Pericapsular Nerve Group (PENG) Block for Hip Pain

A PENG block, short for pericapsular nerve group block, is an ultrasound-guided regional anesthesia technique that numbs the sensory nerves around the hip joint while largely preserving the ability to contract the quadriceps muscle. First described in 2018, it targets the articular branches of the femoral nerve, obturator nerve, and accessory obturator nerve where they converge near the front of the hip capsule. The technique has gained traction rapidly in orthopedic and emergency settings because it offers strong hip pain relief without the leg weakness that older nerve blocks tend to cause, and the evidence behind it has grown quickly enough to reshape how clinicians approach hip fracture pain.

Anatomy Behind the Block

The hip joint receives sensory input from several nerves, but the anterior capsule is the most pain-sensitive region. Three nerves send articular branches to this area: the femoral nerve, the obturator nerve, and (when present) the accessory obturator nerve. These branches travel in a fascial plane between the psoas tendon and the surface of the ilium, near a bony landmark called the iliopubic eminence. The key insight behind the PENG block is that the sensory fibers heading to the hip capsule separate from the motor fibers that control the quadriceps before they reach this plane. By depositing local anesthetic precisely in that space, clinicians can interrupt pain signaling from the hip without blocking the motor pathways that let you straighten your knee.

A cadaveric study confirmed this selectivity: when dye was injected at the PENG target, it stained the articular branches of the femoral nerve and the accessory obturator nerve in every hip specimen tested, achieving a 100% staining rate of the intended sensory targets.¹ That anatomical precision is what distinguishes the PENG block from broader approaches like the femoral nerve block or the fascia iliaca block, both of which bathe larger nerve trunks in local anesthetic and inevitably affect motor fibers too.

How the Block Is Performed

The patient lies on their back. The clinician places a curvilinear ultrasound probe at the front of the hip, starting near the anterior superior iliac spine and sliding downward to find the anterior inferior iliac spine. The probe is then rotated toward the pubic bone until the iliopubic eminence comes into view. Keeping these two bony landmarks on screen at the same time is the visual confirmation that the probe is in the right plane.² A needle is advanced in-plane from lateral to medial, and its tip is guided into the fascial layer between the psoas tendon and the ilium. Once position is confirmed, a volume of local anesthetic (typically 20 to 30 mL in adults) is injected.

Volume matters. Cadaveric work found that at 20 mL, the injectate stained the main femoral nerve trunk about half the time, while at 30 mL it stained the femoral nerve trunk in every specimen.³ That finding is a double-edged sword: higher volumes improve coverage of articular branches but also raise the chance that motor fibers get caught in the spread. In practice, most clinicians use 20 mL for a single-shot block aimed at motor-sparing analgesia and reserve larger volumes for situations where broader coverage is more important than preserving quadriceps strength.

The Motor-Sparing Advantage

The biggest selling point of the PENG block compared with older hip blocks is that patients can still activate their quadriceps afterward, which is critical for standing, walking, and participating in physical therapy. A randomized trial comparing the PENG block with the femoral nerve block in hip fracture patients found that none of the patients who received a femoral nerve block had intact quadriceps strength in the recovery unit, compared with about 60% of those who received the PENG block. By the first postoperative day, 90% of the PENG group had intact strength versus half in the femoral nerve block group.⁴

Another randomized trial reported similar numbers: about 71% of the PENG group had intact quadriceps strength at 24 hours, versus roughly 23% in the femoral nerve block group.⁵ A systematic review and meta-analysis of trials in total hip replacement patients pooled the data and confirmed that the PENG block both improved quadriceps strength on the first postoperative day and reduced the time to first mobilization by nearly three hours on average.⁶

Why does preserving quadriceps strength matter so much? For elderly hip fracture patients, immobility is one of the most dangerous consequences of injury. Falls, blood clots, pneumonia, and muscle wasting all become more likely the longer someone stays in bed. A nerve block that controls pain but forces the patient to wait hours or days before their quadriceps can fire is working against the rehabilitation timeline. That tension between pain relief and mobility is precisely what the PENG block was designed to resolve.

How It Compares to the Fascia Iliaca Block

The fascia iliaca compartment block is another widely used technique for hip fracture pain. It is easier to learn and can be performed with or without ultrasound, which makes it popular in emergency departments. But several head-to-head trials now show the PENG block provides stronger early analgesia. In one randomized trial, pain scores at rest 30 minutes after the block were roughly 2 out of 10 in the PENG group versus about 4 in the fascia iliaca group, and the difference during passive leg raise was even more pronounced.⁷

A separate trial measuring pain relief over the first 24 hours found that about three-quarters of PENG block patients achieved at least a 50% reduction in their pain burden, compared with roughly one-fifth of fascia iliaca patients.⁸ Another randomized trial reported that patients who received the PENG block went longer before needing their first postoperative painkiller and used less morphine in the first 24 hours.⁹

That said, the PENG block is not unambiguously superior in every measured outcome. One cohort study comparing it to the femoral nerve block found no meaningful difference in total opioid consumption at 48 hours or in hospital length of stay, though the PENG group still had notably better quadriceps strength.¹⁰ This suggests that the motor-sparing benefit is the most consistent advantage, while differences in total pain medication use depend on the specific clinical setup, the type of surgery, and whether multimodal analgesia is used alongside the block.

Extending Duration with Catheters

A single-shot PENG block with a standard local anesthetic like ropivacaine or bupivacaine typically wears off within 12 to 18 hours. For patients whose surgery might be delayed (which is common with hip fractures in elderly patients waiting for operating room availability) or who need prolonged postoperative analgesia, clinicians can thread a catheter into the PENG space and run a continuous infusion. In a case series of 10 hip fracture patients, placing a PENG catheter dropped pain scores from a median of 7 out of 10 before the block to 2 out of 10 within 20 minutes, and scores stayed at that level for 48 hours.¹¹

Catheter placement in this deep fascial plane does come with practical challenges. Securing the catheter so it does not migrate is more difficult than with superficial blocks, and case reports have flagged catheter-related complications like dislodgement or kinking.¹² Some clinicians have described connecting continuous PENG catheters to portable elastomeric pumps, allowing the patient to receive a steady low-dose infusion without being tethered to an electronic pump.¹³ The technique is still evolving, and most of the continuous-catheter literature consists of case reports or small series rather than large trials.

Adding Medications to Prolong the Block

Another approach to extending duration without a catheter is adding adjuvant drugs to the local anesthetic mixture. Two agents have drawn the most attention for PENG blocks: dexmedetomidine and dexamethasone.

A randomized trial in 60 patients with proximal femoral fractures found that adding dexmedetomidine to bupivacaine significantly extended the duration of pain relief, improved positioning comfort for spinal anesthesia, and lowered postoperative pain scores, all without affecting motor function or causing notable side effects.¹⁴ Meanwhile, a trial examining perineural dexamethasone added to a PENG block for total hip replacement found that the steroid extended analgesia from about 9 hours to about 16 hours and cut opioid use roughly in half, again without weakening quadriceps strength or causing nerve injury. Blood sugar levels were also unaffected, which had been a theoretical concern with steroid use near nerves.¹⁵

Both adjuvants look promising, but the evidence base is still early-stage, consisting of single-center trials with modest sample sizes. Neither is standard practice yet; clinicians weigh the potential benefit against the added complexity and the limited long-term safety data.

Combining the PENG Block with the Lateral Femoral Cutaneous Nerve Block

One limitation of the PENG block is that it targets deep articular nerves and does not reliably numb the skin. For surgeries with an anterior or lateral incision, the surgical wound itself can be painful even if the joint is well-blocked. The lateral femoral cutaneous nerve supplies sensation to the outer thigh and is not covered by the PENG injection. To address this gap, clinicians sometimes pair the PENG block with a separate lateral femoral cutaneous nerve block, adding a small injection near the anterior superior iliac spine to cover skin and subcutaneous tissue.¹⁶

The combination is not always necessary. The lateral femoral cutaneous nerve has considerable anatomical variability from person to person, and its contribution to wound pain depends heavily on the surgical approach. For posterolateral incisions, its territory is mostly irrelevant.¹⁷ In practice, the paired approach is most useful for anterior hip replacements and certain fracture surgeries where the incision crosses the outer thigh.

Use in Children

Most of the PENG block literature focuses on elderly hip fracture patients, but pediatric applications are emerging. A case report described performing the block in two children under five years old undergoing surgery for hip dysplasia. Both had stable vital signs during surgery, needed no extra opioids intraoperatively, and had low pain scores afterward. One child required a single dose of a mild painkiller 12 hours later, but neither needed opioid rescue overnight, and both were participating in physical therapy by the first postoperative day.¹⁸

A broader review of early pediatric reports found that outcomes have been generally favorable, with adequate analgesia and no significant adverse effects such as quadriceps weakness, local anesthetic toxicity, or bleeding.¹⁹ Still, the pediatric evidence remains limited to case reports and small case series. A randomized non-inferiority trial comparing the PENG block to other analgesic approaches in children with developmental hip dysplasia has been registered and was expected to provide more definitive evidence.²⁰

Chronic Hip Pain and Osteoarthritis

The PENG block was designed for acute surgical pain, but researchers have begun exploring it for chronic hip conditions, especially osteoarthritis. A randomized trial compared the PENG block with an intra-articular corticosteroid injection in patients with hip osteoarthritis. Both groups improved, but the PENG block gave much better pain relief on the first day, with a large effect size. The corticosteroid injection pulled ahead at the four- and eight-week marks, as you would expect from a slowly acting anti-inflammatory. The authors concluded that the PENG block is a safe, easy alternative for hip osteoarthritis that improves both function and quality of life for up to two months.²¹

A more intriguing case report described a patient with chronic hip osteoarthritis who received repeated PENG blocks using short-acting local anesthetic over several sessions. After five blocks, she could walk without assistive devices, and her pain had not returned six months later.²² Why a short-acting block might produce long-lasting relief is unclear. One possibility is that interrupting the pain cycle repeatedly allows central sensitization to reset, but this is speculative and a single case proves nothing. It does suggest that the block’s utility could extend beyond the operating room if future research supports these early observations. Transient quadriceps weakness occurred in two of the five sessions, a reminder that even a well-placed PENG block is not perfectly selective every time.

Beyond Hip Fractures

Because the PENG target sits near the anterior pelvic structures, clinicians have tried using it for fractures beyond the hip joint. Case reports describe its use for acetabular fractures and pubic rami fractures in the emergency department, settings where regional anesthesia options have traditionally been limited.²³ A separate report described using a continuous PENG catheter for a traumatic pubic rami fracture, an injury that can cause severe pain with every movement but does not always warrant surgery.²⁴ These uses make anatomical sense given how the injectate spreads, but the evidence is limited to isolated case reports. Whether the PENG block can become a standard approach for pelvic fracture analgesia will depend on larger studies.

Impact on Hospital Stay

Shorter hospital stays benefit patients and institutions alike, and there is early evidence that the PENG block can help on this front. A trial of patients undergoing elective anterior total hip replacement found that those who received a PENG block had a median stay of two days, compared with four days in the placebo group.²⁵ A two-day difference is substantial in an era when health systems are focused on enhanced recovery pathways. Better pain control without motor impairment means patients hit their physical therapy milestones faster, and that accelerated timeline ripples through the discharge process.

A systematic review and meta-analysis looking at the PENG block under general anesthesia for hip surgery described it as a safe and effective regional technique overall.²⁶ The safety profile across published studies has been reassuringly clean: no reports of serious nerve injury, no cases of local anesthetic toxicity in the trial literature, and no major bleeding events directly attributed to the injection.

Learning Curve and Emergency Department Adoption

One practical barrier to any new nerve block is training. The PENG block requires comfort with curvilinear ultrasound imaging of the pelvis, which is less familiar territory for many physicians than the linear-probe scanning used for more superficial blocks. A simulation-based training study tested 21 emergency physicians, none of whom had fellowship-level ultrasound training. Before the workshop, they averaged 61% on a knowledge quiz and rated their comfort with the block at 2.4 out of 5. After a hands-on session, quiz scores jumped to 95% and comfort rose to 4.0 out of 5. Participants also reported a much higher likelihood of performing the block in practice afterward. That trajectory suggests the technique is learnable in a single training session for physicians already familiar with ultrasound-guided procedures, though translating simulation confidence into consistent clinical performance is a separate question.

Emergency departments have a particular incentive to adopt the PENG block because hip fracture patients often wait hours for surgery, and systemic opioids in elderly patients carry serious risks including delirium, respiratory depression, and nausea. A motor-sparing block that can be placed at the bedside with ultrasound and standard equipment fills a gap that emergency physicians have felt acutely. Whether it displaces the fascia iliaca block as the go-to emergency department hip block will depend on how quickly training spreads and whether the technique can be standardized across different ultrasound skill levels.