Radiofrequency ablation of hip joint articular nerves

Introduction

Chronic hip pain from osteoarthritis and other intraarticular pathologies is a common condition, and the prevalence increases with age and obesity. Patients with chronic hip joint pain may not respond well to conservative treatments such as physical therapy, analgesics, and intraarticular injections. In these cases, percutaneous radiofrequency ablation (RFA) of the articular sensory nerves of the hip joint is an effective alternative treatment to provide pain relief and improve ambulation. ^, The RFA procedure should be trialed before arthroplasty surgery. It can also be offered to patients who are not candidates for surgery due to comorbidities, young age, or other reasons. Due to gaps in knowledge about innervation patterns and the short course of articular branches in the posterior aspect of the hip joint, current established technique of RFA for treating chronic hip joint pain is focused on the nerves innervating the anterior joint, namely the articular branches of the femoral nerve and the obturator nerve. ^, Diagnostic nerve block of these articular branches prior to ablation is usually performed to provide both diagnostic and prognostic information.

Anatomy of hip joint nerves

The innervation of the hip joint is complex, receiving contributions from multiple nerves. These include the articular branches of the femoral, obturator, accessory obturator nerve, nerve to the quadratus femoris, superior gluteal, and perhaps the inferior gluteal and sciatic nerves ( Fig. 9.1 , Tables 9.1 and 9.2 ). ^,

Table 9.1

Innervation of the Anterior Hip Joint and Their Landmarks ^,

	Q uadrants in the anterior hip
Nerve (N)	Superolateral	Superomedial	Inferolateral	Inferomedial	Landmarks
Femoral N	+++++	++++	+++++	+++
High femoral N	++++	+++	+++	++	Iliopubic eminence AIIS
Low femoral N	+	+	++	+	None
Obturator			+++	+++++
High obturator N			+	+++	Inferomedial acetabulum (teardrop)
Low obturator N			++	++	Inferomedial acetabulum (teardrop)
Accessory obturator N		++		+++	Iliopubic eminence

+: presence of nerves at the quadrants of the hip joint capsule; number of +: predominance of the nerve presence; AIIS: anterior inferior iliac spine.

Table 9.2

Innervation of the Posterior Hip Joint

	Q uadrants in the posterior hip
Nerve (N)	Medial	Lateral	Superior	Inferior
N to quadratus femoris	Yes		Yes	Yes
Superior gluteal N		Yes
Inferior gluteal N				?
Sciatic N	?	?	Yes

Yes: presence of nerves at the halves of the joint capsule; ?: unclear about the nerve presence.

There are variations in the articular branches of both femoral and obturator nerves ( Table 9.1 ). ^, Articular branches from the femoral nerve were categorized as either high or low femoral nerves, corresponding to their origin superior or inferior to the inguinal ligament, respectively. Similarly, articular branches of the obturator nerve were also classified as high or low, with the high obturator nerve originating just proximal to or within the obturator canal and the low obturator nerve from the posterior branch of the obturator nerve. The corresponding landmarks of these nerves are listed in Table 9.1 .

Diagnosis of chronic hip joint pain

Patient history

Important information to collect when evaluating chronic hip joint pain includes patient age, inciting events, pain onset, duration, location, radiation, intensity, quality, alleviating factors, aggravating factors, function, associated symptoms, and so on. Anterior hip or groin pain usually suggests intraarticular pathology of the hip joint. Common causes of hip joint pain include osteoarthritis, femoral acetabular impingement, and labral tear.

Osteoarthritis is the most likely diagnosis in older patients with gradual onset of pain and limited motion. These patients typically have a constant deep aching pain and stiffness, worse with prolonged standing and walking.

Patients with femoral acetabular impingement are often young and physically active. The pain is located primarily in the groin with occasional radiation to the lateral hip and anterior thigh. The pain has an insidious onset and is worse with sitting, rising from a seat, getting in or out of a car, or leaning forward.

Pain from hip labral tears also has an insidious onset, but occasionally occurs acutely after a traumatic event. Patients with a labral tear describe a dull or sharp pain in the groin, and half of them have pain that radiates to the lateral hip, anterior thigh, and buttock. In addition to pain, mechanical symptoms, such as catching or painful clicking with activity, are seen in about half of patients with this injury.

Physical exam

Physical exams, although helpful, are not highly sensitive or specific for most diagnoses. Commonly used exams include gait, range of motion, FABER test (ﬂexion, abduction, external rotation), FADIR test (ﬂexion, adduction, internal rotation), log roll test, and straight leg raise against resistance test.

Patients with pain from intraarticular pathologies can have an antalgic gait. Examination usually reveals decreased range of motion, and provocative hip motion exams such as the FABER and FADIR tests often cause hip pain.

Imaging

Radiography of the hip should be performed if there is any suspicion of any bony pathology. It should include an anteroposterior view of the pelvis and a frog-leg lateral view of the symptomatic hip. It is the first-line imaging modality for diagnosing osteoarthritis. In patients with osteoarthritis, plain radiographs demonstrate the presence of asymmetrical joint space narrowing, osteophytosis, and subchondral sclerosis and cyst formation. For diagnosing femoral acetabular impingement, in addition to the anteroposterior and lateral view radiographs, a Dunn view is recommended to help detect subtle lesions. Computed tomography (CT) provides detailed visualization of the hip joint segments that may be difficult to appreciate on radiographs, such as the inferoposterior and posterolateral hip joint.

Magnetic resonance imaging (MRI) of the hip can detect many soft tissue abnormalities, such as labral tears and cartilage lesions. It is preferred if plain radiography does not identify specific pathology in a patient with persistent hip pain. Magnetic resonance arthrography is considered the diagnostic test of choice for labral tears.