Method of preoperative planning to correct spine misalignment of a patient

Abstract

This invention relates to a method of preoperative planning to correct spine misalignment of a patient, comprising a step of making a translation and a rotation, in a sagittal plane, of each vertebra of a set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said set of imaged vertebrae presents afterwards, in the sagittal plane, the same cervical lordosis and/or the same thoracic kyphosis and/or the same lumbar lordosis as a model adapted for said patient, wherein it also comprises, before said step of making said translation and said rotation in a sagittal plane: a step of making a translation and a rotation, in a coronal plane, of each vertebra of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said set of imaged vertebrae becomes straight in said coronal plane, and of making a rotation, in an axial plane, of each vertebra of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said set of imaged vertebrae becomes axially aligned.

Claims

1. A method of preoperative planning to correct spine misalignment of a patient, comprising a step of making a translation and a rotation, in a sagittal plane, of each vertebra of a set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said set of imaged vertebrae presents afterwards, in the sagittal plane, the same cervical lordosis and/or the same thoracic kyphosis and/or the same lumbar lordosis as a model adapted for said patient, wherein it also comprises, before said step of making said translation and said rotation in said sagittal plane a step of making a translation and a rotation, in a coronal plane, of each vertebra of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae becomes straight in said coronal plane, and of making a rotation, in an axial plane, of each vertebra of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae becomes axially aligned.

2. The method of preoperative planning to correct spine misalignment of said patient according to claim 1, wherein said method of preoperative planning to correct spine misalignment of said patient is applied to a set-of several thoracic and several lumbar imaged spine vertebrae of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said set of several thoracic and lumbar imaged spine vertebrae (2)-presents, in the sagittal plane, the same thoracic kyphosis and the same lumbar lordosis as said model adapted for said patient.

3. The method of preoperative planning to correct spine misalignment of said patient according to claim 2, wherein said method of preoperative planning to correct spine misalignment of said patient is applied to all thoracic and all lumbar spine vertebrae of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said patient spine presents, in the sagittal plane, the same thoracic kyphosis and the same lumbar lordosis as said model adapted for said patient.

4. The method of preoperative planning to correct spine misalignment of said patient according to claim 1, wherein: in said step of making said translation and said rotation in said coronal plane, said translation and rotation are performed simultaneously, in said step of making said translation and said rotation in said sagittal plane, said translation and rotation are performed simultaneously.

5. The method of preoperative planning to correct spine misalignment of said patient according to claim 1, wherein said method of preoperative planning to correct spine misalignment of said patient also comprises, after said steps of making translations and rotations, a step of pre-twisting at least one rod, to be integrated within said patient body to support said patient spine, according to position and orientation of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae after said step of making said translation and said rotation in said sagittal plane.

6. The method of preoperative planning to correct spine misalignment of said patient according to claim 5, wherein in said step of pre-twisting at least one rod, said at least one rod comprises two rods that are pre-twisted which are to be integrated respectively on both sides of said patient spine.

7. The method of preoperative planning to correct spine misalignment of said patient according to claim 1, wherein said method of preoperative planning to correct spine misalignment of said patient also comprises, after said steps of making translations and rotations in said coronal plane and in said sagittal plane, a step of editing a pattern of at least one pre-twisted rod to be integrated within said patient body to support said patient spine, according to position and orientation of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae after said step of making said translation and said rotation in said sagittal plane.

8. The method of preoperative planning to correct spine misalignment of said patient according to claim 1, wherein said method of preoperative planning to correct spine misalignment of said patient also comprises, after said steps of making translations and rotations in said coronal plane and in said sagittal plane, a step of calculating the length of at least one rod, to be integrated within said patient body to support said patient spine, according to position and orientation of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae after said step of making said translation and said rotation in said sagittal plane.

9. The method of preoperative planning to correct spine misalignment of said patient according to claim 1, wherein a set of several thoracic and/or lumbar imaged spine vertebrae of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae is a 3D spine image reconstructed from two 2D radiographic spine images, or alternatively from two 2D radiographic spine images which are a coronal image and a sagittal image.

10. The method of preoperative planning to correct spine misalignment of said patient according to claim 1, wherein a lumbar lordosis position is obtained by moving two end markers corresponding respectively to higher extreme lumbar vertebra and sacral plate and a lumbar lordosis curvature is obtained by moving an intermediate marker corresponding to an intermediate lumbar vertebra located between both extreme lumbar vertebrae, and/or wherein a thoracic kyphosis position is obtained by moving two end markers corresponding respectively to both extreme thoracic vertebrae and a thoracic kyphosis curvature is obtained by moving an intermediate marker corresponding to an intermediate thoracic vertebra located between both extreme thoracic vertebrae, and/or wherein a cervical lordosis position is obtained by moving two end markers corresponding respectively to both extreme cervical vertebrae and a cervical lordosis curvature is obtained by moving an intermediate marker corresponding to an intermediate cervical vertebra located between both extreme cervical vertebrae.

11. The method of preoperative planning to correct spine misalignment of said patient according to claim 1, wherein said model is adapted for said patient first by getting an adapted lordosis from one or more patient based parameters and second by getting an adapted kyphosis from said adapted lordosis and from one or more patient based parameters.

12. The method of preoperative planning to correct spine misalignment of said patient according to claim 11, wherein said adapted lordosis is obtained from patient pelvic incidence and from patient population type and preferably also from patient age.

13. The method of preoperative planning to correct spine misalignment of said patient according to claim 12, wherein said adapted kyphosis is obtained from said adapted lordosis and from patient sagittal vertical axis.

14. The method of preoperative planning to correct spine misalignment of said patient according to claim 13, wherein said adapted kyphosis is obtained by varying said adapted lordosis curvature within a limited range, or alternatively within a limited range of plus or minus 10 degrees, while minimizing said patient sagittal vertical axis.

15. The method of preoperative planning to correct spine misalignment of said patient according to claim 1, wherein said spine misalignment comes from a scoliosis and/or from a degenerative spine.

16. A pre-twisted rod, to be integrated within said patient body to support said patient spine, which has been pre-twisted according to position and orientation of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae after a step of making said translation and said rotation in said sagittal plane performed during said method of preoperative planning to correct spine misalignment of said patient according to claim 1.

17. A method of preoperative planning to correct spine misalignment of a patient, comprising a step of making a translation and a rotation, in a sagittal plane, of each vertebra of a set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said set of imaged vertebrae presents afterwards, in the sagittal plane, the same cervical lordosis and/or the same thoracic kyphosis and/or the same lumbar lordosis as a model adapted for said patient, wherein it also comprises, before said step of making said translation and said rotation in said sagittal plane a step of making a translation and a rotation, in a coronal plane, of each vertebra of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae becomes straight in said coronal plane, and of making a rotation, in an axial plane, of each vertebra of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae, so that said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae becomes axially aligned; and wherein said method of preoperative planning to correct spine misalignment of said patient also comprises, after said steps of making translations and rotations, a step of pre-twisting at least one rod, to be integrated within said patient body to support said patient spine, according to position and orientation of said set of several cervical and/or thoracic and/or lumbar imaged spine vertebrae after said step of making said translation and said rotation in said sagittal plane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a frontal patient spine view, the patient suffering from scoliosis, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(2) FIG. 2 shows a frontal patient spine view, the spine having been partly derotated during preoperative planning, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(3) FIG. 3 shows a frontal patient spine view, where a starting phase of translation and rotation, in a coronal plane, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(4) FIG. 4 shows a frontal patient spine view, where an ending phase of translation and rotation, in a coronal plane, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(5) FIG. 5 shows a frontal patient spine view, where a starting phase of translation and rotation, in an axial plane, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(6) FIG. 6 shows a frontal patient spine view, where an ending phase of translation and rotation, in an axial plane, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(7) FIG. 7 shows a lateral patient spine view, with a high value of thoracic kyphosis, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(8) FIG. 8 shows a lateral patient spine view, with a high value of lumbar lordosis, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(9) FIG. 9 shows a lateral patient spine view, with a close to zero value of sagittal vertical axis, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(10) FIG. 10 shows a lateral patient spine view, with a lumbar lordosis concentrated in the middle region of lumbar vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(11) FIG. 11 shows a lateral patient spine view, with a lumbar lordosis concentrated in the lower region of lumbar vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment or the invention.

(12) FIG. 12 shows a lateral patient spine view, with a lumbar lordosis concentrated in the upper region of lumbar vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(13) FIG. 13 shows a lateral patient spine view, with a thoracic kyphosis concentrated in the middle region of thoracic vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(14) FIG. 14 shows a lateral patient spine view, with a thoracic kyphosis concentrated in the lower region of thoracic vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(15) FIG. 15 shows a lateral patient spine view, with a thoracic kyphosis concentrated in the upper region of thoracic vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DISCLOSURE

(16) FIG. 1 shows a frontal patient spine view, the patient suffering from scoliosis, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(17) A patient spine 1 comprises vertebrae 2 and is ended by pelvis 3. Vertebrae 2 comprise thoracic vertebrae T1 to T12 and lumbar vertebrae L1 to L5. A sane spine 1 should appear as vertical in the coronal plan. Here, one can see that the spine 1 is heavily curved toward left of FIG. 1 in its upper part, corresponding to thoracic vertebrae 2, and slightly curved toward right of FIG. 1 in its lower part, corresponding to lumbar vertebrae 2. This means that represented spine 1 suffers from a disease called scoliosis. This means that represented spine 1 should be made straight in coronal plan. Therefore, imaged thoracic vertebrae T1 to T12 should be moved to the right of FIG. 1, whereas imaged lumbar vertebrae L1 to L5 should be moved to the left of FIG. 1.

(18) FIG. 2 shows a frontal patient spine view, the spine having been partly derotated during preoperative planning, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(19) The thoracic vertebrae 2 comprise thoracic vertebrae T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12. The lumbar vertebrae 2 comprise lumbar vertebrae L1, L2, L3, L4, L5. The spine 1 is straight, what means all vertebrae 2 are vertically aligned. The represented spine 1 is a sane spine with respect to coronal plan. So, the spine 1, represented on FIG. 1, suffering from scoliosis, should be healed so as to become the straight spine 1 in coronal plan of FIG. 2, appearing to be sane with respect to coronal plan. Therefore, all imaged vertebrae 2 of FIG. 1 will have to be derotated, i.e. to undergo a derotation, so as to become straight in coronal plan as on FIG. 2. This derotation will include indeed a rotation and a translation to be performed simultaneously.

(20) FIG. 3 shows a frontal patient spine view, where a starting phase of translation and rotation, in a coronal plane, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention. During derotation, intervertebral space is maintained.

(21) One by one, each vertebra 2 will be simultaneously translated and rotated in the coronal plan of FIG. 3, so that the spine 1 becomes straight in coronal plan of FIG. 3. On FIG. 3, lumbar vertebrae L5 to L1 and thoracic vertebra T12 have already undergone such combined translation and rotation in coronal plan and are already vertically aligned in coronal plan. Thoracic vertebra T11 has just started its combined translation and rotation in coronal plan. Thoracic vertebrae T10 to T1 are still in their original position corresponding to scoliosis of spine 1, waiting for derotation.

(22) FIG. 4 shows a frontal patient spine view, where an ending phase of translation and rotation, in a coronal plane, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(23) On FIG. 4, lumbar vertebrae L5 to L1 and thoracic vertebra T12 have already undergone such combined translation and rotation in coronal plan and are already vertically aligned in coronal plan. Thoracic vertebra T11 is about ending its combined translation and rotation in coronal plan. Thoracic vertebrae T10 to T1 are still in their original position corresponding to scoliosis of spine 1, waiting for derotation.

(24) FIG. 5 shows a frontal patient spine view, where a starting phase of translation and rotation, in an axial plane, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(25) One by one, each vertebra 2 will be simultaneously translated and rotated in the axial plan of FIG. 5, so that the spine 2 becomes straight in axial plan of FIG. 5. On FIG. 5, lumbar vertebrae L5 to L1 and thoracic vertebra T12 to T9 have already undergone such combined translation and rotation in axial plan and are already vertically aligned in axial plan. Thoracic vertebra T8 has just started its combined translation and rotation in axial plan. Thoracic vertebrae T7 to T1 are still in their original position corresponding to scoliosis of spine 1, waiting for derotation.

(26) FIG. 6 shows a frontal patient spine view, where an ending phase of translation and rotation, in an axial plane, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention.

(27) On FIG. 6, lumbar vertebrae L5 to L1 and thoracic vertebra T12 to T9 have already undergone such combined translation and rotation in axial plan and are already vertically aligned in axial plan. Thoracic vertebra T8 is ending its combined translation and rotation in axial plan. Thoracic vertebrae T7 to T1 are still in their original position corresponding to scoliosis of spine 1, waiting for derotation.

(28) FIGS. 3-6 have shown both derotations in coronal plan and in axial plan. In fact, both derotations may be performed the following way: combined translation in coronal plan and rotations respectively in coronal and axial plans are performed either successively or simultaneously with the imaged vertebrae 2 on display device during preoperative planning so that, at the end, spine 1 becomes aligned in coronal and axial plans, in a similar way as will be made with the real vertebrae later during operative treatment.

(29) FIG. 7 shows a lateral patient spine view, with a high value of thoracic kyphosis, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention. Spine curvature should be changed so as to provide for a closer to zero (or better a close to zero) value of sagittal vertical axis.

(30) Spine 1 is articulated on sacral plate S1 of pelvis 3 and comprises vertebrae 2 among which thoracic vertebrae T1 to T12 and lumbar vertebrae L1 to L5. The lumbar lordosis is the curvature of curve C2 of spine 1 on a subset of lumbar vertebrae L1 to L5. It can be determined as the angle between two directions D1 and D2 which correspond respectively to sacral plate S1 of pelvis orientation and to upper plate of lumbar vertebra L1 orientation. Its value on FIG. 7 is 71.4 degrees.

(31) To change the value of lumbar lordosis, an intermediate marker 8 can be moved on the display device by the operator so as to change the curvature of curve C2 between two end markers 7 and 9 which remain fixedly respectively located on first lumbar vertebra L1 and on sacral plate S1 of pelvis 3. By moving the intermediate marker 8, the curve C2 is also displaced, since intermediate marker 8 stays on this curve C2.

(32) The intermediate marker 8 can be moved up and down along spine 1 axis in order to change curvature distribution as well as perpendicularly to spine 1 axis in order to change curvature direction and curvature amplitude. The bounds of this intermediate marker 8 displacement are along spine 1 axis the extreme lumbar vertebrae L1 and L5, and perpendicularly to spine 1 axis the maximum amplitude corresponding to maximal curvature that the lumbar vertebrae L1 to L5 may bear without damage.

(33) The thoracic kyphosis is the curvature of curve C1 of spine 1 on a subset of thoracic vertebrae T1 to T12. It can be determined as the angle between two directions D3 and D4 which correspond respectively to lower plate of thoracic vertebra T12 orientation and to upper plate of thoracic vertebra T1 orientation. Its value on FIG. 7 is 50.7 degrees.

(34) To change the value of thoracic kyphosis, an intermediate marker 5 can be moved on the display device by the operator so as to change the curvature of curve C1 between two end markers 4 and 6 which remain fixedly respectively located on first thoracic vertebra T1 and on last thoracic vertebra T12 or preferably more precisely just in between last thoracic vertebra T12 and first lumbar vertebra L1. By moving the intermediate marker 5, the curve C1 is also displaced, since intermediate marker 5 stays on this curve C1.

(35) The intermediate marker 5 can be moved up and down along spine 1 axis in order to change curvature distribution as well as perpendicularly to spine 1 axis in order to change curvature direction and curvature amplitude. The bounds of this intermediate marker 5 displacement are along spine 1 axis the extreme thoracic vertebrae T1 and T12, and perpendicularly to spine 1 axis the maximum amplitude corresponding to maximal curvature that the thoracic vertebrae T1 to T12 may bear without damage.

(36) The sagittal vertical axis value E1 is −115.4 mm. This value should be brought close to zero, if possible and while respecting the scheduled values of lumbar lordosis and thoracic kyphosis for this specific patient, so that spine 1 becomes more balanced and may correspond to saner thoracic kyphosis and lumbar lordosis. On FIG. 7, the value of thoracic kyphosis, which is too high, should therefore be reduced.

(37) FIG. 8 shows a lateral patient spine view, with a high value of lumbar lordosis, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention. Spine curvature should be changed so as to provide for a closer to zero (or better a close to zero) value of sagittal vertical axis.

(38) The value of lumbar lordosis is on FIG. 8 is 91.1 degrees. To change the value of lumbar lordosis, an intermediate marker 8 can be moved on the display device by the operator so as to change the curvature of curve C2 between two end markers 7 and 9 which remain fixedly respectively located on first lumbar vertebra L1 and on sacral plate S1 of pelvis 3. By moving the intermediate marker 8, the curve C2 is also displaced, since intermediate marker 8 stays on this curve C2.

(39) The value of thoracic kyphosis is on FIG. 8 is 41.0 degrees. To change the value of thoracic kyphosis, an intermediate marker 5 can be moved on the display device by the operator so as to change the curvature of curve C1 between two end markers 4 and 6 which remain fixedly respectively located on first thoracic vertebra T1 and on last thoracic vertebra T12 or preferably more precisely just in between last thoracic vertebra T12 and first lumbar vertebra L1. By moving the intermediate marker 5, the curve C1 is also displaced, since intermediate marker 5 stays on this curve C1.

(40) The sagittal vertical axis value E1 is 4.2 mm. This value should be brought close to zero, if possible and while respecting the scheduled values of lumbar lordosis and thoracic kyphosis for this specific patient, so that spine 1 becomes more balanced and may correspond to saner thoracic kyphosis and lumbar lordosis. On FIG. 8, the value of lumbar lordosis, which is too high, should therefore be reduced.

(41) FIG. 9 shows a lateral patient spine view, with a close to zero value of sagittal vertical axis, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention. Spine curvature is adapted because the value of sagittal vertical axis is already close to zero.

(42) The value of lumbar lordosis is on FIG. 9 is 86.0 degrees. To change the value of lumbar lordosis, an intermediate marker 8 can be moved on the display device by the operator so as to change the curvature of curve C2 between two end markers 7 and 9.

(43) The value of thoracic kyphosis is on FIG. 9 is 34.5 degrees. To change the value of thoracic kyphosis, an intermediate marker 5 can be moved on the display device by the operator so as to change the curvature of curve C1 between two end markers 4 and 6.

(44) The sagittal vertical axis value E1 is −1.5 mm. This value is indeed very close to zero. On FIG. 9, corresponding spine 1 is well balanced and corresponds to sane thoracic kyphosis and lumbar lordosis.

(45) FIG. 10 shows a lateral patient spine view, with a lumbar lordosis concentrated in the middle region of lumbar vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention. Spine curvature should be changed so as to provide for a closer to zero (or better a close to zero) value of sagittal vertical axis.

(46) The value of lumbar lordosis is on FIG. 10 is 76.4 degrees. The lumbar lordosis is concentrated in the middle region of lumbar vertebrae 2; therefore intermediate marker 8 is halfway between end markers 7 and 9. To change the value of lumbar lordosis, intermediate marker 8 can be moved on the display device by the operator so as to change the curvature of curve C2 between two end markers 7 and 9.

(47) The value of thoracic kyphosis is on FIG. 10 is 34.5 degrees. The thoracic kyphosis is concentrated in the middle region of thoracic vertebrae 2; therefore intermediate marker 5 is halfway between end markers 4 and 6. To change the value of thoracic kyphosis, intermediate marker 5 can be moved on the display device by the operator so as to change the curvature of curve C1 between two end markers 4 and 6.

(48) The sagittal vertical axis value E1 is −53.1 mm. This value should be brought close to zero, if possible and while respecting the scheduled values of lumbar lordosis and thoracic kyphosis for this specific patient, so that spine 1 becomes more balanced.

(49) FIG. 11 shows a lateral patient spine view, with a lumbar lordosis concentrated in the lower region of lumbar vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention. Spine curvature should be changed so as to provide for a closer to zero (or better a close to zero) value of sagittal vertical axis.

(50) The value of lumbar lordosis is on FIG. 11 is 68.0 degrees. The lumbar lordosis is concentrated in the lower region of lumbar vertebrae 2; therefore intermediate marker 8 is closer to end marker 9 than to end marker 7. The lumbar lordosis should not be so concentrated in the lower region of lumbar vertebrae 2 and should be better distributed. To change the value of lumbar lordosis, intermediate marker 8 can be moved on the display device by the operator so as to change the curvature of curve C2 between two end markers 7 and 9.

(51) The value of thoracic kyphosis is on FIG. 11 is 34.5 degrees. The thoracic kyphosis is concentrated in the middle region of thoracic vertebrae 2; therefore intermediate marker 5 is halfway between end markers 4 and 6. To change the value of thoracic kyphosis, intermediate marker 5 can be moved on the display device by the operator so as to change the curvature of curve C1 between two end markers 4 and 6.

(52) The sagittal vertical axis value E1 is −91.8 mm. This value should be brought close to zero, if possible and while respecting the scheduled values of lumbar lordosis and thoracic kyphosis for this specific patient, so that spine 1 becomes more balanced.

(53) FIG. 12 shows a lateral patient spine view, with a lumbar lordosis concentrated in the upper region of lumbar vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention. Spine curvature should be changed so as to provide for a closer to zero (or better a close to zero) value of sagittal vertical axis.

(54) The value of lumbar lordosis is on FIG. 12 is 74.4 degrees. The lumbar lordosis is concentrated in the upper region of lumbar vertebrae 2; therefore intermediate marker 8 is closer to end marker 7 than to end marker 9. The lumbar lordosis should not be so concentrated in the upper region of lumbar vertebrae 2 and should be better distributed. To change the value of lumbar lordosis, intermediate marker 8 can be moved on the display device by the operator so as to change the curvature of curve C2 between two end markers 7 and 9.

(55) The value of thoracic kyphosis is on FIG. 12 is 34.5 degrees. The thoracic kyphosis is concentrated in the middle region of thoracic vertebrae 2; therefore intermediate marker 5 is halfway between end markers 4 and 6. To change the value of thoracic kyphosis, intermediate marker 5 can be moved on the display device by the operator so as to change the curvature of curve C1 between two end markers 4 and 6.

(56) The sagittal vertical axis value E1 is −61.7 mm. This value should be brought close to zero, if possible and while respecting the scheduled values of lumbar lordosis and thoracic kyphosis for this specific patient, so that spine 1 becomes more balanced.

(57) FIG. 13 shows a lateral patient spine view, with a thoracic kyphosis concentrated in the middle region of thoracic vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention. Spine curvature should be changed so as to provide for a closer to zero (or better a close to zero) value of sagittal vertical axis.

(58) The value of lumbar lordosis is on FIG. 13 is 72.1 degrees. The lumbar lordosis is concentrated in the lower region of lumbar vertebrae 2; therefore intermediate marker 8 is closer to end marker 9 than to end marker 7. To change the value of lumbar lordosis, intermediate marker 8 can be moved on the display device by the operator so as to change the curvature of curve C2 between two end markers 7 and 9.

(59) The value of thoracic kyphosis is on FIG. 13 is 34.5 degrees. The thoracic kyphosis is concentrated in the middle region of thoracic vertebrae 2; therefore intermediate marker 5 is halfway between end markers 4 and 6. To change the value of thoracic kyphosis, intermediate marker 5 can be moved on the display device by the operator so as to change the curvature of curve C1 between two end markers 4 and 6.

(60) The sagittal vertical axis value E1 is −73.5 mm. This value should be brought close to zero, if possible and while respecting the scheduled values of lumbar lordosis and thoracic kyphosis for this specific patient, so that spine 1 becomes more balanced.

(61) FIG. 14 shows a lateral patient spine view, with a thoracic kyphosis concentrated in the lower region of thoracic vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention. Spine curvature should be changed so as to provide for a closer to zero (or better a close to zero) value of sagittal vertical axis.

(62) The value of lumbar lordosis is on FIG. 14 is 72.1 degrees. The lumbar lordosis is concentrated in the lower region of lumbar vertebrae 2; therefore intermediate marker 8 is closer to end marker 9 than to end marker 7. To change the value of lumbar lordosis, intermediate marker 8 can be moved on the display device by the operator so as to change the curvature of curve C2 between two end markers 7 and 9.

(63) The value of thoracic kyphosis is on FIG. 14 is 26.5 degrees. The thoracic kyphosis is concentrated in the lower region of thoracic vertebrae 2; therefore intermediate marker 5 is closer to end marker 6 than to end marker 4. The thoracic kyphosis should not be so concentrated in the lower region of thoracic vertebrae 2 and should be better distributed. To change the value of thoracic kyphosis, intermediate marker 5 can be moved on the display device by the operator so as to change the curvature of curve C1 between two end markers 4 and 6.

(64) The sagittal vertical axis value E1 is −72.9 mm. This value should be brought close to zero, if possible and while respecting the scheduled values of lumbar lordosis and thoracic kyphosis for this specific patient, so that spine 1 becomes more balanced.

(65) FIG. 15 shows a lateral patient spine view, with a thoracic kyphosis concentrated in the upper region of thoracic vertebrae, allowing performance of a step of the method of preoperative planning according to an embodiment of the invention. Spine curvature should be changed so as to provide for a closer to zero (or better a close to zero) value of sagittal vertical axis.

(66) The value of lumbar lordosis is on FIG. 15 is 72.1 degrees. The lumbar lordosis is concentrated in the lower region of lumbar vertebrae 2; therefore intermediate marker 8 is closer to end marker 9 than to end marker 7. To change the value of lumbar lordosis, intermediate marker 8 can be moved on the display device by the operator so as to change the curvature of curve C2 between two end markers 7 and 9.

(67) The value of thoracic kyphosis is on FIG. 15 is 61.5 degrees. The thoracic kyphosis is concentrated in the upper region of thoracic vertebrae 2; therefore intermediate marker 5 is closer to end marker 4 than to end marker 6. The thoracic kyphosis should not be so concentrated in the upper region of thoracic vertebrae 2 and should be better distributed. To change the value of thoracic kyphosis, intermediate marker 5 can be moved on the display device by the operator so as to change the curvature of curve C1 between two end markers 4 and 6.

(68) The sagittal vertical axis value E1 is −68.7 mm. This value should be brought close to zero, if possible and while respecting the scheduled values of lumbar lordosis and thoracic kyphosis for this specific patient, so that spine 1 becomes more balanced.

(69) The invention has been described with reference to preferred embodiments. However, many variations are possible within the scope of the invention.