Correlation of Hounsfield Unit Measurements on Computed Tomography of the Shoulder with DXA Scan and FRAX Scores: A Potential for Opportunistic Screening.

BACKGROUND The diagnosis of bone mineral density (BMD) abnormalities involves dual-energy x-ray absorptiometry (DXA), but few patients complete this after a fragility fracture. Assessment of BMD utilizing Hounsfield Unit (HU) measurements from Computed Tomography (CT) scans has correlation with DXA results in prior studies. We aimed to evaluate the correlation between shoulder CT HU and DXA scores. METHODS Billing databases of three academic institutions were queried for patients underwent both DXA and CT scan of the upper extremity within one year of each other. DXA T-scores for spine, hip, and femoral neck were recorded. BMD status was defined based on composite T-score, using the lowest T-score in the spine, hip, or proximal femur. CT scans were measured for HU over four slices, recorded to create a bone column, then averaged. The patients' risks of major osteoporosis-related fracture and hip fracture were calculated using the Fracture Risk Assessment Tool (FRAX). RESULTS In total, 300 patients were included. A positive correlation was found between composite T-scores and HU for glenoid and proximal humerus (0.36; 0.17). The proximal humerus HU was significantly associated with the BMD T-score for the hip (p=0.01); the glenoid HU was significantly associated with BMD T-scores for the hip, spine, and femoral neck (p=0.002; p=0.001; p=0.002). A 10-year risk of hip fracture >3% was associated with lower proximal humerus HU. CONCLUSIONS Our study is the first to discover significant correlations between HU at the glenoid and proximal humerus and risk factors as established by the FRAX scoring system. LEVEL OF EVIDENCE Diagnostic Level III. See Instructions for Authors for a complete description of levels of evidence.