BLOCK AT A GLANCE
Infiltration of the local anesthetic into the space between the popliteal artery and the posterior capsule of the knee (iPACK).
Indications: Analgesia after knee arthroplasty, cruciate ligament repair, and procedures involving the posterior aspect of the knee
Goal: Local anesthetic infiltration over the posterior aspect of the femur underneath the popliteal artery
Local anesthetic volume: 15 to 20 mL
Postoperative pain following total knee arthroplasty (TKA) is mediated by branches of the obturator (medial), femoral (anterior), and sciatic nerves (posterior). While the sciatic nerve block results in the best analgesia for the posterior aspect of the knee, motor weakness of the lower extremity preventing early rehabilitation and masking intraoperative common peroneal nerve (CPN) injury discourage the use of this analgesic modality. A muscle strength-sparing infiltration into the interspace between the popliteal artery and the posterior capsule of the knee (iPACK) is an alternative analgesic supplement to the femoral or adductor canal blocks for posterior knee pain. The iPACK block targets the sensory articular branches of the sciatic nerve while sparing the motor branches of the tibial nerve (TN) and CPN, avoiding the foot drop that occurs with the sciatic nerve block.
Limitations and Specific Risks
The iPACK block provides analgesia limited to the posterior aspect of the knee capsule, and therefore it should be viewed as a supplement to the femoral and/or adductor canal block. Additionally, ultrasound (US) imaging of the popliteal vessels and sciatic nerve to avoid their injury during iPACK can be difficult in obese patients.
The specific risks related to this technique are vascular injection or inadvertent nerve injury due to the proximity of the popliteal vessels and the sciatic nerve to the posterior knee capsule, where the needle passes during the infiltration. With the medial-lateral needle insertion technique, the saphenous nerve may be on the way and can be injured. Routine ultrasonographic identification of the nerve is recommended to determine the safe needle insertion site and pathway.
Innervation of the posterior knee is provided by articular branches that originate from the TN, CPN, sciatic, and the posterior division of the obturator nerve (Figure 31-1).
Anatomy of the anterior and posterior knee joint innervation.
Articular branches from the TN are the main source of innervation to the posterior knee joint capsule. They originate either proximal or distal to the superior border of the medial femoral condyle and course transversely to the intercondylar region, where they further branch.
The articular branches from the sciatic and/or the CPN further divide into anterior and posterior branches to innervate the anterolateral and posterolateral capsule, respectively.
Finally, the articular branch from the posterior obturator ...