title: A mechanism-based pain sensitivity index to characterize knee osteoarthritis patients with different disease stages and pain levels.
abstract: BACKGROUND
  In a cohort of well-characterized patients with different degrees of knee osteoarthritis (OA) and pain, the aims were to utilize mechanism-based quantitative sensory testing (QST) to (1) characterize subgroups of patients; (2) analyse the associations between clinical characteristics and QST; and (3) develop and apply a QST-based knee OA composite pain sensitivity index for patient classification.
  
  
  METHODS
  Two hundred seventeen OA pain patients and 64 controls were included. Kellgren and Lawrence (KL) grading scores were obtained, and pressure pain thresholds (PPTs), temporal summation of pain to repeated painful pressure stimulation and conditioning pain modulation (CPM) were assessed. Associations between pain score/area/duration, radiological findings and QST-related parameters were analysed. A pain sensitivity index was developed and applied based on PPT, temporal summation and CPM. z-Score, as statistical tool, was calculated for statistically comparing the pain index of a single patient with a healthy control group.
  
  
  RESULTS
  High knee pain associated with low KL grade showed particular signs of pain sensitization. Patients showed significant associations between clinical knee pain intensity/duration and lowering of knee PPTs (p < 0.01), facilitation of temporal summation (p < 0.01), reduction of CPM function (p < 0.01) and high pain sensitivity index (p < 0.01). The index classified 27-38% of the OA patients and 3% of the controls as highly sensitive with no association to KL. The index increased for high knee pain intensities and long pain duration.
  
  
  CONCLUSIONS
  Radiological scores, contrary to clinical pain intensity/duration, were poorly associated with QST parameters. The pain sensitivity index could classify OA patients with different degrees of OA and pain.
authors.affiliation: Center for Sensory-Motor Interaction, Aalborg University, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Arendt-Nielsen
authors.affiliation: Center for Sensory-Motor Interaction, Aalborg University, Denmark.|CCBR, Aalborg, Denmark.
authors.forename: L L
authors.initials: LL
authors.lastname: Egsgaard
authors.affiliation: Center for Sensory-Motor Interaction, Aalborg University, Denmark.
authors.forename: K K
authors.initials: KK
authors.lastname: Petersen
authors.affiliation: Center for Sensory-Motor Interaction, Aalborg University, Denmark.|CCBR, Aalborg, Denmark.
authors.forename: T N
authors.initials: TN
authors.lastname: Eskehave
authors.affiliation: Center for Sensory-Motor Interaction, Aalborg University, Denmark.
authors.forename: T
authors.initials: T
authors.lastname: Graven-Nielsen
authors.affiliation: CCBR, Aalborg, Denmark.|C4Pain, Aalborg, Denmark.
authors.forename: H C
authors.initials: HC
authors.lastname: Hoeck
authors.affiliation: Sygehus Vendsyssel, Frederikshavn, Denmark.
authors.forename: O
authors.initials: O
authors.lastname: Simonsen
mesh_terms: D000368:Aged; D018771:Arthralgia / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods*; D017288:Pain Threshold / Q000502:physiology*