Mechanics of the external fixation test in the lumbar spine. A roentgen stereophotogrammetric analysis.

STUDY

DESIGN

By implanting tantalum indicators percutaneously during application of pedicular screws, lumbosacral mobility could be studied with roentgen stereophotogrammetric analysis in seven patients having a diagnostic external fixation test.

OBJECTIVES

To determine the mechanical effects on the segmental mobility during an external fixation test of the lumbar spine.

SUMMARY OF BACKGROUND DATA: External pedicular fixation test of the lumbar spine has been reported a valuable prognostic instrument in fusion for low back pain.

METHODS

A Magerl external fixation device was applied in seven patients with low-grade spondylolysis-olisthesis. By using roentgen stereophotogrammetric technique, the intervertebral translations in the lumbosacral segment were determined. Each patient had three separate examinations; with the frame fixed, with the frame loosened, and without frame 6 weeks after screw removal.

RESULTS

With the external frame fixed, the sagittal intervertebral translations were significantly reduced, in three cases to a level beneath the accuracy of the measuring method. One patient had the same immobilizing effect even with the frame loosened while for the others loosening of the frame meant regained mobility of the segment.

CONCLUSION

The properties of the external fixator give an adequate mechanical basis for the prognostic external fixation test in lumbar fusion.