Preferential removal of cartilage
Disclosed is a method for preferentially removing cartilage from a bone in a joint that is effective at removing the cartilage while minimizing any removal of the cortical bone.
1. A method for preferentially removing cartilage from a bone in a joint comprising:
inserting a burr into a joint comprised of cartilage attached to subchondral bone; and
maneuvering the burr within the joint against the cartilage while rotating the burr at a speed not more than about 10,000 revolutions per minute (rpm), wherein the burr comprises a plurality of cutting flutes that have a negative rake angle of −15 to −50 degrees, whereby the cartilage is preferentially removed from the subchondral bone and the rotating burr provides a tactile feedback to the operator when the rotating burr has gone through the cartilage and contacts the subchondral bone.
2. The method of claim 1 , wherein the burr is rotated at a speed not more than about 9,000 rpm.
3. The method of claim 1 , wherein the burr is rotated at a speed not more than about 8,000 rpm.
4. The method of claim 1 , wherein the burr is rotated at a speed not more than about 7,000 rpm.
5. The method of claim 1 , wherein the burr is rotated at about 6,000 rpm.
6. The method of claim 1 , wherein maneuvering the burr within the joint against the cartilage involves urging the rotating burr against the cartilage.
7. The method of claim 1 , wherein
the plurality of cutting flutes have a negative rake angle of about −17 degrees, and
the burr is rotated at about 6,000 rpm.
8. The method of claim 1 , wherein the plurality of cutting flutes have a negative rake angle of −20±5 degrees.
9. The method of claim 1 , wherein the plurality of cutting flutes have a negative rake angle of −30±5 degrees.
10. The method of claim 1 , wherein the plurality of cutting flutes have a negative rake angle of −40±5 degrees.
11. The method of claim 1 , wherein the plurality of cutting flutes have a negative rake angle of −50±5 degrees.
12. The method of claim 1 , wherein the plurality of cutting flutes are arranged in a helical configuration.
13. The method of claim 1 , wherein each of the plurality of cutting flutes comprise a plurality of chip splitters.
14. The method of claim 1 , wherein the burr has tangential flute spacings that are the same.
15. The method of claim 1 , wherein the burr has variable tangential flute spacings.
16. The method of claim 1 , wherein the burr has a diameter of about 2 to 4 mm.
17. The method of claim 1 , wherein the burr has a diameter of about 2 mm.
18. The method of claim 1 , wherein the burr has a diameter of about 3 mm.
19. The method of claim 1 , wherein the burr has a diameter of about 4 mm.
20. The method of claim 1 , wherein
each of the plurality of cutting flutes includes a plurality of chip splitters,
a size of the chip splitters is: depth=0.008±0.004 inches; internal angle=45°±10°; radius at full depth=0.005 inches; and pitch=0.31±0.010 inches, and
pitch is an axial distance from one chip splitter to the next, i.e. center-to-center distance.