title: Examining sex differences in knee pain: the multicenter osteoarthritis study.
abstract: OBJECTIVE
  To determine whether women experience greater knee pain severity than men at equivalent levels of radiographic knee osteoarthritis (OA).
  
  
  METHODS
  A cross-sectional analysis of 2712 individuals (60% women) without knee replacement or a recent steroid injection. Sex differences in pain severity at each Kellgren-Lawrence (KL) grade were assessed by knee using visual analog scale (VAS) scale and Western Ontario and McMaster Universities Arthritis Index (WOMAC) with and without adjustment for age, analgesic use, Body mass index (BMI), clinic site, comorbid conditions, depression score, education, race, and widespread pain (WSP) using generalized estimating equations. Effect sizes (Cohen's d) were also calculated. Analyses were repeated in those with and without patellofemoral OA (PFOA).
  
  
  RESULTS
  Women reported higher VAS pain at all KL grades in unadjusted analyses (d = 0.21-0.31, P < 0.0001-0.0038) and in analyses adjusted for all covariates except WSP (d = 0.16-0.22, P < 0.0001-0.0472). Pain severity differences further decreased with adjustment for WSP (d = 0.10-0.18) and were significant for KL grade ≤2 (P = 0.0015) and 2 (P = 0.0200). Presence compared with absence of WSP was associated with significantly greater knee pain at all KL grades (d = 0.32-0.52, P < 0.0001-0.0008). In knees with PFOA, VAS pain severity sex differences were greater at each KL grade (d = 0.45-0.62, P = 0.0006-0.0030) and remained significant for all KL grades in adjusted analyses (d = 0.31-0.57, P = 0.0013-0.0361). Results using WOMAC were similar.
  
  
  CONCLUSIONS
  Women reported greater knee pain than men regardless of KL grade, though effect sizes were generally small. These differences increased in the presence of PFOA. The strong contribution of WSP to sex differences in knee pain suggests that central sensitivity plays a role in these differences.
authors.affiliation: University of Iowa, Iowa City, IA, USA.
authors.forename: N
authors.initials: N
authors.lastname: Glass
authors.affiliation: University of Iowa, Iowa City, IA, USA.
authors.forename: N A
authors.initials: NA
authors.lastname: Segal
authors.affiliation: University of Iowa, Iowa City, IA, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Sluka
authors.affiliation: University of Iowa, Iowa City, IA, USA.
authors.forename: J C
authors.initials: JC
authors.lastname: Torner
authors.affiliation: University of California at San Francisco, San Francisco, CA, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Nevitt
authors.affiliation: Boston University, Boston, MA, USA.
authors.forename: D T
authors.initials: DT
authors.lastname: Felson
authors.affiliation: University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Bradley
authors.affiliation: Boston University, Boston, MA, USA.
authors.forename: T
authors.initials: T
authors.lastname: Neogi
authors.affiliation: University of Alabama at Birmingham, Birmingham, AL, USA.
authors.forename: C E
authors.initials: CE
authors.lastname: Lewis
authors.affiliation: University of Iowa, Iowa City, IA, USA. Electronic address: laura-freylaw@uiowa.edu.
authors.forename: L A
authors.initials: LA
authors.lastname: Frey-Law
mesh_terms: D000368:Aged; D000700:Analgesics / Q000627:therapeutic use; D018771:Arthralgia / Q000188:drug therapy / Q000209:etiology*; D015992:Body Mass Index; D015897:Comorbidity; D003430:Cross-Sectional Studies; D003863:Depression / Q000453:epidemiology; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology; D020370:Osteoarthritis, Knee / Q000150:complications* / Q000000981:diagnostic imaging / Q000453:epidemiology; D010147:Pain Measurement; D011859:Radiography; D012720:Severity of Illness Index; D012737:Sex Factors
chemical_list: D000700:Analgesics
keywords: Knee osteoarthritis; Knee pain; Sex differences