Comparing Efficacy of Different Methods for Postoperative Analgesia in Patients Undergoing Total Knee Arthroplasty: Several Issues Need Special Attention

By a randomized, double-blind, placebo, parallel, and controlled study including 80 patients who underwent unilateral primary total knee arthroplasty (TKA), Li et al[1] assessed the benefits of combining the femoral triangle block (FTB) and the interspace between the popliteal artery and the capsule of the posterior knee (IPACK) block by comparing with intraarticular cocktail analgesic mixture local injection (ICAMLA). They showed that a combination of FTB and IPACK block significantly increased postoperative quadriceps strength, with an improved early postoperative pain control and reduced consumptions of intraoperative anesthetics and postoperative morphine for pain control. Given that the use of nonopioid or opioid-sparing multimodal analgesia protocol to improve postoperative pain control is being emphasized in current practice of enhanced recovery after surgery (ERAS) protocols,[2] their findings have clinical implications. Other than the limitations described in discussion, however, there are several issues in method and results of this study that need further clarification and discussion.

First, this study did not include a sample size evaluation, though it is a crucial content in designing a randomized controlled trial for preventing the type I and type II statistical errors.[3] Furthermore, the authors did not clearly describe the expected minimal clinically important difference of primary end point between the groups. Because of these limitations, we argue that primary findings of this small sample study must be interpreted with caution.

Second, the visual analogue scale (VAS) scores of resting and active pain at nearly all time points after surgery were significantly higher in patients receiving the ICAMLA compared with those receiving a combination of FTB and IPACK block. We would like to remind the readers that for patients undergoing TKA, the recommended minimal clinically important difference of postoperative pain score is 1.5 at rest state and 1.8 during motion on a 0–10 pain scale.[4] In this study, other than VAS scores of resting pain at postoperative 2 hours, the between-group differences in mean VAS scores of resting and active pain at all other time points did not exceed the above recommended minimal clinically important differences. Furthermore, a VAS pain score of more than 3 is generally considered as an unsatisfactory postoperative pain control.[2] We noted that mean VAS scores of active pain postoperatively until the 12-hour mark in the two groups were more than 4.5, indicating that significant proportion of patients experienced moderate to severe active pain. This is evidently not conducive to early postoperative activity and functional exercise, which are important components of ERAS protocols for patients with TKA.[5] Most importantly, this study did not assess and compare patient satisfaction with postoperative pain control. In this case, it is difficult for readers to determine whether improvement of postoperative pain control with a combination of FTB and IPACK should be considered as being clinically important.

Third, total morphine consumption for postoperative pain control was significantly decreased in patients receiving a combination of FTB and IPACK block compared with those receiving ICAMLA. However, the between-group difference of mean morphine consumptions did not exceed the recommended minimal clinically important difference, i.e., an absolute reduction of 10 mg intravenous morphine in 24 hours.[4] Thus, we questioned the clinical significance of this small opioid sparing with a combination of FTB and IPACK block.

Finally, this study assessed the range of keen motion, quadriceps strength, the occurrence of postoperative complications and length of hospital stay, but it did not evaluate the quality of postoperative recovery, as performed in other studies assessing postoperative benefits of nerve blocks in patients undergoing TKA.[6] [7] As a quality outcome of ERAS protocols, the quality of postoperative recovery is very important for determining efficacy and clinical availability of an intervention for postoperative pain control[2] and is very easily measured by a comprehensive QoR-15 score ranging from 0 to 150, with a higher score indicating an improved quality of postoperative recovery.[8] Thus, we believe that this study would have provided more useful data regarding clinical values of a combination of FTB and IPACK block in patients with TKA, if the design had included the assessment on the quality of recovery.

Publication History

Received: 16 February 2022

Accepted: 26 April 2022

Article published online:
10 June 2022

• References

• 1 Li X, Wang Y, Chen Y. et al. Comparison of femoral triangle block in combination with IPACK to local periarticular injection in total knee arthroplasty. J Knee Surg 2022; (e-pub ahead of print) DOI: 10.1055/s-0041-1741395.
• 2 Mancel L, Van Loon K, Lopez AM. Role of regional anesthesia in enhanced recovery after surgery (ERAS) protocols. Curr Opin Anaesthesiol 2021; 34 (05) 616-625
• 3 Greene T. Randomized controlled trials 5: determining the sample size and power for clinical trials and cohort studies. Methods Mol Biol 2015; 1281: 225-247
• 4 Laigaard J, Pedersen C, Rønsbo TN, Mathiesen O, Karlsen APH. Minimal clinically important differences in randomised clinical trials on pain management after total hip and knee arthroplasty: a systematic review. Br J Anaesth 2021; 126 (05) 1029-1037
• 5 Kumar L, Kumar AH, Grant SA, Gadsden J. Updates in enhanced recovery pathways for total knee arthroplasty. Anesthesiol Clin 2018; 36 (03) 375-386
• 6 Kanadli H, Dogru S, Karaman T. et al. Comparison of the efficacy of femoral nerve block and fascia iliaca compartment block in patients with total knee replacement. Minerva Anestesiol 2018; 84 (10) 1134-1141
• 7 Wang Q, Hu J, Zeng Y, Li D, Yang J, Kang P. Efficacy of two unique combinations of nerve blocks on postoperative pain and functional outcome after total knee arthroplasty: a prospective, double-blind, randomized controlled study. J Arthroplasty 2021; 36 (10) 3421-3431
• 8 Stark PA, Myles PS, Burke JA. Development and psychometric evaluation of a postoperative quality of recovery score: the QoR-15. Anesthesiology 2013; 118 (06) 1332-1340