People with radiographic OA of the foot fall into two distinct groups, having disease either restricted to the first metatarsophalangeal joint or distributed more widely throughout the midfoot, new research suggests.
British rheumatologist Dr Ed Roddy, from Keele University, and colleagues recruited 533 patients aged 50 or older who reported foot pain in a survey, although they had not necessarily sought treatment.
All participants had standardised weight-bearing dorso-plantar and lateral radiographs of both feet interpreted by a single radiologist.
Dr Roddy and colleagues wrote in Arthritis Care and Research that three distinct classes emerged: 64% had no or minimal foot OA, 22% had OA only in the MTP joint, and 15% had polyarticular foot OA that usually included the first and second cuneometatarsal, first cuneiform and talonavicular joints.
“The symptom and risk factor profiles in individuals with polyarticular foot OA indicate a possible distinctive phenotype,” they said.
Risk factors for polyarticular disease included older age, higher BMI and being female.
Women accounted for 54% of patients with isolated first MTP disease but 74% of those with polyarticular disease.
Both types of foot OA were usually symmetrical, but polyarticular involvement caused more pain and disability.
The subgroup with isolated first MTP joint involvement suggested that some people have a predilection for developing OA in this joint, possibly as a result of altered foot structure or inappropriate footwear.
“Although non-statistically significant, there was a slight increase in the probability that individuals had worn high or very high-heeled shoes between the ages of 20 to 49 years, which is consistent with a previous study that found high-heeled footwear to be associated specifically with disorders of the forefoot and toes,” they said.
Systemic factors probably contributed more strongly to polyarticular disease than to isolated first MTP changes. “This is consistent with the strong patterns of symmetry and multiple joint involvement that has been seen in hand OA,” they said.
“This has been ascribed to post-menopausal changes, increasing the susceptibility of females to the development of generalised OA.”
The findings had to be confirmed and explored in more detail but they could have implications for the choice of treatment in the subtypes, including the role of steroid joint injections, insoles and a range of surgical procedures.