Disc degeneration is a common and troublesome source of low back pain for many people. When conservative care fails, spinal fusion is often the next step. As you pointed out, there are many advantages to spinal fusion.
owever, sometimes it doesn't work. In fact, up to half the spinal fusions fail to fuse leaving the patient in pain with ongoing disability. Pain at the donor site is a problem. Bone taken from the pelvic bone is often used in the fusion. Some patients have more pain along the donor site than where the fusion is done.
Other pitfalls include bone spurs around the area of fusion or disc degeneration above or below the level of fusion. An unstable spine may be the final result.