Pain is one of the most common complaints after inguinal hernia repair, but the incidence of chronic pain can vary significantly from study to study.
Estimates of chronic pain after open mesh and laparoscopic repairs tend to fall between 4% and 30% (Surg Endosc 2010;24:1707-1711; Ann Surg 2006;244:212-219), but some trials report values of greater than 50% (Br J Anaesth 2005;95:69-76). Studies evaluating chronic pain after pure tissue repair report ranges from about 4% to 14% for various techniques (Anesthesiology 2000;93:1123-1133).
“Such huge variations, caused by different definitions of pain or pain severity, make it almost impossible to identify specific causes or treatments,” said Uwe Klinge, MD, a surgeon in the Department of General, Visceral and Transplant Surgery, University Hospital of the RWTH Aachen, in Germany.
A new study published in Surgery attempted to better understand one facet of pain after inguinal hernia repair: the effect of intraoperative infiltration of local anesthetic on the development of chronic postoperative pain (Surgery 2015;157:144-154). The main hypothesis, according to study author Anita Kurmann, MD, a surgeon in the Department of Visceral Surgery and Medicine at Bern University Hospital, in Switzerland, was that intraoperative local anesthesia may disrupt nociceptive signals and thus may decrease the incidence of chronic postoperative pain.
In the study, Dr. Kurmann and her colleagues randomized 356 patients with 402 hernia repairs to three procedures: Lichtenstein (open mesh), Barwell (open autogenous similar to Bassini or Shouldice) and totally extraperitoneal (TEP) inguinal hernia repair (laparoscopic), with or without a local anesthetic. The authors defined chronic pain as any pain lasting more than three months, as described by the International Association for the Study of Pain (Pain Suppl 1986;3:S1-S226).
A total of 322 inguinal hernia repairs were performed using the Lichtenstein technique, with 168 receiving local infiltration of bupivacaine 0.25% 20 mL (intervention group) and 154 receiving a saline solution (placebo group); 13 underwent the Barwell technique, with six in the intervention group and seven in the placebo group; and 51 underwent TEP, with 26 in the intervention group and 25 in the placebo group. About half of the patients in the intervention (44%) and placebo (48%) groups had a nerve resection of the ilioinguinal, iliohypogastric or genitofemoral nerves. Chronic pain was evaluated three months postoperatively using the visual analog scale (VAS).
After accounting for patients lost to follow-up, the analysis included 347 hernia repairs in 307 patients. Three months postoperatively, the authors reported an incidence of chronic pain of 5.8% (10 of 173 hernias) in the intervention group and 2.3% (four of 174) in the placebo group (P=0.114). The study also analyzed several outcomes one year postoperatively and found that the incidence of surgical complications—including recurrent hernia, and superficial and deep surgical site infections—bodily pain and physical functioning were similar in the intervention and placebo groups.
The authors could not confirm a difference in the development of chronic pain three months postoperatively between patients who received intraoperative infiltration of local anesthesia and those who did not. “We concluded that there is not enough evidence that intraoperative infiltration of local anesthesia has an influence on the development of chronic postoperative pain and should not be practiced,” Dr. Kurmann wrote in an email.
Commenting on the study, Robert Bendavid, MD, FACS, FRCS(C), a surgeon at the Shouldice Hospital in Toronto, Ontario, Canada, remarked that once the activity of the local anesthetic agent has passed, it should not affect pain after surgery.
Dr. Bendavid also found the definition of chronic pain too limited. “Three months is not an adequate time frame to evaluate chronic pain,” he said. “There can still be healing and scarring going on up to a year after surgery, and chronic pain can take even longer to manifest. I’ve seen patients reporting pain six years after surgery.”
Although the current study did not explore the mechanisms of pain, the investigators surmised that postoperative chronic pain may arise from a range of factors, including intraoperative nerve injury, inflammatory reactions after surgery or scar tissue from the implanted mesh.
Dr. Bendavid noted that nerve entrapment could also explain chronic pain in inguinal hernia repair using mesh. In a recent study, he found that nerves can grow within scar tissue and through the pores and interstices of mesh (Int J Clin Med 2014;5:799-810).
“Pain is incredibly complex, and there are many reasons patients can experience chronic pain after inguinal hernia repair,” Dr. Klinge said.
Dr. Kurmann concluded that “further studies should focus on the pathophysiological pathway of chronic pain to identify specific interventions.”
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