Method and device for cup implanting using inertial sensors

A computer-assisted surgery (CAS) system comprising:

• a cup implanting device including
• a shaft having a tooling end and a handle end with a handle for being manipulated, the shaft having a longitudinal axis, the tooling end adapted to support a cup for being received in an acetabulum of a patient, and
• a rotation indicator having a visual guide representative of a device plane, the visual guide being a light source producing a single light beam,
• wherein the device plane is in a known position and orientation relative to a center of the cup on the tooling end;
• and
• a CAS processing unit including at least one inertial sensor unit connected to the cup implanting device, the inertial sensor unit configured to output three-axes readings, the CAS processing unit configured to:
• obtain a virtual preset orientation for the inertial sensor unit, the virtual preset orientation including a planned trigonometric relation with a reference axis of a pelvis of the patient, the virtual preset orientation being based on pre-operative imaging specific to the pelvis of the patient, the reference axis of the pelvis passing through a center of rotation of said acetabulum of the pelvis and through a reference landmark of the pelvis;
• trigonometrically calculate an instant three-axis orientation of the longitudinal axis of the cup implanting device relative to the reference axis when the cup is in the acetabulum of the patient and the single light beam passes through the reference landmark;
• calibrate the inertial sensor unit on the cup implanting device relative to the pelvis using the instant three-axis orientation.