title: Association between altered somatosensation, pain, and knee stability in patients with severe knee osteoarthrosis.
abstract: OBJECTIVE
  To examine the relationship between knee pain, altered somatosensation, and self-reported instability in individuals with knee osteoarthrosis (OA) during a step-up-and-over task.
  
  
  METHODS
  Quantitative sensory testing, including mechanical detection threshold (MDT), allodynia, vibration perception threshold, and pressure pain threshold (PPT), was assessed in 16 individuals (mean age, 52 ± 7 y) with knee OA and in 16 age-matched and sex-matched controls. Pain intensity ratings and subjective reports of instability/buckling were recorded at rest and while performing a step-up task, and these findings were correlated with somatosensory measures.
  
  
  RESULTS
  In the OA group, all participants reported allodynia on MDT testing. Compared with healthy controls, MDT was significantly increased (P<0.001), and vibration perception threshold was increased (P=0.02) at the medial knee, indicating hypoesthesia. PPT was significantly decreased at the medial joint line (P=0.03) and 12 cm distal (P=0.02). Comparing participants with OA having severe versus mild radiographic changes, PPT was lower at the medial joint line (P<0.01) but not at 12 cm distal. Fourteen (87.5%) participants with knee OA reported pain and instability during the step task as compared with none or 1 (6%) of the controls. On the step task, longer duration of symptoms was associated with increased pain (P=0.02). A moderate correlation between greater self-reported instability and increased vibratory hypoesthesia at the knee (r=-0.633; P=0.01) was demonstrated, suggesting a potential relationship between somatosensory changes and functional deficits.
  
  
  CONCLUSIONS
  Severe OA may result in both hyperalgesia and hypoesthesia at the affected knee. Perceived instability during functional tasks may be mediated in part by pain in individuals with knee OA.
authors.affiliation: Departments of Physical Therapy, University of Illinois at Chicago, 60304, USA.
authors.forename: Alicia J Emerson
authors.initials: AJ
authors.lastname: Kavchak
authors.forename: César
authors.initials: C
authors.lastname: Fernández-de-Las-Peñas
authors.forename: Leah H
authors.initials: LH
authors.lastname: Rubin
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Chmell
authors.forename: Reuben K
authors.initials: RK
authors.lastname: Durr
authors.forename: Carol A
authors.initials: CA
authors.lastname: Courtney
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000209:etiology*; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000150:complications* / Q000473:pathology*; D010146:Pain / Q000209:etiology*; D017288:Pain Threshold / Q000502:physiology; D010812:Physical Stimulation / Q000009:adverse effects; D011597:Psychomotor Performance / Q000502:physiology; D020886:Somatosensory Disorders / Q000150:complications* / Q000175:diagnosis; D014732:Vibration