Interrater Reliability of Diagnostic Ultrasound of the Plantar Fascia.

Background: Musculoskeletal ultrasound has been demonstrated to be an accurate measurement tool in the diagnostic evaluation of plantar fasciitis. Previous authors have shown a high degree of reliability between different machines and well-trained, experienced operators in evaluating the thickness and echogenicity of the plantar fascia. We aimed to demonstrate through this study that accurate ultrasonic measurements of the plantar fascia can be reliably reproduced by inexperienced operators as well by demonstrating reliability of measurements between medical student and physician operators.

Methods: Fifty-one healthy participants volunteered for this study. Each participant had both feet examined. The Lumify musculoskeletal ultrasound unit with a 12- to 4-MHz linear transducer was used for this evaluation. Three independent images of each participant's foot were taken by each operator and de-identified. For blinding, each de-identified image was then evaluated later by each evaluator using the ImageJ processing program. Plantar fascia thickness was measured at both the insertion on the calcaneus and a point 1 cm distal from the insertion. Each evaluator's three measurements at each point of the participant's fascia were then averaged for use in statistical analysis. An intraclass correlation coefficient (ICC) and Bland-Altman plots were used for statistical and visual interpretation of the results.

Results: Using the ICC method, the results indicated excellent reliability between operators of different experience levels. The ICC for each rater was 0.967 when evaluating the same image of the plantar fascia at 1 cm from the insertion and 0.804 when evaluating the same fascia using six different images.

Conclusions: The excellent reliability indicates the ease of use and practicality of the musculoskeletal ultrasound for clinical practice. For the most reliable results, we recommend that the point of measurement should be 1 cm from the insertion.