Abstract:
A suture anchor comprises a shell and an anchor member. The shell comprises a body having a distal end, a proximal end and sidewalls therebetween defining an axial cannulation therethrough. The anchor member comprises a body having a distal end and a proximal end which is sized to fit within the cannulation. The sidewalls define a lateral cut-out such that with the anchor member received within the cannulation a first lateral portion of the anchor member is exposed laterally and a second, laterally opposite, lateral portion of the anchor member is enclosed by the sidewalls. A friction enhancement on the first lateral portion frictionally engages a bone surface when the suture anchor is disposed within a bone tunnel defined by the bone surface. Suture is trapped between the shell and the anchor and also between the anchor and the bone surface.

Description:
BACKGROUND 
       [0001]    This application relates to suture anchors and more particularly to knotless suture anchors. 
         [0002]    Knotless suture anchors allow fixation of suture to bone without requiring a surgeon to tie a knot to fix the suture with respect to the anchor. Certain knotless anchors capture suture in a notch at their distal end and are then inserted into a bone tunnel trapping the suture between the anchor and the bone to effect fixation. In soft bone the suture may cut into the bone over time, thereby loosening the tension in the suture. Certain other designs capture the suture between interlocking parts which also expand outwardly to limit their retraction from a bone tunnel. These anchors have many benefits but do not typically achieve the same level of fixation into bone as a regular threaded anchor. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention overcomes these and other limitations of the prior art in a simple and elegant design. 
         [0004]    A suture anchor according to the present invention comprises a shell and an anchor member. The shell comprises a body having a distal end, a proximal end and sidewalls therebetween defining an axial cannulation therethrough. The anchor member comprises a body having a distal end and a proximal end sized to fit within the cannulation. The sidewalls define a lateral cut-out such that with the anchor member received within the cannulation a first lateral portion of the anchor member is exposed laterally and a second, laterally opposite, lateral portion of the anchor member is enclosed by the sidewalls. A friction enhancement on the first lateral portion is adapted to frictionally engage a bone surface when the suture anchor is disposed within a bone tunnel defined by the bone surface. 
         [0005]    Preferably, the friction enhancement comprises exterior threading about the anchor member body. Also preferably, complimentary internal threading is provided on an interior surface of the sidewall engaged with the exterior threading of the anchor member body. 
         [0006]    Preferably, the cut-out extends to the shell proximal end. Preferably, the shell distal end completely encircles the anchor member. 
         [0007]    Preferably, a distal portion of the anchor member is smooth and free of the friction enhancement, thus easing its entry and alignment into the bone tunnel. 
         [0008]    Preferably, one or more sutures are locked between the sidewall and the anchor member. An axially extending suture receiving recess can be provided along the sidewall adjacent the anchor member second lateral portion configured to keep the suture positioned therein despite rotation of the anchor member relative to the shell. Preferably, the suture extends proximally out of the shell over its proximal end so that the shell can act to protect the bone forming the bone tunnel from being abraded by the suture. 
         [0009]    In one aspect of the invention, a suture is threaded distally down the cannulation between the sidewall and the anchor member, out of the cannulation at the shell distal end and up along the anchor member first lateral portion. 
         [0010]    In another aspect of the invention, a suture threader extends between the anchor member and the sidewalls. The threader comprises an elongated flexible member which extends out of the shell proximal end and terminates in a suture capture configuration. Preferably, the suture capture configuration comprises a suture capture loop. 
         [0011]    A method according to the present invention provides for anchoring a soft tissue to a bone. The method comprises the steps of: threading a suture through the soft tissue; preparing a bone tunnel in the bone; positioning a shell of a suture anchor into the bone tunnel, and engaging an anchor member with the shell. The shell comprises a body having a distal end, a proximal end and sidewalls therebetween defining an axial cannulation therethrough. The anchor member is disposed within the cannulation with the suture extending from the soft tissue between the anchor member and the sidewall and the step of engaging locks the suture between the anchor member and the sidewall. 
         [0012]    Preferably, prior to engaging the anchor member with the shell, the suture extending from the soft tissue is tensioned to a desired extent. 
         [0013]    Preferably, the suture is also locked between the anchor member and the bone in the bone tunnel. 
         [0014]    Preferably, the suture extends out of the bone hole by extending out of the shell over its proximal end toward the tissue whereby the shell thus reduces chafing between the suture and the bone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is an exploded perspective view of a suture anchor according to the present invention; 
           [0016]      FIG. 2  is a side elevation view in cross-section of a bone and soft tissue; 
           [0017]      FIG. 3  is a perspective view of the suture anchor of  FIG. 1  loaded onto a driver tool; 
           [0018]      FIG. 4  is a side elevation view in cross-section bone of  FIG. 2  into which the suture anchor of  FIG. 1  is being initially implanted 
           [0019]      FIG. 5  is a side elevation view in cross-section showing an anchor member of the suture anchor of  FIG. 1  being implanted; 
           [0020]      FIG. 6 . is a side elevation view in cross-section showing the fully implanted suture anchor of  FIG. 1 ; 
           [0021]      FIG. 7A  is an outside perspective view of an alternative embodiment of a shell of a suture anchor according to the present invention; 
           [0022]      FIG. 7B  is an inside perspective view of the shell of  FIG. 7A ; and 
           [0023]      FIG. 8  is a top plan view of the shell of  FIG. 7A  with an anchor member (shown in section) disposed therein. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  illustrates a suture anchor  10  according to the present invention. It comprises a shell  12  and an anchor member  14  for receipt within the shell  12 . The shell  12  comprises a body  16  having a distal end  18  and a proximal end  20  with sidewalls  22  therebetween defining an axial cannulation  24  adapted to receive the anchor member  14 . 
         [0025]    The anchor member  14  comprises an elongated body  26  having a distal end  28  and a proximal end  30  and which is sized to fit within the cannulation  24 . A distal nose  32  of the body  26  has a reduced diameter and a smooth outer surface  34  lacking threading. A chamfer  36  at the distal end  28  eases entry into a bone tunnel (not shown in  FIG. 1 ). A tool engaging recess  38 , for example a hexagonal shape, is provided at the body proximal end  30 . The body proximal end  30  has a slightly larger diameter creating a boss  40  at the smaller distal nose  32 . Bone engaging threads  42  encircle the body  26  at its proximal end  30  and extend to the boss  40 , with a second start of parallel threads  44  at the proximal end  30  for additional holding in harder cortical bone (not shown in  FIG. 1 ). 
         [0026]    The sidewalls  22  at the shell distal end  18  encircle the cannulation  24  and have an internal diameter sized to accommodate the anchor member distal nose  32 . The sidewalls  22  at the shell proximal end  20  have a larger internal diameter sized to accommodate the anchor member body proximal end  30 , thus creating a boss  46  which engages the boss  40  to limit distal movement of the anchor member  14  through the shell  12 . Internal threads  48  on the sidewalls  22  at the proximal end  20  mate with the threads  42  and  44 . The sidewalls  22  do not enclose the cannulation  24  at the proximal end  20  but rather open to form a lateral cut-out  50  exposing one side of the anchor member  14  including the threads  42  and  44 . 
         [0027]    The shell  12  is adapted to receive one or more sutures  52  through the cannulation  24  and between the shell  12  and anchor member  14 . A longitudinal suture path  54  is created by a reduction in the crest height of the internal threads  48  therealong. Suture  52  in the path tends to thus not be moved out of the path  54  by the interaction of the threads  42  and  44  with the threads  48 . 
         [0028]    The crest height, or diameter, of the threads  42  and  44  is larger at the proximal end  30  of the anchor member  14 . A smaller diameter on the distal threads  42  allows a “smaller profile” of the device construct as it enters a bone hole (not shown if  FIG. 1 ). After the shell  12  is advanced into the bone hole, the anchor member  14  is rotated and driven relative to the static shell  12 . The larger proximal threads  42  and  44  force the shell  12  to expand and also compress the suture strands  52  between the two components. 
         [0029]    The suture anchor  10  is formed of a suitable biocompatible material and is preferably provided sterile and packaged within a bacteria-proof enclosure (not shown) such that it is ready for a sterile surgical procedure. Many biodegradable materials have less strength and are more brittle than non-biodegradable materials such as PEEK polymer (polyetheretherketone) or stainless steel. The simple design of the anchor  10 , allows easier use of such biodegradable materials while maintaining structural integrity. 
         [0030]    The novel suture anchors of the present invention may be made from a metallic material, a non-biodegradable polymer, a biodegradable polymer, or a composite of a biodegradable polymer or copolymer and a bioceramic. The term biodegradable as used herein is defined to mean materials that degrade in the body and then are either absorbed into or excreted from the body. The term bioceramic as defined herein is defined to mean ceramic and glass materials that are compatible with body tissue. The bioceramics are preferably biodegradable. 
         [0031]    The metallic materials that can be used to manufacture the anchors of the present invention include stainless steel, titanium, alloys of nickel and titanium, or other biocompatible metallic materials. 
         [0032]    The non-biodegradable materials that can be used to manufacture the anchors of the present invention include polyethylene, polypropylene, PEEK, or other biocompatible non-absorbable polymers. 
         [0033]    The biodegradable polymers that can be used to manufacture the anchors used in the present invention include biodegradable polymers selected from the group consisting of aliphatic polyesters, polyorthoesters, polyanhydrides, polycarbonates, polyurethanes, polyamides and polyalkylene oxides. Preferably, the biodegradable polymers are aliphatic polyester polymers and copolymers, and blends thereof. The aliphatic polyesters are typically synthesized in a ring opening polymerization. Suitable monomers include but are not limited to lactic acid, lactide (including L-, D-, meso and D,L mixtures), glycolic acid, glycolide, .epsilon.-caprolactone, p-dioxanone (1,4-dioxan-2-one), trimethylene carbonate (1,3-dioxan-2-one), .delta.-valerolactone, and combinations thereof 
         [0034]    The bioceramics that can be used in the composite anchors of the present invention include ceramics comprising mono-, di-, tri-, .alpha.-tri-, .beta.-tri-, and tetra-calcium phosphate, hydroxyapatite, calcium sulfates, calcium oxides, calcium carbonates, magnesium calcium phosphates. It is particularly preferred to use a .beta.-tritricalcium phosphate. In addition to bioceramics, bioglasses may also be used in the composite screws. The bioglasses may include phosphate glasses and bioglasses. 
         [0035]    Suitable biocompatible synthetic polymers can include polymers selected from the group consisting of aliphatic polyesters, poly(amino acids), copoly(ether-esters), polyalkylene oxalates, polyamides, tyrosine derived polycarbonates, poly(iminocarbonates), polyorthoesters, polyoxaesters, polyamidoesters, polyoxaesters containing amine groups, poly(anhydrides), polyphosphazenes, polyurethanes, poly(ether urethanes), poly(ester urethanes), polypropylene fumarate), poly(hydroxyalkanoate) and blends thereof. 
         [0036]    For the purpose of this invention aliphatic polyesters include, but are not limited to, homopolymers and copolymers of lactide (which includes lactic acid, D-,L- and meso lactide); glycolide (including glycolic acid); .epsilon.-caprolactone; p-dioxanone (1,4-dioxan-2-one); trimethylene carbonate (1,3-dioxan-2-one); alkyl derivatives of trimethylene carbonate; .delta.-valerolactone; .beta.-butyrolactone; .gamma.-butyrolactone; .epsilon.-decalactone; hydroxybutyrate; hydroxyvalerate; 1,4-dioxepan-2-one (including its dimer 1,5,8,12-tetraoxacyclotetradecane-7,14-dione); 1,5-dioxepan-2-one; 6,6-dimethyl-1,4-dioxan-2-one; 2,5-diketomorpholine; pivalolactone; .alpha.,.alpha. diethylpropiolactone; ethylene carbonate; ethylene oxalate; 3-methyl-1,4-dioxane-2,5-dione; 3,3-diethyl-1,4-dioxan-2,5-dione-; 6,6-dimethyl-dioxepan-2-one; 6,8-dioxabicycloctane-7-one and polymer blends thereof. Additional exemplary polymer or polymer blends include, by non-limiting example, a polydioxanone, a polyhydroxybutyrate-co-hydrox-yvalerate, polyorthocarbonate, a polyaminocarbonate, and a polytrimethylene carbonate. Aliphatic polyesters used in the present invention can be homopolymers or copolymers (random, block, segmented, tapered blocks, graft, triblock, etc.) having a linear, branched or star structure. Poly(iminocarbonates), for the purpose of this invention, are understood to include those polymers as described by Kemnitzer and Kohn, in the Handbook of Biodegradable Polymers, edited by Domb, et. al., Hardwood Academic Press, pp. 251-272 (1997). Copoly(ether-esters), for the purpose of this invention, are understood to include those copolyester-ethers as described in the Journal of Biomaterials Research, Vol. 22, pages 993-1009, 1988 by Cohn and Younes, and in Polymer Preprints (ACS Division of Polymer Chemistry), Vol. 30(1), page 498, 1989 by Cohn (e.g., PEO/PLA). Polyalkylene oxalates, for the purpose of this invention, include those described in U.S. Pat. Nos. 4,208,511; 4,141,087; 4,130,639; 4,140,678; 4,105,034; and 4,205,399. Polyphosphazenes, co-, ter- and higher order mixed monomer based polymers made from L-lactide, D,L-lactide, lactic acid, glycolide, glycolic acid, para-dioxanone, trimethylene carbonate and E-caprolactone such as are described by Allcock in The Encyclopedia of Polymer Science, Vol. 13, pages 31-41, Wiley Intersciences, John Wiley &amp; Sons, 1988 and by Vandorpe, et al in the Handbook of Biodegradable Polymers, edited by Domb, et al., Hardwood Academic Press, pp. 161-182 (1997). Polyanhydrides include those derived from diacids of the form HOOC-C.sub.6H.sub.4-O-(-CH.sub.2).sub.m-O-C.sub.6H.sub.4-COOH, where “m” is an integer in the range of from 2 to 8, and copolymers thereof with aliphatic alpha-omega diacids of up to 12 carbons. Polyoxaesters, polyoxaamides and polyoxaesters containing amines and/or amido groups are described in one or more of the following U.S. Pat. Nos. 5,464,929; 5,595,751; 5,597,579; 5,607,687; 5,618,552; 5,620,698; 5,645,850; 5,648,088; 5,698,213; 5,700,583; and 5,859,150. Polyorthoesters such as those described by Heller in Handbook of Biodegradable Polymers, edited by Domb, et al., Hardwood Academic Press, pp. 99-118 (1997). 
         [0037]    Turning also now to  FIG. 2 , a length of the suture  52  has been threaded through a soft tissue  60  (such as for instance a rotator cuff tendon) adjacent a bone tunnel  62  prepared into a bone  64  (such as a humerus). The bone has a hard, outer cortical layer  65  and a softer inner cancellous portion  66 . 
         [0038]    Turning also now to  FIG. 3 , the anchor  10  is loaded onto a driver tool  68 . The driver  68  comprises an inner driver  70  comprising an elongated shaft  72  having a distal tool end  74  (such as a hex driver), which is co-axially received within an elongated outer tube  76 . The tool end  74  is received within the tool receiving recess  38  of the anchor body  14  and a distal end  78  of the outer tube  76  abuts the shell proximal end  20 . 
         [0039]    The suture  52  from the soft tissue  60  extends up out of a cannula  80  used to access the bone tunnel  62  in an arthroscopic procedure. A suture threader  82  comprising an elongated flexible wire  84  having a distal suture capture loop  86  and a proximal threader tab  88  extends between the shell  12  and anchor member  14  along the suture path  54 . The suture  52  is captured in the loop  86  and as the threader  82  is drawn along the path  54  the suture is drawn and threaded through the path  54  thus loading it into the anchor  10 . 
         [0040]    Turning also now to  FIG. 4 , the suture anchor  10  on the driver tool  68 , which carries the suture  52  from the soft tissue  60  and which has been fed down the cannula  80 , is placed into the bone tunnel  62  with the cut-out  50  facing away from where the suture  52  passes through the soft tissue  60 . Force on the outer tube  76  drives the shell  12  into the bone tunnel  62  beneath the surface of the bone  64 . The anchor member threads  42  and  44  are not yet engaged with the shell threads  48  or the bone  64 . The suture  52  extends from the soft tissue  60  to the anchor  10  and distally down the path  54  and then over the distal end  18  and back proximally up and out of the bone tunnel  62 . The suture  52  is now tensioned to draw the soft tissue  60  into a desired position and to put a desired tension into the suture  52 . 
         [0041]    Turning also now to  FIG. 5 , the outer tube  76  can be retracted and the inner driver  70  rotated to drive the anchor member  14  into the shell  12  and bone tunnel  62 . With the anchor member  14  fully seated as shown in  FIG. 6 , the suture  52  is trapped between the shell  12  and the anchor member  14  along the path  54  and also between the bone  64  and the anchor member threads  42  and  44 . The second thread  44  provides additional holding in the hard cortical bone  65 . The shell  12  protects the suture  52  from cutting into the bone  64 . 
         [0042]      FIGS. 7A and 7B  illustrate a further embodiment of a shell  90  similar to the shell  12  except that an exterior surface  92  of the sidewalls  22  has both longitudinal and lateral protruding fixation ridges  94  and  96  respectively. The lateral ridges  96  extend circumferentially about the shell  12  and provide additional holding force in a bone against pull-out. The longitudinal ridges  94  provide resistance against rotation induced by torque applied during implantation of the anchor member  12  (not shown in  FIGS. 7A  or  7 B). Alternatively, an anti-rotational engagement can be made between the shell  90  and the outer tube  76  to hold the shell against rotation as the anchor member is implanted. For instance one or more proximal protrusions  98  can be formed on the shell  90  and interface with mating indentations (not shown) on the outer tube distal end  76 . This embodiment also shows a suture path  100  comprising a more distinct interruption in the internal threads  102 . 
         [0043]    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