iPACK Block
Indications: Analgesia for posterior knee procedures including ACL reconstruction, MPFL repair, and total knee arthroplasty. Most commonly used in conjunction with adductor canal and genicular blocks to provide motor-sparing, circumferential analgesia.
Special Considerations
Avoid lateral or deep spread to prevent sciatic nerve involvement and foot drop. Ultrasound-guided injection under general or neuraxial anesthesia is recommended. Pediatric volumes should be carefully titrated to size.
Coverage
Posterior knee: articular branches of tibial, common peroneal, and obturator nerves.
Potential Complications
Foot drop (due to spread to sciatic branches)
Vascular injury (popliteal artery/vein)
Local anesthetic systemic toxicity (LAST)
Infection
Bleeding
Dose: 0.5 - 1.5mg/kg of Bupivacaine or Ropivacaine (roughly 0.1 - 0.3mL/kg). Max 15 -20 mL total.
Patient Positioning & Probe Orientation:
Supine position, knee slightly flexed or frog-legged
Probe placed posteriorly over distal femur
Anatomy of the IPACK:
Femoral condyles, femur, muscles, popliteal artery and vein
Lateral border: femur anterior to the popliteal artery
Anterior border: posterior aspect of the femur
Medial border: medial edge of the femur
Technique:
The IPACK is essentially a field block of the terminal genicular branches of the posterior knee. Scanning is performed along the femur to find the posterior view of the femoral condyles. The probe is translated proximally until the condyles disappear from view and the femur is seen as a flat hyperechoic line.
The needle is advanced in-plane to make contact with the femur proximal to the knee joint on the medial aspect of the popliteal artery. Local anesthetic is deposited along the femur taking care not to deposit local anesthetic lateral to the popliteal artery so as to avoid sciatic nerve involvement and a foot drop.
The iPACK block (first described by Thobhani in 2017) was designed to spare distal motor function while providing posterior knee analgesia in total knee arthroplasty. Cadaveric studies (Niesen, Tran) showed consistent spread to articular branches and the middle genicular artery without major nerve involvement when performed correctly.
While adult evidence is robust, pediatric data are limited. PRAN does not categorize iPACK separately, reflecting the block's novelty in younger patients. The SPAIN-ACL trial (71 patients) is the largest pediatric series but lacks anesthetic concentration or volume detail. At HSS, over 1,100 pediatric iPACK blocks have been performed since 2021 for ACL and MPFL surgeries. Technique is practitioner-dependent but commonly involves ultrasound guidance, neuraxial or general anesthesia, and 0.25% bupivacaine with dexamethasone. Volume is scaled to size (10–20 ml).
Proximal vs distal approach is under investigation:
Distal (at femoral condyles): More anterolateral spread
Proximal (1 cm above patella): More consistent anteromedial spread
Pediatric
Sadacharam, K. , Mandler, T. , Staffa, S. , Pestieau, S. , Fuller, C. , Ellington, M. , Sparks, J. & Fernandez, A. (9900). Regional Anesthesia and Pain Outcomes After Anterior Cruciate Ligament Reconstruction Surgery in Pediatric Patients: Society of Pediatric Anesthesia Improvement Network. Anesthesia & Analgesia, Publish Ahead of Print , doi: 10.1213/ANE.0000000000007376.
Govender-Davies S, Davies L, Pillay-Addinall S. A cadaveric study investigating the spread of injectate following an interspace between the popliteal artery and the capsule of the posterior knee block in a neonatal sample: a pilot study. Anat Cell Biol. 2024 Jun 30;57(2):229-237. doi: 10.5115/acb.23.274. Epub 2024 Mar 29. PMID: 38551026; PMCID: PMC11184435.
Nguyen KT, Marcelino R, Jagannathan N, Suresh S, Sawardekar A. Infiltration Between Popliteal Artery and Capsule of the Knee Block to Augment Continuous Femoral Nerve Catheter for Adolescent Anterior Cruciate Ligament Reconstruction: A Case Series. A A Pract. 2020 Jan 15;14(2):37-39. doi: 10.1213/XAA.0000000000001135. PMID: 31770127.
Wagner KJ 3rd, Beck JJ, Carsen S, Crepeau AE, Cruz AI Jr, Ellis HB Jr, Mayer SW, Niu E, Pennock AT, Stinson ZS, VandenBerg C, Ellington MD. Variability in Pain Management Practices for Pediatric Anterior Cruciate Ligament Reconstruction. J Pediatr Orthop. 2023 Apr 1;43(4):e278-e283. doi: 10.1097/BPO.0000000000002344. Epub 2023 Jan 9. PMID: 36728478.
Schlechter JA, Gornick BR, Harrah T, Sherman B. Do Continuous Peripheral Nerve Blocks Decrease Home Opioid Use Following Anterior Cruciate Ligament Reconstruction in Children and Adolescents? The Envelope Please. J Pediatr Orthop. 2022 Apr 1;42(4):e356-e361. doi: 10.1097/BPO.0000000000002082. PMID: 35132012.
Markiewitz ND, Swarup I, Talwar D, Muhly WT, Wells L, Williams BA. Perioperative pain management practices vary across time and setting for pediatric ACL reconstruction: trends from a national database in the United States. Orthop J Sports Med. 2022;10:23259671211068831.
Malige A, Bram JT, Maguire KJ, McNeely LW, Ganley TJ, Williams BA. Decreased prescribing of postoperative opioids in pediatric ACL reconstruction: treatment trends at a single center. Orthop J Sports Med. 2021;9:2325967120979993.
Daoud AK, Mandler T, Gagliardi AG, et al. Combined femoral-sciatic nerve block is superior to continuous femoral nerve block during anterior cruciate ligament reconstruction in the pediatric population. Iowa Orthop J. 2018;38:101–106.
Santana L, Lovejoy JF, Kiebzak G, Day J, Atanda A Jr, Mandel D. Comparison of pain scores and medication usage between three pain control strategies for pediatric anterior cruciate ligament surgery. Cureus. 2019;11:e5498.
Walker BJ, Long JB, Sathyamoorthy M, et al.; Pediatric Regional Anesthesia Network Investigators. Complications in pediatric regional anesthesia: an analysis of more than 100,000 blocks from the Pediatric Regional Anesthesia Network. Anesthesiology. 2018;129:721–732.
Luo TD, Ashraf A, Dahm DL, Stuart MJ, McIntosh AL. Femoral nerve block is associated with persistent strength deficits at 6 months after anterior cruciate ligament reconstruction in pediatric and adolescent patients. Am J Sports Med. 2015;43:331–336.
Muhly WT, Gurnaney HG, Ganesh A. Regional anesthesia for pediatric knee surgery: a review of the indications, procedures, outcomes, safety, and challenges. Local Reg Anesth. 2015 Nov 5;8:85-91. doi: 10.2147/LRA.S73458. PMID: 26609245; PMCID: PMC4644165.
Adult
Albrecht E, Wegrzyn J, Dabetic A, El-Boghdadly K. The analgesic efficacy of iPACK after knee surgery: A systematic review and meta-analysis with trial sequential analysis. J Clin Anesth. 2021 Sep;72:110305. doi: 10.1016/j.jclinane.2021.110305. Epub 2021 Apr 28. PMID: 33930796.
Hussain N, Brull R, Vannabouathong C, Speer J, Lagnese C, McCartney CJL, Abdallah FW. Network meta-analysis of the analgesic effectiveness of regional anaesthesia techniques for anterior cruciate ligament reconstruction. Anaesthesia. 2023 Feb;78(2):207-224. doi: 10.1111/anae.15873. Epub 2022 Nov 3. PMID: 36326047.
Martin R, Kirkham KR, Ngo THN, Gonvers E, Lambert J, Albrecht E. Combination of femoral triangle block and infiltration between the popliteal artery and the capsule of the posterior knee (iPACK) versus local infiltration analgesia for analgesia after anterior cruciate ligament reconstruction: a randomized controlled triple-blinded trial. Reg Anesth Pain Med. 2021 Sep;46(9):763-768. doi: 10.1136/rapm-2021-102631. Epub 2021 May 26. PMID: 34039734.
Sinha, S.K., Clement, A. & Surette, AM. Infiltration Between the Popliteal Artery and Capsule of the Knee (iPACK): Essential Anatomy, Technique, and Literature Review. Curr Anesthesiol Rep 9, 474–478 (2019). https://doi.org/10.1007/s40140-019-00358-5
Abdallah FW, Brull R, Joshi GP, (SAMBA) SfAA. Pain management for ambulatory arthroscopic anterior cruciate ligament reconstruction: evidence-based recommendations from the Society for Ambulatory Anesthesia. Anesthesia and Analgesia 2019; 128: 631-40.
Vorobeichik L, Brull R, Joshi GP, Abdallah FW. Evidence basis for regional anesthesia in ambulatory anterior cruciate ligament reconstruction: part I-femoral nerve block. Anesthesia and Analgesia 2019; 128: 58-65.
Sehmbi H, Brull R, Shah UJ, el-Boghdadly K, Nguyen D, Joshi GP, Abdallah FW. Evidence basis for regional anesthesia in ambulatory arthroscopic knee surgery and anterior cruciate ligament reconstruction: part II: adductor canal nerve block-a systematic review and meta-analysis. Anesthesia and Analgesia 2019; 128: 223-38.
Yung EM, Brull R, Albrecht E, Joshi GP, Abdallah FW. Evidence basis for regional anesthesia in ambulatory anterior cruciate ligament reconstruction: part III: local instillation analgesia-a systematic review and meta-analysis. Anesthesia and Analgesia 2019; 128: 426-37.
Tran J, Giron Arango L, Peng P, Sinha SK, Agur A, Chan V. Evaluation of the iPACK block injectate spread: a cadaveric study. Reg Anesth Pain Med. 2019 May 6:rapm-2018-100355. doi: 10.1136/rapm-2018-100355. Epub ahead of print. PMID: 31061110.
Guo J, Hou M, Shi G, Bai N, Huo M. iPACK block (local anesthetic infiltration of the interspace between the popliteal artery and the posterior knee capsule) added to the adductor canal blocks versus the adductor canal blocks in the pain management after total knee arthroplasty: a systematic review and meta-analysis. J Orthop Surg Res. 2022 Aug 12;17(1):387. doi: 10.1186/s13018-022-03272-5. PMID: 35962410; PMCID: PMC9373358.
Anthony CA, Westermann RW, Bedard N, Glass N, Bollier M, Hettrich CM, Wolf BR. Opioid Demand Before and After Anterior Cruciate Ligament Reconstruction. Am J Sports Med. 2017 Nov;45(13):3098-3103. doi: 10.1177/0363546517719226. Epub 2017 Aug 14. PMID: 28806097.
Hussain N, Brull R, Vannabouathong C, Speer J, Lagnese C, McCartney CJL, Abdallah FW. Network meta-analysis of the analgesic effectiveness of regional anaesthesia techniques for anterior cruciate ligament reconstruction. Anaesthesia. 2023 Feb;78(2):207-224. doi: 10.1111/anae.15873. Epub 2022 Nov 3. PMID: 36326047.
