Abstract: A system and method for creating a cavity to receive an acetabulum in a pelvic bone with the aid of a navigated tool are provided. A tear-drop point on a pelvic bone is located by means of a scanning instrument. A tear-drop plane is determined from position data of the tear-drop point and the plane of the pelvic inlet. The tear-drop plane lies perpendicular to the plane of the pelvic inlet, extends parallel to a line connecting the two anterior superior iliac spines, and runs through the tear-drop point. A reference point is determined which is at a defined height above the tear-drop plane, in a defined position in an anterior-posterior direction, and at a defined spacing from an outer surface of the pelvic bone in a lateral-medial direction. A tool is worked into the pelvic bone in a desired direction relative to the reference point.

Abstract: In order to improve the computation of the position of the tangential plane in a method for determining the position of a tangential plane which rests tangentially on three non-collinear extreme points of structures of a body, in which one determines the position of the three extreme points approximately by using three starting points disposed in the locality of the structures and computes the tangential plane as being a plane passing through these three starting points, it is proposed that one investigates the structure of the body in the vicinity of the three extreme points using a navigated ultrasonic head which emits ultrasonic radiation in an investigation plane and displays the ultrasonic image of each investigated structure on a display screen, in that one overlays a line of intersection of the investigation plane and the tangential plane on the ultrasonic image in the display screen, in that, for each structure, one selects as an improved extreme point that point of the structure which is located in t

Abstract: Methods and apparatus using a surgical navigation system during hip joint replacement surgery without separately affixing a marker to the femur. The navigation system acquires the center of rotation of the hip joint as well as at least one point on the femur in the pelvic frame of reference. From these two points, the navigation system calculates the position and length of a first line between the center of rotation of the hip joint and the point on the femur. A prosthetic cup is implanted and its center of rotation is recorded. A tool for forming the bore within which the stem of the femoral implant component will be placed is tracked by the navigation system. The navigation system calculates the position and length of a first line between the center of rotation of the prosthetic cup and the re-palpated first point. The surgical navigation system uses this information to calculate and display to the surgeon relevant information about the surgery.

Abstract: To facilitate assistance of the operating surgeon when determining the disposition of a receiving cavity in the case of a method and a navigation system for creating a cavity to receive an acetabulum in a navigated pelvic bone with the aid of a navigated tool, it is proposed that the tear-drop point on the pelvic bone is located by means of a navigated scanning instrument, from the position data and the plane of the pelvic inlet of said pelvic bone there is determined a tear-drop plane, which lies perpendicular to said plane of the pelvic inlet and extends parallel to a line connecting the two anterior superior iliac spines and through the scanned tear-drop point, that a reference point is determined at a defined height above the tear-drop plane and in a defined position in the anterior-posterior direction and at a defined spacing from the outer surface of the pelvic bone in the lateral-medial direction, and that the tool is worked into the pelvic bone in a desired direction relative to the reference point un

Abstract: In a method for indicating the position and orientation of a tool for preparation of a femur for a femur implant which with a joint ball fits into the acetabulum of the pelvis or into a joint socket inserted in the pelvis or for preparation of such a femur implant for insertion into a femur relative to the femur and to the center point of the joint ball, in order to provide the operating surgeon with an easily understandable representation for targeted positioning of the tool or the femur implant, it is proposed that the center point of the joint ball and a line of intersection of a transversal plane of the femur and an instrument plane, which line of intersection passes through the center point of the joint ball, be represented in this transversal plane of the femur at the level of the center point of the joint ball.

Abstract: Methods and apparatus using a surgical navigation system to position the femoral component of a prosthetic hip during hip joint replacement surgery without separately affixing a marker to the femur. The navigation system acquires the center of rotation of the hip joint as well as at least one point on the femur in the pelvic frame of reference. From these two points, the navigation system calculates the position and length of a first line between the center of rotation of the hip joint and the point on the femur. Optionally, a second point on the femur that is not on the first line is palpated. The system can calculate the position and length of a second line that is perpendicular to the first line and that runs from the first line to the second palpated point on the femur. The prosthetic cup is implanted and its center of rotation is recorded. A tool for forming the bore within which the stem of the femoral implant component will be placed is tracked by the navigation system.

Abstract: A method for determination of the mobility of a hip joint prosthesis is proposed, comprising a bearing cup that can be inserted in the hip bone and a prosthetic shaft that can be inserted in the femur and is pivotally mounted by a spherical joint surface in the bearing cup, which is characterised in that the femur with the prosthetic shaft is pivoted as far as possible in various directions, in that it is determined whether the central point of the bearing cup and the central point of the spherical joint surface move apart from one another during this process, and in that, for each pivoting direction, the maximum pivoting angle is thus determined, at which the central points begin to move apart from one another. A device for carrying out this method is also proposed.

Abstract: To make available a method for checking a marking element for displacement in relation to a holding structure, in particular a bone, on which this marking element is fixed, said marking element being used for determining position in navigational surgery, and said marking element functioning with the greatest possible precision, it is proposed to choose a point of orientation which is in a unique relationship to the holding structure and to monitor the position of the point of orientation in a reference system of the marking element.

Abstract: To enable the contour of a recess in a piece of material, which is worked into the material by means of a tool, in particular in a piece of bone, to also be determined without a direct view of the machining region with a method for determining this contour, it is proposed that the position of the piece of material in space is established by a navigation system, that the position of the tool in space is established by a navigation system, that the respective position of the tool in relation to the piece of material is determined from the position data obtained in this manner, that during the machining of the piece of material with the tool, the relative positions of the tool in relation to the piece of material are stored and that the prepared contour on the piece of material is determined from extreme values of these relative positions with respect to a fixed reference position of the piece of material. A device for performing this method is also specified.

Abstract: To make available a method for checking a marking element for displacement in relation to a holding structure, in particular a bone, on which this marking element is fixed, said marking element being used for determining position in navigational surgery, and said marking element functioning with the greatest possible precision, it is proposed to choose a point of orientation which is in a unique relationship to the holding structure and to monitor the position of the point of orientation in a reference system of the marking element.