INDICATION
Surgery or analgesia of the lower leg, ankle and foot
e.g. fracture fixation, tibial osteotomy, ankle arthroplasty, club foot repair, tendon transfers/lengthening
The popliteal block is a distal sciatic block that provides sensory and motor block to the whole lower limb below the knee (except for the skin on the medial side of the leg which is innervated by the femoral nerve.
NOTE: In combination with a femoral or adductor canal block, complete anaesthesia of the lower limb can be achieved
Considerations
The tibial compartments can present a risk for compartment syndrome, particularly after trauma. Ensure the risk is recognised and acknowledged, adequate consent and pre-operative counselling of the patient, use low concentration local anaesthetic, avoid additives, and post operative monitoring is essential.
(Compartment Syndrome Guidelines)
Contraindications
See general contraindications for regional anaesthesia
ANATOMY
The sciatic nerve originates from the ventral rami of the lumbosacral plexus (L4-5 and S1-3) and provides sensory and motor innervation to the lower limb. It is the largest nerve in the human body.
In the gluteal region, the sciatic nerve emerges between gluteus maximus and the inner muscle layers and exits the pelvis through the greater sciatic foramen. It then traverses further down the posterior thigh, bordered by the long head of the biceps femoris muscle (lateral and superior border) and the semimembranosus and semitendinosus muscles (medial and superior border). As it approaches the popliteal fossa, it splits into the tibial (anterior division) and common peroneal nerves (posterior division). The bifurcation where both nerves are split but still encased by the sciatic sheath (= Vloka’ssheath) is the target level for the popliteal block and can be identified with ultrasound.
PATIENT POSITION
Lateral decubitus: block side up in extension and non-block side leg flexed underneath for stability - pillow in between legs (preferred position)
Alternative positions
SONOANATOMY
Ultrasound probe selection: linear high frequency probe
At the level of the crease, the sciatic nerve has bifurcated, and the tibial and peroneal nerve will appear as 2 hyperechoic structures with honeycomb patterns in between the biceps femoris (laterally) and semimembranosus and semitendinosus muscles (medially)
NOTE: pressure and tilting the probe caudally will help distinguish the nerves from surrounding tissue
NOTE: active/passive plantar- and dorsiflexion of the ankle may help identifying the nerves as they will be seen moving up and down with the muscular sheath (see-saw sign)
NEEDLING
Use a 50-60mm block needle
Target depth:
Levobupivacaine 0.25% 0.2-0.5ml/kg (max. 15mls)
(+/- clonidine 1mcg/kg for increased duration)
NOTE: for in plane technique: inserting the needle further from the probe (more anteriorly on the thigh) allows for a needle approach that is more parallel to the probe which will improve needle visualisation
When inserting a catheter