Pain management is a critical part of the recovery process after surgery. Improved postoperative analgesia has benefits for not only patient outcomes but also healthcare costs. Some surgeries come with significant postoperative pain and have benefitted from multimodal analgesia pathways and peripheral nerve blocks. For example, hip and knee surgery are considered among the most painful surgeries, and total hip replacement (THR) and total knee replacement (TKR) constitute the most expensive procedures covered by Medicare in the United States, costing over $6.5 billion in 2013 alone, with annual case numbers expected to continue growing. A key component of early patient discharge lies in the balance between maximizing analgesia and minimizing motor blockade associated with peripheral nerve blocks. Motor-sparing nerve blocks are a relatively recent innovation with much promise for faster recovery.
Motor blockade with traditional peripheral nerve block techniques remains associated with delayed rehabilitation and an increased incidence of patient falls following orthopedic surgery (2). Recently, traditional nerve blocks have been increasingly replaced by motor-sparing alternatives, resulting in enhanced patient recovery without necessarily compromising analgesia. As a result, there is growing interest in selecting and combining motor-sparing peripheral nerve blocks to decrease pain, reduce opioid use, and prevent postoperative motor blockade (2). Although there are various different kinds of motor-sparing nerve blocks, some of the most-commonly used are the pericapsular nerve block (used in hip surgery) and the adductor canal block (used in knee surgery).
In a pericapsular nerve group (PENG) block, the nerves supplying the anterior capsule of the hip (femoral, obturator, accessory obturator nerve) are anesthetized. In a 2022 multicenter, randomized controlled trial, Lin et al. compared postoperative pain scores with PENG block compared with sham (placebo) block in patients receiving local infiltration anesthesia and spinal anesthesia (3). They found a statistically significant difference in patients reporting no pain 3 hrs after surgery with PENG block (47%) versus placebo (20%). In addition, they found no significant difference in the Oxford muscle scale grading between the PENG group versus the placebo group, demonstrating that PENG blockade is truly a motor-sparing nerve block (3). Furthermore, in the setting of hip fracture, a randomized controlled trial comparing the PENG block to the femoral nerve block (FNB), found a statistically significant difference in pain scores in the postoperative recovery unit with 63% of PENG group patients reporting no pain versus 30% of FNB patients, P = 0.04. This further demonstrates the superior analgesic effects of the PENG block (2).
The adductor canal block (ACB) was first performed as an alternative to femoral nerve block (FNB) for total knee replacement, to preserve motor function (2). In a single-center, randomized controlled trial, Grevstad et al. studied whether ACB or FNB along with local anesthesia could provide enough pain relief to increase rather than lose functional motor strength following total knee replacement. Two hours following the block, the maximum voluntary isovolumetric contraction (MVIC) of the quadriceps muscle relative to preoperative baseline values was tested. As expected, this study demonstrated that patients in the ACB group did not lose any functional motor strength in the postoperative period (4). Interestingly, a meta-analysis of 33 studies by Hasabo et al. compared FNB to ACB with no difference in pain control or opioid consumption at any time point, at rest or with mobilization. However, ACB showed better strength preservation than FNB up to 2 days postoperatively, specifically when measuring muscle strength with manual motor testing. Based on the aforementioned studies, the ACB does not appear to provide better pain control than the FNB, but it is almost certainly superior at preserving motor function and strength.
References
1. Layera S, Aliste J, Bravo D, Saadawi M, Salinas FV, Tran Q. Motor-sparing nerve blocks for total knee replacement: A scoping review. J Clin Anesth. 2021;68:110076. doi:10.1016/j.jclinane.2020.110076
2. Restrepo-Holguin M, Kopp SL, Johnson RL. Motor-sparing peripheral nerve blocks for hip and knee surgery. Curr Opin Anaesthesiol. 2023;36(5):541-546. doi:10.1097/ACO.0000000000001287
3. Lin DY, Brown B, Morrison C, et al. The Pericapsular Nerve Group (PENG) block combined with Local Infiltration Analgesia (LIA) compared to placebo and LIA in hip arthroplasty surgery: a multi-center double-blinded randomized-controlled trial. BMC Anesthesiol. 2022;22(1):252. Published 2022 Aug 6. doi:10.1186/s12871-022-01787-2
4. Grevstad U, Mathiesen O, Valentiner LS, Jaeger P, Hilsted KL, Dahl JB. Effect of adductor canal block versus femoral nerve block on quadriceps strength, mobilization, and pain after total knee arthroplasty: a randomized, blinded study. Reg Anesth Pain Med. 2015;40(1):3-10. doi:10.1097/AAP.0000000000000169
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