Chemical neurolysis in peripheral nerve blocks: are we ready for wider adoption as the elderly population expands?

The geriatric population, defined as those 65 years and older, is predicted to exceed the population under age 18 years in the United State by 2035 (1). Unfortunately, aging itself contributes to chronic musculoskeletal issues, such as muscle imbalances, reduced mobility, and chronic pain (2). Thus, this medically complex aged population disproportionately utilizes healthcare resources, seeking to preserve their independence and overall quality of life. At the same time, 70% or more will report musculoskeletal pain, including osteoarthritis, in almost half over those over 80 years of age (2). With this in mind, the British Journal of Anaesthesia recently presented the work of Reysner and colleagues on pericapsular nerve group (PENG) ablations with 95% ethanol for patients with pain from hip osteoarthritis (3). This randomized controlled trial included 100 patients who received PENG blocks with ethanol neurolysis or a sham procedure. They found that the PENG ethanol neurolysis group had significantly lower pain scores at all time periods assessed though 6 months after the procedure, higher quality of life, and no neurological deficits compared to the sham block group. This technique could be an important minimally invasive alternative to hip arthroplasty in select patients.

Hip osteoarthritis is a common condition that has a detrimental effect on quality of life due to significant pain, and patients are not always able to undergo hip arthroplasty for definitive treatment for various reasons. With the aging population in the United States, the demand for total hip arthroplasty will increase to over 500,000 procedures per year by the end of the decade (4). Combined with an expected orthopedic surgeon shortage (5), it may be difficult to receive timely care for hip osteoarthritis in the future, especially in underserved areas. Hip arthroplasty itself is a major operation with a recovery time of at least several weeks and may not be desirable for patients with severe comorbidities or advanced age. In this context, minimally invasive alternatives to hip arthroplasty to improve pain and quality of life may become more attractive.

The PENG block is a relatively new technique that was first described in 2018 (6). It was developed as an alternative to older regional anesthetic techniques for hip pain, such as the femoral nerve block and fascia iliaca block, which may contribute to motor blockade and quadriceps weakness. Since the development of the PENG block, it has been studied extensively in the hip arthroplasty population. Randomized controlled studies have noted significantly lower pain scores and opioid consumption in patients randomized to PENG blocks versus no block or placebo (7,8). Compared to the fascia iliaca block, PENG block has comparable analgesia, while quadriceps strength was consistently better in the PENG block groups (9-13). Overall, the PENG block has demonstrated analgesic benefits in the hip arthroplasty population, while still preserving motor function essential to performing physical therapy or otherwise participating in the recovery process.

Although risks of a PENG block do not substantially differ from risks common to all peripheral nerve blocks (i.e., bleeding, infection, failed block, and local anesthetic systemic toxicity), the risk most relevant in the context of chemical nerve ablation is undesirable spread of injectate. According to Giron-Arango and Peng, developers of the PENG block, femoral spread is possible either through intramuscular spread after improper needle positioning, spread through an intramuscular septum or the medial border of the psoas muscle, or potentially retrograde spread through the initial needle pass (14). Thus, if utilizing 95% ethanol for neurolysis, femoral spread could potentially result in permanent motor weakness. However, Girón-Arango and Peng also note that the spread of injectate is volume dependent, with higher volumes having a higher likelihood of undesirable spread outside the target area to the femoral nerve. In one cadaveric study, the maximum volume of dye in 90% of cases required to stain the iliac bone while avoiding staining of the femoral nerve was 13.2 mL (15). In the recent work of Reysner et al., the volume of 95% ethanol injected was 2.5 mL, after an initial blockade with 5 mL of 2% lidocaine 2%. This total volume of 7.5 mL is considerably lower than a standard PENG block performed for analgesic purposes prior to hip arthroplasty, which usually uses 20 mL of injectate, and almost 50% lower than the 13.2 mL described in the cadaveric study. This volume seems to provide a good margin of safety for avoiding undesired spread to the femoral nerve. Overall, the PENG block’s analgesic potential seems to make this block an attractive candidate for a potential chemical neurolysis procedure as long as caution is used to avoid impacting the femoral nerve.

Chemical neurolysis was initially described primarily for treatment of cancer-related pain but less frequently for other types of chronic pain. In fact, practice guidelines published by the American Society of Anesthesiologist Task Force on Chronic Pain Management and the American Society of Regional Anesthesia and Pain Medicine in 2010 recommended against the routine use of chemical neurolysis for patients with chronic noncancer pain (16). While no updated guidelines have been published since, the literature base for use of chemical neurolysis in non-cancer pain has expanded significantly since 2010, including many publications specifically regarding its use in musculoskeletal pain. Editorials and cases series of chemical neurolysis of the genicular nerves for chronic knee pain appeared in 2018 and 2019 and described improved pain and quality of life (17,18). Summarized in a 2025 scoping review, additional case series, cohort studies, and one randomized controlled trial have since described positive findings (19). Similarly, a more recent randomized controlled study by Reysner et al. compared ethanol neurolysis to sham block in genicular nerve blocks for knee osteoarthritis and found patients randomized to neurolysis to have significantly reduced pain scores, less opioid consumption, and improved quality of life (20). While less there are less publications focusing on chronic hip pain, a recent retrospective case series showed both lower pain scores and decreased opioid consumption in patients with chronic pain due to avascular necrosis of the hip who received PENG alcohol neurolysis (21).

Duration of analgesia after chemical neurolysis remain under investigation. A 2025 scoping review of 192 patients in eight publications utilizing either phenol or alcohol for genicular chemical neurolysis reported improved analgesia, greater physical function, and decrease opioid consumption throughout the follow-up period, which varied from 6 weeks to 12 months depending on the study (19). Included in this review was a case series in which the two patients who underwent alcohol neurolysis had pain relief until 9 and 12 months (18). Elashmawy et al. maintained follow-up through 6 months and found that pain scores continued to be significantly lower at that time, which also suggests that analgesic duration may persist beyond this time period. This duration of pain relief is similar to physical neurolytic techniques, such as cryoablation and radiofrequency ablation (22). However, unlike cryoablation and radiofrequency ablation, which require costly specialized equipment and the use of fluoroscopy for radiofrequency ablation, alcohol and phenol neurolysis can be done under ultrasound guidance. Additionally, while phenol requires preparation by a pharmacist, alcohol formulations are available in shelf-stable, single-dose vials. These characteristics may make alcohol neurolysis accessible to a broader population of patients than other neurolytic techniques.

As the geriatric population continues to comprise a greater percentage of the population, osteoarthritis and associated chronic musculoskeletal pain are likely to rise as well. In addition to utilizing more healthcare resources, this aged population values mobility and often experiences increased adverse effects from opioid pain medications. In regions where surgical joint replacement is limited, neurolytic techniques may present a reasonable technique for managing chronic pain. It may also serve an alternative analgesic solution in patients wishing to delay arthroplasty or who are deemed poor surgical candidates. While larger studies may still be warranted to improve our understanding, publications—such as the work by Reysner et al. (3)—present promising results not only in decreasing pain score and opioid consumption, but also in highlighting meaningful improvements in functional outcome measures.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Annals of Joint. The article has undergone external peer review.

Peer Review File: Available at https://aoj.amegroups.com/article/view/10.21037/aoj-2025-1-101/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://aoj.amegroups.com/article/view/10.21037/aoj-2025-1-101/coif). E.L.H.J. reports travel funding from MUSC Department of Anesthesia, which is unrelated to this work. J.C. reports travel funding from MUSC Department of Anesthesia, which is unrelated to this work. S.H.W. reports travel funding from MUSC Department of Anesthesia, American Board of Anesthesiology (ABA), and American Society of Regional Anesthesia and Pain Medicine (ASRA), which are unrelated to this work. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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