The objective of this study was to directly compare in situ femoral dual-energy X-ray absorptiometry (DXA) and in vitro chemical analysis (ash weight and calcium) with mechanical failure loads of the proximal femur, and to determine the influence of bone size (volume) and density on mechanical failure and DXA-derived areal bone mineral density (BMD, in g/cm2). We performed femoral DXA in 52 fixed cadavers (age 82.1 +/- 9.7 years; 30 male, 22 female) with intact skin and soft tissues. The femora were then excised, mechanically loaded to failure in a stance phase configuration, their volume measured with a water displacement method (proximal neck to lesser trochanter), and the ash weight and calcium content of this region determined by chemical analysis. The correlation coefficient between the bone mineral content (measured in situ with DXA) and the ash weight was r = 0.87 (standard error of the estimate = 16%), the ash weight allowing for a better prediction of femoral failure loads (r = 0.78; p < 0.01) than DXA (r = 0.67; p < 0.01). The femoral volume (r = 0.61; p < 0.01), but not the volumetric bone density (r = 0.26), was significantly associated with the failure load. The femoral bone volume had a significant impact (r = 0.35; p < 0.01) on the areal BMD (DXA), and only 63% of the variability of bone volume could be predicted (based on the basis of body height, weight and femoral projectional bone area. The results suggest that accuracy errors of femoral DXA limit the prediction of mechanical failure loads, and that the influence of bone size on areal BMD cannot be fully corrected by accounting for body height, weight and projected femoral area.
The objective of this study was to determine the effect of fixation, soft tissues, and scan projection on bone mineral measurements with dual energy X-ray absorptiometry (DXA). In seven fresh cadavers, DXA scans were obtained within 48 hours of death and after 10 months of fixation with 5% formalin/95% ethanol. The measurements showed a high linear relationship (r2 > 0.97; SEE% < 10%), with no significant deviation after fixation (except for total body BMD: -3.1%). In 14 specimens, the precision of femoral and spinal analyses was determined under in situ and ex situ conditions. There was no significant difference between ex situ and in situ reproducibility, the coefficient of variation being < 3% for the BMC and < 2% for the BMD (except at the greater trochanter). The effect of the soft tissues and scan projection was assessed in 83 cadavers aged 80.4 +/- 10.3 years. The soft tissues had only a small effect on analyses of the total femur (r2 > 0.90; SEE% < 9%), but led to more substantial deviations in regional femoral analyses and in the spine (r2 = 0.78-0.90; SEE% = 8-22%). Comparing lateral with anterior-posterior (AP) spinal scans, the vertebral bodies were found to occupy 40.2 +/- 7.2% of the BMC, and 62.0 +/- 11.2% of the BMD, the ranges being 26-58%, and 38-91%, respectively. There were large deviations from linearity between in situ AP and ex situ lateral spinal scans with r2 values of 0.63 and 0.73 for BMD and BMC (SEE% = 52% and 27% relative to the vertebral body), respectively.
At least in this case, our treatment led to shorter recovery and avoidance of halo fixation. Our new therapeutic approach to patients with Grisel's syndrome might lead to a shorter recovery.
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