Impact of Posterior Quadratus Lumborum Block on Acute Pain Relief and Chronic Pain Prevention in Breast Cancer Surgery

Abstract

Introduction

Breast cancer surgery is a common surgical procedure often associated with acute and chronic postoperative pain. As part of multimodal analgesia, the erector spinae plane block (ESPB) has been shown to effectively alleviate pain after breast cancer surgery. This study is the first to apply the posterior quadratus lumborum block (posterior QLB) for perioperative analgesia in breast cancer surgery. The aim of this research was to evaluate whether ESPB and QLB2 can relieve acute and chronic pain following breast cancer surgery.

Methods

A total of 120 female patients undergoing breast cancer surgery were randomly assigned to receive either ESPB, posterior QLB, or no intervention. All patients were administered sufentanil patient-controlled intravenous analgesia postoperatively. The primary outcome was the visual analog scale (VAS) pain scores recorded at 2, 6, 18, 24, and 48 h post-surgery under rest and motion conditions. Secondary outcomes included the incidence of moderate-to-severe pain within 24 and 48 h post-surgery, intraoperative fentanyl cumulative dosage, postoperative rescue analgesia, chronic pain incidence, recovery quality of life, and adverse events.

Results

Compared to the group receiving conventional treatment (group C), the incidence of moderate-to-severe pain within 24 h post-surgery was significantly lower in both the group receiving ESPB (group E; 16.7% vs. 46.2%, P < 0.05) and the group receiving QLB (group Q; 20.5% vs. 46.2%, P < 0.05). Additionally, the proportion of patients requiring rescue analgesia was significantly reduced in both group E and group Q, compared to group C (group C vs. E vs. Q: 30.8% vs. 7.1% vs. 10.3%, P = 0.007; group C vs Q: 30.8% vs. 10.3%, P = 0.025; group C vs. E: 30.8% vs 7.1%, P = 0.006; group Q vs. E: 10.3% vs. 7.1%, P = 0.141). At 3 months post-surgery, group Q had a significantly lower incidence of chronic pain compared to both group C (19.5% vs. 71.8%, P < 0.05) and group E (19.5% vs. 57.1%, P < 0.05). No significant differences were observed between the groups in terms of VAS scores at 2, 6, 18, 24, or 48 h, intraoperative fentanyl consumption, postoperative nausea and vomiting, time to first mobilization, time to first oral intake, the length of hospital stay, or Quality of Recovery—15 Items (QoR-15) scores at 3 months post-surgery (all P > 0.05).

Conclusion

Compared with conventional intravenous analgesia, the combination of ultrasound-guided ESPB and posterior QLB significantly reduces the incidence of moderate-to-severe pain and the need for rescue analgesia within 24 h post-surgery. Furthermore, a single posterior QLB significantly reduces the incidence of chronic pain at 3 months post-surgery in patients with breast cancer.

Trial registration

Clinical trial number: ChiCTR2000041471.

Key Summary Points

Why carry out this study?

This study marks the first application of the posterior quadratus lumborum block (posterior QLB) for perioperative analgesia in patients with breast cancer, with the aim to evaluate whether the erector spinae plane block (ESPB) and the posterior QLB can alleviate acute and chronic pain following breast cancer surgery

What was learned from this study?

The findings demonstrate that both the posterior QLB and the ESPB can reduce the incidence of moderate-to-severe pain within 24 h after breast cancer surgery

The posterior QLB significantly reduces the incidence of chronic pain at 3 months post-surgery

Introduction

Breast cancer is the most common malignancy among women globally, including in China, and surgical treatment remains one of the most effective therapeutic options. However, due to the extensive surgical field and the size of the incision, postoperative stimuli, such as wound negative pressure drainage and compression bandaging, can exacerbate pain, hinder recovery, and diminish the postoperative quality of life [1]. Studies indicate that approximately 50–60% of patients experience moderate-to-severe pain within 24 h after surgery [2] and that the incidence of chronic postoperative pain (CPSP) can range from 30% to 50% [3, 4]. Regional nerve blocks have proven effective in providing adequate pain relief, reducing the need for analgesics and anesthetics during the perioperative period, and decreasing the incidence of chronic pain [5]. Techniques such as pectoral muscle blocks (PECS 1 and 2) or anterior serratus plane block (ASPB) have been successfully employed for perioperative analgesia in breast surgeries [6]. However, these techniques are employed in close proximity to the surgical site, and there is a potential risk that the dissemination of anesthetics might disrupt the subsequent surgical procedures. As a result, identifying more effective analgesic methods that are distant from the surgical incision has become an important focus in postoperative pain management for breast cancer surgeries.

In recent years, ultrasound-guided chest wall truncal blocks have become widely used in pain management. Among these, the erector spinae plane block (ESPB) and quadratus lumborum block (QLB) have gained the attention of researchers due to their effective analgesic effects and relatively low side effects [7–9]. Previous studies have demonstrated the effectiveness of ESPB in controlling pain after breast surgery [10–13]. The posterior quadratus lumborum block (posterior QLB) is a fascial plane block in which local anesthetics are injected into the fascial plane between the quadratus lumborum (QL) and erector spinae (ES) muscles. The anesthetic then diffuses along the thoracolumbar fascia into the paravertebral space, directly blocking the lumbar plexus nerve roots and branches, as well as the sympathetic nerve network on the surface of the thoracolumbar fascia [9] The posterior QLB technique has been widely utilized in abdominal and lower limb surgeries for postoperative analgesia [14], but reports on its application for pain management after breast cancer surgery are limited. In this study, our aim was to compare the analgesic effects of ultrasound-guided posterior QLB block and ESPB after breast cancer surgery, providing valuable clinical insights for future pain management strategies.

Methods

Study Design

This prospective, randomized, patient-blinded, controlled trial was approved by the Ethics Committee of the Affiliated Drum Tower Hospital of Nanjing University School of Medicine (Approval No. 2020–258) and registered with the Chinese Clinical Trial Registry (Registration No. ChiCTR2000041471; 12.26.2020). All participants provided written informed consent. This study was performed in accordance with the Helsinki Declaration of 1964 and its later amendments.

Study Population

From November 2023 to June 2024 we enrolled female patients aged 18–65 years who were scheduled for breast cancer surgery (e.g., radical operation of mastocarcinoma, modified radical operation of mastocarcinoma, extensive radical operation of mastocarcinoma). The exclusion criteria included: (1) American Society of Anesthesiologists (ASA) class IV or higher; (2) low educational level; (3) chronic opioid dependence or use of painkillers for > 3 months; (4) allergy to the investigational drug; (5) epilepsy and intellectual disability; (6) body mass index (BMI) > 40 kg/m²; (7) severe cardiovascular adverse events that occurred during the procedure; (8) postoperative severe adverse events (e.g., septic shock or acute renal failure); and (9) severe renal (serum creatinine > 442 μmol/L or requiring renal replacement therapy) or liver (Child–Pugh grade C) insufficiency.

Randomization

Patients were randomly assigned to one of three groups, namely, a group receiving conventional treatment, with no nerve block (group C), an group receiving ESPB (group E), or a group receiving posterior QLB (group Q), using computer software, at a ratio of 1:1:1. An assistant, who was not involved in the study, prepared the randomization list and concealed group assignments in consecutively numbered, sealed, opaque envelopes. A senior anesthesiologist, who was not involved in the study, opened the envelopes to reveal the group allocation shortly before the nerve block performance. While complete double-blinding is inherently challenging in regional anesthesia techniques, we implemented several measures to minimize potential bias. Firstly, all nerve blocks were performed after anesthetic induction in all groups, a design specifically intended to eliminate bias arising from subjective perceptions in control group patients. Secondly, the surgical team, anesthesia team, and postoperative follow-up personnel were blinded to group allocation and did not have access to randomization until data analysis was completed. This randomization method follows the method applied in previous research [15].

Fascial Plane Block Procedure

Group E (ESPB)

Patients were positioned laterally, and the back of the patient was disinfected and draped. A low-frequency convex probe (TE9S; Mindray, Shenzhen, China) wrapped in a sterile sheath was placed 2–3 cm lateral to the spinous process. The probe was used to identify the T5 transverse process and erector spinae muscle. Using an in-plane technique, the needle was inserted from caudally to cranially (Fig. 1). After confirming no blood or air upon aspiration, 3 mL of saline was injected to verify the location. Subsequently, 0.375% ropivacaine (0.4 ml/kg) was injected. The success of the block was determined by the lift of the erector spinae muscle from the transverse process under ultrasonographic scanning. During the procedure, real-time observation confirmed the cephalocaudal spread of the injectate along the fascial plane, covering the T2 to T6 vertebral levels.

Fig. 1.

Sonoanatomy of the erector spinae plane block. ESM Erector spinae muscles, TP transverse process

Group Q (Posterior QLB)

Patients were positioned laterally, and the side abdominal wall and back were disinfected and draped. A low-frequency convex probe wrapped in a sterile sheath was positioned parallel to the iliac crest. The probe was adjusted to visualize the quadratus lumborum, erector spinae, and psoas major muscles, forming the “shamrock” sign. Using an in-plane technique, the needle was passed through the skin, subcutaneous tissue, and posterior border of the erector spinae, until the needle tip reached the thoracolumbar fascia behind the quadratus lumborum [16, 17] (Fig. 2). After confirming no blood or air upon aspiration, 3 mL of saline was injected to verify the location. Then, 0.375% ropivacaine (0.4 ml/kg) was injected. The successful blockade was evidenced by hypoechoic fluid collection displaying a crescent distribution pattern between the quadratus lumborum and elector spinae muscle. Under real-time ultrasound guidance, the injectate was observed to dissect through interfascial planes, propagating along the craniocaudal axis.

Fig. 2.

Sonoanatomy of the posterior quadratus lumborum block. ESM Erector spinae muscles, PM posterior quadratus lumborum, QLM quadratus lumborum muscle, TP transverse process

Group C (Conventional Treatment)

The patients in group C did not undergo nerve block. Only routine monitoring of vital signs was carried out before the induction of anesthesia.

Anesthesia Implementation

Patients were instructed to undergo conventional fasting with no preoperative medication. Upon entering the operating room, an intravenous line was established, and vital signs (heart rate, blood pressure, pulse oximeter, and electrocardiogram [ECG]) were monitored. Anesthesia induction involved midazolam (0.05 mg/kg), fentanyl (3 μg/kg), propofol (2–2.5 mg/kg), and vecuronium (0.1 mg/kg), followed by endotracheal intubation and mechanical ventilation. Ventilation was set to volume-controlled mode with a tidal volume of 6–8 mL/kg, an inspiratory-to-expiratory ratio of 1:2, and a respiratory frequency adjusted to maintain end-tidal CO² pressure between 35 and 45 mmHg. Anesthesia maintenance was achieved with a continuous infusion of propofol (5–8 mg/kg/h), and vecuronium was intermittently administered based on TOF® muscle-relaxant monitoring. The depth of anesthesia was adjusted by supplement with propofol to maintain the bispectral index in the range of 40–60. At skin closure, flurbiprofen axetil 50 mg was administered for supplemental analgesia (for patients without contraindications), along with ondansetron 8 mg to prevent nausea and vomiting.

After the procedure, the patient was transferred to the Post Anesthesia Care Unit (PACU), and patient-controlled intravenous analgesia (PCIA) was initiated immediately. Patients were extubated in the PACU and observed for at least 30 min after extubation. They were transferred to the general ward when the modified Aldrete score reached 10 points. The PCIA formula was sufentanil (1.5 μg/kg), dexamethasone (10 mg), and ondansetron (8 mg) with normal saline to 100 mL. The PCIA pump rate was set at 2 mL/h with a lockout time of 15 min. Patients could press the PCIA button if the visual analog scale (VAS) exceeded 4, and if pain persisted (VAS > 7); flurbiprofen axetil 50 mg was administered as rescue analgesia. The target was to maintain the VAS for pain intensity at < 4.

Primary and Secondary Outcomes

The primary outcome was postoperative VAS pain scores, recorded at 2, 6, 18, 24, and 48 h post-surgery under rest and motion conditions (lifting the arm 10 cm). The Brief Pain Inventory (BPI) scale was used to assess pain intensity and interference with daily life at 24 and 48 h post-surgery. The BPI scale is a validated tool used to assess pain intensity and its impact on daily functioning. It evaluates pain intensity through four items (current, worst, least, and average pain) and pain interference through seven domains (general activity, mood, sleep, et.); each item is scored on a 0–10 scale (0 = no pain/interference, 10 = most severe pain/completely interferes). Secondary outcomes, including chronic pain incidence and Quality of Recovery—15 Items Scale (QoR-15) scores were recorded at 3 months post-surgery. The QoR-15 scale assesses postoperative recovery in five domains: physical comfort, physical independence, emotional state, psychological support, and pain, with a total score ranging from 0 to 150 (higher scores indicating better recovery) [17]. Other secondary outcomes included intraoperative fentanyl dosage, postoperative rescue analgesia, incidence of nausea and vomiting, and complications related to nerve blocks (hematoma, infection, nerve injury, lower limb weakness), as well as the length of hospital stay.

Statistical Methods

Sample size estimation was performed using PASS 11.0 software (PASS, LLC, Alexandria, VA, USA) , with a target VAS pain score of < 3 for the primary outcome. Based on prior studies, the effect size was 0.4, 0.85, and 0.72 for the conventional group (group C), posterior QLB group (group Q), and ESPB group (group E), respectively. With an assumed sample variance of 0.65, α = 0.05, β = 0.2, and a 20% dropout rate, the required sample size was estimated to be 117 patients (39 per group). Data were analyzed using SPSS 27.0 software (SPSS IBM Corp., Armonk, NY, USA). Continuous variables were tested for normality with the Shapiro–Wilk test. Normally distributed data were presented as the mean ± standard deviation (SD) and compared using one-way analysis of variance (ANOVA). Non-normally distributed data were presented as median (M) and interquartile range (P25, P75) and analyzed using the Kruskal–Wallis test. Categorical variables were presented as percentages and analyzed with the Chi-square test or Fisher’s exact test, with pairwise comparisons adjusted using the Bonferroni correction. A P-value of < 0.05 was considered to be statistically significant, and adjusted P-values for pairwise comparisons were considered to be significant at < 0.0167.

Results

Characteristics of the Demographic Data

The CONSORT flow diagram for this trial is shown in Fig. 3.

Fig. 3.

CONSORT flow chart of study design

Patients were recruited from November 2023 to 26 June 2024; follow-up of the last enrolled patient was completed in September 2024. Of the 127 patients initially enrolled, seven were excluded (4 refused participation, 2 changed surgical procedures, and 1 required a second surgery), leaving a final sample size of 120 patients: 39 patients in group C, 39 patients in group Q, and 42 patients in group E. There were no statistically significant differences in age, BMI, ASA classification, and other general data among the three groups (P > 0.05).

There were no statistically significant differences among the three groups in terms of intraoperative fentanyl dosage, crystalloid fluid volume, colloid fluid volume, and the number of patients requiring vasopressors (P > 0.05) (Table 1).

Table 1.

Clinical characteristics of patients

Clinical characteristics of patients	Study groupsa			P-value
	Group C (n = 39)	Group E (n = 42)	Group Q (n = 39)
Age (years)	50.6 ± 10.1	50.2 ± 7.6	51.7 ± 8.6	0.734
Body mass index (kg/m2)	24.67 ± 4.44	23.99 ± 3.56	23.48 ± 2.55	0.567
ASA class, n (%)				0.145
I–II	33 (84.6%)	38 (90.5%)	38 (97.3%)
III	6 (15.4%)	4 (9.5%)	1 (0.7%)
Preoperative chemoradiotherapy, n (%)	14 (36.9%)	10 (23.8%)	7 (17.9%)	0.181
Hypertension, n (%)	12 (30.8%)	9 (21.4%)	8 (20.5%)	0.501
Diabetes mellitus, n (%)	1 (2.6%)	5 (11.9%)	1 (2.6%)	0.114
coronary heart disease, n (%)	0 (0%)	1 (2.4%)	0 (0%)	0.392
Cerebral infarction	1 (2.6%)	1 (2.4%)	0 (0%)	0.612
Duration of operation (min)	120 (105, 130)	117.5 (95, 137.5)	115 (95, 40)	0.592
Length of hospital stay (days)	7 (6, 9)	7.5 (5, 10)	7 (6, 9)	0.623
Crystalloid fluid (mL)	1000 (500, 1000)	1000 (1000, 1000)	1000 (500, 1000)	0.592
Colloid fluid (mL)	500 (500, 500)	500 (500, 500)	500 (500, 500)	0.171
Vasoactive agent, n (%)	7 (17.9%)	5 (11.9%)	10 (25.6%)	0.332
Fentanyl (mg)	0.5 (0.5, 0.55)	0.5 (0.44, 0.56)	0.5 (0.4, 0.5)	0.234

Values are expressed as a number with the percentage in parentheses, as the mean ± standard deviation (SD), or the median with the inter-quartile range (P25, P75) in parentheses

ASA American Society of Anesthesiologists

^aGroup C, group receiving conventional care, with no nerve block; group E, group receiving erector spinae plane block (ESPB); group Q, group receiving posterior quadratus lumborum block (posterior QLB)

Postoperative VAS Pain Scores at Different Time Points

Compared with group C, there were no significant differences in the VAS pain scores at rest and during movement at 2, 6, 18, 24, and 48 h post-surgery in group E and group Q. The VAS scores in all three groups showed no statistical differences (P > 0.05) (Table 2).

Table 2.

Comparison of visual analog scale pain scores between the three groups

VAS scores at post-surgery time points	Study groupsa			P-value
	Group C (n = 39)	Group E (n = 42)	Group Q (n = 39)
VAS at rest
2 h	0 (0, 1)	0 (0, 1.25)	0 (0, 1)	0.597
6 h	0 (0, 1)	0 (0, 1)	1 (0, 1)	0.346
18 h	0 (0, 2)	0 (0, 1)	0 (0, 1)	0.311
24 h	0 (0, 1)	0 (0, 1)	0 (0, 1)	0.419
48 h	0 (0, 1)	0 (0, 1)	0 (0, 1)	0.712
VAS on movement
2 h	1 (0, 2)	1 (1, 2)	1 (1, 2)	0.914
6 h	1 (1, 2)	1 (1, 2)	1 (1, 2)	0.445
18 h	2 (1, 3)	1 (1, 2)	1 (1, 2)	0.064
24 h	2 (1, 4)	2 (2, 3)	2 (1, 2)	0.196
48 h	1 (1, 2)	1 (1, 2)	1 (1, 2)	0.565

Values are expressed as the median with the inter-quartile range (P25, P75) in parentheses

VAS Visual analog scale

^aGroup C, group receiving conventional care, with no nerve block; group E, group receiving erector spinae plane block (ESPB); group Q, group receiving posterior quadratus lumborum block (posterior QLB)

Incidence of Moderate to Severe Acute Postoperative Pain

According to the BPI scale at 24 h and 48 h post-surgery, there was a statistically significant difference in the incidence of moderate-to-severe pain within 24 h (P < 0.05). Pairwise comparisons showed that both the Q and E groups had a significantly reduced incidence of moderate-to-severe pain within 24 h post-surgery compared to group C (group Q vs. group C: P = 0.016, odds ratio [OR] 0.301, 95% confidence interval [CI] 0.111–0.819; group E vs. C: P = 0.004, OR 0.233, 95% CI 0.084–0.652). However, there were no significant differences in the incidence of moderate-to-severe pain at 48 h post-surgery (P > 0.05). (Table 3; Fig. 4). The proportion of patients requiring rescue analgesia within 24 h was statistically significantly different (group C vs. E vs. Q: 30.8% vs. 7.1% vs. 10.3%, P = 0.007; group C vs. Q: 30.8% vs. 10.3%, OR 0.257, 95% CI 0.075–0.887, P = 0.025; group C vs. E: 30.8% vs. 7.1%, OR 0.173, 95% CI 0.045–0.672, P = 0.006; group Q vs. E: 10.3% vs. 7.1%, P = 0.141) (Table 3).

Table 3.

Data on postoperative acute and chronic pain in the three groups of patients

	Group C	Group E	Group Q	P value	P value	P value	P value
	n = 39	n = 42	n = 39		C vs Q	C vs E	Q vs E
Moderate to severe pain
Within 24 h	18 (46.2%)	7 (16.7%)	8 (20.5%)	0.006	0.016a	0.004b	0.656
Within 48 h	3 (7.7%)	2 (2.4%)	3 (7.7%)	0.496	1	0.27	0.27
Rescue analgesia within 24 h	12 (30.8%)	3 (7.1%)	4 (10.3%)	0.007	0.025c	0.006d	0.141
Chronic pain
Incidence of chronic pain at 3 months	28 (71.8%)	24 (57.1%)	11 (19.5%)	< 0.01	< 0.001e	0.246	0.009f
Maximum VAS in chronic pain	1(1, 2)	1(1, 2)	1(1, 2)	0.923	–	–	–
Neuropathic pain	10 (25.6%)	11 (26.2%)	3 (7.7%)	0.065	–	–	–

Values are expressed as a number with the percentage in parentheses

CI Confidence interval, OR odds ratio, VAS visual analog score

^aGroup C, group receiving conventional care, with no nerve block; group E, group receiving erector spinae plane block (ESPB); group Q, group receiving posterior quadratus lumborum block (posterior QLB)

^bOR = 0.301, 95% CI: 0.111-0.819

^cOR = 0.257, 95% CI: 0.075–0.887

^dOR = 0.154, 95% CI: 0.058–0.414

^eOR = 0.233, 95% CI: 0.084–0.652

^gOR = 0.173, 95% CI: 0.045–0.672

^gOR = 3.394, 95% CI: 1.343–8.579

Fig. 4.

The incidence of moderate-to-severe pain within 24 and 48 h post-surgery, and the incidence of chronic pain at 3 months post-surgery. Group C Group receiving conventional care, with no nerve block, Group E group receiving erector spinae plane block (ESPB), Group Q group receiving posterior quadratus lumborum block (posterior QLB)

Incidence of Chronic Pain at 3 Months Post-Surgery

There was a statistically significant difference in the incidence of chronic pain at 3 months post-surgery among the three groups (P < 0.001). Pairwise comparisons with Bonferroni correction (P = 0.0167) revealed that group Q had significantly lower incidence of chronic pain at 3 months post-surgery compared to both group C (19.5% vs. 71.8%, OR 0.301, 95% CI 0.111–0.819, P < 0.001) and group E (19.5% vs. 57.1%, OR 0.494, 95% CI 0.281–0.869, P = 0.009) (Table 3' Fig. 4).

There were no significant differences among the three groups in terms of the incidence of neuropathic pain at 3 months post-surgery or the maximal intensity of chronic pain (Table 3).

Postoperative Data Comparison

Other outcomes, including postoperative nausea and vomiting, postoperative sufentanil consumption, the time to first ambulation, time to first intake of food, flatus and defecation within 24 h, and postoperative recovery quality of life at 3 months, showed no statistically significant differences (P > 0.05). No adverse events, such as lower limb muscle weakness or respiratory depression, were observed in any of the groups (Table 4).

Table 4.

Postoperative data of the three groups

Postoperative data	Study groupsa			P-value
	Group C (n = 39)	Group E (n = 42)	Group Q (n = 39)
Postoperative chemoradiotherapy	38 (97.4%)	36 (85.7%)	33 (84.6%)	0.128
QoR-15 score at 3 months	137.5 (126, 143)	137.5 (126.5, 143)	138 (127, 145)	0.224
First ambulation (min)	1197.18 ± 184.02	1233.33 ± 211.36	1121.79 ± 191.69	0.707
PONV	12 (30.8%)	10 (23.8%)	6 (15.4%)	0.274
First oral intake (min)	1050 (860, 1200)	1077.5 (970, 1203.75)	1080 (975, 1215)	0.311
Flatus and defecation within 24 h	29 (74.4%)	30 (71.4%)	31 (79.5%)	0.7
Postoperative sufentanil consumption	88.5 (79.5, 95.2)	87 (79.5, 97.5)	94.5 (88.63, 97.88)	0.093

Values are expressed as a number with the percentage in parentheses, as the mean ± standard deviation, or as the median with the inter-quartile range (P25, P75) in parentheses

PONV Postoperative nausea and vomiting, QoR-15 Quality of Recovery—15 Items Scale

^aGroup C, group receiving conventional care, with no nerve block; group E, group receiving erector spinae plane block (ESPB); group Q, group receiving posterior quadratus lumborum block (posterior QLB)

Discussion

This is the first prospective randomized trial to demonstrate that the posterior QLB can effectively control the incidence of acute moderate-to-severe pain within 24 h after surgery in patients with breast cancer. Its analgesic effect is comparable to that of the ESPB. Additionally, the posterior QLB is a favorable technique in controlling chronic pain at 3 months after mastectomy.

The somatic pain following breast cancer surgery is frequently attributed to surgical incision pain, nerve traction injuries from axillary lymph node dissection, and postoperative inflammatory responses [2]. Effective postoperative analgesia following mastectomy plays a crucial role in improving the quality of life of and facilitating recovery in patients with breast cancer. Our study indicates that the posterior QLB is as effective as ESPB in controlling acute moderate-to-severe postoperative pain. Furthermore, posterior QLB outperforms ESPB in reducing the incidence of CPSP at 3 months post-surgery. This technique, which can be performed distant from the surgical site, minimizes interference with surgical manipulation and offers a promising new option for postoperative analgesia in patients undergoing mastectomy.

Previous studies have demonstrated that the ESPB effectively controls pain after breast surgery [10, 12]. The results of a meta-analysis suggested that the blockade typically spans three to five segments above and below the injection site; in the present study, we chose the fifth thoracic vertebra (T5) plane for injection. Our results showed that the ESPB significantly reduced both the incidence of moderate-to-severe pain and the number of patients requiring rescue analgesia within 24 h. These findings are consistent with those of prior studies that employed ESPB to alleviate acute postoperative pain following breast surgery [18, 19].The analgesic effect of ESPB in alleviating acute pain following breast cancer surgery may be attributed to its multi-segmental nerve blockade, anti-inflammatory properties, and reduction of central sensitization. This comprehensive mechanism targets both peripheral and central pathways, providing effective postoperative pain management.

Magnetic resonance imaging photos from Blanco et al. revealed that injecting contrast agents at the posterior border of posterior QLB produced a more reliable paravertebral spread [20]. Based on our prior research, posterior QLB provides effective pain relief following mastectomy, particularly in the T2–T11 dermatomes. Although previous studies suggested that the blockade range of posterior QLB extends from T7 to L1, cadaver studies may only serve as a reference for clinical practice and cannot fully predict the effects in clinical settings. Respiratory movements may exert an upward suction effect on the local anesthetic within the thoracolumbar fascia, and movements of the lumbar muscles could accelerate the diffusion of the anesthetic, resulting in a broader blockade [9]. During the administration of the posterior QLB, we orient the needle bevel upward to facilitate the cephalad spread of the anesthetic solution. This approach likely facilitated the cranial spread of the anesthetic, explaining the effectiveness of posterior QLB in relieving postoperative pain in breast cancer surgery.

In the present study, the BPI scale was utilized to assess the highest numeric rating scale (NRS) scores within 24 and 48 h post-surgery, with a maximum NRS score of ≥ 4 serving as the diagnostic criterion for moderate-to-severe postoperative pain. Compared with the conventional method of assessing transient pain intensity at isolated time points, the BPI scale may better reflect peak pain levels and cumulative pain effects. Our findings demonstrated that although no significant differences were observed in mean pain intensity at specific time points among groups, both ESPB and posterior QLB significantly reduced the incidence of moderate-to-severe pain within 24 h post-surgery and decreased the requirement for rescue analgesia during the same period. These results suggest that both regional anesthesia techniques may offer superior efficacy in preventing pain exacerbation during the early postoperative period.

CPSP is a frequent complication in breast cancer surgery patients, with an incidence ranging from 20% to 50% [3, 4]. Numerous risk factors contribute to chronic pain, particularly severe acute postoperative pain, which can lead to peripheral and central sensitization through sustained inflammatory pain stimuli, ultimately causing chronic pain [21]. Therefore, peripheral nerve blocks may prevent the generation of central afferent pathways by alleviating acute peripheral pain, thereby blocking both peripheral and central sensitization and reducing the incidence of chronic pain [22]. Our study shows that the posterior QLB significantly reduced the incidence of chronic pain at 3 months post-surgery compared to both the ESPB and conventional analgesia. This suggests that Posterior QLB may offer a distinct advantage in preventing CPSP. This finding aligns with the results of Borys et al., who reported that patients who received QLB after cesarean section had significantly lower pain levels at 1 month and 6 months compared to the control group [23]. The proposed mechanism for this effect is that posterior QLB targets the fascial plane between the quadratus lumborum muscle and the thoracolumbar fascia, influencing both somatic and visceral nerves. The posterior QLB offers broader analgesia than the ESPB by covering multiple nerve pathways involved in breast cancer surgery [9, 24, 25]. Further studies are needed to explore the specific mechanisms.

No complications such as needle injury, local anesthetic toxicity, infection, hematoma, or postoperative lower limb motor dysfunction were observed in either group. All block procedures were performed by a senior physician, ensuring safety and consistency. Although both the ESPB and posterior QLB are performed at a distance from blood vessels, pleura, and nerves, there have been reports of adverse events such as Horner’s syndrome, severe hypotension, and bradycardia following posterior QLB [26, 27], and temporary motor dysfunction after ESPB causing lower limb weakness [28]. While no adverse reactions were observed in the present study, continuous monitoring and prompt management of any adverse effects are essential in clinical practice.

While this study provides valuable evidence for postoperative analgesia in breast cancer surgery, several limitations exist. First, the sample size was relatively small, which may limit statistical power and the generalizability of the results. Future studies should involve larger sample sizes and, moreover, multicenter studies are also needed in the future to confirm the reliability of these findings. Second, the study only assessed the incidence of chronic pain at 3 months post-surgery and did not evaluate the long-term analgesic effects. Further research should extend follow-up to examine the long-term impact of the posterior QLB on CPSP. Third, individual differences, such as pain sensitivity, psychological status, and postoperative recovery, were not fully assessed and may have affected the results. Fourthly, in our study, we did not include the pectoralis major and minor muscles block II (PECS II) or the serratus anterior plane block (SAPB), which are commonly used during the perioperative period of breast cancer surgery. Incorporating these blocking techniques into studies could provide a more comprehensive reference for clinical decision-making, and also serve as an important direction for future research. Moreover, we did not track the diffusion patterns of local anesthetics in live patients, as this study was primarily designed to focus on clinical feasibility and real-time efficacy assessment. Finally, due to the use of compression bandages on the surgical wounds of patients with breast cancer, sensory testing after both blocks was difficult, and the duration of analgesia for the ESPB and posterior QLB could not be accurately determined.

Conclusions

In conclusion, both the ESPB and posterior QLB significantly reduced the incidence of moderate-to-severe pain within the first 24 h post-surgery. Moreover, the posterior QLB demonstrated a significant advantage in reducing the incidence of chronic pain at 3 months post-surgery. These findings provide new clinical evidence for postoperative analgesia in breast cancer surgery and emphasize the role of regional block techniques in multimodal analgesia strategies.

Author Contributions

Conceptualization: Bingbing Li. Methodology: Bingbing Li and Qun Fu. Formal analysis, investigation, postoperative follow-up:Min Wang, Shujie Niu, Jin Wu, Yiwei Zhong, and Ziyun Lu. Writing—original draft preparation: Min Wang. Writing—review and editing: Bingbing Li and Qun Fu. Resources: Bingbing Li. Supervision: Bingbing Li.

Funding

The Affiliated Drum Tower Hospital, Medical School of Nanjing University provided funding (2023-LCYJ-MS-31 AND 2024-LCYJ-PY-18). The funding supported the study and the Rapid Service Fee.

Data Availability

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Conflict of interest

Min Wang, Shujie Niu, Jin Wu, Yiwei Zhong, Ziyun Lu, Qu Fu and Bingbing Li have nothing to disclose.

Ethical Approval

This study was approved by the Ethics Committee of Nanjing Drum Tower Hospital (approval number 2020–258). This study was conducted in accordance with the Consolidated Standards of Reporting Trials criteria and in accordance with the Helsinki Declaration of 1964 and its later amendments. Written informed consent was obtained from all patients.