Abstract:

Objective　To design a posterior dynamic stabilization of lumbar vertebrae by percutaneous placement and evaluate its biomechanical propertiesby experiments.　Methods　Medical titanium alloy was usedto design a set of pedicle screw rod fixation system. The combining site of body with U screw tail was similar to joint structure. There were 2° range of motion (typeⅠ) and 10° (typeⅡ) range of screw, and hollow screw, and cylindrical connecting rods. Seven adult fresh pig lumbar spine specimens were used for mechanical testing: six lumbar vertebrae were tested three dimensional motion, and all 7 specimens underwent compression test. When tested three dimensional motion, five patterns of state of every specimen were tested in sequence, respectively. The five patterns of state was as followings: complete state (group A), instability state (group B), stiff fixation state (group C), dynamic fixation stateⅠtype (group D), dynamic fixation stateⅡtype (group E). Motions of flexion/extension, lateral bending and axial rotation were produced by six pure moments with maximum of 10.0 N·m and measured with stereo photogrammetry.　Results 　(1)The results of the three dimensional motion test: ①After fixation with typeⅠor typeⅡ, motions of flexion was (1.577±0.177)° and (1.988±0.096)°, respectively. Extension was (1.900±0.119)° and (2.135±0.143)°, respectively. Left lateral bending was (2.549±0.280)° and (2.712±0.215)°, respectively. Right lateral bending, respectively was (2.454±0.201)° and (2.590±0.203)°. Left axial rotation was (1.458±0.294)° and (1.694±0.250)°, respectively. Right axial rotation was (1.666±0.221)° and (1.842±0.163)°, respectively, which was significantly decreased when compared with that the complete state and the state of instability（P<0.05）and were significantly enhanced when compared with that of the stiff fixation state（P<0.05）.②Two kinds of dynamic state of fixed type (ⅠandⅡ) between each other, Ⅱ more thanⅠproneness activity (P<0.05)，but there was no obvious difference of extension, lateral bending and axial rotation (P>0.05). (2)Stiffness measurement results: the maximum load of the two dynamic typeⅠfixed specimens was 3571 N and 2839 N, respectively; The maximum load of the two specimens with dynamic typeⅡ fixed was1961 N and 2365 N, respectively. dynamic fixedⅠandⅡ, and strong fixation stiffness were greater than complete state, and typeⅡless rigid than typeⅠstate.　Conclusion　The posterior dynamic stabilization of lumbar typeⅠand typeⅡ can ensure stability of the spine, and keep a range of motion，10° of screw motion closer to the spinal physiological activities. The range of motion of screw has effects on the strength of the internal fixator.

Key words: Percutaneous, Minimal invasive, Posterior dynamic stabilization, Lumbar, Biomechanical