That's a good question considering hip pain is rarely treated by fusion and that's been the treatment for disc degeneration. Disc replacements actually date back to the late 1950s. The results weren't that good. Without today's advanced imaging, doctors didn't know why.
Artificial disc replacements (ADRs) have made a come back recently. This is due, in part, to new understanding of how the spine works. Spinal motion occurs because of two joints and the disc. The spine bends forwards and backwards and sideways. Twisting to the right and left also occurs in the spine. Designing a disc that can do all those motions has taken quite a while.
Another reason ADRs are being tried again is the increased experience surgeons have gathered over the last 10 years with spine surgeries. Fusions and cage implants from the front of the spine (anterior approach) have shown that implants can be placed easily and safely.
Some doctors say ADRs are the wave of the future for the treatment of spine problems.