Ultrasound-guided sacral multifidus plane block for perioperative analgesia: A comprehensive systematic review, meta-analysis, and trial sequential analysis

Abstract

Background and Aims:

The sacral multifidus plane block (SMPB) is an emerging regional anaesthesia technique targeting the dorsal rami of sacral spinal nerves, with potential applications in lower limb, pelvic, and perineal surgeries. Evidence from randomised controlled trials (RCTs) has not been systematically synthesised.

Methods:

We conducted a systematic review and meta-analysis following the PRISMA 2020 guidelines, and the study was registered prospectively in PROSPERO. PubMed, Scopus, Cochrane Library, and ClinicalTrials.gov were searched (January 2019–May 2025) for RCTs comparing SMPB with other regional techniques or no block. The primary outcome was time to rescue analgesia. Secondary outcomes included 24-h opioid consumption, postoperative pain scores, patient satisfaction, and adverse events. Data were pooled using a random-effects model; trial sequential analysis (TSA) and GRADE assessment were performed.

Results:

Twelve RCTs (n = 768; 348 received SMPB) were included. SMPB significantly prolonged time to first rescue analgesia, reduced 24-h opioid consumption, and lowered pain scores at rest and movement during the first postoperative day, particularly during the intermediate (6–12 h) and late (24 h) postoperative periods. Patient satisfaction was generally higher with SMPB, correlating with improved analgesia and reduced opioid use. TSA confirmed the robustness of findings for time to rescue analgesia and opioid consumption, although the required sample size was not reached. No serious block-related complications were reported.

Conclusions:

SMPB appears to be a safe, effective regional anaesthesia technique, offering opioid-sparing benefits, prolonged analgesia, and high patient satisfaction. However, current evidence is limited by small sample sizes, methodological heterogeneity, and potential publication bias.

INTRODUCTION

Effective postoperative analgesia remains a cornerstone of enhanced recovery protocols across a wide range of surgical specialties. In recent years, regional anaesthesia (RA) has evolved beyond traditional neuraxial techniques, with a growing emphasis on peripheral nerve blocks and fascial plane blocks that provide simplicity, safety, and opioid-sparing advantages.[1] Among these, various paraspinal interfascial plane blocks have gained considerable popularity as essential components of multimodal analgesia protocols. The sacral multifidus plane block (SMPB) is conceptually and anatomically aligned with this group, representing a relatively new technique that extends the application of this approach to the sacral region. SMPB has become a promising option for analgesia in a variety of surgical and chronic pain procedures and is increasingly adopted in clinical practice.[2]

In 2019, Tulgar et al.[3] first introduced the ‘sacral erector spinae plane block’ as a caudal extension of the thoracolumbar erector spinae plane block, aiming to provide analgesia through sensory blockade of the dorsal rami of the sacral nerves. This technique targeted the osseomuscular plane located between the median or intermediate sacral crest (MSC or ISC) and the multifidus muscle (multifidus lumborum) at the S2 level.[3,4,5,6] Anatomically, the structures overlying the multifidus muscle, listed from superficial to deep, include the skin, subcutaneous tissue, latissimus dorsi aponeurosis originating from the posterior layer of the thoracolumbar fascia, and the longissimus thoracis muscle and aponeurosis [Figure 1]. Among the three muscles comprising the erector spinae group (iliocostalis, longissimus, and spinalis), only the longissimus thoracis and iliocostalis extend to the sacral level—and even then, as an aponeurosis. The multifidus muscle belongs to the transversospinales group, which is anatomically distinct from the erector spinae group. To rectify this anatomical discrepancy and eliminate confusion in nomenclature, Hamilton[7]—and subsequently, Piraccini and Taddei[8]—proposed renaming the block as the SMPB to reflect better the fascial plane anatomy involved. In our systematic review and meta-analysis, we have adopted the term SMPB to ensure anatomical precision, improve clarity, and support standardisation of terminology in the literature.

Figure 1.

Cross-sectional schematic illustration of the sacral multifidus plane block (SMPB) at the S2 level (caudocranial view), depicting key anatomical structures and local anaesthetic deposition points. 1 and 2 represent the midline approach at the median sacral crest (MSC) and the paramedian approach at the intermediate sacral crest (ISC), respectively. ST = subcutaneous tissue; GMM = gluteus maximus muscle; LDA = latissimus dorsi aponeurosis originating from the posterior layer of thoracolumbar fascia (PTLF); LTMA = longissimus thoracis muscle aponeurosis; MFM = multifidus muscle; SSL = supraspinous ligament; ILMA = iliocostalis lumborum muscle aponeurosis; PSIL = posterior sacroiliac ligament; LSC = lateral sacral crest

Despite growing clinical interest and emerging clinical studies on SMPB, the current evidence remains fragmented and heterogeneous. However, individual studies vary considerably in design, patient population, technical details of SMPB, comparators, and outcome reporting, making interpretation and synthesis difficult. High-quality, consolidated data on its analgesic efficacy, opioid-sparing potential, and safety profile are lacking. This systematic review and meta-analysis aim to clarify its role in perioperative analgesia, support evidence-based clinical decision-making, and highlight areas for future research. We conducted a systematic review and meta-analysis of randomised controlled trials (RCTs) to synthesise the existing evidence on SMPB across various surgical settings. We hypothesise that SMPB offers superior pain control and opioid-sparing benefits compared to conventional techniques in both paediatric and adult surgical populations.

METHODS

This systematic review and meta-analysis was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines.[9] The review was prospectively registered with PROSPERO at https://www.crd.york.ac.uk/PROSPERO (ID: CRD420251030133).

Search strategy

We conducted a systematic search in PubMed, Scopus, Cochrane Library, and ClinicalTrials.gov for RCTs that compared SMPB with either other RA techniques or placebo/no block, using relevant keywords from January 2019 to May 2025. The entire search strategy, including truncations and Boolean operators, is presented in Supplementary Table 1.

Supplementary Table 1.

Truncations

Database	Search details
PubMed	((sacral erector spinae plane block) OR (sacral multifidus plane block)) OR (sacral paraspinal block) Filters: in the last 10 years Sort by: Most Recent (((“sacrale”[All Fields] OR “sacralisation”[All Fields] OR “sacralised”[All Fields] OR “sacralization”[All Fields] OR “sacralized”[All Fields] OR “sacrals”[All Fields] OR “sacrum”[MeSH Terms] OR “sacrum”[All Fields] OR “sacral”[All Fields]) AND (“erector”[All Fields] OR “erectores”[All Fields] OR “erectors”[All Fields]) AND “spinae”[All Fields] AND (“aircraft”[MeSH Terms] OR “aircraft”[All Fields] OR “plane”[All Fields] OR “planes”[All Fields]) AND (“block”[All Fields] OR “blocked”[All Fields] OR “blocking”[All Fields] OR “blockings”[All Fields] OR “blocks”[All Fields])) OR ((“sacrale”[All Fields] OR “sacralisation”[All Fields] OR “sacralised”[All Fields] OR “sacralization”[All Fields] OR “sacralized”[All Fields] OR “sacrals”[All Fields] OR “sacrum”[MeSH Terms] OR “sacrum”[All Fields] OR “sacral”[All Fields]) AND (“paraspinal muscles”[MeSH Terms] OR (“paraspinal”[All Fields] AND “muscles”[All Fields]) OR “paraspinal muscles”[All Fields] OR “multifidus”[All Fields]) AND (“aircraft”[MeSH Terms] OR “aircraft”[All Fields] OR “plane”[All Fields] OR “planes”[All Fields]) AND (“block”[All Fields] OR “blocked”[All Fields] OR “blocking”[All Fields] OR “blockings”[All Fields] OR “blocks”[All Fields])) OR ((“sacrale”[All Fields] OR “sacralisation”[All Fields] OR “sacralised”[All Fields] OR “sacralization”[All Fields] OR “sacralized”[All Fields] OR “sacrals”[All Fields] OR “sacrum”[MeSH Terms] OR “sacrum”[All Fields] OR “sacral”[All Fields]) AND (“paraspinal”[All Fields] OR “paraspinally”[All Fields] OR “paraspinals”[All Fields] OR “paraspinous”[All Fields]) AND (“block”[All Fields] OR “blocked”[All Fields] OR “blocking”[All Fields] OR “blockings”[All Fields] OR “blocks”[All Fields]))) AND (y_10[Filter]) Translations sacral: “sacrale”[All Fields] OR “sacralisation”[All Fields] OR “sacralised”[All Fields] OR “sacralization”[All Fields] OR “sacralized”[All Fields] OR “sacrals”[All Fields] OR “sacrum”[MeSH Terms] OR “sacrum”[All Fields] OR “sacral”[All Fields] erector: “erector”[All Fields] OR “erectores”[All Fields] OR “erectors”[All Fields] plane: “aircraft”[MeSH Terms] OR “aircraft”[All Fields] OR “plane”[All Fields] OR “planes”[All Fields] block: “block”[All Fields] OR “blocked”[All Fields] OR “blocking”[All Fields] OR “blockings”[All Fields] OR “blocks”[All Fields] sacral: “sacrale”[All Fields] OR “sacralisation”[All Fields] OR “sacralised”[All Fields] OR “sacralization”[All Fields] OR “sacralized”[All Fields] OR “sacrals”[All Fields] OR “sacrum”[MeSH Terms] OR “sacrum”[All Fields] OR “sacral”[All Fields] multifidus: “paraspinal muscles”[MeSH Terms] OR (“paraspinal”[All Fields] AND “muscles”[All Fields]) OR “paraspinal muscles”[All Fields] OR “multifidus”[All Fields] plane: “aircraft”[MeSH Terms] OR “aircraft”[All Fields] OR “plane”[All Fields] OR “planes”[All Fields] block: “block”[All Fields] OR “blocked”[All Fields] OR “blocking”[All Fields] OR “blockings”[All Fields] OR “blocks”[All Fields] sacral: “sacrale”[All Fields] OR “sacralisation”[All Fields] OR “sacralised”[All Fields] OR “sacralization”[All Fields] OR “sacralized”[All Fields] OR “sacrals”[All Fields] OR “sacrum”[MeSH Terms] OR “sacrum”[All Fields] OR “sacral”[All Fields] paraspinal: “paraspinal”[All Fields] OR “paraspinally”[All Fields] OR “paraspinals”[All Fields] OR “paraspinous”[All Fields] block: “block”[All Fields] OR “blocked”[All Fields] OR “blocking”[All Fields] OR “blockings”[All Fields] OR “blocks”[All Fields]
Scopus	(TITLE-ABS-KEY (sacral erector spinae plane block) OR TITLE-ABS-KEY (sacral multifidus plane block) OR TITLE- ABS-KEY (sacral paraspinal block))
Cochrane Library	sacral erector spinae plane block in Title Abstract Keyword OR sacral multifidus block in Title Abstract Keyword OR sacral paraspinal block in Title Abstract Keyword

Eligibility criteria

Only RCTs were included in the quantitative analysis. We utilised a structured Population, Intervention, Comparator or Control, Outcome, and Study (PICOS) design to select pertinent studies:[10]

Population: Adults (≥18 years), paediatric / adolescent patients (6 months–17 years) undergoing lumbosacral spine, lower abdominal, or lower limb surgeries under general anaesthesia.

Intervention: SMPB.

Control or comparator: Use of other RA techniques (caudal epidural, nerve block, or any fascial plane block) or no block/placebo.

Outcomes: Time to first rescue analgesia (primary outcome), 24-h opioid consumption (converted to IV morphine equivalents), postoperative pain scores (immediate and at 24 h), number of patients requiring rescue analgesia, incidence of adverse events such as postoperative nausea and vomiting (PONV), and patient satisfaction (secondary outcomes).

Study design: RCTs

Exclusion criteria included non-English publications, animal research, studies without available full texts, systematic reviews, literature reviews, scoping reviews, case reports/series, editorials, and conference abstracts.

Study selection and data extraction

Two authors (AN and TM) independently screened the identified studies manually using the established inclusion and exclusion criteria. A third author (RG) served as arbiter to resolve any disagreements regarding study inclusion. The corresponding author of articles for which full-texts were not available, in which outcome details were not clear or incomplete, was contacted for the information. Once the articles were finalised, their data were extracted into a standardised table under the following headings: author and year of publication, country, study design, number of participants per group, description of intervention and control or comparator arms, and primary and secondary outcomes.

Methodological risk of bias assessment

Two authors independently assessed the methodological quality of the included articles by using the Cochrane Handbook for Systematic Reviews of Interventions and the Cochrane Risk of Bias 2.0 (ROB2) tool.[11] Domains assessed included bias arising from the randomisation process, deviations from intended interventions, missing outcome data, outcome measurement, and the selection of reported results. Discrepancies were resolved through discussion or by consulting a third author.

Strength of quality across all trials

The methodological quality of evidence across pooled outcomes was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) guidelines.[12] The quality of evidence for pooled outcomes was determined based on the study design, bias risk, consistency, directness, precision, and other factors (confounding, large effect, and publication bias). The certainty of the evidence was categorised as: (1) high-quality: additional research is improbable to alter the confidence in the estimate of effect, (2) moderate-quality: further research is likely to affect the estimate’s confidence significantly and may alter it, (3) low-quality: additional research is highly likely to alter the estimate, or (4) extremely poor quality: the estimate is uncertain.

Quantitative meta-analysis

Meta-analysis was performed using Review Manager software (RevMan 5.4) by the Cochrane Collaboration.[13] The odds ratio (OR) and the 95% confidence interval (CI) were used for dichotomous or binary variables. For continuous variables, the mean difference (MD) with 95% CI was used. The effect estimates were derived from forest plot analysis comparing similar groups. A P value < 0.05 was considered statistically significant. Inconsistencies were evaluated using the χ² and I² to assess the clinical heterogeneity in the included studies, and P < 0.10 and I² >50% showed that χ² had statistical differences.[14] A fixed-effects model was utilised if the study results showed low heterogeneity (P > 0.10, I² <50%). The random-effects model was used for meta-analysis in all other cases.[15] For comparison purposes between the trials, different opioids (IV and oral) were converted to IV morphine equivalents using the conversion chart and online calculator (https://short-link.me/1agX2).[16]

Sensitivity analysis

The results were compared with those from the random- and fixed-effects models, and the reliability of the combined results was subsequently analysed based on the degree of consistency among the results. Each study was sequentially removed from the analysis to rule out any particular study exerting greater influence on the interpretation of the results.[17] A funnel plot was constructed to assess publication bias.[18]

Trial Sequential Analysis (TSA)

A TSA was conducted to control for Type I and Type II errors in the cumulative meta-analysis, focusing on outcomes that demonstrated statistical significance in the quantitative meta-analysis.[19] We calculated the required information size (RIS) based on a two-sided α of 5%, power (1− β) of 80%, the anticipated intervention effect, and the event proportion in the control group. Sequential monitoring boundaries for benefit, harm, and futility were constructed using the O’Brien–Fleming α-spending function. A cumulative Z-curve was plotted after adding studies that reported a particular outcome. If the Z-curve crossed the monitoring boundaries or entered the futility zone, firm evidence was considered established; otherwise, further trials were deemed necessary. TSA was performed using the TSA software (version 0.9.5.10 beta) from the Copenhagen trial unit, Denmark.[20]

RESULTS

Using the predefined inclusion criteria, a total of 78 articles were identified through database searches. After removing duplicates and irrelevant titles, 41 articles underwent title and abstract screening. Among the remaining fourteen articles assessed for full-text eligibility, two were excluded as they could not be retrieved. Ultimately, 12 RCTs[21,22,23,24,25,26,27,28,29,30,31,32] met the inclusion criteria and were chosen for a quantitative meta-analysis and a qualitative systematic review. The study by Olgun Keles et al.[25] investigated SMPB for the prevention of catheter-related bladder discomfort in patients undergoing urological surgery. Although the primary outcome differed from typical pain-related outcomes, the study still reported analgesic efficacy parameters, including pain scores and rescue analgesia requirements, aligning with our inclusion criteria. Hence, the study was included in the analysis.

The detailed study selection process is illustrated in the PRISMA flow diagram [Figure 2]. Tables 1 and 2 summarise an overview of study characteristics and outcome details.

Figure 2.

PRISMA 2020 flow diagram. PRISMA = Preferred Reporting Items for Systematic Reviews and Meta-Analyses

Table 1.

Summary table of the included studies

Table 2.

Outcome table

Study	Groups	No. of patients	Opioid consumption per day (MME)	Pain score (rest) 1st day	Pain score (movement) 1st day	Pain score in the recovery room	No. of patients needing Rescue analgesia	Patient Satisfaction In Likert scale scores [IQR]	Time to rescue analgesia (h)	PONV
Mermer et al.[21] 2023 ADULT	SMPB	35	10.16(0.2)	NRS: 0 (0–2)	--	0 (0-0)	3		--	--
	C	35	10.95(2.09)	1 (0–2)	--	0 (0–0)	28		--	--
Elbadry et al.[22] 2023 PAEDS	SMPB	39	2.47(1.45)	3 (2–4)	-	1 (1–2)	--	--	9.33(4.14)	3
	CEB	40	2.35(1.25)	FLACC: 3 (2–4)	--	1 (1–2)	--	--	8.63(4.35)	4
	PB	41	3.33(1.17)	3 (2–5)	--	2 (1–2)	--	--	5.12(1.55)	5
Behera et al.[23] 2024 ADULT	SMPB	30	1.17(2.52)	VAS: 2.37(0.25)	--	--	0	--	19.5(22.6)	--
	C	30	1.56(3.41)	3.19 (0.23)	--	--	4	--	5.2(6.5)	--
Olgun Keleş et al.[24] 2024 ADULT	SMPB	25	8.11(8.16)	VAS: 1(1.48)	--	0(1.48)	6	10 (9–10) 10(0.74)	7.33(2.33)	2
	C	25	21.94(18.59)	2(0.74)	--	1(1.48)	19	8 (6–10) 8(2.96)	0.81(1.93)	11
Olgun Keleş et al.[25] 2024 ADULT	SMPB	27	--	NRS: 0 (0–2)	--	0 (0–3) 0(2.22)	7	9 (6–10) 9(2.96)	7.5(2.6)	--
	PNB	27	--	0 (0–2)	--	0 (0–2) 0(1.48)	9	9 (8–10) 9(1.48)	8.6(4.3)	--
Bansal et al.[26] 2024 PAEDS	SMPB	20	--	FLACC 0.1(10.44)	--	0	--	--	15.1(4.7)	--
	C	20	--	2.6(3.34)	--	1.85(3.19)	--	--	1.06(1.67)	--
Elghamry et al.[27] 2024 ADULTS	SMPB	33	--	--	--	--	--	--	10.71(1.77)	--
	C	34	--	--	--	--	--	--	1.75(0.18)	--
Özen et al.[28] 2024 PAEDS	SMPB	30	--	FLACC: 0	-	0	2	--	22.65 [22.30–23] 22.65(0.5)	--
	CEB	30	--	0	-	0	12	--	6 [4–6] 6±1.48	--
Bansal et al.[29] 2024 PAEDS	SMPB	25	--	FLACC: 0.31(0.81)	--	--	20	--	21.30(3.06)	--
	CEB	25	--	1.14(1.54)	--	--	25	--	9.36(1.71)	--
Satici et al.[30] 2024 ADULTS	SMPB	25	8 [6–14]	--	--	--	20	5 [4–5] 5(0.74)	6 (IQR: 5–8) 6(2.22)	3
	C	25	22.5 [19.5–26]	--	--	--	25	3 [2–3] 3(0.74)	4 (IQR: 4–6) 4 (1.48)	18
Satıcı et al.[31] 2025 PAEDS	SMPB	25	--	--	--	FLACC: 2 (2–3)	--	4 [4–5]	4 [2–6] 4(2.96)	--
	RB	25	--	--	--	3 (3–5)	--	3 [3–3]	1 [0–1] 1(0.74)	--
Sancak Demirci et al.[32] 2025 PAEDS	SMPB	34	--	FLACC: 2.2(0.8)	--	0.8(0.5)	3	3 (8.8) 16 (47.1) 15 (44.1)	6.3(1.6)	--
	CEB	33	--	2.3(0.7)	--	0.6(0.6)	1	2 (6.1) 3 (9.1) 28 (84.8)	9.7(2.8)	--

C=control; SMPB=sacral multifidus plane block; CEB=caudal epidural block; RB=ring block; PB=penile block; PNB=pudendal nerve block; VAS=visual analogue scale; NRS=Numeric Rating Scale; FLACC=Face, Legs, Activity, Cry, and Consolability; QoR-15=Quality of Recovery-15 scale; IQR=Interquartile Range; PONV= postoperative nausea and vomiting; MME=Intravenous morphine milligram equivalent

Qualitative systematic review

The risk of bias in the included trials, assessed using the ROB2 tool, is depicted in Figure 3a (traffic light plot) and Figure 3b (summary plot). The bias from the randomisation process was low in all 12 studies.[21,22,23,24,25,26,27,28,29,30,31,32] Bias due to deviations from intended interventions (allocation concealment) was low in 10 studies[22,23,24,25,27,28,29,30,31,32] but high in two studies.[21,26] Five studies showed low risk,[23,28,29,30,31] while seven lacked sufficient information.[21,22,24,25,26,27,32] Outcome measurement bias was low in seven studies[25,27,28,29,30,31,32] and high in five studies.[21,22,23,24,26] Bias arising from the selection of reported results was low in 11 studies[21,22,23,25,26,27,28,29,30,31,32] and high in one study.[24]

Figure 3.

Risk-of-bias assessment- a: Traffic light plot; b: Summary plot

Quality of evidence

A GRADE level of evidence assessment was conducted for four outcomes [Table 2]. The LOE was assessed as ‘very low’ for three outcomes (24-h opioid consumption, patient requiring rescue analgesia, and time to rescue analgesia) and as ‘low’ for 24-h pain scores.

Quantitative meta-analysis

Time to rescue analgesia

Eleven studies reported time to rescue analgesia as an outcome (313 patients in the SMPB group and 314 in the control group).[22,23,24,25,26,27,28,29,30,31,32] A pooled analysis revealed a statistically significant increase in time to rescue analgesia in the first 24 h in the SMPB group compared to the control group (MD: 6.52; 95% CI: 2.15, 10.89; P = 0.003) [Figure 4a]. However, a random-effects model revealed considerable heterogeneity (I² = 99%) (GRADE level of evidence: Very low). This finding is consistent with Figure 4a, which also depicts results favouring the SMPB group.

Figure 4.

a: Forest plot showing comparison of time to rescue analgesia between the SMPB group and control group. b: Funnel plot between outcome time to rescue analgesia between the SMPB group and control group, showing asymmetry; c: TSA graph showing comparison of time to rescue analgesia between the SMPB group and control group.. CI = confidence interval; IV = inverse variance; SD = standard deviation; SMPB = sacral multifidus plane block; TSA = trial sequential analysis

The funnel plot revealed asymmetry, suggesting publication bias [Figure 4b]. The calculated Q statistic was 7669.34, and the P value was essentially 0. This indicates very strong evidence of heterogeneity among the studies, suggestive of a publication bias or other sources of variability that are not due to chance alone.

In the TSA for the outcome time to rescue analgesia, the cumulative Z-curve crossed the conventional boundary, suggesting statistical significance. However, the RIS estimated by the TSA software was 792, whereas the total sample size used in the meta-analysis was 627, approximately 80% of the required sample size [Figure 4c].

24-h opioid consumption

Five studies reported 24-h opioid consumption as an outcome (154 patients in the SMPB group and 155 in the control group).[21,22,23,25,30] A pooled analysis revealed a statistically significant reduction in opioid consumption in the first 24 h in the SMPB group compared to the control group (MD: 4.19; 95% CI: −6.97, −1.41; P = 0.003) [Figure 5a]. However, a random-effects model showed considerable heterogeneity (I² = 96%) (GRADE level of evidence = Very low).

Figure 5.

a: Forest plot showing comparison of 24-h opioid consumption between the SMPB group and control group. b: TSA graph showing comparison of 24-h opioid consumption between the SMPB group and control group. CI = confidence interval; IV = inverse variance; SD = standard deviation; SMPB = sacral multifidus plane block; TSA = trial sequential analysis

In the TSA, for 24-h opioid consumption, the cumulative Z-curve crossed the conventional boundary, suggesting statistical significance. However, the RIS was 568, and while the meta-analysis included only 309 participants, representing 54.40% of the required sample size, which is considerably less [Figure 5b].

Patients requiring rescue analgesia

Seven studies reported the number of patients requiring rescue analgesia as an outcome (201 in the SMPB group and 202 in the control group).[21,23,24,25,29,30,32] The pooled analysis demonstrated a statistically significant reduction in the number of patients requiring rescue analgesia in the SMPB group compared to the control group (MD: 0.54; 95% CI: 0.31, 0.93; P = 0.03) [Figure 6a]. However, a random-effects model revealed considerable heterogeneity (I² = 86%) (GRADE level of evidence = Very low).

Figure 6.

a: Forest plot showing comparison of patients requiring rescue analgesia between the SMPB group and control group. b: TSA graph showing comparison of patients requiring rescue analgesia between the SMPB group and control group. CI = confidence interval; IV = inverse variance; SD = standard deviation; SMPB = sacral multifidus plane block; TSA = trial sequential analysis; M-H = Mantel-Haenszel method

In the TSA for patients requiring rescue analgesia, the cumulative Z-curve crossed the conventional boundary, indicating statistical significance. The RIS was 44, while the total sample size included in the analysis was 401, comprising 170 events, which far exceeded the RIS [Figure 6b].

24-h pain scores

Nine studies reported 24-h pain scores as an outcome (265 patients in the SMPB group and 265 in the control group).[21,22,23,24,25,26,28,29,32] A pooled analysis revealed a statistically significant reduction in pain scores at 24 h in the SMPB group compared to the control group (MD: −0.56; 95% CI: −0.90, −0.21; P = 0.002) [Supplementary Figure 1a ^{(5.3MB, tif)} ]. However, a random-effects model indicated considerable heterogeneity (I² = 71%) (GRADE level of evidence = Low).

In the TSA for 24-h pain scores, the cumulative Z-curve also crossed the conventional boundary. The RIS was 380, and the sample size used in the meta-analysis was 530, indicating that the available evidence is close to meeting the optimal information threshold [Supplementary Figure 1b ^{(5.3MB, tif)} ].

Four studies reported 24-h pain scores in adult patients (117 in the SMPB group and 117 in the control group).[21,23,25,30] The pooled analysis revealed a statistically significant reduction in pain scores at 24 h in the SMPB group compared to the control group (MD: −0.81; 95% CI: −0.93, −0.70; P < 0.00001) with moderate heterogeneity (I² = 36%) [Supplementary Figure 2a ^{(3MB, tif)} ].

Five studies reported 24-h pain scores in paediatric patients (148 in the SMPB group and 148 in the control group).[22,26,28,29,32] The analysis showed comparable pain scores between the groups (MD: −0.22; 95% CI: −0.50, 0.07; P = 0.14) with moderate heterogeneity (I² = 37%) [Supplementary Figure 2b ^{(3MB, tif)} ].

Postoperative pain scores

Eight studies reported postoperative pain scores as an outcome (235 patients in the SMPB group and 235 in the control group).[21,22,24,25,26,28,30,32] A pooled analysis showed comparable postoperative pain scores between the two groups (MD: −0.29; 95% CI: −0.75, 0.17; P = 0.22) [Supplementary Figure 3a ^{(5MB, tif)} ]. However, a random-effects model revealed considerable heterogeneity (I² = 76%) (GRADE level of evidence = Low).

Three studies reported postoperative pain scores in adults (87 in the SMPB group and 87 in the control group).[21,22,23] The pooled analysis revealed no statistically significant difference in pain scores between the groups (MD: −0.54; 95% CI: −1.52, 0.43; P = 0.27), with moderate heterogeneity (I² = 56%) [Supplementary Figure 3b ^{(5MB, tif)} ].

Five studies reported postoperative pain scores in adult patients (148 in the SMPB group and 148 in the control group).[22,26,28,30,32] The pooled analysis demonstrated comparable pain scores between both groups (MD: −0.18; 95% CI: −0.70, 0.34; P = 0.50) with moderate heterogeneity (I² = 82%) [Supplementary Figure 3c ^{(5MB, tif)} ].

Pain assessment methods varied across studies: visual analogue scale (VAS); numeric rating scale (NRS); Face, Legs, Activity, Cry, Consolability (FLACC) scale; and Children’s Hospital of Eastern Ontario Pain Scale (CHEOPS). This inconsistency in outcome measurement further contributed to heterogeneity.

Subgroup analysis for time to rescue analgesia, 24-h opioid consumption, and patients requiring rescue analgesia

A subgroup analysis for time to rescue analgesia, separately for adults and paediatric patients was done. In adults, there were five studies included (140 patients in the SMPB group and 142 in the control group).[23,24,25,27,30] The pooled analysis showed comparable efficacy between the two groups in terms of time to rescue analgesia (MD: 3.92; 95% CI: −0.35, 8.22; P = 0.07), with considerable heterogeneity (I² = 99%) using a random-effects model [Supplementary Figure 4a ^{(3.4MB, tif)} ].

In paediatric patients, six studies reported time to rescue analgesia (173 patients in the SMPB group and 173 in the control group).[22,26,28,29,31,32] The pooled analysis demonstrated no statistically significant difference between the two groups (MD: 7.15; 95% CI: −0.66, 14.96; P = 0.07), with substantial heterogeneity (I² = 100%) using a random-effects model [Supplementary Figure 4b ^{(3.4MB, tif)} ].

Four studies involving adult patients reported 24-h opioid consumption (117 in the SMPB group and 117 in the control group).[21,23,25,30] The pooled analysis revealed a statistically significant reduction in opioid consumption in the SMPB group (MD: −7.09; 95% CI: −8.35, −5.84; P < 0.00001), again with substantial heterogeneity (I² = 99%) using a random-effects model [Supplementary Figure 5a ^{(3.2MB, tif)} ].

Five studies reported the number of patients requiring rescue analgesia in adults (142 in the SMPB group and 144 in the control group).[21,23,24,25,30] The pooled analysis showed no difference in the number of patients requiring rescue analgesia with SMPB compared to the control group (MD: 0.36; 95% CI: 0.12, 1.12; P = 0.08), with significant heterogeneity (I² = 91%) [Supplementary Figure 5b ^{(3.2MB, tif)} ].

Patient satisfaction

Only three studies involving adult patients reported patient satisfaction (77 patients in the SMPB and control group, each).[25,26,30] A pooled analysis revealed significant satisfaction in the SMPB group (MD: 1.42; 95% CI: 0.27, 2.57; P = 0.01), with considerable heterogeneity (I² = 78%) [Supplementary Figure 6a ^{(2.6MB, tif)} ].

PONV

Three studies reported PONV as an outcome (8 events out of 89 patients in the SMPB group and 33 events in the control group). Pooled analysis revealed lower PONV events in the SMPB group compared to the control group, which was statistically significant (RR: 0.24; 95% CI: 0.12, 0.49; P < 0.0001), with minimal heterogeneity using a fixed-effects model (I² = 36%) [Supplementary Figure 6b ^{(2.6MB, tif)} ].

TSA

TSA was performed for the outcomes that demonstrated statistical significance in the quantitative meta-analysis. In the TSA for the outcome time to rescue analgesia, the cumulative Z-curve crossed the conventional boundary, suggesting statistical significance. However, the required information size (RIS) estimated by the TSA software was 792, whereas the total sample size used in the meta-analysis was 627, approximately 80 percent of the required sample size (Figure 4c). In the TSA, for 24-h opioid consumption, the cumulative Z-curve crossed the conventional boundary, suggesting statistical significance. However, the RIS required was 568, and while the meta-analysis included only 309 participants, representing 54.40 percent of the required sample size, this is considerably less (Figure 5b). In the TSA for patients requiring rescue analgesia, the cumulative Z-curve crossed the conventional boundary, indicating statistical significance. The RIS was 44, while the total sample size included in the analysis was 401, comprising 170 events, which far exceeded the RIS (Figure 6c). In the TSA for 24-h pain scores, the cumulative Z-curve also crossed the conventional boundary. The RIS was 380, and the sample size used in the meta-analysis is 530, indicating that the available evidence is close to meeting the optimal information threshold [Supplementary Figure 1b ^{(5.3MB, tif)} ].

Publication bias

The funnel plot revealed asymmetry, suggesting publication bias (Figure 4b). The calculated Q statistic is 7669.34, and P value is <0.001. This indicates very strong evidence of heterogeneity among the studies, suggestive of a publication bias or other sources of variability that are not due to chance alone.

DISCUSSION

This Systematic review and meta-analysis evaluated the analgesic efficacy and safety of the SMPB across a range of surgical indications in both adult and paediatric populations. To our knowledge, this is the first comprehensive SRMA focused exclusively on SMPB, incorporating TSA and GRADE assessments to support evidence synthesis and interpretation. A key strength of this SRMA is the inclusion of only RCTs, ensuring a high level of evidence. Across 12 randomised controlled trials encompassing 768 patients, SMPB (n = 348) was associated with favourable analgesic outcomes compared to control or comparator groups, which included no block, caudal epidural block, pudendal nerve block, and penile or ring blocks. The meta-analysis demonstrated that SMPB significantly prolonged the time to first requirement of rescue analgesia, reduced 24-h opioid consumption, and decreased the number of patients requiring rescue analgesia. A statistically significant reduction in 24-h pain scores was observed, although immediate postoperative pain scores remained comparable between groups.[21,22,23,24,25,26,28,29,32] Improved patient satisfaction was also noted, though it was reported in only four studies.[21,24,25,30] Additionally, TSA was performed to quantify uncertainty when the required information size (RIS) was not achieved and to provide a more robust framework for decision-making, rather than relying solely on conventional meta-analytic results. TSA revealed that the cumulative Z-curve crossed the conventional significance boundary for three outcomes: time to rescue analgesia, 24-h opioid consumption, and patients requiring rescue analgesia. However, the RIS was not achieved for time to rescue analgesia (80% of target) and 24-h opioid consumption (54% of target), indicating the need for further high-quality studies to confirm these findings. Although the risk of bias was low in most domains, some studies lacked sufficient information for a comprehensive assessment. There was substantial clinical and statistical heterogeneity due to differences in control interventions, surgical procedures, patient populations, unilateral versus bilateral blocks, local anaesthetic types, volumes, concentrations, and perioperative opioid regimens. The overall certainty of evidence, as assessed by the GRADE approach, was low to very low. Furthermore, evidence of publication bias was detected through funnel plot asymmetry and Egger’s test.

The inclusion of both adult and paediatric trials in this SRMA has important strengths and limitations. On the one hand, it captures the full spectrum of SMPB’s clinical applications across age groups, thereby enhancing the generalisability of the findings. It also enables identification of age-specific trends in efficacy, safety, and pharmacodynamic responses, while increasing the overall sample size to improve statistical power and precision of effect estimates. On the other hand, combining these populations introduces considerable clinical and methodological heterogeneity, as paediatric studies often employ different block techniques, dosing regimens, timing of outcome assessment, and behavioural pain scales (e.g. FLACC, CHEOPS) compared with adult self-reported measures (VAS and NRS). Developmental differences in analgesic thresholds and susceptibility to adverse effects further complicate synthesis and may yield misleading pooled estimates if not interpreted cautiously. Moreover, such diversity necessitates subgroup analyses, sensitivity analyses, and in some cases separate forest plots, as undertaken in this review, to preserve interpretability.

Postoperative analgesia

The most consistent finding was a clinically meaningful prolongation of analgesia. Across pooled adult and paediatric datasets, SMPB extended the time to first rescue analgesia by approximately 5–12 h relative to comparators, with some paediatric CEB-controlled trials showing more than double the duration.[22,28,29] In one study, the duration of analgesia with CEB was observed to be longer than that of the SMPB group.[32] SMPB may achieve its analgesic effect through craniocaudal, mediolateral, and dorsoventral spread of local anaesthetic solutions. Two approaches have been described in the literature: a single injection at the MSC and bilateral injections at the ISC. In this SRMA, six studies employed the ISC approach.[21,23,24,27,30,31] Among the six studies using the MSC approach, five were conducted in paediatric patients[22,26,28,29,32] and only one in adults.[25] In a cadaveric and radiological dye study, Keleş et al.[33] compared the MSC and ISC approaches. The MSC approach demonstrated dorsal dye staining from the S1 to S5 vertebral levels, with an anterior spread via the sacral foramina along the spinal nerves (S2–S5). In contrast, the ISC approach showed bilateral longitudinal spread between L2 and S3 without any anterior transition. Nanda et al.[34] demonstrated that a 20-mL dye injection at the S3 ISC level resulted in extensive staining of the multifidus, with variable involvement of the posterior sacral rami and middle cluneal nerves, but without spread into the sacral foramina, ventral rami, pudendal nerve, or sciatic nerve. Atalay et al.[35] reported that with 20 mL of dye solution, the posterior sacral foramina (S2–S4), the anterior and posterior surfaces of the erector spinae and multifidus muscles, and the dorsal rami at the L5 level were stained. Diwan et al.[36] demonstrated that continuous SMPB at the S2 foramen consistently stained the dorsal rami, with occasional spread to the epidural space and ventral nerve roots via the sacral foramina. Catheter use and higher injection pressures may also facilitate ventral diffusion into the sacral plexus. Clinically, several case reports/series have documented extensive dermatomal sensory involvement from T12 to S5 in various acute and chronic pain settings.[3,5,37,38,39,40] In this SRMA, only one study reported clinical numbness in the L2–S2 dermatomes.[29] Collectively, these findings indicate that the spread of injectate, subsequent analgesic effect, and dermatomal involvement in sacral SMPB are highly dependent on approach, injection volume, and delivery method, with potential implications for targeting dorsal versus ventral sacral nerve components.

Postoperative pain scores

Across the included studies, SMPB generally resulted in lower postoperative pain scores than control or comparator techniques on the first postoperative day, with the benefit most pronounced during the intermediate (6–12 h) and late (24 h) postoperative periods. Immediate postoperative pain scores were often comparable between groups, likely due to the residual effects of intraoperative analgesia. While the magnitude and duration of analgesic benefit varied across surgical settings, the overall evidence indicates that SMPB provides effective postoperative analgesia, with the greatest impact observed within the first 24 h.

Opioid-sparing effect

Postoperative opioid consumption, expressed in morphine milligram equivalents, could be extracted from only five studies.[21,22,23,24,30] In the remaining seven studies, conversion was not possible as paracetamol or ibuprofen was used as the rescue analgesic.[25,26,27,28,29,31,32] The reduction in 24-h opioid consumption was robust in adult studies,[21,23,24,30] with two trials demonstrating 50%–65% lower opioid requirements compared with controls.[24,30] Paediatric studies, although less frequently reporting opioid metrics, showed parallel trends in reduced rescue analgesic need.[22] This opioid-sparing effect has important implications for enhanced recovery pathways, particularly in ambulatory and paediatric settings where opioid-related adverse events are of concern.

Patient satisfaction

Patient/parenteral satisfaction, reported in six studies, was generally higher in the SMPB groups compared to controls or alternative RA techniques.[21,24,25,30,31,32] Only one study reported patient satisfaction using the QoR-15 scale,[21] while the others used Likert scale scores. In adult populations, significantly higher satisfaction scores were observed in the SMPB group, correlating with improved pain control and reduced opioid consumption.[21,24,25,30] Of the two paediatric cohorts, one study reported higher parental satisfaction with SMPB,[31] while the other favoured caudal epidural block (CEB).[32] This variation suggests that the relative efficacy of the comparator group may influence satisfaction. Overall, available data indicate that SMPB can enhance patient or caregiver satisfaction, particularly when it delivers superior analgesia and reduces the need for rescue analgesics.

Comparison with established techniques

When compared with other RA techniques, SMPB demonstrated variable relative performance depending on the surgical context and comparator. In paediatric studies, SMPB showed comparable or superior analgesia to penile block and ring block, with lower pain scores, reduced rescue analgesic use, and higher parental satisfaction in circumcision surgeries.[22,28,31] Against CEB, results were mixed: Two studies reported comparable analgesia,[22,29] while others found CEB to provide longer duration of analgesia and higher satisfaction in hypospadias repair.[32] In adults, SMPB outperformed no-block controls across multiple surgical procedures, including perianal surgery, lumbar discectomy, and hip arthroplasty, with lower pain scores, reduced opioid consumption, and improved satisfaction.[21,23,24,27,30] Compared with pudendal nerve block in TURP, SMPB showed similar analgesic outcomes but required less time to perform.[25] These findings suggest that SMPB is an effective and versatile alternative to established techniques. However, its relative advantage may be procedure-specific, depending on technical proficiency and the efficacy of the comparator.

Safety profile

Across the included studies involving 348 patients, SMPB demonstrated a favourable safety profile, with no serious block-related complications reported. Minor adverse events, such as bradycardia, hypotension, and PONV, occurred infrequently and at rates comparable to control or comparator groups.[22,24,25,30] These effects are likely unrelated to the block itself and may instead reflect the perioperative use of other agents, such as opioids. Importantly, no cases of motor weakness, urinary retention, haematoma, infection, or local anaesthetic systemic toxicity (LAST) were documented in adult or paediatric patients. A few comparator groups, such as those receiving caudal epidural block or pudendal nerve block, had procedure-specific adverse effects (e.g. penile engorgement) which was not observed with SMPB.[22] Overall, the evidence indicates that SMPB is a safe technique when performed under ultrasound guidance, with a low incidence of minor, self-limiting side effects.

During the preparation of this manuscript, Pilia et al.[41] published an SRMA in the Indian Journal of Anaesthesia (September 2025) evaluating ultrasound-guided SMPB in adults undergoing surgery under spinal anaesthesia. Their meta-analysis included only three RCTs and assessed a limited outcome set, with the primary endpoint being the need for rescue opioid analgesia.[21,23,30] While their findings support reduced rescue analgesia rates and lower 24-h pain scores, they reported no significant differences in opioid consumption or time to rescue analgesia. In contrast, our review includes 12 RCTs across both adult and paediatric populations, multiple surgical contexts, and a wider range of comparators; incorporates subgroup analyses; evaluates additional outcomes such as patient satisfaction and PONV; and uses anatomically precise SMPB nomenclature. These differences provide a broader and more generalisable synthesis applicable to varied clinical settings.

This SRMA has several limitations. First, the number of available RCTs on SMPB is relatively small, with heterogeneity in patient populations, surgical procedures, comparator techniques, and outcome measures, which may limit the generalisability of the findings. Second, variations in block technique, including needle approach (MSC vs ISC), injection site, local anaesthetic type, volume, and use of adjuvants, introduce procedural variability that could influence analgesic outcomes. Third, most paediatric studies used non-opioid rescue analgesics, preventing conversion to morphine milligram equivalents and limiting the pooled analysis of opioid consumption. Fourth, few studies incorporated long-term follow-up; thus, the potential impact of SMPB on chronic postoperative pain remains unknown. As we included studies published in the English language only, we acknowledge that studies published in other languages might not have made it to the list of articles fulfilling the inclusion criteria. Finally, the risk of publication bias cannot be excluded, as most included trials were single-centre studies with small sample sizes, and several originated from the same research groups.

CONCLUSIONS

SMPB appears to be a safe and effective RA technique, providing opioid-sparing effects, prolonged analgesia, and improved patient or caregiver satisfaction, with benefits most evident within the first 24 h after surgery. These advantages are particularly notable in adult surgical populations and comparisons with no-block controls, though outcomes against other RA techniques vary by procedure and comparator. However, the current evidence base is limited by methodological heterogeneity, small sample sizes, limited paediatric opioid data, and potential publication bias. Therefore, the results of this review should be interpreted cautiously. Larger, well-designed multicentre RCTs with standardised protocols, comprehensive sensory mapping, and long-term follow-up are warranted to establish its definitive role in multimodal analgesia strategies.

Presentation at conferences/CMEs and abstract publication

None.

Data availability

The data for this systematic review and/or meta-analysis may be requested with reasonable justification from the authors (email to the corresponding author) and shall be shared upon request.

Disclosure of use of artificial intelligence (AI)-assistive or generative tools

The AI tools or language models (LLMs) have not been utilised in the manuscript, except that software has been used for grammar corrections and references.

Declaration of use of permitted tools

The scales, scores, figures, and tables are not copyrighted.

Authors contributions

ASN: Design, Definition of intellectual content, literature search, data acquisition, data analysis, manuscript preparation, editing, review and approval. TM: Concepts, Definition of intellectual content, literature search, data acquisition, manuscript preparation, editing, review and approval. RG: Concept, manuscript editing, review and approval.

Conflicts of interest

Dr. Rakesh Garg, who is one of the co-authors of this manuscript, is an Editor of this journal. He was not involved in any decision-making process, and an independent editor handled this manuscript. The authors declare that they have no other conflicts of interest.

Supplementary material

This article has supplementary material and can be accessed at this link. Supplementary Material at http://links.lww.com/IJOA/A50.

Supplementary Figure 1

a: Forest plot showing comparison of 24-h pain scores between the SMPB group and control group. b: TSA graph showing comparison of 24-h pain scores between the SMPB group and control group. CI = confidence interval; IV = inverse variance; SD = standard deviation; SMPB = sacral multifidus plane block; TSA = trial sequential analysis

Supplementary Figure 2

a: Forest plot showing comparison of 24-h pain scores between the SMPB group and control group (adults). b: Forest plot showing comparison of 24-h pain scores between the SMPB group and control group (paediatrics). CI = confidence interval; IV = inverse variance; SD = standard deviation; SMPB = sacral multifidus plane block; TSA = trial sequential analysis

Supplementary Figure 3

a: Forest plot showing comparison of postoperative pain scores between the SMPB group and control group. b: Forest plot showing comparison of postoperative pain scores between the SMPB group and control group (adults). c: Forest plot showing comparison of postoperative pain scores between the SMPB group and control group (paediatrics). CI = confidence interval; IV = inverse variance; SD = standard deviation; SMPB = sacral multifidus plane block; TSA = trial sequential analysis

Supplementary Figure 4

a: Forest plot showing comparison of time to rescue analgesia between the SMPB group and control group (adult). b: Forest plot showing comparison of time to rescue analgesia between the SMPB group and control group (paediatrics). CI = confidence interval; IV = inverse variance; SD = standard deviation; SMPB = sacral multifidus plane block; TSA = trial sequential analysis

Supplementary Figure 5

a: Forest plot showing comparison of 24-h opioid consumption between the SMPB group and control group (adults). b: Forest plot showing comparison of patients requiring rescue analgesia between the SMPB group and control group (adults). CI = confidence interval; IV = inverse variance; SD = standard deviation; SMPB = sacral multifidus plane block; TSA = trial sequential analysis; M-H = Mantel-Haenszel method

Supplementary Figure 6

a: Forest plot showing comparison of patient satisfaction scores between the SMPB group and control group. b: Forest plot showing comparison of PONV between the SMPB group and control group. CI = confidence interval; IV = inverse variance; SD = standard deviation; SMPB = sacral multifidus plane block; TSA = trial sequential analysis; PONV = postoperative nausea and vomiting; M-H = Mantel-Haenszel method

Funding Statement

Nil.