Adequate administration of perioperative analgesia, without adverse effects, is critical for enhanced recovery and physical therapy, particularly in patients who have undergone orthopedic surgery^1,2). Opioid-sparing analgesia with a combination of systemic non-opioid analgesics, intraoperative periarticular infiltration, and peripheral nerve or fascia plane blocks (FPBs) are currently considered indispensable components of perioperative pain management in these types of surgery³⁾. Total hip arthroplasty (THA) is regarded as the standard treatment for osteoarthritis of the hip unresponsive to conservative medical therapy. However, this surgery can be associated with moderate to severe postoperative pain, particularly within the first 48 hours postoperatively and during physical activity, resulting in a prolonged hospital stay and recovery period⁴⁾. The hip joint is supplied by several nerves from the lumbosacral plexus, and the anterior aspect of the hip joint capsule is dense with nociceptors^5,6). Therefore, when administering regional anesthesia in hip surgery, ultrasound-guided FPBs, including suprainguinal fascia iliaca block (SFIB) (also known as the anterior lumbar plexus block), which anesthetizes the femoral and lateral femoral cutaneous nerves, and possibly the obturator nerve, have been suggested in combination with general or neuraxial anesthesia to reduce opioid consumption, postoperative pain, and length of hospital stay, despite the risk of weakness of quadriceps muscle^7-9). However, the obturator, accessory obturator, and articular branch of femoral nerves, which supply the anterior aspect of the hip capsule, may not be adequately or completely anesthetized by SFIB due to insufficient diffusion of anesthetic to the lumbar plexus¹⁰⁾.

The ultrasound-guided modified pericapsular nerve group (PENG) block was initially described by Girón-Arango et al.¹¹⁾ in 2018. The local anesthetic administered when using this technique can reach the articular branch of the accessory obturator and femoral nerves, as well as the articular branch of the obturator nerve that supplies the hip capsule and holds promise as a motor-preserving block. Therefore, several studies have focused on demonstrating the preferability of the PENG block to SFIB in terms of preserving the strength of quadriceps muscle while providing comparable analgesia during performance of hip surgeries^12-15). However, the analgesic effect of the PENG block and its efficacy in comparison to SFIB in patients undergoing hip arthroplasty remains unclear.

Therefore, a randomized controlled trial was designed for comparing the analgesic efficacy of ultrasound-guided PENG block and SFIB in patients undergoing primary elective THA, under general anesthesia combined with a multimodal analgesia. According to our hypothesis the PENG block would reduce opioid consumption in the first 24 hours following surgery as compared to SFIB (primary outcome). The secondary outcomes included a requirement for perioperative intravenous opioid, postoperative pain scores at rest and during movement, hip sensorimotor function, and immediate functional outcomes up to 48 hours after surgery.

This single-center, prospective, double-blind, randomized controlled trial was conducted in accordance with the CONSORT (Consolidated Standards of Reporting Trials) (Fig. 1). The trial was monitored according to the Institutional Review Board (IRB) of Chulalongkorn University in Bangkok, Thailand (October 14, 2021, IRB No. 688/64) and registered at the Thai Clinical Trials Registry (https://www.thaiclinicaltrials.org; TCTR20210929001; date of registration: September 29, 2021). Written informed consent was obtained from patients prior to their inclusion.

Figure 1. CONSORT (Consolidated Standards of Reporting Trials) statement flow diagram. ASA: American Society of Anesthesiologists, NSAIDs: nonsteroidal anti-inflammatory drugs, SFIB: suprainguinal fascia iliaca block, PENG: pericapsular nerve group block, ITT: intention-to-treat.

1. Patient Population

Screening of patients with osteoarthritis of the hip scheduled to undergo elective primary THA under general anesthesia was performed and information about the study protocol was provided one day before surgery. Written informed consent was obtained from patients prior to their inclusion. The exclusion criteria were as follows age <18 years or >80 years, American Society of Anesthesiologists Physical Status IV, body mass index (BMI) <18 kg/m² or >40 kg/m², refusal to participate or inability to cooperate, required spinal anesthesia, relevant drug allergies or contraindications to any of the medications described in the study protocol, chronic pain treated with opioids, and pregnancy. In addition, contraindications to regional anesthesia (neuropathy, coagulopathy, and infection at the puncture sites) were also included in the exclusion criteria.

2. Randomization and Blinding

Patients were randomly assigned to one of two groups using an online randomization computer generator (https://www.sealedenvelope.com) on a 1:1 basis. A modified PENG block was administered in the PENG group, while the SFIB group received an SFIB. The blocks were permuted using a computer program to achieve randomization. The group allocations were concealed in sealed opaque envelopes. Drug injections were administered by an experienced anesthesiologist (W.K.) proficient in ultrasound-guided regional anesthesia, who was not involved in the perioperative assessment. The envelopes were opened by the anesthesiologist (W.K.) and nurse anesthetist when performing blocks and anesthetic drugs were prepared for each patient in the randomized group. The intraoperative anesthesiologists, surgeons, patients, and assessors were blinded to the group allocation. Basic information, including baseline functional outcomes, including the timed up and go (TUG) test, quadriceps muscle strength (QMS) test, and pain scores using the numerical rating scale (NRS) were recorded by the blind assessors before surgery.

3. Interventions

Two 325-mg paracetamol tablets were administered to patients 30 minutes before surgery. On entering the operating room, all patients received standard monitoring. Immediately after induction of general anesthesia, an ultrasound-guided PENG block was added under sterile conditions for patients in the PENG group. The ultrasound transducer was placed transversely over the anterior–inferior iliac spine and aligned with the pubic ramus. To obtain a short-axis view of the iliopsoas muscle and tendon lying on the ramus pubic adjacent to the iliopubic eminence, the medial edge of the probe was rotated parallel to the pubic ramus (Fig. 2A). The block needle was advanced until its tip was positioned between the periosteum and psoas tendon using an inplane technique and a lateral-to-medial direction¹¹⁾. A total of 30 mL of 0.33% bupivacaine with adrenaline (1:200,000) was injected in 5 mL increments with intermittent negative aspiration under the psoas tendon above the pubic ramus. For patients in the SFIB group, the ultrasound transducer was placed in a parasagittal orientation over the inguinal ligament, posteromedially to the anterior superior iliac spine, where the deep circumflex artery was located above the fascia iliaca (Fig. 2B). Following negative aspiration, 30 mL of 0.33% bupivacaine with adrenaline (1:200,000) was injected beneath the fascia iliaca and above the iliacus. Subsequently, all patients in both groups received a transversalis fascia plane block (TFPB) with an ultrasound-guided injection of 15 mL of 0.25% bupivacaine with adrenaline (1:200,000) to separate the transversalis fascia from the transversus muscle using a linear or curvilinear transducer placed over the lateral abdomen between the iliac crest and the costal margin (Fig. 2C). During performance of these blocks, the screen on the ultrasound machine and the location of the ultrasound transducer were concealed from the intraoperative anesthesiologists.

Figure 2. Ultrasound image of PENG (A), suprainguinal fascia iliaca (B), and transversalis fascia plane (C) blocks. White lines indicate the direction of the needle for injection. PENG: pericapsular nerve group, FA: femoral artery, FN: femoral nerve, IM: iliac muscle, PT: psoas muscle tendon, IPE: iliopubic eminence, IOM: internal oblique muscle, DCIA: deep circumflex iliac artery, EOM: external oblique muscle, TAM: transversus abdominis muscle, QL: quadratus lumborum muscle.

General anesthesia with endotracheal intubation was induced using a standard protocol with propofol 1.5-2 mg/kg±fentanyl 0.5-1 μg/kg for induction. Cisatracurium was administered at a dose of 0.15-0.2 mg/kg for achievement of muscle relaxation. Prior to the surgical incision, a combination of intravenous medications, including 20 mg nefopam, 1 g tranexamic acid, and 10 mg dexamethasone was administered to the patient. During the procedure, the depth of anesthesia was maintained using a mixture of oxygen/air/sevoflurane with a minimum alveolar concentration of 1.0, cisatracurium, and intravenous fentanyl if the mean blood pressure, systolic blood pressure, or heart rate exceeded 20% of the preoperative baseline, which was titrated using a bispectral index monitor to a value between 40 and 60, according to the discretion of the anesthesiologist. Mini-posterior THA was performed by the same surgical team with no infiltration of the local anesthetic into the surgical site. The patient received 40 mg of parecoxib and 4-8 mg of ondansetron intravenously, 30 minutes before the end of surgery. The decision to administer intravenous fluid during surgery was made at the discretion of the intraoperative anesthesiologist.

In the post-anesthetic care unit (PACU), 25 μg of fentanyl was administered intravenously every 30 minutes until the patient’s NRS pain score was <4 for patients with pain in the hip or a surgical wound. Postoperative multimodal analgesia was administered to all patients, including patient-controlled analgesia (PCA) with 15 μg of fentanyl at 15-minute intervals and no basal rate (with a maximum of 200 μg of fentanyl in 4 hours), two doses of parecoxib 20 mg intravenously every 12 hours, paracetamol 500 mg orally every 6 hours, Lyrica 75 mg orally once a day before bed, and Celebrex 400 mg orally once a day after the second day following surgery. Other medications included esomeprazole 40 mg intravenously once a day and ondansetron 4 mg intravenously every 6 hours if the patient experienced nausea or vomiting.

4. Outcome Measures

The primary outcome was the total cumulative consumption of intravenous fentanyl 24 hours after surgery, including both intravenous fentanyl administered in the PACU, and intravenous fentanyl administered via the PCA. Secondary outcomes included consumption of intravenous fentanyl during the intraoperative period, in the PACU, and at 6 hours and at 48 hours postoperatively; the demanded and delivered ratio (DD ratio) of PCA fentanyl at 6, 24, and 48 hours postoperatively; the comprehensive Silverman integrated approach (C-SIA) score at 6, 24, and 48 hours postoperatively¹⁶⁾; the NRS pain scores (0-10, where 0=no pain and 10=the worst pain imaginable) at rest and during movement in all aspects of the operated hip, anterior (described as pain at the front of hip) and posterior (described as pain in the buttock area) of the hip, and surgical incision site, assessed at preoperative, PACU, 6, 12, 24, and 48 hours after surgery; the duration and incidence of loss of cutaneous sensory perception in the hip region covered by the femoral nerve, lateral femoral cutaneous nerve, subcostal nerve, ilioinguinal nerve, and obturator nerve (0=normal sensation; 1=absence of cold sensation; 2=absence of both cold and touch sensation); the TUG test, a performance-based measure of immediate functional mobility¹⁷⁾, measured by blinded orthopedic residents preoperatively and 48 hours postoperatively; the muscle strength test included the QMS test¹⁷⁾ (measured in N [newton]; values were determined by requiring the patient to sit with legs dangling from a bed and kicking the operative leg with a knee joint angled at 0° and 90° preoperatively and 24 hours postoperatively or with the patient in supine position with hip flexed at a 45° angle and the knee against resistance at the same degree [12 hours postoperatively]) was measured by blinded assessors. In addition, other outcomes included the incidence of sleep disturbance (preoperatively and 6, 12, 24, and 48 hours postoperatively), duration of postoperative hospitalization (defined as the time from surgery to completion of discharge criteria), patient satisfaction, nausea and vomiting, and scores for dizziness (NRS 0-10).

5. Sample Size Calculation

Calculation of the sample size was based on the anticipated difference in opioid consumption between study groups. According to a previous study reported by Gasanova et al.¹⁸⁾, patients who underwent general anesthesia and ultrasound-guided SFIB required 51.7±20.1 mg of morphine in the first 24 hours postoperatively. Using a power calculation for a 30% difference (14±20 mg) in opioid consumption, a 0.05 α probability level, and a power of 0.80 (1–β), a sample size of 27 patients per group was determined. Thirty patients were included in each group to ensure safe margins.

6. Statistical Analysis

Statistical analysis was performed on an intention-to-treat basis using Stata (ver. 17.0; StataCorp). Evaluation of the normal distribution was performed using quantile-quantile plots and histograms. Continuous data that followed a normal distribution are shown as mean±standard deviation and intergroup comparisons were performed using the Student’s t-test, whereas skewed continuous data are shown as median (interquartile range) and intergroup comparisons were performed using the Mann–Whitney U test. Categorical variables are represented numerically and as percentages and were analyzed using Fisher’s exact test or the chi-square test, as applicable. To account for imbalances in patient characteristics (BMI) between the two groups, a multivariate adjustment for the repeated measurements (including NRS pain scores and opioid consumption) was performed using a linear mixed-effects regression model. The group, time, and group-by-time interactions were treated as fixed effects, and a subject-specific random intercept was used as the random effect¹⁹⁾. P<0.05 was considered statistically significant.

Between October 2021 and December 2022, 79 patients were screened for eligibility to participate in this trial. Following the assessment, 60 patients were randomly assigned to one of the two groups, with 30 patients per group. All 60 participants completed the study and were included in the intention-to-treat analysis without loss to follow-up. Except for BMI, no significant changes in baseline parameters or operative data were observed (Table 1)²⁰⁾.

Table 1 . Baseline Characteristics.

Variable	SFIB (n=30)	PENG (n=30)	P-value
Age (yr)	62.3±13.4	63.6±13.9	0.738
Sex, female/male	21/9	21/9	>0.999
Weight (kg)	65.6±14.5	60.6±12.0	0.157
Height (cm)	157.5±9.9	157.6±9.3	0.984
BMI (kg/m2)	26.3±4.6	24.2±2.6	0.036*
ASA classification, 1/2/3	3/24/3	2/26/2	0.785
Walking aid, none/cane/walker	14/9/7	13/11/6	0.703
Clinical frailty scale (1-7)†	3 (3-4.5)	3 (2.5-3)	0.060
Side, left/right	14/16	14/16	>0.999
Duration of surgery (min)	135.5±27.9	139.6±29.0	0.582
Urine (L)	1.6±0.7	1.6±1.0	0.946
Estimates blood loss (mL)	506.9±320.6	412.1±187.9	0.176
Duration of PNBs (min)	6.9±3.0	6.4±2.6	0.426
Duration from PNBs to skin incision (min)	33.6±8.8	34.4±8.4	0.716

Values are presented as mean±standard deviation, number only, or median (interquartile range)..

SFIB: suprainguinal fascia iliaca block, PENG: pericapsular nerve group block, BMI: body mass index, ASA: American Society of Anesthesiologists, PNB: peripheral nerve block..

*P<0.05..

^†Clinical frailty scale: 1=very fit, 2=well, 3=well, with treated comorbid disease, 4=apparently vulnerable, 5=mildly frail, 6=moderately frail, and 7=severely frail²⁰⁾..

Although the 24-hour total intravenous consumption of fentanyl was lower in the SFIB group than in the PENG group, no statistically significant difference was observed between the two groups (117.4±99.8 μg in the SFIB group vs. 145.9±122.7 μg in the PENG group; mean difference 22.6 [95% confidence interval –36.6, 81.8]; P=0.454). In addition, no significant difference in intraoperative, PACU, and 6 hours and 48 hours postoperative consumption of intravenous fentanyl; C-SIA score at 6, 24, and 48 hours postoperatively; and DD ratio of PCA fentanyl at 6, 24, and 48 hours postoperatively was observed between the groups (Table 2). Regarding scores for postoperative pain between the two groups during the first 48 hours postoperatively, although lower scores for rest and dynamic pain were observed in the PENG group compared with the SFIB group in the PACU, the difference was not statistically significant. In addition, there were no statistically significant differences in scores for pain at rest and during movement in any of the anterior and posterior aspects of the hip region at other time points, and no statistically significant differences in scores for pain were observed in the surgical incision area (Table 3, Supplementary Table 1).

Table 2 . Opioid Consumption.

Variable	SFIB	PENG	Beta coefficient (95% CI)	P-value
Intraoperative fentanyl (µg)	72.4±52.3	63.8±57.3	–5.0 (–34.0, 24.0)	0.736
Fentanyl dose at PACU (µg)	25.2±30.8	26.6±27.3	1.7 (–13.4, 16.8)	0.821
Postoperative PCA fentanyl
6 hours
Total fentanyl (µg)	59.5±44.7	69.8±55.3	7.0 (–19.6, 33.6)	0.605
Demand	8.4±10.5	9.7±10.7	0.8 (–4.8, 6.4)	0.782
Delivery	4.0±3.0	4.7±3.7	0.5 (–1.3, 2.2)	0.605
DD ratio	1.8±1.0	1.9±1.5	0.1 (–0.6, 0.8)	0.787
C-SIA score	0.5±3.4	1.2±4.1	0.4 (–1.6, 2.4)	0.695
24 hours
Total fentanyl (µg)	117.4±99.8	145.9±122.7	22.6 (–36.6, 81.8)	0.454
Demand	13.5±15.2	16.2±15.0	2.2 (–5.9, 10.2)	0.598
Delivery	7.8±6.7	9.7±8.2	1.5 (–2.4, 5.5)	0.454
DD ratio	1.8±0.9	1.7±1.3	0.0 (–0.6, 0.6)	0.943
C-SIA score	4.3±7.0	6.1±8.4	1.0 (–3.1, 5.0)	0.635
48 hours
Total fentanyl (µg)	167.6±176.0	198.1±159.3	25.7 (–63.2, 114.5)	0.572
Demand	17.8±22.8	20.3±18.0	1.9 (–8.9, 12.8)	0.727
Delivery	11.2±11.7	13.2±10.6	1.7 (–4.2, 7.6)	0.573
DD ratio	1.6±0.6	1.6±1.2	0.0 (–0.5, 0.5)	0.975
C-SIA score	7.5±12.0	9.6±10.9	0.8 (–5.2, 6.8)	0.795

Values are presented as mean±standard deviation and were compared using a mixed-effects linear regression and adjusted by body mass index..

SFIB: suprainguinal fascia iliaca block, PENG: pericapsular nerve group block, CI: confidence interval, PACU: post-anesthetic care unit, PCA: patient-controlled analgesia, DD ratio: demand and delivery ratio, C-SIA: the comprehensive Silverman integrated approach..

Table 3 . Postoperative Pain Scores.

Variable	SFIB	PENG	Beta coefficient (95% CI)	P-value
NRS all hip at rest
Preoperative	1.2±1.7	1.0±1.4	0.0 (–0.8, 0.8)	0.960
PACU	4.4±3.1	3.8±3.2	–0.1 (–1.6, 1.5)	0.949
6 hours	2.2±1.9	2.2±1.8	0.2 (–0.8, 1.1)	0.771
12 hours	1.6±1.6	1.3±1.1	–0.2 (–0.9, 0.6)	0.647
24 hours	1.3±1.6	1.0±1.1	0.0 (–0.7, 0.7)	0.995
48 hours	0.9±1.0	1.0±1.2	0.1 (–0.5, 0.7)	0.692
NRS all hip during movement
Preoperative	4.8±2.2	4.5±2.2	–0.1 (–1.3, 1.0)	0.830
PACU	5.5±3.7	4.9±3.5	–0.3 (–2.1, 1.6)	0.785
6 hours	3.9±2.7	4.3±2.5	0.8 (–0.6, 2.1)	0.260
12 hours	3.3±2.2	3.4±2.2	0.1 (–1.0, 1.3)	0.836
24 hours	3.5±2.4	3.3±1.7	0.2 (–0.9, 1.2)	0.779
48 hours	3.2±2.1	3.1±1.7	0.0 (–1.0, 1.1)	0.937
NRS anterior hip at rest
Preoperative	0.7±1.1	1.0±1.4	0.5 (–0.2, 1.1)	0.142
PACU	2.8±3.0	2.1±2.5	–0.4 (–1.8, 1.0)	0.552
6 hours	1.4±2.0	0.9±1.2	–0.2 (–1.1, 0.6)	0.593
12 hours	0.8±1.5	0.7±0.9	–0.1 (–0.8, 0.5)	0.708
24 hours	0.8±1.2	0.4±0.7	–0.2 (–0.8, 0.3)	0.352
48 hours	0.4±0.8	0.4±0.7	0.1 (–0.3, 0.5)	0.662
NRS anterior hip during movement
Preoperative	3.1±2.2	4.0±2.3	1.0 (–0.1, 2.2)	0.086
PACU	3.8±3.7	3.1±2.8	–0.6 (–2.2, 1.1)	0.496
6 hours	2.6±2.4	2.7±2.2	0.6 (–0.6, 1.7)	0.335
12 hours	2.2±2.2	2.2±2.0	0.1 (–1.1, 1.2)	0.901
24 hours	2.4±2.3	2.4±2.0	0.3 (–0.8, 1.4)	0.566
48 hours	1.7±1.6	1.8±1.5	0.4 (–0.4, 1.2)	0.297
NRS posterior hip at rest
Preoperative	1.0±1.6	0.8±1.3	0.0 (–0.8, 0.7)	0.962
PACU	4.2±3.1	2.8±3.3	–0.9 (–2.6, 0.8)	0.287
6 hours	1.6±1.8	1.7±1.8	0.2 (–0.8, 1.2)	0.694
12 hours	1.1±1.5	0.8±1.1	–0.2 (–0.9, 0.5)	0.548
24 hours	1.2±1.9	0.6±1.0	–0.3 (–1.0, 0.5)	0.513
48 hours	0.6±1.0	0.4±0.7	–0.2 (–0.7, 0.3)	0.411
NRS posterior hip during movement
Preoperative	4.1±2.4	2.9±2.5	–0.9 (–2.2, 0.4)	0.152
PACU	5.0±3.6	4.1±3.3	–0.5 (–2.3, 1.2)	0.549
6 hours	3.0±2.4	3.6±2.6	0.7 (–0.6, 2.0)	0.319
12 hours	2.5±2.0	2.2±1.9	–0.1 (–1.1, 0.9)	0.879
24 hours	2.8±2.8	2.3±2.0	0.1 (–1.1, 1.3)	0.912
48 hours	2.0±1.8	1.8±1.4	–0.2 (–1.1, 0.7)	0.656

Values are presented as mean±standard deviation and were compared using a mixed-effects linear regression and adjusted by body mass index..

SFIB: suprainguinal fascia iliaca block, PENG: pericapsular nerve group block, CI: confidence interval, NRS: numerical rating scale, PACU: post-anesthetic care unit..

The duration of cutaneous sensory loss in the hip region was significantly longer in the SFIB group than in the PENG group (1,247.8±698.0 minutes vs. 611.6±420.0 minutes, P<0.001). In addition, significantly fewer incidences of loss of cutaneous sensory perception were observed in the hip region in the PENG group compared with the SFIB group (P<0.05), except for areas covered by the subcostal nerve (Table 4). Regarding immediate functional outcomes and testing for postoperative muscle strength (Table 4), no statistically significant difference on the TUG and QMS tests was observed between the two groups, except for the QMS 90° test at 12 hours postoperatively, which showed a significantly higher result in the PENG group than in the SFIB group (32.4±8.9 vs. 26.9±5.6, P=0.006). None of the patients developed complications as a result of the procedure, and no significant difference in terms of length of stay, patient satisfaction, incidence of postoperative nausea and vomiting, dizziness, or sleep disturbance was observed between the groups (Supplementary Table 2).

Table 4 . The Incidence of Loss of Cutaneous Sensory Perception and Functional Outcomes.

Variable	SFIB	PENG	P-value
Duration of sensory loss (min)	1,247.8±698.0	611.6±420.0	<0.001*
Sensory loss level
Subcostal area at PACU	0 (0-1)	0 (0-1)	0.714
Subcostal area at 6 hours	0 (0-1)	0 (0-0)	0.385
Subcostal area at 12 hours	0 (0-0)	0 (0-0)	0.703
Lateral femoral cutaneous area at PACU	1 (1-2)	1 (1-1)	0.439
Lateral femoral cutaneous area at 6 hours	1 (1-1.5)	1 (0-1)	0.001*
Lateral femoral cutaneous area at 12 hours	1 (0-1)	0 (0-1)	0.001*
Femoral area at PACU	1 (1-2)	1 (0-1)	0.007*
Femoral area at 6 hours	1 (0.5-2)	0 (0-1)	<0.001*
Femoral area at 12 hours	1 (0-1)	0 (0-0)	<0.001*
Ilioinguinal area at PACU	1 (1-2)	1 (0-1)	0.006*
Ilioinguinal area at 6 hours	1 (0-1)	0 (0-1)	0.004*
Ilioinguinal area at 12 hours	1 (0-1)	0 (0-0)	0.001*
Obturator area at PACU	1 (1-2)	0 (0-1)	0.001*
Obturator area at 6 hours	1 (0-1)	0 (0-0.5)	<0.001*
Obturator area at 12 hours	1 (0-1)	0 (0-0)	<0.001*
Functional outcomes
TUG at preoperative (sec)	38.4±32.3	40.8±58.5	0.849
TUG at 48 hours (sec)	106.4±61.8	91.1±48.2	0.315
QMS 0° (n)
Preoperative	36.6±12.3	38.4±14.9	0.609
12 hours	21.7±6.1	24.4±7.7	0.146
24 hours	28.6±8.2	29.5±7.4	0.649
QMS 90° (n)
Preoperative	49.3±12.3	50.3±11.8	0.754
12 hours	26.9±5.6	32.4±8.9	0.006*
24 hours	35.8±9.9	38.2±8.6	0.331

Values are presented as mean±standard deviation or median (interquartile range)..

SFIB: suprainguinal fascia iliaca block, PENG: pericapsular nerve group block, PACU: post-anesthetic care unit, TUG: timed up and go, QMS: quadriceps muscle strength..

*P<0.05..

In this double-blind randomized clinical trial, use of the ultrasound-guided PENG block did not result in reduced consumption of opioid during the first 24 hours postoperatively in patients undergoing surgery using an elective posterior approach to THA under general anesthesia combined with a multimodal analgesia regimen when compared with ultrasound-guided SFIB. In addition, comparable intraoperative and 48 hours postoperative consumption of fentanyl, postoperative analgesia in all aspects of the hip joint, surgical incision during rest and motion for 48 hours postoperatively, initial functional assessments, and length of hospital stay was observed between the two groups. However, use of the PENG block resulted in improved strength of the quadriceps muscle by 90° at 12 hours postoperatively and the incidence of loss of cutaneous sensory awareness around the hip joint was reduced.

The posterior approach, the most commonly used approach to THA at our institution,, required various precautions for the hips during postoperative recovery, including avoiding hip dislocation (limiting hip flexion to ≤90° and internal rotation or adduction of the affected hip) and protecting soft tissue repair^21,22); therefore, maintaining muscle strength for early physical therapy in the immediate postoperative period, particularly within the first 12 hours, was not preferable in our case. In addition, most studies focusing on rapid recovery or ambulation on the day of surgery have reported on the use of an anterior approach²³⁾. However, postoperative relief of pain prior to gait ambulation is crucial. Our study focused primarily on comparing the two analgesic FPB techniques, and our comparable analgesic results were consistent with those reported in the previous study by Aliste et al.¹²⁾. However, the sample size for this study was small and the primary concern was to compare the effectiveness of the two techniques for maintaining strength of the quadriceps muscle.

In contrast, previous studies comparing the analgesic efficacy of the SFIB and PENG blocks in performance of hip fracture surgery reported that the PENG block can provide an enhanced analgesic effect^13-15). This may be attributed to the differences between hip fractures and osteoarthritis, including baseline characteristics, differences in tissue injury or inflammatory response postoperatively, as well as differences in postoperative pain mechanisms^24,25). Other possibilities include leakage of anesthetic during opening of the hip capsule during performance of the THA procedure, resulting in insufficient distribution of anesthetic to the articular branch of the accessory obturator or obturator nerves (observed by the surgeon). The interval between the PENG block and the operation should also be considered. Consequently, there could be differences in the analgesic effects of the PENG block in these two types of hip surgeries. However, adequate multimodal analgesia may have been effective in postoperative analgesia after THA to the extent that determining or differentiating the efficacy of the SFIB and PENG blocks may be possible. In addition, distribution of local anesthetic to the obturator and/or accessory obturator nerves supplying the anteromedial aspect of the hip joint by the PENG block may not improve analgesia for use of a posterior approach to THA when multimodal analgesia is administered²⁶⁾. The analgesic efficacy of the PENG block when using the anterior approach to THA should be examined in future trials.

To minimize the impact of pain caused by the postoperative surgical incision, TFPB was administered to patients who participated in our study to conceal the upper surgical incision site²⁷⁾. Consequently, in our study the effect of the SFIB and PENG blocks on surgical incision sites could not be determined. However, to the best of our knowledge, this is the first study to evaluate postoperative pain in each aspect of the hip joint in patients undergoing SFIB and PENG blocks under general anesthesia. In our study, the maximum scores for pain were observed 6 hours after surgery, consistent with the findings of a previous study that examined pain after hip arthroplasty²⁸⁾. Of particular interest, during the early postoperative period, particularly in the PACU, the pain scores for the posterior hip were higher than those for the anterior hip. This was likely because the anterior hip joint was predominantly affected by both FPBs, while THA using the posterior approach was associated with fascia and muscle injury of the posterior hip²⁹⁾, which was not observed in previous comparative studies. The analgesic efficacy of the muscle-sparing posterior hip block for THA using the posterior approach should be examined in the future.

This study has some limitations. First, the design of our study did not include a control group. However, the PROSPECT recommendation guidelines support single-injection SFIB for postoperative pain following THA³⁰⁾, and SFIB is already an integral component of the standard of care at our institution. Second, this was a single-center study, which might have affected external validity. However, our posterior approach to THA is considered a standardized procedure, and in this single-center study, all procedures were performed by the same surgical team using the same surgical approach with standardized administration of multimodal systematic analgesia. Third, despite the calculation of a priori sample size based on a difference in clinical relevance of 30%, the study was underpowered for detecting a significant difference in opioid consumption between the two groups due to lower consumption of opioid compared with previous studies¹⁸⁾, The reduced prescription of opioids after surgery observed in our study may also be a contributing factor. Therefore, conduct of additional studies including relatively larger sample sizes is warranted. Fourth, although spinal anesthesia has been promoted over general anesthesia, this remains debatable. Our surgeons preferred general anesthesia in performance of THA because it allowed for a rapid assessment of the complications of common peroneal nerve paralysis postoperatively, as well as making the patients comfortable. Finally, the amount of anesthetic used for the PENG block was larger compared with previous studies. However, the purpose of our study was to compare the analgesic effects of the two techniques without concentrating on preventing diffusion of anesthetic into the nerves for preservation of muscle strength. Therefore, we decided to use the same volume and concentration of anesthetic in both procedures.

Compared to ultrasound-guided SFIB, the effect of ultrasound-guided PENG block on opioid consumption or pain scores at rest and during movement showed no clinical significance in all aspects of the hip joint after THA with administration of a multimodal analgesic regimen.

This work was supported by the Ratchadapisek Sompoch Endowment Fund of Chulalongkorn University (grant No. GA65/14).

The authors acknowledge the assistance and support of the intraoperative anesthesiologists, orthopedic residents, and nurses who participated in the trial at King Chulalongkorn Memorial Hospital. The authors would also like to express their gratitude to the biostatisticians who provided statistical comments and analyses.

No potential conflict of interest relevant to this article was reported.

Supplementary data is available at https://hipandpelvis.or.kr/.