Technique

Scanning technique

  • Place the transducer transversely over the medial aspect of the knee, approximately 2-3 cm above the patella.
  • Slide the transducer proximally/distally to identify the distal femoral shaft and popliteal artery.

    SmM, semimembranosus muscle; PA, popliteal artery; PV, popliteal vein; TN, tibial nerve; CPN, common peroneal nerve.

TIPS

  • If the femoral condyles are initially visualized, slide the transducer proximally until the condyles disappear, and the femoral shaft is identified.
  • While scanning, routine identification of the saphenous nerve is recommended to avoid its injury during needle insertion.
  • Use color Doppler to facilitate identification of the popliteal vessels.

Needle insertion

  1. Insert the needle in-plane, from the anteromedial aspect of the knee, toward the space between the popliteal artery and femur. 
  2. When the posterior aspect of the popliteal artery is reached, inject 2 mL of the local anesthetic to confirm proper needle position.

    SmM, semimembranosus muscle; StM, semitendinosus muscle; PA, popliteal artery; PV, popliteal vein; TN, tibial nerve; CPN, common peroneal nerve.

TIPS

  • Use a steep angle of needle insertion to always stay close to the femoral shaft. This decreases the risk of popliteal nerves and vessel injury.
  • An adequate spread should layer the local anesthetic in the space between the popliteal artery and femur shaft.

Let’s review the block:

IPACK block; transducer position and sonoanatomy. SmM, semimembranosus muscle; PA, popliteal artery; PV, popliteal vein; TN, tibial nerve; CPN, common peroneal nerve.

IPACK block; Reverse Ultrasound Anatomy. SmM, semimembranosus muscle; StM, semitendinosus muscle; PA, popliteal artery; PV, popliteal vein; TN, tibial nerve; CPN, common peroneal nerve.

Alternative approach

  • Place the transducer over the popliteal fossa crease in order to visualize the tibial nerve, common peroneal nerve, popliteal artery, and femoral condyles.
  • From this location, slide the transducer proximally until the flat posterior aspect of the shaft of the femur becomes visible.
  • Insert the needle in-plane from the medial (or lateral) side, toward the space between the popliteal artery and femur.
  • Inject 1-2 mL of local anesthetic to confirm correct needle position.
  • Complete the block with 15-20 mL.
  • This approach can be performed with the patient either in prone or supine position.

Alternative transducer positions for an IPACK block.