Intra- and inter-rater reliability of medial elbow joint space width on static ultrasound images: a cross-sectional reliability study

In this study of static ultrasound images from healthy elbows, intra-rater variability was found to be small, while inter-rater agreement was good among seven orthopedic surgeons with varying experience. These findings reflect measurement reproducibility under standardized static image conditions, independent of image acquisition variability. For practical interpretation, an inter-rater threshold of approximately 0.8-0.9 mm was required to exceed the measurement noise in this dataset, supporting the use of two-session averaging when feasible. Because the present study only evaluated the measurement component, these results likely represent the upper limit of achievable reliability in clinical practice.