Method and apparatus for reducing malalignment of fractured bone fragments
View Patent ↗A method and system for intraoperative, image-based reduction control for long bone shaft fracture treatment. The method includes preoperative steps of a) implanting markers into the proximal fragment and into the distal fragment of the broken bone, b) creating a 3D reference model of bone by taking a CT scan of the healthy bone, a CT scan of the broken bone and c) defining landmarks in the reference model based on the marker positions. The method further includes intraoperative steps of d) extracting the 3D position of the same landmarks from a series of 2D fluoroscopic images, using a reference object and e) comparing the positions the preoperatively defined landmarks and the positions of the intraoperatively extracted landmarks to calculate the malalignment of the fracture fragments.
1. A method of reducing malalignment of a fractured bone that defines a proximal bone fragment and a distal bone fragment that is separated from the proximal bone fragment by a fracture, the method comprising:
identifying at least one first anatomical landmark on the proximal bone fragment, and identifying at least one second anatomical landmark on the distal bone fragment;
providing a first set of images of a bone that is contralateral with respect to the fractured bone, and a second set of images of the fractured bone including the first and second anatomical landmarks;
obtaining a first 3D representation of the proximal bone fragment and the at least one first anatomical landmark from the second set of images, a second 3D representation of the distal bone fragment and the at least one second anatomical landmark from the second set of images, and a mirrored 3D representation of the contralateral bone from the first set of images;
extracting a first set of 3D coordinates of the at least one first anatomical landmark from the first 3D representation, and a second set of 3D coordinates of the at least one second anatomical landmark from the second 3D representation;
transferring the first set of 3D coordinates onto the mirrored 3D representation, and transferring the second set of 3D coordinates onto the mirrored 3D representation;
determining a planned relative position between the proximal bone fragment and the distal bone fragment based on a position of the transferred first set of 3D coordinates relative to the transferred second set of 3D coordinates;
after the determining step, reducing the fractured bone by moving at least one of the proximal bone fragment and the distal bone fragment relative to the other of the proximal bone fragment and the distal bone fragment;
ascertaining an on-site actual relative position between the identified at least one first anatomical landmark of the proximal bone fragment and the identified at least one second anatomical landmark of the distal bone fragment by (a) positioning the proximal and the distal bone fragments on an upper, flat surface of a reference plate, the upper surface having a plurality of adjacent markings separated by a known distance between adjacent markings; (b) acquiring a first-moved set of at least two fluoroscopic images with different perspectives of the proximal bone fragment, and a second-moved set of at least two fluoroscopic images with different perspectives of the distal bone fragment; (c) extracting a first moved-set of 2D image coordinates of the first anatomical landmark on the proximal bone fragment from the first-moved set of at least two fluoroscopic images, and extracting a second-moved set of 2D image coordinates of the second anatomical landmark on the distal bone fragment from the second-moved set of at least two fluoroscopic images; (d) calculating a first moved-set of 3D coordinates of the first anatomical landmark on the proximal bone fragment and a second moved-set of 3D coordinates of the second anatomical landmark on the distal bone fragment with respect to the plurality of adjacent markings on the reference plate by using the first and second moved-sets of 2D image coordinates of the first and second anatomical landmarks on the proximal bone fragment and the distal bone fragment, respectively; and (e) determining the on-site actual relative position between the first anatomical landmark on the proximal bone fragment and the second anatomical landmark on the distal bone fragment after the reducing step based upon the calculated first moved-set of 3D coordinates of the first anatomical landmark on the proximal bone fragment and the calculated second moved-set of 3D coordinates of the second anatomical landmark on the distal bone fragment; and
calculating a set of malalignment parameters by comparing the on-site actual relative position to the planned relative position.
2. The method of claim 1 , further comprising:
performing a first 3D registration of the first 3D representation and the mirrored 3D representation prior to the transfer of the first set of 3D coordinates onto the mirrored 3D representation;
performing a second 3D registration of the second 3D representation and the mirrored 3D representation prior to the transfer of the second set of 3D coordinates onto the mirrored 3D representation.
3. The method of claim 1 further comprising:
defining a proximal configuration of at least one anatomical landmark on a proximal bone part of the contralateral bone corresponding to the proximal bone fragment of the fractured bone from the mirrored 3D representation; and
defining a distal configuration of at least one anatomical landmark on a distal bone part of the contralateral bone corresponding to the distal bone fragment of the fractured bone from the mirrored 3D representation.
4. The method of claim 1 , wherein the step of providing the first set of images is performed using a medical imaging device.
5. The method of claim 4 , wherein the medical imaging device is a computer tomograph or a medical X-ray device.
6. The method of claims 1 , wherein the mirrored 3D representation is used as a reference to establish a local system of coordinates.
7. The method of claim 1 , further comprising reducing the fractured bone in accordance with the set of malalignment parameters.
8. The method of claim 7 , wherein the reducing step further comprises:
comparing the set of malalignment parameters with a pre-defined set of acceptable malalignment parameters;
determining deviations between the set of malalignment parameters and the pre-defined set of acceptable malalignment parameters;
deciding whether the deviations are acceptable; and
fixing the proximal and distal fragment relative to each other if the deviations are acceptable.
9. The method of claim 8 , further comprising performing at least one reduction step at the fractured bone on the basis of the set of malalignment parameters, if the deviations are not acceptable.
10. The method of claim 1 , further comprising determining the imaging characteristics of the fluoroscope corresponding to the first and second set of fluoroscopic images.
11. The method of claim 10 , further comprising determining calibration parameters of the fluoroscope.
12. The method of claim 1 , further comprising obtaining a 3D representation of the contralateral bone from the first set of images, and obtaining the mirrored 3D representation from the 3D representation of the contralateral bone.
13. The method of claim 1 , wherein the relative position further comprises a relative orientation.
14. The method of claim 1 , further comprising the step of
defining a proximal configuration of the proximal bone fragment based on the transferred first set of 3D coordinates, and a distal configuration of the distal bone fragment based on the transferred second set of 3D coordinates,
wherein the defining step is performed based on the proximal and distal configurations.
15. The method of claim 1 , wherein the moving step comprises translating at least one of the proximal and distal bone fragments toward the other of the proximal and distal bone fragments.
16. The method of claim 15 , wherein the moving step comprises rotating at least one of the proximal and distal bone fragments relative to the other of the proximal and distal bone fragments.
17. The method of claim 1 , wherein the moving step comprises rotating at least one of the proximal and distal bone fragments relative to the other of the proximal and distal bone fragments.