[Volume changes of intervertebral disc and vertebral body after dorsal fusion]

Even today, different opinions can be found concerning realignment loss of the adjoining intervertebral disc after fracture followed by dorsal fusion. There is still disagreement on intervertebral disc excision and the subsequent necessity of intercorporal fusion.

In this context, fractures of the thoracolumbar transition and its operative repair via instrumented bisegmental dorsal fusion at T11 - L1 and T12 - L2, respectively, have been examined. Immediately after the accident and after removal of the implant, sagittal MR images (T1-, TE-, T2-weighted) with a standard 4 mm slice thickness were made. Eighteen patients with fractures of the thoracolumbar transition (A3 and B1 according to the AO classification) could be included in this study. All fractures were of traumatic genesis. The implant was removed after an average of ten months.

Allowing for planimetric measuring errors, our analysis generated a 14 % volume decrease of the upper and a 15 % volume decrease of the lower intervertebral disc. A volume change of 3 % in the bridged or fractured vertebral body was found to be without any verifiable significance. Tendentially, a slight volume loss of both adjacent intervertebral discs could be observed.

In our opinion, the realignment loss after a mean ten months cannot be explained by the volume changes of the discs alone. The creeping of the intervertebral disc into the adjacent vertebral body accounts for the post-traumatic malalignment.