Bone and tool tracking with mems in computer-assisted surgery

Abstract

A method tracks a tool with respect to a bone in computer-assisted surgery. A reference tracker with a MEMS unit is secured to the bone. The tracker outputs data relating to its orientation. A tool provided with a MEMS unit and secured to the bone is preset with an initial orientation. The tool outputs tracking data related to orientation of the tool once initialized. A trackable frame of reference relating the bone to the orientation of the tracker is created. The MEMS unit of the tool is initialized. A relation between the initial orientation of the tool and the orientation of the tracker at initialization of the MEMS unit of the tool is recorded. Orientational data of the tool relative to the frame of reference of the bone calculated using the relation is displayed. A computer-assisted surgery system for tracking a tool with respect to a bone after an initialization of a MEMS unit is also described.

1 . A method for tracking a tool with respect to a bone in computer-assisted surgery, comprising:
 securing a reference tracker with a MEMS unit to the bone, the reference tracker outputting tracking data relating to an orientation of the reference tracker;   providing a tool with a MEMS unit, the tool being preset with an initial orientation and outputting tracking data related to an orientation of the tool once initialized;   securing the tool to the bone;   creating a trackable frame of reference relating the bone to the orientation of the reference tracker;   initializing the MEMS unit of the tool;   recording a relation between the initial orientation of the tool and the orientation of the reference tracker at initialization of the MEMS unit of the tool; and   displaying orientational data of the tool relative to the frame of reference of the bone calculated using the relation.   
     
     
         2 . The method according to  claim 1 , wherein providing the tool comprises providing a cutting block secured to the bone by an orientation adjustment mechanism allowing the adjustment of the orientation of the cutting block, and wherein displaying orientational data comprises displaying data pertaining to an orientation of cutting slots in the cutting block relative to the frame of reference of the bone. 
     
     
         3 . The method according to  claim 2 , wherein securing the reference tracker and the cutting block to the bone comprises securing the reference tracker and the cutting block to a tibia. 
     
     
         4 . The method according to  claim 3 , wherein creating the trackable frame of reference comprises determining at least a mechanical axis of the tibia. 
     
     
         5 . The method according to  claim 2 , wherein securing the reference tracker and the cutting block to the bone comprises securing the reference tracker and the cutting block to a femur. 
     
     
         6 . The method according to  claim 5 , wherein creating the trackable frame of reference comprises determining at least a mechanical axis of the femur. 
     
     
         7 . The method according to  claim 1 , wherein creating a trackable frame of reference comprises creating a coordinate system of three axes. 
     
     
         8 . The method according to  claim 1 , wherein providing the tool preset with the initial orientation comprises providing the tool with axes being orthogonal to the MEMS unit on the tool. 
     
     
         9 . The method according to  claim 1 , wherein securing the reference tracker and the tool to the bone comprises securing the reference tracker and the tool to a bone without direct rigid connection between the reference tracker and the tool. 
     
     
         10 . The method according to  claim 1 , further comprising performing bone alterations using the tool while the orientational data of the tool is displayed. 
     
     
         11 . The method according to  claim 1 , wherein the method is performed on a bone model or a cadaver. 
     
     
         12 . A computer-assisted surgery system for tracking a tool with respect to a bone, comprising:
 a reference tracker with a MEMS unit for outputting tracking data relating to an orientation of the reference tracker, the reference tracker being adapted to be secured to the bone;   a tool with a MEMS unit preset with an initial orientation for outputting tracking data relating to an orientation of the tool once initialized, the tool being adapted to be secured to the bone;   a CAS processing unit comprising:
 an orientation setting unit for creating a trackable frame of reference relating the bone to the orientation of the reference tracker; 
 a tool calibrator for recording a relation between the initial orientation of the tool and the orientation of the reference tracker at initialization; 
 a tracking processor for calculating orientational data of the tool in the frame of reference of the bone using the relation from the tracking data; and 
 an interface for displaying the orientational data. 
   
     
     
         13 . The computer-assisted surgery system according to  claim 12 , wherein the tool is a cutting block connected to the bone with an orientation adjustment mechanism, and wherein the orientational data comprises an orientation of at least one cutting plane of the cutting block relative to the frame of reference of the bone. 
     
     
         14 . The computer-assisted surgery system according to  claim 12 , wherein the frame of reference comprises at least a mechanical axis of the bone. 
     
     
         15 . The computer-assisted surgery system according to  claim 12 , the initial orientation of the tool comprises axes being orthogonal to the MEMS unit on the tool. 
     
     
         16 . The computer-assisted surgery system according to  claim 12 , wherein the reference tracker and the tool are not in direct rigid connection when secured to the bone.