BACKGROUND AND OBJECTIVE Osteoarthritis(OA) of the knee is a major cause of disability,affecting 10%of people over the age of 55 years.A prior mullicenter study found intra-articular clodronate,a bisphosphonate,to be as effective as hyaluronic acid,for the treatment of OA,with significant progression in improvement of pain and functional outcomes.This study further assessed the tolerability and efficacy of intra-articular clodronate for patients with OA of the knee.