Knee prosthesis with a rotational plate

Abstract

The knee prosthesis with rotary plate comprises a metal base ( 2 ) and a tibia plate ( 3 ) which are equipped with guide means ( 22, 22′, 22″, 26, 29, 5, 6, 5′, 9, 50, 51, 52, 13, 15, 18; 34, 34′, 34″, 35, 37, 7, 8, 10, 12, 53, 54, 55, 10′, 17 ) defining a center of rotation (C, C′) which may be offset from that of the tibia bone axis (YY′), so as to allow the tibia plate ( 3 ) to slide in rotation over the said base, the said guide means being positioned a certain distance away from the center of rotation (C, C′).

1 . Knee prosthesis comprising a metal base secured to an anchoring rod for fixing it into the tibia of a patient, and a plastic tibia plate which can slide freely over the said base, characterized in that the metal base ( 2 ) and the tibia plate ( 3 ) are equipped with guide means ( 22 ,  22 ′,  22 ″,  26 ,  29 ,  5 ,  6 ,  5 ′,  9 ,  50 ,  51 ,  52 ,  13 ,  15 ,  18 ;  34 ,  34 ′,  34 ″,  35 ,  37 ,  7 ,  8 ,  10 ,  12 ,  53 ,  54 ,  55 ,  10 ′,  17 ) defining a center of rotation (C, C′) which may be offset from that of the tibia bone axis (YY′), so as to allow the tibia plate ( 3 ) to slide in rotation over the said base, the said guide means being positioned a certain distance away from the center of rotation (C, C′):  
     
     
         2 . Knee prosthesis according to    claim 1   , characterized in that the guide means consist of at least one upstand ( 22 ,  22 ′,  22 ″,  5 ,  6 ,  5 ′,  9 ,  50 ,  51 ,  52 ,  13 ) in the shape of an arc of a circle secured to the metal base ( 2 ) and of a housing ( 34 ,  34 ′,  34 ″,  7 ,  8 ,  10 ,  12 ,  53 ,  54 ,  55 ,  10 ′) with the same radius of curvature made in the tibia plate ( 3 ) to allow the latter to slide in rotation about the center of rotation (C, C′) of the said upstand.  
     
     
         3 . Knee prosthesis according to    claim 2   , characterized in that the guide means consist of an upstand ( 22 ,  5 ,  5 ′,  51 ,  13 ) in the shape of an arc of a circle, which upstand is positioned in the anterior part of the metal base ( 2 ) and oriented in a substantially medio-lateral direction.  
     
     
         4 . Knee prosthesis according to    claim 1   , characterized in that the additional guide means ( 26 ,  29 ,  6 ,  9 ,  15 ,  50 ,  52 ) are positioned on or near to the center of rotation (C, C′) of the tibia plate ( 3 ) on the metal base ( 2 ).  
     
     
         5 . Knee prosthesis according to    claim 4   , characterized in that the additional guide means ( 26 ,  6 ,  9 ) are secured to a device ( 28 ,  60 ,  90 ) making it possible to prevent the tibia plate ( 3 ) from lifting from the metal base ( 2 ).  
     
     
         6 . Knee prosthesis according to    claim 1   , characterized in that the guide means consist of at least two pegs ( 18 ) set out in an arc of a circle and defining a center of rotation (C, C′), and of a housing ( 34 ) of the same radius of curvature formed in the tibia plate ( 3 ), the said pegs being positioned in the anterior part of the metal base ( 2 ) and oriented in a substantially medio-lateral direction.  
     
     
         7 . Knee prosthesis according to    claim 2   , characterized in that the metal base ( 2 ) comprises an upstand ( 22 ) in the shape of an arc of a circle having a central part ( 23 ) secured to lateral edges ( 24 ,  25 ) which are not as tall as the said central part, while the tibia plate ( 3 ) comprises, on its lower face ( 30 ), a housing ( 34 ) in the shape of an arc of a circle.  
     
     
         8 . Knee prosthesis according to    claim 2   , characterized in that the upstand ( 22 ,  22 ′,  22 ″,  5 ,  6 ,  5 ′,  9 ,  50 ,  51 ,  52 ,  13 ) has a center of rotation (C) which is borne by the tibia bone vertical axis (YY′), while the said upstand is a certain distance away from its center of rotation.  
     
     
         9 . Knee prosthesis according to    claim 2   , characterized in that the upstand ( 22 ,  22 ′,  22 ″,  5 ,  6 ,  5 ′,  9 ,  50 ,  51 ,  52 ,  13 ) has a center of rotation (C′) which is offset from the tibia bone vertical axis (YY′), while the said upstand is a certain distance away from its center of rotation.  
     
     
         10 . Knee prosthesis according to    claim 2   , characterized in that the metal base ( 2 ) has two upstands ( 22 ′,  22 ″) in the shape of an arc of a circle, of constant height and having one and the same center of rotation (C, C′), while the tibia plate ( 3 ) comprises two housings ( 34 ′,  34 ″) in the shape of an arc of a circle.  
     
     
         11 . Knee prosthesis according to    claim 10   , characterized in that the upstands ( 22 ′,  22 ″) are set out opposite one another, and have one and the same center of rotation (C, C′).  
     
     
         12 . Knee prosthesis according to    claim 1   , characterized in that the metal base ( 2 ) has, opposite the upstand ( 22 ), a retaining peg ( 26 ) borne by a center of rotation so as to engage with a cutout ( 35 ) formed in the tibia plate ( 3 ) to prevent the latter from lifting off the base ( 2 ) as the said plate slides in rotation about its center of rotation.  
     
     
         13 . Knee prosthesis according to    claim 11   , characterized in that the retaining peg ( 26 ) consists of a cylindrical pin ( 27 ) integral with a head ( 28 ) which has a larger diameter than the said pin so that the said head engages with inclined faces made in the cutout ( 35 ).  
     
     
         14 . Knee prosthesis according to    claim 1   , characterized in that the metal base ( 2 ) has, opposite the upstand ( 22 ), a centering peg ( 29 ) borne by the center of rotation (C, C′) so as to engage with a blind hole ( 37 ) formed in the tibia plate ( 3 ) to guide the latter with respect to the base ( 2 ) as the said plate slides in rotation about its center of rotation.  
     
     
         15 . Knee prosthesis according to    claim 1   , characterized in that the metal base ( 2 ) and the tibia plate ( 3 ) respectively comprise a cutout ( 4  and  38 ) through which the posterior cruciate ligament can pass.  
     
     
         16 . Knee prosthesis according to    claim 1   , characterized in that the metal base ( 2 ) has two upstands ( 5  and  6 ) in the shape of an arc of a circle curved in the same direction and centered about the same center of rotation (C, C′), while the tibia plate ( 3 ) comprises housings ( 7  and  8 ) intended to receive the said upstands ( 5  and  6 ) respectively, so as to allow the said plate to slide in rotation about the center of rotation (C, C′).  
     
     
         17 . Knee prosthesis according to    claim 16   , characterized in that the upstand ( 6 ) is integral with a flange ( 60 ) which engages in a slot ( 80 ) in the housing ( 8 ) to prevent the tibia plate ( 3 ) from lifting off the metal base ( 2 ) as the said plate slides in rotation about the center of rotation (C, C′).  
     
     
         18 . Knee prosthesis according to    claim 1   , characterized in that the metal base ( 2 ) comprises two upstands ( 5 ′ and  9 ) in the shape of an arc of a circle in opposite directions and centered about the same center of rotation (C, C′), while the tibia plate ( 3 ) comprises an element ( 10 ) and a housing ( 12 ) which are intended to receive the said upstands ( 5 ′ and  9 ) respectively to allow the said plate to slide in rotation about the center of rotation (C, C′).  
     
     
         19 . Knee prosthesis according to    claim 18   , characterized in that the upstand ( 5 ′) is set out on the external periphery of the horizontal disk ( 20 ) of the metal base ( 2 ) so as to engage with a peripheral recess ( 10 ) in the tibia plate ( 3 ).  
     
     
         20 . Knee prosthesis according to    claim 18   , characterized in that the upstand ( 9 ) is offset from the center of rotation (C, C′) and comprises a flange ( 90 ) which snap-fastens into the housing ( 12 ) in the tibia plate ( 3 ) to, on the one hand, guide the plate ( 3 ) as it slides in rotation about its center (C, C′) and, on the other hand, retain the said plate so that it does not lift off the metal base ( 2 ).  
     
     
         21 . Knee prosthesis according to    claim 1   , characterized in that the metal base ( 2 ) comprises a peripheral upstand ( 13 ) in the shape of an arc of a circle integral with a flange ( 14 ) directed toward the tibia bone vertical axis (YY′) and a housing ( 15 ) set out in the region of the center of rotation (C, C′), while the tibia plate ( 3 ) has, on its external periphery, a recess ( 10 ′) in which there is formed a horizontal slot ( 16 ) intended to receive the flange ( 14 ) of the said upstand ( 13 ) and, on its lower face ( 30 ), a stub ( 17 ) which engages with the housing ( 15 ).  
     
     
         22 . Knee prosthesis according to    claim 1   , characterized in that the metal base ( 2 ) comprises three peripheral upstands ( 50 ,  51 ,  52 ) extending vertically above the horizontal disk ( 20 ), while the tibia plate ( 3 ) has, on its external periphery, three recesses ( 53 ,  54 ,  55 ) intended to receive the said upstands ( 50 ,  51 ,  52 ) respectively to allow the said plate to be guided as it slides in rotation about the center of rotation (C, C′).  
     
     
         23 . Knee prosthesis according to    claim 6   , characterized in that the pegs ( 18 ) are set out in an arc of a circle about a center of rotation (C, C′), while the tibia plate ( 3 ) has a housing ( 34 ) intended to receive the said pegs.  
     
     
         24 . Knee prosthesis according to    claim 6   , characterized in that the pegs ( 18 ) have a center of rotation (C) which is borne by the tibia bone vertical axis (YY′), while the said peg is a certain distance away from its center of rotation.  
     
     
         25 . Knee prosthesis according to    claim 6   , characterized in that the pegs ( 18 ) have a center of rotation (C′) which is offset from the tibia bone vertical axis (YY′), while the said peg is a certain distance away from its center of rotation.  
     
     
         26 . Knee prosthesis according to    claim 1   , characterized in that the metal base ( 2 ) comprises at least one upstand or peg ( 22 ,  22 ′,  22 ″,  26 ,  29 ,  5 ,  6 ,  5 ′,  9 ,  50 ,  51 ,  52 ,  13 ,  15 ,  18 ) which engages with a housing ( 34 ,  34 ′,  34 ″,  35 ,  7 ,  8 ,  10 ,  12 ,  53 ,  54 ,  55 ,  10 ′,  17 ) of the tibia plate ( 3 ) so that the said plate can slide in rotation over the metal base ( 2 ) only within the limit set by the difference in size between the said upstand or peg and the said corresponding housing.  
     
     
         27 . Knee prosthesis according to    claim 26   , characterized in that the rotational travel between the tibia plate ( 3 ) and the metal base ( 2 ) is reduced to zero when the dimensions of the housing ( 34 ,  34 ′,  34 ″,  7 ,  10 ,  10 ′,  53 ,  54 ,  55 ) are made so as to engage without clearance with the upstand ( 22 ,  22 ′,  22 ″,  5 ,  5 ′,  13 ,  50 ,  51 ,  52 ,  18 ).  
     
     
         28 . Knee prosthesis according to    claim 1   , characterized in that the short height of the guide means and of their anterior positioning on the metal base ( 2 ) allows the tibia plate ( 3 ) to be mounted on the said base via a strictly anterior approach, the said plate requiring upward clearances only by the height of the said guide means.