Validity of MRI and Ultrasound Volume Measurements of Foot Muscles and Plantar Fascia Cross-Sectional Area Within Older Adults With and Without Chronic Plantar Fasciitis.

INTRODUCTION

Intrinsic foot muscles and the plantar fascia are crucial for foot health, which diminishes with age and conditions such as chronic plantar fasciitis (PF). Ultrasound (US) is an accessible and cost-effective method for evaluating these structures. This study aims to assess the repeatability, reliability, and validity of plantar fascia thickness and flexor digitorum brevis (FDB) muscle measurements using US compared with MRI in individuals with and without PF.

METHODS

Foot muscle volume and plantar fascia thickness were measured via US and MRI in 28 participants with and without PF. Subsequently, the plantar fascia thickness and FDB volume were calculated using the OsiriX semiauto volume segmenter software for MRI and the truncated cone formula for both MRI and US. Intraclass correlation coefficients (ICCs), Pearson product correlations (r), minimal detectable differences (MDD), and standard error of measurement (SEm) were calculated.

RESULTS

High ICCs (r = 0.988-0.990) indicated excellent repeatability for all measurement techniques of the plantar fascia and FDB muscle. Reliability for plantar fascia and FDB measurements ranged from 3.98% to 5.50% and 5.06%-9.84%, respectively, across both groups. Validity was high with correlation values between 0.94 and 0.99 and Bland-Altman limits of agreement ranging from 2.6% to 9.2%.

CONCLUSIONS

US provides repeatable, reliable, and valid measurements of plantar fascia thickness and FDB muscle volume compared with MRI. It offers a cost-effective and accessible alternative for assessing foot health in clinical and research settings.