[Low dose X-irradiation promotes callus mineralization: experiment with rats]

To investigate the effect of low dose irradiation (LDI) on callus formation and mineralization.

80 SD rats were subjected to standard closed fracture on right femur so as to establish animal models and then were randomly divided into 2 equal groups: LDI group undergoing low dose whole body X-ray irradiation of 1Gy right after fracture induction and control group without irradiation. 1, 2, 3, 4, and 8 weeks later blood samples were collected from the heart to examine the amounts of white blood cells and platelets and alkaline phosphatase (ALP) level. Conventional X-ray films were taken and MicroCT was conducted to evaluate the callus bridging. Then the rats were killed to take out the femurs to undergo histological examination. Peripheral quantitative computed tomography (pQCT) was conducted to quantify the bone mineral content (BMC). Four-point bending test was used to examine the mechanical properties of the callus.

The maximum load value and histological score 2 weeks later of the LDI group were both lower than those of the control group, however, the serum ALP, BMC, maximum load level, callus bridging score, and histological score 3 weeks later of the LDI group were all significantly higher than those of the control groups (all P<0.05). 4 and 8 weeks later there were not significant differences in all these parameters between the 2 groups. The WBC amount in the first 2 weeks of experiment of the LDI group was remarkably lower in these 2 groups, however, in the third week, the WBC value of the LDI group was higher than that of the control group (P<0.05).

LDI promotes the mineralization at the stage of hard callus formation which is probably associated with progenitor cell mobilization.