Abstract:
Disclosed is a device and method of bicompartmental arthroplasty of the knee. The device permits arthroplasty of the medial or lateral and patellofemoral compartments of the knee while leaving the opposite compartments and the anterior and posterior cruciate ligaments intact. The device provides a femoral prosthesis component that includes a trochlear surface and a tibial prosthesis component which can be secured to the tibia. The femoral component is essentially “u” shaped having an anterior leg upon which the trochlear surface is positioned and a posterior leg which engages the posterior surface of the distal end of the femur. The femoral component also has a convex articulating surface which engages a concave articulating surface of the tibial prosthesis component to approximate the articulation of a healthy knee.

Description:
FIELD OF THE INVENTION 
   This invention relates to a device and method for bicompartmental arthroplasty for resurfacing of either the medial joint and the patellofemoral joint of the knee or the lateral and patellofemoral joint of the knee in order to treat the pain associated with arthritis. The present device and method resurfaces either the medial or lateral joints depending on which compartment is diseased, but does not resurface both the lateral (outside) and medial (inside) compartment of the knee at the same time. 
   BACKGROUND OF THE INVENTION 
   Total knee joint replacement (arthroplasty) is a common and very successful surgery for people with degenerative arthritis (osteoarthritis) of the knee. Over 200,000 patients a year in the United States undergo total knee replacement surgery. Total knee replacement puts an artificial surface on all parts of the knee joint that contact each other as the knee bends. The damaged cartilage is removed, a small amount of bone is removed, the knee implant is attached to the distal end of the femur and proximal end of the tibia, and the patella is resurfaced if necessary. The implant typically is made of metal and plastic and provides an artificial articulating surface which causes no pain to the patient. Unfortunately total knee replacement results in sacrifice of the anterior and posterior cruciate ligaments. 
   More recently, unicompartmental knee arthroplasty has been utilized where there is arthritic damage to only a single compartment of the knee and no damage to the other compartments. The inside (medial) component (medial tibial plateau and the medial femoral condyle) is most commonly involved and replaced using unicompartmental arthroplasty. However, occasionally, the outside (lateral) compartment (the lateral tibial plateau and the lateral femoral condyle) is sometimes involved and must be replaced. Also the knee cap, i.e., the patellofemoral compartment (the patella and femoral trochlear notch) may also develop osteoarthritis. Heretofore, if more than a single compartment of the knee had arthritic disease, total knee replacement was the only available treatment. The present invention provides a device and method for bicompartmental arthroplasty which permits the resurfacing of the medial and patellofemoral joints of the knee or the lateral and patellofemoral joints without the necessity for resurfacing of the opposite compartment of the knee or the sacrifice of the anterior or posterior cruciate ligaments. 
   BRIEF DESCRIPTION OF THE INVENTION 
   A device for bicompartmental arthroplasty of a patient&#39;s knee in accordance with the present invention comprises a femoral prosthesis component configured to resurface the patellofemoral and one other compartment of the knee i.e., either the medial compartment or the lateral compartment depending on which compartment is diseased. The femoral prosthesis component has a first internal surface configured to be secured to a surgically prepared distal end of the one other compartment of the patient&#39;s femur so that the anterior and posterior cruciate ligaments remain intact. The femoral prosthesis component also has a second exterior convex curved surface positioned and configured to replicate a femoral condyle for that compartment and a concave trochlea surface positioned and configured to articulate with the patella. The device also comprises a tibial prosthesis component configured for the one other compartment of the knee having a first interior surface configured to be secured to a surgically prepared proximal end of the one other compartment of the patent&#39;s tibia and a second concave curved exterior surface configured to receive the second convex curved surface of the femoral prosthesis component to permit pivotal articulation between said femoral prosthesis component and the tibial prosthesis component, approximating the articulation of a healthy knee joint. 
   A method of performing bicompartmental arthroplasty of a patellofemoral and one other compartment of a patient&#39;s knee comprises the steps of making an incision along the anterior aspect of the one other compartment of the knee, excising the remnants of the meniscus of the one other compartment, surgically preparing a proximal end of the one other compartment of the patient&#39;s tibia to receive a tibial prosthesis component in a manner so as to preserve the integrity of the anterior and posterior cruciate ligaments. The tibial prosthesis component has a first surface configured to be secured to the surgically prepared one other compartment of the proximal end of the tibia and a second concave curved surface. Next the patella is rotated approximately 90 degrees. The distal end of the one other compartment of a the patient&#39;s femur is surgically prepared to receive a femoral prosthesis component. The femoral prosthesis component has a concave trochlea surface and a first surface configured to be secured to the surgically prepared one other compartment of the distal end of the femur. The femoral component also has a second convex curved surface configured to replicate the condyle and articulate with the second concave curved surface of the tibial prosthesis component to permit pivotal articulation between the femoral prosthesis component and the tibial prosthesis component in a manner approximating the articulation of a healthy knee joint. The femoral component is next secured to the femur and the tibial component is secured to the tibia. The patella is positioned over the concave trochlea surface of the femoral prosthesis component and the incision is closed. 
   If the patella is also diseased, the method also comprises the additional steps of surgically preparing a posterior surface of the patent&#39;s patella to receive a patella prosthesis component having a first surface configured to be secured to the surgically prepared posterior surface of the patella, and a convex curved second surface configured to engage the concave trochlea surface of the femoral prosthesis component, and securing the patella prosthesis component to the patella. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a perspective view of the articular surface of a medial femoral prosthesis component in accordance with the present invention. 
       FIG. 1B  is a side view of the medial femoral prosthesis component of FIG.  1 . 
       FIG. 2  is a front view of the medial femoral prosthesis component of  FIG. 1 and a  medial tibial prosthesis component of the present invention as surgically implanted on a human knee. 
       FIG. 3  is a rear view of a device for bicompartmental arthroplasty of the knee in accordance with the present invention as surgically implanted on a human knee. 
       FIG. 4  is a front view of a device for bicompartmental arthroplasty in accordance with the present invention as implanted on a human knee showing the position of the patella on the device. 
       FIG. 5  is a front view of a human knee flexed 90° showing the medial femoral prosthesis component and the medial tibial prosthesis component implanted on the knee. 
       FIG. 6  is a lateral side view of a knee showing the positioning of the patella and a patella prosthesis component. 
       FIG. 7  is a side view of a patella component that may be used in conjunction with the present invention. 
       FIG. 8  is a side view of one type of medial tibial prosthesis component for use in connection with the present invention. 
       FIG. 9  is an upper side perspective view of the prosthesis of FIG.  8 . 
       FIG. 10  is an upper side perspective view of an alternative medial tibial prosthesis component that may be used in connection with the present invention. 
       FIG. 11  is a side view of the prosthesis shown in FIG.  10 . 
       FIG. 12  is a front view of an alternative embodiment of the present invention for the lateral compartment of the knee as implanted on a human knee. 
       FIG. 13  is a rear view of the embodiment of FIG.  12 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1A and B  illustrate a medial femoral prosthesis component  10  for use in connection with a combination device for bicompartmental arthroplasty of the knee. The prosthesis  10  is essentially u-shaped with one leg of the “u” forming the anterior (front) portion  20  of the prosthesis and the other leg of the “u” forming the posterior (rear) portion  22  of the prosthesis and a base portion  21  connecting the anterior and posterior portions  20  and  22 . The medial femoral prosthesis component  10  has an interior first surface  12  which is configured to be secured to a surgically prepared portion of the distal end of the medial compartment of the femur  26  as shown in  FIG. 2  as will be described in more detail below. The exterior surface  14  of component  10  has a concave trochlear groove  16  formed on the anterior surface of the leg  20  of prosthesis component  10 . A convex second surface  18  is formed on the medial side of the base portion  21  of prosthesis  10  and is configured to replicate the medial femoral condyle of the knee. A post  13  is mounted to the interior surface  12  of base portion  21  and extends essentially perpendicularly from that surface. Post  13  is inserted into a hole drilled in the femur during surgical preparation to aid in securing the component  10  to the femur  26 . More than one post  13  could be mounted to device  10  as necessary. 
   With reference to  FIG. 2 , the prosthesis component  10  is shown in position as it would be on the distal end of the femur  26  of the human knee. The anterior leg  20  of the “u” shaped medial component  10  is positioned over a surgically prepared anterior surface of the femur  26 . With reference to  FIG. 3 , the posterior leg portion  22  of medial component  10  extends upwardly along the posterior surface of a surgically prepared medial compartment of the distal end of the femur  26 . The interior first surface  12  can be textured to facilitate attachment to the femur using a cement or it may have a bone ingrowth surface applied so that the bone will grow into the ingrowth surface thereby securing component  10  to the femur. Prior to implanting, the distal end of the femur  26  is surgically prepared to remove the diseased portions of the distal end of the femur and the remnants of the medial meniscus are excised or removed. The distal end of the femur is then cut to mate with the interior surface  12  of component  10  and a hole is drilled to accommodate post  13 . 
   With reference to  FIG. 2 , a medial tibial prosthesis component  28  is shown secured to a surgically prepared portion of the proximal end of the tibia. With reference to  FIGS. 8 and 9 , the medial tibial component  28  has a first flat surface  30  and a second concave surface  32 . The concave surface  32  of the medial tibial component  28  is configured to articulate with the convex second surface of the medial femoral component  10 . Flat surface  30  has a post  31  extending perpendicularly from that surface and is configured and adapted to be secured to a surgically prepared portion of the medial compartment of the tibia  34 . Flat surface  30  can be textured to facilitate attachment by cement or it can have a bone ingrowth surface applied so that the bone will grow into the ingrowth surface thereby securing the component  28  to the tibia. As illustrated in  FIGS. 2 and 3 , a portion of the tibial plateau is surgically removed so that the medial component  28  can be attached. The medial tibial component  28  illustrated in  FIGS. 8 and 9  is comprised entirely of a plastic material that is biomedically compatible with the human body. 
     FIGS. 10 and 11  illustrate an alternative embodiment of a medial tibial prosthesis component for use in connection with the present invention. The  FIGS. 10 and 11  component comprises a flat metallic base  36  to which a plastic insert  38  with a flat base  37  and a concave upper surface  39  is attached either rigidly to or to allow rotation or movement upon the fixed base plate  37 . The plastic insert  38  can be formed of the same plastic materials as component  28  illustrated in  FIGS. 8 and 9 . Metal base portion  36  has a flat first surface  40  and a downwardly extending flange  42  along one edge which is designed and configured to extend into a corresponding groove cut into the posterior surface of the tibia so as to aid in securing base section  36  to the tibia. Surface  40  can either be textured to aid in securing base portion  36  to the tibia using a cement, or a bone ingrowth surface can be applied to surface  40  so that base portion  36  can be secured to the tibia by bone growth into the bone ingrowth surface. 
   It can be appreciated from  FIGS. 2 ,  3  and  5  that the lateral compartment of the knee remains in its natural state due to the fact that device  10  is affixed only to the medial compartment of the knee. Consequently, the anterior and posterior cruciate ligaments  70  and  72  remain intact and are not compromised by the device  10  or its implantation. 
   With reference to  FIGS. 4 and 6 , patella  50  is shown in its normal position in the trochlear groove  16  of medial femoral component  10 . The patellar tendon  52  covers the patella and is attached at one end  54  to the anterior surface of the tibia and the other end  56  to the quadriceps muscle (not shown). Contraction of the quadriceps muscles pulls the patella through the trochlear groove, thereby lifting the tibia. 
   If there is arthritic disease of the patella, it may be necessary to replace the diseased posterior surface of the patella with a plastic prosthesis component. With reference to  FIG. 6 , patella  50  is shown in dotted lines under the patellar tendon  52 . Also shown in dotted lines is a patellar component  58  as it would be positioned in a surgically prepared posterior surface of the patella  50 . With reference to  FIG. 7 , a side view of a patella prosthesis component  58  is shown. Patella component  58  is configured to have a convex surface  60  configured and dimensioned to engage and articulate in the trochlea surface  16  of the medial femoral prosthesis component  10 . Patellar insert component  58  also comprises a surface  62  which includes a post  64  configured and adapted to be secured to a surgically prepared posterior surface of the patella. 
   As discussed above, the interior surface  12  of femoral component  10  can either be configured to be secured to the femur by the use of a cement, or a bone ingrowth surface may be applied to the interior surface  12  so that the femur bone will grow into and more permanently secure the femoral component to the femur. Such bone ingrowth surfaces are well-known in the art and have previously been used in connection with both unicompartmental and full knee replacement prosthesis. Similarly, the medial tibial prosthesis component  28  can either be secured to the tibia by use of a cement or also by the use of a bone ingrowth surface applied to the tibial component so that the bone structure of the tibia will grow into the bone ingrowth surface to more permanently secure the tibial component to the tibia. 
   With reference to  FIGS. 3 and 5 , it can be seen that the present invention can be implanted in the knee without disturbing or damaging the middle third of the knee joint where the anterior cruciate ligament  70  and the posterior cruciate ligament  72  are located. Thus, the present invention allows a bicompartmental knee arthroplasty that preserves the integrity of the anterior and posterior cruciate ligaments. 
   To implant the  FIG. 1-4  embodiment in a patient, a 3 to 4 inch longitudinal incision is made on the anterior aspect of the knee from the medial aspect of the patellar tendon 1 centimeter below the joint line extending approximately 3 to 4 inches in a vertical fashion. The incision is opened along the length of the incision with a medial parapatellar arthrotomy extending in a minimal fashion into the quadriceps femoris muscle medially. The remnants of the medial meniscus are excised. A portion of the fat pad is excised with care being taken to preserve the integrity of the anterior and posterior cruciate ligaments. 
   Surface cuts are made on the medial tibial articular surface using the technology previously employed by the Accuris® unicompartmental arthroplasty of Smith and Nephew Orthopedics, Inc. After the tibial cut is made, the patella is subluxed or rotated 90°. The intramedullary canal at the distal end of the femur is exposed using a ⅜ inch drill bit. An intramedullary rod is inserted into the distal femur until a distal femoral cutting block is flush against the distal medial femur. A distal femoral cutting block of the appropriate angle is attached after the cutting block is pinned in place, the distal femoral cut is made with an oscillating saw. The jig is removed and a sizing block is placed against the distal femur in order to reference the posterior medial femoral condyle. A stylus is attached in order to reference the anterior thickness of the distal femur and the appropriate size of the femoral prosthesis  10  is selected, the appropriate femoral cutting block is attached to the intramedullary rod in the appropriate rotation. The block is pinned and the distal anterior cutting block is used to remove the anterior surface of the distal femur. 
   Anterior and posterior chamfer cuts are made from the medial aspect of the distal femur followed by a posterior femoral cut for the medial femoral condyle. The anterior chamfer cut is extended over the medial aspect of the lateral femoral condyle and a sagittal saw using a freehand technique is used to complete the trochlear cut. 
   Next, a trial reduction with the femoral component  10  and tibial component  28  is employed to assure correct surgical preparation and sizing. The extent of possible arthritic disease of the patella is next assessed. If there is extensive disease of the patella, the patella is rotated approximately 90° and an inset patella reamer is applied to the posterior surface of the patella and the patella is reamed to permit the inset of a patella prosthesis component  58 . Alternatively, an onset or a mobile bearing patella prosthesis may be used as is well known in the art. 
   A partial lateral facetectomy is typically performed to limit the patellar contact with the transition zone of the distal femur and the femoral component  10 . The patellar implant  58  should be medialized to assist with patella tracking. Release of the medial collateral ligament can be employed as necessary to allow for ligamentous balancing of the arthroplasty. 
   The femoral tibial and patellar implants  10  and  28  are next either cemented in the usual fashion if the trial reduction is found to be satisfactory or securely placed over the prepared bone surface so that bone ingrowth can occur if the components have a bone ingrowth surface applied. The knee capsule is closed with a non-absorbable suture followed by skin closure and sterile metal staples with sterile dressing. 
   With reference to  FIGS. 12 and 13 , an alternative embodiment of the present invention is shown. While in most cases, the medial compartment of the knee is more prone to be subject to arthritic disease than the lateral compartment, in some cases, the lateral compartment may be diseased while the medial compartment remains healthy and unaffected. This alternative embodiment is designed for those situations where the lateral and patellofemoral joints are affected, but the medial compartment is not. 
   A lateral femoral prosthesis component  100  similar to the medial femoral prosthesis component  10  of  FIG. 1  except it is configured for the lateral compartment rather than the medial compartment. Lateral femoral prosthesis component  100  is essentially “u” shaped having a first anterior leg portion  102  and a second posterior leg portion  104  that are joined by a base portion (not shown). Anterior leg portion  102  has a trochlear groove  106  formed on the face thereof to receive and articulate with the patella. Lateral femoral prosthesis component  100  has an interior surface within the “u” (not shown) similar to the interior surface  12  of component  10  that can be secured to a surgically prepared portion of the lateral compartment of the femur  108  using either a cement or a bone ingrowth surface as describe previously. 
   A lateral tibial prosthesis component  110  similar to the medial tibial component  28  of  FIGS. 1-4  is shown in  FIGS. 12 and 13  as implanted on a surgically prepared lateral compartment of tibia,  112 . Component  110  has a flat bottom surface and a concave upper surface that receives and articulates with a convex outer surface (not shown) on the base portion of the femoral prosthesis component  100  in the same manner as describe previously with respect to the  FIG. 1  embodiment. Also, tibial component  110  can be fabricated from both metal base and a plastic insert as shown in  FIGS. 10 and 11 . 
   Femoral component  100  and tibial component  110  are also configured and designed so that they can be implanted without causing any damage to the middle portion of the knee so that the anterior and posterior cruciate ligaments remain intact after implantation. 
   It should be appreciated that both femoral prosthesis components  10  and  100  and tibial prosthesis components  28  and  110  can be fabricated from either a metallic material or from plastic. Typically, one component is fabricated from one material and the opposing component is fabricated from the other material so that there is a metal on plastic articulating joint for wear purposes. However, both parts could be fabricated from the same material. A variety of metallic materials can be used including but not limited to stainless steel, cobalt chrome steel, titanium, Zirconia, ceramics and tantalum. Also, a variety of plastic materials can be used including but not limited to polyethylene, polycarbonate-based polyurethane, and implantable-grade polymethyl methacrylate (PMMA). 
   It should be recognized that the preferred embodiment of the present invention as described above can be varied or modified without departing from the spirit and scope of the present invention as described and claimed in the following claims.