Relationship between axial and bending behaviors of the human thoracolumbar vertebra.
METHODS
The authors studied the mechanical behavior of vertebrae through the use of finite element analyses.


OBJECTIVE
To determine the relation between axial and bending rigidity, and to determine the geometric and densitometric factors that affect this relation.


BACKGROUND
Metrics of vertebral body mechanical properties in bending have not been established despite evidence that anterior bending loads play a significant role in osteoporotic vertebral fracture.


METHODS
Voxel-based finite element models were generated using quantitative computed tomography (QCT) scans of 18 human cadaveric vertebral bodies, and both axial and bending rigidities of the vertebra were computed. Both rigidity measures and their ratio were correlated with vertebral geometric and densitometric factors obtained from the QCT scans.


RESULTS
Bending rigidity was moderately correlated with axial rigidity (r2 = 0.69) and strongly correlated with the product of axial rigidity and vertebral anteroposterior depth squared (r2 = 0.88). The ratio of bending to axial rigidity was independent of bone mineral density (P = 0.20) but was moderately correlated with the square of vertebral depth (r2 = 0.69).


CONCLUSIONS
Vertebral anteroposterior depth plays an important role in bending rigidity. The scatter in the correlation between bending and axial rigidity suggests that some individuals can have vertebrae with a normal axial stiffness but an abnormally low bending stiffness. Because whole-bone stiffness is indicative of bone strength, these results support the concept that use of more than one metric of vertebral strength, for example, compression and bending strengths, may improve osteoporotic fracture risk prediction.
Crawford
R Paul
RP
Department of Mechanical Engineering, University of California, Berkeley, California 94720-1740, USA. crawford@biomech1.me.berkeley.edu
Keaveny
Tony M
TM
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D015519:Bone Density; D019245:Compressive Strength; D005260:Female; D005598:Fractures, Spontaneous / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009038:Motion; D010024:Osteoporosis / Q000150:complications / Q000503:physiopathology; D018583:Pliability; D018570:Risk Assessment; D016103:Spinal Fractures / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control; D013314:Stress, Mechanical; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000502:physiology*; D014057:Tomography, X-Ray Computed; D016474:Weight-Bearing