System for use in knee surgery

Abstract

A femoral component ( 2 ) of a knee joint prosthesis has a bearing surface ( 4 ) for articulation with a tibial bearing surface and an opposite bone facing surface ( 6 ). The bone facing surface has anterior ( 18 ), posterior ( 20 ), distal ( 22 ), anterior chamfer ( 24 ) and posterior chamfer ( 26 ) portions. Medial ( 42, 52, 356 ) and lateral rails ( 40, 50, 350 ) are provided on the distal portion or on at least one of the anterior chamfer portion and posterior chamfer portions of the bone facing surface so that there is at least one recess ( 46, 54, 354, 360 ) between the rails.

1 . A system for use in a surgical procedure on a patient's knee, which comprises:
 a. a femoral component of a knee joint prosthesis having a bearing surface for articulation with a tibial bearing surface and an opposite bone facing surface, in which the bone facing surface has:
 i. an anterior portion for engaging the femur on its anterior side, 
 ii. a posterior portion for engaging the femur on its posterior side, 
 iii. a distal portion for engaging the distal end face of the femur, 
 iv. an anterior chamfer portion located between the anterior portion and the distal portion, which is inclined to each of the anterior portion and the distal portion, and 
 v. a posterior chamfer portion located between the posterior portion and the distal portion, which is inclined to each of the posterior portion and the distal portion, 
   in which each of the distal, anterior and posterior portions of the bone facing surface is characterised by not having a rail at any of its edges so that it is planar and can form close surface-to-surface contact with an adjacent bone surface which is planar, and   b. a guide block having a planar distal surface which can be fastened to the distal face of a patient's femur on which the distal resection cut has been made to define the locations relative to the plane of the distal resection cut of planes on which the anterior and posterior chamfer cuts can be performed, in which the distance between (a) an anterior reference line extending parallel to the plane of the anterior chamfer cut and intersecting the plane of the distal surface at a point midway between the intersections between the planes of the distal surface and the anterior chamfer cuts and the planes of the distal surface and the posterior chamfer cuts and (b) the plane of the anterior chamfer cut is G Ant , and the distance between (a) a posterior reference line extending parallel to the plane of the posterior chamfer cut and intersecting the plane of the distal surface at a point midway between the intersections between the planes of the distal surface and the anterior chamfer cuts and the planes of the distal surface and posterior chamfer cuts and (b) the plane of the posterior chamfer cut is G Post ,   and in which:   (A) the anterior chamfer portion of the bone facing surface of the femoral component has spaced apart medial and lateral rails with at least one recess between them, with the distance between (a) an anterior implant reference line extending parallel to the anterior chamfer portion of the bone facing surface and intersecting the distal portion of the said surface at a point midway between the intersections between the distal portion and the anterior and posterior chamfer portions and (b) the tip edge of the rails being I AntRail , and the distance between (a) the anterior implant reference line and (b) the base of the recess between the rails being I AntRecess , the value of (I AntRecess −G Ant ) being at least about 0.5 mm, so that, when the femoral component is positioned on a patient's femur, there is contact between the anterior, distal, posterior, anterior chamfer and posterior chamfer portions of the bone facing surface of the femoral component and corresponding surfaces of the femur, with the tip edges of the medial and lateral rails in contact with the anterior chamfer surface of the patient's femur and clearance between the anterior chamfer surface of the patient's femur and the base of the recess,   and/or:   (B) the posterior chamfer portion of the bone facing surface of the femoral component has spaced apart medial and lateral rails with at least one recess between them, with the distance between (a) a posterior implant reference line extending parallel to the posterior chamfer portion of the bone facing surface and intersecting the distal portion of the said surface at a point midway between the intersections between the distal portion and the anterior and posterior chamfer portions and (b) the tip edge of the rails being I PostRail , and the distance between (a) the posterior implant reference line and (b) the base of the recess between the rails being I PostRecess , the value of (I PostRecess −G Post ) being at least about 0.5 mm, so that, when the femoral component is positioned on a patient's femur, there is contact between the anterior, distal, posterior, anterior chamfer and posterior chamfer portions of the bone facing surface of the femoral component and corresponding surfaces of the femur, with the tip edges of the medial and lateral rails in contact with the posterior chamfer surface of the patient's femur and clearance between the posterior chamfer surface of the patient's femur and the base of the recess.   
     
     
         2 . The system of  claim 1 , in which rails are provided on the anterior chamfer portion of the bone facing surface and the value of (G Ant −I AntRail ) is at least about 0.05 mm. 
     
     
         3 . The system of  claim 1 , in which rails are provided on the posterior chamfer portion of the bone facing surface and the value of (G Post −O PostRail ) is at least about 0.05 mm. 
     
     
         4 . The system of  claim 1 , in which the medial rail is located at the medial edge of the femoral component and the lateral rail is located at the lateral edge of the femoral component. 
     
     
         5 . The system of  claim 1 , in which, when the medial and lateral rails are provided on the anterior chamfer portion of the bone facing surface, they extend from the distal portion to the anterior portion. 
     
     
         6 . The system of  claim 1 , in which, when the medial and lateral rails are provided on the posterior chamfer portion of the bone facing surface, they extend from the distal portion to the posterior portion. 
     
     
         7 . The system of  claim 1 , in which each of the medial and lateral rails is tapered inwardly towards its exposed bone-facing edge. 
     
     
         8 . The system of  claim 1 , which includes at least one additional rail located between the medial and lateral rails. 
     
     
         9 . The system of  claim 8 , in which the additional rail is aligned with the medial and lateral rails. 
     
     
         10 . The system as claimed in of  claim 8 , in which the additional rail extends between the medial and lateral rails, generally transverse to the medial and lateral rails. 
     
     
         11 . The system of  claim 1 , in which each of the anterior, distal and posterior portions of the bone facing surface is planar so that it does not have a rail at any of its edges. 
     
     
         12 . The system of  claim 1 , in which each of the anterior, distal and posterior portions of the bone facing surface is adapted to promote fixation to bone without the use of a bone cement. 
     
     
         13 . A system for use in a surgical procedure on a patient's knee, which comprises:
 a. a femoral component of a knee joint prosthesis having a bearing surface for articulation with a tibial bearing surface and an opposite bone facing surface, in which the bone facing surface has:
 i. an anterior portion for engaging the femur on its anterior side, 
 ii. a posterior portion for engaging the femur on its posterior side, 
 iii. a distal portion for engaging the distal end face of the femur, 
 iv. an anterior chamfer portion located between the anterior portion and the distal portion, which is inclined to each of the anterior portion and the distal portion, and 
 v. a posterior chamfer portion located between the posterior portion and the distal portion, which is inclined to each of the posterior portion and the distal portion, 
   in which each of the anterior, anterior chamfer, posterior chamfer and posterior portions of the bone facing surface is characterised by not having a rail at any of its edges so that it is planar and can form close surface-to-surface contact with an adjacent bone surface which is planar, and the distal portion of the bone facing surface has spaced apart medial and lateral rails with at least one recess between them,   b. a guide block having a planar distal surface which can be fastened to the distal face of a patient's femur on which the distal resection cut has been made to define the locations relative to the plane of the distal resection cut of planes on which the anterior and posterior chamfer cuts can be performed, the guide block defining a guide block reference line at the intersection of the planes of the anterior and posterior cuts so that the distance between the reference line and the planar distal surface is G Dist ,   and in which the distal portion of the bone facing surface of the femoral component has spaced apart medial and lateral rails with at least one recess between them, with the distance between (a) an implant reference line lying at the intersection of the planes of the anterior chamfer and posterior chamfer portions of the bone facing surface and (b) the tip edge of the rails being I DistRail , and the distance between (a) the implant reference line and (b) the base of the recess between the rails being I DistRecess , the value of (G Dist −I DistRecess ) being at least about 0.5 mm, so that, when the femoral component is positioned on a patient's femur, there is contact between the anterior, distal, posterior, anterior chamfer and posterior chamfer portions of the bone facing surface of the femoral component and corresponding surfaces of the femur, with the tip edges of the medial and lateral rails in contact with the distal surface of the patient's femur and clearance between the distal surface of the patient's femur and the base of the recess.   
     
     
         14 . The system of  claim 13 , in which the value of (I DistRail −G Dist ) is at least about 0.05 mm. 
     
     
         15 . The system of  claim 13 , in which the medial rail is located at the medial edge of the femoral component and the lateral rail is located at the lateral edge of the femoral component. 
     
     
         16 . The system of  claim 13 , in which, the medial and lateral rails extend on the distal portion of the bone facing surface from the anterior chamfer portion to the posterior chamfer portion thereof. 
     
     
         17 . The system of  claim 13 , in which each of the medial and lateral rails is tapered inwardly towards its exposed bone-facing edge. 
     
     
         18 . The system of  claim 13 , which includes at least one additional rail located between the medial and lateral rails. 
     
     
         19 . The system of  claim 18 , in which the additional rail is generally aligned with the medial and lateral rails. 
     
     
         20 . The system of  claim 18 , in which the additional rail extends between the medial and lateral rails, generally transverse to the medial and lateral rails. 
     
     
         21 . The system of  claim 13 , in which each of the anterior, anterior chamfer, posterior chamfer and posterior portions of the bone facing surface is planar so that it does not have a rail at any of its edges. 
     
     
         22 . The system of  claim 13 , in which each of the anterior, anterior chamfer, posterior chamfer and posterior portions of the bone facing surface is adapted to promote fixation to bone without the use of a bone cement.