Toxicity 532Allergy 532Systematic toxicity 532Local tissue toxicity 533

Choosing an anaesthetic agent 533Vasoconstrictors 532Procaine 534Lidocaine 534Bupivacaine 534Etidocaine 535Mepivacaine 535Prilocaine 535

Techniques of administration 535Local infiltration 536Nerve trunk blocks 536

Field block anaesthesia 540First ray or Mayo block 540Fifth ray block 543Middle ray blocks 544

Postoperative supervision 545

Safety considerations 545

17

Local analgesiaD. L. Lorimer

Since the mid-1970s, the use of local anaesthesia bypodiatrists has been a routine part of practice and hasfacilitated the application of many techniques thathave been developed to the benefit of the patient. Themethods employed range from local infiltration of theanaesthetic agent at the site of the lesion to nerve trunkblock techniques that prevent sensory stimulus fromthe area of the foot the nerve supplies. The choice ofmethod and site of injection depend on factors that arein the best interests of the patient and allow the lowestdosage of anaesthetic agent to be used.

A single site on the weight-bearing plantar surfacewill generally involve blocking the tibial nerve,whereas a single site on the dorsum can be anaes-thetized by local infiltration. However, techniques canbe employed whereby local infiltration is used on theplantar surface or is delivered by injecting towards theplantar between the metatarsal heads. Multiple siteson the dorsum may be better anaesthetized by a blockof the nerve that supplies the area, which could be thesural, saphenous, deep or superficial peroneal. If bothof the latter are to be blocked, it is better practice toblock the common peroneal nerve, but it should beremembered that this might also affect motor functionin the leg even if the total dosage of the agent used isclosely controlled and kept to a minimum.

CHAPTER CONTENTS

529

Keywords

Choice of anaestheticDigital nerve trunk blocksField block anaesthesiaLocal infiltrationNerve trunk blocksTechniques of administrationTibial nerve toxicitySafety considerations

18NDF-17(529-548) 8/8/01 6:42 PM Page 529

The most frequently used site for the administrationof anaesthetics in the foot are the digital nerves, pre-dominately those of the hallux. The nerve supply to eachdigit is by four small nerve trunks, two of which supplythe dorsum and two the plantar aspect (Romanes 1987).Textbooks of anatomy identify these nerves as having apredictable location, but in many instances they can beshown to have subdivided well before entry to the toes(Bruce-Scott 1989). Their subdivision is usually accom-panied by a similar branching of the small blood vessels,which will increase the vascularity of the area into whichthe injection is to be made.

As a general consideration, before giving an injec-tion to produce analgesia the operator should have aclear understanding of the anatomical structures in thearea to be injected, together with possible variations(Wildsmith & Armitage 1987). In addition, the follow-ing points should be observed:

● The anaesthetic agent to be injected should bedeposited accurately to ensure that it is in effectivecontact with, and encircling, the nerve trunk. Thiswill ensure that the local anaesthetic agent perfusesinto the nerve trunk equally from all sides in a con-centration sufficient to ensure the blocking of itscentral core fibres. These core fibres are responsiblefor the sensory supply of the most distal area fromthe site of the nerve block (Covino & Vassallo 1976).This is particularly important in the case of thethicker nerve trunks such as the tibial, the commonperoneal and the popliteal nerves. If there are anysuspected anomalies, such as early bifurcation ofthe nerve, the deposition of the fluid should bewider or, if possible, at a point before the bifurca-tion. To prevent an incomplete blockade (Wedenskyblock) of nerve conduction it is suggested that 8 mmof the length of the nerve must be bathed in anaes-thetic solution (de Jong 1994). The ability to judgethe dosage required to achieve this is gained byexperience of administration and any temptation tooverdose should be resisted.

● To minimize the risk of systemic toxic reactions, everyeffort should be made to avoid depositing the localanaesthetic intravascularly by aspirating beforedepositing the local anaesthetic agent. This is par-ticularly important when administering the fluid inhighly vascularized sites. The essence of good prac-tice is to use the minimum dosage of the agent toavoid the risks of toxicity and tissue damage, there-fore excessive quantities should be avoided.

Local anaesthetic agents in current use are very safe(Dollery 1999) but this safety is always dependent upon

530 NEALE’S DISORDERS OF THE FOOT

an accurate assessment of patients’ physical and clini-cal states, the site of the lesion as well as the type andthe composition of the anaesthetic solution (Covino &Vassallo 1976). Before administering a local anaes-thetic, the patient’s medical history should be clearlyestablished and if there are any doubts as to the suit-ability of the patient for the dosage, the opinion of thepatient’s physician should be sought. However, itshould be stressed that allergy or adverse reactions toamide anaesthetics are extremely rare and, if reactionsdo occur, they are usually the result of systemictoxicity, overdose or patient anxiety (Fink 1989). Theprocedures that should be followed to assess thepatient’s state of health are discussed in Chapter 2, butparticular attention should be paid to the followingpoints:

Drug interactions

Interaction with systemic drug therapy relates mainlyto the drugs which impair aspects of the liver’s abilityto detoxify the anaesthetic agents. Two groups ofdrugs have this effect, namely the monoamine oxidaseinhibitors (MAOI) and the procarbazine drugs. MAOIsare used to control acute depressive states and the pro-carbazines are antitumour drugs used in the control ofHodgkin’s disease and in the treatment of other lym-phomas (Dollery 1999). These drugs inhibit the actionof the hepatic microsomes, in particular the microso-mal cytochrome P450 enzymes responsible for the bio-transformation of local anaesthetics to simplerchemical structures (Vickers et al 1984). In the case ofprocarbazine, drug interaction is less clear as this anti-tumour agent is usually administered in conjunctionwith other antitumour drugs (Dollery 1999).

Patients being treated with benzodiazepines shouldalso be treated with special care because, although nota drug interaction, these tranquillizers can act as anti-convulsant drugs and mask the early signs of toxicity(Trimble 1983). If an adverse reaction to the localanaesthetic does occur, the patient may become sud-denly and deeply unconscious (Wildsmith & Armitage1987). Other drugs that can cause problems in associa-tion with local anaesthetics are the antihypertensivedrugs, such as diuretics. This is not a drug interactionbut, because local anaesthetics lower blood pressure(Gianelli et al 1967), and diuretics can cause vasodila-tion and slower heart rate, postural hypotension canresult. Thus the combined effect of local anaestheticsand diuretics may produce a greatly increased risk offainting when the patient resumes an upright positionafter treatment.

18NDF-17(529-548) 8/8/01 6:42 PM Page 530

Steroid therapy

Patients on steroid therapy are more easily put understress and have lower resistance to infection (Dollery1999). Such patients will have a card identifying thedetails of the current steroid therapy. Similarly, patientswho are receiving anticoagulant therapy will also carrya card indicating the drug prescribed – they will needspecial consideration in the control of bleeding. This pre-caution also applies to those who are haemophiliacs orhave other haemorrhagic diseases and to patients withleukaemia, who have a lowered resistance to infection.

Local anaesthetics and pregnancy

Opinion varies regarding the administration of localanaesthetics to pregnant women. It is not seen as a risk insome texts (Dollery 1999), while others (Martindale 1993)maintain that there may be some risk. Provided the preg-nancy is proceeding normally and the procedure is seenas an emergency that cannot wait until the conclusion ofthe pregnancy, and the anaesthetic agent is chosen withcare, then the risks are not seen as great. However, as ageneral rule it is considered inadvisable to use localanaesthetics during the first 3 months of pregnancy.

The choice of anaesthetic agents and the dosagelevels applied to the pregnant patient needs to be care-fully assessed because of the effects on the fetus viatransplacental transfer (Ala Kokko et al 1995). Thelonger-lasting local anaesthetics in particular, but notexclusively, may not be metabolized so easily due tolack of development of the enzyme systems in the fetalliver. The agent that crosses the placenta most easily isprilocaine (de Jong 1977) and its use should be avoidedif possible in such patients.

Liver function

Patients who suffer from impaired liver function fromsuch causes as infective hepatitis or cirrhosis may havea reduced or negative ability to metabolize amide-typeanaesthetic agents. It is suggested that it would only bein extreme cases that the liver’s metabolic reservewould be compromised (de Jong 1994). Care should betaken in the initial assessment of the patient to estab-lish the possibility of liver disease or alcohol drinkingpatterns that could have potentially harmful effects.Systemic reactions have been noted in patients withsevere hepatic disease (Seldon & Sashara 1967). A con-sideration associated with liver function occurs in themetabolism of prilocaine. One of its main metabolitesis a substance called o-toluidine, which can inducemethaemoglobinaemia in humans (Covino & Vassallo

LOCAL ANALGESIA 531

1976). For this reason, high dosage levels of this agentshould be avoided.

Renal function

An understanding of the patient’s renal function isalso necessary, although this is not so important asliver function (de Jong 1994). The kidneys excrete up to10% of lidocaine and mepivacaine, and up to 16% ofbupivacaine, in unaltered form but only 3–6 h afterinjection, therefore impaired renal function could be a complication to the use of local anaesthetics(Wildsmith & Armitage 1987).

Cardiovascular considerations

Patients with hypertensive cardiovascular diseaseshould not be administered anaesthetic agents contain-ing adrenaline as there is an increased risk of car-diotoxicity (de Jong 1994). Similarly, patients withperipheral vasospastic conditions, such as Raynaud’sphenomenon, should not receive anaesthetics withadded vasoconstrictors. The tourniquet effect of theanaesthetic fluid in plain solutions encircling the digitmust be avoided by using the minimum dosage and atechnique that deposits fluid only where neededaround the nerve trunk.

Sepsis

Local sepsis at the proposed site of injection precludesthe administration of the anaesthetic agent as thepassage of the agent through the tissues to the site of itsaction could facilitate the spread of the sepsis. Aroundthe site of sepsis the tissue pH is usually more acidic.Tissue acidity reduces the quantity of local anaestheticbase that can be mobilized and used to produce anaes-thesia. This will inhibit the action of the anaestheticagent and, as a result, the operator may be tempted toadminister higher doses (de Jong 1994). Where an anaes-thetic agent has to be used to facilitate the treatment of aseptic condition, the site for the nerve block should be asfar from the site of the sepsis as possible.

Secondary infections

A number of patients may have a lowered resistance tosecondary infections and could be particularly at risk from infection introduced at the site of the injec-tion. The general conditions that may cause thislowered resistance in patients would be nephritis, theanaemias, improperly controlled diabetes and steroid

18NDF-17(529-548) 8/8/01 6:42 PM Page 531

therapy. Controlled diabetic patients should not be indanger from the use of plain solutions of anaesthetic.Skin preparation before injecting and the use of a suit-able postoperative dressing at the site of the injectionshould be carried out scrupulously at all times.

Epilepsy

Epileptics not well stabilized by drug therapy could beinfluenced by the stimulation of the central nervoussystem, which may result from the administration oflocal anaesthetics. Consultation with the patient’sgeneral practitioner before administering a localanaesthetic is strongly advised.

Patient compliance

The administration of local anaesthetics require goodpatient compliance. Its use in certain groups mayrequire additional justification as the only means ofeffecting treatment. It may not be suitable for use withthe very old or young, the very nervous or hysterical,the mentally impaired and the insane. In all caseswhere local anaesthetics are used, the patient shouldhave the process clearly explained so that rapport isbuilt up between the patient and the practitioner. Inaddition to building a rapport between practitionerand patient, obtaining informed consent is the processby which a clear understanding by the patient of theprocess of the treatment is established and their accep-tance of it recorded.

The administration of local anaesthetics does notrequire the elaborate range of preparations that is asso-ciated with general anaesthetics but the patient shouldbe advised only to have a light meal about 4 hoursbefore the procedure. The patient’s normal medicationcan be taken provided it does not interact with theanesthetic agent, as defined by the previous para-graphs on drug interaction. Immediately prior to theadministration of the local anaesthetic it is good prac-tice to encourage the patient to empty their bladder.The patient should be advised not to drive for at least1 hour after the administration of the local anaesthetic(Martindale 1993).

TOXICITY

Toxic effects from the administration of local anaes-thetics can be considered to fall into three categories,allergy, systemic toxicity and local tissue toxicity(Covino & Vassallo 1976).

532 NEALE’S DISORDERS OF THE FOOT

Allergy

A number of reports of suspected allergies haveappeared from time to time but these were mainlyassociated with the ester type of anaesthetics derivedfrom para-aminobenzoic acid. Most researcherssuggest that allergy to amide-type local anaesthetics isextremely rare (Covino & Vassallo 1976). Additives areused in local anaesthetic agents that may be the causeof allergy but this, too, is extremely rare (Brown et al1981). Examples of such additives include agents toalter the pH of the solution or preservatives in solu-tions stored in multidose bottles.

Systemic toxicity

The most common cause of toxicity is inadvertentinjection into the bloodstream. This can be avoided byaspiration when the needle is located and before depo-sition of the fluid and each time the position of theneedle is changed (Wildsmith & Armitage 1987). Thetoxicity of an anaesthetic agent of the amide type isdependent on its chemical structure and the ability tometabolize it by the liver enzymes. Prilocaine, which ismetabolized at a much faster rate than lidocaine, isconsiderably less toxic. As a result, the practitionershould ensure that their knowledge of local anaesthe-tics is kept up to date regarding the choice of agent andthe subsequent dosage.

The ability of local anaesthetic agents to affect thecentral nervous system (CNS) produces a range of pro-gressive symptoms. At normal dosage levels, accuratelyadministered, the patient may display the early signs ofCNS stimulation, becoming excited, talkative andeuphoric, although the first two of these may also beattributed to nervousness. Another symptom is numb-ness of the tongue and also the tissues around themouth, this may be ascribed to the highly vascularnature of these areas which provide a focus for a purelylocal reaction from the anaesthetic in the blood stream.

The first real sign of CNS toxicity is light-headedness and dizziness, soon to be followed by dif-ficulty in focusing the eyes, and tinnitus. There may beslurred speech, shivering and light muscle twitch inthe face and sometimes in the patient’s extremities(Covino & Vassallo 1976). The patient may appear tobe drowsy, disorientated or even become fleetingly un-conscious. Should the toxic reaction continue thepatient would become convulsive with generalizedtonic/clonic state. Following this, depression of theCNS activity ensues with respiratory depression andarrest of function (Stricharz 1987).

18NDF-17(529-548) 8/8/01 6:42 PM Page 532

The effects on the cardiovascular system at toxiclevels result in decreased myocardial activity andcardiac output, which, combined with peripheralvascular vasodilation, can produce a lowered bloodpressure. Toxic reactions resulting from the mal-administration of local anaesthetics are usually due tointravascular injection, excessive dosage or carelessadministration on vascular sites. The treatment of suchreactions consists of adequate ventilation of the lungs,and anticonvulsant agents such as diazepam.Vasopressor drugs, such as adrenaline, may be used tosupport circulation or physical methods may be usedif necessary. Physical methods of life support are dis-cussed in Appendix 1. Practitioners intending to uselocal anaesthetics should become familiar with theprocedures for resuscitation of patients and ensure, byattendance at appropriate courses at regular intervals,that these skills are kept up to date (Wynne 1986).However, it is good practice to anticipate the poss-ibility of adverse reactions with careful monitoring ofthe patient’s reactions during the progress of theadministration of the agent so that the process may behalted at an early stage.

Local tissue toxicity

Studies have been carried out to investigate the effectsof local anaesthetic agents on certain body tissues todetermine their potential for irritation (Covino &Vassallo 1976). In high concentrations local anaesthet-ics can cause haemolysis of red blood cells but this willbe at concentrations much higher than are used gener-ally in the UK. It is advisable to remember that if bloodis drawn back into the syringe during aspiration it isprudent to discard the remaining anaesthetic agent leftin the syringe and, if necessary, replace it with a newsupply. Always ensure that the total volume and concentration does not exceed the maximum safe dose.

In studies it has been noted that local anaestheticagents, again at high concentrations, have causeddamage to the sciatic nerves of frogs (Covino & Vassallo1976). It has also been noted that the preservatives some-times used in local anaesthetics have caused neurotoxic-ity with some loss of ability to detect sensation (Gissenet al 1984). There are a few reports of some loss of sensa-tion after the application of local anaesthetics but anyneuropathy that develops is more likely to be as a resultof trauma from the needle (Arthur et al 1987). Somereports exist of neuropathy after the use of chloropro-caine but it would seem that this was due to the additionof sodium bisulphite as an antioxidant (Covino 1984).

LOCAL ANALGESIA 533

Inadvertent injection of local anaesthetic agents,particularly the longer-lasting agents (Benoit & Belt1972), into skeletal muscle tissue has been reported ashaving a short-term effect on the tissue. This seems tobe reversible and the effects seem to disappear after 2 weeks (Zener & Harrison 1974). This is an importantconsideration when locating local anaesthetic drugsclose to skeletal muscle.

The effects of added vasoconstrictors are mentionedlater.

CHOOSING AN ANAESTHETIC AGENT

The first factor in the sequence is determined by theprocedure to be performed, its duration and possiblepostoperative pain. Procedures of short duration andlittle postoperative pain can be adequately coveredusing lidocaine or, if a higher dosage is required, prilo-caine, which has a lower level of toxicity. Proceduresthat require longer time, or those that are perceived toproduce unacceptable levels of postoperative pain,may require bupivacaine or etidocaine (where this isavailable). With both of these, clear instructions forpostoperative management are necessary, as there isprolonged loss of sensation and proprioception maybe affected.

The potency of a local anaesthetic is related to itslipid solubility, which determines the ability of theagent to penetrate the cell membranes, which presenta fatty barrier. Greater lipid solubility increases theduration of action that in turn is also enhanced by thedrug’s protein binding ability. Lipid solubility also isimportant in determining the order in which the dif-ferent fibres of a peripheral nerve are blocked(Wildsmith et al 1985).

Vasoconstrictors

Procedures where a prolonged duration of action isrequired of an anaesthetic agent without the toxicpotential of bupivacaine, the use of an added vasocon-strictor such as adrenaline (epinephrine) may berequired. Because of the action of the vasoconstrictor,the toxicity of the local anaesthetic with which it ismixed is lowered as the rate of absorption from the siteof the injection is much slower; local tissue ischaemiawill also be produced. This ischaemia may increase therisk of local damage to the nerve trunk, although it is thought that this could be due to the additionof sodium metabisulphate, which is added to mostsolutions containing adrenaline as an antioxidant(Wildsmith & Armitage 1987). Local ischaemic necro-

18NDF-17(529-548) 8/8/01 6:42 PM Page 533

sis may also result from its use (Dollery 1999). Amongthe other systemic adverse effects that are possiblewith the use of adrenaline are anxiety, palpitations,tremors and coldness of the extremities (Dollery 1999).Adrenaline (epinephrine), the most commonly usedvasoconstrictor, has systemic effects that are particu-larly undesirable in those patients with cardiac diseaseas a result of its effects on blood pressure and heartrate (Dollery 1999). It also can readily cross the pla-centa (Danon & Sapira 1972) and therefore its use inpatients during pregnancy is best avoided (Fan Chung& Barnes 1987). Concentrations of adrenaline greaterthan 1:200 000 should not be used and it is recom-mended that the total dose administered should belimited (Jastak & Yagiela 1983).

Procaine

This was the first of the synthesized local anaestheticagents. It was used extensively until lidocaine and theother amide compounds were introduced. Procaine isan ester-type substance that is metabolized predomi-nantly by the plasma pseudocholinesterases to para-aminobenzoic acid (Van Dyke et al 1976). The durationof action of procaine is short (20–30 minutes) and itschemical structure unstable, particularly in relation toheat. Because of this, a related substance – chloropro-caine – is used because its chemical structure is lesslikely to cause an allergic response (Covino 1984).Procaine is little used clinically but chloroprocaine iswidely used in the US. The use of procaine has largelybeen superseded by lidocaine.

Lidocaine

The normal preparation of the drug is as a hydrochlo-ride salt; it is one and a half times more toxic than pro-caine. Its rate of onset is rapid, its effect is more intenseand lasts longer than procaine, with effective anaesthe-sia of up to 3 hours, although this is normally acceptedas 1.5 hours (Martindale 1993). The maximum safedose (MSD) in the UK for an adult male weighing 70 kis 200 mg (approximately 3 mg/kg body weight) inplain solution and 500 mg (approximately 7 mg/kgbody weight) with added vasoconstrictors (Table 17.1).

Vasoconstrictor additives are used to prolong itsaction unless contraindicated by the site of the injec-tion or the patient’s state of health. Lidocaine is anamino-acyl-amide and as such is detoxified in the liverwith small amounts being excreted unchanged by thekidneys (less than 10%) and in the bile (less than 7%)(Dripps et al 1988).

534 NEALE’S DISORDERS OF THE FOOT

There are few undesirable interactions with lido-caine although the administration of cimetidine, whichinhibits hepatic metabolism, may result on increasedplasma levels and toxicity (Feely et al 1982). Cimeti-dine is a histamine receptor antagonist used in thetreatment of peptic ulceration and other conditionswhere the reduction of gastric acid production is desir-able. The principal preparation is Tagamet. Patientsreceiving this drug should be monitored carefully andthe dosage of anaesthetic kept to a low level. Rani-tidine (Zantac), used in the treatment of excess gastricacid, also impairs hepatic function and similar cautionshould be applied (Robson et al 1985). Propranolol(Inderal) also reduces the clearance of lidocaine due toits effect on hepatic metabolism (Bax et al 1985).

Lidocaine is used in podiatry as a surface anaes-thetic for very nervous patients (EMLA – a eutecticmixture of lidocaine and prilocaine), for local infiltra-tion or nerve trunk block. It is mainly used by podia-trists in 1% and 2% plain solutions, for local infiltrationand nerve trunk blocks, with the exception of digitalblocks, with added adrenaline. As a surface anaes-thetic it has to be applied to the skin for about 1 hour,after which it is possible to carry out venupuncture rel-atively painlessly, but usually little else (Wildsmith &Armitage 1987).

Bupivacaine

As with lidocaine, bupivacaine is prepared as ahydrochloride salt. It is four times as toxic as lidocaine

Table 17.1 Maximum safe dosages (MSDs)

MSD MSD Dose per kgplain with of body solution vasoconstrictor weight(mg) (mg) (mg/kg)

Lidocaine 200 500 3Bupivacaine 150 150 2Etidocaine 300 – 4Mepivacaine 400 – 6Prilocaine 400 600 6

The maximum safe dosages (after Martindale 1993) in this table arein mg of the agent for a 24-hour period. The MSD in column (1) iscalculated on an average body weight of 70 kg based on informationapplicable to the usage of local anaesthetics in the UK. Variationsmay be found in other national formularies. The MSD with addedvasoconstrictors is also shown where appropriate. For the purposesof administering doses of local anaesthetic a more accurate guidelineis to relate the dosage in mg of the agent to kg of the patient’s bodyweight. This takes account of variations in the size of patients andshould be a principal consideration when assessing patients of smallphysique

18NDF-17(529-548) 8/8/01 6:42 PM Page 534

but, when used for specific nerve blocks, it has a dura-tion of action up to 6 hours. The MSD in the UK is150 mg (2 mg/kg of body weight) and it is generallyused in concentrations of 0.25% or 0.50% in plain solu-tion (see Table 17.1). With added adrenaline its dura-tion of action is enhanced and at the same time thequan-tity used may be reduced and the MSD remainsthe same.

Bupivacaine is used when a longer-lasting analgesiceffect is required after techniques that produce somepostoperative pain. Its rate of onset is very slow andallowance should be made for this when using it. Overthe years bupivacaine has been involved with anumber of severe toxic reactions, some of whichresulted in fatalities. All of these seem to have been asthe result of inadvertent injection into the circulatorysystem (Covino 1984). Bupivacaine is detoxified in theliver, although about 4–8% is excreted through theurine (Dernhardt & Kondor 1980).

Bupivacaine is an inhibitor of plasma cholinesteraseand may increase the toxicity of drugs that are metab-olized by that enzyme (Zsigmond 1978).

Etidocaine

This substance (not currently available in the UK) isalso a longer-lasting agent with effective analgesia ofup to 4 hours duration. Although its duration of actionis shorter than bupivacaine, its rate of onset is fasterthan that of lidocaine, which increases patient confi-dence in the effectiveness of the anaesthetic agent andthus the operator. It is capable of producing intensemotor blockade, probably as a result of its high lipidsolubility and, because of its high plasma binding pro-perty, it has the lowest transplacental transfer ratio(Martindale 1993).

It is prepared as a hydrochloride salt and is normallyused in 1% concentration in plain solutions. The MSDis 300 mg in the UK.

Mepivacaine

This drug has properties that are clinically similar tothose of lidocaine. Although it differs chemically, it isprepared and detoxified in the same way. It has asimilar duration of action to lidocaine but is less toxic, the MSD is twice as high as lidocaine at 400 mg(for a body weight of 70 kg) and its rate of onset isfaster. In ankle block techniques, the higher maximumsafe dosage level of mepivacaine is particularly usefulin permitting the use of higher volumes whenrequired.

LOCAL ANALGESIA 535

Prilocaine

Prilocaine has properties similar to lidocaine but hasthe lowest systemic toxicity of all the amide drugs. It issaid not to produce any vasodilation and is also metab-olized to a limited extent in the lungs (Akerman et al1966a). Its effect on the CNS and cardiovascular systemis less pronounced than lidocaine, but one of the mainmetabolites of prilocaine, produced in the first stage ofits metabolism, is ortho-toluidine, which is consideredto be responsible for the production of methaemoglo-bin in humans (Akerman et al 1966b), however, toproduce such an effect it would be necessary to admin-ister in the region of 600 mg, which is far in excess ofthe MSD (which is 400 mg for the average body weightof 70 kg). This may limit its use in podiatry wherepatients may not acknowledge the earlier stages ofpregnancy and where fetal haemoglobin is more sensi-tive to this metabolite (Wildsmith & Armitage 1987). Itis detoxified in the liver.

TECHNIQUES OF ADMINISTRATION

In podiatric practice, two techniques of administrationof local anaesthetic agents are used: local infiltrationand nerve trunk block. Infiltration is used to raise anintradermal, or subdermal weal around a superficiallesion, usually on a non-weight-bearing surface, toproduce anaesthesia. It may also be used in nerveblock techniques to facilitate painless access to deepernerves. Nerve trunk blocks are most commonly usedeither to single nerves or in digital blocks.

Having the patient supine can reduce the risk of thepatient fainting and, in cases where this happens, offurther damage. Some elderly patients, obese patientsor those with breathing difficulty may find it preferableto be semi-recumbent rather than laid flat. In addition,this allows the patient to be more relaxed and to be ableto divert their gaze away from the operating area. Localskin preparation is important to reduce the risks of bac-terial entry through the site of injection. The point ofentry and the adjacent skin should be prepared with asuitable antiseptic skin cleanser, which may be pre-ceded with a soap and water wash if necessary. Theoperator’s hands should be washed thoroughly andsingle-use barrier gloves worn. The site of the injectionshould be further cleansed with a swab impregnatedwith isopropyl alcohol, and allowed to dry, immedi-ately prior to the administration of the anaestheticagent (Wildsmith & Armitage 1987).

The selection of hypodermic needles is important, asthe finest needles (25 or 27 gauge), produce the least

18NDF-17(529-548) 8/8/01 6:42 PM Page 535

pain. However, when it is necessary to advance to amore deeply placed nerve trunk, it may be advisable touse a more rigid needle. The use of blunt needles, i.e.needles produced without the sharp bevelled point orwith a bevel at a much steeper angle, to reach deeplyplaced nerves such as the tibial nerve significantlyreduces the danger of nerve damage and inadvertententry into blood vessels. The use of these needles makesentry through the skin more difficult and makes the useof an intradermal weal essential (see below). In somecases operators use electric stimulating needles, whichare useful to locate the site of deep nerve trunks and areof value to the less experienced practitioners. Theysometimes may cause the patient some discomfort.

The use of plain solutions of local anaesthetic agentsavoids unnecessary impairment of tissue nutrition dueto local vasoconstriction when agents with addedvasoconstrictors are used. Local anaesthetic agentswith added vasoconstrictors, such as adrenaline,should not be used in sites where the blood supply isvia end arteries, as in the digits. Accurate location ofthe site and minimizing the dosage used, coupled withaspiration before injecting will ensure minimal risks oftoxic reactions (Bruce-Scott 1989).

Local infiltration

This technique of administration starts with the raisingof an intradermal weal at a suitably selected site. Thisis done by inserting the needle at an angle of 45degrees to the skin with the bevel uppermost. Whenthe bevel is covered, pressure should be applied to theplunger so that fluid is expelled, sufficient to raise asmall bleb or pool of fluid under the skin, which willshow white against the surrounding skin. The needlecan either be retracted or partially removed from skincontact and realigned to be passed through the skinand directed under the lesion depositing fluid. Toensure an area of complete anaesthesia around thelesion, the needle may have to be withdrawn to thepoint of entry and passed in other directions under thelesion, in a fan-shaped pattern. Local infiltration isseldom possible on weight-bearing areas of the footbecause the subdermal structures will resist thepassage of the fluid and the needle.

Nerve trunk blocks

Digital nerve block

The most commonly used form of nerve block in podi-atry is the digital block, which, because of the nature of

536 NEALE’S DISORDERS OF THE FOOT

the nerve supply, requires separate consideration. Asdiscussed earlier, the nerve supply to a digit is by wayof four small nerves, two serving the dorsal area andtwo serving the plantar area, which may have subdi-vided before entering the septal planes of the digit.The techniques discussed assume that the anatomicalnorm applies; small compensatory deposits, the site ofwhich could be identified by the areas remaining unaf-fected by the anaesthetic agent, would deal with pre-mature subdivision of the nerve trunk.

The digit should be examined to select two sites onthe dorsum so that the medial dorsal and plantarnerves can be reached from one point of entry and thelateral dorsal and plantar nerves can be reached fromthe other (Fig. 17.1). At the same time, it is useful tomentally subdivide the proximal phalanx into thirds,so that the site of injection will be over the proximalend of the medial third. At this point the phalanx isusually at its narrowest and will allow the easiestaccess to the plantar nerve trunk with the least possi-bility of striking the phalanx with the needle and pos-sibly causing damage to the periosteum.

The amount of fluid required to raise the intra-dermal weal is unlikely to exceed 0.25 ml each site. Theneedle should then be directed towards the point ofentry for the weal at a steeper angle (closer to 90degrees) and towards the dorsal nerve trunk. Afteraspirating the syringe to ensure the needle is notinserted into a blood vessel, approximately 0.5 ml offluid should be deposited slowly and steadily. Uponcompletion of this, the needle should be withdrawn.Aspiration should be carried out before each deposi-tion of anaesthetic agent. If, on aspiration, blood isseen to enter the barrel of the syringe, no further use ofthat fluid and syringe should be made. This precautionis to protect against the remote possibility of re-entryinto another blood vessel and the consequent deposi-tion of damaged blood cells into the circulation.

The needle should be inserted through the originalpoint of entry and advanced towards the plantar (seeFig. 17.1) until it is located over the nerve and up to 0.5ml should be deposited around each nerve trunk.Satisfactory anaesthesia should be possible with up to2.5 ml of a 2% anaesthetic agent. It is important indigital anaesthesia to avoid depositing excessiveamounts of fluid or encircling the digit with a subder-mal ring of fluid and producing a tourniquet effect,with risks in restricting circulation.

This two-point entry technique is a modification of theStockholm technique. Although the lesser digits seem toallow further modification of this technique to a singleentry on the dorsum, it is a modification capable of pro-

18NDF-17(529-548) 8/8/01 6:42 PM Page 536

ducing internal damage and it is better to retain twopoints of entry.

Upon completion of the injection procedures, it isbetter to delay testing for loss of sensation until adigital hyperaemia appears, as this indicates the block-ade of the sympathetic fibres and the onset of sensoryloss. The patient may describe the toe as having anumb or tingling sensation. Delaying testing for sen-sation until the outcome is more predictable willensure greater patient confidence in the whole process.

Specific nerve block

Anaesthesia of all or part of the foot may be obtainedby selective nerve trunk blocks. The sensory supplyfrom the larger nerve trunks should be more pre-dictable, but areas on the margin may be served bymore than one nerve trunk, making careful testing ofthe anaesthetic effect essential. The larger size of thenerve trunks allows them to be located accurately bypalpation; digital pressure on the site will producedistal paraesthesia, which can be helpful in identifica-tion.

This precision in locating the nerves reduces thenecessity to use large quantities of solution byenabling it to be deposited accurately as well as mini-mizing the risk of failure of the blockade. Theincreased size of the blood vessels that often accom-pany the nerve trunks necessitates exact location of thehypodermic needle to avoid intravascular injection(Fig. 17.2).

The raising of an intradermal weal is not alwaysseen as essential but it allows pain-free relocation ofthe needle should this be necessary. Deposition of thefluid at the site should be slow, to minimize discomfortfrom the disruption of the fascial planes. The volumeemployed can be reduced to about 0.5 ml but it is

LOCAL ANALGESIA 537

advisable to use higher concentrations to ensure anadequate length of blockade. Where suitable, the useof an added vasoconstrictor will allow a lower concen-tration of the agent. The nerves that can be blocked arethe:

● tibial nerve● sural nerve● saphenous nerve● deep peroneal nerve● superficial peroneal nerve (before or after

subdivision)● common peroneal nerve.

The tibial nerve (Fig. 17.3). At the ankle, the tibialnerve passes behind the medial malleoleus, lying lat-erally to the posterior tibial artery. As it passes behindthe flexor retinaculum, divisions start to take placeinto its three terminal branches (first the medial calca-neus, then the medial and lateral plantar nerves).Examination of cadavers shows that this bifurcationcan take place proximally to the flexor retinaculum ina significant number of cases (Romanes 1987). In viewof this the best clinical practice is to locate the nerveslightly proximally to the medial malleolus (approxi-mately 2.5 cm from the central point of the medialmalleolus towards the shaft of the tibia). On mostpatients, it is possible to elicit paraesthesia usingdigital pressure, thus confirming the location forinjecting the anaesthetic agent. Some practitioners use

Figure 17.1 Location of dorsal and plantar digital nervesand sites for intradermal weals.

Figure 17.2 Location of the nerve trunks at a transverseplane through the ankle joint.

18NDF-17(529-548) 8/8/01 6:42 PM Page 537

low-voltage stimulating apparatus to locate the nervetrunk as described earlier, and this can be useful in theearly stages for less experienced practitioners.

Where the nerve passes behind the medial malleo-lus, or just a little proximal, is usually the best site tolocate it. The raising of an intradermal weal at thepoint of entry assists the operator in locating theneedle accurately and allows it to be advanced slowly.The use of the blunt (non-sharp) needles allows thenerve to be located by eliciting paraesthesia while therisk of penetrating the artery or damaging the nervetrunk is much reduced. Once the patient has feltparaesthesia the syringe can be aspirated – an essentialsafeguard in this site (Zenz et al 1988). Blockade of thisnerve can be effected using 2 ml of a 2% solution oflidocaine but it is sometimes helpful, where accuratelocation cannot be assured, to use a 1% solution, whichallows greater volume to be deposited. It is alsohelpful to use local anaesthetics with added adrenalinewhich also can reduce the volume necessary.

The sural nerve (Fig. 17.4). This nerve is located on aline between the lateral aspect of the tendo-Achillesand the lateral malleolus. It is closely associated with

538 NEALE’S DISORDERS OF THE FOOT

the course of the short saphenous vein. Its sensorysupply is to the lateral aspect of the foot, the fifth toeand, in a significant number of instances, a smallportion of the lateral aspects of the calcaneal area. Itmay have subdivided into a number of its terminalbranches and this, combined with its passage over rel-atively well covered areas, makes palpation difficultbut not impossible. In most instances it can be locatedand blocked using small amounts of anaesthetic butoccasionally, due to early bifurcation, it is necessary tolay a ‘track’ of fluid between the lateral malleolus andthe lateral aspect of the tendo-Achilles (Fig. 17.4). Eventhe latter can be accomplished using 0.5 ml 2% solu-tion. It is generally better to initiate the process with anintradermal weal.

The saphenous nerve (Fig. 17.5). This terminalbranch of the femoral nerve supplies the medial aspectof the dorsum of the foot, occasionally extending toinclude the surface over the medial side of the metatar-sophalangeal joint. It is found on entering the foot onthe anterior aspect of the medial malleolus closelyassociated with the great saphenous vein (Bruce-Scott1989). It is not easily located but it is possible toproduce paraesthesia and thus locate the nerve byapplying pressure at a site close to the vein on the ante-rior aspect of the medial malleolus.

The raising of a weal on the surface midwaybetween the tendon of the tibialis anterior and thegreat saphenous vein (Fig. 17.5) allows the needle to beadvanced towards the medial malleolus where, afteraspirating, the local anaesthetic should be depositedclose to the vein. Effective blockade of the nerve is

Figure 17.3 Site of injection for the tibial nerve.

Figure 17.4 Site of injection for the sural nerve. Figure 17.5 Site of injection for the saphenous nerve.

18NDF-17(529-548) 8/8/01 6:42 PM Page 538

possible with 0.5 ml of 2% solution, however, it may benecessary to use up to 1.5 ml of the solution.

The deep peroneal nerve (Fig. 17.6). This nerve islocated lying deep to the anterior tibial artery placedbetween the tendons of the tibialis anterior and theextensor hallucis longus. This nerve, which is a termi-nal branch of the common peroneal nerve, has a verylimited range of sensory distribution, usually supply-ing the opposing sides of the hallux and the secondtoe.

The artery may be located easily by palpation or byusing Doppler apparatus. An intradermal weal shouldbe raised over the site (Fig. 17.6), which will allow theneedle to be advanced to one side of the artery. At thispoint it is possible to detect the force of the flow of theblood through the expansion of the artery and soon thepatient should experience paraesthesia. In someinstances paraesthesia is not felt and the needle shouldbe advanced steadily until resistance is felt from thetibia. With either resistance or paraesthesia the needleshould be withdrawn slightly (approximately a mil-limetre).

Holding the point of the needle steady in this positionthe syringe should be aspirated and, if this is clear, a suit-able dose of the fluid deposited. This is usually about 1ml of 2% solution. There may be some resistance to the

LOCAL ANALGESIA 539

fluid being deposited because of the closeness of theseptal planes.

The superficial peroneal nerve (Fig. 17.7). This nerve,also a terminal branch of the common peroneal nerve,becomes subdermal at the proximal end of the lowerone-third of the leg on the anterolateral surface. It ispossible to produce paraesthesia at this site by apply-ing firm pressure. On becoming superficial the nervequickly divides into a medial and lateral branch and isresponsible for the sensory supply to the lower ante-rior surface of the leg, as well as most of the dorsalaspect of the foot.

As the nerves pass into the foot, the medial branchlies immediately lateral to the tendon of the extensorhallucis longus. The lateral branch lies lateral to thesestructures at the same level.

The branches may be anaesthetized using smallquantities of fluid (approximately 1 ml of a 2% solu-tion) at either of the sites described or where the nervebecomes superficial in the lower part of the leg.

The common peroneal nerve (Fig. 17.8). This nerve,arising from the popliteal fossa, passes over the neck ofthe fibula before dividing to become the deep andsuperficial peroneal nerves. Where the nerve curvesaround the neck of the fibula it can be palpated easily,and access to it is simple because it is in a situation notcomplicated by the presence of major blood vessels.Raising an intradermal weal allows the needle to be

Figure 17.6 Site of injection for the deep peroneal nerve.

Figure 17.7 Site of injection for the superficial peronealnerve.

18NDF-17(529-548) 8/8/01 6:42 PM Page 539

advanced slowly towards the nerve (Fig. 17.8). Satis-factory anaesthesia can be obtained with 1 or 2 ml of2% solution. Using the common peroneal nervereduces the number of injections when both the deepand superficial nerves have to be blocked and reducessignificantly the total dosage of anaesthetic agentrequired.

FIELD BLOCK ANAESTHESIA

This involves the blocking of nerve conduction to awhole segment of the forefoot, usually from the levelof the base of the metatarsals. It is sometimes referredto as Mayo block or ray block. The location of thenerves at these sites is more predictable but is compli-cated by the close association of the nerves and theblood vessels and the necessity of having to passthrough the dorsal and plantar interosseous musclesas well as the plantar intrinsic muscles. Variations inlocation may make it is necessary to lay a ‘track’ ofanaesthetic fluid so it is essential that the needle iswithdrawn along the same line as it was advanced,due consideration being given to the vascularity of thesite. Variations in the location of the plantar nerve maymake it necessary to supplement with a block to thetibial nerve.

The most commonly used field block in the foot isthat to the first metatarsal segment and it is this that isreferred to as a Mayo block. Blockade of the fifthmetatarsal segment is less common, as is that to theother metatarsal segments, but all of these aredescribed as they have minor variations in technique.

The dosage of anaesthetic substance may be quitehigh, with 6–8 ml of 2% lidocaine being normal for aprofound blockade of a metatarsal segment. It may benecessary to use an anaesthetic agent with an addedvasoconstrictor as the vascularity of the area reducesthe effective time for anaesthesia. Patients who have alower body weight may necessitate the use of lower

540 NEALE’S DISORDERS OF THE FOOT

percentage concentrations to avoid breaching themaximum safe dosage of the anaesthetic.

Anaesthetic block of the metatarsal segmentsinvolves the passage of hypodermic needles betweenthe shafts of the metatarsals close to their base, thus itis necessary to establish clear clinical guidelines todetermine the optimum passage between the bones. A simple guide is to locate a point on the medial aspect of the first metatarsal about 1 cm distal to itsbase, and a point on the lateral aspect of the fifthmetatarsal, 2.5 cm distal to its base (Fig. 17.9). A linedrawn between these two points will ensure clearpassage between the shafts.

First ray or Mayo block

The nerve supply to the first metatarsal segment isfrom one of the terminal branches of the deep peronealnerve (dorsolateral) with the other terminal branchsupplying the dorsomedial aspect of the secondmetatarsal segment. The dorsomedial aspect of thefirst segment is supplied by the medial terminalbranches of the superficial peroneal and in some casesterminal branches of the saphenous nerve. The termi-nal branches of the tibial nerve supply the plantaraspect of the first segment.

Figure 17.8 Site of injection for the common peronealnerve.

Figure 17.9 Guideline to intermetatarsal route.

18NDF-17(529-548) 8/8/01 6:43 PM Page 540

The nerve supply to the medial plantar aspect of thesegment is superficial at the base of the first metatarsaland medial to the plantar aponeurosis. The nervesupply to the lateral plantar aspect of the segment liesdeep to the plantar aponeurosis at the level of the baseof the first metatarsal and is the second terminalbranch of the medial plantar nerve.

The venous arch over the dorsum of the foot pro-vides a good visual guide to locate the various nerveswhen used in conjunction with the osseous landmarksof the base of the first metatarsal. Using these two fea-tures it is possible to identify the two optimum sites ofentry on the dorsum between the first and secondmetatarsals (point A; Fig. 17.10), and on the medialaspect of the first metatarsal shaft (point B; Fig. 17.10)where intradermal weals, to facilitate entry, can beraised. The dotted line (C; Fig. 17.10) represents theline of the venous arch.

To anaesthetize the dorsomedial branches of the firstmetatarsal segment, the hypodermic needle should bepassed through the intradermal weal (B; Fig. 17.10)and directed towards the point where the venous archcrosses over the tendon of the extensor digitorumlongus, where the major trunk will be located. Afteraspirating, up to 1 ml of the anaesthetic agent shouldbe deposited and the needle should then be with-drawn steadily and unhurriedly, leaving a ‘track’ offluid all the way up to the point of entry (Fig. 17.11).This will ensure that any small irregular branches areanaesthetized.

LOCAL ANALGESIA 541

Using the same point of entry, the needle shouldnow be advanced laterally over the plantar surface ofthe metatarsal to a point in line with the lateral aspectof its base. This should be close to the medial edge ofthe plantar aponeurosis (Fig. 17.12). Aspiration shouldnot be necessary at this site and about 1–1.5 ml ofanaesthetic fluid should be deposited. As the needle iswithdrawn, continue to deposit the fluid leaving a‘track’ to deal with any irregular branches of either the

Figure 17.10 Site of injection for first ray block. A and B show the positions of the intradermal weals and the dottedline C is the line of the venous arch.

Figure 17.11 Anaesthetizing mediodorsal nerve trunks.

Figure 17.12 Injection site for medioplantar nerve supply tothe first ray.

18NDF-17(529-548) 8/8/01 6:43 PM Page 541

medial plantar nerve or the saphenous nerve that maybe found at that level. This process will complete theblockade of the plantar medial aspect of the segment.

Small terminal branches of the superficial peronealnerve often supply the dorsolateral aspect of the firstmetatarsal segment and it is necessary to ensure thatthese are also blocked. To accomplish this, the needleis passed through the intradermal weal (Fig. 17.13) andis directed medially over the surface of the metatarsalshaft towards the point where the venous arch crossesthe tendon of extensor hallucis longus. At this pointabout 0.5 ml of the anaesthetic agent should bedeposited after aspirating and the needle withdrawn,keeping positive pressure on the plunger so that a‘track’ of fluid is left to catch any irregular nervesupply which may be present (Fig. 17.13).

To complete the dorsal block, it is now necessary to pass the needle through the intradermal weal(Fig. 17.14) and direct it towards the base of the firstmetatarsal shaft. It is necessary to ensure that thenumerous vessels are avoided and that aspiration iscarried out before depositing usually about 1 ml of theanaesthetic. On withdrawal of the needle it is essentialnot to deposit a ‘track’ of fluid in case of inadvertentintravenous injection in this vascular region.

The remaining nerve trunk serving the first meta-tarsal segment is the second terminal branch of themedial plantar nerve, which also serves the medialaspect of the second ray segment. The best palpableindicator of its position is the tendon of the flexor hal-

542 NEALE’S DISORDERS OF THE FOOT

lucis longus, to which it runs parallel at a distance of 8 to 10 mm on the lateral side.

Entry should be made through the intradermal weal(Fig. 17.15) and the needle directed in an anteromedialdirection towards the plantar surface of the footbetween the metatarsal shafts. The target area is the lateral aspect of the distal one-third of the meta-tarsal shaft and it will be necessary to pass through the

Figure 17.13 Direction of the needle for terminal branchesof the superficial peroneal nerve (dorsolateral nerve supply).

Figure 17.14 Injection to anaesthetize the deep peronealnerve (dorsolateral nerve supply).

Figure 17.15 Injection to anaesthetize the second terminalbranch of the medial plantar nerve.

18NDF-17(529-548) 8/8/01 6:43 PM Page 542

muscle of the flexor digitorum brevis. Once the needleis considered to be in position then up to 2 ml of theanaesthetic should be deposited slowly. On with-drawal of the needle the plunger of the syringe shouldnot be depressed in case of inadvertent intravascularinjection.

Fifth ray block

Nerves from three sources supply this segment. Thelateral branch of the superficial peroneal nerve sup-plies the medial dorsal aspect; the terminal branches ofthe sural nerve supply the lateral, the dorsal and, insome cases, the lateral plantar aspect. The plantar and,in most cases, the lateral plantar aspect of the segmentsare supplied by the lateral branch of the lateral plantarnerve, which lies superficial to the plantar aponeuro-sis, parallel to the line of the flexor digitorum brevis.The medial plantar aspect of the segment is suppliedby the medial terminal branch of the lateral plantarnerve, which also supplies the lateral plantar aspect ofthe 4th metatarsal segment.

Two intradermal weals are necessary, with the firstsite placed proximally to the venous arch (Fig. 17.16)over the space between the two metatarsal shafts, whereit will give access to the terminal branch of the superfi-cial peroneal nerve as it lies superficial and medially tothe tendon of the extensor digitorum longus (Fig. 17.17).It also allows access to the medial branch of the lateralplantar nerve by passing between the 4th and 5th

LOCAL ANALGESIA 543

metatarsal shafts and through the dorsal and plantarinterossei muscles (Fig. 17.18). Because of the vascularityof the area it is necessary to aspirate before depositingthe agent. Approximately 1 ml of the fluid should beadequate for anaesthesia and, again, as a result of thevascularity fluid should not be expelled on the with-drawal of the needle.

Figure 17.16 Sites for intradermal weals in the fifth rayblock.

Figure 17.17 Injection site for the terminal branch of thesuperficial peroneal nerve.

Figure 17.18 Injection towards the medial branch of thelateral plantar nerve.

18NDF-17(529-548) 8/8/01 6:43 PM Page 543

The terminal branches of the sural nerve are blockedby inserting the needle through the intradermal weal(Fig. 17.19) and advancing it posterodorsally towardsthe lateral side of the venous arch, avoiding penetra-tion of the vessel. After depositing approximately 1 mlof the anaesthetic the needle should be withdrawnslowly, leaving a large ‘track’ of the fluid to block anyirregular branches (Fig. 17.19).

544 NEALE’S DISORDERS OF THE FOOT

The lateral branch of the lateral plantar nerve is also reached through the same intradermal weal(Fig. 17.20). The needle should be advanced anterome-dially towards the line of the flexor digitorum longus.Once on site about 1 ml of the fluid can be depositedand the needle withdrawn, leaving a ‘track’ of fluid, asbefore, up to the point of entry. This should ensure thatany small irregular nerves will be blocked (Fig. 17.20).

Middle ray blocks

To block the 2nd, 3rd and 4th metatarsal segments onlyminor modification of the techniques described isrequired. The 3rd/4th segments are usually supplieddorsally, on the medial and lateral borders, respec-tively, by the medial terminating branch of the lateralbranch of the superficial peroneal nerve, which nor-mally passes superficially to the venous arch. Theplantar supply is from the lateral branch of the medialplantar nerve but may also be supplied from the lateralplantar nerve.

Both the dorsal and the plantar nerves may bereached from the intradermal weal sites (A) and (B) inFig. 17.21. The line indicated by (C) in the same figureis the approximate line of the venous arch. On theplantar sites the nerves are accompanied by a numberof blood vessels, making aspiration essential. Similarly

Figure 17.19 Injection towards the terminal branches of thesural nerve.

Figure 17.20 Injection site for the lateral plantar nerve.Figure 17.21 Sites of intradermal weals for the fourth rayblock.

18NDF-17(529-548) 8/8/01 6:43 PM Page 544

fluid should not be expelled from the needle as itpasses through the tissues. The plantar nerves arelocated deeply to the plantar aponeurosis and thedosage of approximately 1 ml of anaesthetic should bedelivered slowly to minimize disruption of the tissuesand discomfort to the patient.

Anaesthesia of the 3rd metatarsal segment can beaccomplished by raising intradermal weals at the sites

LOCAL ANALGESIA 545

indicated in Fig. 17.22 and following the same generaldirections as above. The 2nd metatarsal segment canbe anaesthetized by raising intradermal weals at thepoints indicated in Fig. 17.23. The technique describedin the first ray procedure for the deep peroneal nervealso needs to be applied.

A general consideration, which applies to all theprocedures described for ray blocks, is the location ofthe nerve supply deriving from the medial and plantarnerves and the proximity of the injection site to a verywell-vascularized area. In addition to this there is theneed to pass needles through muscle tissue to reachthe sites. One way to minimize this risk is to block thetibial nerve as it passes behind the medial malleolus.At this site the nerve is more easily accessible and gen-erally it is possible to administer a low dose of theagent. Ultimately, the site chosen must reflect the clin-ical needs of the patient and the limitations imposedby the procedure.

POSTOPERATIVE SUPERVISION

It is important to ensure that the patient is properlyadvised of all of the outcomes of the procedure that hasbeen employed. Although the possibility of adverseresults from the anaesthetic are rare it is wise to ensurethat the patient has clear instructions in written form.This should also be explained to the patient before theyleave the surgery and give details regarding the stepsto be taken in case of problems arising, including emer-gency telephone numbers. It is also important to ensurethat it is possible for the patient to have easy access tothe practitioner who carried out the procedure in the48 hours immediately after the procedure. Whereverpossible, procedures that may have follow-on effectsshould not be performed close to holiday weekends.

SAFETY CONSIDERATIONS

The administration of local anaesthetics using syringesand needles imposes the obligation on the operator toapply stringent safety precautions to prevent the pos-sibility of needle-stick injuries to the operator or thepatient. Opinion varies on the methodology for con-taining the dangers and every effort should be made toensure that the latest local and national regulations areknown and applied.

The person administering the local anaestheticshould ensure that the material drawn up intosyringes is correct. In the case of cartridges, the writingon each cartridge should be checked. Each container oflocal anaesthetic should be retained until the end of

Figure 17.22 Sites of intradermal weals for the third rayblock.

Figure 17.23 Sites of intradermal weals for the second rayblock.

18NDF-17(529-548) 8/8/01 6:43 PM Page 545

the procedure and the details on them recorded in thepatient’s notes. If the containers all have the samedetails they need be recorded only once. All localanaesthetic substances should be transferred from themanufacturer’s container to the syringe. They shouldnot be decanted into galley pots.

All sharps should be discarded in the approved wayin designated sharp disposal containers, which should

546 NEALE’S DISORDERS OF THE FOOT

ensure that they do not pose a risk to cleaning staff andothers who are concerned with the control of thesurgery. Syringes should not be held in the hand apartfrom when being used or transported to their container.The re-sheathing of needles after use is considered toconstitute a risk of needle-stick injury to the operatorand the use of needle holders is recommended.

The operator must wear suitable barrier gloves.

REFERENCES

Akerman B, Astrom A, Ross S, Telc A 1966a Studies on theabsorption, distribution and metabolism of labelledprilocaine and lidocaine in some animal species. ActaPharmacologica et Toxicologica 24:389–403.

Akerman B, Peterson SA, Wistrand P 1966b Methemoglobinforming metabolites of prilocaine. Third InternationalPharmacological Congress (abstracts) Sao Paola, Brazil,237.

Ala Kokko TI, Pienimaki P, Herva R et al 1995 Transfer oflidocaine and bupivacaine across the isolated perfusedhuman placenta. Pharmacology and Toxicology77:142–148.

Arthur GR, Wildsmith JAW, Tucker GT 1987 Pharmacologyof local anaesthetic drugs. In: Principles and practice ofregional anaesthesia. Edinburgh: Churchill Livingstone,ch 4.

Bax NDS, Tucker GT, Lennard MS, Woods HF 1985 Theimpairment of lignocaine clearance – major contributionfrom enzyme inhibition. British Journal of ClinicalPharmacology.

Benoit PW, Belt WD 1972 Some effects of local anestheticagents on skeletal muscle. Experimental Neurology345:264–278.

Brown DT, Beamish D, Wildsmith JAW 1981 Allergicreaction to an amide local anaesthetic. British Journal ofAnaesthesia 53:435–437.

Bruce-Scott D 1989 Techniques of regional anaesthesia.Warwalk, Connecticut: Appleton & Lange Mediglobe.

Covino BG 1984 Current controversies in local anaesthetics.In: Scott DB, McClure JH, Wildsmith JAW (eds) Regional anaesthesia 1884–1984. Sodertalje: ICM, 74–81.

Covino BG, Vassallo HG 1976 Local anesthetics. New York:Grune & Stratton.

Danon A, Sapira JD 1972 The binding of noradrenaline andadrenaline to human serum albumin. Journal ofPharmacology and Experimental Therapeutics182:295–302.

de Jong RH 1977 Local anesthetics. Springfield, Illinois:Charles C Thomas.

de Jong RH 1994 Local anesthetics. St Louis: Mosby.Dernhardt R, Kondor H 1980 Metabolite von bupivacain

beim menschen. Regional Anesthesie 3:25.Dollery C 1999 Therapeutic drugs, 2nd edn. Edinburgh:

Churchill Livingstone.Dripps RD, Eckenhoff JE, Vandam LD 1988 Introduction to

anesthesia, 7th edn. Philadelphia: WB Saunders.

Fan Chung K, Barnes PJ 1987 Prescribing in pregnancy:treatment of asthma. British Medical Journal 294:103–105.

Feely J, Wilkinson GR, McAllister CB, Wood AJJ 1982Increased toxicity and reduced clearance of lidocaine by cimetodine. Annals of Internal Medicine 96:592–594.

Fink BR 1989 Mechanisms of differential blockade inepidural and subarachnoid anesthesia. Anesthesiology70:851–858.

Gianelli R, Von der Groeben JO, Spicavk AP, Harrison DC1967 Effect of lidocaine (xylocaine) on ventriculararrhythmias in patients with coronary heart disease. NewEngland Journal of Medicine 277:1215–1219.

Gissen AJ, Datta S, Lambert D 1984 The chloroprocainecontroversy: II. Is chloroprocaine neurotoxic? RegionalAnesthesia 9:135–145.

Jastak JT, Yagiela JA 1983? Journal of American DentalAssociation 107:623–630.

Martindale, The Extra Pharmacopoeia, 29th edn 1993.London: The Pharmaceutical Press.

Robson RA, Wing LMH, Miners JO, Lillywhite KJ, Birkett DJ1985 The effect of ranitidine on the disposition oflignocaine. British Journal of Clinical Pharmacology20:170–173.

Romanes GJ 1987 Cunningham’s manual of practicalanatomy, volume one, upper and lower limbs, 15th edn.Oxford University Press, Oxford: Oxford MedicalPublications.

Seldon R, Sashara AA 1967 Journal of the American MedicalAssociation June: 137.

Stricharz GR (ed.) 1987 Local anesthetics. Berlin: SpringerVerlag.

Trimble MR (ed.) 1983 Benzodiazepines divided amultidisciplinary review. Chichester: John Wiley.

Van Dyke C, Barash BG, Jatlow P, Byck R 1976 Cocaineplasma concentrations after intranasal application in man.Science 191:859–861.

Vickers MD, Schieden H, Wood-Smith FG 1984 Drugs in anesthetic practice, 6th edn. London: Butterworths.

Wildsmith JAW, Armitage EN 1987 Principles and practiceof regional anaesthesia. Edinburgh: ChurchillLivingstone.

Wildsmith JAW, Gissen AJ, Gregus J, Covino BG 1985 Thedifferential nerve blocking activity of amino-ester local anaesthetics. British Journal of Anaesthesia 57:612–620.

18NDF-17(529-548) 8/8/01 6:43 PM Page 546

Wynne G 1986 Training and retention of skills. In: Evans TR(ed.) ABC of resuscitation. London: British MedicalJournal, 32–35.

Zener JC, Harrison DC 1974 Serum enzyme values followingintramuscular administration of lidocaine. Archives ofInternal Medicine 134:48–49.

LOCAL ANALGESIA 547

Zenz M, Panhans C, Niesel HC, Kreuscher H 1988 Regional anesthesia. London: Wolfe Medical Publications.

Zsigmond EK 1978 In vitro inhibitory effect of amide-typelocal analgesics on normal and atypical cholinesterases.Regional Anaesthesia 3:4–7.

18NDF-17(529-548) 8/8/01 6:43 PM Page 547

18NDF-17(529-548) 8/8/01 6:43 PM Page 548