Test-retest reliability of ultrasound measures of intrinsic foot motor function.

OBJECTIVE: To establish test-retest reliability of Intrinsic Foot Muscle (IFM) motor function measured using ultrasound imaging (USI).

SETTING: Laboratory.

DESIGN: Reliability Study.

PARTICIPANTS: 24 healthy young adults without history of ankle-foot injury.

MAIN OUTCOME MEASURES: Ultrasound measures of Abductor hallucis (AbdH), flexor digitorum brevis (FDB), quadratus plantae (QP) and flexor hallucis brevis (FHB) cross-sectional area (CSA) and thickness were assessed on 2 occasions, 3-10 days apart. The IFM were measured at rest, during active and resisted contraction, and during IFM exercises using USI and reported as activation ratios. Reliability was assessed with intraclass correlation coefficients (ICC2,k ) and interpreted as being excellent >0.75, 0.40-0.75 as fair to good, and <0.40 as poor.

RESULTS: Reliability of AbdH, FDB, QP, and FHB CSA and thickness resting measures were excellent (0.76-0.98). Active and resisted measures and IFM exercises had good to excellent reliability (0.66-0.99). Standard error of measurement (SEM) of resting CSA thickness measures ranged from 0.09 to 0.14 cm2 and 0.05-0.09 cm. Minimal detectable change (MDC) for CSA resting measures ranged from 0.25 to 0.40 cm2 and 0.14-0.24 cm for thickness measures. IFM activation SEM during exercises ranged from 0.01 to 0.11, with MDCs ranging from 0.03 to 0.31.

CONCLUSION: There is potential utility for USI assessment of IFM neuromotor function in research and clinical practice.