Development and Reliability of a Standardized Ultrasound Protocol for Adult Femoral Trochlear Morphology Assessment

Abstract Objective To develop a standardized ultrasound protocol for measuring osseous-based femoral trochlear sulcus angle and trochlear depth in adults and determine its intra-rater and inter-rater reliability and measurement error. Methods In this prospective methodological study, 35 adults contributed 70 knees. A proximal axial ultrasound protocol was developed iteratively from published methods and pilot scanning. Two examiners—an experienced sports medicine specialist and a sports medicine trainee—independently acquired three images per knee in two sessions. Session means were analyzed. Reliability was quantified using 2-way random-effects, absolute-agreement, single-measure intraclass correlation coefficients (ICC[A,1]); 95% confidence intervals were estimated using participant-cluster bootstrap resampling. Standard error of measurement (SEM), minimal detectable change at 95% confidence (MDC95), and Bland–Altman agreement was calculated. Results Intra-rater reliability was excellent for sulcus angle (ICC, 0.928 and 0.921) and trochlear depth (ICC, 0.936 and 0.925). Primary inter-rater reliability was good for sulcus angle (ICC, 0.887; 95% confidence interval, 0.798–0.938) and trochlear depth (ICC, 0.852; 95% confidence interval, 0.708–0.930). The inter-rater MDC95 was 6.65° for sulcus angle and 1.06 mm for trochlear depth. Small fixed inter-rater differences were observed (0.99° and − 0.20 mm, respectively), without proportional bias. Conclusion The standardized proximal axial protocol produced good-to-excellent reliability for adult femoral trochlear morphology assessment across examiners with different ultrasound experience. The accompanying SEM and MDC95 values provide practical thresholds for interpreting repeat measurements.