Abstract:
Embodiments of the bone anchor assembly ( 36, 50 ) described herein have adjustable lengths and therefore accommodate many needs. Therefore, the physician does not need to maintain a multitude of bone anchors having a variety of lengths in order to be prepared for many situations. The bone anchor assembly ( 36, 50 ) has an elongated hollow shaft portion ( 38, 52 ) formed of multiple shaft segments ( 46, 58 ) joined together. The length of the shaft portion ( 38, 52 ) is adjusted after the implanting of the bone anchor assembly into the bone by removing shaft segments ( 46, 58 ).

Description:
RELATED APPLICATION 
       [0001]    This application claims benefit under 35 U.S.C. §119(e) of the Nov. 13, 2014 filing of U.S. Provisional Application No. 62/079,174, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    Bone anchors, sometimes referred to as “suture anchors,” lodge into a bone of a patient and hold one or more sutures securely thereto, and the sutures in turn securely hold soft tissue, such as tendons and ligaments. Accordingly, bone anchors are useful for many types of both open and arthroscopic orthopedic surgery, for example, for rotator cuff repair. 
         [0003]    An exemplary conventional bone anchor  10  is illustrated in  FIG. 1 . This bone anchor  10  has exterior threads  12 , like an ordinary wood screw, and a post  14  on top having an eyelet  16  for a suture  18  to be threaded therethrough. (In other exemplary conventional bone anchors, sutures are embedded within the anchor material instead of remaining easily slidable through an eyelet.) A physician implants the bone anchor  10  using an orthopedic drill, such as one manufactured by Striker, DePuy Synthes Companies of Johnson and Johnson, or Zimmer Biomet. 
         [0004]    Care must be exercised that the bone anchor  10 , while being lodged sufficiently deeply into the bone to secure it thereto, is not lodged so deep that the suture  18  is susceptible to contacting the bone and perhaps weakening the suture  18 . Weakening of the suture  18  may occur due to chemical processes such as hydrolytic and enzymatic degradation caused by bone contact, and these chemical processes can eventually dissolve the suture material. (Although the dissolving of the suture may be desired eventually, it is not desired early in the patient&#39;s healing process.) Also, the drilling of the bone may have roughened the bones&#39; surface where it could contact the suture, and a jagged surface may wear down the suture prematurely. 
         [0005]      FIG. 2  provides an illustration of bone anchors  20  and  22  already implanted in a patient&#39;s bone  24 , so as a result only the top heads of the bone anchors  20  and  22  are visible in the figure. Sutures  26 ,  28 ,  30 , and  32  join the bone anchors  20  and  22  to the patient&#39;s soft tissue  34 . As discussed above, it is undesirable to submerge the bone anchors  20  and  22  so far into the bone  24  that the sutures  26 ,  28 ,  30 , and  32  contact the interior of the drilled hole (not shown). As one can see from  FIG. 2 , it is also undesirable that the heads of the bone anchors  20  and  22  would protrude too far above the surface of the bone  24 . Accordingly, the physician needs bone anchors having a length that is long enough for reaching depths as low as necessary for solid anchorage into the particular bone and the part of that bone being drilled, but bone anchors cannot be so long as to protrude from the bone surface. 
         [0006]    Due to the wide variety of particular bones into which bone anchors may be lodged, the different optimum depths for particular bone areas require a variety of lengths of bone anchors to be available to the physician. That is, for a given bone having a given optimum depth, a bone anchor must have a certain length so that it is not too short and not too long. It can however become burdensome to maintain a supply of bone anchors of different lengths for all the anticipated needs a physician may have. 
         [0007]    As is clear, the purpose of using a longer length for a bone anchor is to effect a more secure lodging. Another way though to effect a more secure lodging while keeping the anchorage shallow is to increase the bone anchor diameter. However, using bone anchors of larger diameters decreases the number of individual bone anchors that may be implanted into a given area of bone. Thus, the stress from the sutured soft tissue is distributed among fewer bone anchors, thus increasing the stress on each individual bone anchor and on the associated sutures in use. Also, after some treatments, the shallow anchorage can lead to the loss of the fixation of the bone anchors, anyway, even if the bone anchor diameters are greater. 
         [0008]    The present inventors decided to develop a bone anchor that was suitable to implantation in bones at a variety of depths according to the particular needs, so thereby (1) not being susceptible to the disadvantages of requiring large diameters that lessen the number of bone anchors that could be implanted, (2) not requiring maintaining a multitude of different bone anchor lengths, and (3) easily supporting sutures in a fashion to avoid contact with the surrounding bone. 
       SUMMARY 
       [0009]    The present inventors have developed a bone anchor assembly that adapts to many applications, because it is adjusted to a suitable length after it has been implanted. Alternate embodiments have different ways to adjust the length of the bone anchor assembly. 
         [0010]    The invention may be embodied as a bone anchor assembly for implanting into a bone. The bone anchor assembly has: an elongated hollow shaft portion; a threaded end portion; and sutures. The elongated hollow shaft portion is formed of multiple shaft segments joined together at shaft segment boundaries. The threaded end portion is joined to the shaft portion. The sutures are joined to the end portion and extend inside the shaft portion. The length of the shaft portion may be adjusted after the implanting of the bone anchor assembly into the bone by removing shaft segments. 
         [0011]    The bone anchor assembly may further have a shaft axis along which the elongated hollow shaft portion extends. For this implementation, shaft segments may be removed by applying a force to the shaft portion in a direction normal to the shaft axis and sufficient to deform the shaft portion to cause the shaft portion to break at one of the shaft segment boundaries between two adjacent shaft segments. 
         [0012]    Alternatively, the bone anchor assembly may further be configured such that the shaft segments have tabs at one axial end and blanks at the opposite axial end so that the shaft segments interlock by mating the tabs of one shaft segment with the blanks of an adjacent shaft segment. 
         [0013]    Embodiments of the present invention are described in detail below with reference to the accompanying drawings, which are briefly described as follows: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention is described below in the appended claims, which are read in view of the accompanying description including the following drawings, wherein: 
           [0015]      FIG. 1  illustrates a conventional bone anchor; 
           [0016]      FIG. 2  illustrates conventional bone anchor, such as that of  FIG. 1 , implanted into a patient&#39;s bone and attached to a patient&#39;s soft tissue by sutures; 
           [0017]      FIG. 3  provides a perspective view of a bone anchor assembly in accordance with a first embodiment of the invention; 
           [0018]      FIG. 4A  provides a side view of a bone anchor assembly in accordance with a second embodiment of the invention; 
           [0019]      FIG. 4B  provides a cross-sectional view of the bone anchor assembly of  FIG. 4A ; 
           [0020]      FIG. 4C  provides a cross-sectional view of the bone anchor assembly of  FIG. 4A  at the A-A cut-away designated in  FIG. 4B  viewing in the direction of the arrows; 
           [0021]      FIG. 4D  provides a cross-sectional view of the bone anchor assembly of  FIG. 4A  at the B-B cut-away designated in  FIG. 4B  viewing in the direction of the arrows; 
           [0022]      FIG. 4E  provides a perspective view of two engaged shaft segments of the bone anchor assembly of  FIG. 4A ; and 
           [0023]      FIG. 4F  illustrates the bone anchor assembly of  FIG. 4A  in use after implantation. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The invention summarized above and defined by the claims below will be better understood by referring to the present detailed description of embodiments of the invention. This description is not intended to limit the scope of claims but instead to provide examples of the invention. As disclosed herein, the present bone anchor assembly may be implanted into bone at a variety of depths. For embodiments of the bone anchor assembly, the length is set after it is lodged into the bone. That is, it is a one-size that fits many applications, because it is adjusted to the particular depth after the implantation procedure begins. 
         [0025]    An exemplary embodiment of the invention is illustrated in  FIG. 3 . As shown, a bone anchor assembly  36  for implanting into a bone has an elongated hollow shaft portion  38 , a threaded end portion  40 , and sutures  42 . (Throughout the disclosure, the term “sutures” may be used to refer to single strand of thread with two segments for tying together, or the term may refer to multiple threads, as non-limiting examples.) The end portion  40  of the bone anchor assembly  36  is joined to the shaft portion  38 , for example, by welding or by forming the shaft portion  38  and the end portion  40  as a unitary piece. The bone anchor assembly  36  of the present embodiment has two sutures  42 , but the invention is not limited accordingly. 
         [0026]    Conventional sutures may be used in this embodiment of the bone anchor assembly  36 . The sutures  42  are joined to the end portion  40  of the bone anchor assembly  36  in any manner determined by one skilled in the art using conventional considerations and technology. For example, the sutures  42  may be joined to the end portion  40  of the bone anchor assembly  36  in the fashion that the suture  18  in  FIG. 1  is joined to the prior art bone anchor  10 . The sutures  42  of the bone anchor assembly  36  extend inside the shaft portion  38  along the shaft portion axis to exit the bone anchor assembly  36  at an opening  44  in the shaft portion  38  at an end distal to the end portion  40 . If desired, the sutures  42  may be sized long enough to extend along the shaft axis and beyond the shaft portion  38  itself. 
         [0027]    The shaft portion  38  is formed of multiple shaft segments  46 , and the shaft segments  46  are joined together at shaft segment boundaries  48 . With reference also to the circled enlarged section of the shaft portion  38  in  FIG. 3 , it is clear that the shaft segments  46  have external cylindrical walls that have a given diameter, and the shaft segment boundaries  48  have external cylindrical walls that have another diameter that is less than diameter of the external walls of the shaft segments  46 . Such is intentional to make the cylindrical wall of the shaft portion  38  weaker at the shaft segment boundaries  48  than at the shaft segments  46 . One non-limiting way to decrease the diameter of the exterior wall of the shaft portion  38  at the shaft segment boundaries  48  to implement laser cutting to remove wall material where desired. Another way to decrease diameter of the exterior wall of the shaft portion  38  is to rotate the bone anchor assembly on a lathe and mechanically remove material where desired. Reducing wall diameter is one way to weaken the wall of the shaft portion  38  at the shaft segment boundaries  48 , but other ways of weakening the wall are within the scope of the present invention. 
         [0028]    The material used to manufacture the shaft portion  38  and the end portion  40  may be determined by those skilled in the art according to needs and available resources. Non-limiting examples of such materials include continuous carbon fibers reinforced polymer, biodegradable materials such as PLDLA (Poly-L-co-D.L-lactic), and metal, such as such as titanium and titanium alloys. 
         [0029]    The length of the shaft portion  38  of the bone anchor assembly  36  may be adjusted after the implanting the bone anchor assembly into a patient&#39;s bone by removing the shaft segments  46  that extend beyond the surface of the bone. One way to remove those shaft segments  46  is to apply a force to the shaft portion  38  in a direction normal to the shaft axis and sufficient to deform the shaft portion  38  to cause the shaft portion  38  to break at one of the shaft segment boundaries  48  between two adjacent shaft segments  46 . As it is desirable to break off and remove all shaft segments  46  that extend beyond the bone after the bone anchor assembly  36  is implanted, the shaft portion  38  should break at the shaft segment boundary  48  between the submerged shaft segment  46  that is closest to the bone surface and the adjacent shaft segment that protrudes from the bone. Thus, while applying the force to the shaft portion  38  normal to the shaft axis, the force should be focused so that it is stronger at the shaft segment boundary  48  to be broken than at another shaft segment boundary  48 . 
         [0030]    One way to focus the shaft-bending force on the shaft segment boundary  48  to be broken is to slide a collar, for example, a long tube, outside and down the shaft segment  46  the bone surface. The collar may be designed to be long enough so that, is use, all shaft segment boundaries are surrounded by either the bone or the collar, except for the shaft segment boundary  48  to be broken. 
         [0031]    After the shaft portion  38  is broken at the desired shaft segment boundary  48 , one broken part of the shaft portion  38  is surrounded by bone, and the other broken part is completely external to the bone. The latter part may be removed and discarded. The sutures  42  may be joined to soft tissue to complete the care for the patient. 
         [0032]    An alternate exemplary embodiment of the invention is illustrated in  FIGS. 4A-4F . As shown, a bone anchor assembly  50  for implanting into a bone has an elongated hollow shaft portion  52 , a threaded end portion  54 , and sutures  56 . The end portion  54  of the bone anchor assembly  50  is joined to the shaft portion  52 , for example, by welding or by forming the shaft portion  52  and the end portion  54  as a unitary piece. The bone anchor assembly  50  of this embodiment has two sutures  56 . 
         [0033]    As in the embodiment of  FIG. 3 , conventional sutures may be used in this embodiment, also. The sutures  56  are joined to the end portion  54  of the bone anchor assembly  50  in any manner determined by one skilled in the art using conventional considerations and technology. The sutures  56  of the bone anchor assembly  50  extend inside the shaft portion  52  along the shaft portion axis to exit the bone anchor assembly  50  at an end distal to the end portion  54 . If desired, the sutures  56  may be sized long enough to extend along the shaft axis and beyond the shaft portion  52  itself. The shaft portion  52  is formed of multiple shaft segments  58 , and the shaft segments  58  join together at shaft segment boundaries  60 . 
         [0034]    With reference to  FIGS. 4A and 4E , it can be seen that the shaft segment boundaries  60  resemble boundaries between jigsaw puzzle pieces. More specifically, a given shaft segments  58  has tabs  62  at one axial end and blanks  64  at the opposite axial end so that the shaft segments  58  interlock by mating the tabs  62  of one shaft segment  58  with the blanks  64  of an adjacent shaft segment  58 . Optionally, the tabs  62  may be formed having grooves  66  extending in the axial direction, the grooves  66  functioning to position the sutures  56  away from the bone as discussed below. 
         [0035]    To rotate the end portion  54  of the bone anchor assembly  50 , a hollow driving rod  68 , sized and shaped to fit into the shaft portion  52 , is inserted therein to engage the end portion  54 . Thus, the driving rod  68  may be coupled to a conventional orthopedic drill, and rotating the driving rod  68  causes rotation of the end portion  54  to drill the bone anchor assembly  50  into the bone of a patient. Upon such engagement of the driving rod  68  with the end portion  54 , the sutures  56  extend inside the driving rod  68  along the shaft axis. 
         [0036]    With reference to  FIG. 4C , along most of the length of the driving rod  68 , the driving rod  68  it has a circular cross section. However, at the end of the driving rod  68  proximal to the end portion  54  the driving rod  68  has an engagement portion  70  with a non-circular cross-section. See  FIG. 4D , which shows that the engagement portion  70  as a square-shaped cross section. (Other shapes, such as that of a hexagon, may be used in other implementations.) The engagement portion  70  of the driving rod mates (engages) with a correspondingly shaped socket  72  in the end portion  54 . 
         [0037]    As with the embodiment of  FIG. 3 , in the present embodiment the length of the shaft portion  52  is adjusted after the implanting the bone anchor assembly  50  into a bone by removing shaft segments  58 . To remove shaft segments  58  in this embodiment, first the driving rod  68  is withdrawn from the interior of the shaft portion  52  and end portion  54 . Then, a collar  74  surrounding the shaft portion  52  is slid thereon toward the end portion  54  until the collar  74  approaches the bone surface. The collar  74  is then aligned with a shaft segment  58  as discussed next and separates the shaft segment  58  from an adjacent shaft segment  58 . Note that the collar  74  positioned as illustrated in  FIG. 4A  needs to be rotated ninety degrees around the shaft axis in order to separate shaft segments  58 . The collar is nonetheless illustrated as shown to provide a better view of its elements. 
         [0038]    The collar  74  has sliding pistons  76  as radially-inward moving elements. As will be explained, the pistons  76  slide in the direction of the arrows in  FIGS. 4A and 4B  to separate shaft segments  58 . The pistons  76  are biased by coil springs  78  so as not to contact the shaft segments  58 . Larger diameter sections  80  of the pistons  76  prevent the pistons  76  from ejecting from the collar  74 . In alternate embodiments, the coil springs  78  may be replaced with leaf springs joined to a collar, with the leaf spring having protrusions extending inwardly in place of the pistons  76  of the present embodiment. 
         [0039]    Regarding the present embodiment, when the collar  74  is aligned along the shaft axis properly with respect to shaft segment  58  that is to be disengaged from an adjacent shaft segment  58 , forcing the pistons  76  to slide against their biasings toward the shaft segment  58  moves the tabs  62  out of engagement with the blanks  64  of the adjacent shaft segment  58 . In some implementations of the present embodiment, to effect the proper alignment of the collar  74  with the shaft segment  58  to be disengaged, the shaft segments  58  have radial holes  82  and the collar  74  has at least one radial hole  84 . A physician can see through the hole  84  in the collar  74  when the hole  84  is aligned with a hole  82  of a shaft segment  58 . 
         [0040]    The holes  82  in the shaft segments  58  have the added benefits of reducing the amount of metal in the bone and allowing bone “in-growth” to improve bone-implant integration and stability. However, because the presence of the holes  82 , it is desired to position the sutures  56  close to the shaft axis to avoid contact with the bone. Accordingly, reference is made to  FIG. 4F  illustrating the bone anchor assembly  50  after its implantation into a bone  86  and after the shaft segments  58  that were not submerged into the bone  86  are removed. The tabs  62  are bent ninety degrees from their original position, and the sutures  56  extend from the bone anchor assembly  50  through the grooves  66  in the tabs  62 , thus keeping the sutures  56  farther from the part of the bone  86  that was drilled. 
         [0041]    Having thus described exemplary embodiments of the invention, it will be apparent that various alterations, modifications, and improvements will readily occur to those skilled in the art. Alternations, modifications, and improvements of the disclosed invention, although not expressly described above, are nonetheless intended and implied to be within spirit and scope of the invention. For example, the disclosed collar may be modified so that it does not completely surround a shaft portion, thereby have a “U-shaped” as opposed to an “O-shaped” cross-section. Accordingly, the foregoing discussion is intended to be illustrative only; the invention is limited and defined only by the following claims and equivalents thereto.