Spondylolisthesis

Spondylolisthesis is forward slippage of one vertebra over the one below.

Two patterns dominate:

• •The young athlete with an isthmic slip, usually at L5-S1 on a pars defect, with extension-related back pain and tight hamstrings
• •The older adult, more often a woman, with a degenerative slip, classically at L4-L5, and neurogenic claudication relieved by sitting

The key decisions are screening for red flags such as cauda equina syndrome, and recognising a high-grade or progressing slip that needs a specialist.

A slip occurs when the posterior bony or ligamentous restraint fails. A pars defect (spondylolysis) removes the bony tether in isthmic slips; facet joint arthritis and disc collapse allow degenerative slips; congenitally deficient L5-S1 facets allow dysplastic slips in children and adolescents.

The Wiltse classification groups slips by cause:

• •Type I, dysplastic: congenital L5-S1 facet deficiency, high risk of progression
• •Type II, isthmic: a pars defect, the commonest type in athletes
• •Type III, degenerative: facet arthritis and disc collapse, classically L4-L5
• •Types IV to VI: traumatic, pathological and post-surgical

Most low-grade isthmic slips progress little after skeletal maturity; the risk is highest in the growth spurt and in dysplastic and high-grade slips. Most isthmic slips follow bilateral pars defects.