The purpose of this trial is to evaluate the effectiveness of arthroscopy (lavage and debridement) in conjunction with the best available non-surgical treatment versus the best available non-surgical treatment alone (medication, health education and physical therapy) in patients with osteoarthritis of the knee.

Osteoarthritis is estimated to affect half of the adult population, and by the age of 75 years, it is anticipated that 85 of 100 elderly patients will have some form of this disease. Osteoarthritis (OA) is characterized by moderate to severe pain that limits functional ability. It is suspected that the causes of this debilitating pain include irritation of the synovium, excessive subchondral bone forces and raised intra-arterial pressure. The knee is the most commonly affected weight-bearing joint. Osteoarthritis has a great social impact, as the second most common reason for work disability in the United States. The prevalence of OA is expected to increase in the coming years due to increased longevity, increased proportion of the population over the age of 75 years, and increased diagnostic ability.

Rather than further evaluations of different forms of arthroscopic surgery (ie lavage vs debridement vs abrasion) in the treatment of knee OA, we feel it is important to establish the efficacy of this technology compared to the best non-surgical treatment alone.

This is an evaluator- blinded, phase III, single-centre, group sequential randomized controlled trial in patients with osteoarthritis of the knee.

Treatment effectiveness is based upon patients' disease specific quality of life at 2 years using the Western Ontario McMaster (WOMAC) Osteoarthritis Index. In addition patients' physical function and cost effectiveness are being assessed. Costs will be estimated from the perspectives of the health care system, the patient,family, and society and will include the use of hospital and other resources as well as the economic implications of lost workdays associated with these alternative treatments.

This randomized clinical trial will provide high quality evidence to determine what the role of this expensive treatment is in the overall management of OA.

Inclusion Criteria:

1. Idiopathic or secondary osteoarthritis of the knee as diagnosed by Altman et al 2 classification tree -83 percent sensitivity, 93percent specificity
2. Grades 2 to 4 severity of OA by radiographic evaluation- modified Kellgren and Lawrence grading system
3. Age greater than 18.

Exclusion Criteria:

1. Inflammatory or post-infection arthritis of the knee
2. Previous arthroscopy for treatment of knee OA
3. Isolated medial compartment OA Grade 3-4 with greater than 5 degrees mechanical varus -ideal candidate for high tibial osteotomy
4. Isolated lateral compartment OA Grade III-IV with greater than 5 degrees mechanical valgus -ideal candidate for high tibial osteotomy or distal femoral osteotomy
5. Grade 4 OA in at least 2 compartments and over 60 years of age -ideal candidate for total knee arthroplasty
6. Cortico-steroid injection within the last three months.
7. Major neurological deficit
8. Major medical illness -life expectancy less than 2 years or with unacceptably high operative risk.
9. Pregnant
10. Unable to speak or read English
11. Psychiatric illness that limits informed consent
12. Unwilling to be followed for 2 years