Abstract
Introduction
Regional anesthesia is commonly utilized to minimize postoperative pain, improve function, and allow earlier rehabilitation following Total Knee Arthroplasty (TKA). The adductor canal block (ACB) provides effective analgesia of the anterior knee. However, patients will often experience posterior pain not covered by the ACB requiring supplemental opioid medications. A technique involving infiltration of local anesthetic between the popliteal artery and capsule of knee (IPACK) targets the terminal branches of the sciatic nerve, providing an alternative for controlling posterior knee pain following TKA.
Materials and Methods
IRB approval was obtained, a power analysis was performed, and all patients gave informed consent. Eligible patients were those scheduled for an elective unilateral, primary TKA, who were ≥ 18 years old, English speaking, American Society of Anesthesiologists physical status (ASA PS) classification I-III. Exclusion criteria included contraindication to regional anesthesia or peripheral nerve blocks, allergy to local anesthetics, allergy to nonsteroidal anti-inflammatory drugs (NSAIDs), chronic renal insufficiency with GFR < 60, chronic pain not related to the operative joint, chronic (> 3 month) opioid use, pre-existing peripheral neuropathy involving the operative limb, and body mass index (BMI) ≥ 40 kg/m2.
Patients were randomized into one of two treatment arms: Continuous ACB with IPACK (IPACK Group) block or Continuous ACB with sham subcutaneous saline injection (No IPACK Group). IPACK Group received single injection of 20 mL 0.25% Ropivacaine. Postoperatively, all patients received a standardized multimodal analgesic regimen. The study followed a double-blinded format. Only the anesthesiologist performing the block was aware of randomization status.
Following surgery, a blinded medical assessor recorded cumulative opioid consumption, average and worst pain scores, and gait distance.
Results
72 people were enrolled in the study and three withdrew. There were 35 people in the IPACK group and 34 in the NO IPACK group. There was no difference demographically between the groups. In the Post Anesthesia Care Unit (PACU), the average (P=0.0122) and worst (P=0.0168) pain scores at rest were statistically lower in the IPACK group. There was no difference in the pain scores during physical therapy. (P=0.2080) There was no difference in opioid consumption in the PACU (P=0.7928), at 8 hours (P=0.2867), 16 hours (P=0.2387), 24 hours (P=0.7456), or 30 hours (P=0.8029). There was no difference in pain scores on POD 1 in the AM (P=0.4597) or PM (P=0.6273), nor was there any difference in walking distance (P=0.5197). There was also no difference in length of stay in the PACU (P=0.9426) or hospital (P=0.2141) between the two groups.
Discussion/Conclusion
Overall, pain was well controlled between the two groups. The IPACK group had lower pain scores at rest in the PACU, but this may not be clinically significant. The routine use of the IPACK is not supported by the results of this study. There may be use of the IPACK block as a rescue block or in patients whom have contraindications to our standard multimodal treatment regimen, or in patients with chronic pain or opioid dependence.
