Pixel-Based DXA-Derived Structural Properties Strongly Correlate with pQCT Measures at the One-Third Distal Femur Site.

Abstract

While bone mineral density has been traditionally used to quantify fracture risk for individuals with spinal cord injuries, recent studies are including engineering measurements such as section modulus and cross sectional moment of inertia. These are almost exclusively calculated by peripheral QCT scanners which, unlike DXA scanners, are rarely found in clinical settings. Using fifty-four fresh frozen femora, we developed and validated a pixel-by-pixel method to calculate engineering properties at the distal femur using a Hologic QDR-1000 W DXA scanner and compared them against similar parameters measured using a Stratec XCT-3000 peripheral QCT scanner. We found excellent agreement between standard DXA and pixel-by-pixel measured BMD (r 2 = 0.996). Cross-sectional moment of inertia about the anteroposterior axis measured using DXA and pQCT correlated very strongly (r 2 = 0.99). Cross-sectional moment of inertia about the anteroposterior axis measured using DXA also correlated strongly with pQCT measured bone strength index (r 2 = 0.99). These correlations indicate that DXA scans can measure equivalent pQCT parameters, and some existing DXA scans can be reprocessed with pixel-by-pixel techniques. Ultimately, these engineering parameters may help better quantify fracture-risk in fracture-prone populations such as those with spinal cord injuries.