Force based digitization for bone registration

A method for determining the position and orientation of a bone comprising steps of:

• obtaining anatomy imaging data, where the anatomy imaging data includes voxels, where each voxel has an estimated tissue density value;
• correlating the estimated tissue density values to an expected force value, where the expected force value is an expected measurement of force on a digitizer tip while digitizing a surface point;
• directing a digitizer tip onto tissue overlying the bone to collect a first surface point location;
• monitoring forces exerted on the digitizer tip while directing the digitizer;
• recording the forces on the digitizer tip and the position of the digitizer tip while digitizing the first surface point location to generate a series of points, where each point in the series of points has a positional depth with an associated recorded force value or range;
• correlating two or more points in the series of points with corresponding points in the anatomy imaging data based at least partially on a similarity between the expected force values and the recorded force values, where each point correlation represents a layer of tissue;
• calculating at least one transformation matrix for a tissue layer using point correlation from at least some of the surface points digitized for the tissue layer;
• and
• combining the at least one transformation matrix with additional matrix data to complete registration of the bone that is indicative of the position and orientation of the bone.

A method for determining the position and orientation of a bone of a patient comprising:

• obtaining imaging data from a CT scan of the bone;
• directing a digitizer tip onto tissue overlying the bone to collect a first surface point location;
• monitoring forces exerted on the digitizer tip while directing the digitizer tip;
• recording the forces on the digitizer tip and the position of the digitizer tip while digitizing the first surface point location to generate a plurality of points, where each point in the plurality of points has a positional depth with an associated recorded force value or range of values;
• correlating two or more points in the plurality of points with corresponding points in the anatomy imaging data based at least partially on a similarity between an expected force threshold and the recorded force values, where each point correlation represents a layer of tissue;
• calculating at least one transformation matrix for a tissue layer using each point correlation from at least some of the surface points digitized for the tissue layer;
• and
• combining the at least one transformation matrix with additional matrix data to complete registration of the bone that is indicative of the position and orientation of the bone.

A computer-assisted surgical system, comprising:

• a percutaneous bone detector having a digitizer tip to collect a set of surface point locations on a bone of a patient;
• a tracking system;
• a surgical robot with an end effector;
• one or more computers with software, wherein said one or more computers receive signals from the tracking system which tracks the position of the digitizer tip and records forces exerted on the digitizer tip;
• a display to display the output from the one or more computers;
• and
• wherein the one more computers with software execute instructions to perform at least one of the following:
• (a) record a position of the digitizer tip when a force on the digitizer tip in contact with the bone is equal to or less than a threshold force;
• or (b) calculate at least one transformation matrix representative of a tissue layers and combine the at least one transformation matrix with additional matrix data to register the bone.