Determining a plane of an anatomical body part

Abstract

A data processing method for determining the position of a main plane of an anatomical body part, comprising the steps of: ·providing absolute auxiliary point data which describe the position of at least one actual auxiliary point of the body part relative to a marker device attached to the body part, the at least one actual auxiliary point being outside the main plane; ·providing relative point data which constrain the possible positions of the main plane relative to the at least one actual auxiliary point; ·providing absolute main point data which describe the position of one or two actual main points of the body part relative to the marker device attached to the body part, said one or two actual main points lying in the main plane and/or calculating the position of at least one virtual main point relative to the marker device, said at least one virtual main point being in the main plane and being calculated based on the absolute auxiliary point data and the relative point data; ·calculating a position of the main plane relative to the marker device, wherein the calculation uses the relative point data and auxiliary point data as well as the provided absolute main point data and/or the calculated position of the at least one virtual main point.

1 . A data processing method for determining the position of a plane of an anatomical body part called main plane, constituted to be performed by a computer and comprising the steps of:
 providing data called absolute auxiliary point data which describe the position of at least one point of the body part, called actual auxiliary point, relative to a marker device attached to the body part, the at least one actual auxiliary point being outside the main plane;   providing data called relative point data which constrain the possible positions of the main plane relative to the at least one actual auxiliary point;   providing data called absolute main point data which describe the position of one or two points of the body part, called actual main points, relative to the marker device attached to the body part, said one or two actual main points lying in the main plane and/or calculating the position of at least one point called virtual main point relative to the marker device, said at least one virtual main point being in the main plane and being calculated based on the absolute auxiliary point data and the relative point data;   calculating a position of the main plane relative to the marker device, wherein the calculation uses the relative point data and auxiliary point data as well as the provided absolute main point data and/or the calculated position of the at least one virtual main point.   
     
     
         2 . The data processing method according to  claim 1 , wherein the step of calculating the position of the main plane includes the step of determining at least one virtual auxiliary point and/or at least one virtual main point on the basis of the relative point data and the absolute main point data and/or absolute auxiliary point data, and wherein the step of calculating the position of the main plane also includes the step of calculating the position of the main plane on the basis of the at least one virtual auxiliary point and/or at least one virtual main point, wherein the at least one virtual main point is not included in the absolute main point data and the at least one virtual auxiliary point is not included in the absolute auxiliary point data. 
     
     
         3 . The data processing method according to  claim 1 , wherein the relative point data describe at least one scalar value used for describing a positional relationship between a particular auxiliary point of the one or more actual auxiliary points and the virtual main point and/or between the particular auxiliary point and the virtual auxiliary point, the position of the virtual auxiliary point being in particular symmetrical to the position of the particular auxiliary point with respect to the main plane, and/or between one or more of the actual auxiliary points and the main plane. 
     
     
         4 . The data processing method according to  claim 1 , further comprising the steps of:
 providing data called body part data which constrain the possible relative positions between landmarks of the body part and/or between the landmarks and the main plane;   providing data called landmark data which respectively correlate at least some of the actual and/or virtual main points and/or auxiliary points with at least some of the landmarks of the body part; and   if more than one solution for calculating the position of the main plane is possible, selecting one of the possible solutions for the position of the main plane on the basis of the landmark data and body part data.   
     
     
         5 . The data processing method according to  claim 1 , wherein all of the actual auxiliary points described by the absolute auxiliary point data and used for calculating the position of the main plane are outside the main plane but on the same side of the main plane. 
     
     
         6 . The data processing method according to  claim 1 , wherein if
 the position of only one main point of the body part relative to the marker device is available for the calculation, then the absolute auxiliary point data describe the position of at least two auxiliary points of the body part relative to the marker device, the at least two auxiliary points being outside the main plane; and if the positions of only two main points of the body part relative to the marker device are available for the calculation, then the absolute auxiliary point data describe the position of at least one auxiliary point of the body part relative to the marker device, the at least one auxiliary point being outside the main plane.   
     
     
         7 . The data processing method according to  claim 5 , wherein the relative point data describe at least one constraint for the possible positions of the main plane relative to the at least one auxiliary point, if there are two main points, and describe at least two constraints for the possible positions of the main plane relative to the at least one auxiliary point, if there is only one main point. 
     
     
         8 . A data processing method which includes the data processing method of  claim 1  and which is a method for determining the position of the main plane of the anatomical body part and of another plane called auxiliary plane of the anatomical body part, wherein in order to determine the main plane, the data processing method of any one of the preceding claims is performed, and in order to determine the auxiliary plane, absolute auxiliary point data describe the position of at least two of the auxiliary points of the body part relative to the marker device, the at least two auxiliary points being outside the main plane; further comprising the step of providing relative auxiliary plane data which describe a predetermined positional relationship between the auxiliary plane and the main plane;
 wherein the position of the auxiliary plane is determined by assuming that the at least two auxiliary points lie in the auxiliary plane, and is determined on the basis of the relative auxiliary plane data. 
 
     
     
         9 . A data processing method which includes the data processing method of  claim 8  for determining the position of the main plane and of the auxiliary plane and which is additionally a method for determining the position of a standard plane which is different from the auxiliary plane, further comprising the steps of:
 providing relative standard plane data which describe the expected positional relationship between the auxiliary plane and the standard plane; and 
 determining the position of the standard plane on the basis of the position of the auxiliary plane and the relative standard plane data. 
 
     
     
         10 . The data processing method according to  claim 1 , wherein: one of the landmarks represented by one of the auxiliary points is the sinistral or dextral anterior superior iliac spine landmark; and/or
 the main plane is the mid-sagittal plane; and/or   the standard plane is the anterior pelvic plane; and/or   the standard plane data describe the angle between the anterior pelvic plane and the auxiliary plane; and/or   the anterior pelvic plane and the auxiliary plane intersect each other along a line connecting the sinistral and the dextral anterior superior iliac spine landmarks of the body part; and/or   another auxiliary point represents a landmark defined by the acetabulum or a part of the acetabulum or the fossa of the acetabulum or another point of the acetabulum; and/or   the relative point data describe a constraint for an inter-fossa distance or an inter-teardrop distance of the pelvis.   
     
     
         11 . A data processing method for determining additional points called additional auxiliary points which can be used for determining the position of a plane of a body part, the plane being called a main plane, in particular according to  claim 1 , comprising the steps of:
 providing at least one auxiliary point;   providing relative auxiliary point data which describe at least one constraint which limits the possible positions for an additional auxiliary point, the additional auxiliary point being symmetrical to one of the one or more auxiliary points with respect to the main plane; and   providing candidate point data in steps, wherein in each step, the position of a new candidate point is described by the candidate point data, wherein in the current step, the following steps are performed:   a) providing new data called new candidate point data which describe a relative position of a new candidate point with respect to the marker device, the new candidate point being a new candidate for a position of the additional auxiliary point;   b) checking whether the positions of the new candidate point comply with the at least one constraint described by the relative auxiliary point data;   c) repeating steps a) and b) if the position of the new candidate point does not comply with the at least one constraint, or accepting the new candidate point as an additional auxiliary point if the position of the candidate point does comply with the at least one constraint.   
     
     
         12 . A program which, when it is running on a computer or is loaded onto a computer, causes the computer to perform the method according to  claim 1 ; and/or
 a program storage medium on which the program is stored; and/or   a computer on which the program is running or in the memory of which the program is loaded; and/or a signal wave, in particular a digital signal wave, carrying information which represents the program.   
     
     
         13 . A navigation system for computer-assisted surgery, comprising:
 the computer of  claim 12 ;   a detection device for detecting the position of the main and auxiliary points and for generating detection signals which represent the position of the main and auxiliary points and for supplying the detection signals to the computer of the preceding claim, the computer being designed to determine the absolute point data and the relative point data on the basis of the received detection signals in order to process the absolute data in accordance with  claim 1 ; and   a user interface for receiving data from the computer in order to provide information to the user, the computer being designed to calculate the data in accordance with the data processing method according to  claim 1 .   
     
     
         14 . A determination method for determining the position of a main plane of an anatomical body part, comprising the steps of:
 generating detection signals by detecting a pointer, said pointer contacting a body part or a tool, called main point detection tool, attached to the body part;   determining, on the basis of the detection signals, the absolute main point data and absolute auxiliary point data as mentioned in  claim 1 , and then performing  claim 1  on the basis of the determined absolute main point data and absolute auxiliary point data.   
     
     
         15 . The navigation system of  claim 13  further comprising a tool, called main point detection tool, for detecting at least one actual main point, the plane point detection tool comprising:
 a proximal side constituted to be fitted to a patient by contacting the patient along a first direction of length-wise extension of the tool, the proximal side is constituted to be able to be aligned with a plane of an anatomical body part along the first direction of length-wise extension, the direction in which the proximal side faces and along which the tool is flexibly bendable for bringing the tool into contact with the patient being a third direction of extension of the tool; 
 a distal side which comprises at least one pointer insertion member comprising a tapered recess for inserting the tip of a pointer, the at least one pointer insertion member being prominently positioned in a first section of the distal side which is, in the direction of length-wise extension, closer to a first end of the plane point detection tool than to a second end; wherein the distal side further comprises a second section having a flat surface and being closer to the second end than to the first end; 
 both the proximal side and distal side extending in the first direction and in a second direction of extension, the second direction being traverse to the first direction, 
 the tool being flexibly bendable in the third direction while being rigid in the second direction, the second direction being a direction of width-wise extension of the tool, the width-wise extension of the tool being smaller than the length-wise extension.