Measurement of midshaft clavicle vertical displacement is not influenced by radiographic projection

BACKGROUND: Measured shortening of midshaft clavicle fracture fragments is known to be influenced by multiple factors. The influence of radiographic projection on vertical displacement is unclear. The aims of this study were (1) to quantify the difference in measurements of vertical displacement in an absolute, relative, and categorical manner between 5 different projections; (2) to quantify the differences in interobserver and intraobserver agreement using a standardized method for measuring vertical displacement; and (3) to assess the association between categorical and continuous descriptions of vertical displacement. MATERIALS AND METHODS: A clinical measurement study was conducted on 31 sets of digitally reconstructed radiographs in 5 different projections (15° and 30° caudocranial, anteroposterior, and 15° and 30° craniocaudal views). Categorical data on vertical displacement in quartiles from 0%-200% were obtained followed by measurements using a standardized method by 3 observers at 2 points in time. Interobserver and intraobserver agreement for each of the 5 views was calculated. RESULTS: The absolute and relative vertical displacement showed no statistically significant difference between any of the caudocranial, anteroposterior, and craniocaudal views. Intraclass correlation coefficients for intraobserver and interobserver agreement were good to excellent. The correlation between categorical outcomes and both absolute and relative vertical displacement was very strong. CONCLUSION: Unlike shortening, absolute and relative vertical displacement of the midshaft clavicle fracture is not significantly influenced by radiographic projection. Standardized measurements of vertical displacement may not be necessary for clinical use because the correlation between categorical and continuous measurements was found to be very strong.