U.S. patent application number 11/050431 was filed with the patent office on 2005-12-01 for computer-aided three-dimensional bending of spinal rod implants, other surgical implants and other articles, systems for three-dimensional shaping, and apparatuses therefor.
Invention is credited to Ballmer, Allison, Beeman, John, Dankowicz, Harry, Dillon, Travis, Lassaletta, Antonio, Leo, Donald J., O'Connor, Ryan.
Application Number | 20050262911 11/050431 |
Document ID | / |
Family ID | 35423706 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050262911 |
Kind Code |
A1 |
Dankowicz, Harry ; et
al. |
December 1, 2005 |
Computer-aided three-dimensional bending of spinal rod implants,
other surgical implants and other articles, systems for
three-dimensional shaping, and apparatuses therefor
Abstract
An implantable rod can be bent three-dimensionally in an
automated system, which is especially useful for pre-surgical
formation of implantable spinal rods. When local and/or global
feedback processing accompanies a series of shaping steps
automatically imposed on a rod or other article being shaped into
three-dimensional form, formation time may be expedited compared to
manual creation, and shapes difficult or impractical to create
manually may be constructed simply.
Inventors: |
Dankowicz, Harry;
(Blacksburg, VA) ; Leo, Donald J.; (Blacksburg,
VA) ; Ballmer, Allison; (Chicago, IL) ;
Beeman, John; (Ashburn, VA) ; Dillon, Travis;
(Radford, VA) ; Lassaletta, Antonio; (Belmont,
MA) ; O'Connor, Ryan; (Denver, CO) |
Correspondence
Address: |
WHITHAM, CURTIS & CHRISTOFFERSON, P.C.
11491 SUNSET HILLS ROAD
SUITE 340
RESTON
VA
20190
US
|
Family ID: |
35423706 |
Appl. No.: |
11/050431 |
Filed: |
February 4, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60541953 |
Feb 6, 2004 |
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Current U.S.
Class: |
72/31.04 |
Current CPC
Class: |
B21D 7/14 20130101; B21D
11/10 20130101; A61B 17/8863 20130101 |
Class at
Publication: |
072/031.04 |
International
Class: |
B21D 007/14 |
Claims
What we claim as our invention is:
1. An automated system that bends a rod, comprising: an input
mechanism for producing a desired three-dimensional bent shape; a
translational control interface; and automated rod-bending
hardware, wherein the automated rod-bending hardware imposes a
series of local bends in the rod until the desired
three-dimensional bent shape has been formed.
2. The rod-bending system of claim 1, wherein the rod is a
medically implantable rod of less than about 1 cm diameter.
3. The rod-bending system of claim 1, wherein the input mechanism
is selected from the group consisting of (1) deforming a deformable
template rod into the desired three-dimensional bent shape followed
by photographic scanning of the deformed template rod; (2)
operating a spatial locator to map a region where the desired
three-dimensional bent shape is to be implanted; (3) computer-aided
design of a virtual rod; (4) operating a surgical imaging
apparatus; and (5) imaging pedicle screws to establish the desired
three-dimensional bent shape.
4. The rod-bending system of claim 1, including real-time automated
correction of local bends for spring-back.
5. The rod-bending system of claim 1, including a sensor operating
at a region where a local bend has just been imposed, information
from the sensor being subjected to at least one of a local feedback
operation and a global feedback operation.
6. The rod-bending system of claim 5, including information from
the sensor being subjected to both a local feedback operation and a
global feedback operation.
7. The rod-bending system of claim 5, wherein as a result of the
feedback operation(s), a current sequence of applicable automated
instructions for bending is automatically modified into a modified
sequence of automated instructions for bending.
8. The rod-bending system of claim 7, wherein feedback is used to
impose additional bending actuation at the same location to achieve
desired local bending accuracy.
9. The automated system of claim 1, wherein in imposition by the
automated rod-bending hardware of the series of local bends in the
rod, the automated rod-bending hardware provides higher
repeatability than could be provided by a human operator manually
attempting to execute a same series of local bends.
10. The automated system of claim 1, including after each
imposition of a local bend, automated global feedback wherein an
actual local bend imposed is automatically compared to the desired
shape and instructions for remaining bending steps are
automatically evaluated.
11. The automated system of claim 1, including an automated cutting
mechanism that reduces the rod to a desired length.
12. The automated system of claim 1, including, after a first set
of automated instructions for imposing a series of local bends has
been formulated but in advance of implementing the first set of
automated instructions, an automated screening of whether
sufficient clearance is physically present to justify initiating
the first set of automated instructions.
13. The automated system of claim 1, including, prior to each
imposition of a local bend according to a bend imposition
instruction, an automated screening of whether sufficient clearance
is physically present to justify ordering execution of the bend
imposition instruction.
14. The automated system of claim 1, including an automated
correction system which, when bend imposition has been proceeding
along the rod according to a first set of instructions for imposing
local bends with the first set of instructions being only partly
executed, the automated correction system (1) detects a point at
which small errors in imposed bends have accumulated to a point
where the first set of instructions cannot viably be completed as a
matter of physical clearance and (2) revises the first set of
instructions to a second set of instructions, wherein the second
set of instructions can be viably completed as a matter of physical
clearance.
15. The automated system of claim 1, wherein the rod being bent is
made of a material selected from the group consisting of: titanium;
titanium alloy; steel and shape-memory alloys.
16. The automated system of claim 1, including one of: (a) a
motorized system responsible for forward movement of the rod
including stopping according to a series of actuator commands, the
actuator commands being computer-generated; or (b) a motorized
system responsible for forward movement of the rod-bending hardware
including stopping according to a series of actuator commands, the
actuator commands being computer-generated.
17. The automated system of claim 1, including one of: (a) a
motorized system responsible for rotary movement of the rod
including stopping according to a series of actuator commands, the
actuator commands being computer-generated; or (b) a motorized
system responsible for rotary movement of the rod-bending hardware
including stopping according to a series of actuator commands, the
actuator commands being computer-generated.
18. An automated method of making an implantable rod, comprising:
non-manual imposition of a series of local bends in an implantable
rod, whereby a three-dimensional bent shape is non-manually
formed.
19. The rod-making method of claim 18, wherein following imposition
of a local bend, at least one feedback loop is operated, with the
feedback loop selected from the group consisting of local feedback
and global feedback, and with the feedback loop being
machine-implemented and human-free.
20. The rod-making method of claim 18, including at least one
automated step of translating a desired bent-shape into a series of
actuator commands for machine-based rod-bending.
21. The rod-making method of claim 20, including actuator command
implementation, resulting in machine-imposed bending of the
rod.
22. The rod-making method of claim 21, including automated
imposition of at least one three-dimensional bend approaching 180
degrees or automated imposition of a sequence of bends whose
combined effect is a three-dimensional bend approaching 180
degrees.
23. The rod-making method of claim 18, including, after automated
imposition of a local bend in the rod, operation of both automated
local feedback and automated global feedback.
24. The rod-making method of claim 18, wherein the
three-dimensional bent shape is constructed before surgical
exposure of the patient's spine.
25. The rod-making method of claim 18, including non-manually
forming a customized bent rod shape corresponding to a spine of a
particular patient having scoliosis.
26. The rod-making method of claim 18, wherein rod-bending is
entirely automated and the rod needs no manual shaping before being
implanted in the patient.
27. The rod-making method of claim 18, including: determining X-Y-Z
coordinates of a desired rod shape; integrated feedback processing
a local bend that has been imposed.
28. The rod-making method of claim 18, including operating an
automatic controller commanding operations performed on the rod,
the controller including: a feed command for feeding movement of
the rod; a rotate command for rotating movement of the rod; and a
bend command for bending movement of the rod.
29. The rod-making method of claim 18, including measuring
spring-back of the rod via an automatic sensor.
30. The rod-making method of claim 18, including collecting
spring-back measurements via an automatic sensor and automated
processing of the spring-back measurements.
31. The rod-making method of claim 18, including a step of
computer-assisted design of a desired three-dimensional bent
shape.
32. The rod-making method of claim 31, wherein the desired
three-dimensional bent shape is actually constructed.
33. The rod-making method of claim 31, including, as rod-bending
progresses, performing a series of automated comparisons of the
bent rod as actually-bent to the desired three-dimensional
shape.
34. The rod-making method of claim 18, wherein bends are imposed
non-manually along the rod in one-direction progression without
doubling-back.
35. The rod-making method of claim 18, including an automated step
in which is determined an end of the rod at which to begin imposing
bends.
36. The rod-making method of claim 18, including disposing the rod
in an automated bending system and before bending is permitted to
begin, an automated step is performed of processing a desired shape
to be constructed to confirm or deny sufficient clearance for
automated bending to successfully proceed.
37. A method of making a rod, comprising: (a) an automated series
of non-manual bending steps on a rod, wherein each bending step
imposes an actual bend on the rod; (b) after a bending step, (i)
automatic local feedback processing wherein data representing the
actual bend is processed for whether the actual bend is according
to instruction or varies from instruction; and (ii) automatic
global feedback processing wherein data representing the actual
bend is processed for formulating at least one next instruction for
a bending step downstream along the rod.
38. The method of claim 37, wherein the information from (b)(i) is
used to further impose bending actuation to reach the desired
bending angle, either in a single step or in a sequence of steps,
either by using an analytical estimate of spring-back based on
material properties or based on measurements from previous
bends.
39. The rod-making method of claim 37, wherein the rod is an
implantable rod.
40. The rod-making method of claim 39, wherein a
three-dimensionally bent rod is formed.
41. The rod-making method of claim 39, wherein the rod is of
titanium or a titanium alloy, and has a diameter of less than about
1 cm.
42. The rod-making method of claim 39, wherein the
three-dimensionally bent rod includes at least one severe bend
approaching 180 degrees.
43. An implantable-rod bending apparatus, comprising: a housing
receiving an implantable-rod to which bending force is to be
applied; and a fully-automated mechanical system that applies
bending force to the rod disposed in the housing and that positions
the rod disposed in the housing, including means for positioning,
orienting and bending the rod into a three-dimensional bent
shape.
44. The apparatus of claim 43, wherein the automated mechanical
system that applies bending force can apply bending force
approaching imposition of a 180 degree bend to the rod.
45. The apparatus of claim 43, wherein the apparatus includes a
minimal clearance that is a void volume such that the rod may be as
long as about 1 yard and may be bent while disposed in the
apparatus into a three-dimensional bent shape.
46. An automated rod-bending system, comprising: a housing
receiving an implantable-rod to which bending force is to be
applied; and a fully-automated mechanical system that applies
bending force to the rod disposed in the housing and that positions
the rod disposed in the housing, including means for positioning,
orienting and bending the rod into a three-dimensional bent shape;
a fully automated control system that delivers a series of
computer-readable instructions to the fully-automated mechanical
system that applies bending force and that positions the rod.
47. The automated rod-bending system of claim 46, including a
sensor from which is obtained digitized information quantifying
bending actually present in the rod.
48. The automated rod-bending system of claim 47, including, after
imposition of each bend, processing data from the sensor according
to at least one or both of automated local feedback and automated
global feedback.
49. The automated rod-bending system of claim 48, including, after
imposition of each bend, both automated local feedback and
automated global feedback.
50. A surgical method, comprising steps of: automated bending of a
rod into a three-dimensional bent shape implantable in a patient;
surgical implantation into the patient of the three-dimensional
bent shape.
51. The method of claim 50, wherein the three-dimensional bent
shape is implanted in a spinal region of the patient.
52. The method of claim 51, wherein the surgical implantation is
for treating scoliosis.
53. The method of claim 51, wherein the three-dimensional bent
shape is constructed and ready for implantation before surgical
exposure of the patient's spine.
54. The method of claim 50, including in advance of surgical
implantation, automated pre-screening of the three-dimensional bent
shape, including a determination of placement in the patient of the
three-dimensional bent shape with reference to cooperating hardware
placed, or to be placed, in the patient.
55. A method of making an implantable article, comprising steps of:
automated shaping of an article, in a direction of a target design
that is a three-dimensional bent shape implantable in a patient,
including a series of automated shaping steps each imposing an
actual local shape; after each automated shaping step wherein an
actual local shape is imposed, automated global feedback wherein
the actual local shape imposed is automatically compared to the
target design and instructions for remaining shaping steps are
automatically evaluated.
56. The method of claim 55, including automatic adjustment of
instructions for at least one automated shaping step still to be
performed.
57. The method of claim 55, including automated local feedback
wherein the actual local shape imposed is automatically compared to
instructions given and additional actuation is imposed to the same
local area of the article to improve the agreement between the
desired local shape and the achieved local shape.
58. The method of claim 55, wherein the implantable article is a
rod.
59. The method of claim 55, wherein the implantable article is
formed in less time via the automated shaping than could be
accomplished by being manually formed.
60. A pedicle screw cap, comprising an article having an opening
which receives a pedicle screw, the article being biocompatible and
of a medically-imageable material.
61. The pedicle screw cap of claim 60, wherein the screw cap has a
shape that accentuates its position and orientation to surgical
imaging apparatus.
62. The automated system of claim 1, wherein the input mechanism
for producing a desired three-dimensional bent shape includes at
least one of: in vivo medical imaging or in vivo biological
imaging.
63. The automated system of claim 1, wherein the hardware comprises
a bending mandrel and a bending arm.
64. The automated system of claim 63, wherein the bending arm is
disposed in a rolling sleeve.
Description
[0001] Priority is claimed based on U.S. provisional application
No. 60/541,953 filed Feb. 6, 2004, titled, "System for
Computer-aided Three-dimensional Bending of Spinal Rod
Implants."
DESCRIPTION
[0002] 1. Field of the Invention
[0003] The present invention is directed to computer-aided design
and construction of medical implants and to surgical procedures,
especially spinal surgery.
[0004] 2. Background of the Invention
[0005] Scoliosis affects about 2% of the population and is most
commonly seen in children 10 years or older. The current clinical
paradigm for designing and shaping the surgical corrective
instrumentation is poorly resolved and highly personnel intensive.
Corrective surgery typically involves the fixation of segments of
the vertical column through the attachment of curved titanium rods
to the spine through an arrangement of hooks and pedicle
screws.
[0006] The shaping of spinal rods is generally effected manually by
a surgeon during surgery with the patient's spine exposed in a
trial and error procedure and using hand tools for bending and
cutting the rods. This part of a surgery may take up to several
hours, and this process is both tiring to the surgeon and involves
increased risks to the patient.
[0007] Conventionally, a (manual) rod bender has been used for
bending a corrective spinal rod to be used in a surgical operation,
such as corrective surgery to treat scoliotic deformity of the
human vertebral column. An example of a manual rod bender used in
manual shaping of a rod for a spinal implant is a three-point
bender (called a "French bender"), in which bending pliers are
manually operated to manipulate the rod. However, these manual rod
benders have limitations for what shapes can be created, the amount
of force and time required to bend a rod, and inability to
precisely create a desired shape because of a material upon being
released from the manual bending device not holding the bend. Such
manual bending of spinal rods is a strenuous exercise.
[0008] Conventionally, there have been several rod benders (none of
which is fully automated) used in spinal surgery. A conventional
rod bender for spinal surgery is disclosed in U.S. Pat. No.
5,490,409 entitled "Adjustable Cam Action Rod Bender for Surgical
Rods." The surgeon manually imposes a series of local bends to
achieve large-scale desired curvature and torsion. In addition to
requiring significant physical effort, a successful transition from
many small bends to a desired overall curvature requires
significant experience. As local errors have long-range effects on
the overall shape of the rod, after-the-fact corrections are often
superposed on prior bends in a trial-and-error fashion thus
reducing the accuracy of the bends and stressing the material.
[0009] See, e.g., U.S. Pat. No. 6,035,691, entitled "Adjustable rod
bending device for a corrective spinal rod which is used in a
surgical operation," which discloses a device that uses a series of
adjustable rollers to achieve the desired curvature and to impose
local bends on the rod by rotary motion. This only reduces the
effort required by the surgeon in achieving the desired shape and
results in a smoother final rod contour as compared to manual rod
benders, and much work and time on the part of a surgeon still is
needed. For example, this system offers no assistance to a surgeon
in formulating a desired shape of the rod. At most, a computer may
be used to calculate the "scale" of each roller that will generate
the desired curvature. There is no automated imposition of
curvature and torsion, and consequently this system is restricted
to planar rods.
[0010] Another rod bender for surgical rods is disclosed in U.S.
Pat. No. 6,644,087 issued Nov. 11, 2003 to Ralph et al. (assigned
to Third Millennium Engineering, Summit, N.J.), for "Rod Bender for
bending surgical rods."
[0011] Another example of spinal rod bending is disclosed in U.S.
Published Patent Application No. 20040144149 published Jul. 29,
2004, "Non-marring spinal rod curving instrument and method for
using the same," by Strippgen et al. Strippgen et al. state that a
non-planar curve is induced in the surgical rod. Manual bending is
provided.
[0012] Some computer-assisted shaping of spinal implants is
described in "A pilot study on computer-assisted optimal contouring
of orthopedic fixation devices," Comput Aided Surg. 1999; 4
(6):305-13, by Langlotz F, Liebschner M, Visarious H, Bourquin Y,
Lund T, Nolte L P. Langlotz et al's study uses a manual bending
tool coupled to a computer system that prescribes required local
curvature and torsion and monitors imposed local curvature and
torsion. As an input mechanism, Langlotz et al. use photographic
scanning as well as the use of a spatial locator. Langlotz et al.
rely on manual effort to bend the rod. Langlotz et al.'s system is
not designed to handle the large bends required for thoracolumbar
rod implants. An interesting feature of Langlotz et al.'s system is
that "at all times a computer display shows the differences between
the current shape of the rod and the desired shape as determined by
MODEL-SHAPE or OPTO-SHAPE" (page 309).
[0013] While some automated three-dimensional rod benders may be
found in non-clinical settings, none are suitable for forming
thoracolumbar rod implants. For example, U.S. Pat. No. 6,260,395,
"Vertically oriented apparatus for bending tubing, and method of
using same," uses a computer for controlling the machine in one
embodiment. Although this machine is capable of creating some
three-dimensional bends, it does not address the imposition of
large three-dimensional bends and clearance for the already bent
portion of the rod that is necessary for the thoracolumbar rods.
There may also be issues with the resolution of the machine, which
refers to the typical distance between bends that the machine is
designed to accommodate. Generally tubing is subjected to bending
at a relatively few places to impose some typical angles, such as
90 degrees or 45 degrees. In such operations, the goal is not
usually to create a smooth-looking curve, but rather to create a
piecewise straight tube with long straight segments.
[0014] Another non-clinical rod bender is U.S. Pat. No. 6,434,995,
"Method of bending small diameter metal pipe and its apparatus."
This automated bending device imposes local curvature and torsion
through a sequence of feeding, rotating, and bending commands, but
does not address the imposition of large terminal three-dimensional
bends and the required clearance for the long thoracolumbar
rods.
[0015] A further example of a non-clinical rod bender is U.S. Pat.
No. 6,318,424, "Multi-purpose hydraulic press, metal bending, and
log splitting apparatus," which configures a log splitter to work
with other materials such as metal. This device uses a controllable
hydraulic ram to achieve desired accuracy in the imposed bends.
[0016] Thus, conventional spinal surgery retains time-consuming
manual components which have not been able to be reduced or
eliminated. That result, although highly desirable, has not
practically proved achievable before the present invention.
SUMMARY OF THE INVENTION
[0017] Computer-aided systems for on-the-fly design and automated
manufacture of implants are provided by the invention. Significant
treatment benefits and cost savings may be realized by using the
inventive computer-aided systems, such as systems for on-the-fly
design and automated manufacture of corrective instrumentation or
scoliosis surgery. The invention in one embodiment provides a
combination of manufacturing hardware and computer-aided design
system to impose desired structure (such as desired curvature) on
an actual article (such as a rod (such as, preferably, a surgical
implant rod), plate, etc.) for surgical use, especially immediate
surgical use. Inventive systems significantly reduce time and
physical effort required of a surgeon during surgery in designing
and shaping a spinal implant. Reducing time required for such
surgical procedures reduces exposure to infection. Also, shaped
articles (such as bent surgical rods, other bent rods, etc.) may be
produced according to inventive automated systems with increased
accuracy compared to manually shaped implants, thereby improving
the likelihood of a desirable outcome of a spinal fixation surgery.
The shaped article may be preformed prior to surgery, completely
eliminating a step during surgery of shaping an article to be
implanted, such as, e.g., completely eliminating a step during
spinal surgery of shaping a spinal rod.
[0018] The invention in one embodiment provides a way to accurately
and automatically reproduce a three-dimensional shape of a spinal
rod or other surgical implant rod for use in a surgical operation
as conceived by medical personnel (such as a surgeon) onto an
actual metallic implant. To do so, there may be used an integrated
computer-aided design and manufacturing tool that translates a
desired shape as specified by the surgeon or medical personnel into
a series of actuator commands for imposing bending, such as for
imposing local bends in arbitrary planes at discrete locations
along the rod.
[0019] In another preferred embodiment the invention provides an
automated system that bends a rod (especially, e.g., a surgical
implant rod), comprising: an input mechanism for producing a
desired three-dimensional deformed shape (such as, e.g., a
three-dimensional bent shape); a translational control interface;
and automated rod-bending hardware, wherein the automated
rod-bending hardware imposes a series of local bends in the rod
until the desired three-dimensional bent shape has been formed,
such as, e.g., automated rod-bending systems; systems including
after each imposition of a local bend, automated global feedback
wherein an actual local bend imposed is automatically compared to
the desired shape and instructions for remaining bending steps are
automatically evaluated (with examples of kinds of automatic
evaluation being local; global; local and global); systems
including, after a first set of automated instructions for imposing
a series of local bends has been formulated but in advance of
implementing the first set of automated instructions, an automated
screening of whether sufficient clearance is physically present to
justify initiating the first set of automated instructions;
automated systems wherein the input mechanism for producing a
desired three-dimensional bent shape includes at least one of: in
vivo medical imaging or in vivo biological imaging; automated
systems wherein the hardware comprises a bending mandrel and a
bending arm (such as, e.g., automated systems wherein the bending
arm is disposed in a rolling sleeve); automated systems including
(a) a motorized system responsible for forward movement of the rod
including stopping according to a series of actuator commands, the
actuator commands being computer-generated; or (b) a motorized
system responsible for forward movement of the rod-bending hardware
including stopping according to a series of actuator commands, the
actuator commands being computer-generated; automated systems
including (a) a motorized system responsible for rotary movement of
the rod including stopping according to a series of actuator
commands, the actuator commands being computer-generated; or (b) a
motorized system responsible for rotary movement of the rod-bending
hardware including stopping according to a series of actuator
commands, the actuator commands being computer-generated; etc.
[0020] In another preferred embodiment, the invention provides an
automated method of making an implantable rod, comprising:
non-manual imposition of a series of local bends in an implantable
rod, whereby a three-dimensional bent shape is non-manually formed;
such as rod-making methods wherein following imposition of a local
bend, at least one feedback loop (local or global) is operated, and
with the feedback loop being machine-implemented and human-free;
rod-making methods including at least one automated step of
translating a desired bent-shape into a series of actuator commands
for machine-based rod-bending; rod-making methods including
actuator command implementation, resulting in machine-imposed
bending of the rod; rod-making methods including automated
imposition of at least one three-dimensional bend approaching 180
degrees; rod-making methods including automated imposition of a
sequence of bends whose combined effect is a three-dimensional bend
approaching 180 degrees; rod-making methods including, after
automated imposition of a local bend in the rod, operation of both
automated local feedback and automated global feedback; rod-making
methods wherein the three-dimensional bent shape is constructed
before surgical exposure of the patient's spine; rod-making methods
including non-manually forming a customized bent rod shape
corresponding to a spine of a particular patient having scoliosis;
rod-making methods wherein rod-bending is entirely automated and
the rod needs no manual shaping before being implanted in the
patient; rod-making methods including: determining X-Y-Z
coordinates of a desired rod shape, and integrated feedback
processing a local bend that has been imposed; rod-making methods
including operation of an automatic controller commanding
operations performed on the rod, the controller including: a feed
command for feeding movement of the rod, a rotate command for
rotating movement of the rod, and a bend command for bending
movement of the rod; rod-making methods including measuring
spring-back of the rod via an automatic sensor; rod-making methods
including collecting spring-back measurements via an automatic
sensor and automated processing of the spring-back measurements;
rod-making methods including a step of computer-assisted design of
a desired three-dimensional bent shape (such as, e.g., rod-making
methods wherein the desired three-dimensional bent shape is
actually constructed); rod-making methods including, as rod-bending
progresses, performing a series of automated comparisons of the
bent rod as actually-bent to the desired three-dimensional shape;
rod-making methods wherein bends are imposed non-manually along the
rod in one-direction progression without doubling-back; rod-making
methods including an automated step in which is determined an end
of the rod at which to begin imposing bends; rod-making methods
including disposing the rod in an automated bending system and
before bending is permitted to begin, an automated step is
performed of processing a desired shape to be constructed to
confirm or deny sufficient clearance for automated bending to
successfully proceed; etc.
[0021] In a further preferred embodiment, the invention provides a
method of making a rod (such as, e.g., an implantable rod, a
three-dimensionally bent rod (such as, e.g., a three-dimensionally
bent rod including at least one severe bend approaching 180
degrees, etc.), etc.), comprising: (a) an automated series of
non-manual bending steps on a rod (such as, e.g., a rod made of
titanium or a titanium alloy, a rod made of steel, a rod made of a
shape-memory alloy, a rod having a diameter of less than about 1
cm, etc.), wherein each bending step imposes an actual bend on the
rod; (b) after a bending step, (i) automatic local feedback
processing wherein data representing the actual bend is processed
for whether the actual bend is according to instruction or varies
from instruction (which information then may be used to further
impose bending actuation to reach the desired bending angle, either
in a single step or in a sequence of steps, either by using an
analytical estimate of the spring-back based on material properties
or based on measurements from previous bends); and (ii) automatic
global feedback processing wherein data representing the actual
bend is processed for formulating at least one next instruction for
a bending step downstream along the rod.
[0022] Herein, "global feedback" and "local feedback" have been
referred to. In this invention, the meanings may be understood more
particularly as follows, referring to a specific case of a rod
(such as, e.g. a surgical implant rod) being bent. "Local feedback"
is concerned with additional bends at the same location on the rod.
"Global feedback" is concerned not with additional bends at the
same location (that being the concern of "local feedback") but only
with subsequent bends downstream along the rod.
[0023] Another preferred embodiment of the invention provides an
implantable-rod bending apparatus, comprising: a housing receiving
an implantable-rod to which bending force is to be applied; and a
fully-automated mechanical system that applies bending force to the
rod disposed in the housing and that positions the rod disposed in
the housing, including means for positioning, orienting and bending
the rod into a three-dimensional bent shape, such as, e.g.,
apparatuses wherein the automated mechanical system that applies
bending force can apply bending force approaching imposition of a
180 degree bend to the rod; apparatuses including a minimal
clearance that is a void volume such that the rod may be as long as
about 1 yard and may be bent while disposed in the apparatus into a
three-dimensional bent shape; etc.
[0024] Also, the invention includes a preferred embodiment
providing an automated rod-bending system, comprising: a housing
receiving an implantable-rod to which bending force is to be
applied; and a fully-automated mechanical system that applies
bending force to the rod disposed in the housing and that positions
the rod disposed in the housing, including means for positioning,
orienting and bending the rod into a three-dimensional bent shape;
a fully automated control system that delivers a series of
computer-readable instructions to the fully-automated mechanical
system that applies bending force and that positions the rod, such
as, e.g., automated rod-bending systems including a sensor from
which is obtained digitized information quantifying bending
actually present in the rod; automated rod-bending systems
including, after imposition of each bend, processing data from the
sensor according to at least one or both of automated local
feedback and automated global feedback; automated rod-bending
systems including, after imposition of each bend, both automated
local feedback and automated global feedback; etc.
[0025] The invention in another preferred embodiment provides a
surgical method, comprising steps of: automated bending of a rod
into a three-dimensional bent shape implantable in a patient; and
surgical implantation into the patient of the three-dimensional
bent shape, such as, e.g., methods wherein the three-dimensional
bent shape is implanted in a spinal region of the patient; methods
wherein the surgical implantation is for treating scoliosis;
methods wherein the three-dimensional bent shape is constructed and
ready for implantation before surgical exposure of the patient's
spine; methods including (in advance of surgical implantation)
automated pre-screening of the three-dimensional bent shape,
including a determination of placement in the patient of the
three-dimensional bent shape with reference to cooperating hardware
placed, or to be placed, in the patient; etc.
[0026] The invention also provides a method of making an
implantable article, comprising steps of: automated shaping of an
article, in a direction of a target design that is a
three-dimensional bent shape implantable in a patient, including a
series of automated shaping steps each imposing an actual local
shape; after each automated shaping step wherein an actual local
shape is imposed, automated global feedback wherein the actual
local shape imposed is automatically compared to the target design
and instructions for remaining shaping steps are automatically
evaluated, such as, e.g., methods including automatic adjustment of
instructions for at least one automated shaping step still to be
performed; methods including automated local feedback wherein the
actual local shape imposed is automatically compared to
instructions given and additional actuation is imposed to the same
local area of the article to improve the agreement between the
desired local shape and the achieved local shape; methods wherein
the implantable article is a rod; methods wherein the implantable
article is formed in less time via the automated shaping than could
be accomplished by being manually formed; etc.
[0027] In another preferred embodiment, the invention provides a
pedicle screw cap, comprising an article having an opening which
receives a pedicle screw, the article being biocompatible and of a
medically-imageable material, such as, e.g., a pedicle screw cap
having a shape that accentuates its position and orientation to
surgical imaging apparatus; etc.
BRIEF SUMMARY OF THE DRAWINGS
[0028] FIGS. 1A and 1B are schematic representations of an example
that may be used in the invention of severe distal bends that may
be used to anchor some thoracolumbar spinal implants in the sacrum.
FIG. 1A is a front view; FIG. 1B is rotated 90 degrees (1/4) and is
a side view corresponding to FIG. 1A.
[0029] FIG. 2 illustrates rod-bending hardware according to an
embodiment of the invention, and which may be used to make, for
example, bent surgical implant rods.
[0030] FIGS. 3, 4 show details from FIG. 2, showing bending mandrel
and sensor.
[0031] FIGS. 5, 6 are respective schematic diagrams showing
components in inventive system embodiments.
[0032] FIG. 7 is a photograph of rod-bending hardware according to
an embodiment of the invention and which may be used to bend, for
example, surgical implant rods. Photographic FIG. 7 may be viewed
in connection with diagrammatic FIG. 6. In FIG. 6, a rod R (such as
a surgical implant rod) undergoes feeding in a linear direction.
The rod R is in a housing. Bending is performed on the rod R.
Sensors sample the rod R. All of the rod-feeding, sensors,
rod-bending is powered, not manual.
[0033] FIG. 8 is a photograph of a bending actuator according to an
embodiment of the invention.
[0034] FIG. 9 is an isometric view of an inventive pedicle screw
cap 9 which screws onto a pedicle screw prior to imaging in an
embodiment of the invention. FIG. 9A is a right view corresponding
to FIG. 9; FIG. 9B is a front view corresponding to FIG. 9; FIG. 9C
is a top view corresponding to FIG. 9. In FIGS. 9A, 9B, 9C, slopes
are marked showing a particular example and the invention is not
limited to a pedicle screw cap having the dimensions shown on FIGS.
9A-C.
[0035] FIGS. 10, 10A, 10B, 10C, 10D, 10E show a rod-bending
sequence according to an embodiment of the invention, which may be
used, for example, for bending surgical implant rods. A rod-bending
mechanism 10 acts on a rod R to bend the rod.
[0036] FIGS. 11, 11A, 11B, 11C, 11D are control flow diagrams
according to an embodiment of the invention. FIG. 11 shows
exemplary main control. FIG. 11A shows rotary direction control.
FIG. 11B shows feeding and rotation control. FIG. 11C shows a
subsystem. FIG. 11D shows bending control. FIGS. 11-11D may be
used, for example, for bending surgical implant rods.
DETAILED DESCRIPTION OF a PREFERRED EMBODIMENT OF THE INVENTION
[0037] There is provided an inventive automated system for
constructing a three-dimensional bent article (such as a rod, a
plate, etc., most preferably a rod (such as, e.g., a rod
implantable in a patient)). A surgical implant rod is a most
preferred example. In the invention, manual shaping (such as manual
bending, etc.) of the article is minimized, preferably completely
eliminated. Such automation is particularly advantageous when
manual shaping of an article to be implanted in a patient can be
minimized or avoided, especially when the manual shaping otherwise
would be done by a surgeon, and most particularly when the manual
shaping would be that of a spinal rod and otherwise would need to
occur while the patient's spine already has been surgically
exposed.
[0038] Shaping herein refers to force application that changes the
shape of an article, such as, e.g., bending, twisting, etc., with
bending being a preferred example, such as bending a surgical
implant rod. A most preferred example of shaping an article
according to the invention is rod-bending, especially bending an
implantable rod (such as, e.g., a titanium rod; a titanium alloy
rod; etc.). Examples of inventive rod-bending systems are, e.g.,
systems wherein in imposition by the automated rod-bending hardware
of the series of local bends in the rod (such as, e.g., a surgical
implant rod), the automated rod-bending hardware provides higher
repeatability than could be provided by a human operator manually
attempting to execute a same series of local bends; systems
including an automated cutting mechanism that reduces the rod to a
desired length; systems in which prior to each imposition of a
local bend according to a bend imposition instruction, an automated
screening is performed of whether sufficient clearance is
physically present to justify ordering execution of the bend
imposition instruction; systems including an automated correction
system which, when bend imposition has been proceeding along the
rod (such as, e.g., a surgical implant rod) according to a first
set of instructions for imposing local bends with the first set of
instructions being only partly executed, the automated correction
system (1) detects a point at which small errors in imposed bends
have accumulated to a point where the first set of instructions
cannot viably be completed as a matter of physical clearance and
(2) revises the first set of instructions to a second set of
instructions, wherein the second set of instructions can be viably
completed as a matter of physical clearance; systems including
real-time automated correction of local bends for spring-back;
systems including a sensor operating at a region where a local bend
has just been imposed, information from the sensor being subjected
to at least one of a local feedback operation and a global feedback
operation (such as, e.g., systems including information from the
sensor being subjected to both a local feedback operation and a
global feedback operation; systems wherein as a result of the
feedback operation(s), a current sequence of applicable automated
instructions for bending is automatically modified into a modified
sequence of automated instructions for bending; systems wherein the
rod (such as, e.g., a surgical implant rod) being bent is made of a
material selected from the group consisting of: titanium; titanium
alloy; steel and shape-memory alloys; etc.
[0039] A preferred example of a rod to use in the invention is,
e.g., a surgical implant rod A preferred example of an implantable
rod is an implantable spinal rod of a titanium or titanium alloy
material, which are mentioned as examples, and the invention is not
limited to such materials. A rod that is a starting material for an
implantable spinal rod may have varying lengths, such as a length
of about 6 inches to about 1 yard, which lengths are given as
examples and not by way of limitation. An example of a diameter of
an implantable spinal rod is about 8 mm, i.e., less than about 1
cm. However, the invention is not limited to dimensions that have
been mentioned, and the dimensions for a starting material of an
implantable rod may vary according to the patient. In designing an
inventive rod-making machine, it is especially preferred to form
openings specifically dimensioned for actual rods, and to have very
small gaps between the rod and opening in the receptacle, to
increase the accuracy of the bending operation.
[0040] A preferred example of a rod-bending device includes rod
bending devices that impose subsequent and non-coplanar-large-angle
bends (half a turn) at the terminal end of long rods (i.e., up to
one meter) used to anchor thoracolumbar rods in the sacrum.
[0041] FIGS. 1A and 1B show an example of a rod (such as, e.g., a
surgical implant rod) with severe distal bends that may be used to
anchor some thoracolumbar spinal implants in the sacrum. Such bends
as in FIGS. 1A and 1B may be imposed at the ends of rods (such as,
e.g., a surgical implant rod), with the rods then being implanted
to go about half the length of the spine. Implanted spinal rods are
anchored into the pelvis (such as by screwing the rods to the
pelvis).
[0042] It will be appreciated that the bends 100 in FIGS. 1A, 1B
are severe bends in a titanium or titanium-alloy rod, i.e., are
almost 180 degree bends. For a rod, it would not be physically
possible to have an actual 180 degree bend. The net bend is
achieved over a finite radius, possibly as a result of several
smaller bends, but with the result that a half turn bend is imposed
over a segment of the rod and possibly with several half-turn bends
imposed in succession in the end part of the rod as would be
necessary in the case of the rods anchored to the sacrum (see FIGS.
1A-1B).
[0043] By automated shaping of articles according to the invention,
a variety of products (especially, most preferably, products
including three-dimensional bent features) may be constructed.
Examples of products constructed according to the invention
include, e.g., three-dimensionally bent rods (such as, e.g.,
surgical implant rods), medical implants (such as, e.g.,
three-dimensionally bent spinal rods, disks, cages, etc.), dental
implants, etc. Three-dimensionally bent spinal rods for medical
implantation are a preferred example.
[0044] In the invention, at least one input system is used.
Examples of an input system for use in the invention are, e.g.,
input systems comprising manually deforming an easily-deformable
template rod (i.e., a "practice" rod of a more deformable material
compared to the material of the actual rod to be shaped) into a
desired three-dimensional bent shape followed by photographic
scanning of that manually-deformed template rod to generate a
virtual representation (which virtual representation can reside
within interface software); input systems comprising operating a
spatial locator to map a region where the desired three-dimensional
bent shape is to be implanted; input systems comprising
computer-aided design of a virtual rod; input systems comprising
operating a surgical imaging apparatus; input systems comprising
imaging pedicle screws to establish the desired three-dimensional
bent shape (such as, e.g., optionally using a surgical fluoroscope
during surgery to determine the position and orientation of the
pedicle screw heads using inventive cooperating pedicle screw caps,
with pedicle screw caps being provided by the present invention);
an input mechanism as in Langlotz et al., supra; input systems
comprising a virtual environment in which the three-dimensional
shape of the rod is designed (especially in which the shape is
designed prior to and/or during surgery); input systems comprising
spatial locators that may be used to generate a sequence of control
points that define the three-dimensional shape of the article to be
constructed; input mechanisms as in U.S. Pat. No. 6,578,280; input
mechanisms as in U.S. Pat. No. 6,500,131 (titled "Contour mapping
system applicable as a spine analyzer, and probe useful therein,"
disclosing various embodiments of spatial locators used in
conjunction with computer software to locate the spinal vertebra
through external palpation and to subsequently quantify the spinal
geometry); other commercially available input systems; customized
input systems; etc.
[0045] With regard to certain input systems comprising operating a
spatial locator to map a region which have been mentioned for use
in the present invention, examples of mapping can be, e.g., mapping
of the vertebral column or mapping the pedicle screws already
attached to the vertebral column. (With regard to working with
pedicle screws, see also Inventive Example 2 below.) Another
example of mapping is mapping a practice rod. For some such mapping
examples (and for certain other examples of imaging), bending an
implantable article during surgery would be likely to be required,
only after the patient has been surgically exposed. Mapping
according to the present invention may be particularly useful in
the case of attaching multiple rods to a segment of the spine,
because the attachment of the initial rod determines the final
shape and the secondary rod is only required to support this shape
rather than to further change this shape.
[0046] Examples of certain input systems having been discussed
above, the input system more generally is now mentioned. In the
various embodiments of the invention, the input system (also
referred to herein as "input mechanism") is used to provide
computer-readable information to the translational control
interface which then in turn communicates with the control
software. The computer-readable information that the input system
provides to the translational control interface represents a
desired three-dimensional shape (such as a desired
three-dimensional bent shape, etc.) to be formed by the automated
hardware as commanded by the control software with which the
translational control interface communicates.
[0047] For applying shaping force according to the invention, there
is provided a motorized apparatus that holds the article to be
shaped and includes an automated (i.e., non-manual) system for
application of shaping force, such as an automated system for
bending a rod. In the invention, the article is shaped
non-manually, such as by operation of a series of
computer-generated actuator commands, such as a series of actuator
commands whereby a series of discrete local bends is imposed on a
rod, with the local bends being imposed one at a time by a
force-applying mechanism.
[0048] Preferably the rod is moved past the force-applying
mechanism, with the rod being moved in a forward direction, being
stopped as needed, but not being reversed, and with the
force-applying mechanism stationary relative to the overall
apparatus.
[0049] Alternately, the rod may be held stationary and a
force-applying mechanism moved along the rod in a single direction
and stopped to impose force.
[0050] It will be appreciated that in the invention any such
movement (including stopping), whether of a rod or of a
force-applying mechanism preferably are as computer-controlled as
possible; as much as possible, with the movement (of the rod or of
the force-applying mechanism) being motorized, not manual.
[0051] The structure of the force-applying mechanism is formed to
coordinate with the article to which shaping force is to be
applied. For example, in the case of bending a rod, an example of a
structure of a force-applying mechanism is a structure having at
least one circular opening through which the to-be-shaped rod fits
snugly, such as being threaded through the circular opening(s).
With such a structure for rod-bending, during motorized operation
of the apparatus, the rod is moved in a "forward" direction until
commanded to "stop" according to an automated control program. A
motor is electrically connected to a rod-movement system which
transports the rod according to a series of actuator commands for
achieving rod movement. A controller is electrically connected to
the motor responsible for linear rod movement (i.e. the controlled
forward advancement and controlled stopping). Most preferably,
movement of and stopping of the rod are controlled entirely by
computer-generated instructions, i.e., during regular operation,
the movement and stopping of the rod are completely free of human
control (such as being completely free, during regular operation,
of a human operating a knob, a keyboard, a joystick, a mouse,
etc.).
[0052] It will be appreciated that the first "stop" of the rod,
i.e., the first place on the rod where force will be applied, as a
practical mechanical matter usually cannot be on the very tip or
edge of the rod. For example, where a bend is wanted at an end of a
rod, usually the starting rod includes an extra length that
ultimately will be chopped-off, with the first bend applied at a
mechanically practical first stop along the rod; the unneeded extra
length of the rod is later removed (preferably, chopped). In the
case of an implantable article, chopping is preferred over sawing.
Selecting chopping operations, such as selecting which end(s) to
chop, generally follow from the order in which the bends are
imposed.
[0053] When the rod reaches a "stop," the force-applying mechanism
is then controllably activated to apply force to the article being
shaped. At least one motor (which may be the same as, or different
from, the motor used for driving the linear movement of the rod) is
connected to the force-applying mechanism for operating application
of force. A controller is connected to the motor that operates the
force-application device, for controlling the motor that powers
force-application. Preferably the number of motors and moving parts
is minimized to the minimal number for accomplishing the desired
application of force. Most preferably, force application is
controlled entirely by computer-generated instructions, i.e.,
during regular operation, the force-application is completely free
of human control (such as being completely free, during regular
operation, of a human operating a knob, a keyboard, a joystick, a
mouse, etc.).
[0054] The inventive motorized apparatus most preferably includes
at least one automated rotating mechanism, such as, e.g., at least
one of: a mechanism for motorized rotating of the article being
shaped (such as an automated, computer-controlled rod-rotating
system).
[0055] In a preferred example of rod feeding and movement, first
the rod is fed through a circular slot in the force-applying
mechanism, with the feeding being done by a linear actuator. The
linear actuator need not be the same actuator as the force-applying
actuator (herein called the bending actuator). After the rod is fed
into the circular slot in the force-applying mechanism, the rod is
rotated (with the rotation being automated rotation, not manual
rotation) to permit determination of the plane in which the
subsequent bend will be applied. The determination of the plane in
which the subsequent bend will be applied is a non-manual
operation. A rotary actuator may be used to achieve such rotation
of the rod. The rotary actuator need not be identical to the
feeding actuator or the bending actuator. After rotation of the
rod, the bending actuator is called upon to impose a bend. After a
bend is achieved satisfactorily (i.e., to the satisfaction of the
computerized system), the cycle repeats.
[0056] In the preceding paragraphs, there has been discussed an
inventive system in which the rod moves according to motorized
movement as commanded by a series of computer-generated actuator
commands, and in which the force applying mechanism remains
stationary compared to the overall system. In alternate
embodiments, which parts are moving and which are stationary may be
modified, such as, for example, a system in which the rod is held
stationary relative to the entire system and it is the force
applying mechanism that is moved along the stationary rod.
[0057] The inventive automated shaping system includes at least one
sensor that measures the local geometry of the article being
shaped, such as, e.g., a sensor measuring the local angle of a rod
that has been locally bent. Most preferably, the sensor conducts
its measurement continuously, so as to allow the controller to
instruct the bending hardware to stop bending when a certain angle
is reached. The sensor dispatches its measurement in
computer-processible form to the control software, where the
measurement information may be run through global feedback and/or
local feedback operations or otherwise compared against the desired
shape information. Sensor positioning is such that each actual bend
imposed is measured. For simplicity it may be preferred to use a
single sensor, but multiple sensors are not excluded. In a system
where a rod is fed, rotated and bent, an example of a sensor used
is an angular sensor. A separate sensor for rotary action can be
avoided by using a rotary actuator that is a stepper motor with a
built in sensor and because this rotary actuation requires no
deformation of the rod and therefore can be achieved with arbitrary
accuracy in a single step. Thus, a "sensor" mentioned herein refers
to an angular sensor measuring a local region of the article being
shaped.
[0058] The information from the sensor is subjected to local
feedback and/or global feedback processing.
[0059] An example of a local feedback algorithm useable in the
present invention is as follows. Suppose that a bend of an angle x
degrees needs to be imposed. The control software calls upon the
bending actuator to commence bending. The sensor continuously feeds
information about the current angle. The control software may stop
the bending when the desired angle is reached (as per the
information from the sensor) or when the desired angle has been
exceeded by some predefined amount, dx1 degrees. In either case, as
the bending actuator is restored to its original position, the rod
springs back by some amount, sp1 degrees. If sp1 is known in
advance, for example, based on an analytical formulation describing
sp1 as a function of x and the material properties, then the
control software can be programmed to ensure that dx1=sp1 in which
case the achieved bend is identical to x. In actuality, sp1 is not
known in advance. Even if such an analytical formulation is
available, it is only approximate and it is likely that dx1 is only
approximately equal to sp1 resulting in a residual error. The
control software may choose to use the deviation between the actual
sp1 and that predicted by the analytical formulation to estimate
the spring back, sp2 degrees, that would result from an additional
attempt to bend the rod at the same location, for example, by
instructing the bending hardware to recommence bending and only
stop bending once the sensor indicates that an angle x+dx2 has been
reached in such a way that dx2=sp2, such that after the bending
hardware is returned to its original position after the second bend
the actual and desired bending angles agree more closely than
before. This may be iterated several times until a desired local
accuracy is achieved. Thus a methodology using an analytical
formulation is provided.
[0060] Alternately, this methodology could be employed without the
use of an analytical formulation, simply by setting dx1=0 and using
the spring-back information from this and subsequent bends at the
same location to achieve the desired location accuracy. Such an
approach to local feedback may be based on extrapolation principles
such as extrapolation principles used in the shaping of plates.
[0061] An example of a translational control interface for use in
the invention is as follows. The information from the input
mechanism is quantified in terms of spatial (x,y,z) coordinates of
a discrete sequence of points along the rod. Consider any three
successive points on the rod. These points are connected by two
straight-line segments (in space, not necessarily on the actual
rod) that lie in a plane. This is the bending plane. The bending
angle to be imposed at the middle of the three points is the angle
between the two straight-line segments. Now consider any four
successive points on the rod. The first three and the last three
lie in two different bending planes. The middle two lie in both
bending planes. The angle between the bending planes is the rotary
angle to be imposed at the second of the four points.
[0062] An example of global feedback for use in the present
invention is as follows. After a local bend has been achieved with
sufficient accuracy, the angular sensor information about the
achieved bending angles up to and including the last completed bend
is used to locate in space the subsequent discrete point on the rod
where the subsequent bend will be imposed. The global feedback uses
this information coupled with the information about the desired
location of all subsequent points (not including those points that
have already passed through the force-applying mechanism nor the
next point on the rod at which a local bend will be imposed) to
recompute the sequence of rotations and bends (with the
recomputation being as discussed above with regard to the
translational control interface).
[0063] Preferably a clearance algorithm is included in systems for
shaping an article, such as rod-bending systems. An example of a
clearance algorithm is as follows. Once you have computed the local
bending and rotary actions, the rod-shaping action may be simulated
in software while accounting for the physical shape of the hardware
mechanism to ascertain whether all segments of the rod that have
exited through the force-applying mechanism remain clear of the
hardware. At each step of the simulation, the information about the
location of all previously completed bends and the amount of
rotation and bending achieved at these locations (as determined by
the angular sensor) is used to reconstruct the global shape of the
rod (which is straightforward three-dimensional geometry) and the
spatial location of points on the rod are compared to the spatial
regions where components of the hardware device reside. The
simulation may be completed prior to any bending, as well as during
bending to accommodate errors in local bends that were not
anticipated prior to commencing bending.
[0064] The inventive motorized apparatus for applying shaping force
(such as an inventive automated rod-bender) has sufficient
clearance to accommodate, during regular operation, the article
during the procedure of the article being subjected to a series of
applications of shaping force. For example, if the article being
shaped is being moved as part of the force-application, the space
through which the article is being moved needs to be free of any
physical object or part. With reference to rod-bending, it can be
appreciated that the automated rod bender needs to have sufficient
void space (clearance) so that the first bend can be applied
without the rod physically contacting any part of the automated
rod-bender. Subsequent bends also will need to be applied without
the rod physically contacting any part of the automated rod-bender.
Where the automated rod bender is to be used for bending
implantable spinal rods, the apparatus is configured so that two or
more large three-dimensional bends each approaching 180 degrees
(herein referred to as "severe" bending) can be imposed in the rod
without a physical clearance problem occurring, i.e., without the
rod encountering obstruction. For example, referring to FIGS. 1A,
1B, it can be seen that it is wanted not just to bend the spinal
rod once into a sharp U (with the sharpness of the bend being a
matter of preference, and could be achieved in a single bend, but
more preferably is achieved in a sequence of bends resulting in a
180 degree bend over some finite radius), but to again bend the rod
another time. Moreover, it is wanted to not be limited to a
two-dimensional planar shape, such as an S shape, but rather, that
the rod may be bent in three dimensions. To permit such
three-dimensional bending of a rod, a sufficient void space is
needed to be designed into the apparatus when the apparatus is
made.
[0065] An angular sensor and feedback processing of information
from the angular sensor has been mentioned above. The current
actuator applies force until the sensor indicates that a stopping
angle has been reached. The actuator transmission is used to
control the amount of torque. By using an angular sensor in
continuous sensing operation, and by operating global and local
feedback, a desired bend can be accomplished without advance
preprogrammed information about the amount of force needed to
effect a particular bend (including springback behavior) of a
particular material to be bent. Also, it may not be necessary to
calibrate and recalibrate (here, referring to resorting to use of a
different transmission to control the torque from the bending
actuator) a machine according to a particular type of material to
be received and bent. A stepper motor rather than a servo motor
could be used for the bending actuator. A stepper motor will bend
until reaching a certain angle and will adjust the amount of torque
without outside control. (Here, and elsewhere in this
specification, a particular type of motor, such as a servo or
stepper motor, is mentioned for example, and the selection of the
type of motor is not considered significant, but rather, a question
of cost or design choice.) In the invention, a single inventive
motorized, computerized system with continuous angular sensing
could receive a rod of a first material for bending, bend that rod,
and immediately afterward without recalibration could receive a rod
of a second different material for bending.
[0066] In a surgical context, rods generally are of the same
diameter. However, if processing of a different diameter rod is
wanted, the automated rod bending machine may be adjusted to
accommodate a different diameter rod, such as by reconfiguring the
slot through which the rod runs, and replacing the bending plate.
In the clinical setting, preferably, rods of a same diameter are
used in a single automated rod bending machine.
[0067] The inventive automated apparatus preferably provides as
small a resolution as possible between two locations at which force
is applied, while considering the fact that too small a bending
radius may result in damage to the rod. Preferably bending takes
into account available engineering data supporting recommended
bending radii for different materials and rod radii. The minimum
distance between bends will be determined by the geometry and
mechanical characteristics of the apparatus, with about one inch
being an example of a typical minimum resolution for an apparatus
accommodating an 8 mm spinal rod. The minimum resolution is not
required to be used, that is, the force-application mechanism is
required to stop if no force-application is wanted, such as if the
target design calls for the rod to remain straight the
force-application mechanism proceeds without stopping until
reaching a linear location at which force-application is
called-for. By way of example, relatively short spinal rods are
usually left almost straight with just a couple of bends; longer
spinal rods generally are more carefully shaped to follow the
desired contour of the vertebral column. For a typical spinal rod,
25 discrete bends which are non-manually imposed is an example of a
relatively high but executable number for an automated rod-bender
according to the invention to perform, and 5-15 discrete bends
which are non-manually imposed is a preferred range of how many
bends an automated rod-bender according to the invention may
execute to construct a desired three-dimensional shape.
[0068] In regular operation of the automated shaping apparatus, the
force application mechanism controllably moves in a linear
direction, stopping according to automatic instructions, and
applying force according to automatic instructions. So that the
force application mechanism may so operate, there is included in
the inventive apparatus or system a translational interface and
control software.
[0069] Examples of a translational interface useable in the
invention are, e.g., one or more of: a digital computer interface
that converts digital photographs from the input system to a
three-dimensional representation (such as, e.g., a
three-dimensional representation of a spinal rod to be formed); a
computer interface that for data received from the input system
automatically computes (such as by applying methods of differential
geometry or planar trigonometry) local curvature and local torsion
of the desired shape (such as the desired bent-rod shape) and
translates the computed values into a sequence of hardware
operational commands (such as, e.g., a sequence of feeding,
rotating and bending commands); a translational interface including
real-time correction of local bends for spring back due to
nonlinear elasticity and material hardening as well as for
adjusting the desired local curvature and torsion of the as-of-yet
unbent portions of the rod to retain global shape accuracy; a
translational interface including correction for local bends using
the analytic formulation for spring-back according to U.S. Pat. No.
6,035,691; a translational interface using other
correction-for-spring-back methodology; etc.
[0070] Before automated rod-bending of the invention, spring-back
could not accurately be corrected-for when imposing a manual bend,
because even if a formula was known for how much to bend so that
the right spring-back was provided to ultimately end at a desired
angle, a human operator could only be so accurate in applying the
degree of bending force wanted to over-bend so that upon release,
spring-back to the desired bend would occur. However, a strong
advantage of the present invention is that by using a machine to
bend a rod, the machine can bend the rod incrementally, according
to a mathematical formulation. A human operator could not achieve
the finesse of incremental bending that a machine can achieve.
[0071] Examples of control software useable in the invention are,
e.g., one or more of: control software depicting a desired
three-dimensional shape, such as, e.g., control software using a
virtual representation of a patient's spinal rod to compute local
curvature and torsion and to generate a sequence of actuator
commands that will ensure satisfactory reproduction of the desired
shape in the rod-bending hardware; control software that translates
a desired target shape (received from the translational control
interface) into a corresponding machine operation(s) such as, e.g.,
operation of an actuator or a motor; control software that
processes actual measurement data from an angular-bend sensor and
compares the actual measurement data to the desired target shape
and, if needed, adjusts the sequence of actuator commands to ensure
satisfactory reproduction of the desired shape (such as, e.g.,
control software that performs a local feedback operation; control
software that performs a global feedback operation, etc.); etc.
[0072] In the case of rod-bending, an example of preferred control
software used in the invention is control software which receives
an actual angular bend measurement for a local bend just imposed,
compares that actual angular bend measurement to the instruction
that underlies that actual bend, and if the underlying instruction
and actual angular bend measurement are at variance, reformulates
the set of remaining bending instructions. For example, if the
machine-based bending instruction was that the force-application
mechanism was instructed to impose a 40 degree local bend, but the
post-bend actual measurement received from the sensor for the local
bend shows a 39 degree local bend actually was imposed, then the
control software recognizes the discrepancy and recalculates the
remaining force-application instructions to retain global accuracy
and to achieve the desired shape. By doing so, advantageously in
the present invention re-bending or placing bends on top of each
other can be avoided.
[0073] The control software used in the invention preferably
includes, for each material composition to be placed in the
apparatus for shaping, at least one computer-readable table
correlating each example of a desired angular bend to respective
corresponding machine instructions for operating the force-applying
mechanism to deliver the desired angular bend. That is, a titanium
rod and a steel rod of the same diameter require different
computer-readable tables of machine operation instructions because
those different materials have non-identical elasticity or
spring-back.
[0074] Optionally, there may be included in inventive systems and
methods an automated pre-screening of the product being
constructed. For example, in the case of a bent-rod medical implant
which is to be connected to cooperating screws, there may be during
construction of the bent-rod a step of confirming that imposition
of a particular local bend in the rod will allow for cooperative
placement of the screws. Another pre-screening example is of a
pre-screening assessment of where a patient's spine may receive
attachment of the rod being constructed.
[0075] Making an automated rod-bender apparatus may be readily
accomplished with reference to the above-mentioned regular
operation of an automated shaping apparatus such as an automated
rod-bender, and with reference to the figures, photographs and
Examples included herein, and the following remarks.
[0076] For example, an inventive automated rod-bending machine may
be constructed using a feeding/rotating/bending sequence of
actuators (arranged in a structure so that desired local curvature
and torsion can be imposed on a rod). For reference, Kataoka, U.S.
Pat. No. 6,434,995, "Method of Bending Small Diameter Metal Pipe
and its Apparatus" is mentioned. The rod-bending hardware, for
example, may include three actuators: a stepper motor feeding
actuator for correct positioning of the spinal rod relative to the
bending mechanism; a stepper motor rotating actuator for correct
orientation of the spinal rod relative to the plane of bending; and
a motor (such as a servo motor or a stepper motor, preferably, a
servo motor) bending actuator for imposing a desired bend of the
spinal rod about the bending mechanism. For ensuring local
accuracy, for the feeding and rotating action, open-loop controlled
high-resolution stepper motors preferably are used. This is because
the feeding and rotary actions do not work against the material but
only reposition the material in space. No deformation occurs as a
result. For the bending action, optionally closed-loop control is
used. In that case, the bending actuation is transmitted from the
servo motor to a bending arm through a 90 degree transmission. (The
close-loop control is optional, not necessary.) The bending arm
uses a rolling segment in contact with the actual rod to allow for
non-concentric arc motion of the bending arm relative to the arc
motion of the point of contact on the bent rod about the bending
mechanism.
[0077] An example of a suitable angular sensor to use is one that
detects the resultant bend and feeds this back to the control
interface for appropriate action.
[0078] To achieve subsequent non-coplanar large angle bends (near
half turn) at the terminal end of long rods (e.g., up to 1 meter)
used to anchor thoracolumbar rods in the sacrum, the device may
incorporate a displaced bending mandrel and sufficient clearance
from the device casing. A sleeve may be used to support the unbent
portion of the rod as bends are applied. It is over the bending
mandrel that the rod is bent, with the bending arm doing the
bending. The bending mandrel preferably uses a low friction (or,
alternatively, rolling) segment in contact with the rod to allow
for non-concentric arc motion of difference radius of the bending
arm relative to the bent rod.
[0079] An example of a bending arm/bending mandrel mechanism is
shown in FIG. 3. A bending mandrel 310 is shown perpendicular to a
rod R. The rod R is sandwiched between the bending mandrel 310 and
the bending arm 320. Looking at FIG. 3, the bending mandrel 310
appears "in front" of the rod R and bending arm 320 appears
"behind" the rod R. The arm 320 rotates and pushes at the rod R,
bending the rod R. The rod R gets pushed up against the mandrel
310. As shown, the arm 320 will not always push at the same point
on the rod R, because the arm 320 makes a circular motion around
the mandrel 310. One way of accomplishing the desired motion of the
bending arm 320 is to form bending arm 320 as a rolling sleeve
structure, such as a hollow cylinder that sits on the outside of
the arm. The desired motion for the bending arm 320 is for the
bending arm 320 that pushes at the rod R to be able to rotate along
the rod R, like a rolling pin, rather than scrape along the rod R.
The desired motion of the bending arm 320 may be accomplished by
other structures, such as, e.g., by using bearings, etc., so that
the bending arm 320 freely rotates as it rolls over the rod R so
that when the rod R bends, it only bends, not scrapes. Thus, damage
to the rod R can be avoided or at least minimized.
[0080] Most preferred for use as the input mechanism is software
with which the surgeon can design the intended rod shape in a CAD
environment. An alternative input mechanism is based on a
photographic scanning of an actual, manually shaped template rod
(i.e., a rod that is relatively much softer and formable than the
ultimate rod to be shaped for use as the actual implant).
[0081] It is not particularly important to strictly distinguish
between the translational interface and the control software, and
whether a desired operation is present in one or the other. In
actual implementation, certain algorithms or computer operations
may reside in various locations.
[0082] A preferred example is, for the translational interface and
control software, to use Matlab (commercially available) and Lab
View (commercially available), applying customization as follows
discussed with reference to FIG. 5 depicting computer-aided spinal
instrumentation manufacture control flow: The three-dimensional
shape information (in the form of X-Y-Z coordinates of desired rod
shape 500) is received from the input mechanism and converted by
the Lab View control program 510 with integrated feedback algorithm
into a sequence of discrete control commands to the three hardware
actuators, corresponding to a feeding distance along the rod
between subsequent bends (feed command 512); a bending angle at
each subsequent bend (bend command 516); and a rotational angle at
each subsequent bend (rotate command 514). In this customization,
the control software also includes a closed-loop, local feedback
algorithm that achieves an acceptable local accuracy in the bending
angle by addressing the spring-back exhibited by the metal rod
after each bending motion. An angular sensor is used to provide
information about the achieved bend. In this customization, the
control software also includes a closed-loop, global feedback
algorithm that achieves an acceptable global accuracy in the curve
shape by updating the subsequent control commands at the conclusion
of each local bend to reflect the achieved bend.
[0083] Referring to FIG. 5, the feed command 512 operates feed
stepper motor actuation 522 which operates feed-linear actuator
532. The rotate command 514 operates rotate stepper motor actuation
524. The bend command 516 operates bend servo motor actuation 526
which operates mechanical bending mechanism 536 the result of which
operation is measured by rod spring back sensor 540 which impacts
bend servo motor actuation 526 and sends measurement information to
Lab VIEW control program 510 with integrated feedback
algorithm.
[0084] More generally, for constructing shaping apparatuses for
acting on other shapes besides rods, a similar basic concept may be
applied, with suitable adjustments for the geometry of the
particular article being shaped. Three-dimensional considerations
of physical clearance should be taken into account, and sufficient
void space should be provided in the apparatus so that the article
being shaped can move without encountering anything solid.
[0085] An inventive automated shaping apparatus thus is designed
and constructed for accomplishing formation of at least one
three-dimensional shaped article, preferably, more than one
three-dimensional shaped article. However, advantageously,
automated shaping apparatuses according to the invention are not
limited to making only the three-dimensional shaped article or
articles which they have been expressly constructed to make. By
including a screening system including at least one sensor and at
least one automated feedback system, inventive automated shaping
apparatuses additionally permit manufacture of any other
three-dimensional article which is not prohibited by its geometry,
i.e., any other three-dimensional article the formation of which in
the apparatus does not cause a physical clearance problem. Thus,
the invention provides an "intelligent" manufacturing tool.
[0086] Herein many mentions and examples have been given referring
to a rod, for simplicity. It will be appreciated that the invention
is not limited to shaping a rod, and may be used for shaping bars,
disks, plates, and other starting shapes (including regular or
symmetric starting shapes, irregular starting shapes, asymmetric
starting shapes, etc.).
[0087] The invention advantageously provides a system where
rebending can be avoided, and placing a second bend on top of a
first bend can be avoided. The invention makes possible a series of
sequential local bending steps occurring in a single direction and
without needing traverse. This is made possible by real-time
processing by the control software of angular measurements taken by
sensor. For example, if the machine-based instruction was that the
force-application mechanism was instructed to impose a 40 degree
local bend and the post-bend actual measurement for the local bend
shows a 39 degree local bend actually was imposed, then the control
software recognizes the discrepancy and recalculates the remaining
force-application instructions to retain global accuracy and to
achieve the desired shape.
[0088] The following inventive Examples are mentioned, but it will
be appreciated that the invention is not limited to the
Examples.
COMPARATIVE EXAMPLE 1
[0089] A surgeon receives information from a computer, giving him
bending instructions for a spinal rod, which he then manually
bends.
INVENTIVE EXAMPLE 1 (FULLY AUTOMATED ROD-BENDER)
[0090] FIG. 2 shows an example of rod-bending hardware 200 in an
embodiment of the invention. A rod R is disposed in the rod-bending
hardware 200. Computer-aided design may be performed with the
hardware of FIG. 2. In FIG. 2, a rotary actuator system 204 rotates
and slides the rod. The rod R is inserted into the rotary actuator
system 204. A linear actuator system 208 in the view shown in FIG.
2 is parallel to the rod R. Inside the linear actuator system 208
is a sliding magnet (not shown). The rotary actuator system 204 is
attached to a bracket which slides on the linear actuator system
208. The actuator makes the magnet move and takes with the moving
magnet anything on the rail, so that the rotary actuator system 204
rides on the linear actuator system 208. The rod R is thus attached
to part of the linear actuator system 208. Another actuator 206 is
shown at the front right of FIG. 2 near the sensor 202.
[0091] FIGS. 3 and 4 show details from FIG. 2, showing bending
mandrel 300 and sensor 202. The rod R is bending up. As shown, the
end of the rod R moves up and to the left. The sensor 202 collects
information about the angle of the rod R. If a 180 degree bend is
imposed, the rod R will almost bend back on itself in the
rod-bending hardware 200 of FIG. 2.
[0092] FIG. 7 is a photograph of rod-bending hardware according to
an embodiment of the invention. The rod-bending hardware used in
this inventive Example consists of a feeding mechanism for correct
positioning of the rod relative to the plane of bending, and a
bending mechanism for imposed a desired bend of the spinal rod
about the bending mandrel as well as a rotary mechanism for correct
orientation of the bending plane.
[0093] FIG. 8 is a photograph of an actuator for a bending
mechanism according to an embodiment of the invention.
[0094] The hardware of Example 1 may be used in an inventive system
for automated rod-bending (such as shown in FIG. 5 or 6). The
hardware of Example is useable in an integrated system for
computer-aided rod bending for the automated imposition of a
three-dimensional geometry on a corrective spinal rod to be used in
a surgical operation, such as corrective surgery to treat scoliotic
deformity of the vertebral column. Such integrated systems may, for
example, consist of an input mechanism, a translational interface
and control software, and automated rod-bending hardware for the
discrete imposition of curvature and torsion on a spinal rod.
[0095] In the rod-bending machinery of the photographs, a spinal
rod is subjected to motorized movement and a bending mechanism
remains stationary. The rod is stopped and moved according to
computerized commands for the actuator responsible for rod
movement. Bending force is applied according to computerized
commands for the actuator responsible for the rod-bending
hardware.
[0096] With regard to Example 1 and the figures and photographs
discussed therein, it will be appreciated that an implantable rod
can be bent three-dimensionally in an automated system, which is
especially useful for pre-surgical formation of implantable spinal
rods. When local and/or global feedback processing accompanies a
series of shaping steps automatically imposed on a rod or other
article being shaped into three-dimensional form, formation time
may be expedited compared to manual creation, and shapes difficult
or impractical to create manually may be constructed simply. Thus,
the embodiment of the present invention discussed with reference to
Example 1 provides an improvement over conventional implant
practices, and also constitutes a system-based approach to
reproducing a desired shape as conceived by a surgeon onto a spinal
rod implant.
[0097] Also, it should be appreciated that an inventive automated
rod-bender such as in Example 1 can be used to put many more bends
in a spinal rod than a human operator (such as a surgeon) can, and
also to do so with more care and accuracy and repeatability
compared to a human.
[0098] A rod bent using the inventive automated rod-bender of this
Example may be processed by sterilization after shaping but prior
to use in a patient, such as in an autoclave. The automated
rod-bender of this Example is designed to impart no physical damage
to the rod that other than the reshaping of its three-dimensional
form.
[0099] In this inventive Example, to accommodate the cooperating
fastening hardware, the translational control interface introduces
points on either side of points corresponding to the location of
the cooperating hardware and computes the necessary rotation and
bending required to achieve the desired curve shape at these former
points, thus ensuring that the rod passes through the positions of
the cooperating hardware with the appropriate spatial
direction.
[0100] In this example, there is nothing particular observed for
large bends versus small bends. The same parts actuate the rod for
these respective bends. It is advantageous from a material stress
point of view, however, to not apply a large bend over too small a
bending radius. Instead, as mentioned before, a sequence of smaller
bends would be imposed to result in an accumulated large bend. The
larger the bend, however, the more significant becomes the rolling
sleeve on the bending mandrel which allows for the difference in
radii and rotation center between the bending arm and bending
mandrel and the rod. The bending arm structure that uses the
rolling sleeve is particularly advantageous when working with
surgical implant rods, to eliminate friction and to reduce
possibility of damage to the rod surface during bending.
[0101] Notably, an inventive automated rod-bender such as that
shown in Example 1 is able to establish the correct bend without
needing the sort of backtracking that the surgeon might sometimes
do when he manually bends a rod and he needs to backtrack and put
new bends in regions already previously bent to compensate for
errors resulting from previous bends. Rather, when the inventive
machine bends several times at the same location, the bends are in
immediate succession to achieve the desired local accuracy and
account for spring back, and no backtracking is needed.
[0102] Even if a computer tells a surgeon what bend to put into a
rod, if the surgeon has to manually bend the rod as in Comparative
Example 1, the procedure is not particularly accurate, is time
consuming, and will be fatiguing to the surgeon. The amount of
force that a human can apply is relatively more limited than what a
machine can delivery. By contrast, bending a spinal rod using the
inventive technology of Example 1 avoids such problems and provides
improved accuracy and other advantages.
INVENTIVE EXAMPLE 2
[0103] A preferred example of a use of the present invention is a
method in which, in advance of surgical implantation, automated
pre-screening of a three-dimensional bent shape is performed,
including a determination of placement in the patient of the
three-dimensional bent shape with reference to cooperating hardware
placed, or to be placed, in the patient.
[0104] An example of cooperating hardware placed, or to be placed,
in the patient is a pedicle screw, which is medical hardware
conventionally in use, such as pedicle screw used in spinal
surgery. An example of a three-dimensional bent shape is a bent
spinal rod. The pedicle screws are used in attaching the spinal rod
to the patient's body. In the invention, placing the bent spinal
rod in the patient may be assisted by an inventive article that
cooperates with the pedicle screw, such as a cap for the pedicle
screw. An example of an inventive pedicle screw cap is a pedicle
screw cap, comprising an article having an opening which receives a
pedicle screw, the article being biocompatible and of a
medically-imageable material. See, for example, the inventive
pedicle screw cap 9 in FIG. 9.
[0105] The cones in the pedicle screw cap are used to provide
enough information during imaging (such as imaging using a
fluoroscope) to determine the position and orientation of the
pedicle screw and thereby the desired location of points along the
rod and the directions of the rod through these points. Features of
the pedicle screw cap are formed so that these features may be
imaged to provide the desired information. For example, in FIG. 9,
the cones have different opening angles, so that from an image
taken of the pedicle screw cap, it can be determined which cone is
being viewed, and orientation thereby inferred. Preferably, the
processing of the imaged cones is by processing using computer
software, such as software detecting the shape of the screw cap and
determining from the different opening angles of the cones the
orientation that has been imaged.
[0106] A preferred shape of the pedicle screw cap is a shape that
accentuates its position and orientation to commonly used surgical
imaging apparatus (e.g., fluoroscopy), thus providing input to the
translational control interface about the position and orientation
of cooperating hardware and the desired position and orientation of
corresponding points along the spinal implant rod for further
processing and shaping by the hardware (with use of hardware
according to the invention being preferred).
[0107] While the invention has been described in terms of its
preferred embodiments, those skilled in the art will recognize that
the invention can be practiced with modification within the spirit
and scope of the appended claims.
* * * * *