Evaluation of the mobility of adjacent segments after posterior thoracolumbar fixation: a biomechanical study.

An investigation was conducted into the effects of double-level T12-L2 posterior fixation on the mobility of neighboring unfused segments. The segmental mobility of adjacent segments above and below the fixation in ten cadaveric human thoracolumbar spine specimens was measured before and after fixation by biomechanical testing in flexion, extension, right lateral bending, and right rotation, and the data were compared. In flexion and extension, mobility of the segment above the double-level T12-L2 posterior fixation was significantly increased (P<0.05). In the adjacent segment below the fixation, there was no significant increased mobility after fixation for each moment applied. There is evidence that the adjacent segment above a double-level T12-L2 posterior fixation becomes more mobile, and this may lead to an accelerated degeneration in the facet joints due to increased stress at this point. This could be responsible for symptoms like low back pain after spinal surgery.