Structural characteristics of GDP
It resolves the distraction problems of plate structure. There was a rack on the sidewall in the plate hole, dentate distraction nut roll in the rack and drive the pedicle screw move, hence the GDP can distraction. According to the measurement of the height of vertebral body and intervertebral space, the length of rack was designed 3 cm, which is equal to the distraction distance. This ensures sufficient space distraction and would fully restore the height of compressed vertebrae. The radian of GDP made different angles between pedicle screw and plate called “screw plate angle”, it plays an important role in restoring the height of anterior and middle column. The structure of gear and “screw plate angle” not only compensate the lack of distraction of plate structure, but also decompose of the compression load of the head of pedicle screw, this is important to reduce bending and broken nails postoperatively[3].
Biomechanical characteristics of GDP
①The GDP has radian and this makes the stress transfer uniformity. The connection between the fixed plate and screws applies embedded structure which make the connection firmly and low profile, so that the fixed plate close to spinal column is conductive the power transmission. Experimental results show the load-strain and load-displacement was smaller than the control group but its axial or level rigidity higher than the control group (P < 0.05). The fixed spine is hard to distortion under physiological loads; this will help bone fusion and maintain vertebral body height rather than stress concentration, plate and screw broken. ②GDP has plate structure, in theory, this structure has strong anti-torsion properties. The experimental results showed the performance of its torsion is better than the control group (P < 0.05). ③The GDP consists of four pedicle screws, two fixed plates, a horizontal rod, dentate distraction nuts and lock nut. The plate has a certain degree of curvature and the curvature match the spine, so the surgeon use the curvature to restore the anterior column of the spine and then distraction to restore the height of vertebrae and intervertebrae space. The fixed plate tightly affixed to the back of the spine structure because of the match curvature and such fixation has strong power, good stability and also restoring the normal physiological curvature of spine. All these are benefit to fracture healing and maintain the balance of the body. ④This experiment does not involve biomechanical muscle and the coordination roleof living body[4]. However, the muscle system influence the fixation device load great[4], so there is still a great challenge to accurately simulate the mechanical situation of internal fixation in the physiological conditions.
The principle of reduction for GDP and the current clinical application of screw-rod system are difference, it belongs to short segment fixation device and does not require bending and rolling rod. It fixes less segment and retained most of the function of spinal activities.
