Method and system for cutting knee joint using robot

Abstract

A method and a system for cutting the knee joint using a robot. A cantilevered cutter is introduced into the knee joint from inside and outside of upper and lower bones of the knee joint to realize a tunnel cutting technique in which cutting is conducted such that tunnels are defined in bone and remnant bone is cleared. The cutter includes a shaft in which a substantial axial portion is fitted into a sleeve and a remaining axial portion serves as a cantilever extending out of the sleeve, and a head which is formed at a distal end of the shaft. A length of the cantilever and a diameter of the head are determined to have minimum sizes as long as the head can be introduced into bone in such a way as to define a tunnel and can be moved in the bone while cutting the bone.

1 . A method for cutting a knee joint, comprising introducing a robotic cantilevered cutter having a small diameter into the knee joint from inside and outside of upper and lower bones of the knee joint, cutting respective tunnels in the bones by means of the cutter and clearing remnant bone from the tunnels. 
     
     
         2 . The method according to  claim 1 , wherein, while a tunnel is being cut in the upper bone of the knee joint, the remnant bone is not removed and serves as a natural safety shield which prevents the cutter from projecting out of the bone and damaging surrounding soft tissue. 
     
     
         3 . The method according to  claim 1 , further comprising forming at least five plane surfaces having different angles when cutting the upper bone. 
     
     
         4 . The method according to  claim 1 , wherein, when the upper bone of the knee joint is cut by moving the cutter toward the inside, the cutter is moved while being kept parallel to a Whiteside's line. 
     
     
         5 . The method according to  claim 1 , wherein, when the upper bone of the knee joint is cut by moving the cutter toward the outside, the cutter is moved while being slanted to a prescribed angle with respect to the Whiteside's line so as to avoid impingement between the cutter and the patella and a ligament structure. 
     
     
         6 . The method according to  claim 1 , further comprising forming a hole for fixing an implant, while cutting the upper bone of the knee joint, by cutting a circular locus such that a central core portion is left, and then removing the central core portion by cutting. 
     
     
         7 . The method according to  claim 6 , further comprising, when cutting the upper bone of the knee joint to form the tunnel therein, overcutting thereby to ensure easy removal of the remnant bone in the tunnel. 
     
     
         8 . The method according to  claim 1 , further comprising, when cutting the lower bone of the knee joint, cutting in three cutting stages in which the cutter is inserted in different directions to form a single plane. 
     
     
         9 . The method according to  claim 8 , wherein the different directions comprises a normal direction, a sideward direction and a diagonal direction. 
     
     
         10 . The method according to  claim 8 , wherein the plane is formed by moving the cutter inward in a zigzag pattern. 
     
     
         11 . The method according to  claim 8 , wherein the cutting of the lower bone of the knee joint is conducted such that a safety rim is left on an edge of the plane thereby to prevent damage to surrounding soft tissue. 
     
     
         12 . The method according to  claim 8 , further comprising, while cutting the lower bone of the knee joint, cutting in four steps in respective medial, lateral, anterior and posterior directions thereby to form a cruciform groove for fixing an implant. 
     
     
         13 . The method according to  claim 12 , wherein, in the lateral direction cutting step the cutting of tunnel in the lower bone of the knee joint is conducted with the cutter slanted inward. 
     
     
         14 . An apparatus for cutting a knee joint, comprising a robotic position-changeable arm, at a distal end of the arm a motor having a housing and a shaft, a sleeve secured to the housing, and a cutter coupled to the shaft of the motor and rotatably supported in the sleeve, wherein the cutter comprises a cylindrical shaft and a substantial axial portion of the shaft is fitted into the sleeve to be rotated by the motor and a remaining axial portion of the shaft serves as a cantilever extending out of the sleeve, and the apparatus further comprises a cutting head formed at a distal end of the shaft extending out of the sleeve, and wherein a length of the cantilever of the shaft and a diameter of the head are determined to define a shape having sizes sufficiently small that the head can be introduced into bone in such a way as to define a tunnel and can be moved in the bone while cutting the bone. 
     
     
         15 . The apparatus according to  claim 14 , wherein the diameter of the head is the same as a diameter of the shaft. 
     
     
         16 . The apparatus according to  claim 14 , wherein the cantilever has a length of 20˜30 mm and a diameter of 1.5˜4.0 mm. 
     
     
         17 . The apparatus according to  claim 14 , wherein the cantilever has a length of 70˜80 mm and a diameter of 4.0˜6.0 mm. 
     
     
         18 . The apparatus according to  claim 14 , further comprising chatter blockers formed on a distal end of the head to prevent chattering during cutting the bone. 
     
     
         19 . The apparatus according to  claim 18 , wherein the chatter blockers are offset by a predetermined distance from a diametric center line. 
     
     
         20 . The apparatus according to  claim 14 , wherein a circumferential outer surface of the head of the cutter has a helix angle of 10˜20° with respect to an axial center line to ensure easy discharge of chips when cutting the bone in a sideward direction. 
     
     
         21 . The apparatus according to  claim 14 , wherein a material of the cutter has a hardness in the range of HRC80˜120.