Abstract
ObjectiveTo investigate the existence of distinct foot osteoarthritis (OA) phenotypes based on pattern of joint involvement and comparative symptom and risk profiles.MethodsParticipants ages ≥50 years reporting foot pain in the previous year were drawn from a population‐based cohort. Radiographs were scored for OA in the first metatarsophalangeal (MTP) joint, first and second cuneometatarsal, navicular first cuneiform, and talonavicular joints according to a published atlas. Chi‐square tests established clustering, and odds ratios (ORs) examined symmetry and pairwise associations of radiographic OA in the feet. Distinct underlying classes of foot OA were investigated by latent class analysis (LCA) and their association with symptoms and risk factors was assessed.ResultsIn 533 participants (mean age 64.9 years, 55.9% female) radiographic OA clustered across both feet (P < 0.001) and was highly symmetrical (adjusted OR 3.0, 95% confidence interval 2.1, 4.2). LCA identified 3 distinct classes of foot OA: no or minimal foot OA (64%), isolated first MTP joint OA (22%), and polyarticular foot OA (15%). After adjustment for age and sex, polyarticular foot OA was associated with nodal OA, increased body mass index, and more pain and functional limitation compared to the other classes.ConclusionPatterning of radiographic foot OA has provided insight into the existence of 2 forms of foot OA: isolated first MTP joint OA and polyarticular foot OA. The symptom and risk factor profiles in individuals with polyarticular foot OA indicate a possible distinctive phenotype of foot OA, but further research is needed to explore the characteristics of isolated first MTP joint and polyarticular foot OA.
Highlights
The pattern and location of joint involvement have played a fundamental role in shaping the current understanding of osteoarthritis (OA)
Our study found few other significant differences between these groups after adjusting for age and sex, the range of information gathered on risk factors was relatively limited
While patterning of OA in the foot has not been examined before in detail, our findings are consistent with previous observations that foot OA seems to affect multiple joints [6], and co-occurrence is present in certain midfoot joints [31]
Summary
The pattern and location of joint involvement have played a fundamental role in shaping the current understanding of osteoarthritis (OA). Whether it is the differing effects of risk alleles and gene expression on hip and knee OA [1], the contrasting risk profiles of tibiofemoral and patellofemoral joint OA [2], or the symmetry and clustering of small joint involvement in hand OA [3], joint-specific perspectives have proved insightful. Supported by Arthritis Research UK (grant 18174) and by the West Midlands North Comprehensive Local Research Network. PhD, Elaine Thomas, PhD, Thomas Downes, George Peat, PhD, Edward Roddy, DM, FRCP: Arthritis Research UK Primary Care Centre, Research
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