Changes in frailty and incident risk of degenerative bone and joint diseases and their multimorbidity: a prospective cohort study

Background: Frailty reflects multisystem physiological vulnerability and has been associated with an array of adverse health outcomes. However, evidence on how frailty and its longitudinal changes relate to degenerative bone and joint diseases (DBJDs) and their multimorbidity remains limited. Methods: We conducted a prospective cohort study using data from the UK Biobank (UKB). Frailty was evaluated using a validated frailty index (FI). Changes in frailty were characterized by frailty status transitions, the rate of change in FI (ΔFI), and cumulative burden (total FI). Incident DBJDs including osteoporosis, osteoarthritis, and intervertebral disc degeneration as well as degenerative bone and joint multimorbidity (DBJM) were ascertained through linkage to health records. Cox regression models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (95%CIs). Results: Compared with baseline non-frail participants, frail individuals had substantially higher risks of both DBJDs (HR = 2.06, 95%CI = 2.01-2.11) and DBJM (HR = 3.89, 95%CI = 3.62-4.18), with pre-frail participants showing intermediate risks. In transitions analyses, compared with participants who remained stable, those who progressed to worse status had increased risks of DBJDs (non-frail → pre-frail/frail: HR = 1.33, 95%CI = 1.21-1.47; pre-frail → frail: HR = 1.39, 95%CI = 1.20-1.60). In contrast, frailty recovery from pre-frailty to non-frailty was associated with a decreased risk of DBJDs (HR = 0.80, 95%CI = 0.71-0.91), although evidence for frailty recovery was less consistent overall. Conclusion: Frailty status and its longitudinal changes are strongly associated with the risk of incident DBJDs and DBJM. Frailty progression and cumulative frailty burden confer substantially increased risks, while frailty recovery may be associated with a lower risk, although the evidence remains limited.