Reliable technique for acromion density assessment on CT

Acromial stress fracture (ASF) is an uncommon but acknowledged complication of reverse total shoulder arthroplasty (RTSA). There is no standardised method to directly measure the bone mineral density of the acromion to allow a detailed analysis of the potential mechanism of ASF. The aim is to establish a reliable and reproducible technique for measurement of acromial density on computer tomography (CT).

A retrospective review on CT scans obtained for three groups of patients: those planned for RTSA (n = 26); age and gender-matched non-operative (n = 26); and young non-operative patients (n = 28) were performed. Standardised axial images of 1 mm thickness at 1 mm increments were created following horizontal straightening on the coronal and sagittal views. To assess inter-rater reliability, two senior CT radiographers performed density measurements using standard region of interest (ROI) tool on the CTs with the ROI placed on the mid (ROI 1) and posterior (ROI 2) acromion. ROIs were selected as the most common locations for acromion fracture post RTSA. Measurements were repeated at least 6 weeks apart. Intra-class coefficients (ICC) were used to determine intra- and inter-rater reliability.

ICCs demonstrated good to high intra-rater and inter-rater reliability for both ROI 1 and ROI 2 across all three groups. The lower margin of 95% confidence intervals was more than 0 for all intra-class coefficients.

This study demonstrates a reliable method of measuring acromion density on CT. This method can be used to assess bone mineral density in the clinical setting and in future studies investigating ASF following RTSA.