Leg length calculation in computer-assisted surgery
A computer-assisted surgery system has inertial sensor unit connected to an instrument and producing readings representative of its orientation. A computer-assisted surgery processor unit has a coordinate system module for setting a pelvic coordinate system from readings of the inertial sensor unit when the instrument is in a given orientation relative to the pelvis, a tracking module for tracking an orientation of the instrument relative to the pelvic coordinate system during movements thereof and a geometrical relation data module for recording preoperatively a landmark orientation relative to the pelvic coordinate system and a distance when the at least one instrument has a first end abutted to a pelvic landmark and a second end abutted to a leg landmark, for recording after implant rejointing the medio-lateral orientation and the distance, and for calculating a leg length discrepancy and/or an offset, based on the distances and the medio-lateral orientations.
1. A computer-assisted surgery system for outputting at least one of a leg length discrepancy and an offset between a preoperative leg condition and a post-implant rejointing leg condition comprising:
at least one instrument;
at least one inertial sensor unit connected to the at least one instrument, the inertial sensor unit producing readings representative of its orientation;
a computer-assisted surgery processor unit operating a surgical assistance procedure and comprising
a coordinate system module for setting a pelvic coordinate system from readings of the at least one inertial sensor unit when the at least one instrument is in a given orientation relative to the pelvis,
a tracking module for tracking an orientation of the at least one instrument relative to the pelvic coordinate system during movements thereof using the readings from the inertial sensor unit on the instrument, and
a geometrical relation data module for recording preoperatively a landmark orientation relative to the pelvic coordinate system and a distance when the at least one instrument has a first end abutted to a pelvic landmark and a second end abutted to a leg landmark, for recording after implant rejointing the landmark orientation and said distance, and for calculating at least one of a leg length discrepancy and an offset, based on said distances and said landmark orientations; and
an interface for outputting at least the leg length discrepancy or the offset between the preoperative leg condition and the post-implant rejointing leg condition.
2. The computer-assisted surgery system according to claim 1 , wherein the at least one instrument is a caliper having a body with a translational joint for expanding/contracting, and legs configured for contacting the pelvic landmark and the leg landmark.
3. The computer-assisted surgery system according to claim 2 , wherein the caliper supports a light source emitting a light beam that is perpendicular relative to a direction of the translational joint.
4. The computer-assisted surgery system according to claim 3 , wherein the given orientation has the light beam illuminating the medio-lateral axis of the pelvis.
5. The computer-assisted surgery system according to claim 2 , further comprising a scale on the translational joint to obtain said distances.
6. The computer-assisted surgery system according to claim 2 , wherein the caliper supports a light source emitting a light beam that is parallel relative to a direction of the translational joint.
7. The computer-assisted surgery system according to claim 1 , wherein the at least one instrument includes a mechanical gauge having a body with a translational joint for expanding/contracting, and bores configured for being connected to pins constituting the pelvic landmark and the leg landmark.
8. The computer-assisted surgery system according to claim 7 , further comprising a scale on the translational joint to obtain said distances.