This double-blinded randomized-controlled trial shows that the PENG block significantly reduces short-term postoperative pain in elective THA when spinal anaesthesia and LIA are used. (p = 0.03). The direct postoperative analgesic advantage of the PENG block in this setting does not remain after surgery on Day 1.
Regional analgesia in THA has traditionally been performed using a femoral nerve or fascia iliaca block. Although partially effective, these blocks result in a decrease in muscle strength. Since the PENG block affects only the articular branches of the femoral and accessory obturator nerves, it is believed to achieve adequate analgesia while also preserving motor function and muscle strength. In the current study, postoperative quadriceps muscle strength was similar in both groups. This allows patients to mobilize early following surgery, which, in itself is associated with fewer complications, shorter length of hospital stay and lower mortality.[27–29] Patients who received the PENG block were thus able to mobilize as soon as the sham group patients, with less pain.
The motor sparing effect is consistent with previous studies focused on anatomy suggesting that the PENG block targets the articular branches of the femoral, obturator, and accessory obturator nerves. It must be mentioned that on Day 0 and Day 1, respectively seven and six PENG patients did experience reduction in quadriceps muscle strength, however, this incidence was similar in the sham group (6 and 7 patients respectively; p = 0.24 and p = 0.75). This could reflect a reluctance to actively move the newly operated hip, or possible spread from the LIA to the femoral nerve, consistent in both groups. Notably, no adverse events directly related to block placement were reported and patient satisfaction was similar across both groups.
A variety of PROMs and outcome measures were used with the aim to objectively quantify possible recovery benefits of the PENG block. Preoperative patient PROMs, quantified using the Pain Catastrophizing Scale, PROMIS anxiety and depression item banks, were all similar between groups. Postoperative PROMs, quality of recovery and the Timed Up-and-Go tests were also similar. This could possibly be due to the timing of these tests on Day 1 postoperatively, after the analgesic effect of the PENG block had finished. A recent RCT comparing PENG to sham in combination with intra-articular injection also showed only short term benefit, without differences in longer term outcomes.
The similar opiate use in both groups, despite a difference in pain scores, may be due to the advanced age of the included patients and their low baseline opiate use. It is also important to note that the study was not powered to detect a difference in opiate use nor in PROMs between both groups, for which larger studies will be required to investigate this in the future.
Some limitations have to be addressed. As indicated above, this trial was conducted on a relatively small number of patients and could not identify differences in secondary outcomes. However, it was powered on the primary outcome, showing a significant difference between both groups.
Quadriceps strength was measured by a blinded clinician. A standardised dynamometric measurement tool would have been more accurate, but this was not available. We recognise that this makes the secondary outcome less reliable due to interobserver variation, but have addressed this by grouping the intermediate scores together.
Due to the standardized spinal anaesthesia in the study protocol, 11% (8/75) patients approached, chose not to participate, potentially inflicting some selection bias. However, randomization took place after inclusion to reduce this bias. In the future, a next randomized-controlled trial to further investigate the efficacy of PENG block in THA patients could therefore be in patients having either spinal or general anesthesia.
BMC Anesthesiol. 2022;22(252) © 2022 BioMed Central, Ltd.