The Effect Of Methylprednisolone On The Ulna Cortical Bone Bone Mass, Microarchitecture And Mechanical Performance In Rats

Objective To evaluate the effect of methylprednisolone on the ulna cortical bone bone mass, microarchitecture and mechanical performance in rats.Methods Twenty female Sprague-Dawley rats of three and half-month-old were randomly assigned to two groups: rats that were subcutaneously injected with methylprednisolone 3.5mg/kg per day (treatment group), and rats that were subcutaneously injected with normal saline as vehicle (control). Rats were sacrificed at 9 weeks after these treatments while body weight and total bone mineral density (BMD) were measured before they were killed. The left ulna was harvested for BMD measurement and the three point bending test. Single axial fatigue loading was performed on the right ulna, bone histomorphometry and microdamage analyses were performed on the middle ulna section.Results Body weight(-15%), total bone BMD(-6.4%) and the ulnas BMD(-4.3%) in treatment group were significantly lower than those of the control rats (P<0.05). The ulna inner perimeter and marrow area in treatment group were increased by 23.3% and 32% respectively, while the outer perimeter were decreased 3.1% (P<0.05). No significant differences were found in cortical area and total area between two groups. The number of microcrack(43%), microcrack density(48%) and microcrack surface density(50%) in treatment groups were higher as compared with those of the control groups (2.33±0.71 vs. 4.16±0.31, 1.20±0.39 vs. 2.30±0.27 and 1296±391 vs. 2592±387 ) (P<0.05), but there was no significant difference in the mean length of microcrack between the two groups. The maximum load(-16.4%), maximum flexibility(-20.8%) and elastic modulus(-37.5%) in treatment group were significantly lower as compared with those of the control groups (20.7±0.8N vs. 24.8±1.7N, 2.00±0.15mm vs. 2.52±0.172mm, 6.45±0.836MPa vs. 10.3±1.61MPa) (P<0.05).Conclusion Methylprednisolone could induce significant bone loss and deterioration of the microarchitecture with great mechanical performance decreasing in rat ulna.