Investigating the Effect of Pericapsular Nerve Group (PENG) Block on Postoperative Pain After Peri-acetabular Osteotomy

Peri-acetabular osteotomy (PAO) is the joint-preserving treatment of choice in young adults with symptomatic hip dysplasia. However, moderate to severe pain occurs frequently in the postoperative period. Pain after PAO comes primarily from the anterior hip capsule which is innervated by the terminal nerves of the lumbar plexus comprising branches from the femoral, obturator and accessory obturator nerves. The articular branches from the femoral nerve reach the plane between the iliopsoas muscle and the iliofemoral ligament (iliopsoas plane) and innervate the anterior and lateral aspects of the hip capsule. The articular branches innervate the anterior and medial aspects of the hip capsule and the accessory obturator nerve contributes to the innervation of the hip in 10%-30% of the patients, and supplies the inferomedial aspect of the hip capsule. The PAO procedure, involving three osteotomies in otherwise healthy individuals, is likely to produce a substantial surgical stress response, which potentially could be alleviated by multimodal analgesia including the pericapsular nerve group (PENG) block.

The PENG block is a novel regional anaesthesia technique that has been proposed as an effective motor-sparing block for total hip arthroplasty. The PENG block targets the articular branches providing innervation to the anterior capsule of the hip joint, including the femoral, obturator and accessory obturator nerves. Its potential analgesic and motor-sparing effect is desirable for early ambulation, better physical therapy, and earlier discharge.

Conventional opioid-sparing regional anaesthetic techniques such as lumbar plexus and femoral nerve blocks are effective but carry a risk of undesirable lower limb muscle weakness. Alternatively, the fascia iliaca block does not consistently provide adequate pain relief for hip surgeries.

The anterior capsule of the hip has a high density of nociceptors and mechanoreceptors and appears to be the primary source of pain after hip surgery. The PENG block targets the articular branches providing innervation to the anterior capsule of the hip joint, including the femoral, obturator and accessory obturator nerves.

A recent study reported improved quality of recovery and reduced opioid requirements for patients undergoing primary THA whereas other studies have reported conflicting results regarding the analgesic efficacy for THA. However, the effect of PENG on PAO has not been investigated.

Thus, in order to investigate if PENG block is superior to placebo in decreasing immediate pain and other complications after PAO, the investigators aim to conduct a randomised, double-blinded trial of ropivacaine 5 mg/ml vs. placebo. The investigators hypothesize that patients given ropivacaine 5 mg/ml will have less pain in the first 24 postoperative hours compared with patients given placebo.