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Ankle Block for Foot Surgery

(Originally posted 5 October 2000 on About Anesthesiology)

INTRODUCTION
Ankle block is a type of regional anesthesia that is suitable for surgeries on the foot. As its name implies, it provides anesthesia from the ankle down and involves three to four injections of local anesthesia. In addition, intravenous medications for sedation and comfort are often given.

Other types of anesthesia can also be used for foot surgery. These options include general anesthesia, spinal anesthesia, other types of regional blocks of the leg and intravenous regional anesthesia of the leg. This article will not discuss these other options in detail other than to mention that they exist. Each has its pros and cons, risks and benefits.

PROS AND CONS OF ANKLE BLOCK
Ankle blocks are used because they offer some significant benefits to the patient. When done properly, an ankle block provides excellent anesthesia with low or no risk of cardiac complications, pulmonary complications, etc. This is especially useful in patients with multiple medical problems - but also of benefit to the healthy patient as well.

Some patients don't like the idea of not being unconscious during their surgery and others do not like the thought of the multiple injections required to achieve a good ankle block. However, the addition of intravenous medications for sedation is commonly used in most patients. This is often enough so that patients are unaware during the actual block and the surgery and not patients generally report high satisfacton rates with the technique.

ANATOMY
The goal of the ankle block is to target five nerves. These five nerves are responsible for all sensation below the ankle. The nerves are the superficial peroneal, the deep peroneal, the saphenous, the sural and the posterior tibial. The saphenous nerve is a terminal branch of the femoral nerve - while all the other nerves are branches of the sciatic nerve system.

All of the nerves are subcutaneous except one - meaning they are located just beneath the skin and therefore are easy to locate and block. The posterior tibial is the one exception - being located a bit deeper from the skin. It is easily located, however, by landmarks (pulse of the tibial artery and muscles running through the area) so it is easily blocked as well.

THE NERVES TO BLOCK

The saphenous nerve provides sensation to the anteromedial foot. It is located, and easily blocked, just anterior to the medial malleolus.

The deep peroneal nerve is a continuation of the common peroneal nerve. In provides sensation to the medial half of the dorsum and is especially involved in toes 1 and 2. It is found lateral to the tendon of the flexor hallucis longus at the medial malleolus. At the level of the intermalleolar line, it is easily blocked with a subcutaneous injection placed just lateral to the tendon of the extensor hallucis longus muscle and medial to the dorsalis pedis artery (you can feel the pulse here).

The superficial peroneal nerve is also a branch of the common peroneal nerve. It provides sensation to the dorsum of the foot and the toes. It can be found at the level of the lateral malleolus lateral to the extensor digitorum longus.

The sural nerve is a continuation of the posterior tibial nerve. It provides sensation to the lateral foot. It is found between the lateral malleolus and the Achilles tendon.

The posterior tibial nerve is sensory to the heel, medial sole and part of the lateral foot. It can be found posterior to the medial malleolus behind the posterior tibial artery. A slightly deeper injection with continued injection while withdrawing the needle is the usual technique for blocking this nerve.

POSSIBLE COMPLICATIONS
It has been reported that ankle block can result in persistent paresthesias in some cases. Part of this may be due to vigorous injection of high volumes of local anesthetic. This may lead to hydrostatic damage (due to the pressure of additional volume in relatively closed compartments of the ankle) - but these complications are fairly rare.

There is always a risk with the injection of local anesthetics of injecting directly into the bloodstream. However, careful adherence to proper technique will make this complication unlikely.

SUMMARY
As you can see, ankle block is an easy to perform technique with a low incidence of risks. The benefits of excellent anesthesia and avoidance of significant risks in terms of cardiovascular, pulmonary and hemodynamic alterations makes ankle block an excellent choice for surgery of the foot.

 

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