Biomechanical competence of iliac crest trabecular bone in autosomal dominant osteopetrosis type I

Abstract

Cylindrical horizontal iliac crest trabecular bone biopsies were obtained from 9 patients with autosomal dominant osteopetrosis type I and 18 normal controls of comparable age/ sex match. Maximum compressive stress, maximum stiffness, energy absorption capacity and maximum strain were calculated from load-deformation curves after a compression test. Ash density of the bone samples was measured after incineration. The maximum compressive stress was significantly increased in the patient group (12.6 ± 2.6 (SE) MPa vs. 3.3 ± 0.4 MPa, p < 0.01), as was the ash density (0.61 ± 0.05 g/cm 3 versus 0.27 ± 0.02 g/cm 3, p < 0.01). After correction for ash density (normalized maximum stress) the strength of the trabecular bone samples was still significantly increased in the patients (19.7 ± 6.4 MPa × cm 3/g versus 12.0 ± 1.2 MPa × cm3/g, p < 0.01). The maximum stiffness and energy absorption capacity were higher in the patients ( p < 0.01), with a corresponding lower maximum strain value ( p < 0.05). The maximum compressive stress correlated closely to the maximum stiffness and energy absorption capacity in both patients and controls, whereas no correlation to maximum strain was found. The maximum compressive stress thus seems to be representative for the two other biomechanical parameters. No significant correlations between age and maximum compressive stress ( R = 0.38), ash density ( R = 0.08), or normalized maximum stress ( R = 0.45) were observed in type I osteopetrosis, whereas significant age-dependent decreases in maximum compressive stress ( R = −0.65, p < 0.02) and in ash density ( R = −0.57, p < 0.02) were observed in normal individuals. A significant correlation between ash density and maximum compressive stress was observed in the patient group ( R = 0.90, p < 0.01). In conclusion, trabecular bone strength is increased in type I osteopetrosis, and does not decrease with age, as in normal individuals. The findings reflect an increase in absolute trabecular bone volume caused by defective bone resorption.