Experimental Study Of Promoting Fracture Healing By Low Frequency Pulse Electrical Stimulator Combined With External Fixator

Objective: This study tried to explore the effect and mechanism of promoting fracture healing by Low frequency pulse electrical stimulator combined with external fixator, so as to provide the theoretic base for it being widely used in clinic.Methods: There are two animal model experiments to make in this experiment, at each time 90 New Zealand rabbits( weighting2.5³.0kg) have a transverse mid-diaphyseal tibial osteotomy with a 2-mm gap performed and stabilized with external fixation. They were then randomly allocated one of three groups: groupI (n=30), the active group, using insulant group: Screw was embedded into insulant(polytef) and only part of thread and screw end were revealed. The fracture was fixed by unilateral external fixator, rubber band being used between screws and connecting rod in order to insulate.Two electrodes of pulse electrical stimulator were connected respectively with two screws nearby fracture line, pulse electrical stimulator standing outside rearing cage ; group II unusing insulant group (n=30): Screw was not embedded into insulant,the rest was as the same as group I; group III (n=30) normal control: The fractre was fixed by common unilateral external fixator and not to connect with pulse electrical stimulator. Electrical stimulation was kept on 5 to 6 hours every day .During the time of electrical stimulation, rabbits run freely in rearing cage. The changes of fracture-site microcirculation at different time were measured with Laser Doppler Perfusion Monitor.The bone mineral density(BMD) was measured with dual energy X-ray absorptionmetry. The animals in group I , II and III were sacrificed seperately at third day and 1, 2, 4, 6,8 weeks after operation. The bending stiffness, torsional stiffness and torsional strength were determined withbiomechanical tests.The expression and positive index of TGF- β₁, BMP₂, bFGF, VEGF and its mRNA were quantitatively analysised by Immunology Histochemistry(IHC) and In Situ Hybridization(ISH). So , we deected the TGF- β₁ , BMP₂, bFGF, VEGF distribution and contents of callus in protein level and in mRNA level.Results: 1.Fractures are observed by X-ray: In fracture forepart,there are no difference in three groups .From the fourth weeks since the animal model having been made, a significant difference in three groups appeared in both the amount and the quality of callus. Result in detail is below: using insulant group >unusing insulant group > normal control.2. At first day after operation, the local blood flow of the three groups were all greatly decreased. It recovered to normal level at seventh day after operation. At 14th day, the local blood flow of two groups which were connected respectively with pulse electrical stimulator was both higher than normal control, and the blood flow of using insulant group was higher than that of unusing insulant group(P<0.05).The peak of control group was at 21th day and then decreased gradually. The peak of two groups which were stimulated by electricity was at 28th day. Compared the blood flow, there was statistical difference among three groups at 21th,28th and 42th day (P<0.01) . The blood flow of two groups which were stimulated was higher than normal control group at 56th day(P<0.05), but there was no statistical difference between two groups((P<0.05).3. At 14th day after operation, the BMD of bones of three groups was just 10% of the normal level and there was no statistical difference among three groups(P>0.05).The BMD of bones of three groups was increased greatly at 21th and 28th day. The BMD of bones of using insulant group was higher than that of the rest two groups(.P<0.01) and the BMD of bones of unusing insulant group was higher than that of control group(P<0.01). At 42th and 56th day, the BMD of bones of three groups were all higher than normal level, but there was no statistical difference among three groups (P>0.05) .4. (1) At 14th day after operation, the bending stiffness of bones of three groups was just 3% of the normal level, there was no statistical difference among threegroups(P>0.05).The bending stiffness of bones of three groups was increased at 21th day, neither statistical difference existed among three groups(P>0.05). At 28th and 42th day, the bending stiffness of bones of three groups was increased greatly, and the bending stiffness of bones of using insulant group was higher than that of the rest two groups (P<0.05),in the meantime, the bending stiffness of bones of unusing insulant group was higher than that of control group(P<0.05).At 56th day, the bend stiffness of bones of three groups were all increased to the normal level, there was no statistical difference among them (P>0.05 ) .(2) At 14th and 21th day after operation, the torsional stiffness of bones of three groups was very low, there was no statistical difference among them(P>0.05).The torsional stiffness of bones of three groups was increased at 28th day, and the torsional stiffness of bones of using insulant group was higher than that of the rest two groups (P<0.05),in the meantime, the bending stiffness of bones of unusing insulant group was higher than that of control group (P<0.01). At 42th day, the result was as the same as the 28th day. The torsional stiffness of bones of the two groups which were stimulated by electricity was normal at 56th day, and that of control group was lower , there was statistical difference too among them (P<0.05) .(3) At 14th and 21th day, the torsional strength of bones of three groups was too low to test. The torsional strength of bones of three groups was greatly increased at 28th day, and the torsional strength of bones of using insulant group was higher than that of the rest two groups (P<0.05),in the meantime, the bending stiffness of bones of unusing insulant group was higher than that of control group (P<0.05). The torsional strength of bones of the two groups which were stimulated by electricity was increased to the normal level at 56th day, that of control group was only 80% of normal level, statistical difference existed too among them (P<0.01).5. (1) TGF- β1 and TGF- β1 mRNA was expressed in mesenchymal cell(MC), osteocyte(OC), bone metrix(BM), osteoblast(OB), and chondroblast(CB). The TGF- β1 and TGF- β1mRNA' positive index(PI) of using insulant group was the highest among three groups at 14th, 21th, 28th day after fracture, the unusing...