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Clinical StudyPercutaneous Transforaminal Endoscopic LumbarInterbody Fusion: Clinical and Radiological Resultsof Mean 46-Month Follow-Up

Sang-Ho Lee,1 H. Yener Erken,2 and Junseok Bae1

1Department of Neurological Surgery, Spine Health Wooridul Hospital, Seoul, Republic of Korea2Department of Orthopaedic Surgery, Spine Health Wooridul Hospital, Seoul, Republic of Korea

Correspondence should be addressed to Junseok Bae; [email protected]

Received 8 November 2016; Revised 30 January 2017; Accepted 6 February 2017; Published 27 February 2017

Academic Editor: William B. Rodgers

Copyright © 2017 Sang-Ho Lee et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Background. Spinal fusion has been shown to be the preferred surgical option to reduce pain, recover function, and increase qualityof life in the treatment of a variety of lumbar spinal disorders.Themain goal of the present study is to report our clinical experienceand results of percutaneous transforaminal endoscopic lumbar interbody fusion (PELIF) applications using the expandable spacerin a single institution. Methods. We performed a retrospective review of 18 patients with >12-month follow-up who had beenoperated on PELIF using expandable spacer from 2001 to 2007. Their clinical and radiological data were collected and analyzed.Results. The mean follow-up period was 46 months. The mean DH before the surgery was 8.3mm which improved to 11.4mm atthe early postoperative period and regressed to 9.3mm at the last follow-up visit. The VAS-B, VAS-L, and ODI scores at the lastfollow-up showed a 54%, 72%, and 69% improvement from the preoperative period, respectively.Conclusions.The presented PELIFtechnique with the expandable spacer seems to be a promising surgical technique for the treatment of a variety of lumbar spinaldisorders. Conversely, radiological results including disc space subsidence make the stand-alone application of the expandablespacer debatable.

1. Introduction

Spinal fusion has been shown to be the preferred surgicaloption to reduce pain, recover function, and increase qualityof life in the treatment of a variety of lumbar spinal disorders[1]. After Bagby [2] had first described lumbar interbodyfusion (LIF) nearly 30 years ago, minimally invasive tech-niques for achieving LIF have become more popular over thepast decade.

Recently, several studies [3–5] have shown thatminimallyinvasive spinal (MIS) techniques, such as minimally invasivetransforaminal interbody fusion (MI-TLIF), offer comparableresults with the traditional open TLIF with the benefits ofa shorter hospital stay, less blood loss, and shorter recoverytime. This approach involves a paramedian incision and usesnatural anatomical corridors by means of tubular retractorapplication, reducing the degree of muscle, fascia, and soft

tissue injury compared to conventional open procedures.However, MI-TLIF still requires an open incision, partiallaminotomy, facetectomy, and ligament flavum dissectionin order to achieve a successful discectomy and effectivelyplace the cage. The need for bone removal and open dis-section may be eliminated when using the transforaminalposterolateral approach, which is the standard route fortransforaminal endoscopic surgery. This approach, with aminimal access port through the Kambin triangle, providesnerve root protection using progressive soft tissue dilatators[6]. It uses a combination of endoscopic visualization anddiscectomy, expandable cage application, and long-actinglocal anesthetics with continuous sedation so that surgery canbe performed without general anesthesia.

With the advancement of percutaneous LIF techniquesa variety of medical equipment and cage designs, includingthe expandable B-Twin spacer, have been developed and the

HindawiBioMed Research InternationalVolume 2017, Article ID 3731983, 9 pageshttps://doi.org/10.1155/2017/3731983

https://doi.org/10.1155/2017/3731983

2 BioMed Research International

clinical use of these devices for various spinal disorders hasbeen validated by multi- and single-center studies in theliterature [7–14].

Themain goal of the present study is to report our clinicalexperience and results of percutaneous endoscopic lumbarinterbody fusion (PELIF) applications with the posterolateraltransforaminal approach using the expandable spacer for avariety of spinal conditions in a single institution with aminimum of a 12-month postoperative follow-up period.

2. Material and Methods

After approval of the institutional review board (IRB), weperformed a retrospective review of 18 patients who had beenoperated on with the described technique between 2001 and2007.We included patients whowere treated with the surgicaltechnique described below into our study and who fulfilledthe following inclusion criteria: patients suffering from aunilateral or a bilateral leg pain and/or lower back pain andwho were diagnosed with a degenerative disc disease (DDD)with a collapsed disc, patients whowere diagnosedwithDDDwith a primary or recurrent disc herniation, mild degenera-tive spondylolisthesis (SL) (grade 1), or failed back surgerysyndrome (FBSS). We excluded patients who completeda postoperative follow-up period of less than 12 months.Patients who had additional central canal stenosis, diseasesthat impair bone quality (e.g., osteoporosis, other metabolicdiseases, neoplasm, infection, or systemic diseases), a historyof drug abuse, alcoholism, and/or noncompliance were alsoexcluded from our study. Since evaluation of the outcomeswould be debatable, the patients who were diagnosed withpolyneuropathy (with or without the diagnoses mentionedabove) using EMG-NCV studies were also excluded from thisstudy.

The patients included in our study were evaluated fortheir baseline demographic characteristics, the pathologiesfor which they were being treated, surgical level, surgicaltime, length of hospital stay, and perioperative complications.We assessed clinical outcomes using the visual analogue scale(VAS) for back (VAS-B) and leg (VAS-L) pain at their pre-operative examination, early postoperative clinical visits, andat the patients’ final follow-up examination. We could alsomaintain patients’ Oswestry disability index (ODI) scores attheir preoperative and final follow-up examinations. Patientoutcomes were graded as excellent, good, fair, and poorusing a modified Macnab criteria [15] at the patients’ finalfollow-up visits. Preoperative radiological studies includedlumbar spine standing X-rays (standing anteroposterior andlateral neutral, flexion, and extension views), computerizedtomography (CT), and magnetic resonance imaging (MRI)studies. Surgical times and duration of hospitalization werealso recorded from patients’ charts.

At the early postoperative and consequent follow-upexaminations, we assessed radiological outcomes using lum-bar spine standing X-rays (standing anteroposterior andlateral neutral, flexion, and extension views). AdditionalMRIor CT scans were only performed for patients with fair orpoor clinical results or those with a VAS score > 4. On thestanding lateral neutral X-rays, wemeasured the preoperative

and postoperative disc height (DH) by measuring the dis-tances between the inferior endplate of the cranial andsuperior endplate of the caudal vertebra at the middle andthe posterior portion of the disc space and by calculatingthe average of these measurements. We also evaluated spinalinstability on standing lateral neutral, flexion, and extensionviews. Measurement of slip was calculated using the methoddescribed by White III and Panjabi [16]. A slip of >3mmin the neutral position, >3mm translation, or >10 degreesangulation on flexion and extension views were defined asinstability. Bone fusion was assessed with flexion-extensionlateral radiographs. If there was no movement seen on thelateral view in flexion-extension in the index level and therewas bony continuity of trabecular bridging, it was termedunion. If there was any movement seen on the lateral viewin flexion-extension or discontinuity of the trabecular bonybridging, it was termed nonunion. Radiological measure-ments were taken using digitalized tools in the PACS system,PiView STAR (Infinitt Co.Ltd., Seoul, Korea). Dependingon these measurements, we defined patients as “Stable” and“Unstable.” Clinical evaluation at the final follow-up visit andall preoperative and postoperative radiological assessmentswere performed by an independent physician who was notinvolved in the surgical procedures.

Statistical analysis was performed using IBM SPSS (Sta-tistical Package for Social Sciences) for Windows 22 software(IBM Corp, Armonk, NY). We used Students’ 𝑡-tests tocompare preoperative, early postoperative, and final follow-up VAS-B, VAS-L, and ODI scores, and DH. 𝑝 value < 0.05was considered to be statistically significant.

3. Surgical Technique

We performed the procedure in all of our patients using theposterolateral transforaminal approach. All of the procedureswere performed in the prone position under local anesthesiawith conscious sedation. Conscious sedationwithmidazolamand fentanyl allowed for continuous feedback from thepatient during the entire procedure to avoid damage to theneural structures.Midazolamwas administered in the dose of0.05mg/kg mg intramuscularly half an hour before surgery,followed by another dose intravenously during the operation,if required. Fentanyl dosage was 0.8 𝜇g/kg intravenously 10minutes before the operation followed by additional dosesintraoperatively, if required. An imaginary line drawn tothe annular puncture site through the foramen designatedthe entry point into the skin and surgical trajectory. Priorto surgery, we used axial MRI and CT images to calculatethe distance of the skin entry point of the needle fromthe midline and the needle trajectory. After infiltrating theintended needle entry tract with 8mL to 10mL of 1% lido-caine, an 18-gauge needle was inserted posterolaterally underfluoroscopic guidance. The location of nerve roots and thesafe triangle were confirmed with the use of an epidurogramwith radio opaque dye (Telebrix, Gluerbet, Aulnay-sous-Bois, France). After infiltrating 5mL of 0.5% lidocaine onthe surface of the annulus, the needle was advanced tothe center of the disc space. Discography was performedby injecting 2-3mL of a mixture of a radio opaque dye,

BioMed Research International 3

(a) (b) (c) (d) (e)

Figure 1: Representative case involving a patient with DDD and instability at the L4-5 level. (a-b) Fluoroscopic images showing disc removalusing endoscopic forceps and endplate preparation using an endoscopic curette. (c) A trial implant without expansion in disc space is shown.(d-e) Fluoroscopic images showing the final construct with an expandable B-Twin spacer.

indigo carmine (Carmine, United Korea Pharma., Yeongi,Korea), and normal saline mixed in 2 : 1 : 2 ratios. The needlewas then replaced with a 0.8mm guide wire. Progressivetissue dilatation was achieved through an 8mm skin inci-sion and a blunt cannulated obturator was passed over theguide wire under fluoroscopic control until its tip reachedthe outer surface of the annulus. We performed a reamedforaminoplasty in patients with foraminal stenosis and acollapsed disc space, in order to undercut the superior facetand to enlarge the foramen without touching or harmingneural structures. We used bone reamers (Joimax GmbH,Karlsruhe, Germany) under the fluoroscopic guidance forforaminoplasty. A 7mm beveled working cannula was placedover the obturator and advanced with twisting motions.After removing the degenerated nuclear material with astandard discectomy using pituitary forceps (Figure 1(a)),an end plate curettage was performed using curettes andrasps through the endoscopic cannula under endoscopicvisualization for endplate preparation (Figure 1(b)). At thispoint in the surgery, our goal was to remove a minimum of80% of the disc nucleus while maintaining the integrity of theannulus, so that it still contained the interbody implant. Atrial implantwithout expansionwas placed into the disc spaceand controlled by fluoroscopy to find the optimal locationand size of the spacer (Figure 1(c)). After retrieving thetrial implant, we placed demineralized bone matrix (DBM),cancellous bone allograft, or autogenous bone graft from theiliac crest through the endoscopic cannula into the anteriorand lateral recesses of the disc space. Then, we introducedthe B-Twin expandable spacer (B-Twin;Disc-O-TechMedicalTechnologies Ltd., Herzliya, Israel) through the endoscopiccannula and expanded it under the lateral C-armfluoroscopiccontrol (Figures 1(d) and 1(e)). In the original description ofthis technique, it is recommended that surgeons not exceedthe measured disc height by more than 10 ± 20% in order toavoid jeopardizing the annulus with excessive tension [12, 13].We placed two expandable implants (one on the left sideand one on the right) with a bilateral approach using thesame technique in all the patients included in this study. The

procedures at each side can be performed simultaneously orone after the other, depending on the surgeon’s preference.Weused endoscopic visualization to confirm the decompressionof the exiting nerve root in all patients, as well as thedecompression of the traversing nerve root in patients whohad a disc herniation. Additionally, the exiting root couldbe mobilized under direct endoscopic vision with a flexibleradiofrequency probe (Ellman; Ellman International LLC,USA). After retrieving the endoscope, the skin was sutured.We did not apply any additional percutaneous posteriorfixation in any of our patients in this series.

The expandable spacer (B-Twin; Disc-O-Tech MedicalTechnologies Ltd., Herzliya, Israel) is made of titanium.When it is collapsed, the spacer is cylindrical in shape with asize of 5mm in diameter and 25mm in length.The expandedfinal shape is a trapezoid. There are three available sizesoptions: 9.5/11, 11.5/13, and 13.5/15. It is a trapezoid in crosssection for the purpose of maintaining a physiological degreeof lordosis in the involved segment.We selected the appropri-ate implant size according to the height of the collapsed disk,which was measured manually on the preoperative X-rays,CT, and MRI scans. The size was adjusted intraoperativelywhen necessary. The implant may be expanded up to 15mmin diameter. After it is inserted into the disc space by a single-use delivery system, the device self-locks.

We generally permitted early ambulation in the uprightposition without forward flexion on the same day of surgeryusing a flexible lumbar orthosis. We discharged the patientson the same day or the day after surgery.

4. Results

The surgeries were performed on the L4-5 level in 13 patients,on the L5-S1 level in four patients, and on the L2-3 level in onepatient. The mean age of the patients was 44.1 years (range,26–63). The mean follow-up period was 46 months (range,12–123).The average surgical timewas 77minutes (range, 62–100). The patients’ preoperative diagnoses included degener-ative disc disease (DDD)with disc herniation in nine patients


(two recurrent, seven primary herniations), DDD in fourpatients, degenerative spondylolisthesis (SL) in two patients,FBSS in two patients, andDDDwith instability in one patient,respectively.

ThemeanDHbefore the surgery was 8.3±1.6mm (range,5.2–11.5) which improved to 11.4±1.8mm(range, 8.8–14.7) atthe early postoperative period. The difference was significant(𝑝 < 0.05). Although the mean DH regressed to 9.3±1.9mm(range, 4.7–12.2) at the last follow-up visit, the differencebetween the last follow-up and the preoperative measure-ments still remained significant (𝑝 = 0.02). The regressionof DH from the early postoperative to the last follow-up wasstatistically significant (𝑝 < 0.05). Additionally, we observedthat the limbs of the implant were broken in five patientsduring the final follow-up X-ray controls.

The mean preoperative VAS-B and VAS-L pain scoreswere 6.5 ± 2.4 (range, 3.5–10) and 7.8 ± 2.0 (range, 4.7–10), respectively. The mean preoperative ODI was 69.9 ±14.3 (range, 44.4–92). The mean VAS-B and leg VAS-Limproved to 2.2 ± 0.9 (range 1–4.1) and 1.3 ± 0.8 (range0–2.5), respectively, at the early postoperative period. Thepercentages of improvement at the early postoperative periodfrom the perioperative period in VAS-B and VAS-L scoreswere 66% and 83%, respectively. The VAS-B, VAS-L, andODI scores at the last follow-up examination were 3.0 ±1.4 (range, 1–5.7), 2.2 ± 1.5 (range, 0–5), and 22.3 ± 17.1(range, 4–71.1) with a 54%, 72%, and 69% improvement fromthe preoperative period, respectively. All differences betweenthe preoperative and postoperative scores including the lastfollow-up examination scores were statistically significant(𝑝 < 0.05). The mean VAS-B and VAS-L scores at thefinal follow-up examination showed worse results than thoseduring the early postoperative period, and the differenceswere statistically significant (𝑝 < 0.05). The demographicdata and all results are summarized in Tables 1 and 2.

Fusion was achieved in 16 out of 18 patients who showedno segmental motion on their flexion-extension X-rays attheir final follow-up examination. In one patient, nonunionand instability occurred accompanied by bone resorption atthe superior endplate of the caudal vertebra. This patienthad a two-level TLIF surgery above the surgical level threeyears before the current PELIF surgery. We recommended arevision surgery for this patient but she refused our advicebecause of her comorbidities and a high anesthetic risk.One patient experienced transitory dysesthesia but recoveredfully three weeks after the surgery. The patient was treatedwith oral gabapentin in the dose of 75mg three times aday for six weeks. Major complications such as a dural tear,CSF leakage, infection, and neurologic injury did not occurin any of the patients in our series. One patient neededa revision surgery with anterior lumbar interbody fusion(ALIF) and percutaneous pedicle screw fixation one monthafter the index surgery due to postoperative migration ofone of the implants. At the final follow-up examination,seven patients rated their clinical results as excellent (41%),six patients as good (35%), three patients as fair (18%), andone patient as poor (6%) according to the modified Macnabcriteria. The patient who was treated with an ALIF revisionsurgery one week after the index surgery was not included

in the final follow-up clinical evaluations and statisticalanalyses.

All patients were ambulated on the same day of surgery.Mean postoperative time until hospital discharge was 25hours (range, 12–50).

5. Discussion

It has previously been reported that MI-TLIF needs anincision of 30mmand the time after surgery until ambulationand hospital discharge may be up to 3.2 days and 9.3 dayson average, respectively [17]. In contrast, the PELIF approachreported in this study is performed through a skin incision of7mm length. All of our patients were ambulated on the sameday after the surgery and were discharged from the hospitalwithin 50 hours.

In the present study, we reported a unique techniqueand showed the practicality of PELIF. Although conventionalfusion surgery is a gold standard for lumbar interbody fusion,we have performed PELIF only in limited patients whohave spinal instability that should be corrected but are notable to undergo general anesthesia or prefer only for “localanesthetic” procedure.The use of endoscopywith progressivetissue dilatation allows for a less invasive approach than theclassical MI-TLIF technique. It requires a small skin incisionand avoids the removal of the facet joints, ligamentumflavum, and lamina which is required for a standardMI-TLIF.PELIF can be performed without general anesthesia. The useof conscious sedation decreases the side effects caused by gen-eral anesthesia and allows for patient-based neuromonitoringwith continuous patient feedback. The distinctiveness of ourtechnique is the endoscopy-based posterolateral approachwhich allows insertion of an interbody fusion cage throughthe foramen and Kambin’s triangle without the need for anybone removal. A small foraminoplasty may be necessaryparticularly at the L5-S1 level, because of more difficultaccessibility here than at the other levels due to the iliac crestsand lumbar lordosis [4, 17].

Expandable cages allow indirect neural decompressionby restoring intervertebral height. The B-Twin spacer thatwe used in our patients is a titanium expandable devicewith a lifting-lever mechanism which provides additionalstability to the end plates on the axial plane, while preventingrotation and providing decent bone integration [12, 13].Indeed, the biomechanical properties of the B-Twin implantprovide mechanical restrictions in all planes, as its expansioncreates distraction and stabilizes the intervertebral disc spaceby a lifting-lever mechanism. The initial penetration ofthe implant limbs to the end plates provides resistance tomigration and axial rotation [8, 12, 13].

Previous reports using the B-Twin expandable spacervia a percutaneous approach have been published in theliterature [8, 11–13]. In our study excellent or good resultswereobtained in 72.2% of the patients. Still, our satisfaction resultsare worse than the satisfaction results of other percutaneousLIF studies using the B-Twin expandable spacer in theliterature (where 86%, 91%, and 83.2%of patients are reportedas having excellent and good results) [8, 11, 12]. The smallsample size of our patients might be the reason for this


Table1:Summaryof

thed

emograph

icdataandresults.

Num

ber

Sex

Age yrs

Level

LastF/U

mon

ths

Diagn

osis

Radiologicalresults

lastF/U

complications

andtre

atment

Satisfaction

lastF/U

1M

28L5-1

114FB

SSStable

Goo

d2

M37

L5-1

101

DDD+recurrentH

NP

Stable

Goo

d3

F50

L4-5

32DDD

Stable.

Limbs

oftheimplantw

ereb

roken

Fair

4F

53L4

-5123

DDD+HNP

Stable.

Limbs

oftheimplantw

ereb

roken

Goo

d5

M52

L4-5

27DDD+HNP

Stable

Excellent

6M

33L4

-526

DDD+HNP

Stable.

Limbs

oftheimplantw

ereb

roken

Excellent

7F

62L2

-378

DegenerativeS

LStable

Goo

d8

M47

L5-1

13FB

SSStable.

Limbs

oftheimplantw

ereb

roken

Fair

9F

47L4

-512

DDD+HNP

Stable

Fair

10F

26L4

-524

DDD

Stable

Goo

d11

F51

L4-5

23DDD

Stable

Excellent

12M

54L4

-516

DDD+recurrentH

NP

Stable

Excellent

13F

63L4

-546

DegenerativeS

LUnstable,no

nunion

Poor

14F

26L4

-534

DDD+HNP

Stable.

Limbs

oftheimplantw

ereb

roken

Goo

d15

M37

L4-5

15DDD+HNP

Stable

Excellent

16M

41L4

-567

DDD+insta

bility

Stable

Excellent

17F

52L4

-532

DDD

Stable

Excellent

18M

35L5-1

—DDD+HNP

Implantm

igratio

n,revisio

nwith

ALIFPP

F—

Note:F/U:follow-up,F:female,M:m

ale,andyrs:years.


Table2:Summaryof

thec

linicalandradiologicalresults.

No

VAS-B

VAS-L

ODI

Disc

height

(mm)

Preop

Early

POLastF/U

Preop

Early

POLastF/U

Preop

LastF/U

Preop

Early

POLastF/U

13.5

1.42

8.6

02

604.4

7.210.6

10.5

27.4

3.1

410

1.24

8220

8.8

12.2

8.9

37.4

3.4

45.3

1.12.5

7831.1

10.4

14.1

11.6

48.1

2.1

38.5

2.4

3.2

44.4

35.6

8.2

8.8

8.7

55.1

1.01.0

8.7

00

804

9.312.8

9.54

64.2

2.1

2.5

8.5

10

8820

10.8

13.3

12.2

710

3.1

4.1

9.22.4

3.1

6237.8

6.4

9.89.7

89.2

4.0

5.2

5.4

2.1

3.2

7528

5.2

9.27.4

94.0

1.13.4

8.4

1.95.0

64.4

3211.5

14.7

11.4

103.8

2.5

2.2

2.4

1.01.0

4713.3

8.7

12.8

11.8

115.0

2.3

1.110

1.52.1

926.7

7.99.9

7.512

4.3

2.1

2.3

8.9

1.11.4

57.5

248.4

10.8

8.14

135.1

2.1

5.7

9.01.5

3.9

73.3

71.1

7.111.1

4.7

148.2

1.84.0

4.7

1.13.0

77.8

186.4

11.4

9.915

41.1

1.48.4

2.1

2.0

604.4

8.1

9.98

1610

2.5

2.1

8.2

1.52.4

8824

8.5

10.9

8.5

1710

1.03.0

80

060

47.5

9.69.6

187.9

4.1

—9

2.5

—70

—10.2

13.6

—Mean

6.5±2.4

2.2±0.9

3.0±1.4

7.8±2.0

1.3±0.8

2.2±1.5

69.9±14.3

22.3±17.1

8.3±1.6

11.4±1.8

9.3±1.9

Note:F/U:follow-up.PO

:postoperativ

e.


(a) (b) (c) (d) (e)

Figure 2: A 37-year-old male patient (patient number: 15 in the tables) with DDD andHNP at the L4-5 level. Lateral standing X-rays showing(a) preoperative, (b) early postoperative, and (c, d, e) final follow-up X-rays including standing lateral neutral, extension, and flexion viewstaken at 50 months after the surgery. Note that there is 1.9mm reduction of the DH at the final follow-up examination compared to the earlypostoperative period. The operated level remained stable in extension and flexion views. The patient’s VAS-B, VAS-L, and ODI scores were1.4, 2, 4.4, respectively, at the final follow-up visit. The patient rated his result as “excellent.”

clinical difference as two of these previous studies had beenperformed as multicenter studies with 107 and 87 patients,respectively [8, 12].

Appropriate selection of patients and appropriate surgicalindication of the procedure might be key factors in obtaininggood results with the PELIF technique. In our series, weobserved excellent or good results in three of the four patientswho had previously been operated on with diagnoses of FBSSand DDD with recurrent HNP. Therefore, we may assumethat the PELIF technique is more favorable for revisionsurgeries because it allows the surgeon to place the interbodycage in a previously-operated level while avoiding scar tissueand reducing the risk of neurological injury.

The collapsed diameter of the B-Twin spacer is 5mm.Bearing this in mind, the PELIF technique may be challeng-ing to perform through an extremely collapsed foramen withan intervertebral disc height < 5mm, particularly in the L5-S1level. Still, the described foraminoplasty in our report allowsfor the safe access to the disc space through the obstructingstructures of the narrow foramen, such as hypertrophic facets,wide transverse processes, and osteophytes.

The postoperative recovery of our patients was fast andthey were discharged from the hospital on an average of25 hours after the surgery. The mean VAS-B, VAS-L, andODI scores significantly improved at the early postoperativeperiod and last follow-up examinations compared to theirrespective preoperative scores (𝑝 < 0.05). At the last follow-up examinations, the VAS-B, VAS-L, and ODI scores ofour patients improved by 54%, 72%, and 69%, respectively,when compared to their respective preoperative examinationscores. Although Folman et al. [12] reported slightly greaterclinical improvement in VAS-B and VAS-L scores at thefinal follow-up (65% and 89%, respectively), our results arecomparable to the reports of Xiao et al. [11] and Folman etal. [12], who also used the B-Twin expandable spacer via thepercutaneous approach.

Our main concern after a stand-alone implantation ofthe B-Twin spacer might be the possibility of subsidenceand disc space collapse because of the limbs of the B-Twinspacer penetrating the vertebral body endplates, or a possiblemigration of the implant.We observed one implantmigrationone month after the index surgery and performed a revisionwith a miniopen ALIF surgery with percutaneous pediclescrew fixation. Additionally, we observed nonunion andinstability accompanied by bone resorption at the superiorendplate of the caudal vertebra in one patient at the finalfollow-up examination 46 months after the index surgery.This patient was diagnosed with a mild degenerative SL andhad a two-level interbody fusion above the current surgicallevel three years prior to this PELIF surgery. We believeit would have been a better option to augment the PELIFsurgery with posterior pedicle screws or other posteriorfixation methods in this patient.

The mean DH which was 8.4mm before our procedureincreased to 11.4mm at the early postoperative period anddecreased to 9.3mm at the final follow-up examination. Anaverage of 2.1mm DH regression between patients’ earlypostoperative period and their final follow-up examinationsis remarkably greater than the 0.56mm and 0.7mm per levelregression which have been reported after percutaneous B-Twin applications in the literature [11, 12]. However, thisamount of subsidence did not jeopardize the stability of theimplant in any of our patients (Figure 2). In all probability,the engagement of the limbs of the implant into the vertebralendplate provided a resistance against migration.The qualityof the existing bone is most crucial in determining the abilityto anchor the implant limbs into the vertebral endplate. Thisconsideration may be of utmost importance when selectingcandidates for PELIF. However, we observed subsidenceeven in younger patients. Therefore, subsidence cannot beattributed to poor bone quality alone. The special designof the implant with opening limbs which penetrates to the


(a) (b) (c)Figure 3: A 50-year-old female patient (patient number: 3 in the tables) with DDD at the L4-5 level. Lateral standing X-rays showing (a)preoperative, (b) early postoperative, and (c) final follow-up X-rays including standing lateral neutral views taken at 32 months after thesurgery. It can be seen that the limbs of the implant are broken and there is a 2.5mm reduction in DH at the final follow-up examinationcompared to the early postoperative period. The patient’s VAS-B, VAS-L, and ODI scores were 4, 2.5, 31.1, respectively, at the final follow-upvisit. The patient rated her result as “fair.”

vertebral endplate providing a less implant-bone surfacecompared to the traditional interbody cages might be themain underlying cause ofDH regression at the final follow-upexamination.We also observed broken limbs of the implant infive patients at the final follow-up X-ray controls (Figure 3).Therefore, we recommend augmentation of the PELIF withpercutaneous pedicle screw fixation or other minimally inva-sive posterior fixation methods particularly for patients whohave degenerative SL, osteoporosis, or a previous adjacent-level fusion. One of the technical drawbacks of the B-Twinspacer placement is the irreversibility of the spacer expansionwhich makes relocation of the implant impossible when ithas been incorrectly placed. In these circumstances, removalof the implant (particularly under continuous sedation)might prove to be very challenging. A new design for theexpandable spacer, one that includes a removal mechanism,would be beneficial for these situations. Additionally, newer,expandable spacers with a greater bone-implant-bone surfacecontact than the current spacer have been reported in theliterature [7, 9, 10, 14]. Further studies with longer follow-upperiods using newer implants are necessary in order to makea definitive decision on the most appropriate implant designfor PELIF.

Our study has some limitations that should be discussed.First, the sample size is too small and the mean postoperativefollow-up period is not extensive enough to make definitiveconclusions on clinical and radiological results. Prospective,multicenter studies comparing the percutaneous interbodyfusion techniques to the traditional MIS techniques wouldallow for a better understanding of the rationale behindimplementing this procedure. Eventually, this procedureshould end up with a fusion rate that is comparable to otherLIF techniques in order to be deemed successful. Definitiveconfirmation of fusion mass in more detail using 3-D CTscans would also be beneficial in proving the efficacy of ourtechnique. In this study, patients were regularly evaluatedusing standing lumbar X-rays only. Additional MRI or CTscans were only performed on patients who represented fair

or poor clinical results with a VAS score > 4. Therefore, wecannot make a definitive conclusion on the fusion rate ofour patients. We can only conclude that all but one of ourpatients’ surgical levels were stable on flexion-extension X-rays at the final follow-up examinations. Additionally, thisprocedure can be applied in a selected group patients and isnot suitable for patients with severe central and lateral recessstenosis as endoscopic ventral decompression of soft disc canonly achieve limited decompression. Osteoporosis needs tobe carefully managed with further pedicle screws fixation toprevent subsidence and fracture of endplate.

6. Conclusions

The presented PELIF technique with the expandable spacerseems to be a promising surgical technique for treatingpatients suffering from DDD with or without disc herniationand instability, mild degenerative SL, and FBSS. Mean post-operative period until hospital discharge was faster than reg-ular MI-TLIF techniques because of the less invasive natureof the PELIF approach. Clinical results of our small sample ofpatients are similar to previous reports using percutaneousLIF techniques. Conversely, radiological results includingdisc space subsidence in all and breakage of implant limbs insome of our patients make the stand-alone application of theexpandable spacer (without any posterior fixation) debatable.We think that using newer expandable implant designs witha greater bone-implant-bone surface contact or applyingPELIF with a minimally invasive posterior fixationmethod isworth considering for patients who need revision surgeries.We believe modifications in implant design are necessaryimprovements as the PELIF technique avoids scar tissuewhileultimately reducing the risk of neurological injury in revisioncases and eliminates the high risks of general anesthesia,especially in elderly patients.

Ethical Approval

The study was approved by our institutional review board.


Competing Interests

The authors have no conflict of interests pertinent to thisstudy.

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