Ultrasound Guided Popliteal Fossa Block. Does Blockade Distal to Sciatic Nerve Bifurcation Speed Onset Time? A Prospective, Randomized Trial
Condition: Ankle/Foot Surgery
Study type: Interventional

Summary: 
      Sciatic nerve block is used routinely in ankle and foot surgery. It is applied often by a
      posterior approach at the popliteal fossa, near where the nerve divides into the common
      peroneal and tibial nerves. Due to the size of the sciatic nerve, the largest in the body,
      infiltration of anesthetic and onset of anesthesia can take a significant amount of time.
      This study hypothesizes that selectively blocking both the common peroneal and the tibial
      nerves distal to the bifurcation may result in a faster block onset than blockade of the
      sciatic nerve proximal to its bifurcation.
    

Detailed description: 
      Sciatic nerve block (SNB) has been shown to reduce postoperative pain and opioid
      requirements, as well as improve patient satisfaction after outpatient foot and ankle
      surgery. The sciatic nerve divides into two terminal branches (the common peroneal and tibial
      nerves) in the popliteal fossa. Through these two branches it innervates the entire leg,
      ankle and foot except for the skin over the anterior-medial aspect of the leg, which is
      supplied by the saphenous nerve, a branch of the femoral nerve.

      Many approaches have been described to sciatic nerve blockade. High in the thigh or buttock
      are the classical posterior approach, the supine approach, and the anterior approach. In the
      popliteal fossa, a posterior, a lateral and a medial approach have been described. The
      popliteal fossa approaches are most commonly used to provide regional anesthesia and/or
      analgesia for major foot and ankle surgery.

      Traditional nerve localization techniques include seeking paresthesiae on needle to nerve
      contact, or alternatively seeking a muscle response to electrical nerve stimulation using a
      blunt insulated needle and a peripheral nerve stimulator. However, block results with
      traditional nerve localization techniques are highly variable, often requiring high local
      anesthetic doses, and a prolonged onset time. When a distal approach in the popliteal fossa
      is used (5-7 cm above the knee crease) with a nerve stimulator technique, a double motor
      response (both tibial and peroneal components) may be required to achieve consistent success.

      Recently, ultrasound guided techniques for SNB at the popliteal fossa have been described.
      Ultrasound guidance offers the unique advantages of real time anatomic assessment of the
      sciatic nerve itself, its site of bifurcation, and its relationship to surrounding muscles
      and the popliteal vessels. In a recent study we have shown that ultrasound guidance
      significantly improves the success rate of SNB at the popliteal fossa via a posterior
      approach.

      Despite these advantages, a prolonged onset time for complete blockade of up to 30-60 minutes
      (depending on the choice and dose of local anesthetic) is common. This may be a limitation to
      the widespread use of popliteal sciatic nerve blockade in a peri-operative environment, where
      a faster block onset may be preferable. This delayed onset has been attributed to the large
      size of the sciatic nerve. Therefore logically it should be faster to induce a block by
      depositing the local anesthetic after the sciatic nerve divides where the connective tissues
      decrease and the nerves are superficial. No exact mathematical data is available looking into
      onset times for nerves with varying diameter, as no previous studies are done in this area.
    

Intervention name(s): Sciatic nerve blockade for ankle/foot surgery
Intervention type(s): Procedure
Intervention description(s): Injection of local anesthetic near the nerve to achieve anesthesia.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Triple (Participant, Investigator, Outcomes Assessor)
Primary purpose: Treatment
Keywords: ultrasound-guided regional anesthesia; nerve block; popliteal fossa; sciatic nerve; common peroneal nerve; tibial nerve; onset time; ankle surgery; foot surgery