Hand Function Trajectories over time in Hand Osteoarthritis in relation to pain trajectories and loss to follow-up

<title>Abstract</title> <bold>Background</bold> Hand function is an important but often overlooked outcome in hand osteoarthritis. We aimed to compare trajectories of hand function and hand pain in patients with primary hand osteoarthritis (OA), and explore the influence of loss of follow-up over time on Latent Class Growth Analysis (LCGA). <bold>Methods</bold> Patients from the HOSTAS (Hand Osteoarthritis in Secondary care) cohort and their annual scores on the Australian Canadian Hand Osteoarthritis Hand Index (AUSCAN) were analyzed with LCGA after two, four, five and eight years. LCGA models of hand function and hand pain were selected on statistical criteria and clinical interpretability. Clinical significance of the modeled AUSCAN change was defined by the minimal clinical important difference. <bold>Results</bold> Of 538 included patients (mean [SD] function 15.6 [SD 8.4, range 0-36] and pain 9.3 [SD 4.3, range 0-20]), 261 patients (45.8%) still participated after 8 years. Loss to follow-up of participants over 8 years was not random: patients who were lost to follow-up differed from the baseline cohort at all time points, with generally worse scores at baseline than those who completed follow-up. Hand function trajectories showed worsening over time and reached clinical significance at the midterm timepoint. Hand pain trajectories remained stable over the course of 8 years. <bold>Conclusion</bold> Moderate and severe hand function trajectories worsened up to 5 years of follow-up, whereas hand pain trajectories remained stable over the course of 8 years. The use of LCGA trajectories in rheumatological cohorts with loss to follow-up warrants careful interpretation. Non-random loss to follow-up has in all likelihood influenced the observed function trajectories.