Anatomic variance of interfacet distance and its relationship to facet arthrosis and disk degeneration in the lumbar spine.

Inadequate separation of the L4-S1 facets predisposes individuals to spondylolytic defects. We proposed that decreased interfacet separation is a risk factor for increased lumbar degenerative disease. This study examined the correlation between interfacet distance and degenerative disease of the lumbar spine. Four hundred forty-four cadaveric lumbar spines were examined for evidence of lumbar facet arthrosis and disk degeneration. Arthrosis at each level was graded from 0 to 4 on a continuum from no arthritis to complete ankylosis. These results were then examined in relation to interfacet spread. Interfacet distances were measured at each level (L1-S1). The difference in interfacet spread (L4-S1) was then correlated to facet arthrosis and disk degeneration. In individuals younger than 50 years (n=251), increased interfacet spread (L4-S1) was associated with less facet arthrosis at the L5/Sl level (P<.05). Similarly, in individuals younger than 40 years (n=149), increased interfacet spread (L4-S1) was associated with less disk degeneration at the L5/S1 level (P<.03). Insufficient increase in interfacet distances (L4-S1) correlates with a greater risk of developing and maintaining spondylolytic defects. Similarly, this study suggests that increased interfacet spread (L4-S1) protects against early degenerative changes at the L5/Sl level. The more pyramidal the L4-S1 facet cascade, the lower the arthrosis. This effect appears early in the degenerative process before facet arthrosis and disk degeneration have become ubiquitous. In individuals younger than 50 years, increased interfacet distance correlates with less L5/Sl facet arthrosis.