Ankle Block

Innervations to the ankle involves five major nerve branches of the foot as indentified in Table 20.12. An ankle block is basically an infiltration block. Peripheral nerves blocked during an ankle blockade are derived from the terminal branches of the sciatic nerve (deep and superficial peroneal and sural nerves) and one from the distal branch of the femoral nerve (saphenous nerve). Motor blockade is not often needed for surgeries carried out under the influence of an ankle blockade.

Table 20.12 Nerve innervation to the ankle.

Cutaneous innervation

Cutaneous innervation

Femoral n.

Medial ankle and foot (saphenous n.)

Sciatic n.

Tibial n.

Lateral and posterior half of ankle above and

below the lateral malleolus (sural n.)

Posterior tibial n.

Anterior two-third on plantar surface of foot

(plantar n.)

Posterior one-third on plantar surface of foot

and entire heal (calcaneal n.)

Common

Dorsal surface of foot (superficial peroneal n.)

peroneal n.

Area between great toe and second toe (deep

peroneal n.)

The deep peroneal nerve is derived from the common peroneal nerve that is a continuation of the sciatic nerve. The common peroneal nerve obtains fibers from the posterior branches of L4, L5, S1, and S2 nerve roots. It descends behind the head of the fibula and after crossing the fibula tunnel the nerve divides into the superficial and deep peroneal nerves. The deep peroneal nerve provides innervation to the space between the first and the second toes and the adjacent dorsal area.

The superficial peroneal nerve, a branch of the common peroneal nerve, descends down along with the extensor digitorum longus muscle dividing into terminal branches above the ankle. The sensory innervation is to most of the dorsum of the foot and also to the toes except in between the first and the second toes.

The sural nerve is a branch of the posterior tibial nerve. It passes around the lateral malleolus from the posterior calf to provide innervation to the posterior lateral aspect of the calf, lateral surface of the foot, fifth toe, and also the plantar surface of the heel.

Indications

As primary anesthetic and/or postoperative pain management. Surgical procedures of the foot (well suited for surgery not requiring high-tourniquet pressure).

Clinical Uses Surgical

Foot surgery.

Postoperative Analgesia

Foot surgery.

Technique Preparation

Arrange sterile towels, sterile gloves, gauze pads, marking pen, antiseptic solution, syringes, and needles for local infiltration and nerve block placement.

Dose

20 ml syringes oflocal anesthetic. Needles

25 or 22 g 5 cm short bevel needle. Agents

2% lidocaine, 0.5% ropivacaine, 0.5% bupivacaine. Surface Anatomy and Landmarks

Landmarks include medial malleolus, lateral malleolus, Achilles tendon, tendons on dorsal surface of foot (Fig. 20.11a-c). It maybe helpful to place the patient in the prone position initially (blockade of the posterior tibial and sural nerves) and then have the patient assume the supine position (saphenous, superficial, and deep peroneal nerves). The ankle block may also be performed with the patient in the supine position, but the leg should be placed on a padded and elevated support for circumferential access of the ankle. The entire ankle is first prepped in sterile fashion with an antiseptic solution. Three separate injection sites around the ankle may block all five nerve branches. The superficial peroneal, deep peroneal, and saphenous nerves can be blocked by inserting the needle between the tendons of the extensor hallucis longus and the anterior tibial muscles (extensor digitorum longus tendon) on the dorsum of the foot. The anterior tibial artery may be palpated and the deep peroneal nerve located immediately lateral to the pulsation. Subsequent to negative aspiration for blood, infiltrate 5 cc of local anesthetic solution in the area to block the deep peroneal nerve (Fig. 20.11a). From the same approach, subcutaneously advance the needle first laterally (superficial peroneal nerve) and then medially (saphenous nerve) to the respective malleoli and inject 3-5 cc of local in each direction (Fig. 20.11b). Second injection site for blockade of the posterior tibial nerve should position the needle to be inserted at the cephalic border of the medial malleolus, just medial to the Achilles tendon, and advanced until eliciting a paresthesia or contact of posterior portion of the medial malleolus (Fig. 20.11c). If a paresthesia is obtained, then inject 5-7 cc of local after negative aspiration for blood or slightly (approximately 1 mm) remove the needle tip contact from the periosteum before injecting. The third injection site will position the block needle lateral to the Achilles tendon at the cephalic border of the lateral malleolus to block the sural nerve. The needle is advanced until contact with the lateral malleolus or obtaining a paresthesia and then injecting 5-7 cc of local upon withdraw (approximately 1 mm) of the block needle from contact with the lateral malleolus.

Figure 20.11 (a-c) Landmarks for the approach of the ankle block. (a) Block of the deep peroneal nerve. Needle insertion site (X) is just lateral to the extensor hallucis longus tendon and deep to the retinaculum. X is distal to the blue dashed line connecting the lateral and medial malleolus. (b) Posterior tibial nerve block. Midway between the Achilles tendon and the medial malleolus identifies the needle insertion site (X). Deep to the retinaculum and posterior to the tibial artery (X) is where the local anesthetic is to be injected. (c) Sural nerve block. Dashed line connecting the lateral and medial malleolus is pointing toward the lateral malleolus.

Figure 20.11 (a-c) Landmarks for the approach of the ankle block. (a) Block of the deep peroneal nerve. Needle insertion site (X) is just lateral to the extensor hallucis longus tendon and deep to the retinaculum. X is distal to the blue dashed line connecting the lateral and medial malleolus. (b) Posterior tibial nerve block. Midway between the Achilles tendon and the medial malleolus identifies the needle insertion site (X). Deep to the retinaculum and posterior to the tibial artery (X) is where the local anesthetic is to be injected. (c) Sural nerve block. Dashed line connecting the lateral and medial malleolus is pointing toward the lateral malleolus.

Figure 20.11 (Continued)

Pitfalls and Pearls Pitfalls

• Vascular puncture

• Painful due to pressure from local injection

Pearls

• Patient can be well sedated as the block is considered a volume and diffusion-type block

• Patients are usually able to ambulate following surgery that may permit shortened or bypass PACU stay with effective analgesia

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