Enhanced graphic features for computer assisted surgery system

Abstract

A computer assisted surgery system with is enhanced graphics features is described for assisting a surgeon in orthopaedic procedures. A system is described for use in inserting multiple guide pins in hip fracture surgery using a single bore drill guide that has a graphical representation comprising its real trajectory and one or more virtual trajectories, the virtual trajectories representing potential positions of other guide pins to be placed during the procedure. Additionally, representations of inserted guide pins and virtual trajectories may be retained on the display at their inserted positions for use in aligning subsequent guide pins. A system is also described for orientation of an acetabular cup in a total hip replacement surgery. During cup insertion, the surgeon is provided with information regarding the orientation of the cup with respect to a pelvic reference frame that is based on accepted pelvic landmarks. The positions of each landmark is calculated by the system when a probe with a virtual tip, separate from its physical tip, is overlaid on the landmark in roughly orthogonal images of the pelvis.

1 . A computer assisted surgery system for orienting an acetabular component during total hip replacement surgery comprising: 
 an imaging device for generating at least two 2-D images of a body part;    means for displaying the 2-D images of the body part;    means for specifying the locations of at least three pelvic landmarks on the 2-D images;    means for calculating a pelvic coordinate frame based on the at least three pelvic landmarks;    a positioning instrument attachable to the acetabular component, said positioning instrument's pose being measured by a localizing device; and    means for displaying the orientation of the acetabular component relative to the pelvic coordinate frame.    
   
   
       2 . The computer assisted surgery system of  claim 1  wherein the means for specifying the locations of the at least three pelvic landmarks comprises: 
 a probe having a real tip portion, said real tip portion defining a virtual tip portion correlating with a point in space located in a fixed and known relationship to the real tip portion, the position of said probe being measured by a localizing device;    means for generating a graphic representation of the virtual tip portion;    means for superimposing the graphic representation of the virtual tip portion over the 2-D images of the body part; and    means for signaling to the system; wherein the surgeon uses the signaling means to indicate to the system that the graphic representation of the virtual tip is aligned over the image of a pelvic landmark in the 2-D images.    
   
   
       3 . A method for orienting an acetabular component during a total hip replacement surgery comprising the steps: 
 (a) acquiring two roughly orthogonal x-ray images of at least three bony landmarks of a patient's pelvis;    (b) specifying the location of each of the three landmarks in the two x-ray images by positioning a cursor over the landmark in both images;    (c) calculating the 3-D position of each of the three landmarks from the specified cursor positions;    (d) defining a pelvic coordinate frame based on the calculated positions of the three landmarks;    (e) attaching the acetabular component to a positioning instrument;    (f) measuring the pose of the positioning instrument with a localizing device;    (g) calculating information regarding the orientation of the acetabular component relative to the pelvic coordinate frame; and    (h) displaying the calculated orientation information to the surgeon; wherein the surgeon uses the information to place the acetabular component into a desired orientation.    
   
   
       4 . The method of  claim 3  wherein positioning the cursor is accomplished in step (b) by manipulating a mouse, trackball, joystick or other input device.  
   
   
       5 . The method of  claim 3  wherein the cursor is a graphic representation of a probe and positioning the cursor in step (b) comprises the steps of: 
 generating a graphic representation of the probe which indicates a virtual tip position at some known distance from the real tip of the probe;    measuring the position of the probe with a localizing device;    superimposing the graphic representation of the virtual tip on the two x-ray images; and    repositioning the probe in space such that the virtual tip coincides with the bony landmark in both x-ray images.    
   
   
       6 . The method of  claim 3  wherein displaying information to the surgeon in step (g) further comprises the steps of: 
 generating a graphic representation of the positioning instrument and acetabular component; and    superimposing said graphic representation on one or more images of the patient's pelvis based on the measured pose of the positioning instrument;    wherein the surgeon is able to view and adjust the orientation of the acetabular component relative to imaged anatomy of the pelvis.    
   
   
       7 . The method of  claim 3  wherein displaying information to the surgeon in step (g) further comprises the steps of: 
 defining an axis of the acetabular component;    calculating the angular difference between the axis of the acetabular component and an axis of the pelvic coordinate frame; and    reporting the angular difference between the axes to the surgeon.    
   
   
       8 . The method of  claim 4  wherein the three bony landmarks comprise the left anterior superior iliac spine, the right anterior superior iliac spine, and the anterior portion of the pubic bone.  
   
   
       9 . A computer assisted surgery system with enhanced graphic capabilities for noninvasively determining the location of a specific point within a body, the system comprising: 
 an x-ray imaging device for generating at least two 2-D images of a body part;    means for displaying the 2-D images of the body part;    a probe having a real tip portion, said real tip portion defining a virtual probe tip portion correlating with a point in space located in a fixed and known relationship to the real tip portion;    a localizing device for measuring the pose of the probe relative to the imaging device;    means for generating a graphic representation of the virtual tip portion; and    means for superimposing a graphic representation of the virtual tip portion over the 2-D images of the body part;    wherein the three-dimensional location of a specific point within the body may be calculated from the pose of the probe when, in the at least two images, the representation of the virtual tip overlays the specific point within the body.