Spondylodesis is the surgical fusion of two or more vertebrae. It is performed to treat certain forms of back pain and spine instability (spondylolisthesis means disc slippage), whereby the vertebrae rub against each other, causing the spine to become unstable and painful. It can be caused by an impact or degenerative processes. The surgery involves inserting screws or cages. The Swiss Atlas of Healthcare contains analyses on the frequency of spinal fusions in inpatient settings and on the frequency of spinal fusions in total (outpatient and inpatient).