Background: Dynamic in-shoe plantar pressure assessment is used both in research and clinical practice to evaluate therapeutic footwear interventions in neuropathic diabetic patients. The aim was to determine the required number of footsteps for reliable and valid in-shoe plantar pressure data in these patients.
Methods: In 30 neuropathic diabetic patients wearing custom-made therapeutic footwear, in-shoe plantar pressures were measured for a minimum of 20 midgait walking steps per foot. For each incremental number of steps and for each of six anatomical regions per foot, peak pressure, pressure-time integral, contact area, contact time, and force-time integral were calculated. Reliability was assessed by calculating intraclass correlation coefficients. Validity was assessed by calculating the coefficient of variation between each n-step protocol and the 20-step reference protocol based on Limits of Agreement analysis. Data was considered reliable with intraclass correlation coefficients >0.90 and valid with coefficients of variation <10%.
Findings: Three steps per foot were required to obtain reliable data for each foot region and parameter. Depending on the parameter, between 7 and 17 steps per foot were required to obtain valid data. With the exception of deviant outcomes in three forefoot regions for force-time integral, overall 12 steps per foot were required for valid data.
Interpretation: For neuropathic diabetic patients wearing custom-made therapeutic footwear, 12 midgait steps per foot are required to obtain valid and reliable in-shoe plantar pressure data. This provides directions for the use of in-shoe plantar pressure analysis in research and clinical practice in this patient group.
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