Ageing Research Reviews 12 (2013) 226–236 Contents lists available at SciVerse ScienceDirect Ageing Research Reviews j ourna l ho me pa ge: www.elsevier.com/locate/arr Review Osteoarthritis of the knee: Why does exercise work? A qualitative study of the literature David Beckwée a , Peter Vaes a , Maarten Cnudde a , Eva Swinnen a , Ivan Bautmans b,∗ a Rehabilitation Sciences Research Department, Vrije Universiteit Brussel, Laarbeeklaan 103, B-1090 Brussels, Belgium b Frailty in Ageing Research Department, Vrije Universiteit Brussel, Laarbeeklaan 103, B-1090 Brussels, Belgium a r t i c l e i n f o Article history: Received 1 June 2012 Received in revised form 17 September 2012 Accepted 21 September 2012 Available online 28 September 2012 Keywords: Osteoarthritis Knee Exercise Aetiology Rationale a b s t r a c t The effectiveness of exercise to reduce pain and improve functioning in osteoarthritis of the knee (OAk) is well substantiated. Underlying mechanisms are still under debate and better understanding of the path- ways involved may contribute to more targeted treatment strategies. The present qualitative analysis of the literature aims to provide an overview of theoretical models that are put forward to explain the benefi- cial treatment effects of exercise in OAk. An inductive qualitative approach, based on the ‘grounded theory’ of Glaser and Straus, was used. Twenty-two studies emphasizing on exercise therapy for OAk, collected from three Cochrane reviews and nine guidelines of the Physiotherapy Evidence Database (PEDRO) pub- lished between 2000 and 2012, were included. The introduction and discussion parts of these papers were screened for explanations of exercise-induced benefits in OAk patients. Seventy-three key points were identified which were subdivided into 16 core theoretical concepts. Finally, 5 categories were formed: neuromuscular, peri-articular, intra-articular, psychosocial components, and general fitness and health. We referred to scientific evidence that was used in the included studies to describe and categorize the concepts. Future research on exercise in OAk should allow distinguishing the contribution of different potential pathways to the treatment effects. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Osteoarthritis (OA) is characterized by a degeneration of artic- ular cartilage in synovial joints. Pain and disability occur in 17% of people aged 45 years and over due to osteoarthritis in the knee (OAk) (Lawrence et al., 2008) and in 40% of people aged 65 years and over due to OAk or OA in the hip (Dawson et al., 2004; Mannoni et al., 2003). Because till now OA is an irreversible condition, the treatment is focused on reducing physical disability and handi- cap, and controlling pain while minimizing the potentially harmful side effects of medications (Zhang et al., 2007). In this context, exercise therapy is considered as an effective conservative treat- ment for OAk-related pain and disability (Fransen and McConnell, 2008), and recommended as ‘first choice conservative treatment’ by several clinical guidelines (Peter et al., 2010; Royal Australian College of General Practitioners, 2009 (South Melbourne); Zhang et al., 2008). However, underlying mechanisms for these beneficial exercise-induced effects are still scarcely understood. Understand- ing the pathways through which exercise influences pain and ∗ Corresponding author. Tel.: +32 02 477 42 07; fax: +32 02 477 63 64. E-mail addresses: David.Beckwee@vub.ac.be (D. Beckwée), pvaes@vub.ac.be (P. Vaes), mcnudde@vub.ac.be (M. Cnudde), eswinnen@vub.ac.be (E. Swinnen), ivan.bautmans@vub.ac.be (I. Bautmans). function in OAk patients may contribute to the design of a compre- hensive treatment plan. Potential explanations for the favourable effects of exercise in OAk are frequently proposed in the intro- duction and discussion sections of scientific papers reporting the effects of exercise interventions. Sometimes these hypotheses are (partly) empowered by scientific data. To our knowledge, com- prehensive overviews of these potential working mechanisms of physical exercise are lacking. The present literature study aims to provide an overview of the potential underlying mechanisms that are proposed in the literature to explain the exercise induced improvements in OAk pain and function. 2. Methods A systematic literature search was performed and extracted data were further analyzed with a qualitative approach, based on the ‘grounded theory’ of Glaser & Strauss, which is induc- tive in nature (Strauss and Corbin, 1998). This approach implies 4 steps: (1) data gathering; (2) extracting key points from the collected data; (3) grouping key points into similar concepts; and (4) forming categories from the concepts. First, in order to gather information, we searched (last search on March 1st 2012) for scientific papers emphasizing on exercise therapy for OAk (systematic reviews and/or practice guidelines) using the search 1568-1637/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.arr.2012.09.005