U.S. patent application number 13/648061 was filed with the patent office on 2013-10-17 for methods and apparatus for locking a band.
This patent application is currently assigned to Simpirica Spine, Inc.. The applicant listed for this patent is Todd ALAMIN, Ian BENNETT, Louis FIELDING, Hugues MALANDAIN. Invention is credited to Todd ALAMIN, Ian BENNETT, Louis FIELDING, Hugues MALANDAIN.
Application Number | 20130274748 13/648061 |
Document ID | / |
Family ID | 41398568 |
Filed Date | 2013-10-17 |
United States Patent
Application |
20130274748 |
Kind Code |
A1 |
BENNETT; Ian ; et
al. |
October 17, 2013 |
METHODS AND APPARATUS FOR LOCKING A BAND
Abstract
A surgical fastening mechanism for releasably locking an
implantable tether includes a housing having a central channel. The
housing has an entry aperture, an exit aperture and a side channel
extending therebetween. A roller element has a sidewall with an
aperture therethrough and the roller is slidably disposed at least
partially in the central channel such that the entry and exit
apertures are at least partially aligned with the roller aperture.
This permits passage of the tether therethrough. Rotation of the
roller element in a first direction winds the tether around the
roller thereby creating a friction interface between the roller
element, the housing and the tether. A locking mechanism is
operably connected with either the housing or the roller element
and is adapted to prevent rotation of the roller in the central
channel and also adapted to prevent release of the tether from the
roller.
Inventors: |
BENNETT; Ian; (San
Francisco, CA) ; FIELDING; Louis; (San Carlos,
CA) ; MALANDAIN; Hugues; (Mountain View, CA) ;
ALAMIN; Todd; (Woodside, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BENNETT; Ian
FIELDING; Louis
MALANDAIN; Hugues
ALAMIN; Todd |
San Francisco
San Carlos
Mountain View
Woodside |
CA
CA
CA
CA |
US
US
US
US |
|
|
Assignee: |
Simpirica Spine, Inc.
San Carlos
CA
|
Family ID: |
41398568 |
Appl. No.: |
13/648061 |
Filed: |
October 9, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12479016 |
Jun 5, 2009 |
8308771 |
|
|
13648061 |
|
|
|
|
61059538 |
Jun 6, 2008 |
|
|
|
Current U.S.
Class: |
606/74 |
Current CPC
Class: |
A61B 17/7053 20130101;
A61B 17/82 20130101; A61B 17/7062 20130101; A61B 17/8869 20130101;
A61B 17/842 20130101 |
Class at
Publication: |
606/74 |
International
Class: |
A61B 17/82 20060101
A61B017/82 |
Claims
1. A method for releasably locking an implantable surgical tether,
said method comprising: advancing the tether through an aperture in
a housing; advancing the tether through an aperture in a roller
element, the roller element at least partially disposed in the
housing; rotating the roller element in a first direction so as to
retract the tether into the housing thereby creating friction
between the roller element and the housing; and releasably locking
the roller element in position relative to the housing.
2. The method of claim 1, further comprising threadably engaging
the roller with the housing.
3. The method of claim 1, wherein rotating the roller in a first
direction comprises rotating the roller approximately 180
degrees.
4. The method of claim 1, wherein rotating the roller comprises
rotating the roller a selected amount so as to retract a desired
length of the tether into the housing.
5. The method of claim 4, wherein the selected amount ranges from
about a 1/4 turn to about two full revolutions of the roller
element.
6. The method of claim 1, wherein rotating the roller element in a
first direction locks the tether in position relative to the
housing.
7. The method of claim 1, wherein rotating the roller element
comprises rotating a tool engaged with the roller element.
8. The method of claim 1, wherein rotating the roller element
retracts both a working end and a tail end of the tether inward
toward the roller.
9. The method of claim 1, wherein rotating the roller element
simultaneously locks the roller element in position.
10. The method of claim 1, wherein releasably locking the roller
element comprises placing a pin in the housing.
11. The method of claim 1, wherein releasably locking the roller
element comprises threadably engaging a set screw with the
housing.
12. The method of claim 1, wherein releasably locking the roller
element comprises threadably engaging the roller element with the
housing.
13. The method of claim 1, wherein releasably locking the roller
element comprises pressing the roller element into the housing
thereby creating a friction fit therebetween.
14. The method of claim 1, wherein releasably locking the roller
element comprises constraining longitudinal movement of the roller
element in a central channel of the housing, thereby also limiting
rotation of the roller element.
15. The method of claim 1, further comprising aligning the housing
aperture with the roller aperture to permit advancement of the
tether therethrough.
16. The method of claim 1, further comprising rotating the roller
element in a second direction opposite the first direction thereby
unwinding the tether from the roller element and reducing the
friction fit between the roller element, the tether and the
housing.
17. The method of claim 1, further comprising monitoring a position
indicator, the indicator indicating the relative position of the
roller with respect to the housing.
18. The method of claim 1, wherein the implantable tether comprises
a spinous process constraint device adapted to limit flexion
between adjacent spinous processes or between a spinous process and
a sacrum.
19. The method of claim 1, wherein the implantable tether comprises
a tether adapted to hold two or more anatomic structures
together.
20. The method of claim 1, wherein the roller element and the
housing are held together and are inseparable from one another
while the construct of the roller element and the housing is
undamaged.
21. The method of claim 1, further comprising maintaining the
tether in an undeformed configuration along planes in which the
tether lies.
22. The method of claim 21, further comprising deforming the tether
along a plane transverse to planes in which the tether lies.
23. The method of claim 1, wherein advancing the tether through the
aperture in the housing and advancing the tether through the
aperture in the roller element are performed in a single linear
motion.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of application
Ser. No. 12/479,016 (Attorney Docket Number: 41564-707.201), filed
Jun. 5, 2009, which claims the benefit of U.S. Provisional
application No. 61/059,538 (Attorney Docket Number: 41564-707.101)
filed Jun. 6, 2008, the entire contents of which are incorporated
herein by reference.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED
RESEARCH AND DEVELOPMENT
[0002] NOT APPLICABLE
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention generally relates to medical methods
and apparatus. More particularly, the present invention relates to
orthopedic internal fixation such as methods and devices for
restricting spinal flexion in patients having back pain or for
providing fracture fixation in long bone and trochanteric fractures
or other orthopedic applications where a tether may be
employed.
[0005] A major source of chronic low back pain is discogenic pain,
also known as internal disc disruption. Patients suffering from
discogenic pain tend to be young, otherwise healthy individuals who
present with pain localized to the back. Discogenic pain usually
occurs at the discs located at the L4-L5 or L5-S1 junctions of the
spine. Pain tends to be exacerbated when patients put their lumbar
spines into flexion (i.e. by sitting or bending forward) and
relieved when they put their lumbar spines into extension (i.e. by
standing or arching backwards). Flexion and extension are known to
change the mechanical loading pattern of a lumbar segment. When the
segment is in extension, the axial loads borne by the segment are
shared by the disc and facet joints (approximately 30% of the load
is borne by the facet joints). In flexion, the segmental load is
borne almost entirely by the disc. Furthermore, the nucleus shifts
posteriorly, changing the loads on the posterior portion of the
annulus (which is innervated), likely causing its fibers to be
subject to tension and shear forces. Segmental flexion, then,
increases both the loads borne by the disc and causes them to be
borne in a more painful way. Discogenic pain can be quite
disabling, and for some patients, can dramatically affect their
ability to work and otherwise enjoy their lives.
[0006] Pain experienced by patients with discogenic low back pain
can be thought of as flexion instability, and is related to flexion
instability manifested in other conditions. The most prevalent of
these is spondylolisthesis, a spinal condition in which abnormal
segmental translation is exacerbated by segmental flexion. The
methods and devices described should as such also be useful for
these other spinal disorders or treatments associated with
segmental flexion, for which the prevention or control of spinal
segmental flexion is desired. Another application for which the
methods and devices described herein may be used is in conjunction
with a spinal fusion, in order to restrict motion, promote healing,
and relieve pain post-operatively. Alternatively, the methods and
devices described should also be useful in conjunction with other
treatments of the anterior column of the spine, including
kyphoplasty, total disc replacement, nucleus augmentation and
annular repair. General orthopedic or surgical applications are
envisioned where a tether, cable or tape may be employed. An
example is trochanteric fracture fixation in which a cerclage
device is wrapped around the bone and is attached and tightened to
facilitate fracture healing. Similarly, the device may also be used
in conjunction with a cerclage device for the fixation of long bone
fractures.
[0007] Patients with discogenic pain accommodate their syndrome by
avoiding positions such as sitting, which cause their painful
segment to go into flexion, and preferring positions such as
standing, which maintain their painful segment in extension. One
approach to reducing discogenic pain involves the use of a lumbar
support pillow often seen in office chairs. Biomechanically, the
attempted effect of the ubiquitous lumbar support pillow is also to
maintain the painful lumbar segment in the less painful extension
position.
[0008] Current treatment alternatives for patients diagnosed with
chronic discogenic pain are quite limited. Many patients follow a
conservative treatment path, such as physical therapy, massage,
anti-inflammatory and analgesic medications, muscle relaxants, and
epidural steroid injections, but typically continue to suffer with
a significant degree of pain. Other patients elect to undergo
spinal fusion surgery, which commonly requires discectomy (removal
of the disk) together with fusion of adjacent vertebra. Fusion may
or may not also include instrumentation of the affected spinal
segment including, for example, pedicle screws and stabilization
rods. Fusion is not usually recommended for discogenic pain because
it is irreversible, costly, associated with high morbidity, and has
questionable effectiveness. Despite its drawbacks, however, spinal
fusion for discogenic pain remains common due to the lack of viable
alternatives.
[0009] An alternative method, that is not commonly used in
practice, but has been approved for use by the United States Food
and Drug Administration (FDA), is the application of bone cerclage
devices which can encircle the spinous processes or other vertebral
elements and thereby create a restraint to motion. Physicians
typically apply a tension or elongation to the devices that applies
a constant and high force on the anatomy, thereby fixing the
segment in one position and allowing effectively no motion. The
lack of motion allowed after the application of such devices is
thought useful to improve the likelihood of fusion performed
concomitantly; if the fusion does not take, these devices will fail
through breakage of the device or of the spinous process to which
the device is attached. These devices are designed for static
applications and are not designed to allow for dynamic elastic
resistance to flexion across a range of motion. The purpose of bone
cerclage devices and other techniques described above is to almost
completely restrict measurable motion of the vertebral segment of
interest. This loss of motion at a given segment gives rise to
abnormal loading and motion at adjacent segments, which can lead
eventually to adjacent segment morbidity.
[0010] Another solution involves the use of an elastic structure,
such as tethers, coupled to the spinal segment. The elastic
structure can relieve pain by increasing passive resistance to
flexion while often allowing substantially unrestricted spinal
extension. This mimics the mechanical effect of postural
accommodations that patients already use to provide relief.
[0011] Spinal implants using tether structures are currently
commercially available. One such implant couples adjacent vertebrae
via their pedicles. This implant includes spacers, tethers and
pedicle screws. To install the implant, selected portions of the
disc and vertebrae bone are removed. Implants are then placed to
couple two adjacent pedicles on each side of the spine. The pedicle
screws secure the implants in place. The tether is clamped to the
pedicle screws with set-screws, and limits the extension/flexion
movements of the vertebrae of interest. Because significant tissue
is removed and because of screw placement into the pedicles, the
implant and accompanying surgical methods are highly invasive and
the implant is often irreversibly implanted. There is also an
accompanying high chance of nerve root damage. Where the tip of the
set-screw clamps the tethers, the tethers are abraded and may
generate particulate debris.
[0012] Other implants employing tether structures couple adjacent
vertebrae via their processes instead. These implants include a
tether and a spacer. To install the implant, the supraspinous
ligament is temporarily lifted and displaced. The interspinous
ligament between the two adjacent vertebrae of interest is then
permanently removed and the spacer is inserted in the interspinous
interspace. The tether is then wrapped around the processes of the
two adjacent vertebrae, through adjacent interspinous ligaments,
and then mechanically secured in place by the spacer or also by a
separate component fastened to the spacer. The supraspinous
ligament is then restored back to its original position. Such
implants and accompanying surgical methods are not without
disadvantages. These implants may subject the spinous processes to
frequent, high loads during everyday activities, sometimes causing
the spinous processes to break or erode. Furthermore, the spacer
may put a patient into segmental kyphosis, potentially leading to
long-term clinical problems associated with lack of sagittal
balance. The process of securing the tethers is often a very
complicated maneuver for a surgeon to perform, making the surgery
much more invasive. And, as previously mentioned, the removal of
the interspinous ligament is permanent. As such, the application of
the device is not reversible.
[0013] More recently, less invasive spinal implants have been
introduced. Like the aforementioned implant, these spinal implants
are placed over one or more pairs of spinous processes and provide
an elastic restraint to the spreading apart of the spinous
processes during flexion. However, spacers are not used and
interspinous ligaments are not permanently removed. As such, these
implants are less invasive and may be reversibly implanted. The
implants typically include a tether and a securing mechanism for
the tether. The tether may be made from a flexible polymeric
textile such as woven polyester (PET) or polyethylene; multi-strand
cable, or other flexible structure. The tether is wrapped around
the processes of adjacent vertebrae and then secured by the
securing mechanism. The securing mechanism may involve the indexing
of the tether and the strap, e.g., the tether and the securing
mechanism include discrete interfaces such as teeth, hooks, loops,
etc. which interlock the two. Highly forceful clamping may also be
used to press and interlock the tether with the securing mechanism.
Many known implementations can clamp a tether with the tip of a
set-screw, or the threaded portion of a fastener. However, the
mechanical forces placed on the spinal implant are unevenly
distributed towards the specific portions of the tether and the
securing mechanism which interface with each other. These portions
are therefore typically more susceptible to abrasion, wear, or
other damage, thus reducing the reliability of these spinal
implants as a whole. Other known methods use a screw or bolt to
draw other components together to generate a clamping force. While
these methods may avoid the potentially damaging loads, the
mechanical complexity of the assembly is increased by introducing
more subcomponents. Other methods use a buckle through which the
tether is threaded in a tortuous path, creating sufficient friction
to retain the tether. These buckles generally distribute the load
over a length of the tether; although they may be cumbersome to use
and adjust as the tether is required to be threaded around multiple
surfaces and through multiple apertures. Many of the aforementioned
methods involve the use of several components, which must often be
assembled during the surgical procedure, often within the wound.
This adds time, complexity and risk to the surgical procedure.
[0014] For the aforementioned reasons, it would be desirable to
provide improved methods and apparatus to secure the tethers of
such spinal implants together. In particular, such methods and
apparatuses should be less invasive and should enable the tether to
be more easily, reversibly, repeatably, safely and reliably secured
to an implant by a surgeon, in a surgery setting.
[0015] 2. Description of the Background Art
[0016] Patents and published applications of interest include: U.S.
Pat. Nos. 3,648,691; 4,643,178; 4,743,260; 4,966,600; 5,011,494;
5,092,866; 5,116,340; 5,180,393; 5,282,863; 5,395,374; 5,415,658;
5,415,661; 5,449,361; 5,456,722; 5,462,542; 5,496,318; 5,540,698;
5,562,737; 5,609,634; 5,628,756; 5,645,599; 5,725,582; 5,902,305;
Re. 36,221; 5,928,232; 5,935,133; 5,964,769; 5,989,256; 6,053,921;
6,248,106; 6,312,431; 6,364,883; 6,378,289; 6,391,030; 6,468,309;
6,436,099; 6,451,019; 6,582,433; 6,605,091; 6,626,944; 6,629,975;
6,652,527; 6,652,585; 6,656,185; 6,669,729; 6,682,533; 6,689,140;
6,712,819; 6,689,168; 6,695,852; 6,716,245; 6,761,720; 6,835,205;
7,029,475; 7,163,558; Published U.S. Patent Application Nos. US
2002/0151978; US 2004/0024458; US 2004/0106995; US 2004/0116927; US
2004/0117017; US 2004/0127989; US 2004/0172132; US 2004/0243239; US
2005/0033435; US 2005/0049708; 2005/0192581; 2005/0216017; US
2006/0069447; US 2006/0136060; US 2006/0240533; US 2007/0213829; US
2007/0233096; Published PCT Application Nos. WO 01/28442 A1; WO
02/03882 A2; WO 02/051326 A1; WO 02/071960 A1; WO 03/045262 A1;
WO2004/052246 A1; WO 2004/073532 A1; and Published Foreign
Application Nos. EP0322334 A1; and FR 2 681 525 A1. The mechanical
properties of flexible constraints applied to spinal segments are
described in Papp et al. (1997) Spine 22:151-155; Dickman et al.
(1997) Spine 22:596-604; and Garner et al. (2002) Eur. Spine J.
S186-S191; Al Baz et al. (1995) Spine 20, No. 11, 1241-1244;
Heller, (1997) Arch. Orthopedic and Trauma Surgery, 117, No.
1-2:96-99; Leahy et al. (2000) Proc. Inst. Mech. Eng. Part H: J.
Eng. Med. 214, No. 5: 489-495; Minns et al., (1997) Spine 22 No.
16:1819-1825; Miyasaka et al. (2000) Spine 25, No. 6: 732-737;
Shepherd et al. (2000) Spine 25, No. 3: 319-323; Shepherd (2001)
Medical Eng. Phys. 23, No. 2: 135-141; and Voydeville et al (1992)
Orthop Traumatol 2:259-264.
BRIEF SUMMARY OF THE INVENTION
[0017] The present invention provides fastening mechanisms and
methods for releasably locking an implantable surgical tether.
Exemplary orthopedic applications include restricting flexion of at
least one spinal segment or securing broken bones together. More
particularly, the provided fastening mechanisms and methods relate
to improvements to the methods and devices of deploying and
implanting spinal implants for the treatment of discogenic pain and
other conditions, such as degenerative spondylolisthesis.
Specifically, such deployment and implantation methods are made
less invasive, easier to operate, and more reliable and reversible
by the provided fastening mechanisms and methods.
[0018] In a first aspect, the invention provides a surgical
fastening mechanism for releasably locking an implantable tether.
The mechanism comprises a housing, a roller element, and a locking
mechanism. The housing has a central channel therethrough and a
first side surface which defines and entry aperture and a second
side surface which defines an exit aperture. A side channel extends
between the entry and exit apertures. The roller element has a
sidewall defining an aperture therethrough. The roller element is
slidably disposed at least partially in the central channel such
that the entry and exit apertures are at least partially aligned
with the roller aperture so as to permit passage of the tether
therethrough. The rotation of the roller element in a first
direction winds the tether therearound, thereby creating a tortuous
or serpentine path in the tether, which generates friction between
the roller element, the housing and the tether. The locking
mechanism is operably connected with either the housing or the
roller element and is adapted to prevent rotation of the roller
within the central channel of the housing and also adapted to
prevent release of the tether from the roller. The tortuous path
created does not result in deformation of the strap within the
plane of the strap.
[0019] In various embodiments, the roller element may further
include various features. The roller element may be rotationally
disposed in the central channel or threadably engaged with the
housing. Threads on either the roller element or the housing may
further be partially deformed, thereby further securing the roller
element with the housing. The roller element may rotationally lock
the tether in position relative to the housing. The roller element
may comprise a driver feature. The driver feature is adapted to
receive a tool to permit rotation of the roller element. The driver
element may be, for example, a Phillips head, a slotted flat head,
a Torx head, or a hex head. The roller element may have a variety
of shapes. For example, it may be substantially cylindrically
shaped or eccentrically shaped. The fastening mechanism further may
comprise a pin coupled with the housing and the roller element may
comprise a groove adapted to receive the pin, thereby locking the
roller element with the housing. The roller element may comprise an
alignment feature that is adapted to limit rotation of the roller
relative to the housing. The housing may comprise a flange adapted
to retain the roller and/or locking elements. The roller element
may comprise an alignment feature adapted to align the roller
aperture with the first and second side apertures in the housing.
The alignment feature may be, for example, a pin or a shoulder. The
alignment feature may also be a feature of the housing that limits
travel of the roller. Although the purpose of the alignment feature
is to constrain rotation of the roller, it may directly limit
translation of the roller along its axis, for example when the
roller element is threadably engaged with the housing. If the
roller is threadably engaged with the housing, rotation of the
roller will also result in translation due to the threads.
Therefore directly constraining translation of the roller, e.g.
with a flange or other surface, the rotation of the roller will
also be constrained. This system may present advantages for
fabrication.
[0020] In some embodiments, the locking mechanism comprises a set
screw threadably engaged with the housing. Threads on either the
locking member or the housing may be partially deformed, thereby
further securing the locking mechanism with the housing. The set
screw may be engaged against the roller element. The set screw may
comprise a driver feature adapted to receive a tool to permit
rotation of the set screw. The driver feature may be, for example,
a Phillips head, a slotted flat head, a Torx head, or a hex head.
The driver feature on the set screw may comprise an aperture large
enough to permit access to the roller element with a tool for
rotation thereof while the set screw is threadably engaged with the
housing. The locking mechanism may be frictionally engaged with the
roller and/or the housing. The locking mechanism may be captively
retained, along with the roller, within the housing by a feature
such as a flange such that the entire fastening mechanism is an
inseparable assembly. The flange may be welded or press-fit to
create this inseparability. In other embodiments, the locking
mechanism may comprise a friction fit between the roller element
and the housing. In preferred embodiments, the housing, the roller
element and the locking mechanism are held together and are
inseparable from one another while the fastening mechanism is
undamaged.
[0021] In some embodiments, the fastening mechanism may comprise a
pin coupled with the housing. The locking mechanism comprises a
groove adapted to receive the pin, thereby locking the locking
mechanism with the housing. In other embodiments, a rotation
limiting element such as a pin or shoulder is coupled with the
housing and the locking mechanism has a receiver for receiving the
rotation locking element, thereby limiting rotation of the locking
mechanism relative to the housing. As for the roller, the rotation
of the locking element may be constrained by limiting translation
of the locking element along its axis. By limiting translation of a
threaded locking element, rotation of the element may also be
limited. The locking and roller elements may be in series with each
other, such that constraining translation and/or rotation of the
locking element thereby constrains translation and/or rotation of
the roller element such that at the limits of rotation of the
roller element, the aperture through the roller is aligned with the
entry and exit apertures of the housing. This facilitates direct
insertion of the tether through these apertures.
[0022] In still other embodiments, the housing may include various
features. The housing may comprise a flange adapted to retain the
locking element. The entry and exit apertures of the housing may be
shaped like rectangular slots. The housing may comprise an
alignment feature such as a pin or shoulder coupled with either the
housing or the roller element, adapted to align the roller aperture
with the entry and exit apertures in the housing. The entry and
exit apertures may be also be referred to as first and second side
apertures, respectively. The housing may have third and fourth
outer surfaces and the central channel may extend from the third
outer surface to the fourth outer surface.
[0023] The fastening mechanism may be configured so that the
rotation of the roller element may serve a variety of purposes. The
roller element may be rotated approximately 180 degrees in order to
create the friction interface. In other embodiments, the roller
element is adapted to be rotated a selected amount so as to retract
a desired length of the tether into the housing. The selected
amount may range from about 1/4 turn to about two full revolutions
of the roller element. The rotation of the roller element may
create a tortuous path for the tether as it passes between the
first and second side apertures. The rotation of the roller may
lock the tether so as to fix the tether's position relative to the
housing. The rotation of the roller may retract both a working end
and a tail end of the tether inward toward the roller. This may
retract an equal or different length of the tether's working end
compared to that of the tail end. The size of the roller may be
designed such that a specific, desired length of the tether is
retracted. The rotation of the roller element in a second direction
opposite of the first direction may unwind the tether therefrom,
thereby reducing the friction fit between the tether and the
fastening mechanism. The roller may be rotated by a variable amount
so that the length of tether that is retracted is controlled by the
operator. This further enhances the continuous adjustability of the
attachment mechanism.
[0024] In many embodiments, the fastening mechanism may further
comprise a position indicator adapted to provide visual, tactile or
audible feedback to an operator on the relative position of the
roller with respect to the housing. The position indicator may
comprise detents or calibration marks on either the housing or the
roller element and they may be radiopaque to permit visualization
under x-ray, fluoroscopy or other radiographic methods.
[0025] Preferably, the tether remains undeformed along planes in
which the tether lies and the tether is only deformed along a plane
that lies transverse to planes in which the tether lies such that
any curvature of the strap is around an axis parallel to the axis
of the roller, such that the tether is not required to be twisted
or bent. The tether often may comprise a spinous process constraint
device that is adapted to limit flexion between adjacent spinous
processes or between a spinous process and a sacrum. The tether may
also be used for other surgical applications such as to hold two or
more anatomic structures together, e.g. holding a fractured bone
together.
[0026] In another aspect, the invention provides a method for
releasably locking an implantable tether. The tether is advanced
through an aperture in a housing and through an aperture in a
roller element. The tether may be advanced through the housing and
the roller element in a single linear motion. The roller element is
at least partially disposed in the housing. The roller element is
rotated in a first direction so as to retract the tether into the
housing, thereby forming the tether into a tortuous path and
creating sufficient friction between the roller element and the
housing to retain the tether. The roller element is releasably
locked in position relative to the housing.
[0027] In various embodiments, the provided method may further
comprise various steps and/or features. The roller may be
threadably engaged with the housing. Rotating the roller in a first
direction may comprise rotating the roller approximately 180
degrees, may lock the tether in position relative to the housing,
may comprise rotating a tool engaged with the roller element,
and/or may retract both a working end and a tail end of the tether
inward toward the roller. Rotating the roller may also
simultaneously lock the roller. Rotating the roller may comprise
rotating the roller a selected amount so as to retract a desired
length of the tether into the housing. The selected amount may
range from about `A turn to about two full revolutions of the
roller element. Releasably locking the roller element may comprise
placing a pin in the housing, or it may comprise threadably
engaging a set screw with the housing. It may also comprise
threadably engaging the roller element with the housing, or it may
comprise manually overcoming a static friction between the roller
and housing. Releasably locking the roller element may comprise
pressing the roller element into the housing thereby creating a
friction fit. Longitudinal movement of the roller element in a
central channel of the housing may be constrained so as to also
limit rotation of a threaded roller element.
[0028] In some embodiments, the roller may be externally
controllable by a controller such as a radiofrequency
transcutaneous transmitter. This allows the patient or physician to
adjust the tether and fine tune the implant without requiring
additional surgery. Thus a patient may easily adjust the tether to
accommodate for different physical activities, body positions and
other factors that affect lower back pain.
[0029] The provided method may further comprise additional steps.
The housing aperture may be aligned with the roller aperture to
permit advancement of the tether therethrough. The roller element
may be rotated in a second direction opposite the first direction,
thereby unwinding the tether from the roller element and reducing
the friction fit between the roller element and the housing. A
position indicator may be monitored. The indicator indicates the
relative position of the roller with respect to the housing. All
components of the mechanism may be captively retained within the
housing, creating an inseparable assembly.
[0030] These and other embodiments are described in further detail
in the following description related to the appended drawing
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a schematic diagram illustrating the lumbar region
of the spine.
[0032] FIG. 1A a schematic illustration showing a portion of the
lumbar region of the spine taken along a sagittal plane.
[0033] FIG. 2 illustrates a spinal implant of the type described in
US 2005/0216017A1.
[0034] FIGS. 3A-3B illustrate additional tissue surrounding the
spinous processes.
[0035] FIGS. 4A-4M show an exemplary method of surgically
implanting a spinal device.
[0036] FIG. 5 illustrates an exemplary compliance element.
[0037] FIGS. 6A-6C illustrate the use of an exemplary fastening
mechanism incorporated in the compliance element for removably
locking a tether.
[0038] FIG. 7 is an exploded view of an exemplary fastening
mechanism.
[0039] FIGS. 8A-8B illustrate the use of a tether and a fastening
mechanism in trochanteric fracture fixation.
DETAILED DESCRIPTION OF THE INVENTION
[0040] FIG. 1 is a schematic diagram illustrating the lumbar region
of the spine including the spinous processes (SP), facet joints
(FJ), lamina (L), transverse processes (TP), and sacrum (S). FIG.
IA is a schematic illustration showing a portion of the lumbar
region of the spine taken along a sagittal plane and is useful for
defining the terms "neutral position," "flexion," and "extension"
that are often used in this disclosure.
[0041] As used herein, "neutral position" refers to the position in
which the patient's spine rests in a relaxed standing position. The
"neutral position" will vary from patient to patient. Usually, such
a neutral position will be characterized by a slight curvature or
lordosis of the spine where the spine has a slight anterior
convexity and slight posterior concavity. In some cases, the
presence of the constraint of the present invention may modify the
neutral position, e.g. the device may apply an initial force which
defines a "new" neutral position having some extension of the
untreated spine. As such, the use of the term "neutral position" is
to be taken in context of the presence or absence of the device. As
used herein, "neutral position of the spinal segment" refers to the
position of a spinal segment when the spine is in the neutral
position.
[0042] Furthermore, as used herein, "flexion" refers to the motion
between adjacent vertebrae in a spinal segment as the patient bends
forward. Referring to FIG. 1A, as a patient bends forward from the
neutral position of the spine, i.e. to the right relative to a
curved axis A, the distance between individual vertebrae L on the
anterior side decreases so that the anterior portion of the
intervertebral disks D are compressed. In contrast, the individual
spinous processes SP on the posterior side move apart in the
direction indicated by arrow B. Flexion thus refers to the relative
movement between adjacent vertebrae as the patient bends forward
from the neutral position illustrated in FIG. 1A.
[0043] Additionally, as used herein, "extension" refers to the
motion of the individual vertebrae L as the patient bends backward
and the spine extends from the neutral position illustrated in FIG.
1A. As the patient bends backward, the anterior ends of the
individual vertebrae will move apart. The individual spinous
processes SP on adjacent vertebrae will move closer together in a
direction opposite to that indicated by arrow B.
[0044] FIG. 2 shows a spinal implant of the type described in
related U.S. Patent Publication No. 2005/0216017 A1 (now U.S. Pat.
No. 7,458,981), the contents of which are herein incorporated by
reference. As illustrated in FIG. 2, an implant 10 typically
comprises an upper strap component 12 and a lower strap component
14 joined by a pair of compliance members 16. The upper strap 12 is
shown disposed over the top of the spinous process SP4 of L4 while
the lower strap 14 is shown extending over the bottom of the
spinous process SP5 of L5. The compliance member 16 will typically
include an internal element, such as a spring or rubber block,
which is attached to the straps 12 and 14 in such a way that the
straps may be "elastically" or "compliantly" pulled apart as the
spinous processes SP4 and SP5 move apart during flexion. In this
way, the implant provides an elastic tension on the spinous
processes which provides a force that resists flexion. The force
increases as the processes move further apart. Usually, the straps
themselves will be essentially non-compliant so that the degree of
elasticity or compliance may be controlled and provided solely by
the compliance members 16.
[0045] FIG. 3A is a side view of the lumbar region of the spine
having discs D separating the vertebral bodies V. The supraspinous
ligament SSL runs along the posterior portion of the spinous
processes SP and the interspinous ligament ISL and multifidus
tendon and muscle M run alongside of and attach to the spinous
processes SP. FIG. 3B is a posterior view of FIG. 3A.
[0046] FIGS. 4A-4M illustrate an exemplary surgical method of
implanting a spinous process constraint such as the embodiment of
FIG. 2. One of the first steps to surgically implant a spinal
implant is to make an incision to access the spinal area of
interest. FIG. 4A shows the lumbar region of back K after an
incision I has been made through the patient's skin. FIG. 4B
illustrates the lumbar region of the spine after the incision I has
been made through the patient's skin. Multifidus muscle and tendon
M have been retracted with retraction tools TR to expose the
spinous processes.
[0047] After the incision has been made, a piercing tool T having a
sharp distal end may be used to access and pierce the interspinous
ligament ISL while avoiding the supra spinous ligament SSL,
creating an interspinous ligament perforation P1 superior of the
first spinous process SSP of interest. This surgical approach is
desirable since it keeps the supra spinous ligament intact and
minimizes damage to the multifidus muscle and tendons and other
collateral ligaments. As shown in FIG. 4C, from the right side of
the spine, tool T accesses and pierces the interspinous ligament
ISL adjacent of the first spinous process SSP of interest. The
distal end of tool T is shown in dotted line. Alternatively, tool T
may access and pierce the interspinous ligament 1SL from the left
side instead. The distal end of tool T is coupled with tether 102,
parts of which are also shown in dotted line. In addition to
accessing and piercing the interspinous ligament ISL, piercing tool
T also advances or threads tether 102 through perforation P1. As
shown in FIG. 4D, tool T is then removed, leaving tether 102
positioned through perforation P1. Multifidus tendon and muscle M
is not shown in FIGS. 4C and 4D so that other elements are shown
more clearly.
[0048] FIG. 4E is a posterior view of a section of the spine after
the above steps have been performed. Often times, the distal tip TI
of tool T is detachable. As shown in FIG. 4E, after tool T accesses
and pierces the interspinous ligament ISL with distal tip TI,
distal tip TI is detached from tool T and is left in place in
perforation P1 (shown in dotted line) above the first spinous
process SSP of interest. Tether 102 lags behind tip TI. In some
cases, distal tip TI may fully pierce through interspinous ligament
ISL. In these cases, distal tip TI has passed through the
interspinous ligament ISL while a portion of tether 102 is left in
place in perforation P1.
[0049] After tip TI or a portion of tether TH is left in place in
perforation P1, another tool may couple with tip TI and pull tip TI
such that it drags tether 102a and compliance element 104a to its
appropriate position relative to the spine, as shown in FIG. 4F.
Compliance element 104a is coupled to tether 102a and is used to
provide a force resistive to flexion of spinous processes SP.
Compliance element 104a includes a fastening mechanism or fastening
element 106a and may further comprise a spring, a tensioning
member, a compression member, or the like. Related compliance
members are described in commonly owned U.S. patent application
Ser. No. 12/106,103 (Attorney Docket No. 026398-000410US), the
entire contents of which are incorporated herein by reference.
[0050] The steps of accessing the 1SL, piercing the 1SL, and
threading tether 102 through a perforation are then repeated for
the opposite, lateral side of the spine for an adjacent spinous
process ISP, inferior of the first superior spinal process SSP of
interest. As shown in FIGS. 4G and 4H, tool T accesses the
interspinous ligament from the left side of the spinal midline and
pierces the interspinous ligament ISL, creating a second
perforation P2 located inferior of a second spinous process of
interest, labeled as inferior spinous process ISP. As shown in FIG.
4G, the inferior spinous process ISP of interest is directly
adjacent to and inferior of the first superior spinous process SSP
of interest. However, it is entirely possible to perform the
described procedure starting with the inferior spinous process ISP
first instead of the superior spinous process SSP, for example,
perforation P2 may be created before perforation P1. It is also
possible that there may be a gap of one or more spinous processes
SP between the spinous processes of interest. Multifidus tendon and
muscle M is not shown in FIGS. 4G and 4H for clarity of the other
shown elements.
[0051] As shown in FIGS. 4H, 4I and 4J, like with the steps shown
in conjunction with the first piercing, tether 102b is pierced
through perforation P2 and left in place along with distal tip TI
of tool T (best seen in FIG. 41). Another tool such as a pair of
forceps, is then used to grasp distal tip TI to pull tether 102b
and compliance element 104b in place relative to the spine, as
shown in FIG. 4J. Opposing compliance members 104a and 104b on
opposite sides of spinous processes SP are oriented in opposite
directions. Each compliance element 104a, 104b is coupled with
their respective tether 102a, 102b and has a respective fastening
mechanism or fastening element 106a, 106b. Fastening mechanism
106a, 106b are configured to couple with the tether 102a, 102b of
the opposing compliance member 104a, 104b. For example as shown in
FIG. 4K, tether 102a is advanced through compliance member 104b and
is coupled with fastening mechanism 106b while tether 102b is
advanced through compliance member 104a and is coupled with
fastening mechanism 106a. Except for their orientation, compliance
members 104a and 104b are identical. One of skill in the art will
appreciate that the tether may enter and exit the fastening
mechanism in a number of different directions and configurations,
and FIG. 4K merely is one exemplary embodiment.
[0052] Fastening mechanism 106 may comprise a driver feature 108.
As shown in FIG. 4L, the driver feature is adapted to receive a
rotating driver tool RT. The driver feature may be a Phillips head,
a slotted flat head, a Torx head, a hex head, or the like. Rotation
of tool RT, which may be either clockwise or counter-clockwise,
changes the configuration of fastening mechanism 106 so as to lock
and secure tether 102 in place. This forms a continuous,
multi-component tether structure or constraint 110 which couples
two spinous processes SP together, as shown in FIG. 4M. Compliance
elements 104a, 104b are used to control flexion between spinous
processes SP while tethers 102a, 102b and respective fastening
mechanisms 106a, 106b contribute to coupling the spinous processes
SP together. Depending on the location of the perforations P1 and
P2 and the lengths of the compliance elements 104a, 104b,
constraint 110 may couple more than two spinous processes SP
together. In general, compliance elements 104a, 104b comprise
spring-like elements which will elastically elongate as tension is
applied through tethers 102a, 102b in an axis generally parallel to
the spine. As the spinous processes or spinous process and sacrum
move apart during flexion of the constrained spinal segment, the
superior tether 102a and inferior tether 102b will also move apart.
Compliance elements 104a, 104b each include spring-like elements
which will elastically resist the spreading with a force determined
by the mechanical properties of the spring-like element. Thus,
constraint 110 provides an elastic resistance to flexion of the
spinal segment beyond the neutral position. Constraint 110 is often
configured to provide a resistance in the range from 7.5 N/mm to 20
N/mm but the resistance may be below 3 N/mm or even below 0.5 N/mm.
Constraint 110 may also be adjustable in certain dimensions to
allow tightening over the spinous processes or spinous process and
sacrum when the spinal segment is in a neutral position. Other,
related tether embodiments and joining methods are disclosed in
U.S. patent application Ser. No. 12/106,103 (Attorney Docket No.
026398-0004 IOUS), U.S. Patent Publication No. 2008/0009866
(Attorney Docket No. 026398-000140US), U.S. Patent Publication No.
2008/0108993 (Attorney Docket No. 026398-000150US), U.S. patent
application Ser. No. 12/106,049 (Attorney Docket No.
026398-000151US) and U.S. Provisional Patent Application No.
60/936,897 (Attorney Docket No. 026398-000400US), each of which,
the entire contents are incorporated herein by reference.
[0053] FIG. 5 illustrates an exemplary embodiment of a spring-like
element 50 of compliance member 104a, 104b. Spring-like element 50
is generally similar to the springlike elements disclosed in
related, co-assigned U.S. patent application Ser. No. 12/106,103,
the entire contents of which are incorporated herein by reference.
Fastening mechanism 106 having a driver feature 108 is housed
within spring-like element 50. Element 50 comprises a housing
having a helical groove machined in the housing body to form the
spring-like element. Element 50 includes an adjustable tether
connector 52 and a fixed tether connector 54, both of which are
preferably formed integrally or monolithically with the helical
spring structure 51. Typically, the helical spring structure 51 and
coupling portions of both tether connectors 52 and 54 will be
formed from one piece of material, usually being a metal such as
titanium, but optionally being a polymer, ceramic, reinforced glass
or other composite, or other material having desired elastic and
mechanical properties and capable of being formed into the desired
geometry. In a preferred embodiment, spring-like element 50 is
machined or laser cut from a titanium rod. Alternatively, a
suitable polymeric material will be polyetherether ketone (PEEK).
Other features may be built into the spring-like element 50, such
as a stress relief hole 56. Components that compose the adjustable
tether connector may potentially include a roller and a lock-nut;
such components could be made from the same material as the element
50 and adjustable tether connector (e.g. titanium components if the
spring-like element 50 is titanium), or they could be made from a
different material (e.g. injection molded PEEK). The exterior of
the spring-like element 50 may be covered with a protective cover,
such as a sheath fabricated from an elastomer, polymer or other
suitable material. The sheath may be placed over the body of the
spring-like element 50 in order to prevent the intrusion of tissue
and body fluids into the spaces between the turns of the coil and
interior of the element.
[0054] FIG. 6A shows a cross-section of spring-like element 50
having tether 102 locked therein. Tether 102 enters and exits the
housing 58 of fastening mechanism 106 through entry aperture 53,
then it passes through central channel 55, winds around roller 60
and the inside surface of housing 58, and finally exits through
exit aperture 57. Roller 60 is housed within central channel 55 and
is rotatable within tension element 50. Roller 60 is often
substantially cylindrically shaped but may also have other shapes,
for example, an eccentric shape. A round symmetrical roller will
allow the tether 102 to spool evenly from both the working end and
the tail end of the tether 102, while an eccentrically shaped
roller will result in uneven spooling. The housing 58 of fastening
mechanism 106 may be formed integrally with spring-like element 50
or may be separate.
[0055] During a procedure similar to the one described with
reference to FIGS. 4A-4M, tether 102 is advanced through top
aperture 53, central channel 55 and roller 60, and out through
bottom aperture 57. As shown in FIG. 6B, top aperture 53, central
channel 55, and bottom aperture 57 are aligned so permit easy
passage of tether 102 therethrough. Roller 60 includes two side
apertures 60a, 60b. Prior to the locking of the tether, entry
aperture 53, side apertures 60a and 60b and exit aperture 57 are
all aligned along a common axis. To provide such alignment, roller
60 may include an alignment feature such as a pin or shoulder.
Thus, the roller 60 may be rotated until stopped by the pin or
shoulder, thereby ensuring alignment of all the apertures. Once
tether 102 is advanced through, roller 60 is rotated, via driver
feature 108, thus creating a friction-based interference fit
between roller 60, the inside surface of the housing and the tether
102. As shown in FIG. 6C, the fastening mechanism is rotated
approximately 180.degree. to create this fit. The rotation of the
roller creates a tortuous path for the tether as it passes between
side apertures 60a, 60b. The rotation may retract the working end
102w and tail end 102t of tether 102, sometimes of different
lengths, inward toward roller 60. Offsetting roller 60 from its
axis of rotation by using an eccentrically shaped roller changes
the amount of tether drawn from either side. The roller may also be
rotated a selected amount in order to draw a desired amount of the
tether into the roller. For example, the roller may be rotated from
about `/4 turn to two or more complete revolutions. Thus, not only
will the locking mechanism secure the tether in position, but it
may also be used to help adjust length or tension of the
tether.
[0056] A friction-based interference fit is advantageous because
the range along the tether to which the mechanism can attach is
continuous, rather than in discrete increments of non-friction
mechanisms such as teeth, hooks, loops, and the like. Thus, forces
between roller 60 and tether 102 are distributed along a longer
portion of tether 102. Additionally, high clamping forces are not
required. Thus, the risk that any specific point of contact will
abrade, wear, or will otherwise be damaged is minimized.
Furthermore, in contrast with other mechanisms that require high
clamping forces, the discrete rotation of a tool is easier and more
repeatable to perform during surgery.
[0057] After the tether is secured, roller 60 is then locked in
place. Various means may be provided to lock roller 60 in place
within housing 58. Roller 60 and/or the inner surface of housing
108 may include male or female threads which engage the two
elements together. The threads may be partially deformed, thereby
helping to secure the roller element with the housing.
Alternatively, a pin 73 may be coupled to housing 58 and roller 60
may comprise a groove adapted to receive pin 73. Another
possibility is that housing 58 may include a flange adapted to
retain roller 60. A set screw as described below with reference to
FIG. 7 may also be provided to lock roller 60 in place. Rotation of
roller 60 in the opposite direction unwinds tether 102 from roller
60 and reduces the interference fit. Roller 60 and/or housing 58
may further include a position indicator, such as detents or
calibration marks, to provide visual, tactile, or audible feedback
to an operator on the relative position of the roller with respect
to housing 58.
[0058] FIG. 7 shows an exploded view of an exemplary fastening
mechanism 70 that uses a locking set screw 75 to lock roller 76 in
place. Roller 71 is generally similar to roller 60. It is
positioned within housing 76 and includes slots 72 for a tether to
be advanced through. Roller 71 has threads 78 on one end that may
be threadably engaged with the housing 76. Roller 71 also has a
shoulder 74 and includes driver features 77. Shoulder 74 is adapted
to be engageable with locking set screw 75 and housing 76. After
roller 71 has been rotated to lock and secure a tether in place,
set screw 75 is set in a position to engage roller 71 with housing
76 and hold it in position relative to housing 76. Shoulder 74, set
screw 75, and/or housing 76 have threads to allow such engagement.
The threads may be partially deformed, thereby further securing the
locking member with the housing. The threads prevent the roller 71
from unrolling thereby allowing release of the tether. Set screw 75
may comprise driver features 79 to allow rotation of the set screw.
Driver features 77 of roller 71 and driver features 79 of set screw
75 each are adapted to receive a tool so as to permit rotation
thereof. The driver features 77, 79 may be a Phillips head, a
slotted flat head, a Torx head, a hex head, or the like. Driver
features 79 of set screw 75 may comprise an aperture large enough
to permit access to roller 71 with a tool permit rotation of roller
71 with a tool while set screw 75 is engaged with housing 76. An
optional end cap 81 having a central aperture 80 may be positioned
adjacent the set screw 75 and welded, bonded or otherwise affixed
to the outer rim 82 of the housing 76 so as to capture all the
components forming an inseparable assembly. The aperture 80 is
sized to allow access to rotation of the set screw. This is
desirable since it prevents parts from falling out during use and
also provides a device which is easier to use since assembly is not
required. In preferred embodiments, the assembly may not be
disassembled without breaking or otherwise damaging the device. In
other embodiments, the assembly may be disassembled without
damaging the device.
[0059] One advantage of the roller locking mechanisms disclosed
herein is that the tether is not deformed in planes in which it
lies. The tether may be folded or rolled in a plane transverse to
the planes in which it lies. This is desirable since it minimizes
the possibility of twisting or tangling of the tether and also
reduces wear and tear.
[0060] While the exemplary embodiments described above illustrate a
fastening mechanism that is coupled with a spring-like compliance
member, one will appreciate that the fastening mechanism may be
used independently of a spring or other internal fixator. Other
uses may include applications where a tether is secured with a
knot, crimped or the like. These may include cerclage applications
such as in trochanteric fixation in addition to application of a
substantially rigid tether to multiple spinous processes or lamina.
FIGS. 8A-8B illustrate the use of a tether and fastening mechanism
for trochanteric fixation. FIG. 8A shows a tether T wrapped around
the trochanter of a femur F. A fastening mechanism FM releasably
locks one end of the tether T, thereby forming a closed loop around
the trochanter. FIG. 8B highlights the tether wrapped around the
trochanter.
[0061] While the above is a complete description of the preferred
embodiments of the invention, various alternatives, modifications,
and equivalents may be used. Therefore, the above description
should not be taken as limiting the scope of the invention which is
defined by the appended claims.
* * * * *