Ultrasound Measurement of Plantar Fascia Thickness: A Learning Curve Analysis Between a Novice and an Expert Examiner

This study aimed to explore interobserver differences, intraobserver consistency, and temporal changes in ultrasound-based plantar fascia thickness measurements between an experienced musculoskeletal sonographer and a student examiner. Additionally, the study described the student’s longitudinal progression during the measurement acquisition period under supervised conditions. Materials and Methods: This cross-sectional, descriptive observational study included 84 adults, of whom 42 presented plantar fasciopathy and 42 had no history of heel pain. All participants underwent ultrasound assessment of plantar fascia thickness performed by two observers—a novice student and an expert examiner—each obtaining two measurements per participant. Statistical analyses focused on detecting differences between observers and temporal changes in measurement performance. Intraclass Correlation Coefficients (ICCs) were calculated to further explore agreement. Results: In the overall analysis, no statistically significant differences were detected at the group level between student and expert measurements. However, when analyses were stratified by time periods, statistically significant differences were observed during the initial phase (November–December 2024; p = 0.026). These differences were no longer consistently detected in subsequent periods. Additionally, interobserver agreement appeared to increase over time; however, this observation is purely descriptive and should be interpreted with caution, as no formal comparisons between ICC estimates were performed and confidence intervals overlap. Conclusions: These findings suggest a progressive reduction in measurement differences between observers over time, consistent with a learning-related effect. However, the results should be interpreted as exploratory and do not constitute evidence of formal interobserver reliability. The findings highlight the potential importance of structured ultrasound training and supervised practice in improving agreement between observers in both clinical and educational settings.