Getting an Angle on Spinal Stability
This is a study of more than 1,000 people with spinal instability (looseness between two or more spinal bones). It was designed to help replace the wide range of results in other studies. Most of those studies were done with fewer patients using poor research or X-ray methods. Researchers from this project were very careful to prevent the problems other studies have had finding answers about spinal instability in the lower back.

An unstable spine may be the cause of low back and leg pain (sciatica). Doctors use patients' symptoms and X-rays to diagnose the problem. Two problems can be seen on X-ray: slippage or tipping of the spinal vertebrae. The authors looked at which one is linked to the patients' symptoms.

Translation is a measure of how much one vertebra slides forward and backward as the patient bends and extends the back. Angulation shows how much one vertebral body tips forward or back as the spine moves. Both movements are measured from the side view.

These two motions were measured at one level (L4/5) in all the patients. Symptoms were compared to the results of these measures. The authors report that translation affects symptoms more than angulation. In fact, too much angulation by itself didn't seem to make any difference in patient symptoms. Too much translation and too much angulation at the same time may cause ongoing symptoms.
References
Tetsushiro Iguchi, MD, et al. Lumbar Instability and Clinical Symptoms. In Journal of Spinal Disorders. August 2004. Vol. 17. No. 4. Pp. 284-290.