Joint · Lumbar spine

Lumbar facet joints

Articulationes zygapophysiales lumbales

The paired synovial joints at the back of the low back. Their surfaces are curved and sit almost in the sagittal plane — front-to-back — which lets the low back bend forward and back freely while strongly blocking twisting. That is the trade-off the lumbar spine makes: mobility in one plane, protection in another. The lowest two levels carry the most load, and these joints are richly innervated, so they are a recognised source of low back pain and of pain referred into the buttock and thigh.