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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 35  |  Issue : 3  |  Page : 209-214

Diagnostic ultrasound-guided lumbar medial branch block of dorsal ramus in facet joint arthropathy: Technical feasibility and validation by fluoroscopy


1 Department of Anaesthesiology, Pain Medicine and Critical Care, All India Institute of Medical Sciences, New Delhi, India
2 Department of Orthopaedics, All India Institute of Medical Sciences, New Delhi, India

Date of Submission22-May-2021
Date of Decision11-Jun-2021
Date of Acceptance26-Jul-2021
Date of Web Publication29-Dec-2021

Correspondence Address:
Prof. Virender K Mohan
Room No. 5011, 5th Floor, Teaching Block, Department of Anaesthesiology, Pain Medicine and Critical Care, All India Institute of Medical Sciences, New Delhi
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijpn.ijpn_50_21

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  Abstract 


Background: Facet joint (FJ)-mediated pain is one of the frequent causes of low back pain. Fluoroscopy and computed tomography guided medial branch blocks (MBBs) are accepted as standard techniques to diagnose FJ arthropathy. Ultrasound-guided (USG) MBB can be an alternative approach for the diagnostic MBB in FJ arthropathy. This study evaluates the feasibility of USG MBB in FJ arthropathy and validates by fluoroscopy. Materials and Methods: Diagnostic USG MBBs were performed in sixty patients. Two medial branches were targeted for each FJ. The needle was inserted in an in-plane technique after identifying the desired site. The needle position was confirmed by fluoroscopy. Pain scores were assessed before and after the nerve block. Results: Out of 161 needle insertions, 139 needles (86.3%) were at the radiologically defined target point as confirmed by fluoroscopy and were labeled as successful. Mean baseline, immediately before, immediately after, and at 24 h, Numeric Rating Scale (NRS) scores were 7.53 (0.93), 7.02 (0.93), 3.03 (1.75), and 2.80 (1.99), respectively (P < 0.05). The mean Modified Oswestry Disability Questionnaire scores before and 24 h after block were 48.77 (8.94) and 32.55 (11.32), respectively. Fifty-three patients had ≥60 points on the 100-point scale given by Helbig, and out of these patients, 44 patients had a ≥50% reduction in the NRS score. Conclusion: Diagnostic USG lumbar MBBs, a minimally invasive procedure without radiation exposure, can be performed with a high success rate in FJ arthropathy.

Keywords: Back pain, diagnostic medial branch block, facet joint arthropathy, Numeric Rating Scale, pain, ultrasound-guided block


How to cite this article:
Soni L, Mohan VK, Garg B, Punj J, Bhoi D. Diagnostic ultrasound-guided lumbar medial branch block of dorsal ramus in facet joint arthropathy: Technical feasibility and validation by fluoroscopy. Indian J Pain 2021;35:209-14

How to cite this URL:
Soni L, Mohan VK, Garg B, Punj J, Bhoi D. Diagnostic ultrasound-guided lumbar medial branch block of dorsal ramus in facet joint arthropathy: Technical feasibility and validation by fluoroscopy. Indian J Pain [serial online] 2021 [cited 2022 Jan 19];35:209-14. Available from: https://www.indianjpain.org/text.asp?2021/35/3/209/334104




  Introduction Top


Low back pain (LBP) is a common health problem. Nearly more than 66% of the population experience some form of LBP in their lifetime.[1] The prevalence of LBP causes an economic burden on society by utilizing health resources and reduced productivity because of absenteeism from the workplace. There are many pain-generating structures in the spine. Unless appropriately diagnosed, it is challenging to manage LBP.

Facet joint (FJ)-mediated pain is one of the frequent causes of LBP.[2] Clinical examination and radiographic imaging cannot make a diagnosis of FJ arthropathy alone because a patient with FJ degeneration on radiography may be asymptomatic, and symptomatic patients may not have any radiological evidence of FJ arthropathy.[3],[4] Due to the nonavailability of any specific diagnostic modality to correlate clinical symptoms of FJ-mediated pain, fluoroscopy, and computed tomography (CT)-guided lumbar facet nerve blocks are accepted as a standard for its diagnosis.[5],[6] However, it has certain disadvantages, i.e., X-ray exposure, device availability problems, and higher cost.

Ultrasound-guided (USG) medial branch blocks (MBBs) are emerging into clinical practice as an alternative to fluoroscopic-guided MBBs both as diagnostic as well as a therapeutic modality. It is portable, equipment is moderately priced, with no risk of radiation exposure, and injury to vessels can be minimized under real-time power Doppler imaging. It has been reported that USG needles were placed accurately to radiologically defined endpoints.[7],[8] However, to date, USG MBBs are not routinely used as an independent technique for FJ nerve block; confirmation by fluoroscopy or CT scan is still required after needle placement.[9] Therefore, the present study was conducted to evaluate the feasibility of USG MBBs in FJ arthropathy and to validate this technique after confirmation by fluoroscopy.


  Materials and Methods Top


Study design

This study was approved by the Institutional Ethics Committee (IEC) and registered in the Clinical Trials Registry, India (CTRI/2017/11/010484).

It is an observational interventional single-arm study. After IEC approval, sixty patients with FJ arthropathy were recruited for the study from the pain clinic. A total of 161 ultrasound-guided blocks were performed in these patients after obtaining written informed consent. Pain scores were assessed before and after the block.

Patients aged 18–80 years with persistent lower back pain after at least 3 months of appropriate medical treatment with clinically/radiologically suspected FJ arthropathy having an Numeric Rating Scale (NRS) score of more than five and history of predominant back pain were recruited. Patients refusal, coagulopathy, known allergy to local anesthetics (LAs) or contrast dye, infection at the site of injection, evidence of significant sensory or progressive motor deficit, major spinal deformity, evidence of severe psychiatric illness, presence of cancer as a cause of back pain, pain extending below the knee joint, history of previous back surgery with implant insertion, presence of diabetes mellitus, multiple sclerosis, cardiac pacemaker, pregnancy, any radiologically proven cause of LBP, i.e., Pott's spine, metastasis, and body mass index (BMI) >30 kg/m2 were excluded from the study.

The pain physician collected the demographic data and detailed history. After the physical examination, evaluation scores in terms of the NRS and Modified Oswestry Disability Questionnaire (MODQ) scores were noted. Reduction in pain was assessed by reduction in NRS score. A 100-point score, developed by Helbig, was given to the patients to predict the diagnostic success of the block.[10] MODQ was applied to individual patients to determine their functional status.

Magnetic resonance imaging (MRI) findings were also noted for the patients to look for any radiological evidence of FJ involvement. On the day of the intervention, intravenous access was established, and standard monitors were attached as per the American Society of Anesthesiologists guidelines.

Procedure

The patient was positioned prone with pillows under the abdomen to abolish the lumbar lordosis, and the lumbar area of the back was cleaned and draped under all aseptic precautions. A 2–5 MHz curvilinear ultrasound probe was used for the procedure. A longitudinal midline sonogram with sacrum as a landmark was obtained to start with, and then, the spinous processes were counted upward till the desired segment. At the target spinous process, the US probe was rotated to obtain a transverse view of the vertebrae, where the transverse process (TP) and superior articular process (SAP) were identified in the same view [Figure 1]. 1 mL of 2% lignocaine was infiltrated with a 25G needle at a point lateral to the ultrasound probe at the desired site of spinal needle insertion to anesthetize the skin locally. A small LA volume was used so that the LA drug did not diffuse around nearby structures and interfere with the results.
Figure 1: Ultrasonographic cross-sectional view of the lumbar spine showing the superior articular process and transverse process in continuation

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A 22G/10-cm echogenic intervention needle was then introduced under real-time, in-plane ultrasound guidance to the target point, which is defined as a groove at the cephalic margin of the TP adjacent to the SAP. Under the cross-sectional view, it is a point where the SAP is in continuation with the TP [Figure 2].
Figure 2: Hyperechoic needle (marked by arrows) is seen during USG in-plane medial branch block performance with a curvilinear probe

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The needle was inserted utilizing an in-plane approach until bony resistance was experienced. Color Doppler was performed to look for any vascular structure in the needle's course and avoid any inadvertent intravascular injection. The final needle position was seen by fluoroscopy in the posteroanterior and oblique views. 0.2–0.3 mL of radiocontrast material was injected to ensure the absence of intravascular uptake of dye [Figure 3]. Needle position was evaluated as per the International Spine Intervention Society guidelines, i.e., slightly medial to the lateral margin of the SAP's silhouette in the posteroanterior view and high on the eye of the Scotty dog in the oblique views. In this study, unsuccessful needle placements were noted first and further manipulation or adjustments of the needle were made for the unsuccessfully placed needles, which did not affect our primary outcome. Although the secondary outcomes aimed at analyzing the reduction in pain score, we included all the cases with suspected FJ involvement in the analysis.
Figure 3: Fluoroscopic oblique view of the lumbar spine showing the successful needle placement after dye injection. The upper level shows cephalocaudal dye spread suggestive of successful needle placement, while the lower level is an unsuccessful needle placement

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Outcome measures

This study's primary outcome was the number of successful needle insertions under ultrasound guidance and later confirmed in fluoroscopic oblique view. The secondary outcome measures were more than 50% reduction in NRS score and improved functional status as measured by the MODQ at before and 24 h after block.

Statistical analysis

The sample size was calculated, assuming 70% agreement between the USG- and fluoroscopy-guided MBBs. Ninety percent sample agreement between the two techniques was targeted for this study. According to the literature, the accurate needle position's success rate during MBB was approximately 95%.[8] nQuery 2.0 Advisor software[11] was used to calculate the sample size of the study before the commencement of study. Assuming the power of the study as 80% and the significance level, alpha as 5% with two-tailed hypothesis testing, the calculated number of needle interventions came out to be 161. A minimum of 2–4 needle placements was required in a single patient depending on the suspected number of FJs involved. Sixty patients were recruited to achieve a target of 161 needle interventions. Statistical analysis was done using SPSS 20.0 software. The data were examined for the assumptions of normality using the Shapiro–Wilk test statistic and homogeneity of variances using Levene's test. One-way ANOVA was used for analyzing NRS scores. Paired t-test was used for the analysis of MODQ scores. Pearson's correlation was used to assess the bivariate relationship between 100-point score and percentage reduction in NRS score.


  Results Top


Patients consisted of 35 males and 25 females, with a mean age of 36.95 (12.93) years, mean weight: 62.28 (6.03) kg, mean height: 1.57 (0.034) m, BMI: 26.44 (18.76) (kg/m2), and mean duration of symptoms: 27.47 (18.76) months [Table 1]. Only one-third of the patients had radiological evidence of FJ arthropathy in MRI. The ultrasonographic landmarks were visible in all cases.
Table 1: Demographic data, patient's characteristics, and successful needle pass in numbers and percentage

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Among 161 needle placements, 139 were placed successfully to radiologically defined endpoint giving a success rate of 86.3% [Table 2]. The localized spread of dye in a cephalocaudal direction was seen in all the successful cases. The number of interventions at different levels and the successful outcomes are shown in [Table 2].
Table 2: Number of interventions and needle passes

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Mean baseline, immediately before, immediately after, and after 24 h of intervention, NRS score was 7.53 (standard deviation [SD], 0.93), 7.02 (SD, 0.93), 3.03 (SD, 1.75), 2.80 (SD, 1.99) respectively. One-way ANOVA results for NRS scores showed a significant difference between the different time points (F [3, 236) =174.06, P < 0.001). Tukey's honestly significantly differenced post hoc test revealed that postintervention (P < 0.001) and after 24 h (P < 0.001), NRS scores were significantly lower than the baseline and before intervention NRS scores [Figure 4].
Figure 4: Graph showing the differences between Numeric Rating Scale scores at different time points. Red line shows a significant reduction in pain scores from baseline to after intervention and after 24 h. Blue line shows a significant reduction in the Numeric Rating Scale from before intervention to after intervention and after 24 h. P < 0.05 was considered statistically significant

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Forty-five patients out of sixty had a ≥50% reduction in NRS. The mean MODQ scores before and 24 h after the block were 48.77 (8.94) and 32.55 (11.32), respectively [Figure 5]. Paired t-test results for MODQ scores showed a significant decrease between scores before and after the intervention (t [59) =12.18, P < 0.001). Fifty-three patients had ≥60 points on the Helbig 100-point scale, and out of these patients, 44 patients had a ≥50% reduction in the NRS score [Figure 6]. Pearson's correlation was used to assess the bivariate relationship between 100-point score and percentage reduction in NRS scores [Figure 6]. A 100-point score was positively related to the percentage reduction in NRS (r = 0.402, P < 0.001) [Figure 6]. Therefore, the percentage reduction in NRS was more in patients with a higher 100-point score. We did not observe any adverse reaction to lignocaine and iodinated dye used in our study.
Figure 5: Graph showing mean reduction in Modified Oswestry Disability Questionnaire score before intervention (Modified Oswestry Disability Questionnaire 1) and after intervention (Modified Oswestry Disability Questionnaire 2). P < 0.05 was considered statistically significant

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Figure 6: Graph showing the correlation between the Helbig 100-point score to the percentage reduction in Numeric Rating Scale

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  Discussion Top


LBP is an increasing problem with the ever-increasing prevalence of FJ-mediated pain (prevalence is 15%–44%).[2] FJ forms the posterolateral articulations in the spine, and pain usually occurs after a twisting or rotatory strain to the spine.[12] Diagnosis of FJ-mediated pain is challenging because symptomatic patients may not have radiological evidence of FJ arthropathy, and the ones with radiological evidence of FJ arthropathy may be asymptomatic. MBB is an accepted standard to diagnose FJ-mediated pain.[6],[13],[14] In the present study, only one-third of patients had MRI suggestive of FJ arthropathy in the form of joint effusions or hypertrophy.

Ultrasound as a modality is nowadays used frequently in pain procedures due to its no risk of radiation exposure, lower cost, device portability, and power Doppler, preventing intravascular injections. Conventionally, MBBs were performed under fluoroscopic guidance. Due to the advantages of ultrasonography over fluoroscopy, we attempted to study the feasibility of USG MBB by conducting 161 blocks in patients with suspected FJ arthropathy. First, Greher et al. attempted to define the sonoanatomic landmarks for USG MBBs in a cadaveric study.[7]

The current study's main finding suggests that 139 out of 161 blocks were performed to a radiologically correct endpoint giving a success rate of 86.3%. The block could successfully be performed once the SAP and TP were seen in the same view. Lumbar MBBs were performed at all lumbar levels (L2–L5) in this study. The level of the block was decided based on the clinical examination at the time of the recruitment of patients in the pain clinic. Two medial branches were blocked per FJ in a sample of sixty patients.

In 2004, Greher et al. performed USG MBBs at L3–L5 lumbar vertebral levels in a nonembalmed cadaver and, on dissection, found that the needles were placed to the correct target point at all three levels. In the same study, ultrasound of the lumbar spine was carried out in 20 healthy volunteers (9 women and 11 men) for defining landmarks to perform MBB.[7]

Further, similar to our study, 28 lumbar MBBs were performed in 5 patients with suspected FJ arthropathy, and the needle placement was confirmed fluoroscopically. Their success rate was reasonably high (25 out of 28 needle placements were accurately placed, as confirmed after dye injection).[7] They suggested a need for further study to investigate the feasibility of USG MBBs because of the small sample size in their study.

Another study obtained a 95% success rate on the performance of lumbar MBBs in 20 patients and found that 96 out of 101 needles were correctly placed to the radiological endpoint.[8]

In contrast to the diagnostic blocks performed in our study, USG MBBs have been used therapeutically in patients with FJ arthropathy and later confirmed using fluoroscopy. The results suggested that 87 out of 95 blocks were successfully performed under ultrasound guidance.[15]

In the current study, the USG in-plane technique was performed for performing the lumbar MBBs in which we tried to visualize the complete trajectory of needle passage toward the target area. Once the needle tip was visualized, an attempt was made to direct the needle in-line to the ultrasound insonation beams without moving the ultrasound probe. The desired site of needle position was the groove between the SAP and TP, preferable at the cephalic end of TP. We recommend that once the desired vertebral level is marked in the mid-sagittal scan, space should be scanned from cephalad to caudal direction. The first hyperechoic structure seen in continuity with the SAP should be targeted. The advantage of using this approach is that the failure attributed to the needle placement at the caudal part of the TP could be minimized. Alternatively, the longitudinal paravertebral scan could be carried out to confirm the needle position at the cephalic portion of the TP after USG placement in the transverse in-plane approach. A similar approach is used in previous studies with the achievement of a reasonably accurate needle position. Therefore, for better visualization of the complete trajectory of the needle, the target point should be focused at one end of the ultrasound screen so that during block using an in-plane technique, the whole length of the needle can be visualized.

In our study, maximum failed interventions were found at the L5 nerve root level, where the landmarks were not apparent in ultrasonography. This finding is in agreement with similar results from previous studies.[8] L5 nerve root block was always performed in the current study using fluoroscopy. Therefore, further studies are needed to define sonoanatomic landmarks for L5–S1 FJ.

In an attempt to validate the USG MBB technique, the needle position was verified by fluoroscopy before and after injecting 0.2-mL iohexol dye. Localized dye spread was seen in all successful cases. The dye spread was limited in cephalocaudal direction by mamilloaccessory ligament, which covers the groove where the medial branch traverses. In contrast to our study, Greher et al. used 1-mL iohexol dye to confirm needle position and found that 7 out of 50 needles showed paraforaminal and 5 out of 50 showed epidural spread.[7] The possible reason for this difference in the dye spread pattern could be the volume of dye used (1 mL vs. 0.2 mL). The large volume of dye could spill in adjacent areas resulting in an aberrant pattern of dye spread. Similar to our study, Shim et al. also used 0.2 mL of iohexol dye for needle tip confirmation and reported no aberrant dye spread.[8]

However, in two of their cases, the injected dye could not be verified under fluoroscopy, which was suggestive of intravascular spread. However, we did not find any intravascular spread in the present study.

Other researchers also employed CT as a confirmation modality for assessing the success rate of needle position. Forty-five out of 50 needles were accurately targeted to the endpoint on 5 embalmed cadavers, as confirmed on the transverse view of CT scan before and after dye injection.[9] Another CT-based cadaveric study obtained an acceptable success rate with 42 out of 50 accurate needle positions.[16] Our patients' mean BMI was 26.44 kg/m2 giving a success rate of 86.3% as opposed to Rauch et al., where the success rate was as low as 64% in obese patients.[17] They performed 84 MBBs in 20 patients with suspected FJ arthropathy with a mean BMI of ≥ 30 kg/m2. This low success rate could be explained because of poor visualization of the needle and spine structures in obese patients. Another factor that may affect the success rate of needle positioning is using a curvilinear ultrasound probe. A curvilinear probe 2–5 MHz was used for block performance in the current study as it offered a deeper penetration. However, the ultrasound beam's poor penetration may result in poor visualization of needle tip with increasing depth of target spine structures in obese patients. The spines of 20 healthy volunteers were scanned, and landmarks were delineated in 19 volunteers with a median BMI = 23 kg/m2. In one volunteer whose BMI was 36 kg/m2, the landmarks could not be clearly defined.[7] Interestingly, these diagnostic blocks may also serve as a prognostic marker for therapeutic FJ interventions such as radiofrequency ablation of medial branches, chemical neurolytic of medial branches, steroid injections, and intra-articular FJ steroid injections. However, the technique of performance of block, selection of nature and amount of drug to be injected, and assessment of outcomes have not been standardized yet. In the current study, 0.5 mL of 2% preservative-free lignocaine was used to perform diagnostic blocks under ultrasound guidance. Moreover, to minimize false-positive results, the skin was infiltrated with 0.5–1 mL of 2% lignocaine, as the larger volume may confound the results. In contrast to our study, Shim et al. used 1 mL of 0.25% bupivacaine.[8] In this study, 2% preservative-free lignocaine was used as the block was only diagnostic and close to neuroaxis.

Pain scores were assessed pre- and postintervention, and a significant reduction was observed in pain according to the results of the present study. The mean baseline, immediately before, immediately after, and after 24 h of intervention, NRS scores were 7.53 (standard deviation [SD], 0.93), 7.02 (SD, 0.93), 3.03 (SD, 1.75), 2.80 (SD, 1.99) respectively, and were comparable to similar studies conducted in the past.[8] Forty-five out of sixty patients experienced a ≥50% reduction in NRS. There was a significant reduction in the MODQ score before and after the intervention from 48.77 (8.94) to 32.55 (11.32), respectively. Different pain questionnaires have been used in other similar studies, including NRS, VAS, ODI, and MODQ. Shim et al. observed a mean reduction in VAS from 52 ± 8 to 16 ± 4 before and after the intervention.[8] Jung et al. found a significant decrease in mean VAS from 6.2 ± 0.9 to 4.0 ± 1.0 before and after the intervention.[15] The Verbal Rating Scale scores before, immediately after, and 24 h after the procedure were 7.1 (standard deviation [SD], 2.4), 4.3 (SD, 3.1), and 3.8 (SD, 2.7), respectively, when blocks were performed in obese patients.[17]

In 1988, a 100-point scoring system was derived from a clinical study, which proposed that a score of ≥60 indicates a very high probability of satisfactory response.[10] This 100-point score was analyzed in our study; however, we did not come across any similar study during the literature search in which this 100-point scoring system was used. In this study, it was found that 44 out of 53 patients whose 100-point score was ≥60 responded well to MBB with a ≥50% reduction in NRS. Therefore, we may conclude that this scoring system can be used in routine practice to predict the successful response to FJ injection or diagnostic MBBs.

The present study's limitations are the sonoanatomic landmarks for the L5 dorsal ramus (which gives the medial branch to L5–S1 FJ.) block's performance could not be defined. Therefore, there is a need for cadaveric studies followed by human studies with a sufficient sample size to define sonoanatomic landmarks for USG L5 dorsal ramus block performance. Obese patients were not included in our study; hence, further studies are needed to check the feasibility of USG MBBs in this specific patient population. In the present study, patients were followed for 24-h duration, which can be justified as we performed diagnostic blocks. Further, long-term studies, along with radiofrequency ablations for long-term pain relief in proven cases of facetopathy diagnosed using lumbar MBBs, are recommended.


  Conclusion Top


USG MBBs are feasible, minimally invasive, without radiation exposure, and can be performed with a reasonable success rate.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Linton SJ, Hellsing AL, Halldén K. A population-based study of spinal pain among 35-45-year-old individuals. Prevalence, sick leave, and health care use. Spine (Phila Pa 1976) 1998;23:1457-63.  Back to cited text no. 1
    
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Schwarzer AC, Wang SC, Bogduk N, McNaught PJ, Laurent R. Prevalence and clinical features of lumbar zygapophysial joint pain: A study in an Australian population with chronic low back pain. Ann Rheum Dis 1995;54:100-6.  Back to cited text no. 2
    
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Schwarzer AC, Wang SC, O'Driscoll D, Harrington T, Bogduk N, Laurent R. The ability of computed tomography to identify a painful zygapophysial joint in patients with chronic low back pain. Spine (Phila Pa 1976) 1995;20:907-12.  Back to cited text no. 3
    
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Schwarzer AC, Aprill CN, Derby R, Fortin J, Kine G, Bogduk N. Clinical features of patients with pain stemming from the lumbar zygapophysial joints. Is the lumbar facet syndrome a clinical entity? Spine (Phila Pa 1976) 1994;19:1132-7.  Back to cited text no. 4
    
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Manchikanti L, Pampati V, Fellows B, Bakhit CE. The diagnostic validity and therapeutic value of lumbar facet joint nerve blocks with or without adjuvant agents. Curr Rev Pain 2000;4:337-44.  Back to cited text no. 5
    
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Saal JS. General principles of diagnostic testing as related to painful lumbar spine disorders: A critical appraisal of current diagnostic techniques. Spine (Phila Pa 1976) 2002;27:2538-45.  Back to cited text no. 6
    
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Greher M, Scharbert G, Kamolz LP, Beck H, Gustorff B, Kirchmair L, et al. Ultrasound-guided lumbar facet nerve block: A sonoanatomic study of a new methodologic approach. Anesthesiology 2004;100:1242-8.  Back to cited text no. 7
    
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Shim JK, Moon JC, Yoon KB, Kim WO, Yoon DM. Ultrasound-guided lumbar medial-branch block: A clinical study with fluoroscopy control. Reg Anesth Pain Med 2006;31:451-4.  Back to cited text no. 8
    
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Greher M, Kirchmair L, Enna B, Kovacs P, Gustorff B, Kapral S, et al. Ultrasound-guided lumbar facet nerve block: Accuracy of a new technique confirmed by computed tomography. Anesthesiology 2004;101:1195-200.  Back to cited text no. 9
    
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Helbig T, Lee CK. The lumbar facet syndrome. Spine (Phila Pa 1976) 1988;13:61-4.  Back to cited text no. 10
    
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nQuery - Sample Size Software and Power Analysis Calculator for Clinical Trials. Available from: https://www.statsols.com/nquery. [Last accessed on 2019 May 05].  Back to cited text no. 11
    
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Schütz U, Cakir B, Dreinhöfer K, Richter M, Koepp H. Diagnostic value of lumbar facet joint injection: A prospective triple cross-over study. PLoS One 2011;6:e27991.  Back to cited text no. 13
    
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Perolat R, Kastler A, Nicot B, Pellat JM, Tahon F, Attye A, et al. Facet joint syndrome: From diagnosis to interventional management. Insights Imaging 2018;9:773-89.  Back to cited text no. 14
    
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Jung H, Jeon S, Ahn S, Kim M, Choi Y. The validation of ultrasound-guided lumbar facet nerve blocks as confirmed by fluoroscopy. Asian Spine J 2012;6:163-7.  Back to cited text no. 15
    
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Galiano K, Obwegeser AA, Bodner G, Freund M, Maurer H, Kamelger FS, et al. Ultrasound guidance for facet joint injections in the lumbar spine: A computed tomography-controlled feasibility study. Anesth Analg 2005;101:579-83.  Back to cited text no. 16
    
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Rauch S, Kasuya Y, Turan A, Neamtu A, Vinayakan A, Sessler DI. Ultrasound-guided lumbar medial branch block in obese patients: A fluoroscopically confirmed clinical feasibility study. Reg Anesth Pain Med 2009;34:340-2.  Back to cited text no. 17
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
    Tables

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