Evaluating Proximal vs Distal IPACK Techniques: A Step-by-Step Sonographic Guide and Anatomical Considerations

: The infiltration between the popliteal artery and the capsule of the knee (IPACK) block is a motor-sparing regional anaesthetic technique that provides analgesia to the posterior knee capsule by targeting sensory articular branches of the tibial, sciatic, common peroneal, and obturator nerves. It is commonly used as part of multimodal analgesia for total knee arthroplasty, cruciate ligament surgery, and other knee procedures, with its clinical effectiveness and safety depending on accurate identification of posterior knee sono-anatomy. This narrative educational review aims to provide a detailed, anatomy-focused sonographic guide to standardise identification of key posterior knee structures relevant to the safe and effective performance of both proximal and distal IPACK block techniques. The review synthesises current knowledge of posterior knee sono-anatomy, procedural considerations, and available clinical evidence. Ultrasound-guided IPACK techniques are described, including patient positioning, probe orientation, identification of sono-anatomical landmarks, needle trajectories, and expected patterns of local anaesthetic spread for proximal and distal approaches. Particular emphasis is placed on anatomical relationships critical for safe needle placement, avoidance of vascular and neural injury, and optimisation of posterior capsular analgesia, with comparison between proximal and distal techniques. Consistent sonographic identification of the femur–popliteal artery interval and adjacent neural structures is essential for reliable IPACK performance. Evidence from existing clinical studies suggests that both proximal and distal approaches provide effective posterior knee analgesia, although the proximal technique may offer more consistent visualisation and a lower risk of unintended motor blockade. Clarifying and standardising relevant posterior knee sono-anatomy may enhance anatomical understanding, improve technical accuracy, and support safer, more effective application of the IPACK block within multimodal perioperative analgesia for knee surgery.