Biomechanical Evaluation Of STB Plate For Thoracolumbar Spine

Objectives Transpedicular screw fixation permits segmental internal fixation of the spine for a number of disorders, including instability following trauma, tumor, spondylotisthesis, multilevel laminectomy and degenerative arthristis. Pedicle screw fixation provides short, rigid segmental stabilization which allows preservation of motion segments and stabilization of the spine in the absence of intact posterior elements which is not possible with non-pedicular instrumentation. Clinical outcome is significant. But old-style transpedicular screw fixations are made of stainless steel. A new-style STB plate has been manufactured, which is made of titanium alloy. The biomechanical properties of STB device and Stefie device were compared to propose the basis of selecting the internal fixation devices for treating thoracolumbar fracture. Materials and Methods 1. Experimental materials Six fresh thoracolumbar spine specimens (T-L4) were obtained from young male cadavers died in accident. Six blocks were made according to American ASTM Standard. 2. Instability Six pure moments with a maximum of IO.ONm were applied to each specimen to produce physiologic movements of thoracolumbar spine in flexion, extension, left and right lateral bending, left and right axial rotation. Two angled TV-cameras recorded images of motions of thoracolurnbar spine at maximum and zero moments. Motion parameters, including neutral zone, elastic zone and range of motion, were calculated. A cadaveric model of T12-L1 instability was produced, then specimens were stabilized with Steffee and STB. The comparing range of motion with intact, traumatic, Steffee and STB were compared. 3. Axial Stiffness and Finite Element Analysis According to ASTM standard, axial compressing testing were performed. Axial stiffness of Steffee and SIB were compared. Stress in screw was analyzed by finite element method( FEM). Results: 1. The ROM of Steffee and STB significantly decreased than traumatic spine in fiexion, extension, lateral bending and axial rotation, even than intact spine in lateral bending. The ROM of Steffee and SIB have no difference. 2. The axial stiffness of SIB and Steffee were 106.8 N/mm ?24.8 N/mm~ 49.5 N/mm?.6N/mm. SIB device was 2.16 times stronger than Steffee device in axial stiffness. It seemed that more stress was at the location circumferential to screw root and screw-plate interface. Conclusion SIB plate can restore the stability of unstable thoracolumbar spine and is worthy recommending and using.