What are the safest sex positions for facet problems or degenerative arthritis?

Flexed positions. Since extension of the spine results in the facet joints approximating causing pain.
Depends on the Sex! Facet join is worsened by extension of the\back. My male patients like the woman on top, less pain for them. Conversely, women with facet arthritis prefer the male on top for less pain. Sideways is the position that both would find uncomfortable. That being said, sex is a great workout for core muscles, which is good for the back. So follow my instructions: have sex with your partner.
Spooning. A good option would be spooning...Allowing both partners to maintain a natural curve in the spine which typically hurts less.