Method and system for determining an angle between two parts of a bone
A method and a system for determining an angle between two parts of a bone that are twisted relative to one another about the axis of a bone shaft. The system is particularly suitable for determining the antetorsion angle of a femur. In order to determine an antetorsion angle of a bone easily intraoperatively, a method with the following steps is proposed: establishing the position of a first orientation feature assigned to a first part of the bone, in particular a femoral neck axis, using an imaging method, establishing the position of a second orientation feature assigned to a second part of the bone, in particular a condyle tangent or a condyle plane, using an imaging method, and determining the angle, in particular the femoral antetorsion angle, from the positions of the two orientation features.
1. A method of determining an angle between two parts of a bone of a patient that are twisted relative to one another about an axis of a bone shaft of the bone, the method comprising:
establishing a position of a first orientation feature assigned to a first part of the bone using an x-ray imaging method;
establishing a position of a second orientation feature assigned to a second part of the bone using the x-ray imaging method;
providing an indication element being an elongate construction element having a defined longitudinal axis;
for establishing the position of at least one of the first and second orientation features, positioning the indication element outside of the patient's body relative to the at least one of the first and second orientation features, wherein the indication element is visible in an x-ray image to be taken, and moving the indication element relative to the bone for positioning the indication element based on a plurality of recordings obtained by the x-ray imaging method; and
determining the angle between the first and second parts of the bone from the positions of the first and second orientation features.
2. The method according to claim 1 , wherein the bone is a femur, the first orientation feature is a femoral neck axis, the second orientation feature is a condyle tangent or a condyle plane, and the determining step comprises determining a femoral antetorsion angle.
3. The method according to claim 1 , which comprises recording the plurality of recordings of the bone used for the positioning of the indication element from mutually different recording angles.
4. The method according to claim 1 , which comprises recording the recordings of the bone when establishing the position of at least one of the orientation features using the x-ray imaging method and aligning a recording device relative to the relevant orientation feature on the basis of the recordings.
5. The method according to claim 1 , wherein the first and second orientation features are bone-inherent orientation features.
6. The method according to claim 1 , wherein the imaging method used for establishing at least one of the positions of the first or second orientation features is an x-ray projection method.
7. The method according to claim 1 , which comprises carrying out the method steps intraoperatively.
8. The method according to claim 1 , which comprises holding the indication element by hand.
9. The method according to claim 1 , which comprises holding the indication element by way of a holder fastened to an operating table or way of a stand.
10. A system for determining an angle between two parts of a bone that are twisted relative to one another about an axis of a bone shaft of the bone of a patient, the system comprising:
a device for establishing a position of a first orientation feature assigned to a first part of the bone, the device including at least one indication element positionable relative to the first orientation feature on the basis of a number of recordings obtained by an x-ray imaging method, the indication element being an elongate construction element having a defined longitudinal axis, and a holder fastened to an operating table or a stand configured to hold said indication element outside of the patient and to move said indication element relative to the bone of the patient;
a device for establishing a position of a second orientation feature assigned to a second part of the bone; and
a device for determining the angle between the first and second parts of the bone from the positions of the first and second orientation features.
11. The system according to claim 10 , wherein the bone is a femur, the first orientation feature is a femoral neck axis, the second orientation feature is a condyle tangent or a condyle plane, and the angle to be determined is a femoral antetorsion angle.
12. The system according to claim 10 , wherein the indication element is configured for alignment with the first orientation feature.