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

Abstract

Elisabeth Kjær Jensen,1,* Thomas K Ringsted,1,* Joakim M Bischoff,1 Morten A Petersen,2 Kirsten Møller,3,4 Henrik Kehlet,5 Mads U Werner1,6 1Department of Anaesthesia, Pain and Respiratory Support, Copenhagen University Hospital-Rigshospitalet, Copenhagen, Denmark; 2Statistical Research Unit, Department of Palliative Care, Bispebjerg Hospital, Copenhagen, Denmark; 3Department of Neuroanaesthesiology, Copenhagen University Hospital-Rigshospitalet, Copenhagen, Denmark; 4Department of Clinical Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark; 5Section for Surgical Pathophysiology, Copenhagen University Hospital-Rigshospitalet, Copenhagen, Denmark; 6Department of Clinical Sciences, Lund University, Lund, Sweden*These authors contributed equally to this workCorrespondence: Elisabeth Kjær Jensen, Multidisciplinary Pain Center 7612, Department of Anesthesia, Pain and Respiratory Support, Neuroscience Center, Rigshospitalet, Ole Maaløes Vej 26, Copenhagen N, 2200, Denmark, Tel [phone], Email [email protected]: 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.Keywords: groin, hernia repair, chronic post-surgical pain, reoperation, sensory thresholds

Keywords

• groin
• hernia repair
• chronic post-surgical pain
• reoperation
• sensory thresholds.