Abstract:
A suture anchor and method is disclosed in which a pair of anchor elements connected by a flexible cord are passed through a piece of soft tissue and embedded deeply into a bone. The cord holds the soft tissue securely to the bone and the anchors are embedded into more dense bone away from the location where the soft tissue contacts the bone.

Description:
BACKGROUND 
     This application relates to bone anchors and more specifically to bone anchors adapted for fixation within soft bone. 
     A common surgical procedure is the attachment of soft tissue to bone. This is typically achieved by embedding a bone screw or anchor into the bone adjacent the soft tissue and then approximating the soft tissue to the bone via a length of suture attached to the anchor and passed through the bone. In some procedures the anchor itself is attached to the soft tissue and embedded into the bone to affix the soft tissue to the bone. 
     Such procedures rely upon achieving strong fixation between the anchor and the bone. However, in many instances the quality of the bone is insufficient for adequate fixation of the anchor. For, instance bone mineral density decreases with age and many older patients lack sufficient bone quality for a typical procedure. Additional anchors can be employed, such as the use of a second row of anchors in a rotator cuff repair, but the quality of the bone under the second, lateral, row is often lower still. Larger diameter anchors are also employed to improve fixation but that adds additional trauma to the procedure. These problems are of particular concern in rotator cuff repairs where bone quality at the site of the cuff reattachment is all too often poor but the stresses on the rotator cuff require a strong fixation to ensure proper healing. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes these and other limitations of the prior art in a simple and elegant design. 
     A method according to the present invention provides for attaching a piece of soft tissue to a bone. The method comprises the steps of: embedding a first anchor into the bone adjacent the soft tissue, the first anchor comprising a first distal end and a trailing elongated first flexible body, the first distal end being passed into the bone along a first pathway having a first entrance into the bone adjacent the soft tissue, a first section of the first pathway adjacent the first entrance comprising cancellous bone of a first density and a second section of the first pathway being deeper into the bone from its first section and having cancellous bone of a second density higher than the first density, the first distal end being positioned in the second section; and holding the soft tissue to the bone adjacent the first entrance via affixation of the soft tissue to the first flexible body. 
     The method preferably further comprises embedding a second anchor into the bone adjacent the soft tissue, the second anchor comprising a second distal end and a trailing elongated second flexible body, the second distal end being passed into the bone along a second pathway having a second entrance into the bone adjacent the soft tissue, a first section of the second pathway adjacent the second entrance comprising cancellous bone of a third density and a second section of the second pathway being deeper into the bone from its first section and having cancellous bone of a fourth density higher than the third density, the second distal end being positioned in the second section of the second pathway; and holding the soft tissue to the bone adjacent the second entrance via affixation of the soft tissue to the second flexible body. 
     Preferably, the first flexible body and second flexible body are interconnected prior to being embedded into the bone. 
     In one aspect of the invention, fixation of the first flexible body into the bone is enhanced with a plurality of barbs extending from the first flexible body and engaging the bone. 
     Preferably, the first flexible body is pushed into the bone via a rigid introducer connected to the first distal end, the introducer then being removed after the step of embedding the first anchor into the bone. The first distal end preferably comprises a rigid tip having a proximally facing surface. The introducer is then pushed against the proximally facing surface to push the first flexible body into the bone. Preferably, that portion of the introducer inserted into the bone has a maximum size of about 15 gauge. In an aspect of the invention, a plurality of barbs extend from the first flexible body and are held in a retracted position against the first flexible body by the introducer. 
     Preferably, the first anchor is driven into the bone without first preparing a pilot hole for it. 
     Preferably, the first path curves. In one aspect of the invention, the soft tissue is a rotator cuff tendon and the bone is a humeral head. In such event, the first path preferably curves medially. Preferably, the first path extends at least half the width of the humeral head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a suture anchor according to the present invention; 
         FIG. 2  is a perspective view of an inserter for use with the suture anchor of  FIG. 1 ; 
         FIG. 3  is a side elevation view of the tip of the inserter of  FIG. 2 ; 
         FIG. 4  is a side elevation view of tip of the inserter of  FIG. 2  with the suture anchor of  FIG. 1  loaded therein; 
         FIG. 5  is a perspective view of an alternative inserter according to the present invention for use with the suture anchor of  FIG. 1 ; 
         FIG. 6  is a side elevation view of a humeral head showing the inserter of FIG.  5  in position for use; 
         FIG. 7  is a side elevation view of the humeral head of  FIG. 6  in cross-section; and 
         FIG. 8  is a side elevation view of an alternative embodiment of an anchor element of a suture anchor according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a suture anchor  10  according to the present invention. It comprises a first anchor element  12  and second anchor element  14  interconnected by a flexible cord  16 . Each anchor member  12 ,  14  comprises a distal conical tip  18  and a proximal tubular body  20  swaged onto the cord  16 . A proximally facing annular flange  22  interfaces between the tip  18  and the body  20 . A plurality of flexible barbs  24  can optionally be disposed on the cord  16  adjacent the anchor elements  12  and  14  with a central section  25  being free of barbs. 
     Turning also now to  FIGS. 2 and 3 , an inserter  26  comprises an elongated shaft  28  having a proximal handle  30  and narrowing to a distal tip  32 . A distally facing socket  34  is sized to receive the body  20  of one of the anchor elements  12 ,  14 . An axial slotted cannulation  36  runs from the tip  32  up the shaft  28  to accommodate and allow the lateral release of the cord  16 . A distal end  38  of the inserter, surrounding the socket  34 , is adapted to abut the flange  22  on the anchor elements  12 ,  14 , as best seen in  FIG. 4 . The anchor element  12  is shown partially pulled out of the socket in  FIG. 4  to more clearly show the flange  22  and distal end  38 . In use they will abut one another. The barbs  24  are held in a retracted position within the cannulation  36 . 
       FIG. 5  shows an alternative embodiment of an inserter  40  having first and second parallel curved shafts  42  and  44 , and a handle  45 , with the first anchor element  12  loaded into a tip  46  of the first shaft  42  and the second anchor element  14  loaded into a tip  48  of the second shaft  44 . 
       FIGS. 6 and 7  illustrate a humeral head  50  and rotator cuff tendon  52 . To effect a repair, the tendon  52  is approximated to the desired location with a tendon grasper (not shown). With the tendon  52  in place, the, the pre-loaded inserter  40  is placed against the tendon and its angle adjusted to achieve a proper trajectory into the humeral head  50 . The inserter  40  is then hammered to drive the shafts  42  and  44  into the humeral head  50  thereby driving the anchor elements  12  and  14  therein until the central section  25  of the cord  16  snugly holds the tendon  52  to the humeral head  50 . The anchor elements  12  and  14  travel in from the tuberosity adjacent the tendon  52  and travel medially along a curved path but stop prior to breeching the articular surface and lodge deeply into the dense interior bone. The desired depth and angle can be determined via pre-operative X-rays or other assessment of the geometry of the humeral head  50 . Depth markings, stops or other techniques can be employed to ensure proper depth. Preferably, the inserter  40  can be provided to a surgeon in various lengths and perhaps levels of curvature (including straight) so that the surgeon can choose based upon the geometry of the patient&#39;s humeral head  50 . After the anchor elements  12  and  14  are inserted to the desired location, the inserter  40  is removed leaving the suture anchor  10  in place. 
       FIG. 7  shows a typical bone density distribution in an osteoporotic bone, illustrating the advantages of the present invention. The bone density in the head  50  near tendon  52  is significantly less than in a more medial bone area  54 . A typical prior suture anchor would be placed into the less dense bone just below the tendon  52  or just lateral of its edge, also of low bone density. In contrast, the suture anchor  10  travels deeply and medially into the humeral head into the more dense bone area  54 . 
     The anchor elements  12  and  14  can be smaller than a traditional suture anchor which would be employed to hold the same tendon  52  due to the enhanced holding from their depth in the tissue and the superior bone into which they are placed. For a rotator cuff repair they may be sized to fit with an introducer the equivalent of a 15 to 18 gauge needle. The anchor elements  12  and  14  can be formed of materials suitable for suture anchors such as stainless steel, titanium, PEEK, Polylactic Acid (PLA), Polylactic/polyglycolic Acid (PLGA), and mixtures with TriCalcium Phosphate (TCP) along with other materials as will be appreciated by those of skill in the art.  FIG. 8  shows an alternative embodiment of an anchor element  56  having a body  58  and sharp tip  60  with multiple barbs  62  to enhance the holding of the anchor element  56  into bone. Alternatively, an anchor element could be detachable from the cord  16 , such as being part of an inserter, or be quickly absorbable into the tissue, in either event to not add appreciable to the fixation but rather leave that function to the cord  16 . 
     The cord  16  can be standard suture, or barbed suture, of either the absorbent or non-absorbent varieties. ORTHOCORD suture available from DePuy Mitek of Raynham, Mass. could be employed. The cord  16  could also be a metal wire, particularly a braided wire preferably with barbs. Alternatively, or additionally, the suture or wire could be treated or coated to enhance its coefficient of friction with bone. 
     To prevent cheese-wiring of the cord  16  into the bone it could be made broader where it exits the humeral head  50 , such as by being of larger diameter or wider and flatter such as a ribbon. Grommets (not shown) could be received on the inserter shaft  28  and embedded into the humeral head  50  thereby where the cord  16  exits the humeral head so that the cord  16  would rub against the grommets rather than the bone at this point. Rather than the cord  16  affixing itself to the tendon  52  or other tissue to be attached, it could have a trailing suture, either attached as provided or through an eyelet or other suture attachment on the cord  16 , which is used to connect to the tissue. 
     The invention preferably includes two or more anchor elements  12  and  14  interconnected by a cord  16 . However, it is envisioned that it could comprise a single anchor element with a cord trailing therefrom. The cord could be connected, such as after the anchor element is implanted, with another cord from another single anchor element, suture anchor or to a different type of suture anchor or to a suture from a different suture anchor. The cord, could be suture and it could be passed up from the implanted anchor element, out through the tendon  52  and over to a self-locking suture anchor (such as disclosed in U.S. Pat. No. 6,770,073) implanted at a different location, perhaps lateral of the tendon  52 , and then tensioned and locked to the self-locking anchor. One such self-locking anchor is the VERSALOK suture anchor available from DePuy Mitek of Raynham, Mass. While described most fully for a rotator cuff repair it is envisioned that the present invention would be useful for many other soft tissue repair procedures, especially where bone quality at the site of repair is degraded. It may also have utility for fracture or other bone repairs. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. For instance, rather than having a fixed length cord  16  spanning two suture anchors  12  and  14 , the cord  16  could be of adjustable length or be separated into portions which could then be tied or otherwise connected together or to other suture anchors etc. Rather than employ barbs  24  and or even the anchor elements  12  and  14  fixation could come from a portion of suture or attachment that expands in contact with bodily fluid. The anchor elements  12  and  14  can comprise any type of body that an inserter can push against for delivery into the bone, e.g., an overhand knot, a folded suture, thermally reformed suture tips, etc.