Supplementary Material for: Incidence and Progression of Foot Osteoarthritis in a Longitudinal Cohort: the Johnston County Osteoarthritis Project

Introduction: To examine the incidence and progression of foot osteoarthritis (OA), as well as associated factors, in a community-based cohort.
Methods: Baseline (2013-2015) and follow-up (2016-2018) foot radiographs were available for 541 participants (71% women, mean age 69 years; 35% Black, 53% with obesity). The LaTrobe Foot Atlas was used to examine osteophytes (OP, score 0-3) and joint space narrowing (JSN, score 0-3) at 5 joint sites. Incident foot radiographic OA (rOA) was a baseline score <2 OP and JSN in all 5 joints with ≥2 OP or JSN at follow-up in any of the joints. Progression was a worsening OP or JSN score in a joint with baseline foot rOA. At baseline and follow-up, participants reported presence/absence of foot symptoms and completed the Foot and Ankle Outcome Score (FAOS) for each foot. Joint-based logistic regression models with generalized estimating equations were used to examine associations (adjusted odds ratio [aOR], 95% confidence interval [CI]) of foot rOA incidence and progression and with covariates.
Results: Among 928 feet without baseline rOA, 4% developed incident foot rOA (2% of those developed symptoms). Among 154 feet with baseline foot rOA, 55% had radiographic progression (16% of those had symptoms). Women and those with higher body mass index (BMI) were more likely to have incident foot rOA (aOR [95% CI] = 4.10 [1.22, 13.8] and 1.60 [1.31, 1.97], respectively); history of gout was associated with incidence or progression of foot rOA (2.75 [1.24, 6.07]. BMI was associated with worse scores on all FAOS subscale (aORs range 1.21-1.40).
Conclusion: Progression of foot rOA is common but not necessarily related to worsening symptoms. BMI may be a modifiable risk factor for foot OA.