Fig. 3

Hypothetical depiction of pain category severity and progressive disease stage over time. While disease progression is likely occurring in limited periods follow by periods of inertia [35], pain trajectories appear to be progressing more steadily, although slowly [19, 32, 33]. Weight-bearing pain is the first pain category to present, followed by non-weight-bearing pain [19]. Variable radiographic disease progression rates may blur the otherwise expected hypothetical association between pain severity and risk of progression at one or very few given time points