Methods and apparatus using a surgical navigation system to position the
femoral component of a prosthetic hip during hip joint replacement
surgery without separately affixing a marker to the femur. The navigation
system acquires the center of rotation of the hip joint as well as at
least one point on the femur in the pelvic frame of reference. From these
two points, the navigation system calculates the position and length of a
first line between the center of rotation of the hip joint and the point
on the femur. Optionally, a second point on the femur that is not on the
first line is palpated. The system can calculate the position and length
of a second line that is perpendicular to the first line and that runs
from the first line to the second palpated point on the femur. The
prosthetic cup is implanted and its center of rotation is recorded. A
tool for forming the bore within which the stem of the femoral implant
component will be placed is tracked by the navigation system. While the
tool is fixed to the femur, the surgeon re-palpates the same point(s) on
the femur that were previously palpated. The navigation system calculates
the position and length of a first line between the center of rotation of
the prosthetic cup and the re-palpated first point. If a second point on
the femur was re-palpated, the navigation system also calculates the
position and length of a perpendicular line between the first line and
the second point. The surgical navigation system uses this information to
calculate and display to the surgeon relevant information about the
surgery, such as change in the patient's leg length and/or
medialization/lateralization of the joint.