Patients who undergo trauma-related amputation are rarely screened for low bone mineral density(BMD) in the post-trauma setting. The current study aims to correlate femoral neck Hounsfield units(HU) measured on CT scan to dual-energy x-ray absorptiometry(DEXA) T-scores allowing evaluation of BMD over time after lower extremity trauma-related amputation.
Retrospective Cohort Study SETTING:: United States Military Trauma Referral Center PATIENTS:: Military combat-related lower extremity amputees with both DEXA and CT scans within six months of each other.
None MAIN OUTCOME MEASURES:: Correlation between femoral neck comprehensive mean HU and BMD, and HU threshold for low BMD.
Regression model correlation(r) between CT HU and DEXA T-score was r=0.84(95%CI 0.52-0.94) and r=0.81(95%CI 0.57-0.92) when CT imaging was separated from DEXA by less than four and five months, respectively. Beyond five months separation, correlation decreased to r=0.60(95%CI 0.29-0.80). Using a receiver operator characteristic curve for mean comprehensive HU to determine low BMD with four-month cut-off, a threshold of 151 HUs was 97% sensitive and 84% specific to identify low BMD, while 98 HUs was 100% sensitive and 100% specific to identify osteoporosis.
Using opportunistic CT, clinicians can reliably estimate BMD in trauma-related amputees. This information will inform providers making decisions regarding weightbearing and bisphosphonate therapy to limit further loss. Future phases of this study will aim to use this correlation to study the effects of weightbearing advancement timing, bisphosphonate therapy, and interventions on the natural history of bone density after amputation.
Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.