Foot and Ankle Surgery

Chris Nixon

RA for foot and ankle surgery

Surgery

Site

Technique

Total ankle arthroplasty Ankle Spinal or Popliteal + Saphenous block
Ankle arthroscopy Ankle Spinal or Popliteal + Saphenous block
Calcaneal fracture Ankle Spinal or Popliteal + Saphenous block
Ankle arthrodesis Ankle Spinal or Popliteal + Saphenous block
Ist metatarsal osteotomy (Bunion

Foot

Post tibial + Deep and Superficial peroneal n
(Saphenous n block  not required)Digital block / Ankle block
Mid foot amputation Foot Pop/Saph or Ankle block
Amputation of toe Foot Digital block or Ankle block

Problems:

Pain control – block wear off
Nerve injury  
Infection

Tourniquet :    Ankle vs thigh.  Risk of ischaemic injury.  Risk of compartment syndrome

Anatomy:

The foot and ankle are supplied by 5 nerves:
The Saphenous N a branch of the femoral nerve; and four branches of the Sciatic nerve, Posterior tibial n, Deep and superficial peroneal nerve and the sural nerve

 

Saphenous nerve (see Adductor canal block)

The saphenous nerve leaves the femoral nerve in the upper third of the thigh and passes down the thigh with the superficial femoral artery between the vastus medialis and adductors. In the mid to lower third of the thigh the Sartorius muscle crosses over the nerve and vasoadductor membrane forming the adductor canal. The distal end of the canal lies between 7 and 11 cm above the patella1. The femoral artery then dives deeper to pass through the adductor canal to the popliteal fossa as the popliteal artery whilst the saphenous nerve passes between Sartorius and Gracilis muscles accompanied by the saphenous branch of the descending geniculate artery (SBDGA) to lie alongside the saphenous vein in the lower leg.   The saphenous nerve is sensory to the skin on the medial side of the leg to the medial malleolus.  Lopez et al 2 demonstrated its distal extent rarely exceeds the mid foot, and is not necessary for bunion surgery.  After dissection of 52 cadavers, Eglitis et al 3 found deep branches of the saphenous nerve innervate the periosteum of the distal tibia and talocrural capsule.

Popliteal Sciatic nerve

The popliteal fossa is a diamond shaped space lying posterior to the knee.  Superiorly it is formed by the diverging semi-membranosis medially and bicpes femoris laterally.  Inferiorly the diamond shape is completed by the medial and lateral heads of gastocnemius muscle.  The floor of the space is formed by the femur superiorly, knee joint capsule and the popliteus muscle. The Sciatic nerve courses down the posterior thigh in the midline and enters the popliteal fossa emerging from under the biceps muscle to lie superficial and lateral to the popliteal artery. As the two course distally the nerve crosses the artery to lie postero-medial to it.  During its passage the sciatic nerve divides into the Tibial and Common Peroneal nerves high up in the popliteal space. Further divisions arise more distally the most notable being the sural nerve postero-medially.   The Common peroneal nerve leaves the midline and heads laterally passing towards the head of the fibula, lying successively on plantaris, gastrocnemius, popliteus tendon and soleus.
The tibial nerve passes distally in the midline in the posterior compartment before padding posterior to the medial malleolus to supple the sole of the foot.

Popliteal fossa sciatic nerve block is a technically straight forward procedure which offers excellent anaesthesia and analgesia for surgery on the knee, leg and foot. When combined with a saphenous nerve block or femoral block, the entire lower leg can be anaesthetised, providing an attractive alternative to neuraxial techniques. In addition, catheter placement is straight forward allowing for extended post-operative analgesia.

Gross anatomy

The sacral plexus is formed by the lumbosacral trunk (L4-5) and the anterior divisions of S1-3. The plexus lies on the back of the pelvis between piriformis muscle and the pelvic fascia. The most important branches for the anaesthetist are the posterior cutaneous nerve of the thigh (L4,5,S1-3) and the sciatic nerve.  The sciatic nerve descends the posterior aspect of the leg and can be found in the subgluteal region midway between the greater trochanter and the ischial tuberosity. It exits the pelvis via the greater sciatic foramen below piriformis and passes under gluteus maximus muscle towards the leg. It lies between the greater trochanter of the femur and the ischial tuberosity. In the upper leg it lies on adductor magnus and crossed obliquely by long head of biceps femoris. The sciatic nerve at this point is a flat ribbon which becomes more round in appearance as it descends down the posterior thigh.  It innervates the muscles of the pelvis and posterior thigh before branching into tibial and peroneal nerves at a variable distance above the knee. These in turn supply most of the sensory and motor innervation of the lower leg and foot. The tibial nerve is the larger of the terminal branches of the sciatic nerve. It descends through the middle of the popliteal fossa to the lower part of popliteus muscle. It then runs with the popliteal artery beneath the soleus arch and into the lower leg. The common peroneal nerve is the smaller of the two branches of the sciatic nerve. It descends to the lateral side of the popliteal fossa towards the head of the fibula and close to the medial margin of biceps femoris. After passing around the neck of the fibula (beneath peroneus longus), it divides into superficial and deep peroneal nerves. The sciatic nerve divides in the subgluteal  region into its two branches, Tibial and Common Peroneal but these are bound together tightly by a paraneural sheath.  In the popliteal fossa  the nerves move apart, and at this point the paraneural sheath is capacious.  A needle introduced between the nerves at their point of separation will penetrate the paraneural sheath and injection of local anaesthetic will surround both nerves. 


Onset times for blocks which penetrate the paraneural sheath are faster (15 vs 23 min) and more successful than those placed outside the sheath.

Sonoanatomy

The sciatic nerve is most easily seen lower in the popliteal fossa after it has split into tibial and peroneal nerves. Here it is in its most superficial position, usually in the middle of the popliteal fossa superficial (posterior) to the popliteal vein and artery. Lateral to the nerves lies the biceps femoris (BF) muscle and medially are semitendinosis (ST) and semimembranosis (SM). As the nerve is traced proximally, the two branches merge to form the sciatic nerve and the nerve becomes more deeply placed beneath the BF muscle.
 

Positioning

We do this block is with the patient in the lateral position, operative side uppermost and facing the anaesthetist. This allows the operator to look down the probe for needle alignment and across the patient to the ultrasound screen. The probe is held comfortably with the probe hand resting on the patient’s leg.

Technique

Place the linear probe on the posterior of the knee at the skin crease, between biceps femoris and semi-membranosis tendons and press firmly. The soft tissues and popliteal vein are compressed and the nerves should be superficial (posterior) to the Popliteal artery.  Angulate the probe to find the nerves (Probe usually perpendicular to the anterior surface of the thigh) then translocate the probe proximally and watch for the Common peroneal (CP) nerve joining the Tibial nerve (TN).  The block is best performed just as the two nerves divide. Passive or active dorsiflexion and plantarflexion of the foot induces the “seesaw sign” with the CP and TN appearing to move up and down like a seesaw. This can help find or confirm the nerves.
Assess depth of the nerves and bring block needle from the lateral side of the knee at the same or slightly greater depth below the probe so it will appear horizontal on the screen with very good imaging. The CP is lateral and more superficial to the TN so the needle can pass under the CP and into the space between the two.  Careful angulation allows the needle to access this space. A pop is usually felt as the needle exits biceps femoris and enters the popliteal fossa. Once the needle is in the popliteal fossa, inject 1ml of LA and assess spread. Using hydrodissection and needle repositioning inject up 15-30ml around the nerves.  Always aspirate before injection to ensure popliteal vessels have not been entered.  The  block onset  takes 23-30 mins.  Faster onset probably implies intraneural injection.

 

Tips:
1. Probe hand should rest on the patients leg to secure probe position
2. Make sure you avoid the Popliteal vein which is compressed by the probe and may not be visible.
3. Aim for paraneural injection  between the two nerves.  The Tibial is the more important.
4. Look for spread around the nerves

Dose
15-20ml    Tabaoda  Anesth Analg 2006;102:593

 

Ankle block

5 nerves provide the neural supply to the ankle.  It is not necessary to block all five for all cases but several injections are usually required which may be painful.  Give fentanyl +/- midazolam before the block.

Post tibial nerve

This nerve supplies the plantar surface of the foot via the medial and lateral plantar nerves. The lateral border of the heel is suppliesd by the sural nerve.  It can be found behind the medial malleolus lying posterior to the post tibial artery and then the probe is moved proximally 10cm where it remains lateral to the PT artery  and its accompanying veins, and between the flexor digitorum longus and soleus muscles. This allows the probe to rest nicely on the skin without probe artefact. Using an in-pane or out of plane technique  5 mls  of LA is injected around the nerve.  As this is the largest of the nerves to be blocked it is best blocked first to allow time for block onset.

Saphenous nerve

May be blocked in the adductor canal, or below the knee adjacenet to the long saphenous vein.  Variable supply of the medial side of the ankle but never distal to the mid foot.   Required in only 4% of foot surgery.  Scan over the anterior-lateral aspect of the tibia and identify the saphenous vein.  The nerve usually lies on the lateral side of the vein.  If the nerve can’t be identified inject 2-3 ml LA around the vein.

Superficial peroneal nerve

This nerve supplies the dorsum of the foot from the great toe to fourth toe excluding the first webspace.  Scan lower fibula then move and identify the Extensor Digitorum longus m. (EDL) anteriorly and Peroneus brevis m. posteriorly with peroneus longus tendon overlying it.  As the probe moves up the leg from the ankle the fibula becomes deeper and the muscle bellies oppose each other. The superficial peroneal nerve lies superficially between these two muscles distally and it dives under the fascia and deeper as it ascends the leg, now lying between EDL and peroneus longus muscle. It is easily blocked using an in-plane technique with 2 -5ml LA.

Deep peroneal nerve

Supplies the first webspace on the dorsum of the foot.  Trace the probe proximally from the anterior surface of the tibia. Identify the anterior tibial artery and veins.  The DPN is usually lateral to the artery and more proximally is anterior then lateral again. As the probe is moved from proximal to distal the nerve can be seen moving from lateral to anterior to lateral of the artery.  Using an In plane approach from the lateral side of the probe inject 2-4 ml around nerve.


Sural nerve

Supplies the lateral posterior calf and lateral boder of the foot. Start over the fibula and scan posteriorly over peroneus brevis toward the Achilles tendon . Between these the short saphenous vein can be identified with the nerve lying deep and posterior to it. As the probe is moved proximally the nerve will come to lie anterior to the Achilles tendon.  Place LA 2-3ml around nerve.

References

Perlas A, Brull R, Chan VWS, McCartney CJL, Nuica A, Abbas S.  Ultrasound guidance improves the success of Sciatic Nerve Block at the Popliteal Fossa.  Reg Anaes Pain Med 2008;33:259-265   (NS endpoint questioned by Alain Borgeat)

Andersen HL, Andersen SL, Tranum-Jensen J.  Injection inside the Paraneural sheath of the Sciatic Nerve.  Reg Anaesth Pain Med  2012;37:410-414
Manickam B, Perlas A, Duggan E, Brull R, Chan VWS, Ramlogan R.  Feasibility and Efficacy of Ultrasound guided block of the Saphenous Nerve in the Adductor Canal.  Reg Anaes Pain Med 2009;34:578-580

Perlas A, Wong P, Abdullah F, Hazrati L_N, Tse C, Chan V.  Ultrasound guided popliteal block through a common paraneural sheath versus conventional injection.   Reg Anaes Pain Med 2013;38:21

Monahan AM et al.    Continuous Popliteal Sciatic Blocks; Does varying perineural catheter location relative to the sciatic bifurcation influence block effects? A dual-center randomized, sunject-masked controlled clinical trial.     Anesth Analg 2016;
- Catheter insertion 5cm proximal to the bifurcation provides superior postoperative analgesia in marked contrast with single-injection popliteal sciatic nerve blocks where distal is better than proximal.

Lopez AM et al.  Ultrasound guided ankle block for forefoot surgery –the contribution of the saphenous nerve.  Reg Anaes Pain Med 2012;37:554-557
-   Ultrasound guided ankle block is highly effective for bunion surgery. The sensory territory of the saphenous nerve seems to only extend to the midfoot.  97% of patients for bunion surgery would not benefit from a Saphenous n block.

CONTACT

Administrative contact

Please contact Karen Patching -
Desk phone: +64 (0) 9 375 7085
Email: karenp@adhb.govt.nz

c/- Department of Anaesthesia & Perioperative Medicine
Level 8 - Support Building, Auckland City Hospital
PO Box 92024, Auckland, New Zealand