ObjectiveTo compare the fixation strength of optimum placed pedicle screw (OS) with re-directionally correctly placed pedicle screw (RS) following a violation of lateral pedicle. MethodsThirty fresh lumbar vertebrae (L1-5) were obtained from 6 pigs weighing 95-105 kg, male or female. Each vertebra was instrumented with a monoaxial pedicle screw into each pedicle using two different techniques. On one side, a perfect screw path was created using direct visualization and fluoroscopy. A pedicle screw of 5 mm in diameter and 35 mm in length was placed with a digital torque driver (OS). On the other side, a lateral pedicle wall violation was created at the pedicle-vertebral body junction with a guide wire, a cannulated tap, and a pedicle probe. This path was then redirected into a correct position, developed, and instrumented with a 5-mm-diameter by 35-mm-long pedicle screw (RS). For each pedicle screw, the maximal torque, seating torque, screw loosening force, and post-loosening axial pullout were measured. Screw loosening and axial pullout were assessed using an MTS machine. ResultsMaximal insertion torque was (111.4±8.2) N·cm and (78.9±6.4) N·cm for OS and RS respectively, showing significant difference (Z=3.038, P=0.002). The seating torque was (86.3±7.7) N·cm and (59.7±5.3) N·cm for OS and RS respectively, showing significant difference (Z=2.802, P=0.005). The screw loosening force was (76.3±6.2) N and (53.0±5.8) N for OS and RS respectively, showing significant difference (Z=2.861, P=0.004). The post-loosening axial pullout force was (343.0±12.6) N and (287.0±10.5) N for OS and RS respectively, showing significant difference (Z=2.964, P=0.003). ConclusionCompared with OS, RS placement after a lateral wall violation shows significantly decreased maximal insertion torque, seating torque, screw loosening force, and post-loosening axial pullout. On this occasion, RS augmentation is a probable option for remediation.
A new fixator for spine was designed to restore the stability of spine in improving the treatment of thoraco-lumbar dislocation. This instrument was composed of six nails, two longitudinal connecting rods and two transverse connecting rods. On the surface of the nails, there were furrows engraved, instead of screw thread. It fixed the spine through pedicle of vertebra from the posterior approach. The fixed vertebrae were limited between two vertebrae. From 1989 th 1995, twelve patients with fracture-dislocation of thoraco-lumbar spine were reduced with this instrument. After four years follow-up, it showed that the deformity was corrected and the spine firmly fixed. Compared with Dick’s screws, it had the following advantages such as simple manipulation, increased strergth of nails and minimal damage to tissue during operation.