	US 7,594,933 B2
	Method and apparatus for positioning a bone prosthesis using a localization system
Sergej Kammerzell, Engen (Germany); Uwe Bader, Tuttlingen (Germany); and Benoit Mollard, Echirolles (France)
Assigned to Aesculap AG, (Germany)
Filed on Aug. 08, 2006, as Appl. No. 11/463,268.
Prior Publication US 2008/0051910 A1, Feb. 28, 2008
Int. Cl. A61F 2/32 (2006.01)

U.S. Cl. 623—22.15 [600/424]

37 Claims

1. A method of using a surgical navigation system for positioning in a femur a femoral prosthetic component of a hip joint replacement prosthesis, said method comprising the steps of:

acquiring a pelvic frame of reference;

acquiring a center of rotation of said hip joint in said pelvic frame of reference;

acquiring a first femoral point substantially fixed with respect to said femur in said pelvic frame of reference while said hip joint is intact;

calculating a length of a first line between said first acquired femoral point and said center of rotation of said hip joint;

implanting a prosthetic cup component of said hip joint replacement prosthesis in said pelvis;

acquiring a position of a center of rotation of said implanted prosthetic cup component in said pelvic frame of reference;

calculating a first difference in position between said center of rotation of said hip joint and said center of rotation of said implanted prosthetic cup component in said pelvic frame of reference;

forming a hole in said femur for accepting said femoral prosthetic component;

rigidly mounting a marker in said hole, said marker having a known position relative to a position of a center of rotation of a prosthetic femoral head of a femoral prosthetic component if implanted in said hole;

calculating a position of a center of rotation of said prosthetic femoral head if implanted in said hole as a function of said position of said marker mounted in said hole;

while said marker is mounted in said hole, re-acquiring said first femoral point relative to said position of said marker mounted in said hole;

calculating a length of a second line between said re-acquired first femoral point and said center of rotation of said prosthetic femoral head;

calculating a second difference in length of said first line and said second line; and

displaying leg length data as a function of said first and second differences.