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

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 less than 0.01), as was the ash density (0.61 +/- 0.05 g/cm3 versus 0.27 +/- 0.02 g/cm3, p less than 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 x cm3/g versus 12.0 +/- 1.2 MPa x cm3/g, p less than 0.01). The maximum stiffness and energy absorption capacity were higher in the patients (p less than 0.01), with a corresponding lower maximum strain value (p less than 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 less than 0.02) and in ash density (R = -0.57, p less than 0.02) were observed in normal individuals.(ABSTRACT TRUNCATED AT 250 WORDS)