Computer-assisted surgery system and method for calculating a distance with inertial sensors
A computer-assisted surgery system for obtaining a distance between at least two fixed points relative to a bone comprises a first accelerometer unit located at a first fixed location on the bone, and producing first acceleration data during a movement of the bone. A second accelerometer unit is located at a second fixed location on the bone, and simultaneously producing second acceleration data during the movement. A gyroscope unit is fixed to the bone and simultaneously producing angular rates of change of said movement. A processor unit obtains the acceleration data and the angular rates of change for calculating the distance between the first fixed position and the second fixed position on the bone using a distance value of a distance vector between the accelerometer units. An interface outputs the distance between the first fixed position and the second fixed position relative to the bone. A method for calculating a distance between at least two points on a bone is provided.
1. A method for calculating a distance between at least two points on a bone, comprising:
obtaining, using one or more processors within a computing system, first acceleration data from a first accelerometer unit located at a first fixed location relative to the bone, during a movement of the bone;
simultaneously obtaining, using the one or more processors within the computing system, second acceleration data from at least a second accelerometer unit at a second fixed location relative to the bone, during said movement of the bone;
simultaneously obtaining, using the one or more processors within the computing system, angular rates of change from at least one gyroscope unit fixed to the bone, during said movement of the bone; and
calculating and outputting, using the one or more processors within the computing system, a distance value of a distance vector between the first fixed location and the second fixed location using the angular rates of change of the at least one gyroscope unit and the first acceleration data and the second acceleration data of the accelerometer units.
2. The method according to claim 1 , wherein calculating the distance value comprises isolating, using the one of more processors within the computing system, a centripetal acceleration value and a tangential acceleration value for the accelerometer units by comparing the first acceleration data and the second acceleration data, and calculating and outputting, using the one or more processors within the computing system, the distance value of the distance vector using the centripetal acceleration value and the tangential acceleration value of said first and second accelerometer units.
3. The method according to claim 1 , further comprising obtaining third acceleration data of a third accelerometer unit at a third fixed location relative to the bone simultaneously with obtaining the first acceleration data, the second acceleration data and the angular rates of change, and wherein calculating and outputting the distance value comprises calculating and outputting the distance values of the distance vectors between the first fixed location, the second fixed location and the third fixed location.
4. The method according to claim 1 , wherein simultaneously obtaining the first acceleration data, the second acceleration data and the angular rates of change includes simultaneously obtaining the first acceleration data, the second acceleration data and the angular rates of change at least at a first time period and a second time period, and wherein calculating the distance value comprises using data from the first time period and the second time period.
5. The method according to claim 4 , wherein using data from the first time period and the second time period includes performing singular value decomposition with said data.
6. The method according to claim 1 , wherein the first accelerometer unit is positioned at a tibial cut, and further comprising validating a depth of the tibial cut by comparing the distance value with a planned distance value.
7. The method according to claim 1 , wherein the first accelerometer unit is positioned on a femur, and further comprising calculating leg length discrepancy by comparing the distance value with a pre-operative distance.
8. The method according to claim 1 , wherein the first and second accelerometer units are positioned on a humerus, and further comprising calculating a humerus length.
9. The method according to claim 1 , wherein at least one of first and second accelerometer units is offset from its fixed location relative to the bone by a support, and wherein calculating the distance value includes removing the offset from the geometry of the support.
10. The method according to claim 1 , wherein the first and second accelerometer units are paired with a respective one of the at least one gyroscope unit, the method further comprising calculating and outputting, using the one or more processors within the computing system, a relative orientation between anatomical landmarks at the first fixed location and the second fixed location using the angular rates of change of the gyroscope units.