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.
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.
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.
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.