The monotonic and fatigue properties of osteoporotic thoracic vertebral bodies.

STUDY

DESIGN

Measurement of the monotonic and fatigue properties of osteoporotic thoracic vertebral bodies.

OBJECTIVES

To determine the loading values at which osteoporotic vertebral bodies are susceptible to failure.

SUMMARY OF BACKGROUND DATA: Vertebral compression fractures are the most common osteoporotic fracture. Eighty-three percent of vertebral compression fractures are caused by moderate or less trauma, and there is not a specific traumatic event in 59% of these cases. Fatigue loading can lead to premature failure, although the relationship between loading and cycles to failure is not well established.

METHODS

Eighteen osteoporotic thoracic vertebral bodies were tested in monotonic compression to determine the correlation between the bone mineral content and the ultimate compressive load. Seventeen osteoporotic thoracic vertebral bodies were cyclically loaded at varying percentages of the ultimate compressive load until failure to determine the relationship between loading and fatigue life.

RESULTS

The bone mineral content was linearly correlated with ultimate compressive load. Based on our regression analysis, a 10% decrease in bone mineral content will lead to an approximate 10% decrease in ultimate compressive load. The percentage of ultimate compressive load was inversely correlated to the logarithm of cycles to failure, with specimens loaded at 60%, 70%, and 80% of ultimate compressive load lasting on average 5.6 x 10, 4.0 x 10, and 31 cycles to failure, respectively.

CONCLUSIONS

The bone mineral content is a strong predictor of the ultimate compressive load, while the percentage of the ultimate compressive load is a strong predictor of the cycles to failure for osteoporotic thoracic vertebral bodies.