Direct visualization-guided PENG block (Pericapsular nerve Group): optimizing postoperative analgesia in total hip arthroplasty

Abstract

Background

The pericapsular nerve group (PENG) block has proven to be an effective strategy for postoperative pain management in total hip arthroplasty (THA). However, its implementation requires specialized equipment and expertise, which limits its reproducibility. The objective of this study was to describe the technique of direct visualization-guided PENG block (PENG-DV) and assess its outcomes for postoperative pain control.

Methods

A retrospective cohort study was conducted in patients who underwent THA through a direct anterior approach (DAA) and received the PENG-DV block as part of a standardized multimodal analgesia protocol. Demographic variables, pain score on the visual analogue scale (VAS), opioid consumption, muscle strength, and ambulation within the first 24 h were evaluated.

Results

Of the 128 patients identified, 112 were included in the analysis. The cohort was predominantly female (60.7%), with a mean age of 63 years. The median postoperative VAS score was 2 and 3 at 12 and 24 h respectively, increasing to 5 during physical therapy. By postoperative day one, 83.9% of patients ambulated, and most achieved muscle strength ≥ 3 for both hip flexion and knee extension. A total of 54.5% of patients required opioid rescue, with a mean morphine equivalent consumption of 10 mg within the first 24 h.

Conclusion

PENG-DV for THA via DAA appears to be a promising strategy for effective pain control in the immediate postoperative period, as part of a multimodal analgesic approach designed to reduce opioid consumption and promote early mobilization.

Background

Total hip arthroplasty (THA) has consistently demonstrated excellent long-term outcomes [1]; however, postoperative pain management remains a challenge in the early postoperative period. Effective pain control facilitates early mobilization and prevent postoperative complications [2, 3]. Furthermore, optimization of postoperative multimodal analgesia reduces opioid consumption, minimizes adverse effects and associated costs [4–6], and promotes the implementation of fast-track clinical pathways and outpatient surgery [7].

The pericapsular nerve group (PENG) block, first described by Girón-Arango et al., is an effective technique for controlling pain, reducing opioid requirements, and facilitating early rehabilitation in patients with hip fractures [7]. In primary THA, the use of PENG block resulted in statistically significant reductions in pain scores compared with placebo [8–10]. However, the conventional PENG block technique requires trained anesthesiologists and the use of ultrasound guidance or nerve stimulators, which limits its broad implementation.

The direct anterior approach for THA allows direct visualization of both the anterior capsule and the anatomical landmarks used for the PENG block. Cadaveric studies have shown that infiltration of the pericapsular branches of the femoral and accessory obturator nerves can be effectively achieved through this approach, with a distribution comparable to that achieved by the ultrasound-guided PENG block [11–13].

The aim of this study is to describe the pericapsular nerve group block under direct visualization (PENG-DV) performed during primary THA via the direct anterior approach, and to assess its impact on postoperative pain control.

Methods

A retrospective observational cohort study was conducted, including adult patients with primary or secondary osteoarthritis who underwent primary THA via the direct anterior approach under spinal anesthesia, in whom the PENG-DV block was performed between January 2023 and January 2025. Patients with physical or cognitive impairments limiting the applicability of pain scales, those requiring conversion from spinal to general anesthesia, and patients with contraindications to opioid use or allergies to contrast media or local anesthetics were excluded.

According to the institutional protocol, all patients received a standardized analgesic regimen consisting of 1 g of oral acetaminophen before entering the operating room, 4 mg of intravenous dexamethasone at the start of surgery, and 4 mg of ondansetron at the end of the procedure. Postoperative pain management in the recovery unit and during hospitalization included of acetaminophen 1 g every 8 h, celecoxib 200 mg every 12 h, dipyrone 1250 mg every 4 h, and opioid rescue analgesia of hydromorphone 0.4 mg every 4 h as needed.

A retrospective review of medical records was performed to collect demographic data, VAS pain scores at 12 and 24 h, opioid rescue requirements within the first 24 h, ability to ambulate with a walker and lower limb strength on postoperative day one, and the presence of lateral femoral cutaneous nerve sensory deficit at the 15-day postoperative follow-up.

Statistical analysis

Continuous data were analyzed according to distribution (Shapiro–Wilk test). Variables with normal distribution were expressed as mean and standard deviation, while non-normally distributed data were reported as median and interquartile range. Categorical variables were summarized as proportions. Statistical analyses were performed using STATA version 17.0 (StataCorp LLC, TX, USA).

Surgical technique

The anterior capsule of the hip is mainly innervated by the obturator nerve, the accessory obturator nerve, and the femoral nerve, whose articular branches emerge near the iliopectineal eminence and the anterior inferior iliac spine [14]. The direct anterior approach for THA provides clear visualization of these anatomical landmarks, allowing for the selective administration of local anesthetics.

To describe the PENG-DV block, the minimally invasive anterior approach (AMIS) for THA is detailed [15]: patients were positioned supine on the operating table, with the operative leg secured in the AMIS Mobile Leg Positioner© (Fig. 1) [16]. A 6 to 12 cm incision was made lateral to the anterior superior iliac spine and extended toward the fibular head. The intermuscular plane between the tensor fasciae latae and sartorius was developed, then the lateral circumflex vessels were identified and ligated, and the joint capsule exposed. A capsulotomy was performed to visualize the femoral neck osteotomy was performed as planned [14, 15]. After the femoral head was extracted, the pubofemoral ligament and the superior and lateral portions of the capsule were released. To expose the proximal femur, the limb was placed in maximal external rotation and extension, then it was prepared with sequential rasps until adequate fit was achieved. With the hip in neutral position, the acetabulum was exposed, the labrum resected, and sequential reaming performed. Stability and leg length were assessed with trial components; definitive implants were placed once satisfactory stability and length were achieved. Correct acetabular cup positioning was confirmed with fluoroscopy and direct visualization (Figs. 2 and 3).

Fig. 1.

AMIS mobile leg positioner© (16)

Fig. 2.

Fluoroscopic visualization of the final acetabular cup

Fig. 3.

Direct visualization of the definitive acetabular component

The PENG-DV block starts with an adequate exposure of the anterior hip capsule following the dissection of the intermuscular plane. After implantation of the definitive acetabular component, the anterior inferior iliac spine (AIIS) and iliopectineal eminence were palpated. A 22-G needle was introduced into the space between the AIIS and the iliopectineal eminence, at an angle of 30–45° relative to the horizontal pelvic plane, advancing from lateral to medial (Fig. 4). The needle was maintained in contact with the bony surface of the iliopectineal eminence to avoid injury of major neurovascular structures. Once correctly positioned, a combination 10 mL of 0.75% bupivacaine, 1 mL of ketorolac (30 mg/mL), 1 mL of epinephrine, and 50 mL of saline was injected. For this study, 10 mL of contrast medium was incorporated into the analgesic solution to allow fluoroscopic visualization. Proper needle positioning ensured optimal distribution of the solution toward the articular branches of the femoral and accessory obturator nerves. Adequate dispersion of the contrast medium along the anterior hip capsule was verified under fluoroscopic guidance (Fig. 5).

Fig. 4.

Needle direction and angulation for PENG-DV infiltration

Fig. 5.

Fluoroscopic visualization of the distribution of the anesthetic–contrast mixture

Results

A total of 128 patients were identified during the study period, and 112 were included in the analysis. Patients were excluded if they initially received general anesthesia or required conversion to general anesthesia following a failed spinal anesthetic. Overall, 60.7% of patients were female, the mean age was 63 years (IQR: 56–71), and the mean BMI was 26.5 (IQR: 23.5–28.7) (Table 1).

Table 1.

Demographic characteristics of the patients included in the study

N = 112
Variables	Median (IQR)
Age (Years)	63 (56–71)
BMI (kg/m2)	26.5 (23.5–28.7)
Variables	Proportion
Sex	–
Female (%)	60.7
Male (%)	39.3

A total of 97.3% of patients received 1 g of acetaminophen prior to surgery. The mean anesthesia and surgical times were 131 min (IQR: 120–150) and 100 min (IQR: 90–115), respectively. Regarding intraoperative complications, five patients sustained a greater trochanter fracture, one patient a calcar fracture, one patient a diaphyseal fracture, and one patient an acetabular fracture.

Median postoperative VAS pain scores were 2 (IQR: 0–4) and 3 (IQR: 0–4) at 12 and 24 h respectively, and 5 (IQR: 3–6) during physical therapy (Fig. 6).

Fig. 6.

Box plot of median postoperative pain measured at different time points

By postoperative day one, 83.93% of patients were able to ambulate with a walker. Median hip flexion strength on the Daniels scale was 4 (IQR: 3–4) at 24 h, with 55.35% achieving strength ≥ 3 for hip flexion and 81.25% for knee extension (Median 4; IQR: 4–4) (Table 2).

Table 2.

Muscle strength according to the Daniels scale 24 h post-op

N = 112
Variable	Median (IQR)
Hip flexion strength	4 (3–4)
Knee extension strength	4 (4–4)
Variable	Proportion
Hip flexion strength
0	0%
1	1.79%
2	42.86%
3	54.46%
4	0.89%
Knee extension strength
0	0%
1	0%
2	18.75%
3	69.64%
4	11.61%

No cases of femoral nerve motor paralysis or lateral femoral cutaneous nerve sensory deficit were observed at the first postoperative follow-up (15 days).

Opioid rescue analgesia was required in 54.5% of patients, who received one or more doses of 0.4 mg hydromorphone (or 4 mg morphine equivalents) within the first 24 h. The median cumulative opioid consumption, expressed as intravenous morphine equivalents, was 10 mg (IQR: 8–20).

Discussion

Patients undergoing joint replacement often experience episodes of severe pain (≥ 7) on the first postoperative day and during mobilization [17], thus, additional pain management strategies are recommended to improve clinical outcomes. Among these, the PENG block has been associated with a lower incidence of motor blockade, sedation, nausea, and catheter-related complications compared to epidural analgesia [18], supporting its safety and effectiveness for postoperative pain management. Furthermore, PENG block has demonstrated proven analgesic efficacy in patients with hip fractures, including both intracapsular and extracapsular fractures. Additionally, multiple studies have reported significantly reduced pain scores in patients receiving PENG block compared with other regional anesthesia techniques or placebo [8–10, 19, 20].

The PENG-DV block performed during total hip arthroplasty via the direct anterior approach offers an innovative and effective alternative for postoperative pain management. In contrast to the conventional PENG block, the PENG-DV block is a simple and reproducible intraoperative technique performed under sterile conditions. This technique avoids additional skin punctures and the need for specialists trained in ultrasound or regional anesthesia, without increasing operative time; the median surgical time in our cohort was 100 min (IQR: 90–115). In addition, it enables precise delivery of the analgesic solution, an effective coverage of the articular branches of the femoral and accessory obturator nerves [12, 13].

In the present analysis, patients who received PENG-DV block had a median VAS score of 2 and 3 at 12 and 24 h postoperatively respectively, reflecting adequate acute pain control. In contrast, previous studies have reported mean pain scores up to 7.2 ± 1.7 [21]. Postoperative pain levels typically increase during mobilization [21–24]; however, in our study, median pain score during physiotherapy was 5 (IQR: 3–6), consistent with “moderate pain” as defined by the World Health Organization criteria [25].

A total of 54.5% of patients required at least one rescue opioid dose within the first 24 h, with a mean consumption of 10 mg in intravenous morphine equivalents. These findings are consistent with previous studies demonstrating that the PENG block provides effective analgesia while reducing opioid requirements and related adverse effects [26, 27]. Similarly, Chung et al. [9] reported a significant reduction in intravenous fentanyl-equivalent opioid consumption among patients receiving the PENG block.

Conversely, Kinder et al. [28], in a retrospective analysis comparing 66 patients who received the PENG block with 70 controls, found no significant differences in opioid consumption between the groups. However, these results should be interpreted with caution, as most of their cases were performed via the posterior approach whereas our cohort underwent THA via the direct anterior approach, which has been associated with reduced postoperative pain and faster functional recovery [28].

Despite being performed at a site distant from the femoral nerve, a residual risk of quadriceps motor impairment remains from inadvertent spread of the analgesic solution toward the nerve [9, 29, 30]. Nevertheless, several studies demonstrated that the PENG block facilitates early ambulation and reduces the incidence of quadriceps motor blockade [10, 27, 30–33]. The median Daniels scale for hip flexion and knee extension at 24 h was 4, indicating mild motor weakness; however, 83.9% of patients were able to ambulate on the first postoperative day. Although this finding may have been influenced by factors other than the block itself, functional assessments were conducted by the physical therapy team, who were blinded to its application.

To the authors’ knowledge, this is the first study to describe the direct visualization–guided PENG (PENG-DV) technique and to report its clinical outcomes in patients undergoing total hip arthroplasty, which represents a relevant strength by providing initial evidence on the feasibility of this approach in clinical practice. Nevertheless, the main limitations of this study include its retrospective design, relatively small sample size, and, most importantly, the absence of a control group, which restricts the ability to draw definitive conclusions regarding the clinical effectiveness of the PENG-DV technique. Additionally, the inclusion of both primary and secondary osteoarthritis without stratified analysis, as well as the potential confounding effect of the direct anterior approach, may have influenced the observed outcomes. These limitations reflect the exploratory nature of this early-phase study, intentionally conducted in accordance with the IDEAL framework to describe and standardize a novel technique [34]; comparative analyses and subgroup stratification are planned for subsequent studies. Despite these limitations, our findings demonstrate a favorable trend toward improved pain control and functional recovery following total hip arthroplasty.

Conclusion

These findings suggest that PENG-DV block during THA via the direct anterior approach is a safe, simple, and potentially effective technique for postoperative pain control. Analgesia was effective within the first 24 h, with a moderate increase in pain during mobilization and low opioid consumption. The PENG-DV block may represent a valuable component of analgesia, enhancing functional recovery and facilitating early discharge pathways. While these results are promising, further comparative studies are necessary to confirm the block’s broader clinical utility, cost-effectiveness, safety, and reproducibility, and to establish its role as an integral part of postoperative pain management protocols.

Abbreviations

PENG

Pericapsular nerve group

THA

Total hip arthroplasty

PENG-DV

Direct visualization-guided PENG

VAS

Visual analogue scale

AMIS

Minimally invasive anterior approach

AIIS

Anterior inferior iliac spine

CEIB

institutional biomedical research ethics committee

Author contributions

MB: Made substantial contribution to the conception and design of the work and also played a major role in the revision of the work.JTA: Made substantial contribution to acquisition and interpretation of the data, also played a major role in the draft and revision of the work.MCG: Made substantial contribution to the analysis and interpretation of the data.AG: Made substantial contribution in the draft of the work.AB: Made substantial contribution to the acquisition of the data.ASV: Made substantial contribution to the conception and played a major role in the revision of the work.

Funding

No funding was received for the conduct of this study.

Data availability

The datasets analysed during the current study.

Declarations

Ethics approval and consent to participate

This study was classified as “minimal risk” research according to Resolution 008430 of 1993 from the Colombian Ministry of Health, as it had a documentary design. No additional interventions or intentional modifications of biological, psychological, or social variables were performed. This study was conducted in accordance with the ethical principles outlined in the Declaration of Helsinki. All procedures involving human participants adhered to these standards and were addressed and approved by the institutional Biomedical Research Ethics Committee (CEIB) under approval number. 2024.321. Given the minimal risk, retrospective nature of the study, the requirement for informed consent was waived by the CEIB.

Consent for publication

Not applicable.

Competing interests

One of the investigators is a paid consultant and speaker for ©Medacta International.