SHAPER FOR VERTEBRAL FIXATION RODS

Abstract

A system for rod bending for use in robotic spinal surgery, enabling the correct bending of a fusion rod to match the shape required to accurately pass through the heads of the pedicle screws. The system uses data generated by information provided to the robot by the surgeon's preoperative plan, optionally augmented by feedback from the robot control system of deviations encountered intraoperatively. Such deviations could occur, for example, when the surgeon decides intraoperatively on a different trajectory or even to skip screws on one vertebra, in which case, the robot will be commanded to perform the alternative procedure, with commensurate instructions relayed to the control system of the rod-bending machine. The system is also able to thin down the rod at predetermined locations along its length, adapted to be at selected intervertebral locations, for maintaining limited flexibility between vertebrae, instead of fixating them.

Claims

1. A method for shaping an intervertebral connection rod for use in a computer assisted spinal stabilization procedure, comprising: providing a surgical plan based on preoperative images of a patient's spine, said plan defining the position and orientation of pedicle screws whose insertion into the patient's vertebrae is to performed with the assistance of either a robotic system or a navigation system; generating from said robotic or navigation system, positional data incorporating the co-ordinates of the points at which said rod sits correctly in each desired pedicle screw head; inputting said positional data to the control system of a rod shaping system, said system adapted to use said positional data to bend a rod inserted therein, such that it adopts a shape that will sit correctly in said desired pedicle screw heads; and actuating said system to generate a correctly shaped rod for use in said spinal stabilization procedure.

2. A method according to claim 1, wherein said robotic system is adapted to insert said pedicle screws, said method further comprising the step of adjusting said positional data according to any deviation from said preoperative surgical plan of the final position of said pedicle screw insertion, as determined by said robot system.

3. A method according to claim 1, wherein said navigation system is used to define the position of said pedicle screw heads by means of a touch probe.

4. A method according to claim 1, wherein said navigation system is used to define the position of said pedicle screw heads by means of reference markers either on said pedicle screw heads, or on a surgical tool adapted to drill a vertebral hole.

5. A method according to claim 1, wherein said rod-shaping system comprises a plurality of plunger pistons disposed laterally to a cavity in which said rod is clamped, and wherein said positional data is used to move said plunger pistons such that they bend said rod to a shape in accordance with said positional data.

6. A method according to claim 5, wherein said rod can be rotated, such that said plurality of plunger pistons can shape said rod in three dimensions.

7. A method according to claim 5, wherein said plurality of pistons are arranged in more than one plane such that said rod can be shaped in three dimensions without being rotated in said cavity.

8. A method according to claim 1, wherein said rod shaping system further comprises a rod thinning module, adapted to reduce the cross-sectional area of said rod at predetermined locations, such that the rod has increased flexibility at said predetermined locations.

9. A method according to claim 8, wherein the rod thinning module is able to adapt the cross sectional dimension of the rod in different planes according to clinical need.

10. A method according to claim 8, wherein said rod thinning module reduces the cross sectional dimension of said rod by means of indentations generated in the rod at said predetermined locations.

11. A method according to claim 10, wherein said indentations are generated by appropriately shaped plunger pistons.

12. A method according to claim 8, wherein said rod thinning module reduces the diameter of said rod by means of mechanical removal of material from said rod at said predetermined locations.

13. A method according to claim 12, where said mechanical removal of material is performed by a controlled milling action.

14. A method for generating an intervertebral connection rod for use in a dynamic spinal stabilization procedure in a subject, comprising: providing a surgical plan of a patient's spine, said plan defining the desired shape of said intervertebral connection rod in three dimensions, and defining vertebrae between which dynamic mutual motion is to be maintained; using a rod shaping system to generate said intervertebral connection rod having said desired shape defined by said surgical plan; and using said rod-shaping system to reduce the cross-sectional area of said rod at rod locations corresponding to regions falling between said vertebrae when said rod is attached to said subject, such that said rod has increased flexibility at said regions.

15. A method according to claim 14, wherein said surgical plan is based on preoperative images of said subject.

16. A system for generating an intervertebral connection rod for use in a dynamic spinal stabilization procedure in a subject, said system comprising: clamps for holding said rod in said system; a bending mechanism for applying predetermined bends to said rod at preselected longitudinal and azimuthal positions such that said rod is shaped in accordance with a surgical plan; and at least one rod thinning element disposed such that the cross section of said rod can be reduced at predetermined locations along the length of said rod.

17. A system according to claim 16, wherein said bending mechanism comprises a set of adjustable rod-bending elements, disposed in positions that enable said elements to apply predetermined bends to said rod at preselected longitudinal and azimuthal positions such that said rod is shaped in accordance with a surgical plan.

18. A system according to claim 16, wherein said bending mechanism comprises a rotatable chuck for gripping said rod, and a controlled bending mandrel adapted to apply a lateral force on said rod at a point distanced from said chuck.

19. A system according to any claim 16, wherein said surgical plan is based on preoperative images of said subject.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:

[0033] FIG. 1 illustrates a typical vertebral fixation rod implementation, in which the rod had been given a curvature to match the lordosis curvature of the spine;

[0034] FIG. 2A illustrates schematically a plan view of a rod shaping apparatus, using mechanical plungers or pistons for bending the rod, and FIG. 2B shows a prior art press bending rod shaping apparatus;

[0035] FIG. 3 illustrates how the robot control provides inputs to the plunger control of the rod shaping apparatus of FIG. 2A, so that the rod is shaped to the desired form; and

[0036] FIG. 4 illustrates a thinning operation being performed using the apparatus shown in FIG. 2A with a pair of oppositely disposed piston plungers.

DETAILED DESCRIPTION

[0037] Reference is now made to FIG. 2A, which illustrates schematically a plan view of a rod shaping apparatus 20, using mechanical plungers or pistons 21 for shaping the rod. The rod 23 is firmly held in end clamps 22, which may be rotatable to enable three-dimensional bent shapes to be executed. The plungers or pistons 21 may be driven by hydraulic or pneumatic cylinders, or by electric motors (none of which are shown in FIG. 2A), or by any other motion impartation device that can provide sufficient force to bend the rod as required. In the exemplary apparatus shown in FIG. 2A, the rod-bending process in the plane shown is performed by sets of plungers or pistons, arranged opposite to each other, such that good control is achieved of the bending process, and the bending can be achieved in either direction of concavity. However, it is to be understood that a bend in any direction can also be achieved by having the plunger or piston oriented only at the intended concave side of the bend to be produced, and by applying force to the rod from that direction only.

[0038] In order to achieve a three-dimensionally shaped rod, as will be required when the patient has any significant extent of scoliotic deformation to add to the natural lordosis curvature, the end clamps 22 may be constructed to be rotatable, and the bends applied in the appropriate plane by the plungers or pistons as the rod is rotated to each appropriate azimuthal angle. Alternatively, a static rod clamp may be used, in which case sets of plungers or pistons are disposed at different azimuthal angles about the axis of the rod, such that the three dimensional shape can be generated with the rod clamped statically.

[0039] Reference is now made to FIG. 2B, which illustrates schematically a plan view of another typical rod shaping apparatus, which may also be used in the implementation of the methods and systems of the present disclosure. Such a bending machine configurations have been known for a long time, and one such example is shown in the above referenced US patent Application Publication No. 2005/0262911. In FIG. 2B, the rod 23 is held in a rotatable clamping chuck 24, mounted on a sliding block base 26, which can move the rod longitudinally along the linear machine base 25. The bending process takes place by applying pressure, such as by means of a hydraulic cylinder 27, to a push die 28, which forces the tube 23 to bend around the forming die 29, which has a radiused contact face to form a smooth curve. The position in the rod of the bend or bends is controlled by the longitudinal position of the sliding base block. Rotation of the rod in the rotatable chuck 24 enables a rod to be formed with three-dimensional curves.

[0040] Reference is now made to FIG. 3 which illustrates how the robot control provides inputs to the plunger control 33 of the rod shaping apparatus, so that the rod is shaped to the desired form. The surgical procedure of defining the position and orientation of the pedicle screws and their associated connection rods is generally performed by the surgeon in a surgical plan 30 generally obtained on the basis of preoperative three dimensional image sets, such as CT or MRI images of the region of interest. The surgical plan is used to define the robot pose to be adopted for the drilling of each pedicle screw hole. In some cases, the control system also supervises the drilling operation to form the hole and to screw in the pedicle screws to the required maximum torque to ensure firm insertion. The required information is extracted from the surgical plan 30 and is input to the robot control system 31, to instruct the robot 32 to perform the desired motions to align the surgical tool as required for the process to be performed on the subject's vertebrae 39, such as the drilling of holes for pedicle screws. In addition to providing instructions to activate the robotic motion, the robot controller 31, or an additional control module for extracting co-ordinate information from the surgical plan, inputs location information to the rod shaping apparatus control module 33. An information bus 37 conveys this information, advantageously in the form of a set of motions which each of the shaping pistons or plungers 34 must perform, to servo-controlled actuators 35 to move the plungers or pistons in order to bend the rod (not shown) clamped in the rod shaping apparatus 33 to the desired shape. In addition, in those implementations where the rod is also rotated to provide three-dimensional shaping, commands are also conveyed through the control bus 37 to the rod rotation servo motor or motors 36. By this means, the rod shaping system is able to automatically produce a fixation rod, correctly bent to the shape required for use according to the initial surgical plan 30, without the need for the surgeon to perform any manual operations on the rod during the surgery, in order to adapt it to match the exact positions of the pedicle screw heads.

[0041] FIG. 3 shows the implementation of the methods of the present disclosure on a rod-shaping machine having plunger bending action, such as that of FIG. 2A, but it is to be understood that these methods can also be applied to any other sort of controllable bending machine, such as that shown in FIG. 2B, with the appropriate commands output from the shaping controller 33 being directed at the longitudinal motion drive, the bending die position actuator, and the rotational position of the clamping chuck.

[0042] Furthermore, in installations where the robot also performs controlled insertion of the pedicle screws, a feedback signal from the robot defining the exact position into which each pedicle screw was inserted, can be used to input further information to the shaper controller, for providing any corrections needed to the bending profile, for instance, in the event that the physiological conditions of the bone were such that the pedicle screws were not inserted to the insertion level requested by the surgical plan, or in the event that the surgeon makes changes intraoperatively to the plan, as mentioned hereinabove. In addition, there is shown in FIG. 3 an additional and alternative input 38 to the shaper controller from a navigation or a tracking system (not shown).

[0043] The above description is applicable to situations where fusion is to be applied to all of the desired section of the patient's spine. However there are many situations in which, because parts of the spinal region being treated may clinically be preferred to have a level of natural flexibility, fusion is not required between all of the adjacent vertebrae of the patient's spine. However, instead of using separate sections of fusion rods excluding those vertebrae sections where fusion may not be required, it may be simpler and more advantageous to use a single rod (generally one on each side of the spine) in order to cover the entire section of the spine to be treated. Moreover, in order to achieve dynamic spinal stabilization between some vertebrae, some rigidity of the rod may be needed between those vertebrae, and this would be missing if two separate sections of rods were to be used. In such situations, some sections of the rod structure have to remain more flexible, such as in locations where the disc is still functional, while other sections of the rod have to maintain their stiffness to assist in providing complete fusion. In order to achieve this structure, at those locations of the patient's spine where some flexibility is desired, the rods can then be provided with thinned sections between the pedicle screw locations. The thinning of the rod can be achieved either by shaving or machining off some of the material of the rod in the region where increased flexibility is desired, or by using the same plungers to generate one or more dimples in the surface of the rod to reduce its thickness, and hence to increase its compliance, at that point. This can be achieved by actuating two opposing plungers operating against each other to thin the rod down in the space between the plungers. This thinning process may be applied either to a pair of rods on either side of the spine, or on a single rod positioned on one side of the spine. The latter procedure is often used in minimally invasive cases, where the use of one rod minimizes the number of skin incisions. Also, if a given compliance between non-fused vertebra is to be maintained in dynamic stabilization, then only one rod with variable rigidity may be preferable.

[0044] Instead of plunger generated thinned segments, a miniature controlled milling cutter (not shown) can alternatively be applied to the rod at the relevant positions either to reduce the diameter of the rod, thus increase its flexibility in all orientations, or to generate an asymmetric radial dimension to increase flexibility in a predetermined radial direction, as now explained.

[0045] The flexibility is generally applied isotropically, by thinning down the rod uniformly in essentially all azimuthal angles. However, there may be pathological situations in which flexibility is to be maintained in one particular plane of the spine, while rigidity is required another plane. This can be achieved by aligning the direction of the flexibility to match what is desired by the physiological situation of the patient's spine. This can be performed by changing the Moment of Inertia (MOI) of the rod in one plane relative to its orthogonal plane, by applying the thinned out section in one azimuthal plane relative to the rod's axis, but not in the other plane. The desired plane can be selected either by use of a rod shaping system having pistons or plungers aligned at a number of azimuthal angles around the rod and by applying the plungers appropriately, or by rotating the rod so that a single or a pair of oppositely located shaping plungers at a fixed azimuthal angle are aligned in the plane where the flexibility is to be applied. Alternatively, a miniature controlled milling cutter can be applied to the rod at the relevant positions and at the relevant azimuthal angles.

[0046] Reference is now made to FIG. 4 which illustrates one example of how such a thinning operation can be performed using the apparatus shown in FIG. 2A. The exemplary implementation shown in FIG. 4 uses a pair of oppositely disposed piston plungers 41 with mushroom shaped heads which generate indentations 42 on diametrically opposite points of the rod's surface. The indentations essentially thin the rod down. Alternatively, the above mentioned miniature milling cutter could equally well be used. In the case of classic die bending operations, such as in FIG. 2B, the mechanical miniature milling cutter can be positioned at any suitable position along the longitudinal length of the machine. In all cases of thinning, care must be taken not to weaken the rod to a point at which there is danger that it will break due to material fatigue.

[0047] Although the above described system has been described with reference to the generation of correctly bent fixation rods for use in spinal fusion using pedicle screw attachment, it is to be understood that the systems are not limited to this particular application, but can be used for bending and shaping orthopedic inserts where the shaping is performed intraoperatively, and where the shape is generally predefined by means of an image-generated preoperative surgical plan.

[0048] It is appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereto which would occur to a person of skill in the art upon reading the above description and which are not in the prior art.