“Spondy” means spine and “listhesis” means slip. Spondylolisthesis refers to one vertebrae shifting or slipping forward or backwards relative to the adjacent vertebrae. This is a sign of instability of the spine. An unstable spine can cause significant back or neck pain. The shifting of the vertebrae with motion can cause traction and irritation of the nerves which can cause arm or leg symptoms. In advanced cases, there may be tightening of hamstrings, a forward leaning posture, or a waddling gait due to atrophy of the gluteal muscles from lack of use.
The most common causes of spondylolisthesis are from degenerative changes in the spine with age or from a fracture of the weakest portion of the vertebrae, the pars interarticularis. When the pars interarticularis fractures (brakes) this is referred to as spondylolysis. When the fracture of the pars leads to a slip of one vertebrae on the other the term applied is isthmic spondylolisthesis.