Retrospective Investigation of Post-operative Opioid Consumption and Pain Scores after Pericapsular Nerve Group (PENG) Block in Elective Hip Arthroplasty, Elective Hip Resurfacing and Hip Fracture Surgery

The number of Canadians requiring elective hip arthroplasties and hip resurfacing for hip osteoarthritis has increased by 20.1% over the last 5 years (CIHI 2020). In 2018-2019, over 62,000 hip replacements were performed in patients 65 years and older (65.7%) with 99% of these patients requiring at least an overnight stay in hospital (CIHI 2020). The estimated total inpatient cost in Canada per hip replacement surgery was over $11,600 excluding rehabilitation (CIHI 2020). Adequate analgesia after primary elective total hip replacement reduces adverse side effects such as postoperative delirium (Aziz et al. 2018; Morrison et al. 2003) which is a risk factor for increased hospital length of stay and perioperative complications such as death (Lalmohamed et al. 2014), functional decline (Jankowski et al. 2011) and cognitive decline (Saczynski et al. 2012; Bin Abd et el. 2015). Similarly, the number of Canadians requiring emergency hip fracture surgery secondary to falls from a combination of osteoporosis, fragility, loss of muscle mass and strength was 146.6 per 100,000 in 2015- 2016 (Public Health Agency of Canada 2021). Hip fractures are the most common type of fracture in Canadians aged 80 and older (Public Health Agency of Canada 2021) and are associated with a substantial economic cost accounting for $2.3 billion or 1.3% of the Canadian healthcare budget in 2008 (CIHI 2010). The incidence of postoperative delirium is high with hip fracture, especially for elderly patients and patients with a history of delirium (Xu et al. 2021). As with elective hip arthroplasty, postoperative delirium is a risk factor for increased length of stay in hospital and complications such as death, functional and cognitive decline (Morrison et al. 2003). In this elderly patient population, effective perioperative multi-modal analgesia is not only necessary but essential to minimize the overall need for opioids and thereby limiting adverse effects such as respiratory depression, pruritis, nausea and vomiting and postoperative delirium (Morrison et al. 2003) in the intraoperative and postoperative period. There are multiple regional anesthetic techniques reported in the literature to aid in multi-modal analgesia such as femoral nerve (FN) block, fascia iliaca block (FIB), iliopsoas plane block (IPB) and the pericapsular nerve group (PENG) block, all of which have been used to reduce opioid consumption and opioid-related adverse effects (Unneby et al. 2017; Foss et el. 2007; Beaudoin et al. 2013; Nielsen et al. 2020; Giron-Arango et al. 2018). The FN block and the FIB do not cover the obturator nerve and hence the analgesic effect from these blocks has been moderate at best (Guay et al. 2017; Marhofer et al. 2000; Swenson et al. 2015). The newly described IPB targets the hip articular sensory branches of the femoral nerve without causing motor blockade (Nielsen et al. 2020). Similarly, the PENG block, specifically targets sensory branches of the obturator, accessory obturator, and femoral nerves in the anterior capsule of the hip and is thought to provide more complete analgesia by depositing local anesthetic within the myofascial plane of psoas muscle and superior pubic ramus (Giron-Arango et al. 2018). The PENG block can target higher branches of the femoral nerve proximal to the inguinal ligament which make it more prone to inadvertent quadriceps weakness (Yu et al. 2019) especially when the full 20 ml volume of local anesthetic is used as originally described (Endersby et al. 2020). A cadaveric radiological evaluation of the PENG block in prosthetic hip replacement showed the diffusion pattern of the PENG block not only to the anterior articular capsular branches of the femoral nerve, obturator nerve and accessory obturator nerve but also to the joint space through the communicating foramen between the synovial space and serous bursa of the iliopsoas thus directly reaching the joint surface (Altinpulluk et al. 2020). A few relatively small single center studies are suggesting that the PENG block is efficacious as an opioid sparing technique for hip surgery. The PENG block has shown to improve short term analgesia when compared with the FN block in a small (n=60) single center double blinded randomized control trial for hip fracture surgery (Lin et al. 2021). A retrospective single institution cohort study showed that patients who underwent elective hip arthroplasty with a PENG block (n=47) had a 2.4 mg reduction in 24h hydromorphone consumption, however there was no impact on length of stay or pain scores with rest or activity (Mysore et al. 2020). Another retrospective single institution cohort study showed that patients who underwent primary elective total hip arthroplasty with a PENG block placed postoperatively (n=48) had a shorter length of stay in hospital, walked farther distance initially postoperatively, required less opioids on postoperative day (POD) #1/POD #2/cumulatively over the entire stay and had lower mean cumulative pain scores until the 48 hour mark (Remily et al. 2020). Unfortunately, these patients also received a FIB along with the spinal anesthetic so the outcomes reported may not solely be as a result of the PENG block. The primary objective of this present study is to examine whether the PENG block reduces total opioid consumption in the post-operative period at 6, 12, 24 and 48 hrs after elective hip arthroplasty, elective hip resurfacing and emergency hip fracture surgery at our institution. The secondary outcomes of this study are to investigate if the PENG block reduces post-operative pain scores at rest and with movement, time to ambulation, distance ambulated, time to hospital discharge and complications including the incidence of nausea/vomiting requiring an anti-emetic, pruritis requiring an anti-pruritic, pain requiring an intravenous steroid administration and requirement for naloxone administration for opioid overdose.

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