Lumbar spinal fusion is an integral component of the surgical management of degenerative disease, trauma, deformity, tumor, and infection of the spine. Pseudarthrosis can, in turn, lead to persistent pain, failure of the instrumentation, and the need for revision surgery. It is a challenge to obtain a solid osseous fusion; therefore, both mechanical and biological variables should be optimized. Mechanical stability is optimized by using pedicle screws and rods for rigid fixation until there is osseous fusion. Internal fixation improves the fusion rates compared with those associated with lumbar fusion without instrumentation, but it does not ensure a 100% fusion rate.