Objective Pain experience is heterogenous and linked to increased risk of fractures. Pain heterogeneity reflects that pain population consists of different subgroups of which the risk of fractures may differ. We sought to compare whether incident fractures risk over 10.7 years are different among three knee pain subgroups/phenotypes we previously identified.
Methods A total of 1099 participants (mean age 63 years) from a population-based cohort study were studied at baseline and followed up at 2.6 (n=875), 5.1 (n=768) and 10.7 years (n=563). Using latent class analysis that considered pain-related factors (i.e., sex, body mass index, emotional problems, education level, comorbidities, number of painful sites and MRI-detected knee structural damage), three knee pain phenotypes were previously identified: Class 1: high prevalence of emotional problems and low prevalence of structural damage (26%); Class 2: high prevalence of structural damage and low prevalence of emotional problems (20%); Class 3: low prevalence of emotional problems and low prevalence of structural damage (54%). Pain severity in the Class 1 and Class 2 was greater than that in Class 3. Fractures were self-reported, and falls risk was measured using the Physiological Profile Assessment.
Results There were 6 new hip, 19 vertebral, and 126 non-vertebral fractures during 10.7-year follow-up. Compared with Class 3, Class 1 had a higher risk of vertebral (risk ratio (RR)=3.32, 95%confident interval (CI): 1.04-10.63) and non-vertebral fractures (RR=1.47, 95%CI:1.04-2.07) after controlling for covariates, bone mineral density and falls risk. Participants in Class 2 also had a higher risk of vertebral fracture relative to those in Class 3 (RR=3.90, 95%CI: 1.02-14.84), but not non-vertebral fracture. No risk difference in hip fractures was found between classes.
Conclusion Class 1 and Class 2 had a higher risk of incident fractures than Class 3, highlighting that targeted preventive strategies for fractures are needed in pain population.