Asian Spine Journal
294 Shu Nakamuraal.
Clinicalet Study

Asian Spine J 2018;12(2):294-299 • https://doi.org/10.4184/asj.2018.12.2.294
Asian Spine J 2018;12(2):294-299

Percutaneous Endoscopic Cervical Discectomy:
Surgical Approaches and Postoperative
Imaging Changes
Shu Nakamura, Mitsuto Taguchi
Department of Orthopedic Surgery, Aichi Spine Institute, Niwa-gun, Aichi, Japan

Study Design: Retrospective clinical study.
Purpose: This study investigated the relationship between surgical approaches and surgical outcomes in patients undergoing percutaneous endoscopic cervical discectomy (PECD), including the reduction in intervertebral disc height and the incidence of Modicchanges.
Overview of Literature: The anterior approach involves partial invasion of the intervertebral disc, with a reported reduction in intervertebral disc height after PECD.
Methods: Forty-two patients with cervical disk hernia who underwent PECD and magnetic resonance imaging at least 3 months postoperatively were divided into four groups according to the hernia sites and the surgical approach used: unilateral hernia treated using
the contralateral approach (group C, n=18), unilateral hernia treated using the ipsilateral approach (group I, n=15), midline hernia (groupM, n=4), and broad and bilateral hernia (group B, n=5). Modic changes and intervertebral disc height were evaluated.
Results: The overall incidence of Modic changes was 52.4%: 72.2% in group C, 26.7% in group I, 25.0% in group M, and 80.0% ingroup B. The reduction in intervertebral disc height was 21.8% across all the patients: 24.5% in group C, 11.0% in group I, 22.8% ingroup M, and 23.9% in group B.
Conclusions: The incidence of Modic changes and the reduction in intervertebral disc height were lower in the patients treated using the ipsilateral approach than in those treated using the contralateral approach. Traditionally, a contralateral approach has beenused for PECD; however, the ipsilateral approach is more appropriate and is therefore recommended.
Keywords: Intervertebral disc displacement; Magnetic resonance imaging; Endoscopes; Minimally invasive surgical procedures

Introduction
Anterior cervical discectomy and fusion (ACDF) is thestandard treatment for cervical disk hernia [1]. However,there is a concern that cervical fusion may accelerate adjacent segment degeneration by increasing mechanicalstress [2-5]. Conversely, percutaneous endoscopic cervicaldiscectomy (PECD) can preserve the intervertebral disc,thereby avoiding adverse effects on the adjacent segments.
PECD uses a small outer tube and an endoscope with apercutaneous full-endoscopic system comprising a lightsource, an endoscope, a working channel, and an irriga-

Received Apr 20, 2017; Revised Jul 23, 2017; Accepted Aug 16, 2017
Corresponding author: Shu Nakamura
Department of Orthopedic Surgery, Aichi Spine Institute, 41 Gouhigashi, Takao, Fuso-cho, Niwa-gun, Aichi 480-0102, Japan
Tel: +81-587-92-3388, Fax: +81-587-92-3304, E-mail: nakamura@itoortho.or.jp

ASJ

Copyright Ⓒ 2018 by Korean Society of Spine Surgery

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Asian Spine Journal • pISSN 1976-1902 eISSN 1976-7846 • www.asianspinejournal.org

Asian Spine Journaltion channel. However, the anterior approach involves
partial invasion of the intervertebral disc, and a reduction
in intervertebral disc height after PECD has been reported[6,7]. Intervertebral disc height is an index of intervertebral disc degeneration, although it is not always associatedwith clinical symptoms. The incidence of Modic changes,
which are considered to be associated with clinical symptoms [8,9], is unknown [10].
Traditionally, a contralateral approach has been used in
PECD because it offers better access than the ipsilateralapproach [6,7]. However, we consider the ipsilateral approach to be more appropriate. To the best of our knowledge, no study has assessed the difference between the twosurgical approaches in the invasion of the intervertebral
disc. This study examined the reduction in intervertebral
disc height and the incidence of Modic changes in patients undergoing PECD and investigated whether these
indices differed between the ipsilateral and contralateralapproaches.

Materials and Methods
1. General information
The study included patients who underwent PECD between August 2011 and December 2015 followed by magnetic resonance imaging (MRI) examination at least threemonths after the surgery. All patients had been diagnosed
with cervical disk hernia on MRI and had not responded
to conservative treatment. Patients with giant hernia andmarked myelopathy were excluded. Overall, 42 patients(33 men and 9 women) with a mean age of 46.0 years,
with surgical levels C3/4 (n=2), C4/5 (n=7), C5/6 (n=21),
and C6/7 (n=12) were included.
2. Surgical method and follow-up
The surgery was performed under general anesthesia withthe patient in a supine position. The head was fixed andpulled cranially with a Mayfield clamp. The upper extremities were placed along the body and pulled caudally.
X-ray fluoroscopy was used to visualize the process. Withthe trachea or larynx pushed toward the contralateral sidewith the fingers, an 18G spinal needle was inserted via theskin of the frontal neck, passing between the airway andthe internal carotid artery, and advanced to the intervertebral disc. After making a 5-mm skin incision, a dilator

PECD: approach – Modic change 295

Fig. 1. The endoscopic system used for percutaneous endoscopic cervical discectomy. This comprised a small outer tube (4.1 mm×6.7 mm,
square-tubular) and an endoscope with a percutaneous full-endoscopic system with a light source, an endoscope, and an irrigation channel.

was inserted over the guide wire. An outer tube (height
4.1 mm, width 6.7 mm, square-tubular) and endoscope(VERTEBRIS cervical anterior system; Richard Wolf Co.
Ltd., Knittlingen, Germany) was inserted (Fig. 1). Under
endoscopic observation using the continuous irrigation
method, the intervertebral disc hernia was dissected andremoved using forceps and a sharp curette. If required,an electric drill was used to dissect bone spurs. Whenthe hernia was extra ligamentous, it was removed with ahook probe and forceps following partial resection of theposterior longitudinal ligament. The patient was allowed
to walk 3 hours after surgery and was discharged the nextday, with the instruction to wear soft collars for one week.
During follow-up, the patients were scheduled to visit theoutpatient clinic at 1, 6, 12, and 24 months postoperatively
and to undergo MRI at 6, 12, and 24 months.
The selection of surgical approach (contralateral or ipsilateral) for patients with unilateral hernia was unrelated
to their individual characteristics. The contralateral approach was used for patients during the first half of thestudy period, whereas the ipsilateral approach was used
for patients during the second half of the study period.
3. Evaluation
The subjects were retrospectively divided into four groups
according to the sites of hernia and the surgical approaches used: unilateral hernia treated using the contralateralapproach (group C), unilateral hernia treated using theipsilateral approach (group I), median localized hernia
resected locally (group M), and broad and bilateral hernia
resected widely (group B). The main focus of the investigation was the differences between group C and group I(i.e., the contralateral and ipsilateral approaches) with regard to the intervertebral disc height, Modic changes, andneck and shoulder pain.

296 Shu Nakamura et al.

Asian Spine J 2018;12(2):294-299

Imaging measurements were made by a blinded orthopedic surgeon using a DICOM viewer with the POP-net
web server (Image ONE Co., Tokyo, Japan) on MRI images obtained 3–12 months after surgery. The intervertebral
disc height at the center of the surgically treated intervertebral disc was measured on a midline sagittal plane image. A T2-weighted fat suppression sequence was carefully
examined for Modic changes in the vertebral bodies. If apatient had Modic changes before surgery, he or she wasconsidered in the analysis to have Modic changes if thesewere exacerbated after surgery but not if they showed areduction. Pain in the neck and shoulder was reported
subjectively by the patient on a scale of 0–10, using a Visual Analog Scale (VAS).
Group C and group I were compared using a 2×2 chisquare test or unpaired Student t-test. Statistical significance was set at p<0.05.

(22/42). In the groups, the incidence of Modic changes
was 72.2% (13/18) in group C, 26.7% (4/15) in groupI, 25.0% (1/4) in group M, and 80.0% (4/5) in group B.
The incidence was significantly lower in group I than ingroup C (chi-square test, p=0.0091). At the time of the last
imaging follow-up, type 1 Modic changes were observedin 14 patients and type 2 changes in 8 patients. In somepatients, the Modic changes changed from type 1 to 2
during the clinical course. Two patients showed Modicchanges before surgery, and the Modic changes in one patient (in group I) disappeared after surgery. There was no
significant difference in the incidence of Modic changes
between subjects where an electric drill was used for bone
resection and those where a drill was not used (50.0%(12/24) versus 55.6% (10/18); chi-square test, p=0.9644).
The mean reduction in intervertebral disc height acrossall the subject was 21.8%±16.3%. The mean reduction foreach group was 24.5%±10.6% in group C, 11.0%±8.8%
in group I, 22.8% in group M, and 23.9% in group B. The
reduction was significantly lower in group I than in groupC (unpaired Student t-test, p=0.0002) (Table 1).
The mean VAS score for neck and shoulder pain was
somewhat higher in the subjects with Modic changes thanin those without Modic changes, but this was not statistically significant (4.4±3.4 versus 3.2±2.1; unpaired Student
t-test, p=0.0913). The general symptom remnant rate
(calculated as current general symptom VAS/preoperative
general symptom VAS×100) was 21.7%±17.9% in group
C, 20.0%±15.1% in group I, 17.5% in group M, and 24.0%
in group B. There was no significant difference between
group C and group I (unpaired Student t-test, p=0.3886).
The mean observation period was 13.8 months.

Results
There were 18 subjects in group C, 15 subjects in group I,
four subjects in group M, and five subjects in group B. The
mean time after surgery when the MRI was obtained was
7.6 months (range, 3–12 months). Comparisons between
group C and group I showed no significant differences in
the mean age of the subjects (43.7±9.5 versus 47.9±14.2,
p=0.1590), the mean resected disk volume (0.55±0.23 g
versus 0.51±0.24 g, p=0.3426), the male-to-female ratio(15:3 versus 11:4, p=0.4133), or the mean period between
surgery and MRI (8.8±3.3 months versus 7.0±3.3 months,
p=0.0629). No subject in either group experienced intraoperative complications.
The overall incidence of Modic changes was 52.4%

Table 1. Summary of the results of the percutaneous endoscopic cervical discectomy procedures

Variable

C

I

M

B

Total

No. of cases

18

15

4

5

42

Age (yr)43.7 (NS)47.9 (NS)

53.0

42.8

46.0

Resected volumes (g)0.55 (NS)0.51 (NS)

0.64

0.78

0.57

Male:female

15:3 (NS)11:4 (NS)

3:1

4:1

33:9

Observation period (mo)8.8 (NS)

7.0 (NS)

6.8

6.0

7.6

Reduction of disc height (%)

*

24.5

*

11.0

22.8

23.9

21.8

Incidence of Modic changes (%)

72.2*

26.7*

25.0

80.0

52.4

C, unilateral hernia treated using the contralateral approach; I, unilateral hernia treated using the ipsilateral approach; M, midline hernia; B, broad
and bilateral hernia resected widely; NS, not statistically significant.
*p <0.05.

Asian Spine Journal

PECD: approach – Modic change 297

Discussion
PECD is not widely used in clinical practice. Currently,
ACDF is a standard treatment for patients with cervical disk hernia. However, there is a concern that cervicalfusion may accelerate adjacent segment degeneration,although there is no consensus in this regard yet [2-5].
PECD can preserve the intervertebral disc, and it does not
result in the acceleration of adjunct segment degeneration
because it does not induce mechanical stress. However,
the anterior approach involves partial invasion of theintervertebral disc, with a reported reduction in intervertebral disc height after PECD of 11.2%–23.0% [6,7].
To the best of our knowledge, no previous studies haveinvestigated Modic changes after PECD without our preliminary study [10]. Although there is no consensus on
their clinical significance, we consider Modic changes tobe important in clinical practice, along with the reduction
in intervertebral disc height, because they are associatedwith local pain [8,9]. In the present study, the incidence ofModic changes was higher than that expected. Although
there was a tendency for neck and shoulder pain among
patients with Modic changes, the association was not statistically significant; this is possibly because several factors
can affect neck and shoulder pain.
There was no significant difference between the clinicaloutcomes of group C and group I, perhaps because there
can be a substantial time lag between the appearance ofchanges in imaging studies and the onset of clinical symptoms of degenerative diseases. Nevertheless, we believethat postoperative degeneration of the intervertebral discshould be minimized.
Several factors affecting the reduction in intervertebral disc height and causing Modic changes have been
discussed here. In our clinical experience, it is rare forpatients to develop Modic changes after percutaneousendoscopic lumbar discectomy (PELD). This suggests thatfactors common to both PELD and PECD, including theforce on the vertebral body when driving the dilator into
the intervertebral disc, irrigation, and radiofrequency
ablation, are unlikely to be the causes of Modic changes.
Furthermore, we used a Mayfield clump during PECD
surgery to increase the intervertebral space and reducethe influence of any direct external force. There were nodifferences in the incidence of Modic changes between
patients for whom an electric drill was used and thosewhere an electric drill was not used. We speculate that use

Fig. 2. The ipsilateral approach (group I) was less invasive on thecentral and nucleus pulposus region of the intervertebral disc than thecontralateral approach (group C). b, bronchial airway; e, esophagus; p,
uncinate process; C, area passed by the contralateral approach; I, area
passed by the ipsilateral approach.

of an electric drill resulted in no significant effects because
it caused limited bone resection, and its heating effect
was reduced by irrigation water. The reduction in intervertebral disc height and incidence of Modic changes was
lower in group I than in group C or group B. This may be
attributable to the less prominent invasion of the intervertebral disc, in particular, the central and nucleus pulposus
region, in group I (Fig. 2). We believe that it is important
to avoid injury to the central nucleus pulposus region
because this region has a shock-absorbing function, andbecause nutrients are barely supplied to the central part ofthe intervertebral disc by diffusion [11] and it is susceptible to injury [12,13].
Cervical disc herniation is often a lateral protrusion of
the disc close to the uncinate process, resulting from theeffect of the posterior longitudinal ligament. The trachea,
esophagus, and thyroid cartilage are located in front of thevertebral bodies and the right and left uncinate processesof the vertebral bodies in the deeper part. This anatomical
structure prevents an outer tube tip from turning toward
the ipsilateral direction, resulting in the contralateral approach being less difficult than the ipsilateral approach.
The contralateral approach has therefore been the approach usually used for patients with unilateral hernia[6,7] (Fig. 3). However, the ipsilateral approach is also
feasible, in our experience, no patients who underwent
PECD using the ipsilateral approach developed complica-298 Shu Nakamura et al.

Asian Spine J 2018;12(2):294-299
contralateral approach. Although the contralateral approach is widely used for patients with unilateral cervicaldisc hernias, we believe that the ipsilateral approach is
sufficiently secure and more appropriate to perform.

Conflict of Interest
No potential conflict of interest relevant to this article wasreported.

ORCID
Shu Nakamura: https://orcid.org/0000-0002-8015-7571

References
Fig. 3. There are airways and thyroid cartilage located in front of thevertebral bodies and the right and left uncinate processes of the vertebral bodies in the deeper part. This anatomical structure prevents
the outer tube tip from turning toward the ipsilateral direction, making
the contralateral approach less difficult than the ipsilateral approach.
Therefore, the contralateral approach is usually used for patients withunilateral hernia; however, the ipsilateral approach is also secure. b,
bronchial airway; e, esophagus; p, uncinate process; C, contralateralapproach; I, ipsilateral approach.

tions such as airway obstruction or esophageal disorder.
Therefore, we recommend the ipsilateral approach for patients with unilateral cervical disc hernia.
This study has some limitations. It was retrospective
and the number of cases was not large. In addition, thefollow-up period was not long; however, our aim was toinvestigate how results were related to the surgical approaches, so we believe that it was reasonable to use midterm results (at 3–12 months) rather than long-term results, which may be greatly affected by the natural course.
In MRI T2 fat suppression imaging, the influence of degeneration and edema is delicately visualized. Therefore,
we used MRI obtained at least 3 months postoperatively,
when there is no longer any influence on MRI of thedirect external force during surgery, in order to strictly
evaluate Modic changes.

Conclusions
In patients with unilateral hernia who underwent PECD,
the incidence of Modic changes and the reduction in intervertebral disc height were lower for those treated using
the ipsilateral approach than for those treated using the

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