Spondylolisthesis can be classified according to broad etiologies as described by Wiltse in 1981 1. Typically when reporting studies with spondylolisthesis the Wiltse type is merely stated without referring to its number, whereas the grade of spondylolisthesis is explicitly stated: e.g. "Grade 1 degenerative spondylolisthesis of L5 on S1" rather than "Grade 1, Type III spondylolisthesis".
Classification
type I (dysplastic/congenital): translation is secondary to an abnormal neural arch
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type II (isthmic): translation is secondary to a lesion involving the pars interarticularis
subtype a (lytic): secondary to stress fracture, in most cases attributed to repeated extension and/or twisting motions
subtype b (elongated pars): result of multiple injury/healing events leading to elongation of the pars
subtype c (acute pars fracture): secondary to a single event and is rare
type III (degenerative): result of chronic instability and intersegmental degenerative changes
type IV (post-traumatic): fracture in a region other than the pars leading to slippage
type V (pathological): diffuse or local disease compromising the usual structural integrity that prevents slippage
type VI (iatrogenic)