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 = 0.996). Cross-sectional moment of inertia about the anteroposterior axis measured using DXA and pQCT correlated very strongly (r = 0.99). Cross-sectional moment of inertia about the anteroposterior axis measured using DXA also correlated strongly with pQCT measured bone strength index (r = 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.

The Effects of Exercise and Activity-Based Physical Therapy on Bone after Spinal Cord Injury

“…Dual-energy X-ray absorptiometry (DXA) is the standard to assess osteoporosis and fracture risk at traditional osteoporosis sites (e.g., lumbar spine and hip), via the quantification of areal (a)BMD and T-scores [ 23 ]. Specialized DXA techniques have also been developed to assess distal femur and/or proximal tibia aBMD after SCI [ 17 , 24 , 25 ], although not all the DXA systems are capable of imaging these locations and T-scores have not been established at these sites. As such, some have suggested using traditional osteoporosis sites as surrogates for the distal femur and proximal tibia.…”