Modality
Proposed mechanism
Intra-articular
Steroid
Anti-inflammatory
Hyaluronic acid
Supplementation of synovial fluid
Platelet-rich plasma
Restoration of joint hemostasis
Extra-articular
Radiofrequency ablation
Denervation of articular branches
Peripheral nerve stimulation
Neuromodulation
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.
Hip
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).
Schematic diagram to show the articular branches to the anterior hip joint capsule. The femoral, obturator, and accessory obturator nerves are color coded. (Reprinted with permission from Philip Peng Educational Series. The original artwork was created and modified with the permission from Dr. Maria Fernanda Rojas, Bucaramanga, Colombia)
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 articular branches of the femoral nerve are classified as either high or low, corresponding to their origin superior or inferior to the inguinal ligament. High branches are much more prevalent than low branches. In this dissection photograph, the left iliopsoas had been removed, and the femoral nerve (orange arrow) was retracted medially to visualize the high articular branches (highlighted in green) supplying the anterior hip joint capsule. Left upper insert showed the region of interest of the left figure. Yellow dot, anterior inferior iliac spine; red dot, iliopubic eminence. The femoral is outlined in the right figure. (Reprinted with permission from Philip Peng Educational Series)
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 AON (highlighted in blue) descended into the anterior thigh region and supplied sensory branches to the medial aspect of the anterior hip joint capsule. Note in the dissection photograph, the iliopsoas had been removed to visualize the AON. The insert in the left upper corner showed the region of the photograph. (Reprinted with permission from Philip Peng Educational Series)
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).
In this figure, a low branch was shown. If a high branch was present, it usually consisted of a single nerve branch. The low branches, when present, were more numerous (green) and traveled either directly to the hip joint or formed a fine plexus that innervated the capsule. The obturator canal was outlined with red circle and the femoral head in white dotted line. The most consistent landmark for both high and low ON branches was the bone thickening of the inferomedial acetabulum (∗) that correlates to the previously described radiographic teardrop. (Reprinted with permission from Philip Peng Education Series)
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 diagram summarized the contribution of various articular branches to the anterior hip capsule. The articular branches from femoral nerve (FN) contribute to all four quadrants including the weight-bearing superior (medial and lateral) quadrants. Articular branches from obturator nerve (ON) only contribute to the lower half and that from accessory obturator nerve (AON) to medial half of the anterior capsule. (Reprinted with permission from Philip Peng Education Series)
Patient Selection
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.
Ultrasound Scan
Position: Supine
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
Sonographic image of the anterior superior iliac spine (ASIS). (Reprinted with permission from Philip Peng Educational Series)
Scan 1
Place the probe over ASIS (Fig. 27.6a).
Sonographic image of the anterior inferior iliac spine (AIIS). Sartorius (SA) and iliacus (IL) are seen superficial to AIIS, which is covered by the straight head of rectus femoris (∗). (Reprinted with permission from Philip Peng Educational Series)
Scan 2
Slide the probe in caudal direction to reveal the AIIS, which is deeper and medial in location compared with ASIS (Fig. 27.6b).
Sonographic image when aligning the ultrasound probe with AIIS and IPE (both indicated by bold arrows). Psoas tendon is marked by the asterisk. FA, femoral artery. (Reprinted with permission from Philip Peng Educational Series)
Scan 3
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).
Sonographic image when the ultrasound probe was placed just distal to the pubic rami as in Fig. 27.6c. Upper left showed the position of the probe. Red rectangle represented the sonographic image on the right upper and lower images without and with label, respectively. The green rectangle is the long-axis view of the femoral head and neck and was shown in the lower left image. IP, iliopsoas; SA, satorius; RF, rectus femoris; ∗, psoas tendon; red dotted line, iliofemoral ligament. (Reprinted with permission from Philip Peng Educational Series)
Scan 4
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.
Left figure showed the position of the ultrasound probe in both positions (red and green rectangles). The middle and right figures were the corresponding sonographic images in red and green rectangles, respectively. SMA, superomedial acetabulum; IMA, inferomedial acetabulum; FA, femoral artery; FH, femoral head; arrow, target of the obturator articular branches. (Reprinted with permission from Philip Peng Educational Series)
Scan 1
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).
Scan 2
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).
Procedure
Diagnostic Block
Needle: 22G 3.5 inch needle
Drug: 3 mL 0.25% bupivacaine
Upper panel. The left diagram showed the needle insertion and the relevant landmark. The corresponding sonographic image was shown on the right with the spread of local anesthetic (∗) deep to the psoas tendon (PS). The needle was outlined by the arrows. Lower panel. The left diagram showed the needle insertion and the relevant landmark. The needle (bold arrows) was directed to the deep end of the inferomedial acetabulum (IMA) with the local anesthetic (LA) shown at the tip. FA, femoral artery. (Reprinted with permission from Philip Peng Educational Series)
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.
- 1.
Rotate the needle to pierce through the psoas tendon
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