# Pericapsular hip chemical denervation with phenol: A case report suggesting the interest of this new tool in rehabilitation medicine

Etienne Foussat, Antoine Geffrier, Charles Guignans, Mickael Ropars, Simon Butet, Isabelle Bonan

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## To cite this version:

Etienne Foussat, Antoine Geffrier, Charles Guignans, Mickael Ropars, Simon Butet, et al., Pericapsular hip chemical denervation with phenol: A case report suggesting the interest of this new tool in rehabilitation medicine. Annals of Physical and Rehabilitation Medicine, 2025, 68 (6), pp.101982. 10.1016/j.rehab.2025.101982. hal-05068067

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Submitted on 14 May 2025

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Research letter

# Pericapsular hip chemical denervation with phenol: A case report suggesting the interest of this new tool in rehabilitation medicine

Etienne Foussat<sup>a,*</sup>, Antoine Geffrier<sup>b</sup>, Charles Guignans<sup>a</sup>, Mickael Ropars<sup>b</sup>, Simon Butet<sup>a</sup>, Isabelle Bonan<sup>a,c</sup>

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## ARTICLE INFO

**Article History:**

Received 11 October 2024
Accepted 17 February 2025
Available online xxx

**Keywords:**

Hip pain
PENG
Phenol
Chemical denervation
Nerve block
Neurolysis
Neuro-orthopedics

## ABSTRACT

**Introduction:** Hip pain is a frequent complaint in Physical and Rehabilitation Medicine. The cause is often joint degradation, often exacerbated by the consequences of neurological or orthopedic conditions. Surgical treatment is not always feasible in fragile patients. When medical treatment is insufficient, the result is loss of autonomy. Based on an innovative technique of locoregional anaesthesia (PEricapsular Nerve Group block or PENG block) and recently adapted with phenol, our multidisciplinary team used it to improve function.

**Observation:** The case reported here is that of a 25-year-old woman presenting with luxating dysplasia of the right hip in the context of Costello syndrome. The main symptom reported was right hip pain with functional discomfort on walking. Medical treatment was only temporarily effective. The benefit/risk balance was unfavorable to surgery due to the young age and degree of dysplasia. In this context, phenol neurolysis of the hip pericapsular nerve group was performed, preceded by a prognostic anesthetic block. The procedure resulted in complete disappearance of hip pain and resumption of walking.

**Discussion:** The achievement of complete analgesia and recovery of the previous functional level in this case give this procedure prospects for use in clinical practice in physical medicine and rehabilitation. Chemical denervation of the anterior hip joint capsule is a simple, inexpensive procedure whose efficacy can be assessed beforehand by a prognostic anesthetic block. This procedure provides pain relief for frail patients, minimizing their loss of function while avoiding the risks of surgery.

**Conclusion:** Pericapsular hip chemical denervation appears to be an interesting alternative in the management of hip pain in therapeutic impasse, as it is likely to improve autonomy and even restore previous functional status.

© 2025 The Author(s). Published by Elsevier Masson SAS. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Dear Editor,

Here we present an innovative therapeutic approach that could represent a novel option for treating frail individuals with functional loss caused by hip joint pain.

Pericapsular hip chemical denervation is derived from a recently developed minimally invasive, ultrasound-guided locoregional anesthesia: the pericapsular nerve group block, or PENG block applied for surgery of upper extremity of femur. Recent studies have

demonstrated a higher density of mechanoreceptors and nociceptors in the anterior part of the hip joint capsule [1], making it the preferred target. The term “pericapsular nerve group” refers to the innervation of the anterior capsule, which includes high and low articular branches of the femoral nerve, high and low branches of the obturator nerve, and less consistent accessory obturator branches [2] (Fig. 2). This locoregional procedure selectively targets the articular sensory nerves supplying the capsule and the acetabular labrum without involving any motor or cutaneous nerves [2,3].

Some teams have adapted this procedure by using phenol (absolute alcohol or phenol of 5 % or 6 %) to achieve chemical denervation for palliative treatment of hip pain in frail individuals, caused by upper femoral fractures [4–6] or neoplastic lesions [7,8].

We propose here to use this chemical denervation for disabled persons. Hip joint pain is prevalent in individuals with disabilities and can lead to significant loss of autonomy [9]. In childhood

<footnote><sup>a</sup> Physical Medicine and Rehabilitation Department, CHU Rennes, Hôpital Pontchaillou, 2 rue Henri le Guilloux, Rennes Cedex 9 35033, France</footnote>

<footnote><sup>b</sup> Orthopedic Surgery Department, CHU Rennes, Hôpital Pontchaillou, 2 rue Henri le Guilloux, Rennes Cedex 9 35033, France</footnote>

<footnote><sup>c</sup> Université Rennes, Unité Empenn U1228, INSERM, INRIA, 263 Avenue Du General Leclerc, Rennes 75700, France</footnote>

<footnote>Abbreviations: AIS, (Anterior inferior iliac spine); IPE, (Iliopubic eminence); PENG, Pericapsular nerve group; P&RM, Physical and Rehabilitation Medicine
Antoine Geffrier is co-first author.</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail addresses: etienne.foussat@chu-rennes.fr (E. Foussat), antoine.geffrier@chu-rennes.fr (A. Geffrier), charles.guignans@chu-rennes.fr (C. Guignans), mickael ropars@chu-rennes.fr (M. Ropars), simon.butet@chu-rennes.fr (S. Butet), isabelle bonan@chu-rennes.fr (I. Bonan).</footnote>
<figure><img src="image_6.png" /><figcaption>Fig. 1. Hip iconography.</figcaption></figure>

disorders (neurological, musculoskeletal, or genetic disabilities), 3 factors contribute to the development of hip pain: hip dysplasia due to insufficient weight-bearing on the lower limb, muscle weakness, and spastic hypertonia leading to imbalance in muscle tension [10]. These conditions often progress to early and disabling osteoarthritis, frequently associated with hip dysplasia and dislocation (complete or partial). In case of neurological disability acquired during adult life, hypertonia can modify the stresses exerted on the joint, promoting cartilage damage or unmasking underlying osteoarthritis, previously silent. In these cases, therapeutic management combines physical therapy, splints, analgesics, and in case of hypertonia, antispastic drugs [11,12] such as obturator phenol nerve blocks or botulinum toxin. Periarticular or intra-articular corticosteroid infiltration may also be used. Yet, surgical interventions remain the gold standard for operable individuals, even in cases of neuromuscular disorders [13]. However, for frail individuals with motor and cognitive impairment, swallowing disorders, and respiratory deficiencies, the risk-benefit balance of hip surgery under general anesthesia must be carefully assessed.

Pericapsular hip chemical denervation represents a therapeutic alternative worth exploring. Phenol has been used for a long time and has seen renewed interest in recent years, particularly for treating spastic hypertonia by targeting motor nerves [14]. To our

knowledge, the use of chemical denervation targeting articular sensory branches for analgesic purposes has not been evaluated from a functional perspective.

The case was a 25-year-old woman with Costello syndrome, a rare genetic disorder characterized by developmental delays, intellectual disability, and orthopedic abnormalities [15]. Her phenotypic included developmental luxating dysplasia at the stage of osteoarthritis (Fig. 1). This complication affects 17 % to 45 % of cases, with adolescence being a key age [15]. There is no pyramidal involvement in this syndrome. The Table 1 summarizes the initial clinical examination.

Before the onset of pain, she could walk without technical aids. Gradual increase in pain led to manual wheelchair use. X-rays confirmed luxating dysplasia complicated with osteoarthritis (loss of sphericity, Reimers index = 40 %) (Fig. 1). She received 3 infiltrations (1 periarticular and 2 intra-articular), with transient efficacy. Paracetamol and non-steroidal anti-inflammatory drugs were used daily.

She was evaluated during a multidisciplinary neuro-orthopedics consultation involving Physical and Rehabilitation (P&RM) doctors and an orthopedic surgeon [16]. The participant and her parents prioritized pain reduction to restore her previous walking ability. Given the complexity of arthroplasty, the degree of dysplasia, young age, and gluteus medius deficit, and following informed consent,

<table><caption>**Table 1**
Clinical assessments, initially and at day 15, 60, and 180.</caption><thead><tr><th>Participant</th><th>Initial evaluation</th><th>Immediate post-lidocaine block</th><th>Post-hip denervation (D15)</th><th>Post-hip denervation (D60)</th><th>Post-hip denervation (D180)</th></tr></thead><tbody><tr><td><strong>PAIN</strong></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Numerical Rating Scale</td><td>8</td><td>1</td><td>1</td><td>0</td><td>0</td></tr><tr><td>Joint range; right lower limb (degrees)</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Hip flexion</td><td>90</td><td>100</td><td>100</td><td>95</td><td>100</td></tr><tr><td>Hip extension, bent knee</td><td>-40</td><td>-40</td><td>-10</td><td>15</td><td>15</td></tr><tr><td>Hip extension, knee straight</td><td>0</td><td>10</td><td>10</td><td>15</td><td>15</td></tr><tr><td>Hip abduction</td><td>20</td><td>25</td><td>NE</td><td>20</td><td>30</td></tr><tr><td>Intercondylar distance (cm)</td><td>25</td><td>29</td><td>NE</td><td>24</td><td>25,5</td></tr><tr><td>Internal hip rotation</td><td>20</td><td>30</td><td>20</td><td>50</td><td>50</td></tr><tr><td>External hip rotation</td><td>20</td><td>30</td><td>45</td><td>35</td><td>45</td></tr><tr><td>Motor testing (Medical Research Council)</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Hip flexion</td><td>3/5</td><td>4/5</td><td>4/5</td><td>4/5</td><td>4/5</td></tr><tr><td>Hip adduction</td><td>4/5</td><td>4/5</td><td>5/5</td><td>4/5</td><td>4/5</td></tr><tr><td>Knee extension</td><td>4/5</td><td>4/5</td><td>4/5</td><td>4/5</td><td>4/5</td></tr><tr><td>Walking assessment</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Non-stop walking perimeter (m)</td><td>63</td><td>60</td><td>-</td><td>237</td><td>&gt; 800</td></tr><tr><td>2-minute walk test (m)</td><td>63</td><td>60</td><td>-</td><td>81</td><td>-</td></tr><tr><td>Analytical assessment: Observational gait analysis (OGA)</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Step length (cm)-Mean (SD)</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Right</td><td>28 (6)</td><td>32 (5)</td><td>-</td><td>33 (7)</td><td>-</td></tr><tr><td>Left</td><td>38 (7)</td><td>37 (6)</td><td>-</td><td>41 (7)</td><td>-</td></tr><tr><td>Walk speed (m/s)-Mean (SD)</td><td>1,8 (0,2)</td><td>1,9 (0,2)</td><td>-</td><td>2,1 (0,3)</td><td>-</td></tr></tbody></table>
<figure><img src="image_7.png" /><figcaption>**Fig. 2.** Anatomical and iconographic support; PENG block procedure. (A) Schematic innervation of the anterior hip capsule on the 3D reconstruction of the case's dislocated hip by superior and inferior femoral branches (green), obturator branches (orange), accessory obturator branches (red), and femoral and obturator nerves (yellow). (B) Ultrasound section before infiltration. FN indicates femoral nerve; FA, femoral artery; IPE, iliopubic eminence; AIIS, anterior inferior iliac spine. (C) Procedure: The individual is placed in a supine position on the procedure table. A flat ultrasound probe is first placed on the anteroinferior iliac spine and then aligned with the iliopubic ramus. This view allowed observation of the iliopubic eminence, the iliopsoas muscle and tendon, the femoral artery and the pectineus muscle. A 21-gauge, 100-mm-long needle was inserted from the outside inwards, using an in-plane approach to target the plane between the iliopsoas muscle anteriorly and the iliopubic ramus posteriorly. (D) Link to video of case's walking pattern: https://we.tl/t/rHEhPTnyLH.</figcaption></figure>

denervation of the right pericapsular hip with phenol was performed. Written consent was obtained to use the data for research purposes.

The procedure was based on the method described by Girón et al. [3] (Fig. 2). First, a prognostic block with Lidocaine (10 mL; 1%) was performed to assess the effect of lidocaine on pain. After 2 h, when the pain had left without any adverse effect or complication, the chemical denervation was performed with 10 mL of glycerol phenol following the same procedure of ultrasound localization performed 2 h prior (Fig. 2).

Outcomes were assessed using the Numerical Rating Scale (NRS), range of motion, walking ability (nonstop walking perimeter in meters), and the 2-minute walk test before and after the procedure (immediately post-lidocaine, and at 15, 60, and 180 days). Gait analysis with footwear and without technical aids using a baro podometer mat (FDM Zebris® system) and 2 cameras (SYNCCamLight) was also performed (Fig. 2). Results are summarized in the Table 1.

As shown in the Table 1, the immediate analgesia obtained with lidocaine motivated the injection of phenol, which proved highly effective at 15 days. We observed a significant reduction in pain, which lasted ≥ 6 months. Functional outcomes were equally promising, with progressive restoration of walking ability, abandonment of

the wheelchair, and unimpeded stair usage. Post-procedural analgesic requirements were limited to occasional paracetamol. Adverse effects included a transient painful hematoma at the injection site and moderate knee pain attributed to patellofemoral syndrome due to resumed ambulation. No muscle weakness was observed.

To our knowledge, this is the first case reported on pericapsular chemical denervation of the hip proposed to a disabled individual able to walk with an over-disability linked to a painful orthopedic deformity, namely developmental dysplasia with osteoarthritis.

This technic involves a sensory block of the hip, targeting its most richly innervated and pain-prone areas. Recent studies have described the anatomy of the sensory innervation of the hip joint and the topographical distribution of the different sensory contingents. Firstly, the capsule has a greater density of sensory receptors on its anterior surface, particularly at the upper pole [1]. Secondly, the sensory branches making up the pericapsular group have been better described. Although of variable distribution and density, the systematic presence of numerous high femoral articular branches, serving precisely the upper part of the anterior capsule, has been demonstrated [2]. Finally, these high femoral articular branches
systematically pass between 2 bony landmarks easily identifiable on ultrasound: the anterior-inferior iliac spine and the iliopectate eminence, and beneath the mass constituted by the iliac muscle and the psoas tendon [2] (Fig. 2).

Pericapsular hip chemical denervation is a simple, minimally invasive, and inexpensive technique. It offers a feasible therapeutic option for any P&RM specialist trained in ultrasound-guided infiltration techniques, especially nerve blocks (Fig. 2). Our result on pain is similar to those already described [4–8]. The potential risks are those of an injection (hematoma, infection, pain on injection, etc.). More specifically, there is a theoretical risk of injury to the femoral nerve (quadrivipital paralysis) [17]. However, no study has reported such a complication [3–8].

The first publications on phenol PENG block were case reports, in a palliative care setting. All reported complete analgesia [5,7,8]. Larger retrospective studies have been carried out on geriatric participants. These participants, too frail to undergo surgery, underwent a phenol PENG block following a fracture of the upper end of the femur [4,6]. Given the high risk of death associated with the care environment, the main challenge was to ensure discharge from hospital and the absence of secondary complications associated with decubitus. After the block, some participants were able to resume walking (3/20 studied [6]). Pain relief was described as satisfactory by > 70% of participants [4]. However, it should be noted that most of these studies used multiple injections aimed at other nerve targets (ie, aiming for more complete analgesia of the hip): accessory obturator and femoral articular branches passing between the AIIS (anterior inferior iliac spine) and the IPE (iliopubic eminence) (PENG block proper), but also obturator articular branches passing opposite the inferomedial acetabulum [5–7] and the plane of the iliopsoas [4]. However, the team that developed the PENG block specifies that it achieved sufficient analgesia without targeting the obturator pericapsular contingent [3]. To our knowledge, only 1 team has performed an isolated PENG block using phenol, and obtained very good results in terms of analgesia [8]. On the other hand, teams performing multiple injections acknowledge the technical difficulty and lack of dedicated markers when injecting several sites [4]. In view of these data, we decided to carry out an isolated PENG block.

This therapeutic was proposed following specialist medical and surgical consult [16]. In our opinion, this multidisciplinary approach is imperative, as it enables the surgical alternative to be discussed and the benefit-risk ratio to be studied. It should also enable more comprehensive care, including treatment of hypertonia and any other factors that may contribute to aggravation of the joint pathology causing the pain.

Regarding the setting of this new therapy, it could be offered to people whose walking autonomy is affected by hip pain and for whom surgery is not desirable or contraindicated. Pain could be the result of subluxation, dislocation, and/or osteoarthritis. Osteoarthritis may or may not be related to the pathology of the disability (dysplasia, hypertonia, over-solicitation). In view of fragilities caused by their disorders, we think that this field includes many childhood (encephalopathy, cerebral palsy, genetic diseases) and adult pathologies (stroke, spinal cord injury, traumatic brain injury, sequelae of poliomyelitis). PENG block therapy could also become an opportunity for the treatment of hip pain in non-walking people, particularly in cases of acquired deforming hypertonia in elderly institutionalized persons.

About limitation, there is no available recommendations on the volume and concentration of phenol to be injected [18]. Those used were based on the usual practices of our department (treatment of spastic hypertonia). However, pericapsular hip chemical denervation raises questions about the evolution of the underlying pathology. Once pain relief has been obtained, and in a context of functional improvement, and therefore increased stress, a worsening of the underlying hip pathology may cause concern, necessitating regular radiological monitoring.

This work paves the way for future studies aimed at integrating the phenol PENG block into neuro-orthopedic treatments. The next step is to define its indications in P&RM and conduct prospective multicenter studies to better assess its potential benefit.

## Author's contribution

EF: Clinical follow-up of the patient, bibliography and writing original draft and review. AG: bibliography and conceptualization, writing and review. CG: Gait analysis, review. MR: review and supervision. SB: Peng block execution and clinical follow-up - writing, review and supervision. IB: writing - review, and supervision. All authors discussed the results and contributed to the final manuscript.

## Declarations of interest

None.

## Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or non-for-profit sectors.

## Declaration of competing interest

None.

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