Biomechanical evaluation of dual-energy X-ray absorptiometry for predicting fracture loads of the infant femur for injury investigation: an in vitro porcine model.
OBJECTIVE
The purpose of this study was to determine the ability of bone mineral density (BMD) measured by dual-energy x-ray absorptiometry (DXA) and geometry measured by biplanar x-ray to predict fracture mechanics in vitro in an immature femur model.


METHODS
Prospective analysis of radiographic and biomechanical data was performed.


METHODS
In vitro experimentation.


METHODS
Bone geometry and DXA data were obtained before mechanical testing. Twenty-two porcine femora from males and females (age 3 to 12 months; body weight 3.6 to 7.0 kilograms) were fractured. Mechanical tests were performed on the diaphysis of the femora in two loading configurations: (a) three-point bending to simulate loads that result in transverse fractures; and (b) torsion to simulate twisting injuries that result in spiral fractures.


METHODS
Correlation of radiographic data with the experimentally determined bone strength.


RESULTS
Three-point bending consistently resulted in transverse fractures. Femoral diaphysis BMD (mean, 0.304 grams per square centimeter; SD, 0.028 grams per square centimeter) strongly correlated (r2 = 0.938) to fracture load in bending. Load at failure ranged from 530 to 1,024 N (mean, 726 N; SD, 138 N), consistent with the findings of Miltner. Empirically derived strength parameters coupling BMD with geometry accurately predicted bending loads (r2 = 0.84, p < 0.001) and energy to failure (r2 = 0.88, p < 0.05). Torsional loading failed to generate spiral fractures consistently, resulting in either end plate or diaphyseal fractures. Load at failure for torsion ranged from 1,383 to 3,559 Newton-millimeters (mean, 2,703 Newton-millimeters; SD, 826 Newton-millimeters). Because of these inconsistent fracture results, empirical strength parameters for torsion could not be derived.


CONCLUSIONS
BMD coupled with geometry is a strong predictor of bending fracture loads in the immature femoral diaphysis. A similar relationship could not be shown for torsion because of inconsistent failure results. This study represents an initial attempt at developing a methodology for predicting the strength of young bones from radiographic measures. Further research is required to establish this methodology and to show the necessary correlation with immature human bone.
Pierce
M C
MC
Children's Hospital of Pittsburgh, Pennsylvania, USA. piercem@chplink.chp.edu
Valdevit
A
A
Anderson
L
L
Inoue
N
N
Hauser
D L
DL
D015502:Absorptiometry, Photon; D000818:Animals; D000831:Animals, Newborn; D001696:Biomechanical Phenomena; D015519:Bone Density / Q000502:physiology*; D004195:Disease Models, Animal; D005260:Female; D005264:Femoral Fractures / Q000000981:diagnostic imaging*; D005269:Femur / Q000000981:diagnostic imaging* / Q000648:ultrastructure; D008297:Male; D008962:Models, Theoretical; D009924:Organ Culture Techniques; D011237:Predictive Value of Tests; D011336:Probability; D012016:Reference Values; D013314:Stress, Mechanical; D013552:Swine; D013718:Tensile Strength; D016474:Weight-Bearing