In vitro comparative biomechanical analysis of transpedicular screw instrumentations in the lumbar region of the human spine.

An analysis of the load-displacement behavior of stabilized spines in comparison with intact spines was undertaken using fresh human cadaveric spines (T12/L1--sacrum). The three-dimensional load-displacement data of the five vertebral bodies of an intact specimen in clinically relevant loading cases were recorded using the Selspot II motion measuring system. After testing the intact specimen, an instability was created at the L4-5 level. The unstable motion segment was stabilized sequentially with three transpedicular screw instrumentations. The stabilized specimens were tested, and the data for the stabilized tests were normalized with respect to the intact data to determine the degree of stabilization achieved in various loading modes as a function of the three devices. The results showed that the three transpedicular devices included in this study were effective in imparting stability to the injured ligamentous spinal segment at a p less than 0.01 level of significance. The differences among the devices were not significant.