Generally, it is considered to be safe in preventing iatrogenic instability if half of the facet joint is left intact during decompression surgeries.

By removing half of the facets can we get adequate decompression of the nerve roots? Is there a difference at different levels in the lower lumbar spine? What is the inclination of the facet joint at each level and how does it affect the stability?

Retrospective study

We analysed 200 consecutive magnetic reasonance imaging (MRI) scans of the lumbosacral spine at L3/4, L4/5, and L5/S1 levels. We measured the difference in the distance from midline to the lateral border of the foramen and from midline to the middle of the facet joint at each level on either sides. The angle of the facet joint was also noted.

The distance to the foramen from the level of the middle of the facet joints seem to be between 5-6mm lateral at every level. The angle of the facet joints at L3/4 is 35.9°+/−7.4°, while at L4/5 it is 43.2°+/−8.0°, and at L5/S1 it is 49.4°+/−10.1°.

In lumbar spine decompression surgeries, after the midline decompression extending up to half of the facet joints, a further undercutting of the facet joints to 5-6mm is therefore required to completely decompress the nerve root in the foramen. The more coronal orientation of the facet joint at L5/S1 conforms better stability than that at L3/4level. Therefore, stabilisation of the spine should be considered if more than 2cm of the posterior elements are removed from midline at L3/4 level.