Symptomatic Course of Foot Osteoarthritis Phenotypes: An 18-Month Prospective Analysis of Community-Dwelling Older Adults

Objective: Osteoarthritis (OA) is a heterogeneous disease, and symptom progression at the foot is unclear. This study investigated the symptomatic course of 3 predefined foot OA phenotypes over an 18-month period. Methods: The Clinical Assessment Study of the Foot is a community-based cohort of adults ages ≥50 years in North Staffordshire, UK. Participants who reported foot pain in a postal health survey and underwent radiographic assessment were mailed an 18-month followup survey. Changes in descriptive and symptomatic outcomes over 18 months were compared across the 3 phenotypes to determine within-phenotype changes and between-phenotype differences. Results: Of 533 participants at baseline, 478 (89.7%) responded at 18 months. All 3 phenotypes showed small within-phenotype improvements in mean foot pain severity (scale range 0–10, where 0 = no pain and 10 = worst pain): no or minimal foot OA (18 months 4.0, mean change −1.15 [95% confidence interval (95% CI) −1.46, −0.83]), isolated first metatarsophalangeal (MTP) joint OA (18 months 4.1, mean change −0.60 [95% CI −1.11, −0.10]), and polyarticular foot OA (18 months 5.1, mean change −0.77 [95% CI −1.42, −0.12]). The isolated first MTP joint OA phenotype had an increased likelihood of hallux valgus in the left foot (adjusted odds ratio 2.96 [95% CI 1.23, 7.12]) compared to the no or minimal foot OA phenotype. Conclusion: Three foot OA phenotypes showed few descriptive or symptomatic changes over 18 months. Future clinical trials should consider that people recruited with mild-to-moderate symptomatic foot OA appear likely to remain relatively stable with usual care. Longer-term followup using additional time points is required to describe further the natural history of foot OA.