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Joint space narrowing, cartilage and physical function: are we deceived by measurements and distributions?
  1. Robert Landewé1,2,
  2. Désirée van der Heijde3
  1. 1Maastricht University Medical Center, Maastricht, The Netherlands
  2. 2CAPHRI School for Public Health and Primary Care, Maastricht, The Netherlands
  3. 3Leiden University Medical Center, Leiden, The Netherlands
  1. Correspondence to Professor Robert Landewé, Maastricht University Medical Center, PO Box 5800, Maastricht 6202 AZ, The Netherlands; r.landewe{at}mumc.nl

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Irreversible physical function loss—that part of physical function loss that remains in the absence of clinically perceptible disease activity—was elegantly conceptualised by Aletaha et al1 a few years ago. They introduced the idea of the irreversible health assessment questionnaire (HAQ) score, which is the residual HAQ score if a patient is in clinical remission. While one may argue the construct validity of an irreversible HAQ score (eg, the absence of clinical disease activity does not necessarily imply the absence of joint inflammation), the model is valuable because it allows the investigator to disentangle the contribution of signs and symptoms and that of structural damage on physical function.

From many studies performed during the past 10 years we have learnt that structural joint damage independently of disease activity contributes to explaining physical function (eg, Welsing et al).2 Therefore, in the absence of disease activity, it is structural joint damage that explains irreversible physical function loss.

Aletaha et al1 have taken up his hypothesis as a starting point, and have tried to unravel the relationship between the two components of radiographic damage—erosions and joint space narrowing (JSN)—and irreversible physical function loss. The analysis they have done, which is presented in this issue of the journal, is in all aspects provocative and challenging, and we truly commend the authors for taking up this exercise (see page 733). Strong elements of their study are the access to databases of large clinical trials with inherently high-quality data and completeness, as well as a hypothesis-driven approach. It is a broadly endorsed idea among clinicians that JSN matters more than erosions. So, the main conclusion of the analysis by Aletaha et al,1 namely that JSN more than erosions impacts irreversible physical function loss, will be easily accepted by the clinical readership. …

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