Lumbar posterior arthrodesis is a spinal fusion (sometimes called a joint fusion) which aims to surgically join three vertebrae together in a 2-level fusion. The surgeon manually straightens out the damaged joints, removes the cartilage, and then stabilizes the bones so that they heal together. This procedure can help restore spinal stability in patients whose spine may become unstable if there's abnormal or excessive motion between two vertebrae, which is a common side effect of severe arthritis in the spine.