitable for orthopedic anchor devices may be employed to construct the bone anchor  22  of the present invention. Preferably, the bone anchor  22  is formed from a metallic material possessing sufficient strength to penetrate the bone. Such materials include titanium 316 LVM stainless steel, CoCrMo alloy, Nitinol alloy, or other suitable materials. In a preferred embodiment, the bone anchor is formed from titanium. 
   Another embodiment of a bone anchor according to the invention is illustrated in  FIG. 5 . The bone anchor  22  of  FIG. 5  comprises a generally cone-shaped head  14  which is able to pierce and securely engage bone. The generally cone-shaped head  14  is coupled to a shaft portion  16  with an oval eyelet  38  therethrough for receiving and holding one or more suture strands. To retain the generally cone-shaped head  14  within the bone, the bone anchor  22  further comprises a collar member  20 . The collar member  20  is used for retaining the bone anchor  22  in place, once it has been driven into the bone, by lodging within the bone in a manner to resist removal of the bone anchor  22 . 
   The shaft portion  16  of the bone anchor  22  is generally cylindrical in shape and has the eyelet  38 , or bore, formed radially therethrough proximate one of its ends. The eyelet  38  may be oval, round, or other suitable shape and is of a sufficient size to permit one or more suture strands to pass therethrough. The circumference of each outer end of the eyelet  38  is chamfered or grounded to provide a bevel portion  32 . It should be appreciated that the bevel portion  32  provides a generally smooth surface for contacting suture strand which has been passed through the eyelet  38 . The eyelet  38  is located on the shaft portion  16  of the bone anchor  22  such that the transverse axis of the eyelet  38  intersects the longitudinal axis of the bone anchor  22 . 
   The generally cone-shaped head  14  of the bone anchor  22  is located at an end of the shaft portion  16  opposite the end having the eyelet  38 . The apex of the generally cone-shaped head  14  is a point  24  which is suitable for piercing and being driven into bone. The diameter of the generally cone-shaped head  14  increases along a longitudinal direction from the point  24  towards the eyelet  38 . 
   As discussed above with reference to  FIGS. 1–4 , the bone anchor  22  has at least two, preferably three or more cutting edges  26 . The cutting edges  26  are preferably sharp. In the disclosed embodiment in  FIG. 5 , the cutting edges  26  are defined by curved or scalloped surfaces. 
   The collar member  20  is rotatably fitted over the shaft portion  16  to form the assembled bone anchor  22  as shown in  FIG. 5 . While there is no need to permanently secure the collar member  20  to the generally cone-shaped head  14 , the collar member  20  may nevertheless be securely attached to the generally cone-shaped head  14 . It will be appreciated, however, that by permitting the generally cone-shaped head  14  to rotate freely with respect to collar member  20 , a suture strand can be rotated by the surgeon after implantation to a position where the forces acting on the suture strand by the bone anchor  22  are more evenly distributed around the region of the shaft portion  16  adjacent to the eyelet  38 . 
   In addition, it should also be appreciated that the two-piece construction of the bone anchor affords machining advantages over a single-piece bone anchor. That is, it is easier to machine each of these two components (i.e., the collar member  20  and the bone anchor  22 , where the bone anchor  22  includes the head  14  and the shaft portion  16 ) separately and subsequently to assemble them together, as opposed to machining the same basic structural features from a single piece of material. 
   Another aspect of the invention is a bone anchor implantation device comprising a hooked-shaped shaft with a bone anchor mount adapted to releasably engage at the distal end of the shaft a bone anchor with at least two cutting edges. The bone anchor mount generally points toward the handle, such that the user can drive the bone anchor into the bone by simply pulling back on the handle and using the patient&#39;s body weight to provide an opposing force. Preferably, the longitudinal axis of the bone anchor mount is aligned with the longitudinal axis of the handle. 
   A representative bone anchor implantation device having a hooked elongated member and a bone anchor with cutting edges are shown in  FIG. 6 . The bone anchor implantation device  210  has a handle  212  having a proximal end  214  and a distal end  216 . The handle  212  may be made of a variety of materials, such as plastic or metal. The elongated member  220  may be made of a variety of materials such as stainless steel, engineering plastics, fiber-bearing components, or other materials. Preferably, the elongated member  220  is made of stainless steel. 
   In the embodiment of the bone anchor implantation device  210  shown in  FIG. 6 , the elongated member  220  comprises a straight proximal section  222 , a first generally curved section  224  distal to the straight proximal section, a second generally curved section  226  distal to the first curved section, a third generally curved section  228  distal to the second curved section, and a fourth generally curved section  230  distal to the third curved section. However, one of skilled in the art would appreciate that the elongated member  220  could also comprise a series of straight segments angled relative to one another to form a hook. 
   The straight proximal section  222  of the elongated member  220  has an annular shoulder  232  which abuts the distal end  216  of the handle. The straight proximal section  222  passes through a lumen (not shown) extending through the handle. The proximal end of the straight proximal section  222  has a threaded bore which is adapted to receive a screw  236  which secures the elongated member  220  to the handle. 
   The handle  212  defines an axis at the proximal end of the anchor implantation device  210 , and then moving distally from the handle  212  the elongated member  220  first curves away from the axis of the handle and then back toward the axis of the handle  212 . The distal end of the elongated member  220  preferably is located in the vicinity of the axis of the handle  212 . In some preferred embodiments, the elongated member  220  at the distal end can be generally perpendicular to the axis of the handle or can actually be curving back toward the handle  212 . 
   A bone anchor mount  238  for releasably engaging a bone anchor  248  is attached to the distal end  240  of the fourth curved section  230  of the elongated member  220 . Preferably, the bone anchor mount  238  is oriented at an angle of approximately 90° relative to the distal end  240  of the fourth curved section  230 , as illustrated in  FIG. 6 . 
   A variety of bone anchors can be releasably engaged to the bone anchor implantation device. In accordance with the invention, the bone anchor used with the device  210  is a bone anchor  248  having a generally cone-shaped head and cutting edges as described above with respect to  FIGS. 1–5 . 
   The bone anchor mount  238  is oriented so that the bone anchor  248  is pointed in the general direction of the handle  212 . In one embodiment, the axis of the bone anchor  248  is generally aligned with the axis of the handle  212 , with the bone anchor pointed toward the handle  212 . 
   The bone anchor mount  238  may be fabricated from the same materials as the elongated member  220  and may be attached to the elongated member  220  by a variety of methods such as brazing. 
   Although this invention has been described in terms of certain preferred embodiments, other embodiments which will be apparent to those of ordinary skill in the art in view of the disclosure herein are also within the scope of this invention. Accordingly, the scope of the invention is intended to be defined only by reference to the appended claims.