Defining discriminative pain trajectories in hip osteoarthritis over a 2-year time period.

Background: Although pain due to osteoarthritis (OA) generally deteriorates over time, there is a large individual variation in the course of pain. This study examines the different longitudinal trajectories of patients with hip pain due to OA.

Methods: Data from a previously performed randomised controlled trial were used to investigate the course of pain over 2 years in 222 patients with clinically and radiographically determined hip OA. Pain was measured with a visual analogue scale (0-100). Latent class growth analysis was used to determine the number of trajectories of patients with hip pain due to OA.

Results: Analyses yielded five trajectories of pain due to hip OA. Trajectory 1 ('mild pain'; n=69) consists of patients with stable mild pain. Patients in trajectory 2 ('moderate pain'; n=31) fluctuated slightly between moderate and severe pain levels. Trajectory 3 ('always pain'; n=32) consists of patients with severe pain. Patients in trajectory 4 ('regularly progressing'; n=48) started with mild pain and progressed slowly to moderate pain. Trajectory 5 ('highly progressing'; n=42) patients also started with mild pain but quickly progressed to severe pain over 2 years. Compared with the 'mild pain' group, patients in the 'always pain' group had more severe radiographic hip OA, morning stiffness and decreased range of motion. The 'highly progressing' group had more severe radiographic hip OA and morning stiffness.

Conclusions: Latent class growth analysis applied to longitudinal data of patients with hip OA identified five distinct trajectories of pain. More studies are needed to externally validate these findings.