As a result, the spine is not normally aligned. For example, anterior spondylolisthesis of L4 on L5 means that the fourth lumbar vertebra has slipped forward on the fifth lumbar vertebra. Spondylolisthesis is forward or backward displacement of the body of one vertebrae in relation to an adjacent vertebra.This defect predisposes to spondylolisthesis (see below) because of spinal instability. Spondylolysis is incomplete development and formation of the connecting part of the vertebra, the pars interarticularis.This is a very different process than spondylosis because spondylosis is degenerative while spondylitis is inflammatory. Spondylitis is inflammation of one or more vertebrae, such as in ankylosing spondylitis, an inflammatory form of arthritis of the spine.There are several medical terms that sound similar to and are often confused with spondylosis including the following:.Multilevel spondylosis means that these changes affect multiple vertebrae in the spine.Lumbosacral spondylosis is spondylosis that affects both the lumbar spine and the sacral spine (below the lumbar spine, in the midline between the buttocks).Thoracic spondylosis frequently does not cause symptoms.Lumbar spondylosis and cervical spondylosis are the most common. Spondylosis can occur in the cervical spine (neck), thoracic spine (upper and mid back), or lumbar spine (low back).For example, the phrase "spondylosis of the lumbar spine" means degenerative changes such as osteoarthritis of the vertebral joints and degenerating intervertebral discs (degenerative disc disease) in the low back. Spondylosis changes in the spine are frequently referred to as osteoarthritis.Spondylosis refers to degenerative changes in the spine such as bone spurs and degenerating intervertebral discs between the vertebrae.The word spondylosis comes from the Greek word for vertebrae.