Asian Spine Journal
968 Shu Nakamuraal.
Clinicalet Study

Asian Spine J 2017;11(6):968-974 • https://doi.org/10.4184/asj.2017.11.6.968
Asian Spine J 2017;11(6):968-974

Area of Ostectomy in Posterior Percutaneous
Endoscopic Cervical Foraminotomy: Images andMid-term Outcomes
Shu Nakamura, Mitsuto Taguchi
Department of Orthopedic Surgery, Aichi Spine Institute, Aichi, Japan

Study Design: Retrospective.
Purpose: To analyze whether the cross-sectional area of the intervertebral foramen at the outermost edge of the resection site is associated with postoperative outcomes and whether our fluoroscopic method for determining the resection area is appropriate.
Overview of Literature: There is no consensus on the criteria for determining an optimal resection area to obtain sufficient decompression while maintaining intervertebral stability in posterior percutaneous endoscopic cervical foraminotomy. Previous reports
have recommended a facet resection rate (FRR) of ≤50%. Intervertebral foramen stenosis often extends to the exit zone. The crosssectional area of the intervertebral foramen is occasionally small at the outermost edge of the resection site. No report has analyzed
whether these aspects are associated with postoperative outcomes.
Methods: Lateral margins of the resection area were set at lateral borders of the vertebral body on frontal fluoroscopic view. Because the percutaneous endoscope has a small diameter, surrounding structures can easily be identified using frontal view fluoroscopy to determine the resection area. FRRs were calculated from postoperative computed tomography images. The smallest crosssectional area of the intervertebral foramen around the lateral edge of the resection area (SALE) was measured and compared withclinical outcomes.
Results: The mean FRR was 41.7% at C5–C6 and 48.9% at C6–C7. SALE was not correlated with clinical outcomes.
Conclusions: Residual stenosis in the lateral portion of the intervertebral foramen is weakly associated with postoperative outcomes. Our process achieved adequate FRRs and favorable postoperative outcomes, suggesting that our criteria for determining theresection area are appropriate.
Keywords: Foramen; Cervical; Percutaneous endoscope; Resection area

Introduction
In posterior percutaneous endoscopic cervical foraminotomy (P-PECF), an endoscope is placed close to the target
to provide an excellent view in a minimally invasive man-ner [1,2]. Unlike anterior cervical decompression, posterior foraminotomy allows safe and efficient nerve root
decompression and also preserves intervertebral mobility
and prevents accelerated degeneration of the adjacent intervertebral discs [3-6]. However, in posterior foraminot-

Received Jan 13, 2017; Revised Mar 21, 2017; Accepted Mar 26, 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 Ⓒ 2017 by Korean Society of Spine Surgery

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

Asian Spine Journalomy, the spinous process restricts the direction of resection. Hence, the facet joint is also resected in proportion
to the extent of intervertebral foramen decompression.
Extensive facet joint resection may induce intervertebral
instability. In three-dimensional finite element analysis
models, facet joint resection by 50% results in 15%–18%
increases in lateral bending and rotation [7]. In vitro models have demonstrated that facet joint resection by >50%
causes segmental hypermobility. Therefore, Zdeblick et
al. [8] have recommended that facet joint resection andcapsule stripping should be limited to <50% of the facet.
Nerve root compression is predominantly observed at theentrance zone of the intervertebral foramen, where thenerve is large. Decompression can be achieved by resecting the medial half of the facet joint [9]. Generally, inposterior foraminotomy, the medial side of the facet joint
is removed while preserving the lateral side. However, inmany cases, intervertebral foraminal stenosis extends tothe exit zone. On resecting the facet joint by ≤50%, thecross-sectional area of the intervertebral foramen at thelateral edge of the resection area cannot be sufficiently enlarged. The association between the cross-sectional area of
the intervertebral foramen at the lateral edge of the resection area and postoperative outcomes remains unknown.
This study aimed to elucidate this association. Although
the resection area is difficult to determine using endoscopy, the percutaneous endoscope has a small diameter anddoes not interfere with surrounding structures on fluoroscopy. In the present study, we determined the resection
area from the intraoperative frontal fluoroscopic view andexamined whether this process is appropriate.

Materials and Methods
1. General information
In addition to conventional axial and sagittal views ofmagnetic resonance and computed tomography (CT) images, T2-weighted images were collected from the rightand left sides at an oblique angle of 30° from the sagittal
plane for detailed preoperative examination of the intervertebral foramen (Fig. 1). This method provided approximate images of the cross-sectional area of the intervertebral foramen. Indications for P-PECF were radiculopathy
due to cervical intervertebral foramen stenosis. This
retrospective study included 104 patients (88 men and 16
women, mean age: 55.2 years) who underwent P-PECF

Area of ostetomy in PECF 969

Fig. 1. T2-weighted magnetic resonance images were collected fromthe right and left sides at an oblique angle of 30° (yellow line) fromthe sagittal plane for detailed preoperative examination of the intervertebral foramen.

performed by the first author between February 2011 andNovember 2015.
2. Surgical method and follow-up
A percutaneous full-endoscopic system was used, which
comprised a light source, an endoscope, an irrigation
channel, and a working channel. Surgery was performed
under general anesthesia with patients in the prone position with a Relton–Hall frame and ProneView system(DUPACO, Oceanside, CA, USA). The neck was slightly
flexed, and the head was fixed with tape. C-arm fluoroscopy was arranged to display frontal and lateral views of
the cervical vertebrae. The operator stood contralateral tothe affected side. A 7-mm-paramedian incision throughthe skin and fascia was made. An inferior oblique φ7.5
sheath (ASAP, Umkirch, Germany) and a percutaneousendoscope (ASAP SES endoscope φ6.3 mm) were inserted through the incisions after dilation using a dilator.
The operator’s elbows were placed on a stand to ensure
the stability of the percutaneous endoscope. Ostectomy
was performed using a percutaneous endoscopic surgical drill with diamond burrs of 3 and 2 mm in diameter.
Sharp points at ostectomy site edges were removed using a
curved curette (Fig. 2). The drain was removed the following day. Patients were ambulated at 3 h after surgery anddischarged the following day. They wore a soft neck collar for 1 week and were scheduled to visit the outpatient
clinic at 1, 6, 12, and 24 months postoperatively.

970 Shu Nakamura et al.

Asian Spine J 2017;11(6):968-974

Fig. 2. Sharp points at the edges of the ostectomy site were removed
using a curved curette.

Fig. 4. Postoperative computed tomography images were reconstructed to obtain several cross-sectional images vertical to the longitudinal
axis of the intervertebral foramen at the operated vertebral level. The
smallest cross-sectional area (yellow line) of the intervertebral foramen around the lateral edge (blue line) of the resection area (SALE)
was selected and measured.

4. Postoperative evaluations

Fig. 3. Lateral aspect of the facet joint was resected sufficiently
beyond the lateral borders of the vertebral body under frontal fluoroscopic view. The lateral borders of the vertebral body are often difficult
to identify on fluoroscopic images and should be located based on thepositional relationship with the pedicle at the cranial and caudal sides
on preoperative radiographs.

3. Facet joint resection area
Although the perineural membrane was preserved, nerve
root relief was visible under hydraulic pressure. Cranialand caudal sides of the facet joint were resected until sufficient decompression was endoscopically confirmed. The
lateral aspect of the facet joint was sufficiently resectedbeyond lateral borders of the vertebral body under frontal
fluoroscopic view. Lateral borders of the vertebral bodyare often difficult to identify on fluoroscopic images andshould be located based on the positional relationshipwith the pedicle at cranial and caudal sides on preoperative radiographs (Fig. 3).

Using the POP-net web server (ImageONE Co., Tokyo, Japan) of a Digital Imaging and Communications in Medicine viewer, postoperative CT images were reconstructedto obtain several cross-sectional images vertical to thelongitudinal axis of the intervertebral foramen at the operated vertebral level. The smallest cross-sectional area of
the intervertebral foramen around the lateral edge of theresection area (SALE) was selected and measured (Fig. 4).
Patients completed self-administered questionnaires onpreoperative and postoperative symptoms. Clinical outcomes were determined based on visual analog scale (VAS)
scores for cervical and upper limb symptoms and thegeneral symptom remnant (GR=current general symptom
VAS/preoperative general symptom VAS×10), which reflects the severity of residual symptoms, including cervicaland upper limb symptoms. GR scores of 0–3 were considered as excellent, 0–6 as responsive to treatment, and ≥7
as poor.
From axial CT images of the middle level of the facet
joint, the preoperative facet length (FL) and postoperative
facet length (poFL) were measured. The facet resection
rate (FRR) was calculated using the following formula:(FL−poFL)/FL×100% (Fig. 5). Hypothetical FRRs (hFRRs)
were calculated for an area extending 2 mm laterally fromouter edges of the vertebral body (Fig. 6). Actual FRRs(aFRRs) were calculated immediately after surgery. All

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Area of ostetomy in PECF 971
between the excellent and poor outcome groups were analyzed using unpaired Student’s t-test or Fisher’s exact test.
A p-value of <0.05 was considered significant.

ResultspoFL

FL

Fig. 5. From axial computed tomography images of the middle levelof the facet joint, the preoperative facet length (FL) and postoperative
facet length (poFL) were measured. The facet resection rate (FRR)=(FL−poFL)/FL.

2 mm

FL
hpoFL

Fig. 6. Hypothetical facet resection rate (hFRRs) were calculated foran area extending for 2 mm laterally (blue line) from the outer edgesof the vertebral body. FL, facet length; hpoFL, hypothetical postoperative facet length; hFRR=(FL-hpoFL)/FL.

measurements were performed by an orthopedist who
was blinded to the clinical outcome.
5. Statistical analysis
We calculated the Pearson’s correlation coefficient to assess the association between GR and SALE. Differences

Of the 104 patients, 10 had lesions in C4–C5, 38 in C5–
C6, 54 in C6–C7, and two in C7–T1. Dural tear or apparent root injury did not occur during surgery in any
patient. Excluding 20 patients enrolled during the early
study period, the mean operative time for the remaining
patients was 76.7 minutes. No patient developed spondylolisthesis after surgery. Data on postoperative outcomes
were obtained from 92 patients (mean follow-up period,
10.1 months [range, 1–24 months]). Excellent outcomes(GR; current general symptom, 0–3) were achieved in
66.3% of them (61 patients, the excellent outcome group).
Patients responsive to P-PECF (GR, 0–6), including thosein the excellent outcome group, accounted for 87.0% of
the total patients (80 patients, the responsive group). Poor
outcomes (GR≥7) were observed in 13.0% patients (12patients, the poor outcome group). Reasons for poor outcomes (including multiple reasons in some patients) were
multiple operations on the neck in four patients (33%),
concurrent stenosis at another site in seven (58%), unknown in two (17%), diagnosis-related problems in one(8%), and insufficient decompression in one (8%) who
was enrolled in the early study period.
Among patients undergoing single-level P-PECF who
did not undergo any other surgical procedure for the operated vertebra, SALE was measured in 82 patients with
GR data. The mean SALE was 0.58 cm2 (range, 0.14–1.18
cm2). No correlation was observed between GR and SALE(r =0.0785, p =0.241). A comparison between 57 patientsin the excellent outcome group (GR, 0–3) and nine in
the poor outcome group (GR≥7) revealed that the mean
SALE was slightly larger in the former (0.59 cm2) than in
the latter (0.48 cm2), but this difference was not significant(unpaired t -test, p =0.088).
A comparison of GRs obtained within 6 months after
surgery and GRs obtained at 1–2 years after surgery indicated that no patient had GR worsened by ≥3 points. No
patient underwent reoperation at the same site because ofdeterioration.
VAS scores for preoperative cervical and upper limb
symptoms were 6.68 and 6.14 in the excellent outcome
group and 6.38 and 7.00 in the poor outcome group, re-972 Shu Nakamura et al.
spectively. Although VAS scores for preoperative upper
limb symptoms were higher in the poor outcome groupthan in the excellent outcome group, no significant difference was observed in VAS scores for cervical or upper
limb symptoms (p =0.378 and 0.201, respectively).
Among consecutive surgical patients enrolled in thelate study period, P-PECF was performed at C5–C6 in 20
patients and C6–C7 in 20 patients. For C5–C6, the meanhFRR was 37.6% (range, 25.8%–52.4%) and the meanaFRR was 41.7% (range, 13.7%–57.7%). For C6–C7, themean hFRR was 46.4% (range, 28.1%–59.0%) and themean aFRR was 48.9% (range, 38.9%–56.7%). A correlation was observed between aFRRs and hFRRs (r =0.48161,
p =0.826×10-3).
Eight patients underwent CT immediately after surgery
and at ≥1 year after surgery. In all patients, CT revealed
reductions in the size of the resection area (at the ostectomy site area shown from the dorsal side using threedimensional CT). Annual reduction rates were 40.4%(range, 15.4%–73.8%) for the resection area, 24.8% (range,
5.3%–50.8%) for SALE, and 37.7% (range, 8.0%–86.9%)
for the width of the facet joint resection area. Despite
these reductions, no patient suffered a relapse of symptoms.

Discussion
1. Setting the resection area
In P-PECF, the perineural membrane is compressed by
perfusion pressure. This makes the nerve root relief clearlyvisible while preserving the perineural membrane, thereby reducing the risk of severe bleeding. Because cranialand caudal edges of the nerve root are visible, determining whether the decompressed area is sufficient at cranialand caudal sides is easy. However, determining whether
lateral sides of the decompressed area are sufficient basedon the morphology of the nerve root in the endoscopic
view is difficult. Unlike the dura, the root is not distended
too much even when it is loosened; therefore, constriction
at the root is unlikely to be distinguished. In addition, theforamen is a narrow space and contains no gap on thedorsal side even under loose conditions. Therefore, checking whether there is sufficient room is not possible fromthe dorsal view. Although adequate facet joint resection isnecessary to decompress the nerve root, the resection area
is limited because of the risk of intervertebral stability.

Asian Spine J 2017;11(6):968-974
Zdeblick et al. [8] have reported that instability slightly increases with an FRR of up to 50% but markedly increases
with an FRR of 75%. They have further indicated that thejoint capsule plays an important role in intervertebral
stability [8]. No consensus has been reached on the diagnostic criteria for determining an optimal resection area
to obtain both adequate decompression and intervertebral
stability. Although the resection area width is determinedbased on preoperative measurement, intraoperatively
determining the amount of resected facet joint is difficult.
One report has stated that using the width of a drill burr
as a measure, an area extending for 3–4 mm from the inner edge of the facet joint can be resected under the endoscopic view [10]. However, this method is ambiguous. As
ostectomy progresses during surgery, the landmarks are
removed, and accurate measurement is consequently difficult.
Due to its small diameter, a percutaneous endoscope
does not interfere in the viewing of surrounding structures on the intraoperative frontal fluoroscopic view. Thus,in the present study, an area extending sufficiently beyond
the outer edges of the vertebral body was decompressedusing the outer edges or pedicle on the intraoperative
frontal fluoroscopic view as a landmark. The distance tothe outer edge of the facet joint was checked to determine
the resection area. This process was easy to execute during
surgery, the decompressed area appeared to be necessary
and sufficient, and favorable outcomes were obtained.
Poor postoperative outcomes were associated with multiple rounds of cervical surgery and stenosis at other sites.
Insufficient decompression was not a major cause. The
severity of preoperative symptoms did not seem to affectpostoperative outcomes.
The mean aFRR was 41.7% at C5–C6 and 48.9% at C6C7, suggesting that the setting methods for the resection
area were appropriate. Although there were patients inwhom the facet joint was resected by >50%, it is assumed
that an FRR of >50% does not cause any problems withintervertebral stability because of postoperative bone regeneration. On preoperative CT images, hFRRs were calculated to be 37.6% at C5–C6 and 46.4% at C6–C7. hFRRs
varied depending on the vertebral level and also variedmarkedly among patients. Furthermore, a correlation wasobserved between aFRRs and hFRRs. It may be preferable to individually set the resection rate for each patient
according to the morphology of the lesion, similar to theprocess used in the present study. Despite the lack of evi-

Asian Spine Journal
dence of intervertebral instability on images, excessively
large resection areas lead to reduced stability and risk, accelerating intervertebral disc degeneration. However, it isassumed that resection by a little more than 50% does notcause any problem because of subsequent articular regeneration. Outcomes tend to be more favorable with a larger
SALE, and the resection area reduces with time. Thus,
it seems better to prioritize sufficient facet joint decompression over its preservation. Furthermore, ostectomy
performed with a drill whose burr tip is spherical leaves
sharp points on the ventral edges of the resection area.
Removing these points with a curved curette may reduce
nerve irritation.
2. SALE and clinical outcomes
FRR is used as an index to reflect the facet joint resection
area. Because FRR is difficult to calculate using a threedimensional model, in most cases, it is calculated fromtwo-dimensional images. Thus, FRR is not precise andcannot be regarded as a direct index of decompression.
Although one report on the association between FRR andclinical outcomes has been published [10], the association
between SALE and clinical outcomes remains unknown.
In the present study, no correlation was found between
clinical outcomes and SALE in the early or late study period and no significant difference in SALE was observed
between the excellent and poor outcome groups. Thesefindings are attributable to the importance of nerve root
decompression in the medial portion of the intervertebral
foramen, where the nerve is large [9]. Intervertebral foramen restenosis progressed from the lateral aspect becauseof bone regeneration at the ostectomy site after surgery;however, the symptoms did not relapse. This may be associated with the absence of a correlation between SALE
and clinical outcomes. Although limiting FRRs to ≤50%
to prevent intervertebral instability may result in insufficient decompression at the lateral aspect of the intervertebral foramen due to a reduced resection area, it seems thatclinical outcomes are not greatly affected.
3. Limitations of the present study
This study was retrospective, and the dropout rate duringfollow-up was relatively high (11.5%). Moreover, the follow-up period was not long. In this study, we investigated
how the resection area relates to clinical results; therefore,

Area of ostetomy in PECF 973
we believe that it is reasonable to assess mid-term results
rather than long-term results, which are greatly affectedby the natural course.

Conclusions
The criteria used to determine the resection area on theintraoperative frontal fluoroscopic view are appropriate
and useful for determining the resection area and achieving an adequate FRR and favorable postoperative outcomes. Residual stenosis at the lateral aspect of the intervertebral foramen is weakly associated with postoperative
outcomes, therefore limiting FRRs to prevent intervertebral instability does not seem to interfere with favorable
clinical outcomes.

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

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

References
1. Ruetten S, Komp M, Merk H, Godolias G. Fullendoscopic cervical posterior foraminotomy for theoperation of lateral disc herniations using 5.9-mm
endoscopes: a prospective, randomized, controlled
study. Spine (Phila Pa 1976) 2008;33:940-8.
2. Ruetten S, Komp M, Merk H, Godolias G. A new
full-endoscopic technique for cervical posterior foraminotomy in the treatment of lateral disc herniations using 6.9-mm endoscopes: prospective 2-year
results of 87 patients. Minim Invasive Neurosurg
2007;50:219-26.
3. Caglar YS, Bozkurt M, Kahilogullari G, et al. Keyhole
approach for posterior cervical discectomy: experience on 84 patients. Minim Invasive Neurosurg
2007;50:7-11.
4. Clarke MJ, Ecker RD, Krauss WE, McClelland RL,
Dekutoski MB. Same-segment and adjacent-segment
disease following posterior cervical foraminotomy. J
Neurosurg Spine 2007;6:5-9.
5. Jagannathan J, Sherman JH, Szabo T, Shaffrey CI,

974 Shu Nakamura et al.
Jane JA. The posterior cervical foraminotomy in thetreatment of cervical disc/osteophyte disease: a single-surgeon experience with a minimum of 5 years’
clinical and radiographic follow-up. J Neurosurg
Spine 2009;10:347-56.
6. Hilibrand AS, Balasubramanian K, Eichenbaum M,
et al. The effect of anterior cervical fusion on neckmotion. Spine (Phila Pa 1976) 2006;31:1688-92.
7. Chen BH, Natarajan RN, An HS, Andersson GB.
Comparison of biomechanical response to surgicalprocedures used for cervical radiculopathy: posterior
keyhole foraminotomy versus anterior foraminotomy
and discectomy versus anterior discectomy with fu-

Asian Spine J 2017;11(6):968-974
sion. J Spinal Disord 2001;14:17-20.
8. Zdeblick TA, Zou D, Warden KE, McCabe R, Kunz D,
Vanderby R. Cervical stability after foraminotomy:
a biomechanical in vitro analysis. J Bone Joint Surg
Am 1992;74:22-7.
9. Tanaka N, Fujimoto Y, An HS, Ikuta Y, Yasuda M.
The anatomic relation among the nerve roots, intervertebral foramina, and intervertebral discs of thecervical spine. Spine (Phila Pa 1976) 2000;25:286-91.
10. Kim CH, Kim KT, Chung CK, et al. Minimally invasive cervical foraminotomy and diskectomy forlaterally located soft disk herniation. Eur Spine J
2015;24:3005-12.