The Study On The Different Bone Density And The Early Stability By The Pedicle Screws Fixation

Objective: Establish the model onnormal bone mass, bone loss, osteoporosis and severe osteoporosis.The Study on four Bone Density and the early Stability by the Pedicle Screws Fixation.It can provide reference of basic mechanics for physicians in clinical practice.Methods: 36 fresh lumbar vertebrae from 3±0.5years sheep, were randomly assigned to four groups by completely randomized design: Group A(no decalcification, the control group), Group B(decalcified with Hcl for 2 hours), Group C(decalcified with Hcl for 4 hours), Group D(decalcified with Hcl for 6 hours). 9 verterbraes of each group. BMD of thoracic and lumbar spine were mesured by dueal energy x-ray absorptiometry(DXA)in four group.there is no significant difference between each specimen of bone mineral density in statistics.The groups were divided into normal bone mass group, osteopenia group, osteoporosis group,serious osteoporosis group by none density. Four screws was performed on the T14-L2 pedicle of vertebral arch of the four groups. Four groups were performed fatigue test of 250 000 times in 4 direction(Flexion, extension, left lateral bending, right lateral bending) by(300+105) N load. The range of motion(ROM), the maximum drawing force of the screws, the axial compressive stiffness, were measured and the differences in every group were compared.Results: After 10 000 fatigue test, range of motion A, B, C, D group of the spine(ROM),the ROM value of the grou A(The normal bone mass)anteflexion(1.45±0.27)°, retroflexion(3.45±0.23)°, left lateral(6.49±1.46)°, and right lateral(4.45±0.94)°the ROM value of the grou B(the osteopenia)anteflexion(1.89±0.28)°, retroflexion(2.23±0.34)°, left lateral(7.61±0.98)°, and right lateral(5.11±0.56)°the ROM value of the grou C( the Osteoporosis group)anteflexion( 2.76±0.16)°, retroflexion(2.23±0.34)°, left lateral(3.45±0.23))°, and right lateral(6.50±0.98)°the ROM value of the grou D(severe osteoporosis group)anteflexion( 3.86±0.25)°, retroflexion(4.45±0.31)°, left lateral(7.61±0.98)°, and right lateral(7.78±0.87)°.The drawing force increased in turn, and screw pullout decreases in turn. Differences between the groups was statistically significant(P < 0.05).Conclusions: 1.Patients for osteopenia and osteoporosis was performedby posterior spinal pedicle fixation,during bone healing spinal stability is poor.2. The patients with osteoporosis can not be performed by pedicle screw fixation Simplely.And before bone healing,they should reduce spinal activity.