Lytic spondylolisthesis usually occurs at L5/S1 and normally presents in the teenage years or 20s. The classical example is the so-called fast (cricket) bowler’s “stress fracture”. It occurs due to repetitive stresses in the lumbar spine but it often appears with no obvious history of repetitive trauma.
Degenerative spondylolisthesis usually occurs in older women, most often at L4/5, but can occur at other levels. This type of slip is due to degeneration of the pair of facet joints between the two affected vertebrae. It is virtually never worse than grade 1.
Spondylolisthesis simply means the abnormal slip of one vertebra with respect to the vertebra immediately below. This is usually occurs forwards (anteriorly) of the upper vertebra, also known as anterolisthesis. Less common is a backwards (posterior) slip, also known as retrolisthesis. Much less common is a sideways (lateral) slip, called a laterolisthesis.