Measurement: function and mobility (focussing on the ICF framework)

While several instruments and measures are available to assess function and mobility, there was no exhaustive list of impairments, limitations and restrictions that are the consequence of ankylosing spondylitis (AS). The International Classification of Functioning, Disability and Health (ICF) facilitates agreement on a comprehensive description of aspects of functioning that are relevant and typical for a specific disease by using ICF categories. The Comprehensive ICF Core Set for AS is the selection of 80 ICF categories that are typical and relevant for AS. Physical functioning and mobility have an essential but partial role in the broad view of functioning and health in AS. Consistent with the bio-psycho-social model, the ICF Core Set for AS also recognises the role of contextual factors, either environmental or personal, when understanding functioning. This new reference for functioning is now available for clinical practice and research. It can help to increase insight into the complexity of functioning and can serve as the starting point for the development of new instruments that address either global functioning or aspects of functioning.