Abstract:
The disclosure provides examples of an open architecture anchor for securing soft tissue to bone, for example, to repair a torn rotor cuff. The anchor includes a helical screw thread having a base and two sidewalls that are non-linear. The non-linear sidewalls extend from opposing ends of the base and meet at a peak. The non-linear sidewalls are circumscribed within a triangle defined by the peak and ends of the base. Compared to the standard triangle profile, the helical screw thread profile has a smaller cross-sectional surface area and, consequently, removes less bone. The helical screw thread having the reduced cross-sectional area preserves bone stock and enhances the holding strength of the anchor in bone.

Description:
BACKGROUND 
     Arthroscopic surgery is a minimally invasive surgical procedure in which an examination and sometimes treatment of damage of the interior of a joint is performed using an arthroscope, a type of endoscope that is inserted into the joint through a small incision. Arthroscopic procedures, such as repairing a torn rotor cuff, often require soft tissue to be reattached to bone. To achieve this, anchors (sometimes called “suture anchors”) are placed in the bone and sutures attached to the anchor are passed through the tissue to securely retain the tissue in place. 
     SUMMARY 
     With the use of structurally weaker implant materials, such as bioabsorble composites, in open construct (architecture) anchors, the width of a thread profile base must be enlarged in order for threads to maintain structural integrity. Structural integrity is lost for open construct anchors when the thread separates from anchor rib(s) or the threads break. While providing the structural strength required, increasing thread cross sectional area reduces the amount of bone stock remaining after implant insertion. Preservation of bone stock and maintenance of thread height/depth with increased standard triangle thread profiles required by bioabsorable materials is therefore problematic. 
     The foregoing needs are addressed by an open construct anchor having a profile that is smaller than the standard triangle thread profile. This new thread profile has the same width (base) and height as the standard triangle thread profile but is circumscribed within the standard triangle thread profile. The cross-sectional area of the new thread profile is thus, smaller than the cross-sectional area of the standard triangle thread profile. Using a thread profile with a reduced cross-sectional area preserves bone stock and enhances anchor fixation. 
     Accordingly, in one aspect, the present disclosure relates to an anchor for securing soft tissue to bone, for example, to repair a torn rotor cuff. The anchor includes at least one open helical screw thread. The at least one open helical screw thread defines an internal volume communicating with a region exterior to the at least one open helical screw thread through a spacing between turns of the at least one open helical screw thread. The at least one open helical screw thread includes a base adjacent the internal volume. The base has a first end and second end. The at least one open helical screw thread further includes two non-linear side walls extending from the base to form a peak. The two non-linear side walls are each circumscribed within a triangle defined by the first end, second end, and peak. The anchor also includes at least one rib disposed within the internal volume, connected to at least two turns of the at least one open helical screw thread. 
     In another aspect, the present disclosure relates to a delivery device and anchor combination for securing soft tissue to bone, for example, to repair a torn rotor cuff. The delivery device of the combination includes a handle and shaft connected to the handle. The shaft includes distal end having at least one groove extending towards a proximal end of the shaft. The anchor of the combination includes at least one open helical screw thread. The at least one open helical screw thread defines an internal volume communicating with a region exterior to the at least one open helical screw thread through a spacing between turns of the at least one open helical screw thread. The at least one open helical screw thread includes a base adjacent the internal volume. The base has a first end and second end. The at least one open helical screw thread further includes two non-linear side walls extending from the base to form a peak. The two non-linear side walls are each circumscribed within a triangle defined by the first end, second end, and peak. The anchor also includes at least one rib disposed within the internal volume, connected to at least two turns of the at least one open helical screw thread. The anchor located on the distal end of the delivery device such that the at least one groove engages the at least one rib of the anchor. 
     Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features, and advantages will be apparent from the following more particular description of the embodiments as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles, characteristics, and features of the embodiments. In the drawings: 
         FIG. 1  is an isometric view of an example open architecture anchor. 
         FIG. 2  is a cross-sectional view of the example open architecture anchor of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of an example of a helical screw thread. 
         FIG. 4  is a cross-sectional view of a helical groove cut by of an example of a helical screw thread. 
         FIGS. 5A and 5B  are cross-sectional views of example profiles of the helical screw thread. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of examples is in no way intended to limit the disclosure, its application, or uses. 
       FIGS. 1 and 2  show an example of an anchor  100  including at least one (open) helical screw thread  105 , a cannulation  112  extending the length of the anchor  100  and defining an internal volume  110 , and a through hole  113  located at the distal end of the anchor  100 , configured for housing of a suture. The internal volume  110  communicates with a region exterior to the at least one open helical coil screw  105  through a spacing  115  between turns of the helical screw thread  105 . After the anchor  100  is inserted to bone and the patient begins to heal, new hone grows into the internal volume  110  through the spacing  115 . For faster and healthier healing “bony ingrowth” is highly desirable. 
     The anchor  100  further includes at least one rib  120  (two as shown) connected to at least two turns of the helical screw thread  105 . Each respective rib  120  engages a corresponding groove of a delivery device. In use, the anchor  100  is located at a distal end of the delivery device such that each respective groove engages the respective rib  120  of the anchor  100 . A surgeon inserts the anchor  100  into bone using the delivery device. 
     Some examples of the anchor  100  have two helical screw threads in a “dual lead” thread arrangement. Dual lead meaning two “ridges” are wrapped around the anchor  100 . The anchor  100  may be constructed from, for example but not limited to, polymers (e.g., polyetheretherketone), bioabsorbable materials, metals (e.g., surgical steel, titanium), or any other suitable material. 
       FIG. 3  shows an example of the helical screw thread  105 . The helical screw thread  105  includes a base  125  having a first end  130   a  and second end  130   b . The helical screw thread  105  further includes two non-linear sidewalls  135   a  and  135   b  (generally  135 ) extending from the first and second ends  130   a,b  of the base  125  towards a peak  140 . The first end  130   a , second end  130   b , and peak  140  form a base triangle  145  (shown in  FIG. 3  as dashed lines). The non-linear sidewalls  135  are each circumscribed by the base triangle  145 . One of the advantage s to foregoing geometry is that the anchor  100  can be smaller (e.g., in size and/or mass) then a screw with a standard triangular profile but have similar pullout strength. As shown, the non-linear sidewalls  135  have a concave profile; however, any profile circumscribed within the base triangle  145  is within the scope of this disclosure. Other example profiles of the helical screw thread  105  are described below. 
     The helical screw thread  105  may be further characterized as having a thread height (T H ) and thread width (T W ). An area  150  enclosed by the base  125  and non-linear sidewalls  135  is called the “cross-sectional area” The cross-sectional area  150  of the helical screw thread  105  is less than the cross-sectional area of a screw thread with a standard (conventional) triangle profile having the same thread width and height but having straight sidewalls instead. Advantageously, the anchor  100  removes less bone then a screw with a standard triangular profile resulting in less trauma to the patient. It may be convenient to describe the helical screw thread  105  and its examples as having a reduced cross-sectional area. 
       FIG. 4  shows part of a helical groove  155  cut into bone  160  by an example of the helical screw thread  105 . The profile of the helical groove  155  is the inverse or reciprocal of the profile of the helical screw thread  105 . In the example shown, the helical groove  155  has a convex profile cut by an example of the helical screw thread  105  having concave sidewalls (e.g., the helical screw thread  105  shown in  FIG. 3 .) 
       FIG. 4  also shows, as a series of dashed lines, the outline of a groove  165  cut by a screw thread with a standard triangle profile. The height (H) and width (W) of the helical groove  155  and the groove  165  are the same. The amount of the bone  160  removed in forming the helical groove  155 , however, is less than the amount of bone removed in forming the groove  165 . The hash marks represent bone not removed by the helical screw thread  105  that would be normally removed by the screw thread with the standard triangle profile. Thus, the reduced cross-sectional area  150  of examples of the helical screw thread  105  advantageously preserves bone stock. 
     The reduced cross-sectional area  150  by the helical screw thread  105  also maintains the same thread height as the conventional triangle profile. As such, the holding strength of the anchor  100  in the bone  160  is comparable to that of a typical anchor with a triangle-profiled thread. The anchor  100 , however, achieves its strength by removing/displacing less bone stock than the typical anchor. Some examples of the helical screw thread  105  have an increased thread height to enhance pullout strength while minimizing the amount of bone stock displaced or removed. 
     As another advantage, the base  125  of the helical screw thread  105  can be enlarged without reducing the amount of bone preserved. Lengthening the base  125  (increasing the thread width) increases the connection strength between the helical screw thread  105  and rib  120  and, thereby, increases the structural strength of the anchor  100 . In this example, the anchor  100  can withstand increased torsional loads, imparted by a delivery device, when inserting the anchor into the hard cortical (outer) layer of bone. 
     Yet another advantage, the anchor  100  and its examples reduce the amount of foreign material that is implanted into bone as contrasted with prior anchors with cross-sectional area larger than the reduced cross-sectional area  150 . In turn, this promotes faster and healthier healing. 
     Returning to  FIG. 3 , the first and second non-linear sidewalls  135  have a concave profile. Additionally, the profile of the first non-linear sidewall  135   a  and profile of the second non-linear sidewall  135   b  are the same. It may be convenient to say that this example of the helical screw thread  105  has a symmetrical thread profile. Other profiles that can be circumscribed within the base triangle  145  are also within the scope of this disclosure. 
       FIG. 5A  shows another example of the helical screw thread  105 . The profile of the first non-linear sidewall  135   a  and the profile of the second non-linear sidewall  135   b  are different. It may be convenient to say that this example of the helical screw thread  105  has an asymmetrical thread profile. 
       FIG. 5B  shows yet another example of the helical screw thread  105  in which the cross sectional area  150  (or shape) varies along the length of the helical screw thread  105 . As shown, the size of the cross sectional area  150  increases from a distal end  170  of the anchor  100  to a proximal end  171  of the anchor  100 , i.e. the helical screw thread  105  has a non-constant cross-sectional area that varies along a helical trajectory. 
     As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described examples, but should be defined only in accordance with the following claims appended hereto and their equivalents.