Sphinx is one of the most gentle of yoga backbends. With the elbows bent, directly under the shoulders, the back muscles work to lift the torso up high. In the hatha version, you can engage your glutes and quads to lift up higher. Tilt the head back and stretch out the neck. (In the yin version, you relax and let your upper body and head sink a bit.)
Dr. Loren Fishman is my guru for bones, joints, and back. After attending many of his workshops, I created my own series of therapeutic workshops for bone health called Dem Bones. Dr. Fishman is the medical director of Manhattan Physical Medicine and Rehabilitation and has conducted the widest-reaching research I'm aware of on yoga and the back.
One of the tips he gives in my book, "From the Boxing Ring to the Ashram," is for people with herniated discs. After your medical practitioner or specialist gives you the green light, try back bends to reduce discomfort from herniated disks. Traditionally, backbends are also welcomed stretches for people with spinal stenosis and other chronic back issues.