Chapter 82F: Ankle Block

INTRODUCTION

Anesthesia of the foot can be accomplished by blocking the five peripheral nerves that innervate the area at the level of the ankle.^1,2,3,4,5 This technique relies on anatomic landmarks that are easily identified. It does not require special equipment, paresthesia elicitation, nerve stimulation, special positioning, or patient cooperation.^1,2,3,4,5 The ankle block can be used for all types of foot surgery and is safe and reliable, and has a high success rate.^2-9

Ankle block impairs ambulation on the affected leg, but to a lesser degree than sciatic or popliteal block, and patients can be discharged home before the block wears off.⁴ Long-acting local anesthetics with ankle block can provide excellent postoperative analgesia.^6,9

Indications and Contraindications

All types of foot surgeries can be carried out with ankle block, including bunionectomy, forefoot reconstruction, arthroplasty, osteotomy, and amputation.^1-10 Ankle block can also provide analgesia for fracture and soft tissue injuries¹¹ and or gout arthritis.¹² Moreover, it can be used for diagnostic and therapeutic purposes with spastic equinovarus¹³ and sympathetically mediated pain.¹⁴ Because motor block of the proximal leg and calf is avoided, ankle block may be preferable to sciatic/femoral (saphenous) nerve block for outpatient forefoot surgery.¹⁵

Ankle block should be avoided in patients with local infection, infection, edema, burn, soft tissue trauma, or distorted anatomy with scarring in the area of block placement.

Clinical Anatomy

The foot is innervated by five nerves (Figures 82F–1 and 82F–2). The medial aspect is innervated by the saphenous nerve, a terminal branch of the femoral nerve (Figure 82F–3). The rest of the foot is innervated by branches of the sciatic nerve:

• The lateral aspect is innervated by the sural nerve arising from the tibial and communicating superficial peroneal branches (Figure 82F–4).

• The deep ventral structures, muscles, and sole of the foot are innervated by the posterior tibial nerve, arising from the tibial branch (Figure 82F–5).

• The dorsum of the foot is innervated by the superficial peroneal nerve, arising from the common peroneal branch (Figure 82F–6).

• The deep dorsal structures and web space between the first and second toes are innervated by the deep peroneal nerve (see Figure 82F–2).^16,17