The role of peripheral afferents in persistent inguinal postherniorrhaphy pain: a randomized, double-blind, placebo-controlled, crossover trial of ultrasound-guided tender point blockade

Quantitative somatosensory assessments in patients with persistent pain following groin hernia repair: A systematic review with a meta-analytical approach

OBJECTIVES

Quantitative sensory testing (QST) provides an assessment of cutaneous and deep tissue sensitivity and pain perception under normal and pathological settings. Approximately 2-4% of individuals undergoing groin hernia repair (GHR) develop severe persistent postsurgical pain (PPSP). The aims of this systematic review of PPSP-patients were (1) to retrieve and methodologically characterize the available QST literature and (2) to explore the role of QST in understanding mechanisms underlying PPSP following GHR.

METHODS

A systematic literature search was conducted from JAN-1992 to SEP-2022 in PubMed, EMBASE, and Google Scholar. For inclusion, studies had to report at least one QST-modality in patients with PPSP. Risk of bias assessment of the studies was conducted utilizing the Newcastle Ottawa Scale and Cochrane's Risk of Bias assessment tool 2.0. The review provided both a qualitative and quantitative analysis of the results. A random effects model was used for meta-analysis.

RESULTS

Twenty-five studies were included (5 randomized controlled trials, 20 non-randomized controlled trials). Overall, risk of bias was low. Compared with the contralateral side or controls, there were significant alterations in somatosensory function of the surgical site in PPSP-patients. Following thresholds were significantly increased: mechanical detection thresholds for punctate stimuli (mean difference (95% CI) 3.3 (1.6, 6.9) mN (P = 0.002)), warmth detection thresholds (3.2 (1.6, 4.7) °C (P = 0.0001)), cool detection thresholds (-3.2 (-4.9, -1.6) °C (P = 0.0001)), and heat pain thresholds (1.9 (1.1, 2.7) °C (P = 0.00001)). However, the pressure pain thresholds were significantly decreased (-76 (-123, -30) kPa (P = 0.001)).

CONCLUSION

Our review demonstrates a plethora of methods used regarding outcome assessments, data processing, and data interpretation. From a pathophysiological perspective, the most consistent findings were postsurgical cutaneous deafferentation and development of a pain generator in deeper connective tissues.

TRIAL REGISTRATION

CRD42022331750.

Update of the international HerniaSurge guidelines for groin hernia management

BACKGROUND

Groin hernia repair is one of the most common operations performed globally, with more than 20 million procedures per year. The last guidelines on groin hernia management were published in 2018 by the HerniaSurge Group. The aim of this project was to assess new evidence and update the guidelines. The guideline is intended for general and abdominal wall surgeons treating adult patients with groin hernias.

METHOD

A working group of 30 international groin hernia experts and all involved stakeholders was formed and examined all new literature on groin hernia management, available until April 2022. Articles were screened for eligibility and assessed according to GRADE methodologies. New evidence was included, and chapters were rewritten. Statements and recommendations were updated or newly formulated as necessary.

RESULTS

Ten chapters of the original HerniaSurge inguinal hernia guidelines were updated. In total, 39 new statements and 32 recommendations were formulated (16 strong recommendations). A modified Delphi method was used to reach consensus on all statements and recommendations among the groin hernia experts and at the European Hernia Society meeting in Manchester on October 21, 2022.

CONCLUSION

The HerniaSurge Collaboration has updated the international guidelines for groin hernia management. The updated guidelines provide an overview of the best available evidence on groin hernia management and include evidence-based statements and recommendations for daily practice. Future guideline development will change according to emerging guideline methodology.

A narrative review on the non-surgical treatment of chronic postoperative inguinal pain: a challenge for both surgeon and anaesthesiologist

INTRODUCTION

Chronic pain is one of the most frequent clinical problems after inguinal hernia surgery. Despite more than two decades of research and numerous publications, no evidence exists to allow for chronic postoperative inguinal pain (CPIP) specific treatment algorithms.

METHODS

This narrative review presents the current knowledge of the non-surgical management of CPIP and makes suggestions for daily practice.

RESULTS

There is a paucity for high-level evidence of non-surgical options for CPIP. Different treatment options and algorithms have been published for chronic pain patients in the last decades.

DISCUSSION AND CONCLUSION

It is suggested that non-surgical treatment is introduced in the management of all CPIP patients. The overall approach to interventions should be pragmatic, tiered and multi-interventional, starting with least invasive and only moving to more invasive procedures upon lack of effect. Evaluation should be multidisciplinary and should take place in specialized centres. We strongly suggest to follow general guidelines for treatment of persistent pain and to build a database allowing for establishing CPIP specific evidence for optimal analgesic treatments.

Somatosensory Outcomes Following Re-Surgery in Persistent Severe Pain After Groin Hernia Repair: A Prospective Observational Study

Purpose

After groin hernia repair (globally more than 20 million/year) 2-4% will develop persistent severe pain (PSPG). Pain management is challenging and may require multimodal interventions, including re-surgery. Quantitative somatosensory testing (QST) is an investigational psychophysiological tool with the potential to uncover the pathophysiological mechanisms behind the pain, ie, revealing neuropathic or inflammatory components. The primary objective was to examine and describe the underlying pathophysiological changes in the groin areas by QST before and after re-surgery with mesh removal and selective neurectomy.

Patients and Methods

Sixty patients with PSPG scheduled for re-surgery and with an inflammatory "component" indicated by blunt pressure algometry were examined in median (95% CI) 7.9 (5.8-11.5) months before and 4.0 (3.5-4.6) months after re-surgery. The QST-analyses included standardized assessments of cutaneous mechanical/thermal detection and pain thresholds. Suprathreshold heat stimuli were applied. Deep tissue sensitivity was tested by pressure algometry. Testing sites were the groin areas and the lower arm. Before/after QST data were z-transformed.

Results

Re-surgery resulted in median changes in rest, average, and maximal pain intensity scores of -2.0, -2.5, and -2.0 NRS (0/10) units, respectively (P = 0.0001), and proportional increases in various standardized functional scores (P = 0.0001). Compared with the control sites, the cutaneous somatosensory detection thresholds of the painful groin were increased before re-surgery and increased further after re-surgery (median difference: 1.28 z-values; P = 0.001), indicating a successive post-surgical loss of nerve fiber function ("deafferentation"). Pressure algometry thresholds increased after re-surgery (median difference: 0.30 z-values; P = 0.001).

Conclusion

In this subset of patients with PSPG who underwent re-surgery, the procedure was associated with improved pain and functional outcomes. While the increase in somatosensory detection thresholds mirrors the surgery-induced cutaneous deafferentation, the increase in pressure algometry thresholds mirrors the removal of the deep "pain generator". The QST-analyses are useful adjuncts in mechanism-based somatosensory research.

The Harald Breivik lecture 2022. Pathophysiology in persistent severe pain after groin hernia repair

The transition from a healthy to a persistent severe pain state following otherwise successful elective surgery is a feared complication. Groin hernia repair, previously considered minor surgery, is a standard surgical procedure annually performed on 2,000 individuals per one million residents. A trajectory into persistent severe pain is, unfortunately, seen in 2-4%, severely impeding physical and psychosocial daily functions.

Chronic postoperative pain: ubiquitous and scarcely appraised: narrative review

The International Association for the Study of Pain chose pain prevention as the theme for the 2020 Global Year. Chronic postoperative pain is one the many types of pain that can be potentially prevented. It develops or increases in severity after a surgery, persists for at least three months, even after ruling out all other possible causes of pain. To perform the present narrative review, the authors searched the PubMed database using the following keywords "postoperative pain" OR "postsurgical pain" AND "chronic" OR "persistent". The present review focused on the incidence, pain development and chronification, and predisposing factors. It also discusses prevention, diagnosis, and treatment of chronic postoperative pain. Awareness of occurrence of chronic postoperative pain and recognizing risk factors is crucial for the day-to-day practice of the anesthesiologist. Hence, numerous surgical patients can have their outcome improved by preventing chronic postoperative pain, a condition scarcely identified and without a well-established treatment.

A national center for persistent severe pain after groin hernia repair: Five-year prospective data

Severe persistent pain after groin hernia repair impairs quality-of-life. Prospective, consecutive cohort study including patients with pain-related impairment of physical and social life. Relevant surgical records were obtained, and examinations were by standardized clinical and neurophysiological tests. Patients demonstrating pain sensitivity to pressure algometry in the operated groin underwent re-surgery, while patients with neuropathic pain received pharmacotherapy. Questionnaires at baseline (Q0) and at the 5-year time point (Q5Y) were used in outcome analyses of pain intensity (numeric rating scale [NRS] 0-10) and pain-related effect on the activity-of-daily-living (Activities Assessment Scale [AAS]). Data are mean (95% CI).Analyses were made in 172/204 (84%) eligible patients. In 54/172 (31%) patients re-surgery (meshectomy/selective neurectomy) was performed, while the remaining 118/172 (69%) patients received pharmacotherapy. In the re-surgery group, activity-related, and average NRS-scores at Q0 were 6.6 (5.6-7.9) and 5.9 (5.6-5.9), respectively. Correspondingly, NRS-scores at Q5Y was 4.1 (3.3-5.1) and 3.1 (2.3-4.0; Q0 vs. Q5Y: P < .0005), respectively. Although both groups experienced a significant improvement in AAS-scores comparing Q0 vs. Q5Y (re-surgery group: 28% (4-43%; P < .0001); pharmacotherapy group: 5% (0-11%; P = .005)) the improvement was significantly larger in the re-surgery group (P = .02).This 5-year cohort study in patients with severe persistent pain after groin hernia repair signals that selection to re-surgery or pharmacotherapy, based on examination of pain sensitivity, is associated with significant improvement in outcome. Analyzing composite endpoints, combining pain and physical function, are novel in exploring interventional effects.ClinicalTrials.gov Identifier NCT03713047.

Management of chronic pain after hernia repair

Chronic pain following inguinal hernia repair is a common problem and feared complication. Up to 16% of people experience chronic pain following the repair of a groin hernia. The aim of this review was to provide an overview of treatment strategies for patients with chronic pain following inguinal hernia repair based on best practice guidelines and current clinical routines. The optimal management of chronic pain following inguinal hernia surgery should begin with a thorough clinical examination to rule out other causes of chronic pain and to rule out a recurrence. A scaled approach to treatment is recommended. Initially, watchful waiting can be tried if it can be tolerated by the patient and then systemic painkillers, escalating to blocks, and surgery as the final option. Surgery should include mesh removal and triple neurectomy following anterior approaches or mesh and tack removal following a posterior approach. The diagnosis and treatment strategies should be performed by or discussed with experts in the field.

Neuropathic Pain: Central vs. Peripheral Mechanisms

PURPOSE OF REVIEW

Our goal is to examine the processes-both central and peripheral-that underlie the development of peripherally-induced neuropathic pain (pNP) and to highlight recent evidence for mechanisms contributing to its maintenance. While many pNP conditions are initiated by damage to the peripheral nervous system (PNS), their persistence appears to rely on maladaptive processes within the central nervous system (CNS). The potential existence of an autonomous pain-generating mechanism in the CNS creates significant implications for the development of new neuropathic pain treatments; thus, work towards its resolution is crucial. Here, we seek to identify evidence for PNS and CNS independently generating neuropathic pain signals.

RECENT FINDINGS

Recent preclinical studies in pNP support and provide key details concerning the role of multiple mechanisms leading to fiber hyperexcitability and sustained electrical discharge to the CNS. In studies regarding central mechanisms, new preclinical evidence includes the mapping of novel inhibitory circuitry and identification of the molecular basis of microglia-neuron crosstalk. Recent clinical evidence demonstrates the essential role of peripheral mechanisms, mostly via studies that block the initially damaged peripheral circuitry. Clinical central mechanism studies use imaging to identify potentially self-sustaining infra-slow CNS oscillatory activity that may be unique to pNP patients. While new preclinical evidence supports and expands upon the key role of central mechanisms in neuropathic pain, clinical evidence for an autonomous central mechanism remains relatively limited. Recent findings from both preclinical and clinical studies recapitulate the critical contribution of peripheral input to maintenance of neuropathic pain. Further clinical investigations on the possibility of standalone central contributions to pNP may be assisted by a reconsideration of the agreed terms or criteria for diagnosing the presence of central sensitization in humans.

Chronic postoperative pain: recent findings in understanding and management

Chronic postoperative pain is a poorly recognized potential outcome from surgery. It affects millions of patients every year, with pain lasting for months to years, resulting in patient suffering and ensuing economic consequences. The operations with the highest incidence of chronic postoperative pain are amputations, thoracotomies, cardiac surgery, and breast surgery. Other risk factors include preoperative pain, psychological factors, demographics, and the intensity of acute postoperative pain. Attempts to prevent chronic postoperative pain have often led to debatable results. This article presents data from recently published studies examining the incidence, risk factors, mechanisms, treatment options, and preventive strategies for chronic postoperative pain in adults. In summary, many of the previously identified risk factors for chronic postoperative pain have been confirmed and some novel ones discovered, such as the importance of the trajectory of acute pain and the fact that catastrophizing may not always be predictive. The incidence of chronic postoperative pain hasn’t changed over time, and there is limited new information regarding an effective preventive therapy. For example, pregabalin may actually cause more harm in certain surgeries. Further research is needed to demonstrate whether multimodal analgesic techniques have the best chance of significantly reducing the incidence of chronic postoperative pain and to determine which combination of agents is best for given surgical types and different patient populations.

The Relationship Between Sensory Loss and Persistent Pain 1 Year After Breast Cancer Surgery

Moderate to severe persistent pain after breast cancer surgery (PPBCS) affects 10 to 20% of the patients. Sensory dysfunction is often concomitantly present suggesting a neuropathic pain state. The relationship between various postoperative pain states and sensory dysfunction has been examined using quantitative sensory testing (QST), but only 2 smaller studies have examined PPBCS and sensory dysfunction in the surgical area. The purpose of this prospective study was to assess the relative importance of sensory function and PPBCS. QST consisted of sensory mapping, tactile detection threshold, mechanical pain threshold, and thermal thresholds. Two hundred ninety patients were enrolled and results showed that 38 (13%) had moderate to severe pain and 246 (85%) had hypoesthesia in the surgical area 1 year after surgery. Increased hypoesthesia areas were associated with pain at rest as well as during movement (P = .0001). Pain during movement was associated with a side-to-side difference of 140% (P = .001) for tactile detection threshold and 40% (P = .01) for mechanical pain threshold as well as increased thermal thresholds in the axilla (P > .001). Logistic regression models controlling for confounders showed larger areas of hypoesthesia as a significant risk factor, odds ratio 1.85 per 100 cm² for pain at rest and odds ratio 1.36 per 100 cm² for pain during movement.

PERSPECTIVE

PPBCS is associated with increasing areas of hypoesthesia as well as intraoperative nerve preservation. Thus, we hypothesize that PPBCS is associated with an interaction between a peripheral nociceptive drive in macroscopically preserved nerves and the central nervous system causing PPBCS as well as hypoesthesia. QST may identify patients suitable for intervention.