Predictive factors of total hip replacement due to primary osteoarthritis: a prospective 2 year study of 505 patients

Objectives: To determine the 2 year total hip replacement (THR) rate and to identify factors predictive of THR due to primary osteoarthritis (OA). Methods: A 2 year prospective cohort study. Inclusion criteria were primary hip OA, with a history of pain for 6 months, and patients' pain assessment of >= 30 mm on a visual analogue scale ( 0 - 100 mm). Predictive factors of THR were identified by univariate then multivariate analysis using logistic regression. Potential predictors considered were demographic, radiographic ( localisation and severity of OA), and patients' assessment of symptomatic severity of OA. Results: Of the 741 patients enrolled, 505 (68.2%) patients, mean (SD) age 64.0 (10.1) years, mean ( SD) disease duration 4.7 (5.2) years, had complete 2 year data. There was no difference between the completer and non-completer groups. During follow up, 189/505 (37.4%) patients had a first THR. By multivariate analysis, predictors of THR were Kellgren-Lawrence radiographic grade ( grade III: odds ratio ( OR) = 3.3 (95% confidence interval ( 95% CI) 1.7 to 6.4); grade IV: OR = 5.3 ( 95% CI 2.6 to 10.8)), high mean patient global assessment during the first 6 months ( OR = 2.2 ( 95% CI 1.4 to 3.2)), and previous non-steroidal anti-inflammatory drug ( NSAID) intake ( OR = 1.5 ( 95% CI 1.0 to 2.4)). For two of these factors together, OR = 3.0 ( 95% CI 1.6 to 5.9), for three factors together, OR = 5.6 ( 95% CI 2.6 to 12.2). Conclusion: The 2 year rate of THR was high in this group of patients with painful hip OA: 37.4%. Radiological grade, mean patient global assessment, and the need for NSAIDs were predictive of THR.