Introduction
Chronic ankle pain is a common condition with consequences of limited mobility, gait instability, and decreased physical activity. Its prevalence increases with age and obesity. It can be the result of intraarticular pathologies, chronic disease, nerve compression, trauma, or fracture. Conservative treatment using analgesics, physical therapy, nerve blocks, or repetitive steroid injections offers temporary pain relief.
The use of percutaneous radiofrequency ablation (RFA) is promising with long-term benefits to patients with chronic ankle pain and should be tried first before surgical intervention especially in patients with comorbid conditions, children, pregnant women, and in those with metallic implants on the heart or on the affected limb away from the areas to be ablated.
Current RFA techniques used to treat chronic ankle pain focus on the articular branches supplying the ankle and foot. Diagnostic nerve blocks are performed prior to RFA to ensure the right place of the target area and help ease the pain during and after the procedure.
There are two types of radiofrequency ablation: pulsed and continuous.
Pulsed radiofrequency ablation (PRF) mechanism is through pain modulation of regulatory gene expression along the nociceptive pathway. The PRF is preferred by some over the continuous one especially when the affected area is supplied by nerves with motor and autonomic fibers, and to avoid continuous heat placement and its consequences on the target areas and surrounding tissues. Others use conventional RFA to treat areas where it is completely sensory for continuous thermal lesion of the affected nerve. ,
Anatomy
The ankle joint innervation is supplied by articular branches from five nerves: the tibial, sural, superficial, and deep peroneal nerves (all are branches of the sciatic nerve), and the saphenous nerve (branch of the femoral nerve) ( Fig. 11.1 ).
The deep peroneal, posterior tibial, and sural nerves have important anatomical vascular landmarks used for ultrasound approach. The superficial peroneal nerve, sural nerve, and saphenous nerve are found subcutaneously, while the posterior tibial nerve and deep peroneal nerve are deep to their surrounding tissues. The nerves supplying the ankle joint and their anatomical landmarks are listed in Table 11.1 .
| Nerve (N) | Anterior | Posterior | Medial | Lateral | Position With Nerve Block |
| Tibial N | Sole and heel | Knee in flexion and hip in external rotation | |||
| Superficial peroneal N | Dorsum of foot and sole | Knee in flexion and hip in internal rotation | |||
| Deep peroneal N | Between first and second toe | Between first and second toe | Knee in flexion and ankle in dorsiflexion | ||
| Sural N | Lateral aspect of heel, proximal lateral third of foot lateral aspect of fifth toe | Knee in flexion and hip in internal rotation | |||
| Saphenous N | medial aspect of ankle and heel | Hip in external rotation |
There are some anatomical variations of the ankle joint innervation ( Table 11.2 ) ; for example, the tibial nerve can be detected mainly behind the medial malleolus, but it can be superior to it in some individuals. Furthermore, the posterior tibial artery is an important landmark found behind the tibial nerve, but it can be difficult to pulsate with edema and vascular disorders, hence the importance of blocking the branches of the tibial nerve proximally (medial calcaneal, medial plantar, and lateral plantar nerve) to ensure effective regional nerve block.
| Nerve | Superomedial | Inferomedial | Anteromedial | Superolateral | Inferolateral | Anterolateral | Landmarks |
| Posterior tibial N | ++ | ++++ |
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| Saphenous N | ++++ |
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| Superficial peroneal N | ++++ |
| |||||
| Deep peroneal N | ++++ | ++++ |
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| Sural N | ++++ |
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Concerning the saphenous nerve (SN), it is found to be at the anterior third of the medial malleolus, between the tibialis anterior tendon (TAT) and long saphenous vein (LSV) or lateral to it. Some of the SN terminal branches were detected proximal to the first metatarsal joint, but they can reach its distal end too, which mandates its inclusion in the ankle nerve block.
In addition, the sural, superficial, and deep peroneal nerves carry some articular branch variations in communication and overlapping neuronal anastomosis on the dorsum of the foot in some cases.
While the sural nerve most commonly supplies the lateral side of the fifth toe, it is seen in some cadaveric studies to reach the lateral two and half toes, hence the importance of targeting multiple points to optimize image-guided nerve block and radiofrequency ablation procedures.
Patient history and diagnosis
A detailed patient history is important to specify the cause of the ankle joint pain. It should include age, history of incidental events, pain characteristics (onset, duration, location, quality, severity, radiation, factors increasing and decreasing), gait, mobility, and any other accompanying symptoms such as injury, trauma, or fracture. The most common causes for chronic ankle pain are trauma or ankle injury, osteoarthritis, and nerve entrapment.
Chronic ankle pain is most commonly caused by ankle injury, sprain, or fracture, and especially sports injuries among younger generations. Symptoms may include pain that is vague or sharp, localized or diffuse pain, crepitus, catching or locking, decreased range of motion, chronic ankle instability, and impaired quality of life. ,
Although osteoarthritis (OA) is the most common degenerative disease affecting the joints, it is rare in the ankle joint with only less than 1% of the adult population where 30% of OA is idiopathic and posttraumatic osteoarthritis takes priority.
Osteoarthritis pain is often of insidious onset, constant dull aching accompanied by swelling, joint stiffness, exacerbated by prolonged rest, and weight bearing-related movements leading to limited range of motion and physical activity.
Entrapment proximal to the articular branches of the posterior tibial nerve (lateral plantar and medial calcaneal nerves) contributes to plantar heel pain, where pain starts with the first steps in the morning after prolonged rest and can be associated with calcaneal stress fracture, increased tension or rupture of the plantar fascia, neuritis, or neuroma formation.
Physical exam
Ankle movements are examined for gait instability, walking, dorsiflexion, plantar flexion, pronation, supination, inversion and eversion of the foot, crepitus, point of tenderness, hematoma, bruises, spur, or fracture. It is important to compare the affected limb with the other side.
A careful physical exam is important to narrow down differential diagnoses between different articular branch involvement. For example, Tinel’s sign is positive in cases of medial calcaneal nerve (MCN) entrapment due to tarsal tunnel syndrome, accompanied by tingling and numbness of the toes and hallux but negative when entrapment is proximal to the first branch of the lateral plantar nerve (FBLPN) with no sensory deficit.
Gauthier’s test (pain with dorsiflexion and plantar flexion at the first metatarsal joint), Sullivan’s sign (splaying of the toes while weight bearing on the interdigital space), and positive Mulder’s click (pressure applied to the intermetatarsal space) are used to diagnose painful neuroma.
Foot drop with common peroneal nerve, positive anterior drawer sign with anterior talofibular ligament rupture (ATFL), squeeze test (Thompson’s test for Achilles tendon rupture), positive windlass mechanism with plantar fasciitis where pain is exacerbated with forced dorsiflexion of the first toe, and hallux valgus with bunion on the first metatarsal joint.
Imaging
Weight bearing radiographs are typically used for all patients, and some need magnetic resonance imaging (MRI) and computed tomography (CT) scans. Myelography, nerve biopsy, and nerve conduction studies are essential in case of radiculopathy, nerve entrapment, and sensory deficits. , ,
Knowing the anatomical site of joint innervation is necessary in targeting diagnostic nerve blocks and RFA.
Diagnostic nerve blocks ,
The following steps describe the diagnostic nerve block procedure:
- 1.
The patient is placed supine on the table with a pillow under the ankle for support.
- 2.
Informed consent was taken and time out was done.
- 3.
Ask patient about point of maximum tenderness.
- 4.
The patient is prepped with chlorhexidine and draped with sterile towels.
- 5.
After skin anesthesia, and with ultrasound guidance, the target points are marked with sterile ink pen and identified with marking needles from the medial malleolus to the lateral malleolus in an imaginary horizontal line as follow:
- a.
The tibial nerve is detected by pulsating the posterior tibial artery behind the medial malleolus, deep to the flexor retinaculum, and advancing the needle to the side of the transducer (in-plane approach) or perpendicular to it (out-of-plane approach) ( Fig. 11.2 A–B).
- a.
