title: The role of peripheral afferents in persistent inguinal postherniorrhaphy pain: a randomized, double-blind, placebo-controlled, crossover trial of ultrasound-guided tender point blockade.
abstract: BACKGROUND
  Severe, persistent inguinal postherniorrhaphy pain (PIPP) is a debilitating condition that develops in 2-5% of patients. PIPP may be neuropathic in nature, yet the lesion in the peripheral nervous system has not been located. Most PIPP-patients demonstrate a tender point (TP) in the medial aspect of the inguinal region that triggers pain upon minimal pressure. As TPs may play a role in the pathophysiology of PIPP, the aim of this trial was to investigate the analgesic effects of local anaesthetic TP-blockade.
  
  
  METHODS
  A randomized, double-blind, placebo-controlled, crossover trial was performed in 14 PIPP-patients and six healthy volunteers. All participated in two sessions, seven days apart, receiving 10 ml of 0.25% bupivacaine or normal saline via an ultrasound-guided fascial plane block at the TP. The TP-area was used for pain assessments (at rest, on movement, with 100 kPa pressure-algometry) and quantitative sensory testing (pressure pain thresholds, thermal detection/pain thresholds, supra-threshold heat perception), before and after the TP-blockade.
  
  
  RESULTS
  The median (95% CI) reduction in pain was 63% (44.1 to 73.6%) after bupivacaine compared with 36% (11.6 to 49.7%; P=0.003) after placebo. Significant increases in cool detection (P=0.01) and pressure pain thresholds (P=0.009) with decreases in supra-threshold heat pain perception (P=0.003) were seen after bupivacaine only. In four out of six volunteers, increased thermal and evoked-pain thresholds after bupivacaine compared with placebo, was demonstrated.
  
  
  CONCLUSIONS
  This trial demonstrates that peripheral afferent input from the TP-area is important for maintenance of spontaneous and evoked pain in PIPP.
  
  
  BACKGROUND
  NCT02065219.
authors.affiliation: Section for Surgical Pathophysiology nelunwij@gmail.com.
authors.forename: N
authors.initials: N
authors.lastname: Wijayasinghe
authors.affiliation: Multidisciplinary Pain Center, Rigshospitalet, Copenhagen University Hospitals, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: T K
authors.initials: TK
authors.lastname: Ringsted
authors.affiliation: Multidisciplinary Pain Center, Rigshospitalet, Copenhagen University Hospitals, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: J M
authors.initials: JM
authors.lastname: Bischoff
authors.affiliation: Section for Surgical Pathophysiology.
authors.forename: H
authors.initials: H
authors.lastname: Kehlet
authors.affiliation: Multidisciplinary Pain Center, Rigshospitalet, Copenhagen University Hospitals, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: M U
authors.initials: MU
authors.lastname: Werner
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000779:Anesthetics, Local / Q000008:administration & dosage / Q000627:therapeutic use; D002045:Bupivacaine / Q000008:administration & dosage / Q000627:therapeutic use; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D064368:Healthy Volunteers; D006552:Hernia, Inguinal / Q000601:surgery*; D059685:Herniorrhaphy / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009407:Nerve Block / Q000379:methods*; D009475:Neurons, Afferent; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects; D010149:Postoperative Pain / Q000503:physiopathology*; D017933:Peripheral Nervous System / Q000503:physiopathology*; D018084:Ultrasonography, Interventional / Q000379:methods*; D055815:Young Adult
chemical_list: D000779:Anesthetics, Local; D002045:Bupivacaine
keywords: bupivacaine; chronic pain; herniorrhaphy; inguinal hernia; nerve blockade; randomized controlled trial