When you use donated bone from someone else it's called an allograft. Using your own donor bone is referred to as an autograft. Problems with allograft surfaced over the years. Often the fusion site didn't hold up. The bone collapsed in up to 30 percent of the patients.

Surgeons started using metal plates to reinforce the graft. There were fewer problems using the hardware but they cost more and increased the amount of time in the operating room. Still problems with the plates and screws did occur in as many as 20 percent of the cases. The fusion rates with plate-assisted fusion were good (94 percent).

As more studies were done it became clear that some way to fuse the spine without bone graft was needed. Titanium cages were designed and tried. At first they were filled with bone graft material but now they are left empty by some surgeons. Fusion rates are good and complications are low. The next step? Finding the best type of fusion cage.