Predicting outcomes in the orthotic management of painful, idiopathic pes cavus

OBJECTIVE: People who have extremely high arched feet are subject to substantial foot pain, despite a lack of obvious pathology. Customized foot orthoses improve pain and function and reduce foot pressure, but their specificity is unclear. This study sought to identify predictive variables for improvement and to determine whether changes in foot pressure were correlated to changes in pain and function. DESIGN: Retrospective analysis of data from a randomized controlled clinical trial. SETTING: Clinical movement analysis laboratory, School of Physiotherapy, University of Sydney. PARTICIPANTS: Subjects with painful, idiopathic pes cavus. INTERVENTIONS: Sixty-six subjects received customized foot orthoses; sixty-seven subjects were allocated a sham intervention. MAIN OUTCOME MEASURES: Foot pressure data, location and intensity of pain, Foot Posture Index values, and anthropometric and quality of life variables. RESULTS: No relationship between change in foot pressure and change in symptoms was found in either group. No individual characteristics were linked to improvement. Subjects who improved most had substantial pain, lowest function scores, and lowest scores for quality of life variables at entry. There was a possible link, in the orthosis group, between improvement and pain confined to the rear-foot region. CONCLUSIONS: The mechanisms by which orthotic intervention is effective in improving pain and function in painful, idiopathic pes cavus remain unclear and equivocal. A strong placebo effect may be in place, or perhaps relatively small changes in foot pressure, even those brought about by a flexible insole with limited shock-absorbing properties, is enough to achieve a clinically meaningful change in symptoms.