This study aims to better understand the way in which painful osteoarthritis affects different people and whether an anti-inflammatory medication such as Arcoxia (etoricoxib) can help to modify this pain. The study will use questionnaires and tests of pain sensitivity to identify arthritis sufferers with more widespread, nerve-type pain and then to investigate whether a daily dose of Arcoxia is more effective than a placebo pill in reducing these symptoms and improving functional movements. The study will also be comparing the same test results of a small group of subjects without knee pain.

Inclusion Criteria:

• unilateral diagnosis of Knee OA > 6 months
• knee pain > 4/10 on WOMAC pain subscale
• if pain in contralateral knee, no greater than "mild"
• no other significant joint involvement
• ARA functional Class I, II or III
• no arthroscopy or injections into index knee in last 6 months

Exclusion Criteria:

• history of systemic inflammatory or chronic pain disorders (especially fibromyalgia)

• neurological deficit

• recent (< 6 months) lower limb surgery

• allergic reaction to NSAIDs or aspirin

• skin allergies, dermatitis

• contraindications to Cox-2 inhibitors:

  • congestive heart failure (NYHA II-IV)
  • unstable hypertension
  • ischaemic heart disease
  • peripheral artery disease
  • cerebrovascular disease including CABG or angioplasty within 1 year

• severe hepatic dysfunction

• active GI bleeding or peptic ulceration

• reduced creatinine clearance < 30 mL/min

• current use of high dose (> 325 mg daily) aspirin