Mechanical properties of bone from iliac crest and relationship to L5 vertebral bone.

Apparent density, yield stress and yield energy were measured in transiliac cores of trabecular bone from iliac crest and craniocaudal cores of L5 vertebra from 26 cadavers. In the iliac crest, bone from the anterior superior spine region had significantly greater apparent density and had greater yield energy than bone from the center of the crest. Yield stress was greater at the anterior superior spine than either the center or at the posterior spine. Lumbar vertebral bone was uniform in its characteristics. Apparent density was the property showing the best correlation between iliac crest and L5 (r = 0.79), while yield energy was less well associated (r = 0.67). In L5, mechanical properties decline more rapidly with age than apparent density. Between the ages of 25 and 75 years the rate of fall of yield stress was twice and yield energy 2.6 times compared with the rate of fall of apparent density. Iliac crest behaved similarly. Yield stress in iliac crest paired for density in subjects less than 40 years and greater than 60 years was 40.7% lower in the older subjects (p = 0.03), suggesting a specific mechanical defect in old age. The yield stress advantage accruing to orientated lumbar bone was more marked at lower values of yield stress in the iliac crest when cores from the same cadaver were matched for apparent density. Mechanical properties of iliac crest bone are very dependent upon site and at no one site in the iliac crest do the physical properties satisfactorily predict those in the lumbar spine.