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Complications of Lateral Obturator and Lateral Femoral Nerve Block and Radiofrequency Ablation for Hip Denervation

Leonardo Kapural MD, PhD and Taif Mukhdomi MD

Weill Cornell Medical College, Weill Cornell Pain Medicine, New York, NY, USA
Carolinas Pain Institute and Chronic Pain Research Institute, Winston-Salem, NC, USA

Introduction

The prevalence of chronic pain from the hip is between 7% and 10% in the population older than 45 years of age [1]. Further, symptomatic painful arthritis of the hip has been shown to affect 9.2% of adults who are ≥ 45 years of age (9.3% female, 8.7% male) [2]. Chronic hip pain is a result of osteoarthritis, hip fractures, and dislocations, labral tears, bursitis, and avascular necrosis [1, 2]. Current conservative therapies include physical therapy, NSAIDS, opioids, intra-articular injections of steroids and visco-supplements [3, 4], while hip arthroplasty is considered the more definitive treatment of chronic hip pain [5]. Lateral femoral and lateral obturator sensory nerves radiofrequency ablation (RFA) provides a significant, clinically meaningful long-term improvement in pain scores for patients with advanced osteoarthritis, avascular necrosis or even previous arthroplasty of the hip joint.

Anatomy

The innervation of the joint is complex [6, 7] involving the lateral branches of obturator nerve (Figure 46.1) and articular branches of the femoral nerve, innervating the anteromedial hip, and anterior portion of the joint capsule, respectively. The sciatic nerve supplies the majority of the posterior hip. Groin hip pain is mostly generated by lateral branches of the obturator nerve (Figure 46.1), while trochanteric pain is carried by lateral articular branches of the femoral nerve [6]. Described approaches to denervation of the affected hip are based on our understanding of anatomy of the hip innervation and location of vulnerable surrounding structures [7–21].

**Figure 46.1** Schematic of the lateral articular branches of the obturator nerves position in relationship to bone structures on fluoroscopic view on the left and target region of RF denervation as suggested by Locher et al. (2008) on the right. Highest frequency of the lateral articular fibers would be located in the anteroposterior fluoroscopic view just at the bottom of incisura acetabuli and the top of the anteror aspect of an ischium. (Source: Taken with permission from Locher S, Burmeister H, Böhlen T, et al. [11].)

Indications

Osteoarthritis
Rheumatoid arthritis
Labral tears of the acetabulum
Osteonecrosis
Post-traumatic arthritis
Chronic infectious coxarthrosis
Avascular necrosis
Persistent post-operative pain following total hip arthroplasty.

Contraindications

Local or systemic infection
Patient refusal or inability to cooperate
Allergy to local anesthetics
Malignancy at the needle entry site or needle path – consider risk benefits of pain relief vs. spreading tumor
Coagulopathy.

Technique

The radiologic landmark for the articular branches of the ON, is the point immediately inferior to the “teardrop” silhouette, formed by the junction of pubic and ischial bones (often referred to as the incisura of the acetabulum), which is seen on anteroposterior fluoroscopy (Figures 46.1 and 46.3). The lateral edge of the obturator foramen lies medial to the needle tip, with the acetabular wall situated laterally (Figure 46.1).

**Figure 46.3** Comparison between various fluoroscopy or fluoroscopy/US-guided approaches to RF denervation of the lateral obturator sensory branches. (a) Lateral approach using only fluoroscopy guide. Notice a longer distance to fluoroscopic landmark (bottom of the incisura acetabuli) underneath the femoral neurovascular bundle to denervate articular branches of the obturator nerve. (b) Inferior approach along the anterior ischium maintaining continuous contact with the bone until incisura acetabuli reached. (c) Anterior approach combining fluoroscopy with US guidance in order to safely pass by the femoral neurovascular bundle. Fluoroscopic landmarks and RF probe angle are shown. (Also, *see* Figure 46.2 for details on US guidance for the safe RF probe passage).

**Figure 46.2** Magnetic resonance imaging (MRI) of the right hip and structures surrounding it. Anatomic relationship between the imaging target of denervation at the acetabulum and location of femoral neurovascular bundle prompted suggestion that the safe approach could be 75° lateral. However, the medial approach, when implemented, seems to require lesser angle and shorter electrode access distance from the skin and is therefore better tolerated by patients [20–22]. A: acetabulum; FA: femoral artery; FV: femoral vein; FN: femoral nerve; G Min: gluteal minor; GMed: Gluteal Medial. (Source: Taken with permission from Locher S, Burmeister H, Böhlen T, et al. [11].)

A point immediately inferior and medial to the anterior inferior iliac spine on anteroposterior fluoroscopy is the landmark for the articular branches of the FN.

Currently, hip denervation techniques include conventional and cooled RF denervation using various approaches: anterior, lateral, and inferior (Figures 46.1–46.3).

First, the anterior ischial and lateral approach using only fluoroscopy guidance has been described [8–13] (Figure 46.3a,b). Authors used a 22G RF probe, providing limited denervation to the rather wide frequency of articular branches with variable courses. Further, any conclusions on efficacy of used techniques were precluded as of few patients studied and short-time interval follow-up [8–18].

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