U.S. patent application number 15/432647 was filed with the patent office on 2017-08-17 for post-operatively adjustable spinal fixation devices.
The applicant listed for this patent is NUVASIVE, INC.. Invention is credited to Shaeffer Bannigan, Justin Doose.
Application Number | 20170231661 15/432647 |
Document ID | / |
Family ID | 59559456 |
Filed Date | 2017-08-17 |
United States Patent
Application |
20170231661 |
Kind Code |
A1 |
Bannigan; Shaeffer ; et
al. |
August 17, 2017 |
Post-Operatively Adjustable Spinal Fixation Devices
Abstract
A system for spinal fixation with a non-rigid portion at least
one of the caudal or cephalad terminus. Various devices and
techniques are described for transition from a rigid fixation
construct to a less rigid support structure applied to a "soft
zone" that will help share the stress created on the spinal levels
caused by the fixed levels below. In specific embodiments the soft
zone is provided by terminating the construct with one of a
flexible tether or a dampening rod.
Inventors: |
Bannigan; Shaeffer; (San
Diego, CA) ; Doose; Justin; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NUVASIVE, INC. |
San Diego |
CA |
US |
|
|
Family ID: |
59559456 |
Appl. No.: |
15/432647 |
Filed: |
February 14, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US17/17700 |
Feb 13, 2017 |
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15432647 |
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62294975 |
Feb 12, 2016 |
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Current U.S.
Class: |
606/263 |
Current CPC
Class: |
A61B 17/7053 20130101;
A61B 17/7043 20130101; A61B 17/7016 20130101; A61B 17/7052
20130101; A61B 2017/00876 20130101 |
International
Class: |
A61B 17/70 20060101
A61B017/70 |
Claims
1. A system for spinal fixation, the system comprising: a first
bone anchor, anchored to a first vertebra in a subject, the first
bone anchor comprising a first bone fastener attached to a first
rod housing; a rigid spinal rod seated in the first rod housing to
restrict translation of the rigid spinal rod relative to the first
bone anchor; a second bone anchor, anchored to a second vertebra in
the subject, the second bone anchor comprising a second bone
fastener attached to a second rod housing, wherein the rigid spinal
rod is seated in the second rod housing to restrict translation of
the rigid spinal rod relative to the second bone anchor; and a
compressible spinal connector, connected to the second bone anchor,
and anchored to a third vertebra in the subject, the compressible
spinal connector comprising a modulation mechanism for modulating
at least one of: the tension on the compressible spinal connector
or the resistance to compression of the compressible spinal
connector, wherein said modulation occurs in response to a remote
signal.
2. The system of claim 1, wherein the remote signal is a spinning
magnetic field.
3. The system of claim 1, wherein at least one of the following is
at least partially composed of a non-absorbable biocompatible
material: the first bone anchor, the second bone anchor, the rigid
spinal rod, and the compressible spinal connector.
4. The system of claim 1, wherein the remote signal is a spinning
magnetic field, and wherein at least one of the following is at
least partially composed of a non-absorbable biocompatible material
that is either non-magnetic or weakly magnetic: the first bone
anchor, the second bone anchor, the rigid spinal rod, and the
compressible spinal connector.
5. The system of claim 1, wherein the compressible spinal connector
is a tether assembly.
6. The system of claim 5, wherein the modulation mechanism is an
adjustable tensioner configured to vary the tension on a flexible
tether between the second bone anchor and the third vertebra.
7. The system of claim 6, wherein the adjustable tensioner is a
turnbuckle comprising a threaded first end coupler, a second end
coupler, and a rotatable magnet that rotates in response to a
spinning magnetic field and that is connected to the threaded first
end coupler to cause the threaded first end coupler to rotate about
its longitudinal axis when the rotatable magnet rotates.
8. The system of claim 6, wherein the adjustable tensioner
comprises a spool about which the flexible tether is wound, and
wherein rotation of a spool magnet drives rotation of the
spool.
9. The system of claim 6, wherein the adjustable tensioner
comprises a locking mechanism configured to maintain tension on the
flexible tether when engaged.
10. The system of claim 5, wherein the flexible tether is
constructed of a non-absorbable biocompatible material.
11. The system of claim 1, wherein the compressible spinal
connector is a dampening spinal rod that is compressible and
expandable.
12. The system of claim 11, the dampening spinal rod comprising: an
elongate rigid portion for insertion into a bone anchor; a flared
portion for receiving a terminal end of a second spinal rod, the
flared portion comprising a rod cavity of sufficient diameter to
accept the second spinal rod.
13. The system of claim 11, wherein the modulation mechanism is a
friction brake configured to vary the resistance of the dampening
rod to compression and tension.
14. The system of claim 13, wherein the friction brake comprises a
set screw in a threaded channel positioned to exert compressive
force on a spring, said spring positioned to exert compressive
force against both the compression and expansion of the dampening
rod.
15. The system of claim 14, wherein the set screw is magnetic and
rotates in the threaded, channel in response to a spinning magnetic
field.
16. The system of claim 1, wherein the compressible spinal
connector is a telescoping spinal rod positioned within the second
rod housing.
17. The system of claim 16, wherein the telescoping spinal rod
comprises: a rod magnet configured to rotate when exposed to a
spinning magnetic field and cause the telescoping spinal rod to
either extend or collapse depending on the direction of the
spinning magnetic field; a first elongate element containing a
cavity; and a second elongate element dimensioned to at least
partially fit within the cavity, and having an internally threaded
region; wherein the modulation mechanism comprises a lead screw
coupled to rotate when the rod magnet rotates, and comprising an
externally threaded region engaged to the internally threaded
region of the second elongate element, such that rotation of the
lead screw causes the second elongate element to translate relative
to the first elongate element.
18. The system of claim 1, wherein a second rigid spinal rod is
seated in an additional rod housing of an additional bone anchor
that is anchored in at least one of the first and second
vertebrae.
19. The system of claim 18, wherein a transverse connector is
fastened to the first rigid spinal rod and the second rigid spinal
rod.
20. The system of claim 1, comprising: a third bone anchor
comprising a third bone fastener and a third rod housing, anchored
to the first vertebra; a fourth bone anchor, comprising a fourth
bone fastener and a fourth rod housing, anchored to the second
vertebra; a second rigid spinal rod seated in the third rod housing
and the fourth rod housing; and a first flexible tether at least
partially wrapped around a structure of the third vertebra and
connected to both of the first and second rigid spinal rods to
exert tension between the third vertebra and the first and second
rigid spinal rods; wherein the compressible spinal connector is an
adjustable tether assembly, the adjustable tether assembly
comprising: a second flexible tether encircling the structure of
the third vertebra and a spinous process of a fourth vertebra; and
a tensioner connected to the first and second rigid spinal rods,
the tensioner comprising a first magnet mounted to rotate in
response to a spinning magnetic field, and a tether connection
configured to increase or decrease then tension on the second
flexible tether depending on the direction of rotation of the first
magnet.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of International
Application PCT/US17/17700, filed 13 Feb. 2017 (pending).
International Application PCT/US17/17700 cites the priority of U.S.
Patent Application No. 62/294,975, filed on 12 Feb. 2016 (expired).
The contents of both of the foregoing applications are incorporated
herein in their entireties.
BACKGROUND
[0002] Field
[0003] The present disclosure relates generally to medical devices,
and specifically to surgical instruments and methods for performing
spinal procedures.
[0004] Background
[0005] The spine is critical in human physiology for mobility,
support, and balance. The spine protects the nerves of the spinal
cord, which convey commands from the brain to the rest of the body,
and convey sensory information from the nerves below the neck to
the brain. Even minor spinal injuries can be debilitating to the
patient, and major spinal injuries can be catastrophic. The loss of
the ability to bear weight or permit flexibility can immobilize the
patient. Even in less severe cases, small irregularities in the
spine can put pressure on the nerves connected to the spinal cord,
causing devastating pain and loss of coordination.
[0006] The spinal column is a bio-mechanical structure composed
primarily of ligaments, muscles, bones, and connective tissue that
forms a series of vertebral bodies stacked one atop the other and
intervertebral discs between each vertebral body. The spinal column
provides support to the body and provides for the transfer of the
weight and the bending movements of the head, trunk and arms to the
pelvis and legs; complex physiological motion between these parts;
and protection of the spinal cord and the nerve roots.
[0007] The stabilization of the vertebra and the treatment for
spinal conditions is often aided by a surgically implanted fixation
device which holds the vertebral bodies in proper alignment and
reduces the patient's pain and prevents neurologic loss of
function. Spinal fixation is a well-known and frequently used
medical procedure. Spinal fixation systems are often surgically
implanted into a patient to aid in the stabilization of a damaged
spine or to aid in the correction of other spinal deformities.
Existing systems often use a combination of rods, plates, pedicle
screws, bone hooks, locking screw assemblies, and connectors, for
fixing the system to the affected vertebrae. The system components
may be rigidly locked together to fix the connected vertebrae
relative to each other, stabilizing the spine until the bones can
fuse together.
[0008] Whatever the treatment, the goal remains to improve the
quality of life for the patient. In the vast majority of cases this
goal is achieved, however in some instances patients who receive
implants to treat the primary pathology develop a secondary
condition called junctional disease. Most commonly this occurs at
the proximal or cephalad area of spinal instrumentation and is then
termed "adjacent segment pathology." Clinical Adjacent Segment
Pathology (CASP) refers to clinical symptoms and signs related to
adjacent segment pathology. Radiographic Adjacent Segment Pathology
(RASP) refers to radiographic changes that occur at the adjacent
segment. A subcategory of CASP and RASP that occurs at the proximal
end of the instrumentation is termed proximal junctional kyphosis
(PJK). PJK may be defined in several manners and commonly is
specified as kyphosis measured from one segment cephalad to the
upper end instrumented vertebra to the proximal instrumented
vertebra with abnormal value defined as 10.degree. or greater. In
practice this often means that the patient's head and/or shoulders
tend to fall forward to a greater degree than should normally
occur. Sometimes the degree is significant.
[0009] Adjacent segment pathology can occur as either a
degenerative, traumatic or catastrophic condition and sometimes as
a result from a combination of factors. Degenerative conditions are
ones that occur over a period of time, normally 5 or 6 years but
can occur at an accelerated rate particularly with altered
mechanics related to spinal fusion. As a result the patient's head
and/or shoulder region(s) fall forward gradually over time.
Traumatic and catastrophic conditions occur as a generally sudden
shifting of the vertebral body immediately cephalad to the upper
end instrumented vertebra and can lead to sudden changes in spinal
alignment with marked symptoms noted by the patient.
[0010] Whether the condition is degenerative, traumatic, or
catastrophic, the exact cause of adjacent segment pathology is
uncertain. Without wishing to be bound by any hypothetical model,
it is generally believed that adjacent segment pathology and more
specifically PJK is a result of excess strain and stress on the
proximal instrumented spinal segment which is then at least
partially transferred to the bone structures, disc, ligaments and
other soft tissues, causing a loss of normal structural integrity
and mechanical properties. The resultant effect can be a forward
(i.e. kyphotic) shift of the adjacent non-instrumented vertebral
body. One such theory is that this strain and stress is caused by
suboptimal alignment and/or balance of the screw and rod construct.
Another theory is that the rigidity of the screw and rod construct
causes the problem in that the transition from a motion-restrained
segment to a motion-unrestrained segment is too much for the
non-instrumented (unrestrained) segment to handle over time. Yet
another theory speculates that the specific level at which the
proximal instrumented vertebra is located is of vital importance in
that some levels may be better suited to handle a proximal
termination of a fixation construct than others.
[0011] Thus there remains a need for continued improvements and new
systems for spinal fixation with a specific goal of preventing the
occurrence of or reducing the degree of adjacent segment pathology
and failures occurring at either the distal junction (DJK) or
proximal junction (PJK). The implants and techniques described
herein are directed towards overcoming these challenges and others
associated with posterior spinal fixation.
SUMMARY
[0012] The problems noted above, as well as potentially others, are
addressed in this disclosure by a system for spinal fixation with a
non-rigid portion at least one of the caudal or cephalad terminus.
Various devices and techniques are described for transition from a
rigid fixation construct to a less rigid support structure applied
to a "soft zone" that will help share the stress created on the
spinal levels caused by the fixed levels below. In specific
embodiments the soft zone is provided by terminating the construct
with one of a flexible tether or a dampening rod.
[0013] In a first aspect, a system for spinal fixation is provided
comprising: a first bone anchor, anchored to a first vertebra in a
subject, the first bone anchor comprising a first bone fastener
attached to a first rod housing; a rigid spinal rod seated in the
first rod housing to restrict translation of the rigid spinal rod
relative to the first bone anchor; a second bone anchor, anchored
to a second vertebra in the subject, the second bone anchor
comprising a second bone fastener attached to a second rod housing,
wherein the rigid spinal rod is seated in the second rod housing to
restrict translation of the rigid spinal rod relative to the second
bone anchor; and a compressible spinal connector, connected to the
second bone anchor, and anchored to a third vertebra in the
subject, the compressible spinal connector comprising a modulation
mechanism for modulating at least one of the tension on the
compressible spinal connector or the resistance to compression of
the compressible spinal connector, wherein said modulation occurs
in response to a remote signal.
[0014] In a second aspect, a spinal tether assembly for providing
non-rigid intervertebral support is provided, comprising: a
flexible tether; and an adjustable tensioner connected to exert
tension on the flexible tether, the adjustable tensioner comprising
a first magnet mounted to rotate in response to a spinning magnetic
field; and a tensioning mechanism configured to convert rotation of
the magnet to a decrease or increase of tension on the flexible
tether, depending on the direction of the first magnet's
rotation.
[0015] In a third aspect, a dampening spinal rod to adjust friction
against tension and compression is provided, comprising: an
elongate rigid portion for insertion into a bone anchor; a flared
portion for receiving a terminal end of a second spinal rod, the
flared portion comprising a rod cavity of sufficient diameter to
accept the second spinal rod, and a friction control mechanism
configured to modulate friction between the second spinal rod and
said dampening spinal rod in response to a remote signal.
[0016] In a fourth aspect, a method of fixing the relative
positions of a first vertebra and a second vertebra in a subject is
provided, the method comprising: anchoring a first bone anchor to
the first vertebra, the first bone anchor comprising a first bone
fastener attached to a first rod housing; seating a rigid spinal
rod in the first rod housing to restrict translation of the rigid
spinal rod relative to the first bone anchor; anchoring a second
bone anchor to the second vertebra, the second bone anchor
comprising a second bone fastener attached to a second rod housing,
seating the rigid spinal rod in the second rod housing to restrict
translation of the rigid spinal rod relative to the second bone
anchor; connecting a compressible spinal connector to the second
bone anchor, the compressible spinal connector comprising a
modulation mechanism for modulating at least one of the tension on
the compressible spinal connector or the resistance to compression
of the compressible spinal connector, wherein said modulation
occurs in response to a remote signal; anchoring the compressible
spinal connector to a third vertebra in the subject; and
transmitting the remote signal to the modulation mechanism
post-operatively, to cause said modulation to occur.
[0017] The above presents a simplified summary in order to provide
a basic understanding of some aspects of the claimed subject
matter. This summary is not an extensive overview. It is not
intended to identify key or critical elements or to delineate the
scope of the claimed subject matter. Its sole purpose is to present
some concepts in a simplified form as a prelude to the more
detailed description that is presented later.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1. An example of a spinal fixation system.
[0019] FIG. 2. A side view of an embodiment of the dampening spinal
rod as part of a larger fixation system, showing only the skeletal
system of the subject.
[0020] FIG. 3. A dorsal (anterior) view of an embodiment of the
spinal fixation system's terminal region having multiple soft
connections.
[0021] FIG. 4. A perspective view of an embodiment of a tensioner
that modules the tension on a flexible tether.
[0022] FIG. 5. An embodiment of a locking mechanism for locking a
tensioner.
[0023] FIG. 6. A cross-sectional view of an embodiment of a
telescoping spinal rod.
[0024] FIG. 7. An embodiment of a turnbuckle tensioner for
modulating the tension on a flexible tether.
[0025] FIG. 8. A dorsal (anterior) view of an embodiment of the
spinal fixation system's terminal region having multiple soft
connections.
[0026] FIG. 9. A top view of an embodiment of the external control
device.
DETAILED DESCRIPTION
[0027] Illustrative embodiments of a system for spinal fixation,
parts, and methods for use thereof, are described below. In the
interest of clarity, not all features of an actual implementation
are described in this specification. It will of course be
appreciated that in the development of any such actual embodiment,
numerous implementation-specific decisions must be made to achieve
the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure. The system for spinal fixation, parts, and methods for
use thereof disclosed herein boasts a variety of inventive features
and components that warrant patent protection, both individually
and in combination.
[0028] This disclosure describes a variety of transitional or
terminal components that may be implanted as part of a spinal
fixation construct 5 to decrease the potential for subsequent
development of junctional disease or failure. In the examples shown
only the cephalad most level (for terminal hardware) or levels (for
multilevel transitional hardware) of the fixation construct 5 (e.g.
those utilizing the exemplary components described herein) are
illustrated. It should be appreciated, however, that the entire
fixation construct 5 may extend any number of levels from a single
level construct to a long construct spanning multiple spinal levels
and multiple spinal regions from the lumbosacral to cervical
regions (such as the example construct illustrated in FIG. 1), and
with any variety of combinations of known anchors, rods, and
connectors. It should also be appreciated that the exemplary
terminal and/or transitional components may additionally or
alternatively be utilized at the caudal end of the fixation
construct. Moreover, although the vertebral fixation systems 5
described herein may be used along any aspect of the spine (e.g.
anterior, posterior, antero-lateral, postero-lateral) they are
particularly suited for implantation along a posterior aspect of
the spine.
[0029] A general embodiment of the system comprises a first bone
anchor 10, anchored to a first vertebra in a subject, the first
bone anchor 10 comprising a first bone fastener 15 attached to a
first rod housing 20. A rigid spinal rod 25 is seated in the first
rod housing 20 to restrict translation of the rigid spinal rod 25
relative to the first bone anchor 10. The rigid spinal rod 25 is
seated in the rod housing 35 of a second bone anchor 30, anchored
to a second vertebra in the subject, so as to restrict translation
of the rigid spinal rod 25 relative to the second bone anchor 30. A
compressible spinal connector 40 is connected to the second bone
anchor 30 and anchored to a third vertebra in the subject. The
compressible spinal connector 40 has a modulation mechanism 45 for
modulating either the tension on the compressible spinal connector
40 or its resistance to compression (or both). The modulation
occurs in response to a remote signal. Consequently modulation of
the tension and/or resistance to compression does not require
access to the device 5 through the patient's tissues, and may be
performed post-operatively. The remote signal may be, for example,
an electromagnetic signal. A specific example of the remote signal
is a spinning magnetic field.
[0030] FIG. 1 illustrates an example of a vertebral fixation system
5 of the type that is used with the devices and methods described
in this disclosure. By way of example, the illustrated vertebral
fixation system 5 is a screw-and-rod construct adapted for
implantation along the posterior aspect of the human spinal column.
The vertebral fixation system 5 includes a pair of elongate rods
(50a, 50b) dimensioned to span multiple vertebral levels, a
plurality of threaded bone anchors 55, a plurality of hook-type
bone anchors 60, and a plurality of transverse connectors 65
dimensioned to rigidly engage each of the elongate rods (50a, 50b)
so as to hold each rod (50a, 50b) in place relative to the other.
The transverse connectors 65 may be provided as fixed connectors or
adjustable connectors, in any quantity that is required by the
surgeon performing the implantation surgery. Proximal bone anchors
70 are provided at the proximal (cephalad) terminus of the assembly
5. Distal bone anchors 75 are provided at the distal (caudal)
terminus of the assembly 5. It is contemplated that any of the
examples of bone anchors and other transition assemblies described
herein may be substituted for the cephalad bone anchors 70 and/or
caudal bone anchors 75 which are traditionally rigid and identical
to the other bone anchors used throughout the construct 5. It is
also contemplated that the examples of flexible or compressible
transition segments 80 described herein may replace existing
hardware at the cephalad and/or caudal terminus of the vertebral
fixation system 5 such that there is no additional surgical
footprint realized. It is further contemplated that the examples of
flexible or compressible transition segments 80 described herein
may augment existing hardware at the cephalad and/or caudal
terminus of the vertebral fixation system 5 such that there is
additional added surgical footprint realized. This may be more
applicable with the various embodiments that can be installed with
minimal disruption of additional muscle tissue and/or ligament
structure. Finally, as previously noted junctional disease or
failure can be a problem at either the cephalad or caudal terminus
(or both) of vertebral fixation systems 5. Therefore, although the
various examples disclosed herein may be described in terms of
cephalad terminus and proximal joint disease (for ease of
disclosure) it is to be understood that any of the example
embodiments are also applicable and may be used at the caudal
terminus of the vertebral fixation system 5 without deviating from
the scope of this disclosure. According to one example, a spinal
fixation construct 5, like that shown in FIG. 1, is applied to the
spinal levels to be fixed. Above the fixed levels a soft-zone is
created by applying non-rigid support elements 85 such as tethers
or adjustable rods that limit some motion and reduce stress, to the
levels of the soft-zone and above, while not inhibiting all motion.
The tension applied to the support elements 85 in the soft zone can
be adjusted post-operatively and non-invasively to account for
changing dynamics in the body, or for any other reason deemed
desirable.
[0031] The components in the system 5 are constructed from one or
more non-absorbable biocompatible materials. Specific examples of
such suitable materials include titanium, alloys of titanium,
steel, and stainless steel. Parts of the system 5 could conceivably
be made from non-metallic biocompatible materials, which include
aluminum oxide, calcium oxide, calcium phosphate, hydroxyapatite,
zirconium oxide, and polymers such as polypropylene. Interference
with the spinning magnetic field can be reduced by constructing one
or more portions of the system 5 from a nonmagnetic or weakly
magnetic material. Specific examples of such nonmagnetic
non-absorbable biocompatible material include titanium, alloys of
titanium, aluminum oxide, calcium oxide, calcium phosphate,
hydroxyapatite, zirconium oxide, and polymers such as
polypropylene. Examples of weakly magnetic materials include
paramagnetic materials and diamagnetic materials. In a specific
embodiment, the weakly magnetic material is austenitic stainless
steel.
[0032] The first, second, and third vertebrae may be adjacent or
non-adjacent to one another, in any combination. Thus it is
contemplated that the first vertebra will be adjacent to the
second, which will be adjacent to the third; the first vertebra
will be nonadjacent to the second, which will be adjacent to the
third; the first vertebra will be nonadjacent to the second, which
will be nonadjacent to the third; and that the first vertebra will
be adjacent to the second, which will be nonadjacent to the
third.
[0033] According to one example the non-rigid support structure 5
is created through the application of a compressible spinal
connector 40 in the form of one or more tether assemblies 95, such
as those shown in the exemplary embodiment in FIG. 3. In the tether
assembly 95 the modulation mechanism 45 is an adjustable tensioner
100 configured to vary the tension on a flexible tether 97. This
will control the tension between the second bone anchor 30 and the
third vertebra.
[0034] The tethers 97 may be attached between the fixation hardware
5 and the soft-zone (e.g. one or more non-fixed levels above),
and/or directly between the bone elements of one or more fixed
levels and the soft-zone, and/or between two or more of the
non-fixed levels in the soft-zone. The tether 97 may be formed of
any material suitable for medical use. For example, the tether 97
may be made from allograft tendon, autograft tendon, braided,
woven, or embroidered polyethylene, braided, woven, or embroidered
polyester, polyether ether ketone (PEEK), or polyetherketoneketone
(PEKK). In some instances the tether 97 may be formed of elastic
material. FIG. 3 depicts multiple tethers 97 applied to the spine
in the soft zone and connected to the fixation construct 5 by
different connectors (e.g. an adjustable tension tether-rod
connector, adjustable tension cross-connector, and turnbuckle (FIG.
7)--these may be collectively referenced herein simply as
adjustable tension connectors 215). It will be appreciated that
while shown in use together, either of these connectors 215 may
also be used on their own. and in any configuration desired. In
use, once the tethers 97 are connected to the fixation construct 5
and the tether 97 coupled to the desired bone structure (or other
bone connection element) the tension on the tether 97 can be
adjusted. Later, the tension on the tether 97 can be adjusted
post-operatively as desired using an external device 155.
[0035] A specific example of the adjustable tensioner 100 is a
turnbuckle 105 comprising a threaded first end coupler 110, a
second end coupler 115, and a rotatable magnet 120 that rotates in
response to a spinning magnetic field and that is connected to the
threaded first end coupler 110 to cause the threaded first end
coupler 110 to rotate about its longitudinal axis when the
rotatable magnet 120 rotates. An embodiment of such a turnbuckle
105 is shown in FIG. 7. The illustration is a cross-section of the
turnbuckle 105, showing a cylindrical magnet 125 oriented to rotate
around its longitudinal axis when exposed to a spinning magnetic
field in the right orientation. The threaded first end coupler 110
in the illustration is a hook 130 with a threaded shank 135. The
threaded shank 135 runs through a threaded channel 140 in the
housing 145 of the turnbuckle 105, which translates rotation of the
shank 135 into translation of the hook 130. Alternatively, the
magnet 125 itself may contain one or more threaded passages 150
that are engaged with the threaded shank(s) 135. As a result the
hook 130 can be extended or retracted by rotating the shank 135. In
some embodiments of the turnbuckle 105 both end couplers (110, 115)
are hooks (130a, 130b) with threaded shanks 135, the threads
oriented such that when the rotatable magnet 125 rotates in a given
direction the two hooks (130a, 130b) translate in opposite
directions (i.e., they either converge or diverge along their
shared longitudinal axis). When the hooks (130a, 130b) are caused
to converge, it will increase tension on the connected spinal
physiology.
[0036] As pictured in FIG. 7, the turnbuckle 105 can be attached to
the spinous process or lamina of two adjacent vertebrae (either
directly, or via tethers looped around the lamina or spinous
process), and the tension between the vertebrae can be adjusted
post-operatively and non-invasively using the external adjustment
device 155 to rotate the turnbuckle magnet 120. Though shown only
across a single level, turnbuckles 105 could be used at multiple
levels. According to one example the turnbuckles 105 can be used
selectively to set the tension differently at each level. By way of
example, the tension can start out higher closest to the fixed
spinal levels, and be sequentially decreased over a series of
levels through the soft-zone. In some embodiments of the system a
pair of turnbuckles (105a, 105b) is used bilaterally and coupled to
tethers 97 looped around the lamina and the superior and inferior
coupled vertebrae. A distraction device 160 is also positioned
between the spinous processes of the same level. It is contemplated
that the distraction device 160 could use a magnetically driven
expansion device (such as one utilizing a lead screw coupled to a
magnet, similar to that described below, to create linear
expansion). This way, both flexion and extension could be
effectively controlled, and adjusted post-operatively. Taking it a
step further, the addition of a rotatable element 220 within the
disc to allow the vertebrae to rotate relative to each other, could
facilitate scoliosis correction in both the sagittal and coronal
planes using the adjustable turnbuckle 105 and distraction devices
160.
[0037] Another embodiment of the adjustable tensioner 100 is a
spool 165 about which the flexible tether 97 is wound, and wherein
rotation of a spool magnet 170 drives rotation of the spool 165. An
example of such an embodiment is shown in FIG. 4, and the remaining
description in this paragraph refers to this example. The spool 165
is connected to a body 175 having a rod passage 180 that couples to
the rod 50. A setscrew 205 or other element may be used to lock the
body 175 to the rod 50. The spool 165 is rotatably connected to the
body 175. The tether 97 is attached to the spool 165 such that when
the spool 165 rotates the tether 97 is wound up on the spool 165 to
create tension. A first end 185 of the tether 97 may be attached to
the spool 165 with the second end 190 being otherwise attached to
the target bone, another adjustable connector, or to itself (e.g.
creating a loop that can be attached to the target bone, or both
ends of the tether (185, 190) may be coupled to the spool 165
creating a loop to attach to or around the bone such that both ends
of the tether (185, 190) are spooled up together). The spool magnet
170 can be driven by application of a magnetic field to rotate the
spool 165. The spool magnet 170 may be a single cylindrical magnet
poled north and south across its diameter to form two 180 degree
sectors, as in FIG. 4. Alternatively, a quadrupole or multipole
magnet may be used. The spool 165 may include a locking mechanism
195, such as a spool 165 and ratchet mechanism 200, to maintain the
tension applied. The locking mechanism 195 may be externally
controlled similar to the spool magnet 170 such that it can be
locked and unlocked if adjustment is needed. According to one
embodiment, the locking mechanism 195 may be a set screw 205
situated to inhibit rotation of the spool 165 when engaged. The set
screw 205 may be a magnetically driven set screw 225, oriented such
that the external drive controller 155 can be positioned to drive
only one of the set screw 205 and drive magnet 230, and then
prepositioned to drive the other. Alternatively, a locking pin or
shaft could be advanced with the set screw 205 to inhibit rotation
of the spool 165. In an alternative embodiment shown in FIG. 5, the
magnet 230 may drive a gear assembly 380 that rotates two opposing
ratchet wheels through 385 which the tether 97 is passed.
[0038] Another embodiment of the compressible spinal connector 40
is a dampening rod 235. The dampening rod 235 is a rod that is both
expandable and compressible, and the resistance to expansion and
compression is controlled by means of the modulation mechanism 45.
The modulation mechanism 45 in this embodiment may take the form of
a friction brake 240. The dampening rod 235 accommodates dynamic
travel or length adjustment of the rod 235 between the fixed
connectors 390. The friction brake 240 can include a set screw 205
that is itself magnetic, or connected to a magnet ("brake magnet")
245 that may be controllable via an external adjustment device 155.
The degree of tension and support provided by the dampening rod 235
can be controlled by increasing or decreasing friction with the set
screw 205. Some embodiments of the friction brake 240 can also lock
down the rod 235 entirely, to prevent any expansion or compression,
should it later become necessary to fix one or more levels in the
soft-zone. An embodiment of the dampening rod 235 is shown in FIG.
2. In that embodiment, each rod 235 has a wider bell region 395 and
a narrower tail region 400. The tail 400 is about the diameter of
an ordinary spinal rod. The bell 395 is open on the inside, and is
dimensioned to accommodate a spinal rod (or the tail of another
dampening rod 235). As shown in FIG. 2, the friction brake 240 may
be, for example, a set screw 205 in a threaded channel 405
positioned to exert compressive force on a spring 250, said spring
250 positioned to exert compressive force against both the
compression and expansion of the dampening rod 235. The
illustration in FIG. 2 shows the spring 250 positioned to exert
compressive force on the tail portion 400 of an adjacent dampening
rod 235. The spring 250 in FIG. 2 is a wave spring 410, although
other kinds of springs (e.g., helical) are contemplated as well.
The set screw 205 may be magnetic (225), or coupled to a magnet,
such that a rotating magnetic field in the proper orientation will
cause the set screw 225 to rotate, either increasing or decreasing
the compressive force that exerts the friction.
[0039] A telescoping rod 255 may also be employed in the system.
The telescoping rod 255 may be implanted at levels above a fixation
construct 5 in patients that are at high risk of developing PJK or
other adjacent segment diseases. The rods 255 may be implanted as a
prophylactic and used if needed to extend the length for pain
relief. An example of the telescoping rod 255 is shown in FIG. 6.
As shown in that figure, the telescoping spinal rod 255 comprises a
rod magnet 260 configured to rotate when exposed to a spinning
magnetic field and cause the telescoping spinal rod 255 to either
extend or collapse depending on the direction of the spinning
magnetic field. The rod magnet 260 may be a cylindrical permanent
magnet (such as a ferrimagnet), but may be another type of magnet.
A first elongate element 265 contains a cavity 270, into which fits
a second elongate element 275. There may be a dynamic seal between
the first 265 and second elongated elements 275, to ensure that no
bodily fluids enter the construct. A thrust bearing may be included
to reduce friction between the spinning magnetic element and the
housing. The second elongate element 275 has an internally threaded
region 280 that is engaged to a lead screw 285 coupled to rotate
when the rod magnet 260 rotates, and comprising an externally
threaded region 290, such that rotation of the lead screw 285
causes the second elongate element 275 to translate relative to the
first elongate element 265. Thus, when the magnet 260 rotates, the
lead screw 285 will also rotate. The threaded interface between the
lead screw 285 and the second elongated element 275 will then cause
the second elongated element 275 to translate, with the
translational direction being dependent upon the rotational
direction of the magnet 260. The threads on the internally threaded
region 280 of the first elongate element 265 may be integral, or
they may be on the inner surface of another structure, such as a
threaded nut.
[0040] Whenever the adjustment mechanism is actuated by the
rotation of a magnet 120, as a safety precaution, a magnetic
immobilization plate 295 may be positioned sufficiently close to
the rotatable magnet 120 to cause the rotatable magnet 120 to
adhere to the immobilization plate 295 in the absence of a strong
external magnetic field. The magnetic immobilization plate 295 will
hold the rotating magnet 120 in position, preventing it from
rotating, until a stronger magnetic field is applied, such as the
rotating magnetic field that is used to adjust the modulation
mechanism 45. Like the rotating magnet 120, the immobilization
plate 295 may be constructed from a suitable magnetic material,
such as a ferromagnetic material. The immobilization plate 295 may
be used on its own, or in combination with a locking mechanism 195
as described above.
[0041] A specific embodiment of the system is shown in FIG. 3. In
that embodiment, the system 5 comprises a third bone anchor 300
(comprising a third bone fastener 305 and a third rod housing 310)
anchored to the first vertebra, and a fourth bone anchor 320
(comprising a fourth bone fastener 330 and a fourth rod housing
340) anchored to the second vertebra. A second rigid spinal rod is
25b seated in the third rod housing 310 and the fourth rod housing
340, running roughly parallel to the first rod 25a. A first
flexible tether 97a is at least partially wrapped around a spinous
process of the third vertebra and connected to both of the first
25a and second rigid spinal rods 25b to exert tension between the
third vertebra and the first 25a and second rigid spinal rods 25b.
The adjustable tether assembly 95 comprises a second flexible
tether 97b encircling the spinous process of the third vertebra and
a spinous process of a fourth vertebra, and a tensioner 350
connected to the first 25a and second 25b rigid spinal rods, the
tensioner 350 comprising a first magnet 355 mounted to rotate in
response to a spinning magnetic field, and a tether connection 360
configured to increase or decrease the tension on the second
flexible tether 97b depending on the direction of rotation of the
first magnet 355. The tensioner 350 extends or retracts the tether
connection 360 depending on the direction of the spinning magnetic
field, either reducing or increasing the tension respectively.
[0042] The system may be bilateral, in which the network of bone
anchors and rods is present on either side of the spine. Such a
bilateral system may comprise a second rigid spinal rod 25b seated
in an additional rod housing 365 of an additional bone anchor 370
that is anchored in at least one of the first and second vertebrae.
As shown in FIG. 1, one or more transverse connectors 65 fastened
to the first rigid spinal rod 25a and the second rigid spinal rod
25b may be present for additional stability.
[0043] Methods of using the system 5 to fix the relative positions
of a first vertebra and a second vertebra in a subject are
provided. In a general embodiment the method comprises anchoring a
first bone anchor 10 to the first vertebra, the first bone anchor
10 comprising a first bone fastener 15 attached to a first rod
housing 20; seating a rigid spinal rod 25a in the first rod housing
20 to restrict translation of the rigid spinal rod 25a relative to
the first bone anchor 10; anchoring a second bone anchor 30 to the
second vertebra, the second bone anchor 30 comprising a second bone
fastener 33 attached to a second rod housing 35; seating the second
rigid spinal rod 25b in the second rod housing 35 to restrict
translation of the rigid spinal rod 25b relative to the second bone
anchor 30; connecting a compressible spinal connector 40 to the
second bone anchor 30, the compressible spinal connector 40
comprising a modulation mechanism 45 for modulating at least one of
the tension on the compressible spinal connector 40 or the
resistance to compression of the compressible spinal connector 40,
wherein said modulation 45 occurs in response to a remote signal;
anchoring the compressible spinal connector 40 to a third vertebra
in the subject; and transmitting the remote signal to the
modulation mechanism 45 post-operatively, to cause said modulation
to occur. The system 5 may have any of the components and
arrangements described above. The compressible spinal connector 40
can be any described as suitable for the system above, including
any of the described embodiments of the tether assembly 95,
dampening rod 235, and telescoping rod 255.
[0044] An example of an external adjustment device 155 used to
non-invasively drive the adjustment mechanisms on the various
implants described herein is represented in FIG. 9. The external
adjustment device 155 is configured for placement on or adjacent to
the skin of the subject and appropriately aligned with the magnet
to be activated, and includes at least one drive magnet 230
configured for rotation. The external adjustment device 155 further
comprising a motor 375 configured to rotate the at least one drive
magnet 230, whereby rotation of the at least one drive magnet 230
of the external adjustment device 155 effectuates rotational
movement of one or more magnets (e.g., rotatable magnet in the
turnbuckle, magnetic set screw, etc). As shown in FIG. 9, the
external adjustment device 155 may have two magnets (230a, 230b).
The two magnets (230a, 230b) may be configured to rotate at the
same angular velocity. They may also be configured to each have at
least one north pole and at least one south pole (i.e., a dipole
magnet), and the external adjustment device 155 is configured to
rotate the first drive magnet 230a and the second drive magnet 230b
such that the angular location of the at least one north pole of
the first drive magnet 230a is substantially equal to the angular
location of the at least one south pole of the second drive magnet
230b through a full rotation of the first 230a and second 230b
drive magnets. More complex systems involving quadrupole and
multipole drive magnets are also contemplated, as is the use of one
or more electromagnets. The foregoing description illustrates and
describes the processes, machines, manufactures, compositions of
matter, and other teachings of the present disclosure.
Additionally, the disclosure shows and describes only certain
embodiments of the processes, machines, manufactures, compositions
of matter, and other teachings disclosed, but, as mentioned above,
it is to be understood that the teachings of the present disclosure
are capable of use in various other combinations, modifications,
and environments and is capable of changes or modifications within
the scope of the teachings as expressed herein, commensurate with
the skill and/or knowledge of a person having ordinary skill in the
relevant art. The embodiments described hereinabove are further
intended to explain certain best modes known of practicing the
processes, machines, manufactures, compositions of matter, and
other teachings of the present disclosure and to enable others
skilled in the art to utilize the teachings of the present
disclosure in such, or other, embodiments and with the various
modifications required by the particular applications or uses.
Accordingly, the processes, machines, manufactures, compositions of
matter, and other teachings of the present disclosure are not
intended to limit the exact embodiments and examples disclosed
herein. Any section headings herein are provided only for
consistency with the suggestions of 37 C.F.R. .sctn.1.77 and
related laws or otherwise to provide organizational queues. These
headings shall not limit or characterize the invention(s) set forth
herein.
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