Abstract:
A prosthetic knee implant for implantation into a mammal, which accommodates an anterior cruciate ligament substitute to provide stability to the knee implant. The prosthetic knee implant includes a femoral component having a pair of condylar surfaces and a tibial component having a surface portion adapted to slidably engage the femoral component upon rotation of the same. The femoral component further includes a central femoral recess between the condyles providing access to the femur for drilling a channel through which a cruciate ligament substitute may be integrated into the femur. The tibial component further includes a center portion defining an aperture through which the ligament substitute maybe threaded through the tibia and integrated therein, or anchored upon its surface. Also disclosed is a method used to replace the total knee joint in a mammal with the improved prosthetic knee implant of the present invention.

Description:
This application claims the benefit of filing priority under 35 U.S.C. §119 and 37 C.F.R. §1.78 from U.S. Nonprovisional application Ser. No. 12/134,713 filed Jun. 6, 2008, for a Total Knee Prosthesis and Method for Total Knee Arthroplasty. All information disclosed in the prior application is incorporated herein by reference 
     FIELD OF INVENTION 
     The present invention relates generally to prosthetic knee implants and corresponding surgical methods used to replace the total knee joint in a mammal. More particularly, the invention relates to a prosthetic knee implant having a femoral component and a tibial component, which are adapted to receive an anterior cruciate ligament substitute for biasing the femur and tibia together. 
     BACKGROUND OF INVENTION 
     Mammalian knees wear out for a variety of reasons, including inflammation from arthritis, injury, or simple wear and tear. Over the past 40 years, total knee arthroplasties (commonly referred to as total knee replacements or “TKR”) have become the standard of care for end-stage arthritis. In most TKR procedures, the natural bearing surfaces of the upper portion of the tibia (tibial plateau) and the lower portion of the femur (femoral condyles) are resected and replaced with artificial material. Specifically, approximately between 0.5 to 1.5 centimeters of the upper portion of the tibia, including both the intercondylar eminence and the medial and lateral tibial plateaus, are resected, leaving a relatively flat surface onto which a rigid support member is affixed. Then, a synthetic surface portion is affixed to the support member, with the surface portion simulating the intercondylar eminence and the tibial plateaus. A lower end portion of the femur is then resected, and a member having bearing surfaces replicating the femoral condyles is then affixed to the remaining end of the femur. 
     The majority of currently available prosthetic knee implants employed for TKR do not retain the natural anterior cruciate ligament. Rather, during the implant procedure, the anterior cruciate ligament is either removed or, if preservation is attempted, has been found to rupture shortly after implant of the prosthesis. This is particularly true for TKR candidates, who often have a sacrificed anterior cruciate ligament going into the surgery. As a result, the mechanical interaction between the femoral and tibial components in a TKR is the primary means to stabilize the anterior-posterior motion of the knee. 
     Although the existing TKR prostheses succeed in increasing patient mobility, and provide the patient with the desired therapeutic result, at least one significant disadvantage remains. Namely, in a TKR wherein the anterior cruciate ligament is lacking, the femoral condyles translate in a posterior direction in full extension and translate in an anterior direction in flexion, which is reverse of the motions in a natural knee joint. Such abnormal translation and pivot shift often results in the patient&#39;s compromised functional abilities, such as quadriceps avoidance, and changed upper body mechanics during activities such as stair climbing and rising from a chair. Even asymptomatic patients show gait abnormalities that could lead to reduced functional ability to perform activities of daily living over time. 
     Further, abnormal anterior translation of the TKR can lead to accelerated wear of the prosthesis. Indeed, current TKR prostheses have a functional lifespan of approximately 15 years, such that younger patients (who are increasingly receiving TKRs) are more likely to require revision surgery as they age. The amount of bone loss that is inherent in a TKR makes a revision procedure much more difficult in the future as even more bone must be removed. 
     Existing TKR prostheses attempt to compensate for the loss of the anterior cruciate ligament by containing or limiting the amount of abnormal translation in the nonstabilized knee. For example, U.S. Pat. No. 5,413,604 discloses a TKR prosthesis wherein the anterior cruciate ligament must be sacrificed, thereby resulting in a nonstabilized TKR with abnormal anterior translation. Without an anterior cruciate ligament, the prosthesis relies primarily on the mechanical interaction between the femoral and tibial components as a means to accommodate the abnormal anterior translation and stabilize the knee. Similarly, U.S. Pat. No. 7,014,660 discloses a TKR prosthesis that incorporates a control arm and stop pin assembly to limit the amount of anterior sliding movement caused by the lack of the anterior cruciate ligament. Unfortunately, neither prosthesis disclosed in the &#39;604 and &#39;660 patents actually prevents the abnormal anterior translation of the nonstabilized TKR; or as shown in recent medical research pertaining to medial and lateral translation of ACL deficient knees, rather, they only attempt to accommodate or limit it. As a result, the patient&#39;s functional abilities remain limited, and the prosthesis is subject to premature wear and tear. The U.S. Pat. Nos. 5,413,604 and 7,014,660 are hereby incorporated by reference in their entireties. 
     Therefore, there exists a constant need in this art for an improved TKR prosthesis that allows for the replacement of an anterior cruciate ligament, and approaches the mobility, stability and longevity of a natural, healthy knee joint. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a prosthetic knee implant, and more particularly, to a prosthetic knee implant having a femoral component including a medial and lateral condyle, and a tibial component including a surface portion adapted to slidably engage the femoral component upon rotation of the same. The femoral component includes diverging curved members extending downward and placed on or near the medial and lateral condyles. These members define a recess in the lower central portion of the femoral component. The tibial component includes a center portion defining an aperture through the tibial component substantially at its center. The central femoral recess and the tibial aperture are adapted to receive an anterior cruciate ligament substitute for biasing the femur and the tibia together. 
     In addition, a method of total knee joint replacement in a mammal is presented consisting of replacing at least a portion of the lower femur with the improved prosthetic femoral component; replacing at least a portion of the upper tibia with the improved prosthetic tibial component; engaging a drill alignment guide to the femur between the femoral condyles and drilling a longitudinal channel through the central femoral recess and into the femur; engaging a drill alignment guide to the tibial component and extending the tibial aperture by drilling a longitudinal channel through the tibia aperture and into the tibia. The method further includes threading an anterior cruciate ligament substitute into the femoral channel and into the tibial channel and anchoring a first end of the ligament substitute to bone leaving a free end; applying tension to the free end; and, anchoring the free end to bone under tension such that said femur and the tibia are biased together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A total knee prosthesis apparatus and a method for total knee replacement incorporating the features of the invention are depicted in the attached drawings which form a portion of the disclosure and wherein: 
         FIG. 1  is an anatomical view of a human knee joint having an anterior cruciate ligament and posterior cruciate ligament; 
         FIG. 2  is a diagram of a prosthetic knee implant in accordance with a preferred embodiment of the present invention, and implanted at the joint between a human femur and tibia to provide a total knee replacement; 
         FIG. 3  is a perspective view of the prosthetic knee implant of  FIG. 2 ; 
         FIG. 4  is an exploded perspective view of the tibial component; 
         FIG. 5  is a partial exploded view of the femoral component; 
         FIG. 6A  is an illustration of the femur of  FIG. 2  having the femoral channel drilled longitudinally through the central femoral recess and into the femur; 
         FIG. 6B  is an illustration of the femur of  FIG. 2  with an aligned drill guide for drilling longitudinally through the central femoral recess and into the femur. 
         FIG. 7  is an illustration of the tibia of  FIG. 2  having the tibial channel drilled longitudinally through the tibial aperture and into the tibia; 
         FIG. 8  is a combined illustration of  FIG. 6A  and  FIG. 7 , further depicting the femoral channel and tibial channel in substantial alignment in accordance with a preferred embodiment of the present invention; 
         FIG. 9  illustrates the anterior cruciate ligament substitute with a self-anchoring umbrella-type anchor being threaded downward through the femoral channel and tibial channel; and 
         FIG. 10  illustrates the anterior cruciate ligament substitute threaded through the femoral and tibial channels, under tension, and anchored to the exterior surfaces of the femur and tibia with umbrella-type anchors. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings for a better understanding of the function and structure of the invention,  FIG. 1  shows a typical patient&#39;s natural knee joint  10  prior to the surgical procedure. Illustrated is upper portion  23  of the tibia  20  the upper portion  26  of the fibula  25 , the lower portion  18  of the femur  15 , the exterior surface  19  of the femur  15 , as well as the medial condyle  16  and lateral condyle  17 . The anterior cruciate ligament  11  and the posterior cruciate ligament  14  are seen to be present in the knee joint  10 . One end  12  of the anterior cruciate ligament  11  is attached to the anterior portion of the intercondylar eminence  21  of the tibia  20 , and the second end  13  of the anterior cruciate ligament  11  is attached to the posterior portion of the medial aspect of the lateral femoral condyle  17 , thereby defining an axis  33  of the anterior cruciate ligament  11 . The posterior cruciate ligament  14  passes upward and forward on the medial side of the anterior cruciate ligament  11 , extending from behind the intercondylar eminence  21  to the lateral side of the medial condyle  16  of the femur  15 . Also seen is the exterior surface  22  of the tibia  20 , the tibial plateau  24 , the medial meniscal cartilage  27  and lateral meniscal cartilage  28 . 
     The femur  15  and tibia  20  extend along a mechanical axis  32  which is generally parallel to the tibia  20  and passes through the head  30  of the natural hip joint (not shown). The tibia  20  rotates about an axis  31  relative to the lower portion  18  of the femur  15  that bisects the condyles  16  and  17  and is generally perpendicular to the mechanical axis  32 . Axis  31  corresponds with what is referred to in the medical industry as the “knee joint line,” this joint line being separated into a medial joint line portion which is the portion of the joint line starting at the intersection of the axis  32  and axis  31  and extending to the right (i.e. in the medial direction) of the knee joint, and a lateral joint line which is the portion of the line starting at the intersection of the axis  32  and axis  31  and extending to the left (i.e. in the lateral direction) of the knee joint. During articulation of the knee joint  10  between flexion and extension, the medial condyle  16  engages the tibia  20  along a medial bearing surface bordered by the medial meniscal cartilage  27 , while the lateral condyle  17  engages the tibia  20  along a lateral bearing surface bordered by the lateral meniscal cartilage  28 . The anterior crucial ligament  11  limits forward movement of the tibia  20  under the femoral condyles  16  and  17 , while the posterior cruciate ligament  14  limits backward movement of the tibia  20  under the femoral condyles  16  and  17 . 
     Referring now to  FIG. 2 , the natural knee joint  10  has been replaced by a prosthetic knee implant  40  constructed in accordance with a preferred embodiment of the present invention. The prosthetic knee implant  40  includes a femoral component  41  affixed to the lower portion  18  of the femur  15  and a tibial component  60  affixed to the upper portion  23  of the tibia  20 . The femoral component  41  includes a tibial axis of rotation  49  relative to the lower portion  18  of the femur  15  that is generally perpendicular to the mechanical axis  32  and is also oriented in substantial similarity to axis  31  of  FIG. 1 . 
     Referring to  FIGS. 3 and 4 , the femoral component  41  includes a replacement medial condyle  42  and a replacement lateral condyle  43  of the femur  15 . Normally, the ends of the femoral condyles  16  and  17  are resected and shaped to receive the femoral component  41  and affixed to the femur  15  as is known in the art, such as adhesion using bone cement and/or pegs extending into the condyles  16  and  17 . 
     The tibial component  60  includes a surface portion  61  adapted to slidably engage the femoral component  41  upon rotation of the tibia  20  about tibial axis  49 , in such a manner as to enable the prosthetic knee implant  40  to serve as a substitute for the natural knee joint  10  for relative motion of the femur  15  and tibia  20  between flexion and extension. In a preferred embodiment, the tibial component  60  provides replacement bearing surfaces in the form of lateral bearing surface  69  for engagement by the lateral condyle  43  and medial bearing surface  70  for engagement by the medial condyle  42  of the prosthetic knee implant  40 . The tibial component  60  further includes a center portion  62  that defines an aperture  63  through the tibial component  60  substantially at its center. Preferably, the tibial aperture  63  is of sufficient size to accommodate a replacement anterior cruciate ligament. 
     Typically, the natural anterior cruciate ligament  11  is removed, along with approximately between 0.5 to 1.5 centimeters of the upper portion  23  of the tibia  20 , including the tibial plateau  24 , the intercondylar eminence  21 , the medial meniscal cartilage  27 , and the lateral meniscal cartilage  28 , thereby leaving a relatively flat surface onto which the tibial component  60  is affixed. In a preferred embodiment, the tibial component  60  includes a support member in the form of a platform  71  having a unitary depending stem  72  inserted into the tibia  20  to assist in the accurate location and affixation of the platform  71  on the tibia  20 . In a preferred embodiment, a surface portion  61  is secured in place on platform  71  to be interposed between the femoral component  41  and platform  71  for providing medial and lateral bearing surfaces  70  and  69  and for engagement by the medial condyle  42  and the lateral condyle  43 , respectively, to enable articulation of the prosthetic knee implant  40 . The condyles  42  and  43  preferably are constructed of a biocompatible high-strength alloy, while the preferred material for the surface portion  61  is a synthetic polymeric material, such as high-density polyethylene. Surface portion  61  may be secured in place on platform  71  by means of any of several securing arrangements as described in greater detail in U.S. Pat. No. 5,413,604. 
     In effecting implant of the prosthetic implant  40 , the anterior cruciate ligament  11  of the natural knee has been sacrificed. Thus, during articulation of the prosthetic implant  40  between flexion and extension the condyles  42  and  43  translate in a posterior direction in full extension and translate in an anterior direction in flexion, as described in greater detail in U.S. Pat. No. 5,413,604, col. 4, lines 41-67. 
     Referring to  FIG. 5 , the femoral component  41  includes the two diverging curved medial and lateral condyle members  42 , 43  that extend downward and define a recess  45  in the lower central portion of the femoral component. The central femoral recess  45  provides access to the femur  15  between the medial and lateral condyles  16  and  17 , now resected in favor of implant condyles  42  and  43 . Preferably, the central femoral recess  45  is of sufficient size to accommodate the integration of an anterior cruciate ligament substitute through a channel in the femur, as will be described. 
     Referring to  FIG. 6A , a longitudinal channel  46  is drilled in a conventional manner through the central femoral recess  45  and into the femur  15 . In a preferred embodiment, the femoral channel  46  has lower opening  47  and upper opening  48 . Alternatively, femoral channel  46  does not extend through the exterior surface  19  of the femur  15  but terminates within the femur  15  bone where it is implanted. The femoral channel  46  is drilled using a conventional two-step process with the engagement of a drill guide (depicted in  FIG. 6B ) to the femoral component  41  between the femoral condyles  42  and  43  in the central femoral recess  45 , followed by a drill  50  to create the femoral channel  46  of sufficient size to accommodate an anterior cruciate replacement. In a preferred embodiment, the drill guide (depicted in  FIG. 6B ) is configured to align the femoral channel  46  with the tibial aperture  66 , as will be discussed. The femoral channel  46  is typically debrided of all surrounding debris at upper opening  48 , and any sharp edges are chamfered using a conventional bone rasp or reamer. 
     Referring to  FIG. 6B , there is shown a drill guide  51  engaged adjacent to the femoral component  41  to provide a temporary guide for the drill  50  while drilling the femoral channel  46  through central femoral recess  45 . In a preferred embodiment, the guide  51  includes a first sleeve  52  and a second sleeve  53  aligned longitudinally along a drilling axis  54 . The first sleeve  52  and second sleeve  53  each include an aperture  55  and  56  disposed longitudinally along the drilling axis  54  suitable for allowing the passage of a drill bit  50 . 
     Referring to  FIG. 7 , a longitudinal channel  64  is drilled in a conventional manner into the tibia  20  and through the tibial aperture  63 . In a preferred embodiment, the tibial channel  64  has lower opening  65  and upper opening  66 . Alternatively, tibial channel  64  does not extend through the exterior surface  22  of the tibia  20  but terminates within the tibia  20  bone and to which it is anchored. The tibial channel  64  is drilled using a conventional two-step process with the engagement of a drill guide  51  ( FIG. 6B ) to the tibial component  60 , followed by a subsequent drill  50  to create the tibial channel  64  of sufficient size to accommodate an anterior cruciate ligament substitute. The tibial channel  64  is typically debrided of all surrounding debris at lower opening  65 , and any sharp edges are chamfered using a conventional bone rasp. In a preferred embodiment, the surface portion  61  is affixed to platform  71  after the drilling of the tibial channel  64  to prevent damage to the surface portion  61  during drilling. Preferably, the tibial channel  64  and the femoral channel  46  are in alignment and are oriented along an axis generally parallel to the axis  33  of an anatomic anterior cruciate ligament  11 . 
     As mentioned above, the drill guide  51  ( FIG. 6B ) may also be engaged with the tibial component  60  to facilitate drilling of the tibial channel  64 . Specifically, the second sleeve  53  may be adapted to nest in and mate with the tibial aperture  63  to define a drilling axis for the drill  50  while drilling the tibial channel  64 . The tibial channel  64  may be drilled from the lower opening  65  to the upper opening  66 , or vice versa. 
     Referring to  FIG. 8 , there is shown a prosthetic knee implant  40  constructed in accordance with a preferred embodiment. The femoral channel  46  extends through the exterior surface  19  of the femur  15  having lower opening  47  and upper opening  48 . The tibial channel  64  extends through the exterior surface  22  of the tibia  20  having lower opening  65  and upper opening  66 . Femoral channel  46  and tibial channel  64  are preferably in alignment and oriented along an axis  67  generally parallel to the axis  33  of a natural anterior cruciate ligament  11 . The prosthetic implant  40  is now ready to have an anterior cruciate ligament substitute implanted. 
     The types of anterior cruciate ligament substitutes that can be used in the present invention include allografts, autografts, xenografts and synthetic grafts. Allografts include ligamentous tissue harvested from cadavers and appropriately treated, disinfected, and sterilized. Autografts consist of the patient&#39;s own ligamentous tissue harvested either from the patellar tendon or from the hamstring, or other substitute. Xenografts include ligamentous tissue harvested from one mammalian species and transplanted into or grafted onto another species, genus, or family (such as from porcupine to a human). Synthetic grafts include grafts made from synthetic polymers such as polyurethane, polyethylene, polyester and other conventional biocompatible, bioabsorbable or nonabsorbable polymers and composites. 
     Referring to  FIG. 9 , an anterior cruciate ligament substitute  80  is threaded down into the femoral channel  46  and the tibial channel  64 . There are numerous methods and instruments known in the art that may be utilized to thread the anterior cruciate ligament substitute  80 , which include the use of a suture passer (such as those disclosed in U.S. Pat. Nos. 5,746,754; 5,439,467; and 5,462,562), a graft-passing wire (such as that disclosed in U.S. Pat. No. 6,623,524), or a ligature carrier (such as that disclosed in U.S. Pat. No. 6,245,073 col. 2 lines 23-25) U.S. Pat. Nos. 5,746,754; 5,439,467; 5,462,562; 6,623,524; and 6,245,073 are hereby incorporated by reference in their entirety. Alternatively, the second end  82  of the ligament substitute  80  is passed down into the upper opening  48  of the femoral channel  46  until it exits the lower opening  47  of the femoral channel  46 . A threading instrument  95  having a proximal handle  96  and a distal notched end  97  for engaging the ligament substitute  80  or a leading guide wire  83  attached to the ligament substitute  80  is provided. The distal end  97  of the threading instrument  95  is inserted into the lower opening  65  of the tibial channel  64  and is moved forward and out of the upper opening  66  of the tibial channel  64 . Once the ligament substitute  80  is engaged in the distal notched end  97 , the threading instrument  95  is withdrawn from the tibial channel  64 , thereby pulling the guide wire  83  and passing the second end  82  of the ligament substitute  80  down through the upper opening  66  of the tibial channel  64  and out the lower opening  65  of the tibial channel  64 . At that time, the guide wire  83  is removed from the threading instrument  95 . The first end  81  of the ligament substitute  80  is anchored to the femur  15  using a conventional securing device such as cross-pins, femoral fasteners, endobuttons, screws, or staples. In a preferred embodiment, the first end  81  of the ligament substitute  80  is anchored to the exterior surface  19  of the femur  15  at the medial aspect of the posterior lateral femoral condyle with a self-anchoring umbrella anchor  90 , as shown. Ideally, the ligament substitute  80  is coated with a substance that facilitates bone ingrowth into the ligament substitute  80 , such as a hydroxyaptite (HA) coating. Then, the second end  82  of the ligament substitute  80  is placed in tension by the surgeon while the second end  82  is anchored to the bone of the tibia  20 , thereby biasing the tibia  20  and femur  15  together. The second end  82  of the ligament substitute  80  may be anchored to the tibia  20  at the tibial anterior medial plateau, as shown, using a conventional securing device such as tibial fasteners, screws and washers, or staples. Alternatively, the ligament substitute  80  may be anchored from within the femur  15  and/or tibia  20  bone through use of a conventional securing device such as cross pins (such as those described in U.S. Pat. No. 7,032,599, col. 2, lines 42-62), screws, or anchors. 
     Referring to  FIG. 10 , there is shown a prosthetic knee implant  40  constructed in accordance with a preferred embodiment. The first end  81  of the ligament substitute  80  is disposed longitudinally through the femoral channel  46  and anchored to the exterior surface  19  of the femur  15 , and the second end  82  of the ligament substitute  80  is disposed longitudinally through the tibial channel  64  and anchored to the exterior surface  22  of the tibia  20  with a self-anchoring umbrella anchor  90 . In the preferred embodiment, the ligament substitute  80  is oriented generally parallel to the axis  33  of the natural anterior cruciate ligament  11 . 
     A surgical kit useful in practicing the method of total knee arthroplasty of the present invention is anticipated by the inventor. Such a kit would include the components previously described above. More specifically, the kit is seen to have a femoral component  41  including a replacement medial condyle  42  and a replacement lateral condyle  43 , a tibial component  60  including a surface portion  61  adapted to slidably engage the femoral component  41  upon flexion and extension of the femoral component  41 , an anterior cruciate ligament substitute  80 , and means to anchor the ligament substitute  80  to the femur  15  and tibia  20 , such as staples, screws or self-anchoring umbrella anchors  90 . The tibial component  60  further includes a center portion  62  that defines an aperture  63  through the tibial component  60  substantially at its center. The kit would further include at least one drill guide component  51  cooperatively shaped to guide a drill bit through the central femoral recess  45  adjacent to the femur and through the aperture  63  of the tibial components  60 . 
     As will be apparent to one skilled in the art, various modifications can be made within the scope of the aforesaid description. Such modifications being within the ability of one skilled in the art for a part of the present invention and are embraced by the claims below. For example, the inventor anticipates variations in the types of anchors used, the depth to which any ligament substitute end might be anchored inside bone, the degree and manner in which tension might be applied to a ligament substitute, and the placement of the apertures in the tibial components  61  and  71  for drilling. The priority in the steps of anchoring the ligament ends, whether above on the femur or below on the tibia, may be varied in accordance with the surgeon&#39;s experience and the particular operating situation is also anticipated.