Regional anaesthesia for foot and ankle surgery

Learning objectives.

By reading this article you should be able to:

• •Plan the use of regional anaesthetic techniques to provide anaesthesia and analgesia for patients undergoing foot and ankle surgery.
• •Select appropriate nerve blocks by understanding the anatomical structures likely to be manipulated as part of the surgery.
• •Explain how to perform ultrasound-guided saphenous, popliteal sciatic and ankle nerve blocks.
• •Describe the use of surgical tourniquets for foot and ankle surgery.

Key points.

• •Patients may present for foot and ankle surgery as elective or urgent/emergency cases.
• •Foot and ankle surgery is associated with significant postoperative pain.
• •Regional nerve block techniques are useful to provide intraoperative anaesthesia, postoperative analgesia, or both.
• •Regional anaesthesia can be used as an alternative to neuraxial or general anaesthesia
• •Ultrasound-guided ankle block is placed more proximally than the traditional landmark approach and will cover surgery to the heel and prolonged use of an ankle tourniquet.

The foot and ankle regions are a complex interplay of muscles, tendons and bone. There is an increased requirement for surgery in the foot and ankle region because of the significant morbidity associated with foot and ankle pathology.¹ Pathology may be isolated or present in the context of a more complex polytrauma patient. Emergency or urgent surgery is often performed on a hospital inpatient basis whereas elective patients are frequently treated in the day surgery setting.² Regional anaesthesia and analgesia can play an important role in the intraoperative and postoperative course of these patients. Recent Procedure Specific Postoperative Pain Management (PROSPECT) guidance recommended the ankle block as the preferred anaesthetic technique for hallux valgus surgery.³ Reduction in general anaesthesia and sedation requirement together with excellent postoperative analgesia impr-oves patient experience and facilitates successful day surgery management.⁴ This article focuses on ultrasound-guided approaches to peripheral nerve blocks used in foot and ankle surgery.

Anatomy

A sound grasp of the anatomy in the foot and ankle region is required to deliver successful regional anaesthesia for surgical procedures. When considering which nerve(s) to target, one should choose structures that may be manipulated during surgery.⁵ A useful strategy is to consider in turn; skin, muscle and bone innervation. The nerves that supply the foot and ankle region arise from the lumbar and sacral plexuses.⁶ They include:

• (i)Saphenous nerve: the terminal branch of the femoral nerve.
• (ii)Superficial and deep fibular nerves (DFNs): branches of the common fibular division of the sciatic nerve.
• (iii)Sural nerve: formed by the union of the medial and lateral sural branch from tibial and common fibular nerves (CFNs), respectively. Gives rise to lateral calcaneal branches.
• (iv)Tibial nerve (TN): produces medial calcaneal branches then supplies the sole of the foot by medial and lateral plantar nerves.

Traditionally, these nerves have been targeted around the ankle joint line, resulting in a block distal to the hindfoot and ankle. However, ultrasound-guided blocks are placed more proximally thereby increasing the blocked territory.⁶ The practitioner should remember that there is considerable variability and overlap of the areas innervated by these nerves, and therefore sensory testing must be carried out before starting surgery.⁷

The muscular innervation of the foot and ankle corresponds to the different compartments in the leg and foot. The lateral compartment being innervated by the superficial fibular nerve (SFN), the anterior compartment by the DFN and the superficial and deep posterior compartments by the TN.⁸

The bone innervation of the foot and ankle joint is summarised in Table 1.^9,10 Remember that the saphenous nerve contributes to the bony innervation of the medial aspect of the ankle.

Table 1.

Description of the different bones in the foot and ankle region with corresponding nerve supply.

Bone	Tibial	Deep fibular	Saphenous	Sural
Medial malleolus	No	No	Yes	No
Lateral malleolus	No	No	No	Yes
Talus	Yes	Yes	Yes	Yes
Calcaneus	Yes	Yes	No	Yes
Navicular	Yes	Yes	No	No
Cuneiforms	Yes	Yes	No	No
Cuboid	Yes	Yes	No	Rarely
Metatarsals	Yes	Yes	Medial phalanx	No
Phalanges	Yes	Yes	No	No

General considerations for regional anaesthesia techniques

Ultrasound imaging with a high-frequency linear transducer is appropriate for most peripheral nerve blocks (shorter transducers may be useful for smaller or paediatric patients), and occasionally a low-frequency convex transducer may be required for larger patients. Using a peripheral nerve stimulator if the target nerves are not clearly visible may reduce the risk of nerve injury. 22G short-bevelled needles are suitable for most patients. Local anaesthetic syringes should be clearly labelled, attached to the needle system and placed on a tray separate from other anaesthetic drugs. A ‘stop-before-you-block’ check moment by block practitioner and assistant should take place just before needle insertion to reduce the risk of wrong-sided nerve block placement.¹¹ The check moment may need repeating if the patient's position is changed during multiple injections.

Compartment syndrome

Consideration should be given to the expected length of anaesthesia and analgesia after a proposed regional block and a risk assessment made with the surgical team in patients deemed at risk of developing postoperative compartment syndrome.¹²

Regional techniques for foot and ankle surgery

Neuraxial blockade

Neuraxial anaesthesia is an excellent alternative to general anaesthesia. Neuraxial anaesthesia will also cover a proximally placed (thigh) tourniquet. Most foot and ankle surgery can be performed in the day surgery setting.

The introduction of the shorter-acting local anaesthetic preparations for spinal anaesthesia: 2-chloroprocaine (10 mg ml⁻¹) and hyperbaric prilocaine (20 mg ml⁻¹), have made day surgery under neuraxial anaesthesia a reliable and attractive option.¹³ The most appropriate choice of local anaesthetic drug depends on duration of surgery, and this should be discussed between surgeon, anaesthetist and the patient.¹⁴

Sciatic nerve

The sciatic nerve can be blocked anywhere distal to its sacral plexus origin, but for foot and ankle surgery is commonly targeted either in the popliteal fossa or more distally for the terminal branches.⁶ Blockade in the popliteal fossa will lead to paresis of the calf muscles, foot drop and more significant impairment of mobility postoperatively compared with a more distal ankle block. The sciatic nerve has been covered comprehensively in this journal recently.⁶

Popliteal fossa sciatic nerve block

The popliteal sciatic nerve is usually easily located in the popliteal fossa. We recommend two methods to locate the nerve.

Method 1. The popliteal artery (pulsatile) and vein (com-pressible) are identified and confirmed using Doppler at the level of the knee crease. The TN is seen lying just posterior to these structures. Scanning proximally, the CFN moves from lateral (just deep to the biceps femoris tendon) to medial to join the TN. Using dynamic scanning (proximal/distal movements of the transducer) helps visualise the CFN and TN. As the sciatic nerve is moving from deep in the thigh to superficial at the knee crease, caudad tilting of the transducer usually aids visualisation, considering the phenomenon of anisotropy.

Method 2. In patients with a high BMI, visualisation of the popliteal vessels and TN/CFN whilst scanning up the thigh can be challenging. An alternative method is to visualise the muscles forming the superior boundaries of the popliteal fossa. Start by defining the lateral border made from the two heads of biceps femoris 10 cm proximal to the popliteal crease (note that if too close to the popliteal crease; the long head is purely tendinous). Then scan medially to demonstrate the large muscle bulk of semimembranosus with semitendinosus lying superficial to it forming the medial border. At the apex of the popliteal fossa, these muscle groups separate. Scan distally down through the popliteal fossa with a caudad tilt on the transducer as described above. The sciatic nerve is visualised within the fossa becoming more superficial and dividing into TN and CFN.

Block conduct

• (i)The patient can be positioned supine with the leg raised, lateral or prone. Keep the patient's leg (and therefore the SN) straight to aid visualisation.
• (ii)Perform the block just distal to the SN bifurcation, where the two branches lie in a common paraneural sheath. This allows injection of local anaesthetic both around and between the CFN and TN, ensuring that local anaesthetic is within the paraneural sheath.
• (iii)A ‘Compton–Cruveilhier septum’ lies between the two branches; this is pierced to achieve spread of local anaesthetic around both branches.¹⁴ Careful ‘hydro-dissection’ and observation of spread around the CFN and TN branches ensures successful blockade.
• (iv)The needle is inserted laterally and passed medially. Choosing an insertion point slightly anterior to the transducer results in better needle visualisation owing to a more parallel transducer/needle orientation.
• (v)Deposit up to 20 ml local anaesthetic around and between the branches.

Ankle block

Tibial nerve

The TN is responsible for the majority of cutaneous innervation to the plantar aspect of the foot. The TN is identified posterior to the medial malleolus adjacent to the posterior tibial artery. Anteriorly, tibialis posterior (TP) and flexor digitorum longus (FDL) can be visualised. Flexor hallucis longus (FHL) is seen deep (posterolateral). The tendon of FHL can easily be mistaken for the TN, so try to identify the fascia overlying the muscle by optimising the transducer angle (the tendon lies deep to this structure within the muscle) and scan proximally to see the FHL tendon regress and become muscular whereas the TN view is maintained. The posterior tibial artery is usually accompanied by a pair of compressible veins (Fig 1).

Figure 1.

Sonoanatomy of the tibial nerve proximal to the medial malleolus. TP, tibialis posterior tendon; TA, tibialis anterior muscle; FDL, flexor digitorum longus muscle; TN, tibial nerve; DT, distal tibia; FHL, flexor hallucis longus muscle.

Block conduct

• (i)Position the patient laterally with the side to be blocked underneath or supine with the leg to be blocked crossed in a figure of 4 shape to allow a posterior needle appr-oach.
• (ii)Classically the TN was blocked at the medial malleolus using a landmark technique.
• (iii)The ultrasound approach allows more proximal blockade (so expect to cover the heel). An approach 5–10 cm proximal to the medial malleolus helps with good skin to transducer contact and moves the bulk of the Achilles tendon (AT) away from an in-plane needle path.
• (iv)A posterior to anterior in-plane needle approach avoids TP and FDL tendons.
• (v)Gentle ‘hydrodissection’ is required to achieve circ-umferential spread with up to 5 ml local anaesthetic.
• (vi)This nerve should be blocked first because it is the largest of the ankle nerves and therefore has the longest onset time.

Deep fibular nerve

The DFN supplies cutaneous innervation to the first webspace on the foot. The nerve is visualised in the distal leg proximal to the ankle joint, usually lying lateral or anterior to the anterior tibial artery (ATA), superficial to the hyperechoic convex shadow of the distal tibia. Tibialis anterior (TA) muscle and tendon lie medially and extensor digitorum longus (EDL) and extensor hallucis longus (EHL) tendons lie laterally to the ATA. The DFN often has a speckled appearance; it is a small nerve and dynamic scanning will help identification as the nerve moves in relation to the vessel (Fig 2).

Figure 2.

Sonoanatomy of the deep fibular nerve proximal to the ankle joint. TA, tibialis anterior muscle; DFN, deep fibular nerve; ATA, anterior tibial artery; EHL, extensor hallucis longus; EDL, extensor digitorum longus muscle.

Block conduct

• (i)Use a lateral to medial in-plane needle approach, depending on the nerve's relationship with the ATA.
• (ii)Use careful ‘hydrodissection’ to deposit 1–3 ml local anaesthetic around the nerve.

Superficial fibular nerve

The SFN supplies the majority of the cutaneous innervation to the dorsal aspect of the foot. The SFN has no vascular markings and is visualised deep to the muscular fascia in the groove formed by EDL anteriorly and fibularis longus (FL) and fibularis brevis (FB) posteriorly and superficial to the curved surface of the fibula on the lateral aspect of the leg. Scanning distally, the nerve pierces the muscular fascia to become superficial and divides into two or more superficial terminal branches (Fig 3).

Figure 3.

Sonoanatomy of the superficial fibular nerve at the lateral aspect of the lower leg. SFN, superficial fibular nerve; FL, fibularis longus muscle; FB, fibularis brevis muscle; EDL, extensor digitorum longus muscle.

Block conduct

• (i)Position the patient with the leg internally rotated.
• (ii)Scan proximally from the lateral malleolus. As the fibula moves deeper, visualise the FL and FB overlying the fibula and the EDL anteriorly. Look at the intersection between the muscle groups and for the nerve passing through the muscular fascia overlying the muscles.
• (iii)Dynamic scanning will help to visualise the nerve as it crosses the fascia.
• (iv)Aim to block the nerve superficial or deep to the muscular fascia (depending on best view) with 1–3 ml local anaesthetic.
• (v)The SFN may give rise to branches (that supply the foot) more proximally after emerging through the fascia, so the block should be placed either just after or before it passes through the fascia to both block any early branches.

Sural nerve

The sural nerve provides cutaneous innervation to the lateral malleolus and the fifth phalanx in both the plantar and dorsal aspects. The sural nerve enters the foot posteriorly to the lateral malleolus. Scanning the lower leg distally towards the lateral malleolus, the nerve and short saphenous vein (SSV) are seen to ‘roll off’ the AT anteriorly to lie in a boat-shaped space posterior to FB. Scanning proximally, the nerve runs with the SSV between the medial and lateral heads of gastrocnemius (Fig 4).

Figure 4.

Sonoanatomy of the sural nerve proximal to the lateral malleolus. FB, fibularis brevis muscle; SSV, short saphenous vein; AT, Achilles tendon; SN, sural nerve.

Block conduct

• (i)The patient can be positioned laterally or with the leg internally rotated.
• (ii)Scan proximally just posterior to the lateral malleolus so that the FB lies anteriorly and the AT posteriorly.
• (iii)Identify the sural nerve and SSV ‘rolling off’ the AT when scanning distally into the space just anterior to the AT.
• (iv)Use an anterior to posterior in-plane needle approach to block the nerve with 1–3 ml local anaesthetic.
• (v)A perivenous injection may be effective if it is difficult to identify the sural nerve. Using ‘hydro-dissection’, adva-nce the needle tip into fluid to avoid nerve contact.

Saphenous nerve

The saphenous nerve provides sensory innervation to structures over the medial aspect of the leg and foot including the medial ankle joint. We approach the saphenous nerve either: (i) deep to sartorius muscle (subsartorius) or (ii) just proximal to the medial malleolus (ankle).

Subsartorius approach

The saphenous nerve runs adjacent to the femoral artery deep to sartorius muscle in the medial thigh. The sartorius muscle lies more laterally in the proximal thigh in relation to the femoral artery, and moves medially as the ultrasound transducer is moved distally. This reflects the proximal origin of sartorius from the anterior superior iliac spine running towards its insertion on the medial tibia. The superficial femoral artery runs adjacent to the vastus medialis and the adductor muscles. The saphenous nerve usually lies between the superficial femoral artery and the vastus medialis muscle. The saphenous nerve lies deep to the several fascial layers under sartorius muscle (sartorius fascia, vastofemoral and vastoadductor membranes) (Fig 5).

Figure 5.

Sonoanatomy of the saphenous nerve in the thigh. SFA, superficial femoral artery; FV, femoral vein; VM, vastus medialis muscle; SN, saphenous nerve.

Block conduct

• (i)Scan at the level of mid-thigh and identify the sartorius muscle.
• (ii)Identify the pulsation of the superficial femoral artery (confirm with Doppler) and the corresponding muscles adjacent to the artery.
• (iii)Use an in-plane needle approach to the saphenous nerve from anterior-lateral to posterior-medial.
• (iv)Ensure the needle pierces the fascia deep to sartorius (a ‘pop’ may be felt) and inject up to 10 ml local anaesthetic.
• (v)Good visualisation of local anaesthetic should be seen to spread on either side of the femoral artery (deep to the sartorius muscle and not into the femoral vein). This is satisfactory as visualisation of the saphenous nerve may be difficult.

Ankle approach

The saphenous nerve runs with the long saphenous vein (LSV) in the distal leg. As the nerve itself is frequently not clearly visible at this level, the vein is used as the landmark for performing a perivenous injection (Fig 6).

Figure 6.

Sonoanatomy of the saphenous nerve at the ankle joint. LSV, long saphenous vein; SN, saphenous nerve; DT, distal tibia; FDL, flexor digitorum longus.

Block conduct

• (i)Apply the transducer lightly (to avoid compression) slightly anterior and proximal to the medial malleolus.
• (ii)Scan proximally and identify the LSV. Using the anterior surface of the tibia as a ‘rail’ for the transducer can help reduce excessive pressure, which occludes the vein.
• (iii)If the nerve is not well visualised, perivascular infiltration around the LSV will suffice with up to 5 ml local anaesthetic. Carefully ‘hydrodissect’ and advance the needle tip into fluid to avoid contact with the nerve.

Digital nerve blocks

Digital nerve blocks are often performed by surgeons in theatre or in the emergency department for management of injuries on the distal toes. These are landmark-guided techniques with infiltration of local anaesthetic on either side of the phalanx to target the digital nerves. This is a safe and effective technique for distal toe surgery and can be performed on all five digits. They may also be used as 'rescue' blocks if there is inadequate block to the toes or the onset of block is unduly delayed after a popliteal fossa sciatic block. Ultrasound can be used to locate the digital arteries and nerves accurately. and correctly place the needle to minimise the risk of vascular puncture or nerve injury.¹⁵

Intraoperative considerations

Positioning the patient

Most foot and ankle surgeries can be performed in the supine position without any further supports. The patient can be positioned semirecumbent for comfort.

Occasionally the patient may need to be positioned laterally or semilaterally with a sandbag under the lower lumbar region. Additional calf region supports in the form of a rigid block may be required. Care should be taken to avoid pressure over the popliteal fossa and the surgical neck of the fibula to avoid nerve injury. Occasionally, surgical access may require prone positioning. Regional anaesthesia enables the patient to position themselves with assistance to find the most comfortable position.¹⁶

Tourniquet management

Thigh, calf or ankle tourniquets are frequently requested. Although most foot surgery can be performed without a tourniquet, haemostasis can be achieved through careful use of electrocautery.¹⁷

Thigh tourniquets are the most efficient at reducing blood flow to the foot and ankle region but require a pressure of approximately 100 mmHg greater than systolic arterial pressure.¹⁸ Thigh tourniquet pain can be managed by providing general or spinal anaesthesia or rarely by proximal blockade of sciatic, femoral and obturator nerves.¹⁹

Calf tourniquets can be used after popliteal sciatic and saphenous blocks in awake patients. Surgeons may not prefer this as cuff pressure on the calf muscles may distort the anatomy and reduce the range of foot movement. In addition, sub-optimal compression of tissue between tibia and fibula makes this tourniquet position less effective than the thigh position.

A small ankle tourniquet placed just proximal to the malleoli provides a good alternative for foot surgery with adequate efficacy and excellent patient tolerance without the need for additional proximal peripheral nerve blocks.²⁰ When using an ankle or calf tourniquet, it is important for the surgeon to exsanguinate before tourniquet inflation to limit venous bleeding.

Meticulous care should be taken when applying a pneumatic tourniquet regardless of position. The underlying skin should be protected, and care taken to avoid any sterilisation liquid migrating beneath the tourniquet. Positioning should also avoid direct pressure to nerves, for example the CFN below the neck of the fibula.

Intraoperative tourniquet pain can be managed with boluses of a short-acting potent opioid or a target-controlled infusion of remifentanil. Some patients may require conversion to general anaesthesia. The provision of regional anaesthetic techniques should not deprive the patient the choice of general anaesthesia after discussion of alternatives and relative risk.

Dexamethasone

The use of intraoperative intravenous dexamethasone may provide several benefits for the patients:

• (i)Prolongation of analgesia after a nerve block.
• (ii)Antiemetic effect.
• (iii)Anti-inflammatory effect.

Postoperative considerations

Non-weight bearing status

Patients may be non-weight bearing for several weeks after foot and ankle surgery and require a risk assessment for deep vein thrombosis and appropriate thromboprophylaxis. A popliteal sciatic nerve block will cause significant motor weakness compared with an ankle block and thus limits weight bearing immediately postoperatively. Patients should be reviewed by the physiotherapy and occupational therapy teams to assess specific needs and provide any required walking aids. In addition to surgical requirements, patients should either be non-weight bearing after a popliteal block until it has worn off, or they should be allowed to mobilise only whilst using a supporting medical boot to avoid accidental injury.

Limb protection

Appropriate patient education is required to prevent the development of pressure area skin breakdown. Nursing staff for in-patients should be familiar with managing patients after regional anaesthesia. Padded heel supports may be required to protect pressure-related tissue ischaemia.

Postoperative pain management

Foot and ankle surgery is associated with significant postoperative pain. Patients that present for these surgeries may have existing chronic pain. Discussion with the acute pain team about complex patients with high daily opioid consumption is required to develop a postoperative pain management plan.

The combination of paracetamol and NSAIDs (if not contraindicated) will be required for most patients. For severe pain, immediate release opioids such as oral morphine sulphate or oxycodone can be prescribed with a specified stop date. The use of modified release opioids is not recommended.^21,22 All patients need to be assessed on an individual basis, and a postoperative pain management plan should be agreed between patient, surgeon and anaesthetist with information passed to the general practitioner after discharge.

Perineural catheters

Perineural catheter infusions of local anaesthetic around the popliteal fossa sciatic or subsartorial saphenous nerves can be used for surgeries that cause severe postoperative pain or where minimising or avoiding the use of strong opioids may particularly benefit patients. Perineural catheters have been managed in the out-patient setting, but logistics of management in terms of inpatient stay, monitoring and follow-up by the acute pain team need careful planning. Training is required to manage catheter delivery systems, and there is an added workload required to troubleshoot problems such as pump failure or disconnections. Catheter management therefore requires a multidisciplinary approach and may not be suited for all clinical settings.

Catheter position can be optimised by accurately visualising the position of the tip during insertion using ultrasound. If the catheter tip is not clear, the position can be assessed by agitating the catheter or by detecting pulsed boluses of fluid with Doppler ultrasound. Placement of catheters for more than 5 days may lead to increased risk of infection and daily review should take place to assess the catheter requirement. Catheter fixation is key to success. Pay meticulous attention to skin preparation, ensuring it is dry and free of blood. Skin glue is useful to secure the catheter but also to occlude the needle insertion point so that there is no leakage of local anaesthetic thus improving efficacy of the infusion.

Subcutaneous tunnelling may help to stabilise the catheter and reduce the risk of infection. Catheter fixation devices may also be used. Take care to protect any catheter dressings placed before surgery from the surgical drapes. Rapid removal of sticky drapes at the end of surgery can cause accidental removal of the catheter.

Declaration of interests

The authors declare that they have no conflicts of interest.

Biographies

Farhaan Moosa FRCA is specialty registrar in anaesthesia who has recently completed a regional anaesthesia fellowship at a centre for major trauma and orthopaedics in the UK.

Nigel Bedforth BMedSci FRCA is a consultant anaesthetist at Nottingham University Hospitals NHS trust and an honorary associate professor at the University of Nottingham. He manages a local regional anaesthesia training programme and has directed an annual national regional anaesthesia course for more than 10 yr.

Anthony Allan BSc FRCA is a consultant anaesthetist with an interest in regional anaesthesia, and acute and chronic pain management using ultrasound-guided block procedures. He has been the director of the Bristol RA-UK cadaveric ultrasound-guided regional anaesthesia course and has taught on a wide range of courses nationally and internationally.

Matrix codes: 1D02, 2G02, 3A09

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