AJA Asian Journal of Anesthesiology

Advancing, Capability, Improving lives

Review Article
Volume 60, Issue 1, Pages 1-10
Chi Te Chou 1 , Sung Wei Yu 1 , Ting Chun Lin 2
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Abstract

Obturator nerve block (ONB) has been widely applied in transurethral resection of bladder tumor and knee surgery to prevent serious complications such as bladder perforation or to improve the quality of anesthesia during knee surgery. The classic/pubic and inguinal ONB methods are the two primary approaches used. The classic and inguinal ONB methods are two techniques for anesthetizing the obturator nerve, and each method may result in different respective outcomes. We aimed to compare the efficacy of the classic and inguinal methods. We presumed the inguinal approach to be an overall superior technique because it was recently invented and has been reported to provide numerous benefits. This study included randomized controlled trials comparing classic and inguinal approaches to ONB. Two independent investigators extracted study-level data for a random-effects meta-analysis of the comparison between the classic approach and inguinal approaches. We identified five studies comprising 312 patients. The pooled results revealed a higher success rate (risk ratio, 1.15; 95% confidence interval [CI], 1.04–1.27), fewer puncture attempts (mean difference, −0.84; 95% CI, −1.55 to −0.12), and shorter procedure time (mean difference, −28.87; 95% CI, −47.19 to −10.54) for patients given inguinal ONB. The inguinal approach is, overall, the superior method for performing the ONB procedure. The inguinal method resulted in a higher success rate, fewer puncture attempts, and shorter procedure time.

Keywords

inguinal, obturator nerve block, pubic


Introduction

Bladder cancer is the 10th most common cancer in the world.1 The first-line procedure for diagnosis, staging, and treatment of visible bladder tumors is transurethral resection of bladder tumor (TURBT).2 More than 70% of bladder tumors have been reported to be non-muscle-invasive bladder cancer2,3, and TURBT is the main procedure for the diagnosis and treatment of this type of cancer.

TURBT is performed with a resectoscope, which usually requires electrical current.4 When TURBT is being performed, specifically for cancers involving the lateral wall of the bladder, the electrical current of the resectoscope may stimulate the obturator nerve, which may result in obturator jerk and thigh adductor muscle contraction.4-8 Single spinal anesthesia cannot prevent obturator nerve stimulation and adductor muscle contraction.4 Thigh adductor muscle contraction may cause serious complications such as bladder perforation.4-8

Many techniques exist for preventing TURBT-induced complications, including avoiding complete filling of the bladder, reducing the intensity of the electric current, administering general anesthesia with muscle relaxants, and administering spinal anesthesia in combination with obturator nerve block (ONB).4-6,9,10 The combination of spinal anesthesia and ONB has been reported to be the safest and most effective method for reducing complications.5 Studies have also shown that ONB applied during TURBT provided a safer surgical area and a decreased tumor recurrence rate because of adequate resection.10 ONB is also highly recommended for treating hip joint pain, relieving adductor muscle spasms, and performing knee surgery in conjunction with femoral block.5,7,11 Recent clinical studies have demonstrated that ONB improves the quality of anesthesia for knee surgery during peripheral nerve block and enhances postoperative analgesia after total knee arthroplasty.11

Two ONB methods are primarily employed: the classic approach and the inguinal approach. The classic approach (Labatt’s technique), or pubic approach, was first described in 1967. In 2005, Choquet et al.11 described a reliable new method: the inguinal approach. In terms of performing the procedure, the puncture point of the classic approach is located at 1.5 cm lateral to the tuberculum pubis and 1.5 cm caudal, whereas the inguinal approach puncture point is located at 0.5 cm below the midpoint of the line drawn between the femoral artery and the inner margin of the adductor longus muscle. The greatest distinction between the two approaches is that with the inguinal approach, the anterior and posterior branches of the obturator nerve are blocked whereas, with the classic approach, only one block at a time is possible before bifurcation of the obturator nerve.4,5,11

Currently, nerve stimulators and ultrasonography are widely applied along with the two ONB methods to provide safe and effective blocks.7,11,12 Although the inguinal approach is a relatively new technique for performing ONB, some controversies still remain between the two approaches regarding the success rate and procedure difficulty.4

In this meta-analysis and systematic review, we aimed to determine whether the inguinal approach for ONB can provide superior efficacy and reliability (as Choquet et al.11 concluded) compared with the classic approach. The primary outcome of this study is a comparison of the success rate and the number of puncture attempts between the two approaches. This paper also reports the results of a meta-analysis of procedure time and needle depth of the two approaches.

Materials and Methods

Inclusion Criteria

This study included randomized controlled trials (RCTs) (reviewed by peers) comparing the classic approach and inguinal approach for patients who underwent TURBT surgery or knee surgery. All included trials clearly identified the inclusion and exclusion criteria for patients: patient characteristics, the definitions and methods of evaluation for success rates, number of puncture attempts, procedure time, and needle depth.

Exclusion Criteria

We excluded non-RCT articles and review articles.

Search Strategy and Study Selection

Relevant trials published before October 2020 were identified from PubMed, Embase, and Cochrane Library databases. The following medical terms were employed: (((arthroscopic knee surgery OR knee surgery) OR (((((((((bladder cancer) OR urinary bladder neoplasms) OR bladder tumour))))) OR ((((TURBT) OR transurethral resection of bladder tumours)))))) AND ((((obturator nerve block) OR ONB))).

We used the “related articles” option in PubMed to broaden the search, and all related abstracts, studies, and citations were reviewed. We restricted the language to only English. The systematic review described herein has been accepted by PROSPERO (CRD42020183349).

Data Extraction

Baseline and outcome data were independently retrieved by two reviewers (Chi Te Chou and Sung Wei Yu). Additionally, data regarding study design, study population characteristics, inclusion and exclusion criteria, success rate, the number of puncture attempts, needle depth, and procedure time were extracted. Decisions recorded individually by the reviewers were compared, and disagreements were resolved by a third reviewer (Ting Chun Lin).

Appraisal of Methodological Quality

Two reviewers (Chi Te Chou and Sung Wei Yu) independently assessed the methodological quality of each study by using the Cochrane Collaboration Risk of Bias Tool. The overall risk of bias grade of the studies was evaluated and categorized as high, some, or low risk of bias. This grade was calculated by assessing five domains: bias arising from the randomization process, bias owing to deviations from intended interventions, bias owing to missing outcome data, bias in outcome measurement, and bias in selection of the reported results.

Outcomes

The primary outcomes were success rate and the number of puncture attempts. The secondary outcomes were procedure time and needle depth.

Statistical Analysis

Data were entered and analyzed with RStudio (ver. 1.2.5042) (PBC, Boston, MA, USA). A meta-analysis was performed following the Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines. Standard deviations (SDs) were estimated by using the provided confidence interval (CI) limits or standard errors. Dichotomous outcomes were analyzed by using risk ratios (RRs) as the summary statistics. Effect sizes of the continuous outcomes were reported as the weighted mean difference (WMD). The precision of effect sizes was reported at a CI of 95%. A pooled estimate of the RRs and WMDs was computed by using the DerSimonian–Laird random-effects model. A statistically significant result was indicated by a P value of less than 0.05 or a 95% CI, not including 1 for the RR and 0 for the WMD.

Statistical heterogeneity and inconsistency of treatment effects across studies were evaluated by using the Cochran Q test and inconsistency index (I2), respectively. Statistical significance was set at P < 0.10 for the Cochran Q tests. Statistical heterogeneity across studies was assessed by using the I2 test, which quantifies the proportion of total outcome variability across studies.

Results

Trial Characteristics

A flowchart of the screening and selection of studies is illustrated in Figure 1. The initial screen yielded 378 studies, of which 285 were ineligible based on the criteria used for screening titles and abstracts; 25 were duplicated articles. Therefore, the full texts of 68 studies were retrieved. However, 37 were not comparative studies, 9 were trials registered on Cochrane but not yet published, and 17 reported interventions or approaches different from that of the control group. Consequently, 5 trials were ultimately eligible for inclusion in this meta-analysis.

Figure 1.
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Fig. 1. Schematic of the Study Selection Process

These 5 trials were published during 2005–2019 and included a total of 312 patients. All 5 trials were RCTs comparing the inguinal and classic ONB approaches; 4 compared success rates.4-7 All 5 trials compared the number of puncture attempts, 2 compared procedure time,7,11 and 2 compared needle depth.5,11 Four trials recruited patients undergoing TURBT,4-7 and 1 trial recruited patients undergoing arthroscopic knee surgery.11 Consistent with the reports of Choquet et al.,11 the classic and inguinal approaches were similar in technique in all 5 trials. However, some slight differences in outcome definitions between studies were observed. Baseline patient characteristics in the 5 trials are illustrated in Table 1.4-7,11

Table 1. Methodological Quality Assessment of Included Studies
Table 1.
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Table 1.
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The success rate was the primary outcome for 4 of the included studies, except the study by Choquet et al.11

Aghamohammadi et al.4 and Jo et al.5 found that of the two approaches, the success rate of the inguinal approach was significantly higher. Except for Moningi et al.6 and Choquet et al.11, the other 3 trials reported significantly fewer puncture attempts being required to complete ONB when the inguinal approach was applied.4,5,7 Choquet et al.11 and Dagli et al.7 compared procedure time between the two approaches. Both studies reported that compared with the classic approach, the inguinal ONB approach could be performed in a significantly shorter time. Choquet et al.11 and Jo et al.5 compared needle depth between the classic and inguinal approaches, but each of their studies yielded completely different results.5,11 The methodological quality of the included trials is summarized in Supplement Table 1. All trials employed per-protocol analysis, and there was no report of patient losing follow-up. Two trials were categorized as having some risk of bias arising from the outcome measurement and selection of the reported result.6,11

Moningi et al.6 and Choquet et al.11 did not provide mean and SD values for puncture attempts; instead, they reported median and the interquartile range (IQR), which provoke some concerns regarding the actual statistical conditions. Moningi et al.6 did not describe the actual tumor side of the patients; rather, they performed bilateral ONB on every patient, and therefore some concerns arose because the actual surgery site might have differed from one of the blocked sites.

Success Rate of ONB

All trials included in this study (except that of Choquet et al.11) reported that the success rate of ONB was higher in the inguinal group than in the classic group, and two studies reported statistically significant differences.4-7 Success was defined as no obturator sign (adductor spasm) occurrence during the whole bladder tumor removal procedure. However, in the study reported by Jo et al.,5 a successful block should also be done within three needle attempts and muscle contraction did not occur during the operation. The intention-to-treat principle was applied to analyze the success rate of ONB. Compared with the classic approach, the inguinal approach had a higher success rate, and it was statistically significant (RR, 1.15; 95% CI, 1.04–1.27; Figure 2).

Figure 2.
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Fig. 2. Forest Plot of Inguinal Versus Classic Approach: Success Rate
Abbreviations: CI, confi dence interval; RR, risk ratio.

Number of Puncture Attempts

All trials compared the number of puncture attempts between the inguinal and classic approaches.4-7,11 The definition of puncture attempt differed slightly in the study of Moningi et al.6, who defined every redirection of the needle as a single attempt. The other trials defined one attempt as one withdrawal and remanipulation of the needle.

The number of puncture attempts of the inguinal approach was significantly lower than that of the classic approach (MD, −0.84; 95% CI, −1.55 to −0.12; Figure 3).

Figure 3.
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Fig. 3. Forest Plot of Inguinal Versus Classic Approach: Number of Puncture Attempts
Abbreviations: CI, confi dence interval; MD, mean difference; SD, standard deviation.

Procedure Time

Two trials compared the procedure time between the inguinal and classic approaches.7,11 The procedure time was defined as the period between the first puncture insertion and the first motor response after the administration of local anesthesia. The procedure time of the inguinal approach was significantly shorter than that of the classic approach (MD, −28.87; 95% CI, −47.19 to −10.54; Figure 4).

Figure 4.
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Fig. 4. Forest Plot of Inguinal Versus Classic Approach: Procedure Time
Abbreviations: CI, confi dence interval; MD, mean difference; SD, standard deviation.

Needle Depth

Two trials compared the needle depth between the inguinal and classic approaches.5,11 The needle depth was defined as the length of the inserted needle from the skin to the depth that stimulated the adductor muscle contraction. Needle depth did not differ significantly between the inguinal and classic approaches (MD, 0.22; 95% CI, −1.35 to 1.79, Figure 5).

Figure 5.
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Fig. 5. Forest Plot of Inguinal Versus Classic Approach: Needle Depth
Abbreviations: CI, confi dence interval; MD, mean difference; SD, standard deviation.

Discussion

The main conclusion of this study is that compared with the classic ONB approach, the inguinal approach provides significant advantages in success rate, number of puncture attempts, and procedure time.

The success rate was the primary outcome of 4 of the included studies that compared the classic and inguinal ONB approaches.4-7 Although the definition of success among the included trials was similar (i.e., no occurrence of the obturator sign [adductor spasm] during the whole bladder tumor removal procedure), some slight differences between the studies were still observed. In the study reported by Jo et al.,5 a successful block should be done within 3 needle attempts and muscle contraction did not occur during the operation.

Aghamohammadi et al.4 mentioned block onset time, which was significantly shorter in the inguinal group than in the classic group. Additionally, they performed a subgroup comparison in which the patients were divided into 3 groups according to their body mass index (normal, overweight, and obese). The results revealed significant differences in puncture attempts between patients with obesity and those with a healthy weight, and the success rate was significantly lower in patients with obesity than in patients who are overweight or have a healthy weight. Jo et al.5 and Moningi et al.6 noted that identifying the pubic tubercle in patients with obesity and patients with blunt pubic bones can be difficult, and because the pubic tubercle is the most definitive landmark in classic ONB, the procedure can be difficult to perform in such individuals. Moningi et al.6 reported that the number of puncture attempts was not significantly different between the inguinal and classic ONB groups. Another difference in the study of Moningi et al.6 is the design of their trial that all patients underwent bilateral ONB, with the inguinal method performed on one side and the classic method performed on the other. Although this design potentially prevents intersubject variation, Moningi et al.6 did not indicate the tumor location side, which presents the possibility that the side with no tumor is always subject to a successful procedure because no stimulation occurs. The study of Choquet et al.11, being the first to introduce inguinal ONB, was included in our study. However, all patients in their study were scheduled to undergo arthroscopic knee surgery, whereas patients from the other 4 studies were all scheduled to undergo TURBT.4-7

Our study had several limitations. First, 2 of the included trials did not provide the mean and SD values for puncture attempts;6,11 therefore, we applied an estimated equation to convert the provided median number and IQR to mean and SD, which might have resulted in errors. Second, patients from the study of Choquet et al.11 were all scheduled to undergo arthroscopic knee surgery, which differed from the other 4 studies;4-7 however, no differences were observed in the number of puncture attempts, procedure time, or puncture depth. Third, although the definition of the outcomes in each study was similar, some slight differences (as mentioned) still existed, which may have affected our results. Fourth, despite the inclusion of 5 RCTs, the study analyzed only 312 patients; further studies are required for comparisons of larger sample sizes. Finally, this study did not discuss the effectiveness of supportive devices. Because ONB success rates vary depending on anatomic variations in obturator nerve coursing,13 equipment, such as ultrasound devices or nerve stimulators, which have been reported to provide some advantages during ONB procedures, may contribute to safer and more effective blocks.12,14-16

In conclusion, this study found that compared with the classic ONB method, the inguinal ONB method is superior for performing ONB procedures because it provides major advantages. First, with the inguinal ONB method, the puncture site is anatomically easier to be located,4-6 which may result in fewer puncture attempts and shorter procedure time compared with the classic method. Second, the inguinal method results in significantly higher success rates. Third, fewer complications were associated with the inguinal approach because of anatomical advantages and because major vessels were easy to be avoided during the procedure.

Author Contributions

Chi Te Chou: This author helped devise, design the study, interpret data, and write the first draft.

Sung Wei Yu: This author helped extract, analyze the data, and revise the draft.

Ting Chun Lin: This author helped revise the draft, and be the guarantor.

All authors contributed to subsequent versions and approved the final article.


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None
None
Anesthesiology. 2005;103(6):1238-1245.
18
Jo YY, Choi E, Kil HK.
Comparison of the success rate of inguinal approach with classical pubic approach for obturator nerve block in patients undergoing TURB.
Korean J Anesthesiol. 2011;61(2):143-147.
19
Moningi S, Durga P, Ramachandran G, Murthy PVLN, Chilumala RR.
Comparison of inguinal versus classic approach for obturator nerve block in patients undergoing transurethral resection of bladder tumors under spinal anesthesia.
J Anaesthesiol Clin Pharmacol. 2014;30(1):41-45.
20
Aghamohammadi D, Gargari RM, Fakhari S, Bilehjani E, Poorsadegh S.
Classic versus inguinal approach for obturator nerve block in transurethral resection of bladder cancer under spinal anesthesia: a randomized controlled trial.
Iran J Med Sci. 2018;43(1):75-80.
21
Dagli R, Dadali M, Emir L, Bagbanci S, Ates H.
Comparison of classic and inguinal obturator nerve blocks applied for preventing adductor muscle contractions in bladder tumor surgeries: a prospective randomized trial.
Urol J. 2019;16(1):62-66.

References

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