Abstract:
A shock absorbent system for a joint prosthesis includes a shock absorbent material. The shock absorbent system may be used in both hip and knee joint prostheses. In one example, a knee joint prosthesis includes a tibial plate, a femoral component having a moveable condyle in contact with a shock absorbent material, wherein movement of the moveable condyle deforms the shock absorbent material, and a tray insert disposed between the tibial plate and the moveable condyle. The moveable condyle deforms the shock absorbent material under compressive forces between the tibial plate and the femoral component, thereby absorbing impact loads

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/956,427 filed Jun. 10, 2013. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to an orthopedic shock damper system, and more particularly to a shock damper system used in artificial hip and knee prosthetic joint systems. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
         [0004]    In the past, surgical techniques and prostheses have been developed to replace damaged or diseased joints. For example, acetabulofemoral joint or hip joint as well as knee joint replacement surgeries have become relatively common. A hip joint replacement surgery may be a total hip arthroplasty where both the femoral head and acetabulum are replaced or a partial hip arthroplasty where only the femoral head is replaced. A hip joint prosthesis typically includes a femoral component and an acetabular cup. The femoral component is a one-piece or two-piece femoral stem with attached prosthetic femoral head (the ball). Bone is removed from the femur, or thigh bone, so as to accept the stem of the femoral component. The acetabular cup may be either a one-piece or modular component and is sized to receive the ball of the femur component. A plastic or ceramic insert may be disposed between the femoral ball and the acetabular cup. The bone and cartilage are removed from the acetabulum so as to accept the acetabular cup. 
         [0005]    Knee joint replacement surgery may a total knee arthroplasty where the weight bearing surfaces of the knee joint are replaced with a knee joint prosthesis or a partial knee arthroplasty where compartments or segments of the weight bearing surfaces are replaced. Generally, the bone is removed from the tibia to form a tibial plateau. A tibial component having a one-piece tibial stem and a tibial platform is then attached to the tibial plateau. An insert component, typically made from polyethylene plastic, is attached to the tibial platform. A femoral component that includes artificial femoral condyles replace either one or both of the condyles of the femur. 
         [0006]    Current hip and knee prostheses are relatively inelastic, with impact loads being directly transferred between the pelvis to the femur and between the femur and the tibia. Attempts have been made to increase the shock absorption characteristics of hip and joint prostheses. For example, U.S. Pat. No. 5,839,107 by Nassar et al. discloses a shock absorbent prosthetic hip that includes a mechanical piston and spring section. However, this prosthesis increases the complexity and cost of the hip prosthesis while simultaneously increasing the chance of mechanical failure within the shock absorbent section. U.S. Pat. No. 5,735,905 by Parr discloses an elastomeric component for a hip prosthesis disposed between the femoral stem and the ball. However, this prosthesis relies on a complicated femoral component with an injected molded elastomer. Accordingly, there is a need in the art for an improved shock absorption system for both hip and knee prostheses that absorbs impact loads while minimizing complexity of the components. 
       SUMMARY 
       [0007]    A shock absorbent system for a joint prosthesis is provided. The shock absorbent system may be used in both hip and knee joint prostheses. In one example of the present invention, a hip joint prosthesis is provided. The hip join prosthesis includes a shock absorbent material disposed between an acetabular cup and an insert. In one example of the present invention, a knee joint prosthesis is provided. The knee joint prosthesis includes a tibial plate, a femoral component having a moveable condyle in contact with a shock absorbent material, wherein movement of the moveable condyle deforms the shock absorbent material, and a tray insert disposed between the tibial plate and the moveable condyle. The moveable condyle deforms the shock absorbent material under compressive forces between the tibial plate and the femoral component, thereby absorbing impact loads. A honey comb pattern may be formed on all areas of the hip joint prosthesis and the knee joint prosthesis that meet the bone of the recipient of the prostheses so as to facilitate bone growth. The characteristics of the shock absorbent material may be gender and weight specific and the prostheses are custom made to a recipient using a bone mapping procedure. 
         [0008]    In one aspect of the present invention, the femoral component includes a base support that defines a slot, and the moveable condyle is disposed within the slot. 
         [0009]    In another aspect of the present invention, the base support includes a back plate, and the shock absorbent material is in contact with the moveable condyle and the back plate. 
         [0010]    In another aspect of the present invention, the back plate includes a stepped portion having a treated surface configured to engage a matching slot on a femur. 
         [0011]    In another aspect of the present invention, the back plate includes a stem configured to be secured within a femur. 
         [0012]    In another aspect of the present invention, the shock absorbent material is comprised of a material having a honeycomb cross-section. 
         [0013]    In another aspect of the present invention, a deformation characteristic of the shock absorbent material is tuned for a recipient of the knee joint prosthesis by adjusting a thickness of walls of the honeycomb material and/or a distance between the walls of the honeycomb material. 
         [0014]    In another aspect of the present invention, a shock absorbent pad disposed between the tibial plate and the tray insert. 
         [0015]    In another aspect of the present invention, the shock absorbent pad completely covers a surface of the tibial plate and a surface of the tray insert. 
         [0016]    Further aspects and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0017]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0018]      FIG. 1  is a side, partial cross-section of a shock absorbent hip joint prosthesis according to the principles of the present invention; 
           [0019]      FIG. 2  is an enlarged, perspective view of a honeycomb structure used for a shock absorbent material; 
           [0020]      FIG. 3  is a front, partial cross-section of a shock absorbent knee joint prosthesis according to the principles of the present invention; 
           [0021]      FIG. 4  is a cross-section of the shock absorbent knee joint prosthesis viewed in the direction of arrows  4 - 4  in  FIG. 3 ; and 
           [0022]      FIG. 5  is a cross-section of the shock absorbent knee joint prosthesis viewed in the direction of arrows  5 - 5  in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0024]    With reference to  FIG. 1 , a shock absorbent hip joint prosthesis according to the principles of the present invention is generally indicated by reference number  10 . The hip joint prosthesis includes a femoral component  12  secured to a femur (not shown) and an acetabular component  14  secured to an acetabulum in a pelvis bone (not shown). The femoral component  12  includes a femoral stem  16  configured to be secured within the femur. The femoral stem  16  may be cemented to the femur or uncemented. The femoral stem  16  is typically metal and may have surface treatments to facilitate adhesion to the femur and/or bone growth. A neck  18  extends out from the femoral stem  16 . A femoral ball  20  is secured to the neck  18 . The femoral ball  20 , the neck  18 , and the femoral stem  16  may be formed of a single unitary piece of metal. Alternatively, the femoral ball  20  may be a separate piece secured to the neck  18 . In this example, the femoral ball  20  may be either metal, plastic, or ceramic. It should be appreciated that the femoral component  12  may have various other shapes, sizes, and configurations without departing from the scope of the present invention. 
         [0025]    The acetabular component  14  includes an acetabular cup  22  configured to be secured to the acetabulum of the pelvis. The acetabular cup or shell  22  is generally hemispherical with a porous outside surface  22 A to promote bone growth and an inside surface  22 B. The acetabular cup  22  is preferably made from metal. 
         [0026]    An insert  24  is disposed within the acetabular cup  22 . The insert  24  is generally hemispherical and includes an outer surface  24 A and an inner surface  24 B. The inner surface  24 B is sized to receive the femoral ball  20  to form a ball joint. The insert  24  is preferably made from a high density polyethylene plastic or ceramic material to reduce friction between the insert  24  and the femoral ball  20 . 
         [0027]    The insert  24  is supported within the acetabular cup  22  by a shock absorbent system or filler  30 . The shock absorbent filler  30  is secured to the inner surface  22 B of the acetabular cup  22  and to the outer surface  24 A of the insert  24 . The shock absorbent filler  30  may be secured to the surfaces  22 B and  24 A using an adhesive or other suitable attachment methods. The shock absorbent filler  30  is made from a deformable, bio-compatible material. The shock absorbent filler  30  is configured to deform under impact or compressive loading between the femur and the pelvis. In a preferred embodiment, the shock absorbent filler  30  has a honey-comb structure, shown in  FIG. 2 . The deformation characteristics (or ability of the shock absorbent filler  30  to absorb impact loads) of the shock absorbent filler  30  are defined by the material, the thickness “t” of the honeycomb walls, and the width “w” of an individual hexagon. Accordingly, the shock absorbent filler  30  may be tuned to the specific weight of the end user by adjusting “t”, “w”, and the material selection. Further factors, such as expected activity level, gender, and age, may also be accounted for in the tuning of the deformation characteristics of the shock absorbent filler  30 . In an alternate embodiment, the shock absorbent filler  30  is made from a biocompatible gel or other deformable or elastic material. 
         [0028]    With reference to  FIG. 3 , a shock absorbent knee prosthesis according to the principles of the present invention is generally indicated by reference number  50 . The knee prosthesis  50  includes a tibial component  52  secured to a tibia (not shown), a femoral component  54  secured to the femur (not shown), and a tray insert  55  and a shock absorbent pad  56  disposed between the tibial component  52  and the femoral component  54 . 
         [0029]    The tibial component  52  includes a tibial plate  58  and a tibial stem  60 . The tibial plate  58  is generally planar and flat. The tibial stem  60  extends out perpendicularly from the tibial plate  58 . The tibial stem  60  is configured to be secured within the tibia. The tibial stem  60  may be cemented to the tibia or uncemented. The tibial stem  60  is typically metal and may have a surface treatment to facilitate adhesion to the tibia or porous surface treatments to facilitate bone growth. It should be appreciated that the tibial stem  60  may have various other shapes, sizes, and configurations without departing from the scope of the present invention. 
         [0030]    Turning to  FIGS. 4 and 5  and with continued reference to  FIG. 3 , the femoral component  54  includes a support base  62  that supports a pair of moveable condyles  64 A and  64 B. For example, the support base  62  includes first and second slots  66 A and  66 B formed therein that are sized to receive the moveable condyles  64 A and  64 B, respectively. A back plate  68  extends along a back side of the support base  62 . The back plate  68  includes a stepped portion  70  configured to interlock with a similarly sized pocket or groove (not shown) formed in the femur. In one example, the stepped portion  70  includes a porous or honeycomb pattern surface to facilitate bone growth. Alternatively, a stem, indicated by dashed lines  72 , may extend out from the back plate  68  in place of the stepped portion  70 . 
         [0031]    The moveable condyles  64 A and  64 B each have an outer, articulation surface  73  that is contoured to substantially match the contour of the femoral condyles (not shown). The moveable condyles  64 A and  64 B are precisely machined to slide within the slots  66 A and  66 B. A shock absorbent material or cushion  74  is sandwiched between the moveable condyles  64 A,  64 B and the back plate  68 . Therefore, the moveable condyles  64 A and  64 B are able to move within the slots  66 A and  66 B relative to the support base  62  by deforming the shock absorbent cushion  74 . 
         [0032]    The shock absorbent cushion  74  may be secured to the moveable condyles  64 A,  64 B or the back plate  68  using an adhesive or other suitable attachment methods. The shock absorbent cushion  74  extends from an inner surface  76  of each of the condyles  64 A and  64 B to the back plate. In the example provided, the shock absorbent cushion  74  may also extend between opposing side walls  78 A and  78 B of the base support  62 , where each side wall  78 A,  78 B cooperates to define the slots  66 A and  66 B. The shock absorbent cushions  74  and base support  62  may further define gaps or spaces  80  to allow for the movement of the condyles  64 A,  64 B during impact loading and deformation of the cushion material  74 . The shock absorbent cushion  74  is made from a deformable, bio-compatible material. The shock absorbent cushion  74  is configured to deform under impact or compressive loading between the tibia and femur. In a preferred embodiment, the shock absorbent cushion  74  has a honey-comb structure, shown and previously described in  FIG. 2 . The deformation characteristics (or ability of the shock absorbent cushion  74  to absorb impact loads) of the shock absorbent cushion  74  are defined by the material, the thickness “t” of the honeycomb walls, and the width “w” of an individual hexagon. Accordingly, the shock absorbent cushion  74  may be tuned to the specific weight of the end user by adjusting “t”, “w”, and the material selection. Further factors, such as expected activity level, gender, and age, may also be accounted for in the tuning of the deformation characteristics of the shock absorbent cushion  74 . In an alternate embodiment, the shock absorbent cushion  74  is made from a biocompatible gel or other deformable or elastic material. 
         [0033]    Returning to  FIG. 3 , the tray insert  55  is disposed between the femoral component  54  and the tibial component  52 . The tray insert  55  includes first and second concave surfaces  55 A and  55 B and a substantially flat, planar back surface  55 C. The first and second concave surfaces  55 A and  55 B are contoured to match the shapes of the moveable condyles  64 A and  64 B, respectively. In this way, in a preferred embodiment the moveably condyles  64 A and  64 B are sized such that no part of the base support  62  contacts the concave surfaces  55 A and  55 B even as the moveable condyles  64 A and  64 B move with respect to the base support  62  during impact loads. The tray insert  55  is preferably made from a plastic and provides a surface on which the femoral component  54  may move relative to the tibial component  52 . 
         [0034]    The shock absorbent pad  56  is sandwiched between the tray insert  55  and the tibial plate  58 . In a preferred embodiment, the shock absorbent pad  56  completely covers a surface  59  of the tibial plate  58  and the surface  55 C of the tray insert  55 . The shock absorbent pad  56  may be secured to the back surface  55 C of the tray insert  55  or to the tibial plate  58  using an adhesive or other suitable attachment methods. For example, the tibial plate  58  may include an annular flange  58 A that peripherally surrounds the shock absorbent pad  56  and a portion of the tray insert  55 . The shock absorbent pad  56  is made from a deformable, bio-compatible material. The shock absorbent pad  56  is configured to deform under impact or compressive loading between the tibia and femur. In a preferred embodiment, the shock absorbent pad  56  has a honey-comb structure, shown and previously described in  FIG. 2 . The deformation characteristics (or ability of the shock absorbent pad  56  to absorb impact loads) of the shock absorbent pad  56  are defined by the material, the thickness “t” of the honeycomb walls, and the width “w” of an individual hexagon. Accordingly, the shock absorbent pad  56  may be tuned to the specific weight of the end user by adjusting “t”, “w”, and the material selection. Further factors, such as expected activity level, gender, and age, may also be accounted for in the tuning of the deformation characteristics of the shock absorbent pad  56 . In an alternate embodiment, the shock absorbent pad  56  is made from a biocompatible gel or other deformable or elastic material. 
         [0035]    It should be appreciated that while the above description uses the shock absorbent pad  56  with the shock absorbent cushion  74 , either one may be used individually in the shock absorbent prosthesis  50  without departing from the scope of the present invention. In addition, it should be appreciated that the shock absorbent prosthesis  50  may be used in partial knee replacement surgery by bifurcating the prosthesis  50  such that only one moveable condyle  64 A or  64 B is employed. The partial knee joint prosthesis may include an interlocking system to accommodate a later full knee replacement without removal of the partial knee joint prosthesis. 
         [0036]    The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.