Predictors of response to prefabricated foot orthoses or rocker-sole footwear in individuals with first metatarsophalangeal joint osteoarthritis

BACKGROUND Osteoarthritis of the first metatarsophalangeal joint (1st MTPJ OA) is a common and disabling condition commonly managed with footwear and orthotic interventions. The objective of this study was to identify factors associated with a successful treatment response in people with 1st MTPJ OA provided with prefabricated orthoses or rocker-sole footwear as part of a randomised clinical trial. METHODS People with 1st MTPJ OA (n = 88) who participated in a randomised trial were allocated to receive prefabricated foot orthoses (n = 47) or rocker-sole footwear (n = 41) and completed a baseline questionnaire including information on demographics, anthropometrics, general health, pain characteristics (including the Foot Health Status Questionnaire [FHSQ] and Foot Function Index [FFI]) and perceptions of the interventions, and a clinical assessment of foot posture, range of motion, radiographic severity and in-shoe plantar pressures. Adherence was documented using diaries. At 12 weeks, participants documented their perception of improvement on a 15-point scale. Those reporting at least moderate improvement on this scale were classified as 'responders'. RESULTS There were 29 responders (62%) in the orthoses group and 16 responders (39%) in the rocker-sole group. In the orthoses group, responders had greater baseline pain severity while walking, a higher FFI difficulty score, and wore their orthoses more frequently. In the rocker-sole group, responders had a higher FFI stiffness score and greater radiographic severity. However, the accuracy of these variables in identifying responders in each group was modest (62 and 53%, respectively). CONCLUSION The response to prefabricated orthoses or rocker-sole footwear in people with 1st MTPJ OA is related to measures of increased pain and disease severity. However, the overall classification accuracy associated with these factors is not sufficient for identifying individuals who are most likely to benefit from these interventions. TRIAL REGISTRATION Australian New Zealand Clinical Trials Registry: ACTRN12613001245785.