Abstract:
A method and implant to treat anterior cruciate ligament (ACL) injuries are disclosed. The method involves advancing the insertion of the patellar ligament to the proximal tibia. The implant includes a spacer ( 30 ) which is inserted between the patellar ligament and the tibia and fixed to the tibia. The spacer decreases the angle between the patellar ligament and the tibia plateau and consequently modifies the internal joint force, restoring stability to the joint even if the ACL is ruptured. The method and implants are applicable to both human and canine patients.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a method and implants to treat a knee with an injured or ruptured anterior cruciate ligament. 
         [0003]    2. Discussion of Related Art 
         [0004]    The Anterior Cruciate Ligament (ACL) in the human knee joint, commonly called Cranial Cruciate Ligament (CrCL) in the canine stifle, is frequently torn in trauma. It also frequently fails, particularly in dogs, after, a degenerative process of still unknown etiology. 
         [0005]    In human orthopedics, the standard procedure calls for replacement by an ACL allograft, a part of the patient&#39;s own patellar ligament, or a part of the tendon removed from his hamstring muscle. The procedure results in a stable knee, but the long-term performance is often unsatisfactory—75 to 90% of cases result in arthrosis of the joint within 15 years of the procedure. 
         [0006]    In dogs, the standard procedure is either an extra capsular suture or one of several geometry modifying surgical techniques. In the extra capsular procedure, a suture is placed outside of the joint, usually on the lateral side, to approximate the function of the ligament. The intention of the suture is to provide stability of the joint for several weeks, while waiting for fibrosis to form around the joint. The fibrosis should provide for long term stability. However, the extra capsular suture technique regularly results in failure. Arthrosis of the joint, at a year or so, is the rule rather exception. 
         [0007]    In surgical techniques, the tibia is cut and a segment of it is repositioned to change the geometry in order to stabilize the stifle. Various techniques have been used including: tibial plateau leveling osteotomy (TPLO; Slocum B, Slocum TD; Tibial Plateau Leveling Osteotomy For Repair Of Cranial Cruciate Ligament Rupture In The Canine, Vet. Clin. North Am. 23: 777-795, 1993), cranial closing wedge osteotomy (CWO; Slocum B, Devine T; Cranial Tibial Wedge Osteotomy: A Technique For Eliminating Cranial Tibial Thrust In Cranial Cruciate Ligament Repair, J. Am. Vet. Med. Assoc. 184: 564-569, 1984), and tibial tuberosity advancement (TTA; Tepic S, Damur D M, Montavon P M; Biomechanics Of The Stifle Joint, in Proceedings of the 1st World Orthopaedic Vet. Congress, Munich, Germany, September 2002, pp 189-190). These are significantly invasive procedures which change the overall geometry of the stifle. Of the surgical approaches used in dogs, TTA seems to be associated with lesser morbidity and faster recovery, while providing immediate and durable stability to the joint. Nevertheless, complications and progressing arthrosis are common with each of these techniques. 
         [0008]    Intra-articular prostheses are also occasionally used. Again, they require significantly invasive procedures to insert them within the stifle. Even then, they generally end up in failure. 
       SUMMARY OF THE INVENTION 
       [0009]    This invention provides a solution for a minimally invasive stabilization of a knee joint, in dog and in human, by cranially (anteriorly) advancing the patellar ligament just proximally to its insertion to the tibia. According to one aspect of the invention, a spacer is configured to be placed between the distal section of the patellar ligament and the tibia. The spacer is sized and shaped to alter the orientation of the patellar ligament by a pre determined amount. The alteration stabilizes the knee joint which has been weakened by an ACL (or CrCL) failure. According to another aspect of the invention, the spacer may be made from an artificial material, e.g. metal (titanium, stainless steel or a cobalt chromium alloy) or polymer (PEEK, UHMWPE), or from bone (autograft or allograft). According to another aspect of the invention, the spacer is fixed to the tibia body by either conventional screw(s) or an anchor screw, similar to those used for dental implants. According to another aspect of the invention, the surface of the spacer facing the patellar ligament is smooth and exhibits low friction. The material for the spacer should be biocompatible and resistant to wear. 
         [0010]    According to another aspect of the invention, the surface of the spacer facing the patellar ligament is engineered so as to provide best conditions for bony ongrowth. For example, a titanium spacer can be anodized, particularly by a process known as Biocer®, or plasma sprayed by either a bone-conductive ceramic or titanium. 
         [0011]    According to another aspect of the invention, the spacer is configured to alter the angle of the patellar ligament relative to the tibial plateau. According to one aspect of the invention, the angle is decreased by between 5 and 15 degrees for dogs. According to another aspect of the invention, the angle is decreased by between 10 and 30 degrees in humans. According to another aspect of the invention, the angle of the patellar ligament relative to the tibial plateau is approximately 90 degrees when the knee is extended. 
         [0012]    According to another aspect of the invention, a procedure provides stabilization of the knee joint caused by failure of the ACL or CrCL. The procedure includes moving the patellar ligament away from the tibia just above the tibial insertion. A spacer is inserted between the patellar ligament and the tibia and fixed to the tibia. According to another aspect of the invention, the procedure includes altering the angle of the patellar ligament relative to the tibial plateau. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a side view of a dog knee joint (stifle) on which the TTA procedure has been performed. 
           [0014]      FIG. 2  is a side view of a dog knee joint having a patellar ligament spacer according to an embodiment of the invention. 
           [0015]      FIG. 2   a  is a cross sectional view of the dog knee joint of  FIG. 2  through the spacer. 
           [0016]      FIGS. 3   a  - 3   d  illustrate mechanisms for fixing a spacer in a dog knee. 
           [0017]      FIG. 4  is a side view of a human knee with a patellar ligament spacer according to an embodiment of the invention. 
           [0018]      FIGS. 5   a - 5   c  are front, side and top views of a spacer for a human knee joint according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    The present invention provides a spacer and a procedure for adjusting the position and angle of the patellar ligament in order to stabilize the knee. The knee is stabilized through geometric changes similar to those achieved by TTA in a much less invasive procedure. The TTA procedure is explained in connection with  FIG. 1  to illustrate stabilization of the knee. The TTA procedure is currently accepted as a standard treatment for ruptured ACL in dogs (Fossum T W, Small Animal Surgery, Elsevier Health Sciences, 3 rd  edition, 2007; Boudrieau R, Tibial Plateau Leveling Osteotomy Or Tibial Tuberosity Advancement?, Vet. Surg. 38:1-22, 2009).  FIG. 1  illustrates the knee joint both before and after the TTA procedure. The tibia  1  and the femur  2  articulate at the knee joint via condyles of the femur  21  and condyles of the tibia, also commonly referred to as the tibial plateau  20 . Pull  24  from the quadriceps muscles acts on the patella  3 , which in turn pulls onto the tibia via patellar ligament  5  (4 in its original orientation). The force between the condyles of the femur and the tibia is approximately parallel to the patellar ligament  5 , having been tilted from its original orientation  6  before the advancement (which was parallel to 4) into the new orientation  7 , which is perpendicular to the plateau  20 . When the joint force  7  is perpendicular to the plateau  20 , neither the cranial (anterior)  8 , nor the caudal (posterior) cruciate ligament  9  are needed to stabilize the joint. When this condition is satisfied in the extended position of the knee, such as shown on  FIG. 1 , the joint will also be stable when flexed, stability provided by the caudal (posterior) cruciate ligament. 
         [0020]    Advancement of the tuberosity, after an opening wedge osteotomy, is maintained by a cage  13  fixed to the tibia with a posterior screw  14  and an anterior screw  15 . The tension of the patellar ligament  5  is transferred to the body of the tibia via a tension-band plate  10 , fixed distally to the tibia with screws  11 , and proximally to the tuberosity with a fork  12 . 
         [0021]    In addition to balancing the internal force  7  of the knee joint, TTA also reduces the force  23  (originally 22) between the patella and the femur. A procedure similar to TTA has been invented and performed in human surgery as well by Maquet (Maquet P; Advancement Of The Tibial Tuberosity, Clin. Orthop. Rel. Res. 115: 225-230, 1976). 
         [0022]    The procedure of the present invention provides similar changes to those of TTA without the need to cut and reattach the tuberosity. The advantages of the invention are obtained through placement of a spacer between the tibia and the patellar ligament.  FIG. 2  shows a medio-lateral view of a dog knee in the extended position with a spacer  30  of the present invention. Patellar ligament has been rotated from its original position  34  to a new position  35  by insertion of a spacer  30  between the patellar ligament and the tibia just proximally to the insertion point  36  of the ligament  35  (34) to the tibia  1 . The angle  31  between the patellar ligament  35  and the tibial plateau  20  should be about 90 degrees when the knee is extended to keep the knee stable. In dogs, this calls for an average rotation of the patellar ligament on the order of 5 to 15 degrees; in humans, a larger correction of 10 to 30 degrees is needed for a full compensation of a ruptured ACL.  FIG. 2   a  shows a cross-section through the spacer  30  and the tibia  1 . The spacer should preferably be slightly grooved under the ligament so as to keep it in a stable position. This, however, is not an essential requirement—proximity of the insertion should guarantee a stable guidance of the ligament over the spacer. 
         [0023]    Under the same pull of the quadriceps  24 , the patella  3  will get slightly displaced distally to a new position, marked as  3   a.  However, this will not affect its function. 
         [0024]      FIG. 3   a  shows fixation of the spacer  30  to the tibia  1  by means of a bone screw  37 , just proximally to the insertion  36  of the ligament  35 . The head  38  of the screw  37  should be well countersunk to avoid contact with the patellar ligament  35  which, with flexion, will wrap to a new position marked as  35   a.  The undersurface  39  facing the tibia bone should preferably be suitable for bony ongrowth or ingrowth. 
         [0025]      FIG. 3   b  shows an alternative method of fixation of the spacer  30  to the tibia  1  by means of an anchor  40 . The anchor  40  is screwed into the bone with its conical head  41  left above the level of the bone. The spacer  30  is provided with a matching conical hole. The angle of the conical head and the hole should preferably be self-locking, e.g. 1:10 or 1:20. The bone facing surface  39  of the spacer  30  should preferably be suitable for bony ongrowth or ingrowth. 
         [0026]      FIG. 3   c  shows yet another method of fixation of the spacer  30  to the tibia  1  by means of at least one flange  50 , which allows placement of a transverse screw  51  from the medial aspect of the tibia. A second flange could be fixed from the lateral side. 
         [0027]    Yet another method of fixation of the spacer  30  is shown on  FIG. 3   d  using a staple-shaped fixation device  60 . 
         [0028]    The surface  42  of the spacer  30  facing the ligament should be highly polished and resistant to wear. Titanium nitride or diamond-like coatings are suitable for that purpose. 
         [0029]      FIG. 4  shows a saggital view of a human knee with a spacer  130  inserted under the patellar ligament  105  to advance it from its original position  104 . The spacer is fixed to the tibia  101 . Patella  103  will be slightly displaced distally from its original position, marked as  103   a,  within the patellar groove  106  of the femur  102 . 
         [0030]      FIGS. 5   a - 5   c  show orthogonal views of an embodiment of a spacer  130  for use in the human knee. The frontal view ( FIG. 5   a ) shows a central section  131  and side sections, or flanges,  132 , provided with holes  133  to accommodate bone screws. The top view ( FIG. 5   c ) shows the central section  131  as being grooved, with the ridges  135  intended for guiding the patellar ligament. Side screws  134  can be comfortably placed into the tibial plateau, which in the human knee is much wider than in the dog knee. All of the bone facing surfaces  136  should be well adapted for bony ongrowth or ingrowth, while all of the ligament facing surfaces, e.g.  131  and  135 , should be polished and preferably hard-coated for resistance to wear. Alternatively, ligament facing surfaces can be optimized for bony ongrowth—in the final adaptation, the ligament would be sliding over a bone surface. 
         [0031]    While the primary indication of the invention is rupture of the ACL in human or CrCL in dog, it can also be used for partial ruptures of the same. It may also be used as a supportive measure for ACL repairs, as well as for intra-articular prosthesis or extra-articular sutures. It can also be used as a substitute for Maquet procedure for patello-femoral joint arthrosis. 
         [0032]    Spacers produced from artificial, biocompatible materials have advantages in terms of convenience of use and selection of sizes, but a surgeon could also use a piece of bone, autograft or allograft, appropriately shaped and fixed to the tibia to achieve the same result. 
         [0033]    The procedure of the present invention includes advancing the orientation of the patellar ligament to alter the relative angle with the tibial plateau. In an embodiment of the invention, the patellar ligament is advanced so that the relative angle with the tibial plateau is approximately 90 degrees when the knee is extended. In another embodiment of the invention, the patellar ligament is advanced so that the angle is decreased in the range of 10 to 30 degrees. In another embodiment of the invention, the patellar ligament is advanced so that the angle is decreased in the range of 5 to 15 degrees for a dog. In another embodiment of the invention, the patellar ligament is advanced so that the angle is decreased in the range of 10 to 30 degrees for a human. The patellar ligament may be advanced by inserting a spacer between the ligament and the tibia proximal to the insertion point of the ligament. The spacer may be fixed to the tibia. 
         [0034]    Having disclosed at least one embodiment of the present invention, various adaptations, modifications, additions, and improvements will be readily apparent to those of ordinary skill in the art. Such adaptations, modifications, additions and improvements are considered part of the invention which is only limited by the several claims attached hereto.