Multi-modality study of the compositional and mechanical implications of hypomineralization in a rabbit model of osteomalacia

Abstract Osteomalacia is characterized by hypomineralization of the bone associated with increased water content. In this work we evaluate the hypotheses that 1) 3D solid-state magnetic resonance imaging (MRI) of31 P ( SSI - PH ) and1 H ( SSI - WATER ) of cortical bone can quantify the key characteristics of osteomalacia induced by low-phosphate diet; and 2) return to normophosphatemic diet ( NO ) results in recovery of these indices to normal levels. Twenty female five-week old rabbits were divided into four groups. Five animals were fed a normal diet for 8 weeks ( NOI ); five a hypophosphatemic diet (0.09%) for the same period to induce osteomalacia ( HYI ). To examine the effect of recovery from hypophosphatemia an additional five animals received a hypophosphatemic diet for 8 weeks, after which they were returned to a normal diet for 6 weeks ( HYII ). Finally, five animals received a normal diet for the entire 14 weeks ( NOII ). The NOI and HYI animals were sacrificed after 8 weeks, the NOII and HYII groups after 14 weeks. Cortical bone was extracted from the left and right tibiae of all the animals. Water content was measured by SSI-WATER and by a previously reported spectroscopic proton–deuteron nuclear magnetic resonance (NMR) exchange technique ( NMR - WATER ), phosphorus content by SSI-PH. All MRI and NMR experiments were performed on a 9.4 T spectroscopy/micro-imaging system. Degree of mineralization of bone ( DMB ) was measured by μ -CT and elastic modulus and ultimate strength by 3-point bending. The following parameters were lower in the hypophosphatemic group: phosphorus content measured by SSI-PH (9.5 ± 0.4 versus 11.1 ± 0.3 wt.%, p < 0.0001), ash content (63.9 ± 1.7 versus 65.4 ± 1.1 wt.%, p = 0.05), ultimate strength, (96.3 ± 16.0 versus 130.7 ± 6.4 N/mm2 , p = 0.001), and DMB (1115 ± 28 versus 1176 ± 24 mg/cm3 , p = 0.003); SSI-WATER: 16.1 ± 1.5 versus 14.4 ± 1.1 wt.%, p = 0.04; NMR-WATER: 19.0 ± 0.6 versus 17.4 ± 1.2 wt.%, p = 0.01. Return to a normophosphatemic diet reduced or eliminated these differences (SSI-PH: 9.5 ± 0.9 versus 10.6 ± 0.8 wt.%, p = 0.04; DMB: 1124 ± 31 versus 1137 ± 10 mg/cm3 , p = 0.2; US : 95.6 ± 18.6 versus 103.9 ± 7.5 N/mm2 , p = 0.2; SSI-WATER: 12.4 ± 0.6 versus 12.2 ± 0.3 wt.%, p = 0.3) indicating recovery of the mineral density close to normal levels. Phosphorus content measured by SSI-PH was significantly correlated with DMB measured by μ-CT ( r2 = 0.47, p = 0.001) as well as with ultimate strength ( r2 = 0.5