Examine the two types of spondylolisthesis (degenerative and isthmic) and how these conditions cause vertebrae to slip causing pain in this animated video. Isthmic spondylolisthesis: In Isthmic spondylolisthesis, there is a defect in a portion of the vertebra called the pars interarticularis. Spondylolisthesis is a degenerative spine condition that occurs when one vertebra in the spine slips over the vertebra below it, indicating spinal misalignment. Spondylolisthesis is a slipping of vertebra that occurs, in most cases. What's Causing Your Low Back Pain? Article. Breast Reduction Surgery: What to Know. What is spondylolisthesis?Spondylolisthesis is a condition in which one bone in your back. Back Pain Health Center. Spondylolisthesis - Topic Overview. Spondylolisthesis causes pain in the lower back, muscle spasms, weakness and/or tight hamstrings. Spondylolisthesis is the forward displacement of a vertebra, especially the fifth lumbar vertebra, most commonly occurring after a fracture. Degenerative spondylolisthesis symptoms include leg pain (sciatica) or a tired feeling down the legs when standing or walking for long periods of time. Spondylolisthesis has several main causes. Doctors have developed a classification system to help talk about the different causes of spondylolisthesis. This in-depth discussion about spondylolisthesis explains what causes a vertebra to slip and what the different grades (eg, grade 1 spondylolisthesis) look like.