The Research On The Change Of Rat Ulnar Microdamage After Fatigue Damage In Vivo

OBJECTIVE:To compare the microcrack parameters after fatigue damage testing, and establish the cortical bone microdamage model for rats in vivo.METHODS:According to four-point principle, our group invented a fixture which can fit the PLD-5010fatigue damage electronic machine used in the fatigue test. Forty SD7-month-aged female rats were randomized into4groups:group A, ovariectomized and loaded for one week(OVX1W, n=10), group B, ovariectomized and loaded for two weeks(OVX2W, n=10), group C, sham-operated and loaded for one week(SHAM1W, n=10), and group D, sham-operated and loaded for two weeks (SHAM2W, n=10). The right ulnae were loaded in vivo using this machine. After fatigue load, the rats were killed respectively, and the right ulnae were bulk-stained in1%basic fuchsin and embedded in methylmethacrylate. The mounted bone slices were used to measure microcrack parameters and osteocyte density (Ot.N/T.Ar).RESULTS:The microdamage could be observed in each sample and microcrack was the most usual damaged type. Significant difference of Cr.Le, Cr.N, Cr.Dn and Cr.SDn was observed between OVX groups and SHAM groups (P<0.05). Significant difference of Cr.Le and Cr.SDn was observed between OVX1W group and OVX2W group(P<0.05). The statistically differences in Cr.Le, Cr.N, Cr.Dn and Cr.SDn between OVX1W and OVX2W were not significant(P>0.05). The statistically differences in Cr.Le, Cr.N, Cr.Dn and Cr.SDn between SHAM1W and SHAM2W were not significant(P>0.05). The Ot.N/T.Ar in OVX groups was higher than which in the SHAM groups(P<0.05). There was no difference between OVX1W and OVX2W while the same as in the SHAM group(P>0.05).CONCLUSION:The cortical bone cmicrodamage model has been successfully established by using the PLD-5010fatigue damage test machine and parallel four-point bending fixture. The microdamage model can be determined and its parameter is0.0555N/g of body weight maximum load,4Hz frequency,10000circles per time, and3times/week for2weeks. OBJECTIVE:To observe change of microdamage of the right ulna at different times after fatigue test in vivo and the self-repair law of OVX rat bone microdamage.METHODS:Forty SD7-month-aged female rats were ovariectomized. The single fixture was upgraded to duel fixture. Then the40rats were loaded on the right ulnae for two weeks and randomized into4groups:OVXlst, OVX2nd, OVX3rd and OVX4th. At the1st,2nd,3rd, and4th week after load the rats were killed respectively. The right ulnae were bulk-stained in1%basic fuchsin and embedded in methylmethacrylate. The parameters of microcrack were measured.RESULTS:The microdamage could be observed in each sample and microcrack was the most usual damaged type. The Cr.Le, Cr.N, Cr.Dn and Cr.SDn in OVXlst, OVX2nd subgroups were higher than that in OVX3rd, OVX4th subgroups (P<0.05). There were no significant difference of the Cr.Le, Cr.N, Cr.Dn and Cr.SDn between OVXlst and OVX2nd (P>0.05) while the same as in the OVX3rd and OVX4th. The difference can be observed between the OVX2nd and OVX3rd subgroups.CONCLUSION:The length and number of right ulnae microcrack was gradually reduced after fatigue load in vivo. The self-repair was significant difference between the2weeks and3weeks after load and the bone microcrack can be repair till the4weeks.