A new internal fixation system using vertebral pedicle screw for unstable lumbar spine: an in vitro biomechanical stability evaluation.

OBJECTIVE: To evaluate the effect of a new internal fixation system utilizing vertebral pedicle screw in fixing unstable lumbar spine in vitro. METHODS: Twelve lumbar spine specimens (L(2 to 5)) obtained from fresh human cadavers were randomly divided into 2 equal groups, namely groups A and B. All intact specimens were subjected to nondestructive testing in 6 loading modalities on a universal testing machine, before complete L(2 to 5) instability was produced by means of a wedge fracture induced by resection of the posterior ligamentous structures. Specimens in group A were fixed with the new internal fixation system, and group B with SOCON pedicle screw. The same nondestructive testing was repeated to determine the structural stability of the spine after fixation in both groups. RESULTS: The injured spines fixed with implants in both groups were significantly more stable than the intact specimens in all modes of tests (P < 0.05), especially in flexion and extension tests, in which a stability increase by 62.8% for flexion and 63.9% for extension was recorded in group A, and 54.9% for flexion and 51.0% for extension in group B. The two fixation systems exhibited similar effect in stabilizing the injured lumbar in all the 6 loading modalities (P < 0.05). CONCLUSION: This internal fixation system with vertebral pedicle screw is capable of providing biomechanical stability for unstable lumbar spine.