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
- Insert the needle in-plane, from the anteromedial aspect of the knee, toward the space between the popliteal artery and femur.
- 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.