Hello, today we will be talking about local anesthesia techniques, part #2 of a two part series.
Male Speaker: Production of this present lecture was made possible by an educational grant from Gill Podiatry Supply & Equipment Company, helping you put your best foot forward.
Dr. Khurrum Khan: The objective of today is we go over intermetatarsal block and do an anatomic review. We will also be discussing the Mayo block, the reverse Mayo block as well as the ankle block in detail. Letâs start with the intermetatarsal block. Uses of the intermetatarsal block include lesser metatarsophalangeal joint work, lesser metatarsal osteotomies and single digit hemato correction. With regards of the intermetatarsal block looking at the anatomical distribution of the nerves, dorsally, the medial dorsal cutaneous nerve has an internal dorsal cutaneous branch. This divides into three dorsal digital branches, one of which supplies the medial side of the great toe, the other, the adjacent sides of the second and third toe. The intermediate dorsal cutaneous nerve divides into four dorsal digital branches which supply to medial and lateral sides of the third and fourth and of the fourth and fifth toes. Plantarly three common digital nerves stem from the medial plantar nerve. They pass between the divisions of the plantar aponeurosis and each splits into two proper digital nerves. Those are the first common digital nerve supply the adjacent sides of the great and second toes plantarly. Those of the second supply the adjacent sides of the second and third toes plantarly. And those of the third give out branches to the third and fourth toe plantarly.
The technique for the intermetatarsal block is quite simple. First palpate for the metatarsal themselves then palpate for the metatarsal interspaces, proximal to the MPJs. You are injecting 90 degrees to the skin, you want to deposit a wheel and go from dorsal to plantar injecting as you go, being careful not to pierce to the plantar aspect of the foot. And as you can see from the picture you want to do adjacent intermetatarsal spaces to block that specific toe.
Next, we will talk about the Mayo block. The Mayo block is used to anesthetize the medial column of the foot at the level of the first met base proximally. The Mayo block is one of the most commonly used blocks in foot and ankle surgery. Itâs uses include Hallux Valgus procedures, Hallux Varus procedures, Hallux Ramidus and Rigidus procedures. This includes Keller arthroplasty and first MPJ fusions. One of the disadvantages is close proximity to the dorsalis pedis both dorsally and in the first center space. A chance of a hematoma formation can happen if the DP is not spared. Therefore you should always aspirate when doing this injection.
The nerves for the Mayo block include dorsally, the medial dorsal cutaneous nerve of the superficial peroneal nerve, divides in the two common branches with further to subdivide into dorsal digital branches, one of which supplies a middle side of the great toe. Plantarly, the common digital nerve from the medial plantar nerve divides into the proper digital nerve of the great toe and supplies the skin on the middle side of the great toe plantarly. The first inner space, the middle terminal branch of the deep peroneal nerve divides into two dorsal digital nerves which supply the adjacent sides of the great and second toes. Before it divides it gives off the first space and interosseous branch which supplies the metatarsal phalangeal joint of the great toe.
The technique for the Mayo block includes the following, first palpate dorsally distal to the flay of the first metatarsal base. Here you inject at 90 degrees and create a wheel. The injection proceeds from dorsal to plantar being careful not to pierce to the plantar aspect of the foot. The next step is to palpate dorsally slightly distal to the flay of the first metatarsal base. If you havenât already done so you can do this without removing the needle from the first injection. Inject dorsally proceeding from medial to lateral staying subcutenous being careful to avoid the branch of the dorsalis pedis. And you may need to aspirate to ensure that there is no blood in the hub of the needle at the end of this injection.
Now that you have gone across the top of the foot for the next step you can palpate the first inner space proximally and raise a wheel if one hasnât already been created. Insert the needle at 90 degrees immediately lateral to the Extensor hallucis longus tendon, but medial to other dorsalis pedis artery and its deep branch. You want to inject dorsal to planar aspirating first to ensure that there is no blood in the hub of the needle. Be careful not to pierce through the plantar aspect of the foot. The last step is to palpate plantarly, slightly distal to the flay of the first metatarsal base. You want to raise a wheel again if one hasnât already been done. And you want to inject plantarly going from medial to lateral being careful to stay in the subcutaneous tissues.
You may or may not see a wheel being drawn as you will inject but you may see blenching of the skin plantarly. Given that this injection is one of the most widely used, it begs a question does the Mayo block actually work? And based on the study the Mayo block and efficacies block for Hallux and first metatarsal surgery, the Mayo block was used on more than 275 patients and they found a failure rate of less than 1%. Their conclusion was learning this technique adds to the anesthetistâs armamentarium of regional anesthesia and aids in rapid case turnover and avoids a risk associated with major conduction in general anesthesia. So therefore if done properly this block should work.
Next we will discuss the reverse Mayo block. As its name suggests the reverse Mayo block is on the opposite side of the foot of the Mayo block. Itâs used to anesthetize the lower column of the foot at the level of the fifth metatarsal base. It uses include fifth metatarsal osteotomies, fifth toe contractual corrections and it can be also used for ulcer debridement on the lateral aspect of the foot. Anatomically the sural nerve form by the cutaneous branches of the posterior and common peroneal nerve turns into the lateral dorsal cutaneous nerve and then from there becomes a dorsal digital nerve and supplies the lateral side of the fifth toe. The intermediate dorsal cutaneous nerve divides into four dorsal digital branches which supply the middle and lateral sides of the third and fourth toe and of the fourth and fifth toes. Plantarly the proper digital branch from the common digital branch of the lateral plantar nerve supplies a lateral aspect of the fourth and both aspects of the fifth toe plantarly. The technique for the reverse Mayo block is similar to the technique for the Mayo block. You begin by palpating dorsally, slightly distal to the flay of the fifth metatarsal base and you raise a wheel. You want to inject proceeding dorsal to plantar, being careful not to pierce through the plantar aspect of the foot.
Next you want to palpate dorsally distal to the flay of the fifth metatarsal base. You want to inject dorsally from medial to lateral being careful to stay in the subcutaneous tissue. Once again you can do this technique without removing the needle from the first injection. Next you want to palpate the fourth inner space proximally and insert the needle at 90 degrees, immediately lateral to the extensor digitorum longus or peroneus tertius. You want to inject from dorsal to plantar being careful not to pierce the plantar aspect of the foot. With this injection you shouldnât have to raise the wheel since one should have already been raised with the first injection. Last you want to palpate plantarly, distal to the flay of the fifth metatarsal base. You may need to raise a wheel and inject plantarly going from lateral to medial being careful to stay in the subcutaneous tissue.
Finally, we shall go over ankle blocks, its uses include any type of forefoot work, close reduction of any type of loose fragments or midfoot fracture, it can be used for neuroma resection and it can be used for major debridement work for ulcers. Disadvantages include a higher chance to infiltrate medication into the blood vessels. The most important aspect of the ankle block is you are getting the posterior tibial nerve block correctly. The posterior tibial nerve is a main branch of the static nerve, it provides sensor to the heel, medial sole and part of the lateral aspect of the foot. Itâs located posterior to the medial malleoli behind the posterior tibial artery. Going to the opposite side is the sural nerve, the sural nerve is formed by the cutaneous branches of the posterior and common peroneal nerve, it provides sensation to the lateral aspect of the foot and supplies a lateral heel via the lateral calcaneal branches. Itâs located between the lateral malleoli and the Achilles tendon.
Dorsally the superficial peroneal nerve which is a branch of the common peroneal nerve provides sensation to the dorsal from the foot and the toes. It is located medial to the lateral malleoli and lateral to the extensor digitorum longus at or above the level of the lateral malleoli itself. The saphenous nerve itâs a cutaneous branch of the femoral nerve. It provides sensation to the anterior medial aspect of the foot. And itâs located just anterior to the medial malleoli. The deep peroneal nerve is a branch of the common peroneal nerve. It provides sensation to the first inner space. Itâs located lateral to the tendon of the extensor hallucis longus at the level of intermalleolar line, medial to the dorsalis pedis artery. Two centimeters distal to the intermalleolar line, the following structures from the medial to lateral are related to the deep peroneal nerve. The tendon of the tibialis anterior, tendon of the extensor hallucis longus, dorsalis pedis artery, deep peroneal nerve and finally the tendon of the extensor digitorum longus, you need to use these anatomical landmarks while doing the ankle block injection to ensure that you are in the proper position.
To start the ankle block technique we will look at first injecting the posterior tibial nerve. To do that palpate the medial malleoli and advance posterior inferiorly toward the Achilles tendon until the pulsation of the posterior tibial artery is felt. The nerve is just posterior to that artery. A quick technique is to use one thumb breathe away from the medial malleoli. With this injection you want to aim at a 45 degree angle in the medial lateral plane just posterior to the artery. You may or may not want to raise a wheel, you want advance towards the tibia maintaining this 45 degree angle. If paresthesia is induced, aspirate to make sure the vessel is nowhere near and wait for the paresthesia to resolve and then inject. If paresthesia is not enlisted in, advance the needle at 45 degree angle until it meets the posterior tibia, withdraw one centimeter and aspirate. If negative for him in the hub of the needle then inject. The Calor and Rubor are the foot due to loss of sympathetic may initially be noted. And you want to inject approximately 46 CC of your anesthetic in this area.
Next letâs block the sural nerve, locate the posterior border of the lateral malleoli and Achilles tendon, place the skin wheel at the site marked, advance a needle through the skin wheel angling towards the Achilles tendon from the lateral malleoli staying parallel to the skin. Next letâs block this superficial peroneal nerve. To do this raise the wheel anterior to the distal aspect of the lateral malleoli. Continuing in transverse fashion medially across the dorsal aspect of the ankle remembering to stay subcutaneous until the middle malleoli is reached. You may need to do this in one to two injections. To block the saphenous nerve start medial to the anterior tibial tendon near the great saphenous vein. At the level of the ankle on the anterior or superior border of the middle malleoli, raise the wheel medial to the anterior tibial tendon and proceed in a superficial transverse line without injecting the tendon itself towards the middle malleoli. Calor and Rubor are the foot do lost of sympathetic tone may initially be noted. The deep peroneal nerve lies lateral to the anterior tibial artery/dorsalis pedis artery and medial to the tendon of the extensor digitorum longus. The needle anterior site is about 2 cm distal to the intermalleolar line. You want to palpate for the dorsalis pedis at this area and inject just laterally, raising a wheel and advancing at 90 degrees in the perpendicular manner until the bone is encountered, usually within 2 cm or less. Withdraw the needle slightly to prevent periosteal injections. If paresthesia occurs in the first web space withdraw the needle slightly until the paresthesia disappears. You also want to aspirate and if negative him is noted at the hub of the needle you may inject your anesthesia. The needle maybe redirected 30 degrees medially and laterally if additional anesthetic injection is required, making sure to aspirate especially when injecting in the middle direction.
For all of the injections discussed both in Part I and Part II if the anesthetic doesnât work, one has to look at information in the area which tends to produce a lower pH in the tissues. Therefore local anesthesia becomes a more ionized and it doesnât penetrate very well. This decreases the ability of the local anesthesia to produce it affects. One also has to wonder about previous history of drug use. This may require a higher more concentrated dosage, this may require a longer time for anesthetic to become effective.
In summary we performed an anatomical review and discuss the techniques for injections of an intermetatarsal block, a Mayo block, a reverse Mayo block as well as an ankle block. This concludes the lecture on anesthesia techniques.