Introduction
Upper extremity surgery, whether elective or emergency, can be done under regional anesthesia in the vast majority of cases. Used alone or as a supplement to general anesthesia, regional anesthesia allows for lower opiate consumption, less postoperative nausea and vomiting and better pain control. This chapter explains how regional anesthesia is used in the upper limb. We will emphasize the important anatomic landmarks to administer regional blocks safely in the upper extremity. We will describe different types of regional anesthesia for the upper limb, their indications and pitfalls. The availability of a wide range of local anesthetics, new drug delivery systems, and use of adjuncts for administration, such as ultrasound (US) or nerve stimulators, make regional anesthesia a very safe and precise procedure. When administered correctly, regional anesthesia has a nearly 100% success rate and fewer side effects. It can be used in an almost unlimited range of conditions, including previously contraindicated situations (eg, anticoagulated patients).
What Is Regional Anesthesia?
Regional anesthesia developed as an offshoot of local anesthesia. In September 1884 Dr. Karl Koller, an ophthalmologist, performed the first operation under local anesthesia (topical cocaine solution) in a patient with glaucoma. That same year Dr. Richard Hall published a report on the first successful nerve block of the inferior dental nerve by Dr. William Halsted using cocaine hydrochloride. Together they went on to develop different regional nerve block techniques. The aim of regional or conduction anesthesia is to make the body part supplied by a nerve insensitive to pain so that surgery can be performed on it. It also causes altered temperature sensation and paralysis of the muscles supplied by the nerve. Regional anesthesia works through the interaction between the drug and the target nerve fibers. Local anesthetics inhibit depolarization of the nerve membrane by blocking voltage-gated sodium channels. These channels are very important for the propagation of action potential that leads to conduction of an electric charge. This conduction of electric charge is how the peripheral and central nervous systems communicate with each other. Clinically approved, commercially available local anesthetic drugs have a reversible effect. All local anesthetics have a similar chemical structure made up of an aromatic portion, an intermediate chain, and an amine group. Onset of action is related to the drug’s lipid solubility and diffusibility. How long the anesthetic effect lasts is related to the drug’s protein-binding ability.
The four most commonly used brachial plexus blocks for upper limb regional anesthesia are the axillary, infraclavicular, supraclavicular and interscalene blocks. With these four distinct approaches, one can cover almost all kinds of upper limb surgery. When administering local anesthetic for nerve blocks, it is crucial to have a clear understanding of the topography of neurovascular structures in the neck, shoulder and upper extremity. The introduction of US guidance in administering regional anesthesia has further improved the safety of this procedure. US-guided regional anesthesia has effectively reduced the incidence of local anesthetic systemic toxicity. US allows us to see instantly what is happening underneath the skin when the needle is introduced. It shows us the nerves we need to block and structures we need to avoid, such as vessels and lungs.
Initial Assessment of Trauma
Stabilization and Primary Management of a Patient With an Injured Limb
Appropriate resuscitation should be started at the accident site following the “life-before-limb” approach. The injured limb is dressed and immobilized as it lies. Avoid the urge to clean the limb on site with antiseptics. Bleeding is controlled by elevation and compression bandaging. If there is projectile massive bleeding from the limb, a tourniquet may be used to prevent exsanguination. It is preferable to use a commercial tourniquet or blood pressure cuff. These cuffs have adequate surface area to distribute the pressure and avoid skin injuries. More important, the amount of pressure applied can be regulated. This is usually set to 100 mm Hg above systolic blood pressure. It is most important to note the time of application, and this information should be handed over to the receiving medical team in the emergency room. This time can be marked or written on the patient’s arm, thigh or forehead. This is to prevent caregivers from forgetting the presence of an inflated tourniquet. Leaving the tourniquet on for a long time causes distal tissue necrosis. This leads to loss of the limb and also has serious systemic effects when released. Intravenous (IV) fluids should be started, and the patient should be transferred immediately to a trauma center. Remember to keep the patient warm during transport and provide IV or intramuscular analgesia. In cases where the accident caused an amputation, the amputated part should be preserved as detailed in Chapter 15 and delivered to the trauma center as soon as possible.
Regional Anesthesia in the Ambulatory Setting
Preoperative Evaluation
In any situation where patients present for surgery days or weeks after the last clinical encounter, it is important for the surgeon to reassess the patient to confirm that surgery is still indicated. Informed consent should have been taken at the time when the patient was listed for surgery, and this consent is reaffirmed with the patient. Generally patients would already have an idea what anesthesia they will receive. For major operations under regional anesthesia, patients are advised to fast 6 hours prior to the procedure just in case there is a need to convert to general anesthesia. It is important to check if the patient had any previous allergic reactions to local anesthetics, even if this is extremely rare. The patient should be weighed to calculate the maximum dose he or she can tolerate. The surgeon or anesthesiologist should also note if the patient is on any antiplatelet or anticoagulation therapy. Depending on the type of surgery and the patient’s medical condition, patients would have been advised whether it is safe to continue these medications during the perioperative period. With the use of US guidance, performing upper limb peripheral nerve blocks in patients taking blood thinners is no longer an absolute contraindication.
In emergency situations where surgery is lifesaving, this detailed approach may not be possible. Members of the surgical team should explain to the patient (if possible) or members of the patient’s family without delaying the surgery.
Preparation for Anesthesia
Once in the operating theater, the patient is prepared in the induction room. IV access is obtained in the nonsurgical limb, and monitoring devices are placed. Patients are asked to confirm their identity, the operative site and any known allergies. Baseline vital parameters are recorded, and patients receive supplemental oxygen before any medication is administered. The entire anesthetic procedure is explained to the patient to help relieve anxiety. It is most important to inform patients about what they may feel in case of an allergic reaction or drug overdose and advise them to report to the doctor immediately should any of these occur. This communication with patients is the best way to detect intolerance to local anesthetic or adverse effects of intravascular injection. A light sedation with midazolam can be given to very anxious patients.
Administration of Anesthesia
Regional anesthesia for upper limb surgery is administered as peripheral nerve blocks. The entire procedure should be done under rigorous aseptic conditions, much like the actual surgery itself. This includes surgical hand scrub for the anesthesiologist, donning of sterile gowns and gloves, and use of sterile covers and transmission gel for the US. Using long-acting anesthetic drugs, the peripheral nerve block can be performed in the induction room, much earlier than the surgical procedure, to decrease operating room turnover time. The use of US guidance has changed the administration of peripheral nerve blocks dramatically. It allows the anesthesiologist to visualize the tip of the needle, the anatomic structures the needle is passing through, and most important, the target nerves to be blocked. This reduces the discomfort for the patient in terms of number of needle passes required. It helps visualize vessels and lowers the risk of intravascular injection of anesthetic. This is further avoided by repeated aspiration prior to injection and observing for small volume dispersion into tissue. It optimizes the placement of the anesthetic drug, leading to faster time to achieve surgical anesthesia. Nerve stimulation may be used in combination with US guidance. It used to avoid intraneural placement of the needle tip. Remember to involve patients by asking them to speak up if they feel any paresthesia or signs of toxicity previously advised. Patients should be continuously monitored by trained personnel throughout the procedure. This does not require any special monitoring equipment. Anxious patients may be given light sedation. After the surgery, patients can go home after a few hours of observation in the postanesthesia care unit or general ward.
Regional anesthesia has a major advantage of providing more than adequate postoperative analgesia. This prolonged pain-free period improves the patient’s trust in the surgical team and gives the patient confidence to start early mobilization of the operated limb when this is appropriate. Patients are educated regarding care for their anesthetized upper limb. This includes wearing a sling properly until they regain active control of the upper limb and avoiding contact with temperature extremes until sensation recovers. All patients are given a prescription for oral analgesics and specific instructions for when to start taking them upon discharge.
Advantages of Regional Anesthesia
Pain Relief
The effect of a well-administered peripheral nerve block can be appreciated even before surgery. It allows for pain-free radiologic examination and removal of dressings in trauma cases. The patient is pain free when transferred over to the operating table. It works as a preemptive analgesia and provides the most effective postoperative pain relief. It attenuates the surgical stress response and causes vasodilation, thus improving blood flow in the extremity. Early passive mobilization under regional anesthesia when appropriate can also accelerate the return of function to the operated limb.
General Anesthetic Risk Reduction
During surgery, regional anesthesia reduces the risk of regurgitation and aspiration pneumonia in patients who have not fully fasted. Dental problems, pharyngeal pain and hoarseness of the voice are avoided when regional anesthesia is successful. Malignant hyperthermia, barotrauma and atelectasis are nonexistent. The risk of severe allergic reaction is lower with regional anesthesia.
Postoperatively, regional anesthesia reduces the risk of drowsiness, respiratory distress, nausea and vomiting. People are more alert right after surgery and have less hemodynamic instability. Hyperalgesia, an increased sensitivity to pain often seen with patients with chronic use of opiates, can be reduced or avoided. Postoperative urinary retention due to bladder dysfunction is significantly lower with the use of peripheral nerve blocks. Volatile anesthetics and sedative hypnotic agents suppress the micturition reflex and decrease detrusor contractions. In regional anesthesia the immune response is preserved.
Early Discharge
The length of hospital stay is considerably reduced. Patients can be discharged a few hours after surgery. While the arm is still numb, patients benefit from the prolonged analgesic effect. This “prolonged sleeping” of the limb gives patients less stress and reduces the demand for additional pain medication.
Economic Considerations
Regional anesthesia reduces cost of care by decreasing the time spent in the operating room, the amount of disposable materials used, the duration and level of monitoring required and the duration of postoperative hospital stay. This translates to better quality of care for the patient.
Anesthesia for the Young, the Pregnant and the Elderly
US-guided regional anesthesia can be used in patients of any age, even in small children. In our hospital, children as young as 4 years old have had surgery under regional anesthesia. In children, anxiety caused by the thought of receiving an injection is prevented by a very light and ultrashort sedation given before performing the nerve block. For the elderly, regional anesthesia is very well tolerated and is our first choice. Patients are mobilized faster after surgery under regional anesthesia, thus reducing the risks of thromboembolism and cognitive disturbances. Surgery in pregnant patients is not advised unless absolutely necessary. When necessary, the use of local or regional anesthesia minimizes the risk to the developing fetus.
Contraindications for Peripheral Nerve Blocks
Although the use of US-guided regional anesthesia (with or without nerve stimulation) has reduced the risks of inadvertent reactions, some contraindications still need to be mentioned. Patient’s refusal should be respected at any time. Peripheral nerve blocks should not be given through sites that appear infected. A needle puncture in an infected area can disseminate and worsen the situation for the patient. One should consider an alternative site to administer the block. Use of certain types of peripheral nerve blocks is not advised for bilateral procedures owing to the risk of drug toxicity. When given on both sides, interscalene or supraclavicular blocks can result in diaphragmatic paralysis and carry the risk of respiratory failure.
Hemostatic disorders, either congenital or acquired, should always be considered when counseling patients regarding the choice of anesthesia. A known allergic reaction to a local anesthetic, though very rare, should also be considered as a possible contraindication. The presence of infection in the operative site is another consideration. It is difficult to achieve dense anesthesia in inflamed or infected tissue. The inflamed tissue is more acidic; thus a smaller proportion of the drug is in the lipid-soluble form that can penetrate nerve membranes. The position of the patient and length of surgery could make the use of regional anesthesia as a sole technique difficult.
Do not perform regional anesthesia if you are not trained to do so or if you are not assisted by someone who knows how to do this properly! Most systemic diseases, such as diabetes, inflammatory syndromes, epilepsy, or major obesity, are not contraindications for US-guided regional anesthesia. It seems that nowadays the choice to administer a peripheral nerve block is dependent on the individual anesthesiologist’s skills and experience.
Local Anesthetics and Adjuvants
Local Anesthetics
Local anesthetics exert their clinical effect through blocking sodium-specific ion channels, the so-called voltage-gated channels. They inhibit the sodium influx in neuronal tissue and in this way stabilize the cell membranes. Action potentials cannot arise and conduction is inhibited. Local anesthetics are potentially toxic and can be dangerous, even life threatening. Therefore they should only be used when proper equipment and skills are available to deal with these rare but not impossible consequences. Factors that influence toxicity are volume, rate of injection and site where the local anesthetic is injected. It is recommended that the maximum doses suggested in the literature be respected rather than those proposed by the manufacturer. Do not forget to always inject slowly (≈5 mL/min). Get familiar with US and use it at all times. You can identify an inadvertent injection instantaneously with use of the ultrasound.
Table 1.1 summarizes the recommended doses of local anesthetics for regional block of the upper limb in a healthy person weighing more than 50 kg. These doses are suggestions only and are listed to compare the different products clinically used in our daily practice. There is probably no reason to give a higher dose than what is recommended in the literature.
| Drug | Max. dose described in the literature for a body weight of 70 kg |
|---|---|
| Lidocaine 1%–2% | 400 mg (axillary) 300 mg (interscalene, supra- and infraclavicular) |
| Lidocaine with epinephrine | 500 mg |
| Mepivacaine 1%–2% | 400 mg |
| Ropivacaine 0.2%–0.75%–1% | 225–300 mg |
| Levobupivacaine 0.125%–0.5% | 150 mg |
Signs of Intoxication due to Local Anesthetic Drugs
Severe toxicity results from rapid absorption of a local anesthetic causing an immediate effect on the brain or heart tissue, with possible life-threatening consequences (tetany, epileptic insult and even cardiac arrest). These situations are rare but can arise with an unintentional intravascular rapid injection of a high dose of a local anesthetic. Once again, US application with direct visualization and the lower doses of drugs required makes this kind of complication very rare. Although extremely rare, it is important to recognize the first neurologic symptoms of intravascular injection: a metallic taste, dizziness, blurred vision, disorientation and convulsions. Bupivacaine, a drug formerly very often used, is known to have in some cases caused cardiac toxicity and difficult resuscitation. Nowadays bupivacaine (Marcaine) is replaced with ropivacaine and levobupivacaine, which have less cardiotoxicity. In the last 8 years, more than 20,000 regional anesthesias have been performed with US in our department. We have not had a single seizure or cardiopulmonary resuscitation due to an inadvertent intravascular injection. We have to stay vigilant, however, and all cases are done with resuscitation equipment and an Intralipid emulsion close at hand.
Adjuvants
Although many adjuvants have been tried, the most common and still clinically used are epinephrine and clonidine.
Epinephrine at a dose of 5 µg/mL of local anesthetic prolongs the effect by slowing the plasma resorption. This is only useful for short-acting local anesthetics like lidocaine and Carbocaine (mepivacaine) and does not seem to have a benefit in our clinical setting.
Clonidine prolongs the block with the administration of 150 mcg.
Other adjuvants described in the literature and that can be used are morphine, tramadol and bicarbonates. Their application remains very limited, and they are not part of our clinical practice.
Recent studies show that dexamethasone attenuates C-fiber response and its systemic application in a low dose seems to prolong the duration of peripheral nerve block analgesia. The mechanism is still unclear, but the dose-response efficacy versus adverse effects seems promising.
Onset Time
The onset and duration of a regional or local anesthesia depends on the drug used, the anatomy of the patient, the volume injected, the vascularization, the proximity of the injection to the nerve, the diffusion of the local anesthetic (circumferential or longitudinal) and the application of adjuvants.
Table 1.2 gives us an idea of the most currently used local anesthetics. In daily practice we often mix a drug with a rapid onset and short action time with a drug that has a prolonged effect.
| Anesthetic drug | Commercial name | Onset time (min) | Action time (min) |
|---|---|---|---|
| Lidocaine 1.5% | Xylocaine | 5–10 | 45–90 |
| Mepivacaine 2% | Carbocaine | 5–15 or more | 60–240 a |
| Ropivacaine 0.5% | Naropin | 5–15 or more | 240 to > 720 a |
| Levobupivacaine 0.5% | Chirocaine | 5–15 or more | 240 to > 720 a |
a There is a large interindividual variability in clinical practice, and these figures are given only as an estimation coming from our own experience.
Equipment and Practical Approach: How to Find the Nerves While Avoiding Arteries and Veins
What We No Longer Do
Looking for Paresthesia
Principally this technique means advancing the needle blind toward the target nerve, expecting to initiate a sudden pricking sensation. That is when the needle touches or brushes a nerve. Risks of inadvertent vascular puncture and damage of nerve tissue are possible. As mentioned, this technique should be abandoned!
Transarterial Puncture in the Axillary Region
After palpating the arterial pulse in the axillary region, the needle is introduced and advanced until arterial blood is aspirated. Then the needle is further advanced until no more blood returns. Now, a single dose of 15 up to 30 mL of local anesthetic should be slowly given after verification that the tip of the needle is not positioned in a vessel. The procedure is simple and easy to perform. However, the transarterial puncture technique can also elicit paresthesia and damage nerves as well. The risk of hematoma and aneurysm are not excluded. This technique is no longer used in our practice.
Current Practice
Nerve Stimulation
Nerve stimulation is losing its popularity as a stand-alone technique. This technique permits us to find specific nerves while observing characteristic motor responses that are linked to a particular nerve. With the aid of a medical device that produces a weak electric current ranging from 0.1–2 mA, with a pulse duration of 0.1–1 ms and a frequency of 1–2 Hz, we search for the nerves we would like to anesthetize. Although we can identify nerves more accurately (if we find them!), the risks of the two previously discussed techniques still exist.
Ultrasound
US is an imaging technique using high-frequency sound waves. We are now able to look at organs and structures inside the body.
The history of US dates to 1880, when Pierre and Jacques Curie discovered the piezoelectric effect in crystals. It was in 1978 that P. La Grange published the first case series of Doppler transducer placement of needles in supraclavicular brachial plexus blocks. In 1994, Steven Kapral and colleagues explored and described brachial plexus blockade using B-mode US. This approach is evolving fast and is highly recommended.
Practical Issues and Equipment for Nerve Stimulation
Needles
In most cases a 50-mm needle is sufficient. We recommend the use of short beveled needles (20–30 degrees). Although scientific publications do not seem conclusive, this type of needle gives us a better tactile perception of the tissues. We also believe that they diminish the risk of inadvertent perforation of a nerve.
In our service we use insulated (Teflon) needles. When we use nerve stimulation with these types of needles it is only the tip that can localize the nerves.
Catheters
Introducing a flexible catheter near a nerve gives us the opportunity to continuously or intermittently inject a drug. The technique of inserting the catheter is identical to the single shot, but the equipment used is slightly different ( Figs. 1.1 and 1.2 ). The goal is to achieve a prolonged postoperative analgesia with a continuous infusion or sequential injections. Risks are migration of the catheter and not attaining the desired pain relief. Catheters may also lead to a higher prevalence of infections if used for a longer duration. Current techniques offer the possibility to readminister a single-shot regional anesthesia with prolonged local drug effects, making the use of these devices redundant. In our practice we no longer use catheters for peripheral regional anesthesia.
The Nerve Stimulator for Regional Anesthesia
A standard nerve stimulator is an electrical device. It should have accurate control of stimulation parameters. The stimulation frequency and current should be constant during use. They should be easily adaptable and very precise according to the needs of the anesthesiologist. Electrical impulse is normally rectangular and monophasic. A screen should visualize the imposed parameters. All equipment should have a visual and audible warning system in case of malfunction. Do not use a system that is not medically approved for performing regional anesthesia in your country or state ( Fig. 1.3 ). The different settings should be very accurate with regard to the intensity of stimulation (0.5–5 mA), impulse time (0.5–1 mL) and frequency of stimulation (1 or 2 Hz).
Nerve stimulation should not be painful. The electric current produced with a small battery is very weak.
When the insulated needle approaches a nerve, the electrical impulse initiates a muscle contraction that is specific for that nerve. This muscle activity can be described as “twitching or jerking movements” at a frequency of 1 or 2 Hz.
For a given nerve or combination of nerve fibers, there is a specific muscular response. While progressing the needle toward a nerve, the amplitude or force of the muscular twitching may increase. Our experience shows that for good regional anesthesia, a motor response found at an electric current of 0.5 mA is excellent. Now the needle is probably very near to the nerve. The injection of a very small quantity of local anesthetic will abolish the motor activity. Before injecting the drug, pulling back on the plunger of the syringe can exclude an intravascular position of the needle. Be very meticulous and do not inject too fast (≈5 mL/min). Try to have an idea of the pressure needed to perform the injection, and always observe the reaction of the patient (grimace, withdrawal reaction).
Ultrasound Combined With Nerve Stimulation
We know that a single injection to a branch, trunk or division of a nerve, with sufficient volume, can give good regional anesthesia of the entire limb. However, the more distally we search for nerves or when a lower volume is injected, the anesthesia can be isolated to just that particular area that the nerve innervates. Nowadays, to optimize anesthesia while respecting the relationship “lower volumes with the best possible anesthetic result versus higher volumes with a probable higher risk ratio,” the use of multiple injection or targeted intracluster injections is encouraged. Here we inject smaller volumes to all the detectable nerves, roots or branches. The question, however, is how can we precisely locate the nerve we want to block?
Since the introduction of regional anesthesia in the late 1800s, there has been much progress. Finally we are able to visualize the needle approaching the nerve, the structures to avoid (artery, vein) and the local anesthetic dispersing into the tissues.
In our department, the clinical use of US has acquired its place in the anesthesiologists’ daily practice. It is considered the best practice when performing regional anesthesia. The introduction of portable US devices with high-frequency transducers makes them easy to use.
Many good US machines are available. Local practice and skills influence the choice of a model, but the principal idea remains the same: an easy-to-use screen and linear high-frequency transducers ranging from 5–13 MHz. The higher the frequency, the better the quality of the image close to the transducer ( Fig. 1.4 ). These kinds of transducers are perfect for the interscalene, supraclavicular, infraclavicular and axillary plexuses, as well as for peripheral nerves.
For obese patients or when performing an infraclavicular approach, a deeper penetration of the US wave is required. A lower-frequency transducer should be used for this approach. At these frequencies there will be better penetration (>5 cm), but the image will not be so clear and detailed.
When using US you will notice that the nerve structures have different appearances. They are accompanied by veins and arteries. The fascicles that form the nerves have a more or less hypoechogenic (dark) appearance in the interscalene and supraclavicular region. When descending toward the arm, their appearance changes and they become more hyperechogenic in the infraclavicular and axillary region and in their terminal branches. They look like ribbons on a longitudinal view and are oval when cut transversely. On a transverse view, they are also easier to recognize.
Arteries and veins are both hypo- and anechogenic. Arteries are far less compressible than veins, and arteries are pulsating vascular structures. This makes them easier to distinguish with Doppler US. As a reminder, fat tissue is hyperechogenic.
Detecting the needle on US is not always easy and demands a certain experience. The most important is the position of the needle tip and the track that it follows. Hydrolocation and hydrodissection may help to find this position more easily.
In-Plane and Out-of-Plane Approaches
The conversion from nerve stimulation to US-guided regional anesthesia is also a conversion from a single-handed technique to a two-handed technique and requires practice.
Sometimes it may be difficult to follow the needle along the entire pathway. This has several explanations:
- •
The beam of the transducer that is capturing and producing the image is very narrow (1 mm).
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The angle of 45 degrees between the transducer and the needle does not optimally reflect the image of the needle.
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The depth and the tissue structures have influence on the visibility.
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Penetrating the different tissues may bend the needle slightly.
When initiating regional anesthesia with US, the in-plane approach seems more secure. The clinician needs to focus on the entire needle, which can be hard to accomplish. It takes time because progression is slower, and aligning the needle in the transducer’s beam is not so easy. With this technique, it seems that more attention is given to the adjacent structures.
With the out-of-plane approach, we focus on the imaginary end of the needle. While penetrating the different structures we can see the compression produced by the tip of the needle on the different types of tissues. This gives us an indication of the needle point without really ever seeing it. Auxiliary methods like hydrolocalization and hydrodissection exist to refine this technique even more. Here we inject tiny incremental volumes that we can appreciate on the screen.
In case of further doubt, the combined use of ultrasound with nerve stimulation would help.
Despite all our existing safety measures, some colleagues still claim unintentional “intraneural injections” without mentioning any permanent damage.
What Are We Looking for When Using Nerve Stimulation?
When performing regional anesthesia with a nerve stimulator (see earlier), we try to find a specific muscle activity; even more, we induce involuntary movements of certain parts of the limb. These movements are a unique footprint for the specific nerve we are electrically stimulating.
While stimulating, for example, the musculocutaneous nerve, the biceps will contract, and this will cause flexion of the forearm toward the upper arm ( Fig. 1.5 ). Stimulation of the ulnar nerve causes contraction of the flexor carpi ulnaris muscle, with flexion and inclination of the ulnar part of the wrist. The ring and little fingers will also flex simultaneously ( Fig. 1.6 ). When we are searching for the median nerve, we look for contraction of the flexor carpi radialis muscle and the flexor digitorum profundus muscle. They provoke flexion of the wrist and flexion of the index and middle fingers ( Fig. 1.7 ). When locating the radial nerve, you will stimulate the long extensor muscle of the thumb, the extensor carpi radialis longus and brevis muscles and the extensor carpi ulnaris. This will provoke supination of the forearm and extension of the wrist and digits, in particular the thumb, when the radial nerve is located ( Fig. 1.8 ).
