Supplementation of synovial fluid
Restoration of joint hemostasis
Denervation of articular branches
Peripheral nerve stimulation
Radiofrequency ablation (RFA) of the knee and hip is an emerging technique that causes a lot of interest in interventionist. Two reviews on the RFA publications concluded more research to be done on those techniques including the anatomy of the articular branches discernable to the imaging modalities such as fluoroscopy or ultrasound. Since then, two seminal publications on the detailed anatomy of the articular branches of the anterior hip and knee have been published. Furthermore, we have two good-quality randomized controlled trials and one long-term (1 year) follow-up study on the application of RFA in knee OA. This chapter will summarize the pertinent anatomy, sonoanatomy, and technique pertinent to the RFA of hip and knee.
Articular Branches of the Hip
The sensory fibers for the anterior hip capsule are mainly nociceptive, while the fibers for posterior capsule are mainly proprioceptive. The three nerves supplying the anterior capsule are femoral, accessory obturator, and obturator nerves (Fig. 27.1).
The femoral nerve (FN) arises from the posterior divisions of the second, third, and fourth lumbar nerves (L2–L4). In the abdomen, the FN course inferolaterally posterior to the psoas muscle and anterior to the iliacus muscle. The sensory nerves to the hip joint commonly branch out at L4–L5 level (high branches) and course intramuscularly through iliacus to reach the periosteal surface of the pubis between the anterior inferior iliac spine (AIIS) and the iliopubic eminence (IPE). At the level of the superior ramus of the pubis, the sensory branches continue to descend deep to the iliopsoas muscle and tendon to reach the anterior hip joint capsule. The main trunk of FN courses superficial to the iliopsoas and continues inferiorly passing beneath the inguinal ligament to enter the femoral triangle (Fig. 27.2).
The accessory obturator nerve (AON) arises as one branch usually from the posterior division of third and fourth lumbar nerves (L3–L4). In the abdomen, the AON courses inferiorly deep to the medial border of the psoas major. At the level of the superior ramus of pubis, the AON courses along the periosteal surface just medial to the iliopubic eminence (Fig. 27.3).
The obturator nerve (ON) articular branches were categorized as high or low according to their point of origin. High branches originated just proximal to or within the obturator canal and low branches from the posterior branch of ON (Fig. 27.4).
Thus, the important landmarks for the articular branches are AIIS, IPE, and inferomedial acetabulum. The distribution of these articular branches to the four different quadrants of the anterior hip capsule is shown in Fig. 27.5.
The best candidate is a patient with moderate to severe pain from osteoarthritis with at least moderate degree of osteoarthritis changes in the radiograph. The patient with other types of arthritis is possible but the literature support is scant. The RFA is selected based on the appropriate response to the diagnostic test.
Probe: Linear 6–15 MHz or curvilinear 2–5 (the latter reserved for the patient with high BMI)
The First Target for AON and FN Is the Interval Between AIIS and IPE
Place the probe over ASIS (Fig. 27.6a).
Slide the probe in caudal direction to reveal the AIIS, which is deeper and medial in location compared with ASIS (Fig. 27.6b).
Rotate the probe to align the AIIS and IPE in the same scan. The articular branches of femoral and accessory obturator nerve can be located between AIIS and IPE deep to the psoas tendon which is hyperechoic (Fig. 27.6c).
Further caudal scan will reveal the femoral head (Fig. 27.6d). Please differentiate the fascia layer between the iliopsoas tendon from the iliofemoral ligament overlying the anterior joint capsule.
The Second Target Is the Obturator Articular Branch
At the present time, the author prefers a combined fluoroscopic and ultrasound technique. The bony target is the inferomedial acetabulum. Direct insertion of the needle under fluoroscopy will be at high risk to the femoral neurovascular bundle because of the close vicinity. Directing the needle initially under ultrasound scan guidance to the inferomedial acetabulum avoids the puncture of the femoral neurovascular bundle. The final position can be adjusted under fluoroscopy.
Similar to the scanning of the anterior recess for hip intra-articular injection, the probe is placed in the long axis of the femoral head and neck (Fig. 27.7 red rectangle).
Moving the probe in the medial and inferior direction until the femoral head disappears, the part of the acetabulum is the inferomedial aspect of the acetabulum (Fig. 27.7 green rectangle).
Needle: 22G 3.5 inch needle
Drug: 3 mL 0.25% bupivacaine
For AON and FN articular branches, place the ultrasound probe as shown in the upper panel of Fig. 27.8. The needle is inserted in-plane from lateral to medial targeting toward the space between AIIS and IPE deep to the psoas tendon. The author prefers the needle closer to the IPE as it is where the AON articular branches are located. After confirming the needle position with hydrolocation, 3 mL of local anesthetic is injected. Optimal injection will result in a transient spread of injectate between the psoas tendon and the pubic bone.