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Long-Term Safety and Efficacy of Minimally Invasive Lumbar
Decompression Procedure for the Treatment of Lumbar Spinal
Stenosis With Neurogenic Claudication
2-Year Results of MiDAS ENCORE
Peter S. Staats, MD, MBA,* Timothy B. Chafin, MD,†Stanley Golovac, MD,‡Christopher K. Kim, MD,§
Sean Li, MD,|| William B. Richardson, MD,** Ricardo Vallejo, MD, PhD,†† Sayed E. Wahezi, MD,‡‡
Edward P. Washabaugh, III, MD,§§ and Ramsin M. Benyamin, MD†† for the MiDAS ENCORE Investigators
Background and Objectives: This study evaluated the long-term dura-
bility of the minimally invasive lumbar decompression (MILD) procedure in
terms of functional improvement and pain reduction for patients with lumbar
spinal stenosis and neurogenic claudication due to hypertrophic ligamentum
flavum. This is a report of 2-year follow-up for MILD study patients.
Methods: This prospective, multicenter, randomized controlled clinical
study compared outcomes for 143 patients treated with MILD versus 131
treated with epidural steroid injections. Follow-up occurred at 6 months
and at 1 year for the randomized phase and at 2 years for MILD subjects only.
Oswestry Disability Index, Numeric Pain Rating Scale, and Zurich Claudica-
tion Questionnaire were used to evaluate function and pain. Safety was eval-
uated by assessing incidence of device-/procedure-related adverse events.
Results: All outcome measures demonstrated clinically meaningful and statis-
tically significant improvement from baseline through 6-month, 1-year, and
2-year follow-ups. At 2 years, Oswestry Disability Index improved by 22.7
points, Numeric Pain Rating Scale improvedby3.6points,andZurichClaudica-
tion Questionnaire symptom severity and physical function domains improved by
1.0 and 0.8 points, respectively. There were no serious device-/procedure-related
adverse events, and 1.3% experienced a device-/procedure-related adverse event.
Conclusions: MILD showed excellent long-term durability, and there
was no evidence of spinal instability through 2-year follow-up. Reopera-
tion and spinal fracture rates are lower, and safety is higher for MILD ver-
sus other lumbar spine interventions, including interspinous spacers,
surgical decompression, and spinal fusion. Given the minimally invasive
nature of this procedure, its robustsuccess rate, and durability of outcomes,
MILD is an excellent choice for first-line therapy for select patients with
central spinal stenosis suffering from neurogenic claudication symptoms
with hypertrophic ligamentum flavum.
Clinical Trial Registration: This study was registered at ClinicalTrials.
gov, identif ier NCT02093520.
(RegAnesthPainMed2018;43: 789–794)
Neurogenic claudication due to lumbar spinal stenosis (LSS) is
associated with debilitating pain in the lower back and extrem-
ities and is the cause of significant functional limitation, especially
in the elderly population.
1
Neurogenic claudication symptoms are
precipitated by walking and relieved by sitting. It is believed that
spinal extension (walking and standing) produces neurogenic clau-
dication symptoms by reducing the cross-sectional area of the cen-
tral canal, resulting in nerve root compression and painful nerve
root ischemia. This compression is relieved with spinal flexion,
which causes the central canal to expand, leading to pain relief
and resolution of neurogenic claudication symptoms.
2,3
Unlike
symptoms of radicular pain, the distribution of symptoms related
to neurogenic claudication is not usually dermatomal. Radicular
pain is related to inflammation of an affected nerve root and
generally radiates from the back and buttock into the leg in a
dermatomal pattern.
4,5
Patients suffering from neurogenic claudication almost always
present with degenerative soft tissue and bony pathology related to
a combination of disc protrusion, thickened or ossified ligamentum
flavum, facet joint hypertrophy, or osteophytes.
1–3
In1reportby
Hansson and colleagues,
3
ligamentum flavum hypertrophy (LFH)
contributed to between 50% and 85% of central canal narrowing,
leading the authors to conclude that the ligamentum flavum plays
a dominant role in the load-induced narrowing of the lumbar spinal
canal. Further, one of the common characteristics of neurogenic
claudication is the high frequency of multiple-level stenosis.
2,6
The MiDAS ENCORE study was approved by the Centers for
Medicare & Medicaid Services (CMS) as a Coverage with Evi-
dence Development study for the purpose of providing level I evi-
dence to support the safety and effectiveness of the MILD
procedure. This randomized controlled trial assessed outcomes of
the MILD procedure compared with epidural steroid injections
(ESIs) in subjects with LSS and neurogenic claudication symptoms,
From the *National Spine and Pain Centers, Shrewsbury, NJ; †Department of
Pain Management and Rehabilitation Medicine, VidantRoanoke-Chowan Hos-
pital, Ahoskie, NC; ‡Florida Pain Institute, Merritt Island, FL; §The Center for
Pain Relief, Charleston, WV; ||Premier Pain Centers, Shrewsbury, NJ; **Southeastern
Spine Institute, Mount Pleasant, SC; ††Millennium Pain Center, Bloomington, I L;
‡‡Departments of Physical Medicine and Rehabilitation and Anesthesiology,
Albert EinsteinCollege of Medicine at Montefiore,Montefiore Medical Center,
Bronx, NY; and §§Michigan Pain Specialists, Ypsilanti, MI.
Accepted for publication June 8, 2018.
Address correspondence to: Peter S. Staats, MD, MBA, National Spine and Pain
Centers, 170 Avenue at the Common, Ste 6, Shrewsbury, NJ 07702
(e‐mail: peterst aats@hotmail.com).
P.S.S. and R.M.B. are study principal investigators for MiDAS ENCORE. In
this role, they have been responsible for study oversight. Responsibilities
include protocol review, assistance with site selection, site investigator
support, oversight of patient enrollment and protocol compliance, and
adjudication of adverse events.
This trial was sponsored by Vertos Medical. The sponsorship includes study-
related supplies and expenses, as well as funding for statistical analysis
services by an independent provider.
The authors declare no conflict of interest.
Supplemental digital content is available for this article. Direct URL citations
appear in the printed text and are provided in the HTML and PDF versions
of this article on the journal's Web site (www.rapm.org).
Copyright © 2018 The Author(s). Published by Wolters Kluwer Health, Inc. on
behalf of the American Society of Regional Anesthesia and Pain Medicine.
This is an open-access article distributed under the terms of the Creative
Commons Attribution-Non Commercial-No Derivatives License 4.0
(CCBY-NC-ND), where it is permissible to download and share the work
provided it is properly cited. The work cannot be changed in any way or
used commercially without permission from the journal.
ISSN: 1098-7339
DOI: 10.1097/AAP.0000000000000868
CHRONIC AND INTERVENTIONAL PAIN
ORIGINAL ARTICLE
Regional Anesthesia and Pain Medicine •Volume 43, Number 7, October 2018 789
with verified LFH as a contributing factor. Study follow-up inter-
vals occurred at 6 months and 1 year for the randomized phase of
the study, and subjects in the MILD treatment group were followed
at 2 years. Study design and 6-month and 1-year follow-up compar-
ative results between MILD and ESI were previously reported.
7–9
This is a report of 2-year clinical outcomes of patients treated with
the MILD procedure in the MiDAS ENCORE study.
METHODS
This study was conducted at 26 interventional pain manage-
ment centers throughout the United States. The trial protocol was
approved by institutional review boards for all participating sites
and registered with the US clinical trial registry (NCT02093520).
Study patients were required to be 65 years or older and Medicare
beneficiaries. Enrolled patients had central LSS with neurogenic
claudication symptoms for at least 3 months and ligamentum
flavum of greater than 2.5 mm in thickness. Subjects with Oswestry
Disability Index (ODI) score of less than 31, Numeric Pain Rating
Scale (NPRS) score of less than 5, prior surgery at any treatment
level, or spondylolisthesis of grade III or higher were excluded from
the study. The MiDAS ENCORE protocol was developed as a Cov-
erage with Evidence Development study in collaboration with
CMS. As designed and approved by CMS, the primary end point
for the randomized phase of this study was 1-year follow-up. Two-
year outcome data were collected for patients in the MILD group
only. An economic analysis demonstrating the cost-effectiveness
of MILD versus other LSS therapies is the subject of a separate
report that will be published subsequently.
MILD is a minimally invasive lumbar decompression proce-
dure that is performed percutaneously through a 5.1-mm port,
thereby limiting trauma to tissue and bony structures of the spine.
Generally using only moderate sedation and local anesthetic, the
MILD procedure is conducted by accessing the interlaminar space
from the posterior lumbar spine. Using the MILD devices together
with contrast-enhanced fluoroscopic guidance, small amounts of
lamina and hypertrophic ligamentum flavum are selectively removed,
thereby achieving lumbar decompression. Fluoroscopic guidance
is used throughout the MILD procedure, and visualization of the
epidurogram contrast flowallows assessment of the amount of de-
compression. Following treatment with MILD, epidurogram con-
trast flow becomes thicker and straighter (Fig. 1). Once adequate
decompression has been observed, all devices are removed, and
the access site is usually closed with a sterile adhesive strip, with
no sutures. The contralateral side and other levels may then be
treated, as medically indicated. The MILD procedure leaves no
implants behind and therefore preserves the option for patients
to undergo subsequent more invasive treatment options that may
require implants. The MILD procedure has been previously
described.
7
Validated assessments including ODI, NPRS, and Zurich Clau-
dication Questionnaire (ZCQ) were used to evaluate function and
pain. Because neurogenic claudication symptoms are often intermit-
tent, study patients were instructed to respond to these outcome as-
sessments based on their experience over time as supported by
TABLE 1. MILD Patient Characteristics
Characteristic MILD (n = 149)
Age,* y 75.6 ± 7.0
Gender
Male 49.7% (74)
Female 50.3% (75)
Presenting LSS cofactors
LFH 100.0% (149)
Bulging disc 89.9% (134)
Foraminal narrowing 87.2% (130)
Facet hypertrophy 86.6% (129)
Facet arthropathy 76.5% (114)
Degenerative disc disease 67.8% (101)
Disc space loss 59.1% (88)
Lateral recess narrowing 57.0% (85)
Osteophytes 47.7% (71)
Spondylosis 47.0% (70)
Spondylolisthesis 44.3% (66)
Nerve root impingement 33.6% (50)
Herniated disc 27.5% (41)
Scoliosis 22.1% (33)
Other 19.5% (29)
ODI* 53.0 ± 12.9
NPRS* 7.7 ± 1.4
ZCQ*
Symptom severity domain 3.5 ± 0.5
Physical function domain 2.9 ± 0.5
*Mean ± SD.
Staats et al Regional Anesthesia and Pain Medicine •Volume 43, Number 7, October 2018
790 © 2018 American Society of Regional Anesthesia and Pain Medicine
validation studies. Clinically meaningful improvement in function
was defined as equal to or greater than 10-point improvement in
ODI score from baseline to follow-up.
10,11
Clinically significant
efficacy thresholds were defined as a 2-point improvement in
NPRS,
10–14
a 0.5-point improvement in ZCQ domains, and an
absolute ZCQ patient satisfaction score of 2.5 or less.
15–17
Safety
was evaluated by assessing incidence of device- or procedure-
related adverse events. Continuous data were tabulated with means
and SDs, and categorical data were reported using frequency counts
and percentages. For graphical displays, continuous data were
reported using means and 95% confidence intervals (CIs). All
Pvalues presented are 2-sided, with P< 0.05 considered significant.
RESULTS
One hundred forty-nine MILD patients were enrolled from
June 2014 through April 2015. Of these, 6 subjects voluntarily
withdrew prior to treatment, resulting in 143 MILD patients.
Patient demographics and presenting LSS cofactors are presented
in Table 1. Bulging disc, foraminal narrowing, facet hypertrophy,
facet arthropathy, and degenerative disc diseasewere the most fre-
quently reported presenting LSS cofactors. Ninety-five percent of
patients presented with 5 or more spinal comorbidities. Baseline
clinical presentation, ODI, NPRS, and ZCQ domains are also pre-
sented in Table 1.
At 2 years, a total of 26 patients had been withdrawn because
of receipt of disallowed secondary intervention or study with-
drawal with the intent to receive disallowed secondary interven-
tion. The remaining 117 MILD patients were then potentially
available for 2-year follow-up. Of those patients, 8 missed the
2-year follow-up visit, 5 withdrew for unrelated reasons, and 5
died of reasons unrelated to the MILD procedure including stroke
and cardiac arrest. The remaining patients comprise the modified
intent-to-treat population of 99 MILD patients who returned for
2-year follow-up. The modified intent-to-treat analysis includes
all observed data for each follow-up visit reported. Subjects who
missed a given follow-up, or who withdrew prior to that follow-
up, are not included in the analysis for that visit.
At 2-year follow-up, all primary and secondary efficacy out-
come measures showed clinically meaningful and statistically
TABLE 2. Mean Change for MILD Efficacy Outcome Measures**
Outcome
Assessments*
6-mo (n = 133) Mean Improvement
(95% CI)
1-y (n = 119) Mean Improvement
(95% CI)
2-y (n = 99)†Mean Improvement
(95% CI)
ODI 20.4 19.5 22.7
(17.1–23.7) (16.1–23.0) (18.5–26.9)
NPRS 3.1 3.3 3.6
(2.5–3.6) (2.8–3.9) (3.1–4.2)
ZCQ symptom
severity
0.8 0.9 1.0
(0.7–1.0) (0.8–1.1) (0.8–1.2)
ZCQ physical
function
0.7 0.6 0.8
(0.6–0.8) (0.5–0.8) (0.6–0.9)
*Clinically meaningful improvement: ODI ≥10 points, NPRS ≥2.0, ZCQ ≥0.5.
†ODI and ZCQ symptom severity consisted of 98 subjects completing the 2-year follow-up.
**Based on modified intent-to-treat statistical analysis.
FIGURE 2. Oswestry Disability Index mean improvement at all follow-up intervals was clinically meaningful and statistically significant
(P< 0.001) using modified intent-to-treat statistical analysis method. The modified intent-to-treat analysis includes all observed data foreach
follow-up visit reported. Subjects who missed a given follow-up, or who withdrew prior to that follow-up, are not included in the analysis for
that visit.
Regional Anesthesia and Pain Medicine •Volume 43, Number 7, October 2018 Long-Term Safety and Efficacy of MILD
© 2018 American Society of Regional Anesthesia and Pain Medicine 791
significant improvement from baseline and remained stable com-
pared with 6-month and 1-year follow-ups. At 2 years, ODI im-
proved by 22.7 points (95% CI, 18.5–26.9), NPRS improved by
3.6 points (95% CI, 3.1–4.2), and ZCQ symptom severity and
physical function domains improved by 1.0 (95% CI, 0.8–1.2)
and 0.8 (95% CI, 0.6–0.9) points, respectively (Table 2). Figure 2
shows mean ODI values at baseline and 6-month, 1-year, and
2-year follow-ups. Figures 3 and 4 show similar mean values for
NPRS, ZCQ symptom severity, and ZCQ physical function at base-
line and all follow-ups. Mean changes from baseline exceeded the
clinically meaningful threshold and achieved statistical significance
at P< 0.001 for all efficacy end points and follow-up times. The
ZCQ patient satisfaction score of 2.0 (95% CI, 1.8–2.2) at 2-year
follow-up exceeded the validated clinically meaningful threshold
of 2.5 or less. At 2 years, responder rates for ODI, NPRS, and
ZCQ symptom severity, physical function and patient satisfaction
were 72.4%, 71.7%, 73.5%, 59.6% and 76.8%, respectively.
During 2-year follow-up, no MILD patients underwent a sub-
sequent MILD procedure at any level. Eight (5.6%) of 143 patients
underwent a subsequent surgical procedure at the index level, 22
(15.4%) of 143 received an ESI or nerve block at the level of sur-
gery, and one of these patients also received a spinal cord stimulator
as a treatment for the pain at the index level. One additional patient
received a rhizotomy at the index level, and 1 patient received an
intrathecal infusion pump (Table 3).
There were no serious device- or procedure-related adverse
events reported for these patients, and there was no evidence of
spinal instability at 2 years after the MILD procedure. As previ-
ously reported, 2 MILD patients (1.3%) experienced a device- or
procedure-related adverse event in this study, which was the same
FIGURE 3. Numeric Pain Rating Scale mean improvement at all follow-up intervals was clinically meaningful and statistically significant
(P< 0.001) using modified intent-to-treat statistical analysis method. The modifiedintent-to-treat analysis includes all observed data foreach
follow-up visit reported. Subjects who missed a given follow-up, or who withdrew prior to that follow-up, are not included in the analysis for
that visit.
FIGURE 4. Mean improvement for ZCQ symptom severity and ZCQ physical function domains at all follow-up intervals was clinically
meaningful and statistically significant (P< 0.001) using modified intent-to-treat statistical analysis method. The modified intent-to-treat
analysis includes all observed data for each follow-up visit reported. Subjects who missed a given follow-up, or who withdrew prior to that
follow-up, are not included in the analysis for that visit.
Staats et al Regional Anesthesia and Pain Medicine •Volume 43, Number 7, October 2018
792 © 2018 American Society of Regional Anesthesia and Pain Medicine
rate as the ESI patients in the control arm during the randomized
phase of this study (P=1.00).
8,9
During 1 MILD case, intraopera-
tive oozing was observed at the decompression site, and Gelfoam
was administered through the cannula into the interlaminar
space. The patient was discharged on the same day as the pro-
cedure with no complications. A second patient experienced
postoperative pain possibly related to MILD that resolved within
3 days of the index procedure.
DISCUSSION
Two-year follow-up results of this study demonstrate excel-
lent durability of the MILD procedure for LSS patients suffering
from neurogenic claudication symptoms and hypertrophic
ligamentum flavum. All outcome measures demonstrated clini-
cally meaningful and statistically significant improvement from
baseline through 6-month, 1-year, and 2-year follow-ups. MILD
patients experienced a mean ODI improvement of 22.7 points
from baseline to 2 years postprocedure. This is markedly higher
than the 10-point improvement that has been validated to be the
threshold for clinically significant improvement for ODI.
10,11
Further, 72.4% of MILD patients at 2 years achieved at least
a 10-point improvement in ODI. All other validated efficacy
measures also showed clinically meaningful and statistically
significant improvement, including NPRS, ZCQ physical func-
tion, and ZCQ symptom severity (Table 2). Zurich Claudication
Questionnaire patient satisfaction also exceeded the clinically
meaningful threshold.
The overall surgical reoperation rate for MILD patients in
this study was only 5.6% (8/143) at 2-year follow-up (Table 3).
MILD has demonstrated an excellent safety profile with no
device- or procedure-related serious adverse events, and a 1.3%
rate of device- and procedure-related adverse events, which was
similar to the rate for ESIs.
9
Further, there was no evidence of spi-
nal instability through 2-year follow-up.
As a benchmark, the rate of patients undergoing reoperations
through 2 years after nonfusion decompression surgery was re-
ported by the SPORTinvestigators to be 7.8%.
18
At 2 years, reop-
eration rates after spinal fusion have been reported to be 12.5% to
16.9%,
19–21
and after interspinous process distraction were
14.4% to 26.0%.
22,23
Although this study did not provide a head-
to-head comparison to other LSS therapies, a discussion of safety
outcomes for the broad range of LSS treatments provides impor-
tant context related to the overall clinical management of LSS
and effects on decision making regarding treatment algorithms
for these pati ents. A rand omized controlled investigational device
exemption study comparing 2 spacers reported device-related adverse
event rates of 11.6% and 7.5%, and procedure-related advers e
event rates of 14.2% and 15.9% through 2-year follow-up.
22
The SPORT investigators reported a 9.9% rate of intraoperative
complications and a 12.3% rate of postoperative complications
following surgical decompression through 2 years.
18
Spinal fusion
studies have reported related complication rates as high as
23.3% through 2 years.
24,25
The rate of device removal at 2-year
follow-up has been reported to be 16.3% for a currently marketed
IPD device.
22
The rate of lumbar spine fracture has been reported
to be 4.2% for fusion procedures
21
and 16.3% for a currently
marketed spacer
22
at 2-years.
The addition of MILD to the array of treatment options for
spinal stenosis is valuable to treating physicians as well as pa-
tients. MILD is safe and has been shown to provide durable results
through 2-year follow-up. MILD does not involve the use of im-
plants, is performed as an outpatient procedure without general
anesthesia, requires only a small 5.1-mm port for access, and does
not require sutures (although some surgeonselect to place a single
suture at the portal site). In the comparative trial of MILD against
ESIs, the success rate including durability was greater than ESIs,
with a comparable safety profile.
9
Given the minimally invasive
nature of this procedure, its robust success rate, and durability of
outcomes, MILD is an excellent choice for patients suffering from
neurogenic claudication symptoms with LFH, who are refractory
to conservative care.
While open surgery is often an excellent choice and may be re-
quired for certain patients, MILD can be offered for patients who may
not tolerate a more invasive procedure, and it has a unique role as a
solution when conservative therapies have failed, and the risks of
more invasive approaches may not be warranted. It is important to
note that MILD does not affect surgical options for the few patients
who do not respond to this treatment. Because of the very minimally
invasive approach and targeted subtle decompression, there is mini-
mal or no scar tissue that would increase the risk of possible future
open spine surgery. Another important consideration related to treat-
ment planning is that patients undergoing open surgical decompres-
sion are no longer candidates for less invasive approaches.
The average age of patients in this study was 75.6 years, with
patients as old as 93 years. This can be compared with an average
age of 63.6 years for the surgical patients in SPORT
18
and 66.9
and 66.2 years for the treatment and control arms, respectively,
of the recent US Food and Drug Administration randomized con-
trolled trial comparing safety and clinical outcomes of spacers.
22
In addition, there was a high rate of presenting spinal comorbidities
for MILD patients enrolled in this study (Table 1). MILD is
intended for patients with central stenosis due to LFH; however,
bulging discs, foraminal narrowing, and facet hypertrophy or ar-
throsis were common and actually were associated with higher
rates of response than the ENCORE population as a whole
(Table 4). Further, responder rates for patients with bulging disc
and facet hypertrophy were statistically significantly higher than
those without these comorbidities. Thus, our data suggest that
TABLE 3. Reoperations and Retreatments Through 2-Year
Follow-Up for MILD Patients
MILD, n/N (%)
Surgical procedure 8/143 (5.6)
ESI or nerve block* 22/143 (15.4)
Rhizotomy 1/143 (0.7)
Intrathecal pump 1/143 (0.7)
*Includes 1 patient who also received a spinal cord stimulator.
TABLE 4. ODI Response Rate by LSS Cofactor Subgroup at 2-Year
Follow-Up
Characteristic Not Present Present P
Bulging disc 27.3% (3/11) 77.3% (68/88) 0.002*
Foraminal narrowing 60.0% (9/15) 73.8% (62/84) 0.351
Facet hypertrophy 47.1% (8/17) 76.8% (63/82) 0.019*
Facet arthropathy 68.2% (15/22) 72.7% (56/77) 0.789
Degenerative disc disease 65.5% (19/29) 74.3% (52/70) 0.463
Disk space/height loss 61.0% (25/41) 79.3% (46/58) 0.069
Lateral recess narrowing 65.0% (26/40) 76.3% (45/59) 0.259
ODI responder defined as improvement of ≥10 points from baseline.
*Statistically significant at P<0.05.
Regional Anesthesia and Pain Medicine •Volume 43, Number 7, October 2018 Long-Term Safety and Efficacy of MILD
© 2018 American Society of Regional Anesthesia and Pain Medicine 793
the mere presence of these comorbidities should not be used as
an exclusion.
The experience of MILD patients in this study is similar and
compares favorably to 2-year MILD results previously reported.
26
In the report by Chopko,
26
patients demonstrated a statistically
significant reduction of pain and statistically significant improve-
ment in physical function and mobility as measured by ODI and
all ZCQ domains, from baseline through 2 years. At 2 years, mean
ZCQ patient satisfaction indicated that patients were satisfied with
their procedure. In addition, no major device or procedural com-
plications were reported.
The limitations of this study include lack of a control group
at 2-year follow-up. The randomized controlled portion of the
study concluded at the primary end point of 1 year, and supple-
mentary follow-up through 2 years was conducted for the MILD
patient group only. This study did not compare efficacy directly with
open surgical approaches, including lumbar decompression, fusion,
or spacers. Study limitations have been previously described.
7–9
Two-year follow-up for MILD patients in this study showed
excellent durability of the MILD procedure for treatment of LSS
patients with neurogenic claudication and LFH. All efficacy out-
comes achieved clinically meaningful and statistically significant
improvement from baseline to all follow-up intervals through
2 years. There was no evidence of spinal instability at 2 years after
the MILD procedure. A comparison of reoperation rates, spinal
fractures, and safety between MILD and the broad range of lumbar
spine interventions, including spacers, surgical decompression, and
spinal fusion, shows a dramatically lower rate for MILD in all cat-
egories. These results confirm the importance of this therapy, and
support MILD's position as an optimal interventional option for
patients suffering from neurogenic claudication symptoms with
hypertrophic ligamentum flavum.
ACKNOWLEDGMENTS
The authors thank the MiDAS ENCORE Investigators for
their valuable contributions to this study (see the Appendix, Sup-
plemental Digital Content 1, http://links.lww.com/AAP/A275, for a
listing). They also thank Scott Brown, PhD, of Altair Biostatistics
LLC for statistical analysis and the editorial board of Regional
Anesthesia and Pain Medicine for review of this manuscript.
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