Biomechanics of Steffee plate fixation

An investigation is made of the biomechanical strength and kinematic characteristics of lumbar spines under the flexion-compression mode of loading. The decrease in strength, and hence stability, due to trauma, the improvement in the load carrying capacity, and the change in motion due to fixation using pedicle screws and Steffee plates were determined. It is shown that, in general, the strength of the specimen was restored with fixation. The initial failure forces ranged from 1581 to 3897 N with deformations of 6 to 16 mm. With the fixation, the failure forces and deformations ranged from 927 to 3120 N and 16.1 to 37.7 mm, respectively. These deformations exceed the initial deformations to failure, indicating that the specimen did not fail at the same level of deformation as in the intact spine