ORIGINAL ARTICLE

Comparative observational study of surgical outcomes of lumbarforaminal stenosis using minimally invasive microsurgicalextraforaminal decompression alone versus posterior lumbarinterbody fusion: a prospective cohort study

Ho-Joong Kim • Jin-Hwa Jeong • Hyeon-Guk Cho •

Bong-Soon Chang • Choon-Ki Lee •

Jin S. Yeom

Received: 2 June 2014 / Revised: 19 September 2014 / Accepted: 20 September 2014 / Published online: 25 September 2014

� Springer-Verlag Berlin Heidelberg 2014

Abstract

Introduction There is no comparative study regarding

surgical outcomes between microsurgical extraforaminal

decompression (MeFD) and posterior lumbar interbody

fusion (PLIF) for the treatment of lumbar foraminal ste-

nosis (LFS). Therefore, the purpose of this study was to

compare the surgical outcomes of LFS using two different

techniques: MeFD alone or PLIF.

Methods For the purposes of this study, a prospectively

collected observational cohort study was conducted. Fifty-

five patients diagnosed with LFS who were scheduled to

undergo spinal surgery were included in this study.

According to the chosen surgical technique, patients were

assigned to either the MeFD group (n = 25) or the PLIF

group (n = 30). The primary outcome was Oswestry Dis-

ability Index (ODI) score at 1 year after surgery.

Results The baseline patient characteristics and preoper-

ative ODI score, visual analog scale (VAS) scores for back

and leg pain, and Short Form-36 score were not signifi-

cantly different between the two groups. At 12 months

postoperative, the mean ODI score in the MeFD and PLIF

groups was 25.68 ± 14.49 and 27.20 ± 12.56, respec-

tively, and the 95 % confidence interval (-9.76–6.73) was

within the predetermined margin of equivalence. The

overall ODI score and VAS scores for back and leg pain

did not differ significantly over the follow-up assessment

time between the two groups. However, the ODI score and

VAS scores for back and leg pain improved significantly

over time after surgery in both groups. In the MeFD group,

revision surgery was required in three patients (12 %).

Conclusions This study demonstrated that MeFD alone

and PLIF have equivalent outcomes regarding improve-

ment in disability at 1 year after surgery. However, the

higher rate of revision surgery in the MeFD group should

emphasize the technically optimal amount of

decompression.

Keywords Lumbar foraminal stenosis � Microsurgical

extraforaminal decompression � Posterior lumbar interbody

fusion

Introduction

For surgical treatment of lumbar foraminal stenosis

(LFS), recent studies have demonstrated the efficacy of

microsurgical extraforaminal decompression (MeFD) [1–

6]. This procedure involves unroofing of the stenotic

foramen. Previous studies have shown very promising

surgical outcomes, not only in the short term, but also in

long-term follow-up assessments [3–6]. However, most

of these studies were clinical case series, and the surgical

outcomes of this decompression technique can worsen

over time owing to the progression of degenerative

changes in corresponding segments. Although this tech-

nique is minimally invasive, minimally invasive decom-

pression does not arrest the natural history of the

degenerative process already underway in the segment.

For this reason, posterior lumbar interbody fusion (PLIF)

H.-J. Kim � J.-H. Jeong � H.-G. Cho � J. S. Yeom (&)

Spine Center and Department of Orthopaedic Surgery, Seoul

National University College of Medicine and Seoul National

University Bundang Hospital, 166 Gumiro, Bundang-Gu,

Sungnam 463-707, Republic of Korea

e-mail: highcervical@gmail.com

B.-S. Chang � C.-K. Lee

Department of Orthopaedic Surgery, Seoul National University

College of Medicine and Seoul National University Hospital,

101 Daehangno, Jongno-Gu, Seoul 110-744, Republic of Korea

123

Eur Spine J (2015) 24:388–395

DOI 10.1007/s00586-014-3592-4

also has been advocated for direct or indirect decom-

pression and for preventing restenosis and further

degeneration of the operated segment [7–9].

Nonetheless, there is no comparative study regarding the

surgical outcomes of LFS between MeFD alone and PLIF.

Compared with minimally invasive MeFD, fusion surgery

has the advantage of preventing restenosis of the index

segment, but the disadvantage of requiring more extensive

exposure. Therefore, the purpose of this study was to

compare the surgical outcomes of LFS using these two

different techniques.

Methods

Study design and patients

This study was approved by the hospital’s institutional

review board. For the purposes of this study, a pro-

spectively collected observational cohort study was

conducted. All prospective data were obtained as part of

routine patient care and were included in the medical

records. Because all processes were considered part of

routine care, no written informed consent was obtained

from the patients. Inclusion criteria included patients

aged 40–80 years, diagnosed with LFS in the mid and

exit zones of the foramen, and scheduled to undergo

spinal surgery. Diagnosis of LFS required one or more

of the following symptoms: leg pain, numbness, or

motor deficits in the lower extremities and buttocks [10,

11], with confirmation of a stenotic lesion in the mid

(under the pedicle) and exit zones of the foramen of the

lumbar spine on magnetic resonance imaging (MRI) [7].

Patients were excluded if they had spinal instability,

including spondylolysis, foraminal stenosis caused by

only extruded disc, stenosis severe central stenosis more

than grade C by Schizas’s classification [12], and ste-

nosis with an element of entry zone foraminal stenosis

[7]. On flexion–extension lateral radiographs of the

lumbar spine, anterior translation of the index segment

[4.5 mm in the sagittal plane or sagittal plane motion

[15 from L1–L2 to L3–L4, [20 at L4–L5 and [25 at

L5–S1 from extension to flexion were considered spinal

instability [13]. Furthermore, such patients were exclu-

ded that they had a history of peripheral vascular dis-

ease, any concurrent serious medical condition causing

disability, or general health status including sepsis or

cancer. The study was performed at the spinal center of

a tertiary care teaching institution from June 2012 to

March 2013. Patients were assigned to the MeFD alone

group or the PLIF group. In both groups, surgical

indication was identically lumbar foraminal stenosis at a

single level.

Decision of surgical technique

In the present study, the surgical technique was determined

through a preference-based, shared-decision making sys-

tem. The patient was educated about his/her current status

of degenerative LFS and the available surgical options.

Furthermore, his/her own MRI was shown and explained.

Finally, the first author informed the patient about the

evidence to support the advantages and disadvantages of

each available surgical option based on previous studies [7,

8, 11]. After the patient-education stage, the patient was

asked to describe the decision-making process, the pros and

cons of the various surgical options, and whether the

treatment decision made was congruent with his/her pref-

erences. A surgeon did not recommend any specific sur-

gical option to patients. According to the patient’s

preference and shared decision, the patient was allocated to

either the MeFD alone group or the PLIF group (Fig. 1).

All surgical procedures in both groups were performed by

the first author, who has experienced approximately 100

and 600 cases of MeFD and PLIF surgery, respectively,

over the past 3 years.

MeFD group

Figure 2 shows a photograph of an actual operative field.

First, the lateral portion of the pars interarticularis and the

facet joint was exposed by a paramedian approach. Using

an operating microscope and high-speed drill, the supero-

lateral portion of the facet joint and the upper and lateral

margins of the interarticular part were drilled away.

Afterward, the intertransverse ligament was partially

excised or released to expose the nerve root lateral to the

foramen. Then, the affected nerve root was followed along

the intervertebral foramen. Sufficient nerve root decom-

pression was carefully confirmed by moving a small nerve

hook from the lateral side through the foramen. If neces-

sary, the disc space was also exposed for complete nerve

root decompression.

In this technique, an intertransverse interval approach is

used via a paraspinal muscle-splitting route, and the

superolateral part of the superior articular process of the

lower vertebrae, the lateral part of the pars interarticularis,

and the superomedial part of the superior articular process

are resected, resulting in unroofing of the stenotic foramen.

Inferior partial pediculectomy can be performed to achieve

adequate decompression [1–6].

PLIF group

PLIF was performed in the usual manner [14, 15]. A single

midline incision of approximately 8 cm in length was

made, followed by exposure of the spine to the facet joints

Eur Spine J (2015) 24:388–395 389

123

and the lateral tips of the transverse processes to allow

clear identification of the bony landmarks. First, a pedicle

screw was inserted using the Weinstein method. Following

the decompression procedures, including laminectomy and

facetectomy, the compressed nerve root in the extrafora-

minal area was identified and the final decompression state

was confirmed. In the case of unilateral LFS, unilateral

decompression and interbody fusion with bilateral fixation

was performed. Finally, discectomy was performed and the

cage filled with auto bone was inserted.

Surgical outcome assessment

Baseline data, which were collected by a blinded clinical

research assistant, included sex, age, height, weight,

symptom duration, walking distance in a single trial, pre-

operative visual analog scale (VAS) scores for back and leg

pain, preoperative Oswestry Disability Index (ODI) score,

and general health status using the Short Form (SF)-36.

The primary outcome was ODI score at 1 year after sur-

gery. The ODI is based on a self-administered question-

naire measuring ‘‘back-specific function.’’ The

questionnaire comprises 10 items, each with 6 levels of

response. Each item is scored from 0 to 5, and the total

summation is converted to a 0–100 scale [16]. Secondary

outcome measures included ODI and VAS scores for back

and leg pain over all follow-up assessments, and general

health status at 1 year after surgery. The VAS for back pain

and leg pain comprised a 10-cm line with ‘‘none’’ (0) on

one end of the scale and ‘‘disabling pain’’ (10) on the other.

Patients were asked to place a mark on the line, which

represented their perceived level of back pain, and the

measured distance (cm) from the mark to the zero point

was considered the score. The ODI score and VAS score

for back pain and leg pain were assessed at 3, 6, and

12 months after surgery. The SF-36 score was assessed

preoperatively and at 12 months after surgery. The raw

scores for the eight subscales (physical function, role

Fig. 1 Enrollment, assigned interventions, and follow up of the study participants

390 Eur Spine J (2015) 24:388–395

123

physical, bodily pain, general health, vitality, social func-

tion, role emotion, and mental health) and two summaries

(Physical Component Summary [PCS] and Mental Com-

ponent Summary [MCS]) of the SF-36 were transformed

into norm-based scoring [17]. Rates of revision surgery

also were assessed at 12 months after surgery.

Statistical analysis

Preoperative ODI score, VAS scores for back and leg pain,

MCS and PCS scores of the SF-36, and demographic data

were compared between the two groups using an inde-

pendent t test. The outcome analysis was performed by

comparisons between the MeFD alone and PLIF groups.

All data were evaluated using intention-to-treat analyses.

The ODI scores (mean and 95 % confidence interval [CI])

at 1 year after surgery were compared between the MeFD

and PLIF groups using an independent t test. If the CIs of

the differences between the two groups were within ± the

predetermined margin of equivalence (minimal important

change of 10 for the ODI score) [18], the two surgical

methods were considered equivalent. Analysis of variance

for repeated measures was performed to examine the sur-

gical outcome measures (VAS scores for back and leg pain

and ODI score) between the two groups over the follow-up

assessment period. In addition, general health status (PCS

and MCS scores) at 12 months after surgery was examined

using an independent t test. Furthermore, in each group,

any changes in general health status, such as PCS and MCS

scores, from study enrollment to 12 months after surgery

were compared with a paired t test. All statistical analyses

were performed with the SPSS 20.0.0 statistics package

(IBM Corporation, Armonk, NY), with an alpha level of

significance set at 0.05.

Fig. 2 Schematic drawing and

photograph of actual operative

field during microsurgical

extraforaminal decompression

(asterisk indicates left L4 root,

star indicates left L4 lamina).

a Illustration for lumbar

foraminal stenosis (arrow and

greyed area is resected using

burr). b Illustration after

microsurgical extraforaminal

decompression. c Photographs

of actual operative field (low

and high magnifications)

Eur Spine J (2015) 24:388–395 391

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Results

Between June 2012 and March 2013, 75 patients were

assessed for study eligibility. Fifty-five participants met the

inclusion criteria. According to the chosen surgical tech-

nique, patients were assigned to either the MeFD group

(n = 25) or the PLIF group (n = 30). Figure 1 shows the

number of patients involved in the present study, from

eligibility assessment through 12 months of follow-up. At

the 12 month assessment after surgery, complete data were

available for 22 and 27 patients in the MeFD and PLIF

groups, respectively. The baseline characteristics of the

patients were similar between the two groups (Table 1). All

patients had a single-level lumbar stenotic lesion. The

mean age of the two groups was 73.12 ± 6.75 years and

70.00 ± 5.62 years in the MeFD and PLIF groups,

respectively. Preoperative ODI score, VAS scores for back

and leg pain, and PCS/MCS scores of the SF-36 were not

significantly different between the two groups (Table 1).

According to surgical technique, the ODI scores (pri-

mary endpoint) at 12 months after surgery were equivalent

between groups (Fig. 3). At the 12 month assessment, the

mean ODI score in the MeFD and PLIF groups was

25.68 ± 14.49 and 27.20 ± 12.56, respectively, and the

95 % CI (-9.76–6.73) was within the ± predetermined

margin of equivalence (ODI score, 10).

There were no significant differences in any of the sec-

ondary endpoint variables, including ODI score and VAS

scores for back and leg pain, over the follow-up assessments

for 1 year between the two groups (Fig. 3). The overall

changes in ODI and VAS scores for back and leg pain did

not differ significantly over a 12 month period between the

two surgical techniques (effect of surgical technique on

overall changes in ODI and VAS scores for back and leg

pain for follow-up periods, P = 0.978, 0.626, and 0.909,

respectively). The patterns of changes in the ODI and VAS

scores for back pain and leg pain during the follow-up

period were not significantly different between the both

cohorts (effect of the interaction between surgical technique

and postoperative follow-up assessment time on ODI and

Table 1 Descriptive statistics of the subjects in the study

Extraforaminal

decompression

group (25)

Interbody

fusion group

(30)

P value

Age (years) 73.12 ± 6.75 70.00 ± 5.62 0.067

Male:female 9:16 9:21

BMI (kg/cm2) 25.63 ± 5.34 24.98 ± 3.23 0.215

VAS for back pain 6.05 ± 3.02 7.21 ± 2.80 0.194

VAS for leg pain 7.81 ± 1.63 7.75 ± 2.42 0.924

ODI 46.45 ± 15.98 53.52 ± 13.73 0.114

Symptom duration

(months)

13.67 ± 4.68 14.42 ± 6.34 0.329

Walking distance

at a single trial

(min)

19.34 ± 22.32 22.43 ± 19.59 0.296

SF-36 PCS 26.35 ± 6.95 26.55 ± 6.57 0.928

SF-36 MCS 38.61 ± 11.91 37.70 ± 12.81 0.822

Operated level (n) L3–L4:3 L1–L2:1

L4–L5:13 L3–L4:1

L5–S1:9 L4–L5:14

L5–S1:14

Values are mean ± SD

BMI body mass index, SD standard deviation, VAS Visual Analog

Pain Scale, ODI Oswestry Disability Index, SF-36 Short Form-36,

PCS physical component summary, MCS mental component

summary

Fig. 3 Surgical outcomes at each follow-up assessment (3, 6, and

12 months). Error bars indicate 95 % confidence intervals. a Osw-

estry Disability Index (ODI): equivalent comparison at 12 months

(primary endpoint). b Visual analog scale (VAS) for back pain.

c VAS for leg pain

392 Eur Spine J (2015) 24:388–395

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VAS scores for back and leg pain, P = 0.381, 0.246, 0.364,

respectively). However, the ODI score and VAS scores for

back and leg pain improved significantly with time after

surgery in both groups (effect of postoperative follow-up

assessment time on ODI and VAS scores for back and leg

pain, P \ 0.001 for all variables). General health status,

represented by PCS and MCS scores of the SF-36, at 1 year

after surgery did not differ significantly between the two

groups (P = 0.643 and 0.818, respectively) (Fig. 4).

However, compared with the initial values, both the MeFD

and PLIF groups showed significant increases in the PCS

score at 12 months (P = 0.010 and 0.021, respectively),

whereas the MCS scores at 12 months were not different

from the initial values in both groups (Fig. 4).

In the MeFD group, revision surgery was required in 3

of 25 patients (12 %). Two patients underwent revision

surgery (PLIF) at 2 and 3 months, respectively, after the

first MeFD due to foraminal stenosis at the level of first

decompression surgery, and one patient underwent revision

surgery (PLIF) due to iatrogenic pars and pedicle fractures

at the level of first decompression surgery at 3 months

postoperatively (Fig. 5).

Discussion

This study demonstrates that MeFD alone for LFS can

provide equivalent results regarding improvement in ODI

score at 1 year after surgery, compared with PLIF. Fur-

thermore, there were no differences in improvement in

disability, back and leg pain, and general health status

(PCS and MCS scores of the SF-36) between the two

groups across 1 year of follow-up assessments after sur-

gery. However, it should be acknowledged that revision

surgery was required in 3 of 25 patients (12 %) within

3 months after the initial surgery in the MeFD group.

These two surgical methods can be considered equiva-

lent regarding improvement in ODI score at 1 year after

surgery. Furthermore, the overall improvements in ODI

score and VAS scores for back and leg pain with time after

surgery did not differ between the two groups. These

results agree with those of previous studies [8, 19]. They

reported no obvious additional benefit by combining

decompression with instrumented fusion in degenerative

LSS, compared with decompression alone; thereby advo-

cating decompression alone [8, 19]. Furthermore, the

exclusion of patients with spinal instability would con-

tribute to this result. The present study also suggests that

MeFD can yield not only equivalent improvement in dis-

ability at 1 year after surgery, compared with PLIF, but

also overall improvement in disability, back pain, and leg

pain across 1 year postoperatively were not different

between the two groups.

Notably, in the MeFD group, three patients required

revision surgery due to recurrence of similar leg pain,

whereas no patient required revision surgery in the PLIF

group. All revision surgeries were PLIFs, which were

performed within 3 months after the initial operation. Two

patients underwent revision surgery due to foraminal ste-

nosis at the level of first decompression surgery, and one

patient due to iatrogenic pars and pedicle fractures at the

level of first decompression surgery. The former two cases

are not considered as degenerative restenosis at the

decompression level, but as inadequate decompression in

the first MeFD, because the patient’s symptoms, such as

leg pain, arose again within only 2 and 3 months, respec-

tively. The latter case is considered as over decompression.

Excessive decompression can cause the operated segment

to be more vulnerable to external moments or load, which

can result in pars and pedicle fractures at the same level

within 2 months after the initial MeFD surgery. In sum-

mation, these findings indicate that MeFD is more techni-

cally demanding regarding the optimal amount of

decompression. In our study, the two inadequate decom-

pression cases could have been treated successfully with

additional partial pediculectomy, which has been suggested

in previous studies regarding MeFD [2, 3, 6]. However, the

Fig. 4 Quality of life represented by physical component summary

(PCS) and mental component summary (MCS) of the Short Form

(SF)-36 at initial enrollment and 12 months after surgery between

groups. Error bars indicate SDs. a PCS. b MCS

Eur Spine J (2015) 24:388–395 393

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one case of pedicle fracture has also raised worries

regarding over decompression. Therefore, an ideal amount

of decompression optimized for each case is necessary for

successful outcomes of MeFD.

The current study has both strengths and weaknesses.

Most of all, the homogenous diagnosis in both groups is a

strength. All patients in both groups had single-level LFS.

Regarding limitations of this study, first, the present study

was not a randomized controlled trial, but a prospective

observational cohort study. Even though there were no

differences in the demographic data between the two groups

(Table 1), patient allocation was decided by a preference

under the shared-decision-making system. The individual

preference was associated with psychosocial factors and

socioeconomic status [20], which could have influenced the

results. Therefore, it should be acknowledged that the

present results might have unrevealed bias due to the study

design. Second, patients in the present study were followed

up for 1 year postoperatively. In the long term, patients who

underwent MeFD alone could develop restenosis at the

operated level due to progression of degenerative changes

[5], while patients in the PLIF group have higher risk of

adjacent segment degeneration. Therefore, a long-term

follow-up study would provide more comprehensive

understanding regarding the effectiveness of both surgical

methods. Nonetheless, the present results after 1 year of

follow-up show a higher rate of revision surgery after

MeFD alone, which emphasizes the technically optimal

amount of decompression. Third, authors did not use a more

specific questionnaire for lumbar stenosis, such as the

Zurich claudication questionnaire because there was not a

language-validated version. In a future study of outcome

analysis for spinal stenosis, this should be included for a

more verified comparative outcome analysis.

Fig. 5 Cases requiring revision surgery after microsurgical extrafo-

raminal decompression (MeFD). a Case 1: foraminal stenosis was

noted even after MeFD. (arrow head indicates foraminal stenois).

b Case 2: pedicle and pars fractures were noted. (arrow head indicates

pars fractures after extraforaminal decompression)

394 Eur Spine J (2015) 24:388–395

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In conclusion, we demonstrated that MeFD alone and

PLIF have equivalent outcomes regarding improvement in

disability at 1 year after surgery. However, the higher rate

of revision surgery in the MeFD group should emphasize

the technically optimal amount of decompression.

Conflict of interest The authors have no conflict of interest to

declare.

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