U.S. patent application number 14/732633 was filed with the patent office on 2016-05-26 for methods and apparatus for coupling a prosthesis to a spinal segment.
The applicant listed for this patent is Simpirica Spine, Inc.. Invention is credited to Todd Alamin, Colin Cahill, Manish Kothari, Hugues Malandain.
Application Number | 20160143670 14/732633 |
Document ID | / |
Family ID | 41797481 |
Filed Date | 2016-05-26 |
United States Patent
Application |
20160143670 |
Kind Code |
A1 |
Alamin; Todd ; et
al. |
May 26, 2016 |
METHODS AND APPARATUS FOR COUPLING A PROSTHESIS TO A SPINAL
SEGMENT
Abstract
A method for coupling a prosthesis to a spinal segment in a
patient includes the steps of selecting first and second reference
points disposed along the spinal segment and pre-operatively
measuring a target distance. The target distance extends between
the first and second reference points while the patient is in a
preferred posture such as the standing position. A prosthesis is
coupled to the spinal segment and the prosthesis is then
intra-operatively adjusted in order to set the distance between the
first and second reference points based on the target distance.
Inventors: |
Alamin; Todd; (Woodside,
CA) ; Kothari; Manish; (San Carlos, CA) ;
Malandain; Hugues; (Mountain View, CA) ; Cahill;
Colin; (Portola Valley, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Simpirica Spine, Inc. |
San Carlos |
CA |
US |
|
|
Family ID: |
41797481 |
Appl. No.: |
14/732633 |
Filed: |
June 5, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13037039 |
Feb 28, 2011 |
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14732633 |
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PCT/US2009/055914 |
Sep 3, 2009 |
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13037039 |
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61093922 |
Sep 3, 2008 |
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Current U.S.
Class: |
606/263 |
Current CPC
Class: |
A61B 2017/00725
20130101; A61B 17/7055 20130101; A61B 17/7067 20130101; A61B
17/7062 20130101; A61B 17/7053 20130101 |
International
Class: |
A61B 17/70 20060101
A61B017/70 |
Claims
1. A system for restricting flexion of a spinal segment in a
patient, said system comprising: a tether structure comprising one
or more straps adapted to be coupled with a superior spinous
process and an inferior spinous process or sacrum; a first
compliance element coupled with the tether structure and configured
to elastically elongate as tension is applied through the tether
structure; and a first constraining tool releasably coupled with
the compliance element so as to hold the compliance element in a
first desired position and allow a first predetermined amount of
elastic elongation of the first compliance element as tension is
applied to the first compliance element though the tether
structure.
2. A system as in claim 1, wherein the tether structure is
substantially non-distensible.
3. A system as in claim 1, wherein the first constraining tool
comprises an elongate shaft.
4. A system as in claim 1, wherein the first constraining tool
comprises a cradle adapted to releasably hold the first compliance
element.
5. A system as in claim 1, wherein the first constraining tool
comprises a plurality of elongate arms, the plurality of arms
forming a constraint to elongation of the compliance element.
6. A system as in claim 1, wherein the first tool holds the first
compliance element in a desired tension.
7. A system as in claim 1, wherein the first constraining tool
applies a compressive force to the first compliance element.
8. A system as in claim 7, wherein the compressive force is
variable.
9. A system as in claim 1, wherein the first constraining tool does
not limit extension or elongation of the first compliance element
until the first compliance element has extended or elongated by the
first pre-determined amount.
10. A system as in claim 1, wherein the first constraining tool is
adjustable so as to vary the desired position, tension or the
range.
11. A system as in claim 1, further comprising: a second compliance
element coupled with the tether structure and configured to
elastically elongate as tension is applied through the tether
structure; and a second constraining tool releasably coupled with
the second compliance element so as to hold the second compliance
element in a second desired position and allow a second
predetermined amount of elastic elongation of the second compliance
element as tension is applied to the second compliance element
through the tether structure, and wherein the first and the second
constraining tools are releasably and symmetrically coupled
together so as to facilitate alignment and positioning of the first
and the second compliance elements on opposite sides of a midline
of the spinal segment.
12. A system as in claim 11, wherein the first and the second
constraining tools are movable relative to one another along one
degree of freedom, thereby accommodating spinous processes of
varying thicknesses.
13. A system as in claim 11, wherein the first or the second
compliance element comprises a locking mechanism, and at least one
of the first or the second constraining tools comprise an elongate
shaft having a lumen adapted to receive and align a driver or other
tool concentrically with the locking mechanism.
14. A system as in claim 11, wherein the first or the second
compliance element releasably locks with the first or the second
constraining tool.
15. A system as in claim 13, wherein the first or the second
constraining tool is adapted to provide a counter torque when the
locking mechanism is actuated.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 13/037,039 (Attorney Docket No.
41564-703.301), filed Feb. 28, 2011, which is a continuation of
International Patent Application No. PCT/US2009/055914 (Attorney
Docket No. 41564-709.601), filed Sep. 3, 2009, which claims
priority to U.S. Provisional Application No. 61/093,922 (Attorney
Docket No. 41564-709.101), filed Sep. 3, 2008, the full disclosures
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to medical methods
and apparatus. More particularly, the present invention relates to
methods and apparatus used to couple a prosthesis to a spinal
segment and adjust the prosthesis during orthopedic internal
fixation procedures. This includes but is not limited to treatment
of patients having back pain or other spinal conditions.
[0004] 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-S 1 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.
[0005] 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 herein 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.
[0006] Patients with discogenic pain accommodate their syndrome by
avoiding positions such as sitting, which cause their painful
segment to go into flexion, 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 attached to 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.
[0007] 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 lightly 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.
[0008] 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.
[0009] An alternative solution that avoids some of the challenges
associated with cerclage devices involves the use of an elastic
structure, such as tether structures, 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.
[0010] 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 significant chance of nerve root damage. Additionally,
the tip of the set-screw clamps the tethers, and this may result in
abrasion of the tethers along with generation of particulate wear
debris.
[0011] 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.
[0012] 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 occurring during flexion. However, extension-limiting
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
structure and a securing mechanism for the tether. The tether may
be made from a flexible polymeric textile such as woven polyester
(PET) or polyethylene (e.g. ultra high molecular weight
polyethylene, UHMWPE); 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 includes 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 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. Other locking methods include the use of
a friction fit and are disclosed in greater detail below. While
these methods may avoid the potentially damaging loads, the
mechanical complexity of the assembly may be increased by
introducing more subcomponents.
[0013] A key to proper implantation of many of the spinous process
constraint devices described above is adjusting the tension or size
of the device when wrapped around the spinous processes. If the
band is not properly adjusted, it may be too loose and therefore
may disengage from the anatomy, or it may not provide adequate
resistance to flexion resulting in failure to alleviate the pain or
instability. On the other hand, if the band is too tight or too
small, the device may provide too much resistance to flexion and
unnecessarily restrict the spinal segment's ability to bend, or
effect higher than necessary loads to portions of the vertebrae or
soft tissues. It is therefore imperative to properly adjust the
size and/or tension of the spinous process device. The device
ideally should have a predetermined and preferred configuration
while the patient is in a preferred posture (e.g. the standing
position) and the device should also provide a force resistive to
flexion of the spinal segment while still allowing significantly
unrestricted extension of the spinal segment. For the
aforementioned reasons, it would be desirable to provide improved
methods and apparatus for coupling a prosthesis to a spinal segment
and adjusting the prosthesis, especially during orthopedic internal
fixation procedures. In particular, such methods and apparatuses
should be easy to perform and be minimally invasive.
[0014] 2. Description of the Background Art
[0015] 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; 2008/0009866; 2008/0108993; 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;
WO2008/051806; WO2008/051423; WO2008/051801; WO2008/051802; 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; A1Baz 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
[0016] The present invention relates to methods and apparatus used
to couple a prosthesis to a spinal segment and adjust the
prosthesis during orthopedic internal fixation procedures. This
includes but is not limited to treatment of patients having spinal
pain or other spinal conditions.
[0017] In a first aspect of the present invention, a method for
coupling a prosthesis to a spinal segment in a patient comprises
selecting a first and a second reference point disposed along the
spinal segment and pre-operatively measuring a target distance. The
target distance extends between the first and the second reference
points while the patient is in a preferred posture. The method also
includes coupling the prosthesis to the spinal segment and
intra-operatively adjusting the prosthesis in order to set the
distance between the first and second reference points based on the
target distance.
[0018] The first reference point may be disposed on a first
vertebra and the second reference point may be disposed on a second
vertebra or a sacrum. The first reference point also may be
disposed on a superior surface of a first spinous process of a
first vertebra and the second reference point may be disposed on an
inferior surface of a second spinous process of a second vertebra.
The first reference point may also be disposed on an inferior
surface of a first spinous process of a first vertebra and the
second reference point may be disposed on a superior surface of a
second spinous process of a second vertebra. The first vertebra may
be disposed cranial to the second vertebra. The preferred posture
may comprise the standing position or a pain-free position.
[0019] The measuring of the target distance may comprise observing
a radiograph of the patient taken while the patient is in the
preferred posture. The radiograph may be taken pre-operatively and
may comprise a lateral view of the spinal segment. The prosthesis
may comprise a tether structure and the coupling may comprise
engaging a first portion of the tether structure with a superior
spinous process and engaging a second portion of the tether
structure with an inferior spinous process or a sacrum.
[0020] The adjusting may comprise adjusting the prosthesis so that
the prosthesis is in a neutral position when the patient is in the
preferred posture and the prosthesis may provide a force resistive
to flexion of the spinal segment while still allowing significantly
unrestricted extension of the spinal segment. The adjusting may
also comprise adjusting the prosthesis while the patient is in a
position other than the preferred posture or observing calibration
markings on the prosthesis. Adjusting may also comprise setting the
distance between the first and second reference points to the
target distance.
[0021] The method may further comprise verifying that the distance
between the first and second reference points substantially matches
the target distance. Verifying may comprise using a gauge to
determine the distance between the first and second reference
points. The method may also comprise re-adjusting the prosthesis
until the distance between the first and second reference points
substantially matches the target distance.
[0022] The prosthesis may comprise a first compliance element and
the method may further comprise engaging and locking a first
constraining apparatus with the first compliance element in order
to limit extension or contraction thereof during adjustment of the
prosthesis. The first constraining apparatus may be disengaged from
the first compliance element so as to allow movement thereof. The
prosthesis may also comprise a second compliance element and the
method may comprise engaging a second constraining apparatus with
the second compliance element in order to limit extension or
contraction thereof during adjustment of the prosthesis. The first
and second constraining apparatus may be coupled so as to
facilitate alignment and positioning of the first and the second
compliance elements on opposite sides of a midline of the spinal
segment. The first constraining apparatus may be moved relative to
the second constraining apparatus along one degree of freedom in
order to accommodate spinous processes or mid-line ligaments (e.g.
interspinous ligament and superspinous ligament) of varying
thicknesses. A driver or tool may be positioned in a central lumen
of first or the second constraining apparatus thereby
concentrically aligning the driver or the tool with a locking
mechanism on the compliance element. The constraining apparatus may
be used to provide a counter torque when the first or the second
compliance elements are adjusted or when the first and the second
constraining apparatus are releasably coupled together. The
prosthesis may be pre-tensioned to a desired value.
[0023] The target distance may define a major axis length, and
wherein the adjusting comprises using the target distance to
determine a target prosthesis circumference, and adjusting the
prosthesis to the target circumference. The major axis length may
be correlated with the target circumference in a lookup table or
with calibration markings on the prosthesis.
[0024] The method may also include verifying that the prosthesis
circumference substantially matches the target circumference.
Verifying the prosthesis circumference may comprise observing
calibration markings on the prosthesis. The prosthesis may be
re-adjusted until the prosthesis circumference substantially
matches the target circumference.
[0025] The method may also comprise selecting a third and a fourth
reference point disposed along the spinal segment. The distance
between the third and fourth reference points may define a minor
axis having a minor axis length with the minor axis being
transverse to the major axis. The method may also include measuring
the minor axis length on the pre-operative image in order to
determine the target prosthesis circumference. The target
circumference may be sufficient for the prosthesis to form a loop
encircling a superior spinous process and an inferior spinous
process. The prosthesis may provide a force resistant to flexion
beyond a desired posture. The third and fourth reference points may
be on opposite sides of a spinous process and may be used to
estimate the length of the prosthesis required to accommodate
spinous process width. The third and fourth reference points may be
disposed on a single vertebra. The minor axis length may be
correlated with the target circumference in a lookup table or the
minor axis length may be correlated with calibration markings on
the prosthesis. The method may further comprise decompressing a
portion of the spinal segment.
[0026] In another aspect of the present invention, a system for
restricting flexion of a spinal segment in a patient comprises a
tether structure adapted to be coupled with a superior spinous
process and an inferior spinous process or sacrum, and a first
compliance element coupled with the tether structure. The system
also includes a first constraining tool releasably coupled with the
compliance element so as to hold the compliance element in a
desired position or to limit motion of the compliance element to a
predetermined range. The tether structure may be substantially
non-distensible and the first constraining tool may comprise an
elongate shaft. The first constraining tool may comprise a cradle
adapted to releasably hold the first compliance element. The first
constraining tool may also comprise a plurality of elongate arms
that form a receptacle for releasably holding the first compliance
element and that constrain elongation of the compliance element.
The first tool may hold the first compliance element in a desired
tension or apply a compressive force to the first compliance
element. The compressive force may be variable.
[0027] The first constraining tool may not limit extension of the
first compliance element until the first compliance element has
extended a pre-determined distance. The first constraining tool may
be adjustable so as to vary the desired position, tension or the
range. The system may also include a second compliance element
coupled with the tether structure and a second constraining tool.
The second tool may be releasably coupled with the second
compliance element so as to hold the second compliance element in a
desired position or to limit motion of the second compliance
element to a predetermined range. The first and the second
constraining tools may be releasably and symmetrically coupled
together so as to facilitate alignment and positioning of the first
and the second compliance elements on opposite sides of a midline
of the spinal segment. The first and the second constraining tools
may be movable relative to one another along one degree of freedom,
thereby accommodating spinous processes or midline soft tissues of
varying thicknesses. The first or the second compliance element may
comprise a locking mechanism and at least one of the first or the
second constraining tools may comprise an elongate shaft having a
lumen adapted to receive and align a driver or other tool
concentrically with the locking mechanism. The first or the second
compliance element releasably locks with the first or the second
constraining tool. The first or the second tool may also be adapted
to provide to provide a counter torque when the locking mechanism
is actuated.
[0028] In another aspect of the present invention, a method for
treating lower back pain in a patient comprises providing
instructions to the patient to place the lower back into varying
positions of flexion and determining a threshold position of the
lower back in which the patient does not experience lower back pain
or where lower back pain is reduced. A first image or a set of
images of the patient's lower back in the threshold position is
provided and features of the patient's lower back are measured
using the first image or the set of images. A constraint device is
coupled to the patient's lower back and features of the lower back
are re-measured with the constraint device coupled thereto. The
re-measured features are compared with the measured features and
the constraint device is adjusted so that the patient's lower back
is in a position below the threshold position based on the
comparison of measured and re-measured features. Thus, the lower
back pain or lower back instability is reduced or eliminated.
[0029] The step of determining may comprise providing the patient
with means for indicating when pain is experienced. The means may
comprise an actuatable switch. The first image or the set of images
may comprise one of an x-ray, MRI, and a CT scan. The providing
step may comprise acquiring the set of images from a single
continuous movement of the patient's lower back between painful and
pain-free or reduced pain postures.
[0030] The measured features may comprise one of intervertebral
disc angle, interspinous process distance, and interpedicular
distance. The measuring may comprise using calipers or an angle
measuring device to quantify the features.
[0031] The step of coupling may comprise engaging the constraint
device with a superior spinous process and an inferior spinous
process or a sacrum. The constraint device may be adapted to
provide a force resistant to flexion of the lower back.
[0032] The step of re-measuring may comprise providing a second
image or a set of images of the patient's lower back with the
constraint device coupled thereto. The second image or the set of
images may comprise one of an x-ray, MRI, and a CT scan.
Re-measuring may comprise placing one or more radiopaque markers
into engagement with the patient's lower back. The radiopaque
markers may be coupled with a spinous process in the patient's
lower back. The comparing step may comprise visually comparing the
first and the second radiographic images or sets of images.
Adjusting may comprise adjusting length or tension of the
constraint device.
[0033] The method may further comprise evaluating presence and
shape of spinous processes of the lower back for coupling of the
constraint device thereto. Facet joint engagement in the lower back
may also be evaluated. Evaluating may comprise measuring linear
overlap of articular processes of the facet joint. Adjusting the
constraint device may comprise adjusting the constraint device so
as to increase facet joint engagement in at least one facet joint
in the lower back. Adjusting may also comprise adjusting the
constraint device so as to prevent hyperextension or locking of at
least one facet joint in the lower back. The method may further
comprise manipulating the patient's lower back intraoperatively so
that the lower back is in a position at or below the threshold
position based on the comparison of measured and re-measured
features. The manipulating may comprising manipulating the
patient's lower back to form or increase lordosis therein.
[0034] In another aspect of the present invention, a method for
treating degenerative spondylolisthesis in a lower back of a
patient comprises providing instructions to the patient to place
the lower back into varying positions of flexion and providing a
plurality of images of the lower back in the varying positions. A
threshold position of the lower back in which a facet joint of the
patient's lower back begins to sublux is determined, and a first
image of the patient's lower back while in the threshold position
is then provided. A constraint device is coupled to the patient's
lower back, and a second image of the patient's back is provided
intraoperatively after the constraint device has been coupled to
the patient's lower back. The first and the second images are
compared and the constraint device is adjusted so that the
patient's lower back is in a position below the threshold position
based on the comparison of the first and the second images. Thus,
subluxation of the facet joint is reduced or eliminated.
[0035] The step of determining may comprise providing the patient
with means for indicating when pain is experienced such as an
actuatable switch. A neural decompression may be performed
concurrently. The determining may also comprise assessing
engagement of a facet joint or ability of the facet joint to resist
anterior translation of the cranial vertebra with respect to the
caudal vertebra.
[0036] The first image may comprise one of an x-ray, MRI, and CT
scan. The coupling may comprise engaging the constraint device with
a superior spinous process and an inferior spinous process or a
sacrum. The constraint device may be adapted to provide a force
resistant to flexion of the lower back. The second image may
comprise an x-ray, MRI, or a CT scan. One or more radiopaque
markers may be placed into engagement with the patient's lower
back. The placement may comprise coupling a radiopaque marker with
a spinous process in the patient's lower back.
[0037] The comparing step may comprise comparing intervertebral
disc angle, interspinous process distance, facet joint engagement,
or interpedicular distance between the first and the second images
or sets of images. The comparing may also comprise using calipers
or an angle measuring device to quantify lower back features in the
first and the second images. The first and second images may be
visually compared with one another.
[0038] The adjusting step may comprise adjusting length or tension
of the constraint device. The method may also comprise evaluating
presence and shape of spinous processes of the lower back for
coupling of the constraint device thereto.
[0039] In another aspect of the present invention, a method for
treating lower back pain in a patient comprises manipulating the
patient's lower back into a position where the lower back pain is
reduced or eliminated and recording the position. The position is
intraoperatively reproduced in the patient's lower back and a
constraint device is coupled to the lower back.
[0040] The step of manipulating may comprise manually manipulating
the patient's lower back, forming, or increasing lordosis in the
patient's lower back. The manipulating may also comprise placing
the patient in a frame or a chair with an adjustable lumbar member,
or flexing a hip. The flexing of the hip may comprise directing a
force proximally through a femoral head to antevert a pelvis
thereby forming or increasing lordosis in the patient's lower back.
The knee may be restrained.
[0041] The step of recording may comprise providing the patient
with means for indicating when pain is experienced such as an
actuatable switch. The step of reproducing may comprise manually
manipulating the patient's lower back into the position or forming
or increasing lordosis in the patient's lower back. The step of
coupling may comprise engaging the constraint device with a
superior spinous process and an inferior spinous process or a
sacrum. The constraint device may be adapted to provide a force
resistant to flexion of the lower back.
[0042] The method may further comprise providing an image of the
patient's lower back in the position. The image may comprise an
x-ray, MRI, or a CT scan. The method may also comprise providing an
intraoperative image of the patient's lower back after reproducing
the position. The intraoperative image may comprise one of an
x-ray, C-arm fluoroscopy, MRI, or CT scan. A radiopaque marker may
be coupled with the patient's lower back, such as with a spinous
process. The method may further comprise intraoperatively
characterizing range of motion, segmental stability, linear
stiffness, or bending stiffness of a segment of the patient's lower
back. The constraint device may be adjusted based on the
characterization of the patient's lower back. The adjusting step
may comprise adjusting length or tension in the constraint device.
Additionally, the characterization of the patient's lower back may
be compared with a reference guide and the constraint device may be
adjusted based on information provided by the reference guide.
[0043] In still another aspect of the present invention, a method
for treating spondylolisthesis in a patient comprises providing
instructions to the patient to place the lower back into varying
positions of flexion and determining a threshold position of the
lower back in which the patient does not experience translational
instability or wherein translation instability is reduced. A first
image or a set of images of the patient's lower back is provided
while the patient is in the threshold position and features of the
patient's lower back are measured from the first image or the set
of images. A constraint device is coupled to the patient's lower
back and features of the patient's lower back are re-measured with
the constraint device coupled thereto. The re-measured features are
compared with the measured features, and the constraint device is
adjusted so that the patient's lower back is in a position below
the threshold position based on the comparison of measured and
re-measured features, thereby reducing or eliminating the lower
back instability.
[0044] These and other embodiments are described in further detail
in the following description related to the appended drawing
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1A is a schematic diagram illustrating the lumbar
region of the spine.
[0046] FIG. 1B a schematic illustration showing a portion of the
lumbar region of the spine taken along a sagittal plane.
[0047] FIG. 2 illustrates a spinal implant of the type described in
US 2005/0216017A1.
[0048] FIGS. 3A-3B illustrate additional tissue surrounding the
spinous processes.
[0049] FIGS. 4A-4M show an exemplary method of surgically
implanting a spinal device.
[0050] FIGS. 5A-5B show a lateral view of a lumbar region of the
spine highlighting different reference points.
[0051] FIGS. 6A-6B illustrate the reference points in FIGS. 5A-5B
in a simplified anterior-posterior view of the lumbar region of the
spine.
[0052] FIGS. 7A-7B illustrate a simplified anterior-posterior view
of a lumbar region of the spine highlighting a plurality of
reference points that may be used to estimate prosthesis
circumference.
[0053] FIGS. 8A-8B illustrate an exemplary embodiment of
calibration markings on a spinous process constraint device.
[0054] FIGS. 9A-9C illustrate an exemplary embodiment of a
constraining tool.
[0055] FIGS. 10A-10C illustrate another exemplary embodiment of a
constraining tool.
[0056] FIGS. 11A-11C illustrate curvature of a patient's spine in
different postures.
[0057] FIGS. 12A-12B illustrate a spinal motion segment in kyphosis
and lordosis.
[0058] FIGS. 13A-13B illustrate a spinal motion segment with
degenerative spondylolisthesis.
[0059] FIGS. 14A-14B illustrate a patient in different
postures.
[0060] FIGS. 15A-15B illustrate a spinal motion segment in kyphosis
and lordosis.
[0061] FIGS. 16A-16C illustrate application of a lumbar force to a
patient's lower back.
[0062] FIG. 17 illustrates measurement of various features a spinal
segment.
[0063] FIG. 18 illustrates the relationship between intervertebral
angle and segmental bending moment under various conditions.
[0064] FIGS. 19A-19B illustrate the segmental contribution to total
lumbar motion versus total lumbar motion under various
conditions.
[0065] FIG. 20 illustrates an exemplary algorithm for diagnosing
and treating lower back pain.
[0066] FIGS. 21A-21C illustrate an exemplary tool for constraining
two compliance elements.
[0067] FIG. 22 illustrate an exemplary compliance element.
DETAILED DESCRIPTION OF THE INVENTION
[0068] FIG. 1A 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. 1B 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.
[0069] 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 lumbar 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.
[0070] Furthermore, as used herein, "flexion" refers to the motion
between adjacent vertebrae in a spinal segment as the patient bends
forward. Referring to FIG. 1B, 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. 1B.
[0071] 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.
1B. 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.
[0072] FIG. 2 shows a spinal implant of the type described in
related U.S. Patent Publication No. 2005/02161017 A1, the entire
contents of which are incorporated herein by reference. As
illustrated in FIG. 2, an implant 10 typically comprises a tether
structure having an upper strap component 12 and a lower strap
component 14 joined by a pair of compliance elements 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 element 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 elements 16.
[0073] 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.
[0074] 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.
[0075] After the incision has been made, a piercing tool T having a
tapered 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. Exemplary embodiments of
piercing tool T are disclosed in U.S. patent application Ser. No.
12/478,953 (Attorney Docket No. 026398-000610US), the entire
contents of which are incorporated herein by reference. 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 ISL 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.
[0076] 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.
[0077] After tip TI or a portion of tether 102a 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
elements 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.
[0078] The steps of accessing the ISL, piercing the ISL, 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. One of skill in
the art will appreciate that the piercing may also be performed
from the opposite direction. 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.
[0079] As shown in FIGS. 4H, 4I and 4J, similar to 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 elements 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 element 104a, 104b. Further details on
exemplary embodiments of fastening mechanisms are disclosed in U.S.
patent application Ser. No. 12/479,016 (Attorney Docket No.
026398-000710US) and U.S. Provisional Patent Application No.
61/059,543 (Attorney Docket No. 026398-000800US), the entire
contents of which are incorporated herein by reference. For example
as shown in FIG. 4K, tether 102a is engaged with compliance element
104b and is then releasably coupled thereto with fastening
mechanism 106b. Similarly, tether 102b is also engaged with
compliance element 104a and is also releasably coupled thereto with
fastening mechanism 106a. Except for their orientation, compliance
elements 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.
[0080] 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.
026398-000410US), 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.
Provisional Patent Application No. 60/936,897 (Attorney Docket No.
026398-000400US), the entire contents of which are incorporated
herein by reference.
[0081] In order for the spinous process constraint device of FIGS.
4A-4M to effectively reduce back pain and/or spinal instability,
the constraint device should be sized to prevent or limit painful
or unstable positions, e.g. the constraint should provide a force
resistive to flexion of the spinal segment while still allowing
significantly unrestricted extension of the spinal segment. A
physician therefore will require methods and apparatus for coupling
and adjusting the constraint device to a spinal segment.
[0082] FIG. 5A illustrates a lateral view of a portion of the
lumbar region of the spine including lumbar vertebrae L3-L5 having
spinous processes SP and discs D disposed between vertebrae. One
exemplary method of determining the appropriate size of the
constraint device involves obtaining a pre-operative image, such as
a radiograph, of the affected spinal segment. The radiograph is
taken while the patient is in a desired, preferably pain-free
posture so that the spinal segment is in the final desired neutral
position for the device. From the radiograph, two reference points
are selected and these reference points are used to estimate the
size to which the constraint device should be adjusted.
Additionally, radiopaque gauges may be used to help determine
magnification and distortion effects in the radiograph. A scale may
be used in the radiograph for measuring the distance between
reference points and the physician may compensate for magnification
and/or image distortion. In a preferred embodiment, a first
reference point A1 is selected on a superior surface of a first
spinous process SP coupled to a first vertebra and the second
reference point A2 is selected on an inferior surface of a second
spinous process coupled to a second vertebra. The second vertebra
is below the first vertebra when the patient is in the standing
position. The length between points A1 and A2 define a target
distance as indicated by the arrow in FIG. 5A. Thus, once the
constraint device is applied to the spinal segment, it may be
adjusted intra-operatively until the distance between reference
points A1 and A2 is returned to the pre-operative target distance.
This helps to ensure that the constraint device is in a neutral
position when the patient is standing but will provide a force
resistive to flexion of the spinal segment while still allowing
significantly unrestricted extension of the spinal segment. The
target distance may be measured with calipers, rulers, digital
radiographic measurements or other suitable gauges. After the
distance between reference points A1 and A2 have been measured and
adjusted, a verification step may be performed in order to ensure
that the proper distance is maintained prior to completing the
surgical procedure. If the distance has changed from the target
value, the surgeon may re-adjust the constraint device in order to
reposition the spinous processes so that the distance between the
two reference points A1, A2 is brought closer to the target
distance. This fine tuning and re-adjustment may be repeated as
required. FIG. 6A illustrates a simplified anterior-posterior view
of the spinal segment seen in FIG. 5A. The target distance may also
be estimated using an anterior-posterior radiograph instead of, or
in conjunction with the lateral radiograph.
[0083] In another preferred embodiment, the two reference points
may be located along different regions of the spinous processes.
For example, FIG. 5B illustrates the same view of the spinal
segment as in FIG. 5A, yet here, the first reference point B1 is
located along an inferior surface of a first spinous process
coupled to a first vertebra and the second reference point B2 is on
a superior surface of spinous process coupled to a second vertebra.
The second vertebra is below the first vertebra when the patient is
in a standing position. A radiograph or other image of the spinal
segment while the patient is in a preferred posture such as
standing, may be used to obtain the pre-operative length between
points B1 and B2 and this is used to define the target distance as
indicated by the arrow in FIG. 5B. This length may be used to
control adjustment of the constraint device in a manner similar to
that previously described with reference to FIG. 5A. One advantage
of using the reference points illustrated in FIG. 5B is that it may
be easier to measure this distance intra-operatively using
calipers, rulers, gauge pins or sizing blocks than measuring the
distance between reference points in FIG. 5A. In FIG. 5B, the
distance is an "inside" dimension as opposed to the "outside"
dimension in FIG. 5B and thus may be easier to measure at a
consistent location. Adjustment, verification and re-adjustment may
also be performed as previously disclosed above. FIG. 6B
illustrates a simplified anterior-posterior view of the spinal
segment illustrated in FIG. 5B. The target distance may also be
estimated using an anterior-posterior radiograph instead of, or in
conjunction with the lateral radiograph. Once the constraint device
size has been set to the target value, optional further adjustment
of the device allows a physician to set a desired pre-tension
value. In still other embodiments, the measured distance may be the
distance between superior surfaces of both spinous processes.
[0084] Another embodiment of a sizing algorithm estimates the
circumference of the spinous process constraint device from the
pre-operative radiograph of the affected spinal segment. FIG. 7A
illustrates an anterior-posterior view of a portion of the lumbar
region of the spine. This includes lumbar vertebrae L3-L5 having
spinous processes SP and discs D disposed between vertebrae. A
spinous process constraint device SPD encircles two spinous
processes SP. In this example, the two spinous processes are
adjacent one another, however in other embodiments, one or more
spinous processes may be disposed in between the two spinous
processes to which the spinous process constraint device is
coupled. A first pair of reference points may be selected on the
pre-operative radiograph to help estimate the circumference to
which the spinous process constraint device should be adjusted. In
FIG. 7A, a first reference point C1 is disposed on a superior
surface or slightly thereabove of a first spinous process coupled
with a first vertebra and a second reference point C2 is disposed
on an inferior surface or slightly therebelow of a second spinous
process coupled with a second vertebra. The first vertebra is
cranial, or above the second vertebra when the patient is in a
standing position. The reference points C1 and C2 define a major
axis and have a major axis length. The major axis length may be
measured from the radiograph using calipers, a ruler or other
measuring techniques including those previously discussed above.
Additionally, the physician may adjust measurements to account for
distortion or magnification in the radiograph. The major axis is
shown by the vertical dotted line extending through C1 and C2 in
FIG. 7B. The major axis length may also be estimated from a lateral
view of the affected spinal segment. The circumference of the
spinous process constraint device SPD may be estimated as twice the
major axis length plus a constant which accommodates for the
constraint device wrapping around the apex of the upper and lower
spinous processes. The constant may be measured from the radiograph
or obtained from a lookup table based on other characteristics of
the patient's body (e.g. height, body type, etc.).
[0085] A second pair of reference points optionally may also be
selected on the pre-operative radiograph to further help estimate
the adjusted size of the spinous process constraint device SPD. In
FIG. 7A, reference points D1 and D2 are taken on either side of one
of the spinous processes SP around which the constraint device SPD
is encircled. FIG. 7A shows D1 and D2 on either side of the
inferior spinous process, but they may also be located on either
side of the superior spinous process. Reference points D1 and D2
define a minor axis transverse to the major axis and having a minor
axis length. The minor axis is illustrated by the dotted line
extending through points D1 and D2 in FIG. 7B. Minor axis length
may be similarly measured as the major axis length.
[0086] Once major axis length and optional minor axis length have
been measured from the pre-operative radiograph or other
pre-operative image, the circumference of the spinous process
constraint device may be estimated. The spinous process constraint
device circumference may be estimated as a rectangle and thus is
calculated as twice the major axis length plus twice the minor axis
length. The constraint device circumference may also be estimated
using other models such as by calculating the circumference of an
oval or ellipse. Furthermore, the major axis length and minor axis
length may be correlated to constraint device circumference and a
lookup table may provide the corresponding adjustment size to use.
Once the constraint device is implanted around the spinous
processes, its size is adjusted until its circumference matches the
calculated value or the value provided by the lookup table. The
circumference of the constraint device may be measured directly or
calibration markings on the constraint device may be used to
indicate constraint device size. Once the constraint device size
has been set to the target value, optional further adjustment of
the device allows a physician to set a desired pre-tension
value.
[0087] FIGS. 8A-8B illustrate an exemplary embodiment of
calibration markings that may be included on the spinous process
constraint device to help estimate device length or circumference.
In FIG. 8A, the tether portion 402 of a spinous process constraint
device 400 is illustrated. The tip 404 of the tether is cut at an
angle and opposite end 406 is folded against itself and secured to
form an aperture that may be coupled with a compliance element
having a locking mechanism (not illustrated). The angle on the tip
allows that end to easily be inserted into a locking mechanism of
this or another spinous process constraint device when two or more
devices are coupled together. Calibration markings 408 may be
printed, etched or otherwise affixed to the tether portion 402 of
the device. Calibration markings 408 may be spaced apart at a known
distance from one another or numbers may also be included with the
markings to facilitate reading. The calibration marking may
indicate tether length or circumference or another parameter that
allows the physician to adjust the tether to the target value
estimated from the pre-operative standing radiograph. FIG. 8B is an
enlarged view of FIG. 8A.
[0088] In addition to estimating device length or circumference, it
may also be desirable to characterize the patient's lower lumbar
spine in various positions to establish a threshold position where
pain is experienced. Once this threshold position is determined,
the constraint device may be applied to the patient's spine and
adjusted to help ensure that the patient's back remains at or below
the threshold position. Thus clinical evaluation of flexion
exacerbated pain may be linked with imaging based diagnostic
techniques and various factors may be quantified in the
characterization of lower back pain. For example, the amount of
flexion that causes or exacerbates pain or subluxation of facet
joints may be measured and the ability of the native tissue
structures to resist flexion or translation may be determined. The
nature and degree of any instability may also be evaluated. The
presence and shape of spinous processes on the sacrum may also be
evaluated for coupling with a constraint device. The shape of
spinous processes may also be evaluated along with a determination
of whether modification of the spinous processes is required for
receiving the constraint device. Also, the stiffness, size and/or
tension of the constraint device used to limit flexion may be
estimated in order to best treat a specific patient.
[0089] FIGS. 11A-11C illustrate the curvature of a patient's lower
lumbar spine when the patient is in different postures. In FIG.
11A, the patient 1102 is in a neutral, standing position and the
lower lumbar spine 1104 has a dorsally-concave curvature indicated
by dotted line 1106 that is referred to as lordosis. When the spine
flexes, as in a forward bending (FIG. 11B) or a seated posture
(FIG. 11C), the lordotic curvature of the lumbar spine flattens
out. As the spine continues to flex the curvature may shift to
anterior concavity, as illustrated by dotted line 1108. This is
referred to as kyphosis.
[0090] Flexion exacerbated pain is often referred to as mechanical
low back pain and involves pain when the spine is in a flexed
posture. Flexion exacerbated pain may be associate with
degeneration of the intervertebral disc (the degenerative cascade
is described in greater detail by Kirkaldy-Willis). Prior
diagnostic techniques often focused more on degenerative disc
disease as the basis of the clinical evaluation, including plain
film x-ray analysis of disc height, range of motion (ROM) and MRI
based (magnetic resonance imaging) grading of disc degeneration
(e.g. the Pfirrmann MRI classification system).
[0091] FIG. 12A illustrates a spinal segment 1202 having two
vertebrae V and a disc D with overlapping facet joints 1208. The
spinal segment is often pain free in a neutral (lordotic) posture
as indicated by dotted line 1210. However, the segment may become
more painful as the segment flexes, as illustrated in FIG. 12B. The
flexion 1204 changes the curvature of the spinal segment from
lordosis to kyphosis as indicated by dotted line 1212 resulting in
pain 1206. The amount of flexion that causes pain may vary from
patient to patient.
[0092] Other pathologies such as degenerative spondylolisthesis
(DS) may be exacerbated by flexion as well. In DS, degeneration of
the facet joints reduces the motion segment's inherent ability to
resist shear translation. This is exacerbated in flexion as facet
joint engagement decreases. FIG. 13A illustrates a spinal motion
segment 1302 having two vertebrae an a disc D. The facet joints
1304 have degenerated and thus do not overlap as much as healthy
facet joints (e.g. as illustrated in FIG. 12A). As the spinal
segment 1302 is moved into flexion 1306, the facet joints 1304
separate from one another and thus are less able to resist shear
movement 1308 of one vertebra V relative to the other vertebra V
and thus they move, distorting the disc D and causing pain as
illustrated in FIG. 13B. Typical diagnostic techniques for
degenerative spondylolisthesis focus on neurological symptoms and
assessment of gross mechanical instability (e.g. range of motion
and intervertebral translation).
[0093] Plain-film radiographs (x-rays) may be taken with the
patient in various postures, to determine what posture causes pain
or instability. X-rays may be used to measure intervertebral disc
angle, inter-spinous process or pedicular distance for preoperative
planning and sizing of any implant. For example, a patient may be
told to bend forward until pain is felt. An X-ray taken in this
posture will indicate to the clinician the segmental posture that
elicits pain. This posture represents a threshold position above
which the patient experience pain and below which pain is either
reduced or eliminated. FIG. 14A illustrates a patient 1402 bending
forward so that the lumbar spinal segment 1404 is in flexion 1406
and FIG. 14B illustrates the patient 1402 standing up so that the
spinal segment 1404 is in the neutral position. The patient may
actuate a button or switch to indicate that the pain has started or
stopped. The switch may be integrated with the radiography
equipment so that the image is captured at the pain threshold and
other postures.
[0094] Because radiographic images of spinous processes can be
variable (particularly when cartilaginous tissue is present),
radiopaque markers may be used to provide consistent
landmarks/fiducials to measure anatomic parameters. For example,
tantalum beads may be implanted into the spinous processes to
enable consistent measurement of the separation of the spinous
processes. With the beads providing a consistent reference for
measurement, the desired (likely pain-free) posture may be more
reliably reproduced in the operative setting.
[0095] In addition to evaluating pain vs. posture, this technique
may evaluate other posturally-dependent attributes such as
facet-engagement. Engagement of the facet joints decreases with
segmental flexion, which may exacerbate conditions such as
degenerative spondylolisthesis. Radiographs may be used to
determine the posture at which the facet joints begin to sublux and
resistance to shear load and translational motion is reduced. Then,
the techniques described above may be used to apply and adjust the
flexion constraint in order to prevent these postures. FIG. 15A
illustrates a lumbar spinal motion segment 1502 having two
vertebrae V, a disc D, and facet joints 1504. The spinal segment
1502 is in flexion 1506 while the spinal segment in FIG. 15B is in
the neutral position where the spinal segment has a lordotic curve
1508. The distance between spinous processes SPD may be measured
along with the intervertebral disc angle IVDA from the radiographic
images, and these parameters may be used to characterize the
threshold position. Anatomical measurements from radiographs in
painful (FIG. 15A) and pain-free or reduced pain (FIG. 15B)
postures may assist a surgeon in correctly positioning the patient
on the operating table, and applying the correct size or tension to
a flexion-constraining implant. The objective being to implant the
constraint such that pain-free motion is permitted, while the
painful or unstable motions are restricted. Measurements of
interest may include the distance between spinous processes (SPD)
and intervertebral disc angle (IVDA).
[0096] Plain-film radiographs and resulting measurements may also
be correlated to postural measurements of flexion during a
patient's normal activities of daily living to determine modes and
frequency of motions that cause pain. For example, a patient may be
fitted with a goniometer that measures spinal flexion, or strain
gauges on the skin of the lower back. Measurements from the
goniometer or strain gauges can be correlated to radiographic
measurements described above to estimate lumbar flexion. The
patient wears the device during their normal routines, possibly for
a day or a week. The device records lumbar flexion, as well as
inputs by the patient to indicate pain. Data recorded by the device
can inform the physician regarding the mode, frequency and postural
dependency of the patient's pain.
[0097] The patient's spine may be manually manipulated by the
physician, to effect a pain-free posture, evaluate segmental
instability, or post-operative effectiveness of treatment. In a
clinical, diagnostic setting, this will typically be done by
pushing against the lower lumbar spine to create a lordotic curve
(much as a back brace in a car seat works to support the curvature
of the spine). A frame or chair with an adjustable lumbar bolster
(such as a plunger) may be used to apply a repeatable manipulation
to the spine. Alternatively, hip flexion (via the seat angle) may
be used to manipulate the spinal posture. These techniques may also
use a proximally-directed force through the femoral head and hip to
antevert the pelvis (rotate forward), and thus induce the lordotic
curvature. The proximally-directed force through the femoral head
will typically be accomplished by applying a force or restraint to
the knee.
[0098] These methods and systems may be used by the physician to
assess lumbar postures which are painful vs. pain-free. As
described above, the patient may actuate a switch to indicate the
pain threshold. The switch could provide a time-stamp for dynamic
radiography, or trigger an x-ray machine to capture an image. If
the frame or chair is radiolucent, then radiographic images may
further enable the physician to reproduce the pain-free posture
intra-operatively and apply the constraint structure so that it
will prevent motion into the painful posture. Also as described
above, implanted radiopaque markers such as tantalum beads may
provide consistent reference points for radiographic
measurements.
[0099] FIG. 16A illustrates a normally painful posture where a
patient's 1602 spine 1604 is flexed 1606. The patient may be
sitting or the patient may be in any other position where the spine
is in flexion. FIG. 16B shows how pain is relieved with application
of a force 1610 or support that restores lordosis 1608 in the
lumbar spine 1604 (similar to the lumbar support in car seats).
Radiographic images in the manipulated, pain-free posture may be
used as described above to implant a flexion constraint device such
that a spinal alignment is altered to relieve pain, in a
previously-painful posture.
[0100] Diagnostic spinal manipulation, as described above, may be
performed more repeatably with a system to apply consistent
postural manipulation. One example is a chair as seen in FIG. 16C.
The patient 1602 is sitting in the chair having a seat 1616, a back
1614, and a knee brace 1618. A plunger 1612 can apply manipulative
pressure to the lumbar spine 1604, and the knee brace 1618 helps
maintain the patient in a desired position. The chair preferably is
radiolucent so that radiographs may be obtained and used to implant
a flexion constraint as described previously.
[0101] An apparatus which may be used for this purpose and operates
on principles similar to the system illustrated above, is the
commercially available "Nada Chair" (http://www.nadachair.com/). A
strap looped around the lumbar spine provides lordosis-restoring
lumbar support. The opposite end of the strap is looped around the
knees so that it can be tensioned and apply forces to both the
lumbar spine and femoral head (via the knee). Such an apparatus may
be used to apply mechanical manipulation to the lumbar spine and
determine the postural effect on pain. Other braces or orthoses may
similarly be used to diagnose flexion-exacerbated, postural
pain.
[0102] Manual or mechanical manipulation may also be used
intraoperatively to assess segmental biomechanics and instability.
The surgeon may use an adjustable table (such as the Jackson Axis
table), or instruments such as laminar spreaders or the Mekanika
Spinal Stiffness Gauge device to measure ranges of motion or
segmental stability to determine the amount and type of
restabilization needed from the flexion constraint. This may be
particularly useful for potentially-destabilizing procedures, such
as a decompression, where segmental stability may be assessed
before and after the decompression procedure to understand how the
segmental biomechanics were affected by the procedure. For example,
a surgical instrument may measure applied load and displacement of
vertebral structures (typically the spinous processes or laminae)
to assess a linear stiffness of the spinal structure (usually in
N/mm). With the linear stiffness and a measurement or estimate of
the distance from the surgical instrument to the segmental center
of rotation (COR), the segmental bending stiffness can be
estimated, usually in Newton-meters per degree. This may be
calculated as:
K = 0.001 P .DELTA. L R 2 .pi. 180 .degree. , ##EQU00001## [0103] K
is segmental bending stiffness (usually in N-m/deg); [0104] P is
the load applied by the surgical instrument (usually in N); [0105]
.DELTA.L is the distraction or compression applied by the
instrument (usually in mm); [0106] R is the moment-arm, or distance
from the instrument to the segmental center of rotation (usually in
mm); and [0107] The factor 0.001 is used to accommodate the
variable L and R being in millimeters, while the variable K is in
Newton-meters/degree.
[0108] FIG. 17 shows a spinal motion segment having two vertebrae V
separated by a disc D and schematically illustrates these
measurements. A surgical instrument 1702 is inserted between the
spinous processes SP of adjacent vertebrae V and measures the
distraction or compression, and the load applied to the vertebral
structures. The moment arm 1706 is distance from the center of
rotation 1704 of the motion segment to the surgical instrument
1702. With an assessment of segmental bending stiffness, the
surgeon can make decisions about appropriate instrumentation for
stabilization (e.g. spinal rods), as well as stiffness and
tightness of the instrumentation. A template, look-up table,
software program or other algorithm may be provided with an implant
system to make such decisions with these measurements. In one
exemplary embodiment, a system for providing an elastic resistance
to flexion may come in multiple stiffnesses. A table provided for
use with the implant systems may recommend which stiffness is
appropriate for a particular patient based on
intraoperatively-measured parameters.
[0109] Dynamic radiography, such as obtained from video fluoroscopy
or several frames of x-ray imaging, may also be used to assess
instabilities with more specificity and resolution. In degenerative
spondylolisthesis, dynamic radiography may help to identify the
intervertebral angle at which the facets become unstable.
Quantitative motion analysis of the vertebrae may further identify
the nature of flexion instability of a specific motion segment. For
example, as the entire spine moves into flexion, a greater portion
of the motion may occur at a single motion segment, indicating
flexion instability in that segment. Furthermore, the instability
may present predominantly within a specific portion of the total
range of motion. Use of these diagnostic, dynamic radiographic
techniques may enable the physician to apply a constraint to
flexion which allows as much natural motion as possible, while
preventing pathologically unstable or painful flexion motions.
Similar dynamic radiographic measurements may be used to assess the
biomechanical efficacy of any treatment.
[0110] As described above, the patient may use a switch to indicate
the pain threshold, possibly as a timestamp on the dynamic
radiograph. The dynamic radiographs may also be used to determine
facet joint engagement or subluxation, or intervertebral
translation, across the range of motion. Implantable, radiopaque
markers may provide consistent measurement references that enable
the surgeon to reproduce a desired posture intraoperatively. These
techniques may then be used to apply the flexion constraint such
that undesired postures are restricted.
[0111] FIG. 18 graphically illustrates the relationship between
intervertebral angle and segmental bending moment in two different
situations. Dynamic radiography may help to identify the nature of
an instability, such as instability around the neutral zone (curve
A), vs. hypermobility or excessive total ROM (curve B). The nature
of the instability may affect the application of the constraint
device. For example curve A may require the constraint to be
implanted more tightly; while curve B may require a stiffer
constraint.
[0112] FIGS. 19A-19B graphically illustrate the relationship
between segmental contribution to total lumbar motion and total
lumbar motion in two different situations. Dynamic radiographs can
show the relationship between different motion segments through the
total range of motion. FIG. 19A illustrates five motion segments
flexing equally throughout the total range of lumbar motion. FIG.
19B illustrates five motion segments, where the L4-L5 segment
accounts for the largest share of motion as the spine begins to
flex. However, the total range of motion for the five segments is
the same. Dynamic radiography may detect the early-phase
instability of L4-L5, whereas conventional x-rays may show simply
that all segments have the same total range of motion.
Understanding the nature of the segmental instability allows the
physician to appropriately apply the flexion constraining
implant.
[0113] Any of the diagnostic and treatment techniques described
above may utilize software as part of the process. Software may
facilitate measurement of the anatomical properties, such as
intervertebral disc angle, tissue stiffness, strain, or dynamic
motion properties. The software package may use these measurements
to calculate the appropriate parameters of the flexion constraint
implant, such as the appropriate size, stiffness or tension. The
software may intra- or post-operatively verify that the constraint
is implanted such that it has the intended biomechanical effect. An
exemplary method is illustrated in FIG. 20 where the posture that
causes pain or instability is first determined 2010 and then
anatomical features are measured in the painful and pain-free or
reduced pain postures 2020. Appropriate parameters for a flexion
constraint are calculated (e.g. stiffness, size, tension, etc.)
2030 and the surgeon then implants the constraint 2040. The
postural correction may then be verified 2050.
[0114] As previously described above with respect to FIGS. 4A-4M,
the spinous process constraint device often includes one or more
compliance elements positioned on opposite sides of a spinous
process, across the spinal segment midline. The compliance elements
act like springs to help provide the force resistant to flexion of
the spinal segment as the spinous processes move away from one
another. Because of the compliance element, adjusting the device to
position the spinous processes at a target distance from one
another or to provide a target prosthesis size such as
circumference may be difficult. As the device is tensioned, the
compliance element will elongate and prevent the determination of
the reference distance. It would therefore be advantageous to
provide a constraining tool that can prevent elongation of the
compliance element during adjustment of the constraint device. The
constraining tool may be used during the deployment and
implantation procedure previously described. The constraining tool
is applied to the compliance element to temporarily restrict its
elongation or limit extension to a desired value, during adjustment
of the device length or circumference. Once the compliance element
is adjusted, the constraining tool may be removed. A physician may
then continue to adjust the constraint device in order to establish
a desired pre-tension therein.
[0115] FIGS. 9A-9C illustrate an exemplary embodiment of a
constraining tool 500 adapted to hold the compliance element 514
during adjustment of the spinous process constraint device. In FIG.
9A, a plurality of arms 504, 506, 508, 510 extend from an elongate
shaft 502 to define a cradle or receptacle 512 for receiving the
compliance element 514. The compliance element 514 is placed or
snap fit in the cradle 512 and the arms 504, 506, 508, 510 engage
opposite ends of the compliance element 514 and prevent expansion
thereof. In other embodiments, the cradle size may be variable or
sized larger than the compliance element in order to allow a
pre-determined amount of extension. Additionally, the plurality of
arms 504, 506, 508, 510 are spaced apart sufficiently to allow easy
access to adjustment screws or apertures on the compliance element
514. The constraining tool 500 may be fabricated from any number of
metals such as titanium, stainless steel or polymers such as ABS
that are commonly used for surgical instruments. FIG. 9B shows a
side view of the constraining tool 500 with a compliance element
514 disposed in the cradle 512. FIG. 9C illustrates a perspective
view of FIG. 9B. Arms 504, 506, 508, 510 preferably do not
interfere with operation of the device or affect sizing, for
example by interfering with the behavior of the constraint device
or offsetting the constraint device away from the spinous
processes.
[0116] Another exemplary embodiment of a constraining tool 600 is
illustrated in FIGS. 10A-10C. In FIG. 10A, constraining tool 600
includes an elongate shaft 602 and a frame having a plurality of
axially extending arms 604, 606, 608, 610. The plurality of arms
604, 606, 608, 610 define a cradle or receptacle 612 for holding a
compliance element 616. The cradle 612 is sufficiently open to
allow easy access to the compliance element including any
adjustment screws and apertures that may be included with the
compliance element. Additionally, aperture 614 also allows access
to the locking mechanism of compliance element 616. The locking
mechanism may comprise a locking roller, details of which are
disclosed in U.S. patent application Ser. No. 12/479,016 (Attorney
Docket No. 026398-000710US), the entire contents of which have
previously been incorporated herein by reference. The constraining
tool 600 may be fabricated from any of the materials disclosed
above with reference to FIGS. 9A-9C. FIG. 10B illustrates a side
view of the constraining tool 600 with compliance element 616
disposed in the cradle 612 and FIG. 10C is a perspective view of
FIG. 10B.
[0117] In embodiments where the constraint device has two
compliance elements, it is advantageous to have two constraining
tools that can simultaneously restrict movement of both the
compliance elements during adjustment. FIGS. 21A-21C illustrate an
exemplary embodiment of such a tool. The tool includes two
constraining tools 2102a, 2102b that mate together. Each tool
includes an elongate tubular shaft 2104a, 2104b with a rotatable
knob 2106a, 2106b near the proximal end. The tubular shaft may be a
tapered shaft that is threadably coupled with the knob such that
rotating the knob advances or retracts the shaft. Thus, when the
shaft is retracted, the arms 2118a, 2118b will compress and close
around the compliance element.
[0118] A central lumen 2108a, 2108b extends from the proximal end
of the shaft to the distal end of the shaft and tools may be
positioned in the central lumen as will be discussed below. A
flanged region 2120a, 2120b near the proximal end of each shaft
includes a pin 2112a, 2112b and an aperture 2110a, 2110b. The pin
of one tool may be positioned in the aperture of the opposite tool
thereby releasably coupling the two tools together and holding them
substantially parallel to one another. The distal end of the shaft
includes an arm 2114a, 2114b extending radially outward from the
shaft and having a slotted region 2116a, 2116b. The distal end of
the shaft also has a second arm 2118a, 2118b. The two arms on each
tool form a cradle for receiving the compliance element of the
constraint device and restricting expansion thereof during
adjustment. The flanged region 2120a, 2120b may be sized to
accommodate different patient anatomies, but in preferred
embodiments, the longitudinal axes of the two tools are separated
by a distance 2130 (best seen in FIG. 21C) adequate to straddle a
spinous process or interspinous/supraspinous ligament complex. This
distance may vary depending on the patient, but in preferred
embodiments may be 10 mm to 25 mm, and more preferably 15 mm to 20
mm wide. Additionally, by using the pin-aperture coupling mechanism
described above, the two tools still have one degree of freedom and
can be moved in the medial-lateral directions. The compliance
element is held in the cradle such that the lumen is lined up with
adjustment features on the compliance element. For example, FIG. 22
illustrates an exemplary embodiment of a compliance element 2202
having a helical spring-like body 2204. A pin 2208 on one end of
the compliance element secures the tether structure 2206 of the
compliance device thereto and the opposite end includes a locking
screw 2212 and an tether adjustment rolling mechanism (not
illustrated) in the compliance element housing 2210. When the
locking screw 2212 is loosened, a tool may be inserted into the
housing to rotate the rolling mechanism thereby tightening or
loosening the tether which passes therethrough. Once the adjustment
is completed, the locking screw may be tightened to lock the roller
in place, fixing tether length or tension. These features may be
accessed by passing a tool (e.g. a screw driver, hex driver, etc.)
through the lumen of the constraint device shaft, where they will
line up concentrically with the locking screw or roller mechanism.
Another advantage of the constraint tool is that it will provide a
counter torque during the process of tightening the roller
mechanism and the locking screw.
[0119] 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.
* * * * *
References