Reliability of Various Measurement Stations for Determining Plantar Fascia Thickness and Echogenicity

Abstract

This study aimed to determine the relative and absolute reliability of ultrasound (US) measurements of the thickness and echogenicity of the plantar fascia (PF) at different measurement stations along its length using a standardized protocol. Twelve healthy subjects (24 feet) were enrolled. The PF was imaged in the longitudinal plane. Subjects were assessed twice to evaluate the intra-rater reliability. A quantitative evaluation of the thickness and echogenicity of the plantar fascia was performed using Image J, a digital image analysis and viewer software. A sonography evaluation of the thickness and echogenicity of the PF showed a high relative reliability with an Intra class correlation coefficient of ≥0.88 at all measurement stations. However, the measurement stations for both the PF thickness and echogenicity which showed the highest intraclass correlation coefficient (ICCs) did not have the highest absolute reliability. Compared to other measurement stations, measuring the PF thickness at 3 cm distal and the echogenicity at a region of interest 1 cm to 2 cm distal from its insertion at the medial calcaneal tubercle showed the highest absolute reliability with the least systematic bias and random error. Also, the reliability was higher using a mean of three measurements compared to one measurement. To reduce discrepancies in the interpretation of the thickness and echogenicity measurements of the PF, the absolute reliability of the different measurement stations should be considered in clinical practice and research rather than the relative reliability with the ICC.

Keywords: musculoskeletal; plantar fascia; reliability; sonography.

Figure 1

Image showing protocol for standardization of transducer head placement with yellow line marking the width of the sole of the foot at a point aligned parallel with the navicular tuberosity; black line marking the midpoint of the sole of the foot; red line marking placement of middle of transducer probe 1 cm medial to the middle of the foot; the blue outline shows the total surface area of the plantar surface of foot in contact with transducer head.

Figure 2

Sonograph showing measurement of plantar fascia (PF) thickness at five various points: its insertion at medial calcaneal tubercle; 0.5, 1, 2 and 3 cm distal, with red lines showing caliper positioning for analysis and measurements.

Figure 3

(A) Sonograph showing placement of regions of interest (ROI) at measurement stations along the length of the PF distally from insertion (0) to 1 cm distal; and (B) 1 to 2 cm distal from its insertion at the medial calcaneal tubercle with the yellow frame indicating the selected ROIs along the lengths of the PF.