title: Intra-articular Injections of Hyaluronic Acid and Other Drugs in the Knee Joint.
abstract: BACKGROUND
  Degenerative osteoarthritis of the knee (OA) affects 35% of persons older than 65 years. If pain persists after non-invasive treatment, some intra-articular drugs can be tried before surgical treatment.
  
  
  OBJECTIVE
  The purpose of this article is to review the literature after 2006 with the aim of answering two questions: (1) Are intra-articular injections of corticosteroids (CS), hyaluronic acid (HA) and platelet-rich plasma (PRP) effective in painful knee OA? and (2) Which of these drugs is more effective?
  
  
  METHODS
  The search engines were MedLine and the Cochrane Library. The keywords used were: knee, osteoarthritis, and intra-articular injections. Eight hundred and forty-four articles were found but only 142 had been published after 2006. Of those, only 14 were selected and reviewed because they were strictly focused on the topic and the questions of this article.
  
  
  RESULTS
  The clinical efficacy of intra-articular injections of HA and CS in patients with knee OA has been demonstrated. Pain reduction after three to five weekly injections of HA lasts between 5 to13 weeks (sometimes up to 1 year). Pain reduction is less durable after CS injections (2 to 3 weeks). Recent reports indicate that PRP could have a better performance than HA in younger patients.
  
  
  CONCLUSIONS
  Three to five weekly intra-articular injections of HA are recommendable in patients with knee OA before surgical treatment. CS injections have a very short effect. The efficacy and duration of PRP injections require further studies.
authors.affiliation: Department of Orthopaedic Surgery, La Paz University Hospital, Paseo de la Castellana 261, 28046 Madrid, Spain ; School of Medicine, Autonomous University, Madrid, Spain.
authors.forename: E Carlos
authors.initials: EC
authors.lastname: Rodriguez-Merchan
keywords: corticosteroids; hyaluronic acid; intra-articular injections; knee; osteoarthritis; platelet-rich plasma