Abstract:
An anchor for fixing a ligament or tendon replacement in a bore formed in a bone has two parts. A first partially cylindrical part has a semi-circular bore therethrough extending along an axis. The bore tapers conically inwardly with respect to the axis from a larger radius at a first end to a smaller radius at second end. The outer surface of the partially cylindrical part is spaced at a constant radius from the axis between the first and second ends. The first and second parts have side walls formed between the bore and the outer surface which walls extend along a plane which forms an angle with respect to the central axis. When the two parts are engaged along their side wails and slide with respect to the axis the outer diameter of the two parts enlarges.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a tendon anchor to be used within the knee or other parts of the body. 
   The present invention is directed to the reconstruction of the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). The ACL helps stabilize the knee joint, and prevents posterior displacement of the femur on the tibia in hyperextension of the knee joint. 
   The ACL is sometimes torn during sports or as a result of traumatic stresses. Ligament reconstruction with allograft or autograft tissue has been shown to improve joint function and provide long term improvement in restoration of physical activity. A typical surgical procedure for ligament replacement and reconstruction involves obtaining a tissue graft or a suitable synthetic graft to replace the damaged ligament. A graft may come from either another part of the patient&#39;s body (autograft), from a cadaver donor (allograft), or the graft may be synthetically manufactured. 
   Structurally, the ACL attaches to a depression in the front of the intercondylar eminence of the tibia and extends posterior-superiorly to the medial wall of the lateral femoral condyle. Partial or complete tears of the ACL are common, comprising over a 120,000 cases annually in the United States. 
   The preferred treatment of the torn ACL is ligament reconstruction, using a bone-ligament-autograft. Methods for placement of such bone-ligament-bone grafts are generally described in Goble et al., U.S. Pat. Nos. 4,772,286; 4,870,957; 4,927,421; 4,997,433; 5,129,902; and 5,147,362. Other methods are shown in U.S. Pat. No. 4,400,833 to Kurland; U.S. Pat. No. 4,467,478 to Jurgustis; U.S. Pat. No. 4,597,766 to Hillal et al.; U.S. Pat. No. 4,668,233 to Seedhom et al.; U.S. Pat. No. 4,744,793 to Parr et al.; U.S. Pat. No. 4,834,752 to Vankampen; and U.S. Pat. No. 5,013,520 to Rosenberg. 
   Although the use of a bone-tendon-bone graft may provide the advantage of effective healing due to the efficient integration of the bone graft to the bone host, the harvesting of a bone-tendon-bone graft typically results in extensive morbidity to the donor knee joint. It is, therefore, often preferable to harvest grafts made up entirely of tendon tissue such as the hamstring. However, it has been found to be more difficult to effectuate and maintain accurate fixation of such grafts throughout the healing period where high-tension forces of the knee may act to disrupt the graft construct. 
   ACL reconstruction procedures generally include the formation of a tunnel through the patient&#39;s femur and tibia bones and implanting a natural ligament or tendon or a synthetic ligament in the bone tunnel which eventually attaches itself to the bone and holds the tibia and femur together. 
   In order to anchor the ligament within the bore or tunnel a device is necessary for grasping the ligament which can then integrate itself with the bone surrounding the bore. In the past, devices such as interference screws have been used when a bone-tendon-bone system has been used. See Mahony, U.S. Pat. No. 5,062,843; or Roger et al., U.S. Pat. No. 5,383,878; Steininger et al., U.S. Pat. No. 5,425,767; and Hubner U.S. Pat. No. 5,454,811. Interference screws function by creating a tight fit between the bone graft and the surrounding bone. Such a system may result in the tendon being damaged which can result in impeded healing or loosening of the interference fixation. 
   There has been a need for a ligament anchor which can fix the ligament in the bone bore which anchor includes a porous inner and outer surface for tissue ingrowth. 
   SUMMARY OF THE INVENTION 
   One aspect of the present invention is to provide a tendon anchor which can be used to anchor a tendon or ligament within a bone bore in the femur and tibia. 
   It is another aspect of the invention to provide a tendon anchor which can expand externally under load to securely anchor the tendon within the bone tunnel or within a tunnel from within an implant. 
   It is yet another aspect of the invention to provide a tendon anchor having an inner and outer surface which is porous and preferably being made from porous material such as titanium foam. 
   When the entire tendon anchor is made from the titanium foam, it has been shown to host new bone ingrowth and ongrowth when implanted in bone with new tendon-like tissues growing in the pores of the inside of the tendon anchor. Thus the titanium foam anchor acts as an interface between the bone and tendon. The tendon anchor can be made in the form of a tube and a tendon graft can be passed through the tube and can be fixed to the end of the tube by passing the Bunnell criss-cross stitch through the poles on the tube, which is then tightly fit into the bone tunnel. The suture can also be fixed outside the bone tunnel in any manner. To avoid the possible difficulty in passing the tendon graft through the tube, the tube can be fabricated in two halves. 
   Preferably, the device consists of two half tubes split along a small angle wedge creating a first and a second part. In the preferred embodiment the first and second parts are not identical but form a tube of constant diameter when longitudinally aligned. The internal diameter of the tube consists of a tapered cone with multiple barbs locking against the direction towards the larger diameter. After the bony anchoring site is drilled to create a bore, the larger end of one half tube is inserted into the bone, the tendon with suture attached at the end is inserted and the suture is passed through the exit hole in the bore. The smaller end of the second half of the tube is then inserted with force which will lead to the expansion of the two half tubes due to the wedge split. The tendon is pulled against the inner taper of the tubular body which will further expand the foam tube for tight contact to the tendon and the bone. The tubular body can have internal barbs to help prevent the tendon from slipping out. The final lock is achieved by fixing the suture anchor to an anchor outside the bone tunnel. 
   Thus attachment of tendon to bone can be used in primary ACL reconstruction surgery, semitendinosus-gracillis (hamstring) and quadricept tendon autografts. Use of these ligaments is associated with less graft harvesting morbidity than the patella tendon graft. However, fixation of tendon to bone tunnel remains a concern using these tendons. 
   Use of allografts and synthetic tendon substitutes have been tried with the success of using this material in tendon reconstruction depending on the healing of the material with bone. The fixation must be secure to prevent changes of the position and tension of the graft. In addition, fixation is a prerequisite for early rehabilitation. The tendon anchor of the present invention can be used as an interface in these procedures. 
   These and other aspects of the present invention are achieved by a tendon anchor for fixing a tendon in a bore in a bone which anchor has an elongated tubular body extending along the longitudinal axis. The body comprises first and second parts each of the parts having an elongated outer surface and an elongated inner bore. The inner bore and the outer surface defines a wall therebetween having elongated side surfaces. The side surfaces taper in a radial direction with respect to the axis from a first end toward the second end of the tubular body. 
   A plane containing the side surfaces of each of the first and second parts crosses the longitudinal axis of the tubular body preferably midway between the first and second ends of the body, and preferable at a small angle of about 1.5-5°. The tendon anchor outer surface may have a bone engaging element such as a circumferential ridge extending outwardly therefrom. The inner bore of each of the first and second parts includes plurality of inwardly extending tendon engaging elements which may be in the form of inwardly extending barbs having sharpened points. 
   In the preferred embodiment, the inner and outer surface of each of the first and second parts has a tissue ingrowth surface thereon. The inner and outer surface may have different porosities, the outer for bone ingrowth and the inner for tendon tissue ingrowth. Preferably, the entire tubular body is made of a porous metal structure such as titanium foam. The average pore size of the titanium foam is preferably 100 to 1000 micron more preferably 300 to 400 microns. The biocompatible porous metal may be titanium, titanium alloy, tantalum, ceramic or alternatively a porous biodegradable material such as PGA or PLLA may be used. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded isometric view of the two-part porous tendon anchor of the present invention; 
       FIG. 1   a  is a side elevation view of the assembled tendon anchor of  FIG. 1 ; 
       FIGS. 2 ,  2   a  are respective side elevation views of each of the parts of the two-part porous tendon anchor shown in  FIG. 1 ; 
       FIG. 3 ,  3   a  are cross-sectional views of the tendon anchor parts shown in  FIGS. 2 ,  2   a  along lines  3 - 3  and  3   a - 3   a  respectively; 
       FIGS. 4 ,  4   a  are end views looking in at the left side of  FIGS. 2 and 2   a;    
       FIGS. 5 ,  5   a  are end views looking at the right hand end of  FIGS. 2 and 2   a ; and 
       FIG. 6  is an enlarged view of detail A of  FIG. 2  showing the circumferential ridge for engaging the replacement ligament or tendon. 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 1 and 1   a  there are shown isometric views and side views of the two-piece tendon anchor generally denoted at  10 . Tendon anchor  10  consists of a first part  12  and a second part  14  which are generally wedge-shaped such that movement of part  12  with respect to part  14  increases the overall diameter of the anchor  10 . Each part  12  and  14  includes an outer circumferential ridge  16  located intermediate a first end  18  and  18 ′ of the first and second part  12  and  14  respectively and a second end  20  and  20 ′ of  12  and  14  respectively. Ridge  16  has a relatively sharp edge  22  designed to imbed itself in the bone as the anchor  10  expands by the relative movement of part  12  with respect to part  14 . In first part  12  end  20  is the thicker wedge wall and in second part  14  end  20 ′ is the thicker wedge wall. Ends  18  and  18 ′ are the thinner wedge wall since the inner diameter of the anchor is larger at this end. The circumference of parts  12  and  14  is tapered. End  18 ′ is the larger circumferentially extending end of wedge of part  14  and end  18  is the smaller circumferentially extending end of wedge  12 . End  20 ′ is the smaller circumferentially extending end of wedge part  14  and end  20  is the larger end of part  12 . 
   Each part  12 ,  14  has a hollow interior  24  designed to receive a replacement tendon or ligament (not shown). The replacement ligament may be an autograft or allograft tendon or ligament, such as a patella Achilles tendon or may be a synthetic tendon such as those made from collagen or polymers. The internal surface  24  of both parts  12  and  14  includes a series of ridges  26  which function to imbed themselves into the replacement ligament or tendon. 
   Referring to  FIGS. 2 and 2   a  there is shown respective side elevation views of one of the parts  12  and  14 . As can be seen in  FIGS. 2 ,  2   a  inner surface  24  of each part  12 ,  14  tapers inwardly from ends  18 ,  18 ′ to ends  20 ,  20 ′. In the preferred embodiment the inner bore taper is between 1.5° and 5° with ridges  26  spaced at intervals along the entire length of parts  12  and  14 . In the preferred embodiment the surfaces  24  of each part  12  or  14  are part circular centered about an axis  30  through the center of each part  12  and  14 . 
   Referring to  FIG. 3 ,  3   a  there are shown respective cross-sections of the tendon anchor parts of  FIG. 2 ,  2   a  showing a cross-section wall  32  which increases in thickness from end  18 ,  18 ′ to end  20 ,  20 ′. In addition wall  32  of part  12  tapers in circumferential extent from a large circumference at end  20 , to a smaller circumference at end  18 . In part  14  the circumferential taper increases from a smaller circumference at end  20 ′ to a larger circumference at end  18 ′. In the preferred embodiment the larger circumferential extent is greater than 180°. Wall  32 ′ increases in thickness on moving from end  18 ′ to end  20 ′. In the preferred embodiment the taper of wall  32 ,  32 ′ is constant between the first and second ends with the increase in radius at end  20  of part  12  equal to the reduction in radius at end  18 . The same reduction in radius occurs from end  18 ′ to end  20 ′ of part  14 . Thus a plane containing surfaces  32 ,  32 ′ of each of the first and second parts  12  and  14  crosses axis  30  at a point between end  18 ,  18 ′ and end  20 ,  20 ′. In the preferred embodiment the angle formed by the plane containing surfaces  32 ,  32 ′ and axis  30  is between 1° and 10° and more preferably between 3° to 6°. 
   As best seen in  FIGS. 2 ,  2   a  ridge  16  tapers outwardly on moving from the side thereof adjacent end  20 ,  20 ′ towards a side thereof facing end  18 ,  18 ′ at an angle α. In the preferred embodiment α is 10°. 
   Referring to  FIGS. 4 ,  4   a  and  5 ,  5   a  there is respectively shown end views of the tendon anchor parts of  FIG. 2 ,  2   a  of ends  18 ,  18 ′ and  20 ,  20 ′ respectively. Each end view shows ridge  16  with  FIG. 4 ,  4   a  showing the thinner end wall of end  18 ,  18 ′ and  FIGS. 5 ,  5   a  showing the thicker end wall of end  20 ,  20 ′.  FIGS. 4   a  and  5  show end  18 ′ or end  20  with walls  32 ,  32 ′ tapering from a larger circumferential extent across the longitudinal axis  30  toward the end with the smallest circumferential extent while  FIGS. 4 and 5   a  show walls  32 ,  32 ′ increasing in circumferential extent from a smaller circumferential extent at end  18 ,  20 ′ across the axis  30  to the end with the larger circumferential extent. 
   Referring to  FIG. 6  there is shown an enlarged view of detail A of  FIG. 2 ,  2   a  in which a single ridge  26  is shown extending into the part&#39;s circular bore of each piece  12  and  14 . When surfaces  32 ,  32 ′ of each piece  12  and  14  are placed adjacent one another surface  24  of each piece forms a circular bore conically tapering outwardly on moving from end  18  to end  20  of part  12  and outwardly from end  18 ′ to  20 ′ of part  14 . While when ends  18 ,  18 ′ and  20 ,  20 ′ of each piece are aligned along axis  30  the tendon anchor  10  has a constant outer diameter. As parts  12  and  14  are slid along surface  32 ,  32 ′ in opposite directions along axis  30  with respect to one another, the diameter increases because of the taper of surfaces  32 ,  32 ′ with respect to axis  30 . This causes a wedging action which locks the tendon anchor in a bone bore as will be described below. 
   To use the tendon anchor of the present invention the surgeon first drills the typical bore in a bone forming the joint, such as the tibia and femur, for receiving the replacement tendon or ligament. In the case of ACL reconstruction, a bone tunnel in the tibia and in the femur is prepared for receiving the replacement ligament. The larger circumferential end  20  of the first part  12  of the tendon anchor for the femur is inserted into the bone bore of the femur. The graft, preferably with a suture attached at its end, is advanced through the bone tunnel and out through the anterolateral femoral cortex. The smaller circumferential end  20 ′ of the second tendon anchor part  14  is then inserted and force is applied to the larger end, which causes the expansion of the two parts due to the wedge-shaped split formed by surfaces  32 ,  32 ′. While the second part is pushed tension is kept on the graft to prevent folding of the graft inside the tendon anchor. The internal ridges  26  help prevent the tendon from slipping out after the whole anchor is embedded in the bone tunnel. The tendon is fixed to the femur at the lateral cortex. 
   Likewise the tendon anchor first part  12  for the tibial fixation is introduced first into the knee. The larger circumferential part  20  of the anchor is inserted into the bone tunnel towards the portal at the tibial cortex. The second part  14  is then inserted with end  20 , first to embrace the tendon graft. With the graft in tension, the second part is pushed along the bone tunnel. A hook can be inserted through the tibial tunnel to pull the anchor until it is totally in the bone tunnel. The suture is fixed on the cortex of the tibia. The internal ridges  26  help prevent the tendon from slipping out. The final locking of the tendon is achieved by fixing the suture to an anchor outside the bone tunnel. 
   In the preferred embodiment the entire bone anchor  10  first and second parts  12 ,  14  are formed from a porous titanium or titanium alloy. Preferably the porous titanium is manufactured by selective laser sintering (SLS). To make the porous tendon ligament anchor using SLS, a layer of metal powder is deposited on a substrate. The substrate is not intended to be an integral part of the finished product. After an individual layer of powder is deposited, a scanning process may be preformed to selectively melt the powder to form portions of a plurality of predetermined unit cells. The scanning process includes scanning a laser beam onto the metal powder. 
   As successive layers are deposited and scanned a structure is built from one end to an opposite end. The structure includes a plurality of predetermined unit cells. The unit cells provide the structure with interconnecting pores as well as porosity. The size of the pores and porosity as well as other factors may all be predetermined. 
   In one preferred embodiment the size of the pores of the porosity of the porous tendon/ligament anchor are specifically chosen to provide the structure for bone and ligament ingrowth. 
   The method of producing a three-dimensional porous tissue in-growth structure preferably includes depositing a first layer of a powder made from a metal selected from the group consisting of titanium, titanium alloys, stainless steel, cobalt chrome alloys, tantalum and niobium onto a substrate. The layer of powder is then scanned using a laser beam. The laser beam has a power, and scans the powder layer for a period of time with a point distance. The power of the laser beam is preferably within the range of 5 to 1000 watts. The exposure time is in a range between 100 μsec to 1000 μsec. The laser beam scans the powder layer to form a portion of a plurality of predetermined unit cells. The predetermined unit cells include struts having cross-sectional dimensions. The cross-section of the struts may be any regular of irregular shape. A few such examples include circular, rectangular, cubic cross-sections or the like. The laser power is preferably 90.5 W, the exposure time is 1000 μsec and the point distance is 90 μm. 
   The manufacturing method also preferably includes depositing at least one additional layer of the powder onto the first layer and repeating the step of scanning the additional layers with a laser beam for at least one of the deposited layers in order to continue forming the predetermined unit cells which eventually form the tendon anchor. 
   The predetermined unit cells may take the shape of the first and second tendon anchor parts. The unit cells may be in the shape of a tetrahedron, dodecahedron or octahedron as well as other symmetrical structures. As mentioned, the unit cells may not have such uniformity and may have an irregular shape. The unit cells may also be truncated, which includes eliminating some of the struts, which form a unit cell. Truncated unit cells located at the exterior surface of a built product provide a barbed effect to the product. 
   A porosity range is programmed for at least one deposited powder layer and scanning the layer in a manner to provide the deposited layer with porosity within the predetermined porosity range. Portions of the powder layers may be fused and or sintered to the base or core. The base or core is then separated from the finished first or second part of the tendon anchor. 
   Generally, the method of producing a three-dimensional construct such as the first and second tendon anchor parts includes loading a file of the parts component into an engineering design package. The component is scaled down in the file from its original size. A Boolean operation is next performed to subtract the scaled down component from the original component. This creates a jacket. The jacket can then be processed using a bespoke application that populates the jacket with a repeating open cellular structure. 
   The open cellular structure is then sliced using the bespoke application to a predetermined thickness. Such a system by fabricating parts using laser sintering is taught in U.S. Ser. Nos. 10/704,270 (US2004/0191106) and 11/027,421, the disclosure of which is incorporated herein by reference. 
   The main body of the file component jacket is loaded into a user interface program and the jacket is sliced into layers having a predetermined thickness. Hatching is then applied to the file component jacket as required to build a construct and the jacket is merged with the open cellular lattice structure. Once a representation has been obtained the depositing and scanning steps of the SLS process may be conducted to build the tendon anchor parts. 
   While laser sintering is the preferred method of fabricating the porous tendon anchor, injection molding could also be used wherein the titanium powder is mixed with a polymeric binder and then injection molded into the desired shape. The polymeric binder is then removed by a solvent and the part sintered to form the high strength tendon anchor implant. 
   Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.