Morphometry of the lumbar zygapophyseal facet capsule and cartilage with special reference to degenerative osteoarthritic changes: an anatomical study using fresh cadavers of elderly Japanese and Korean subjects

Morphometric data were obtained from fresh cadaver dissections, and observations of degenerative changes in the joint cartilage (DCs) were analyzed to determine whether the morphometric parameters of the lumbar zygapophyseal joint capsule varied according to the presence and severity of DCs. There have been no previous morphometric studies of the facet capsule that describe age-related DCs. Using 23 fresh osteoligamentous lumbar spines from donated cadavers, we performed morphometric investigations of the surface areas of the joints and their capsules and measured the capsular thickness. We hypothesized that the ratio of the inner capsular area to the joint surface area for each facet (the capsule/facet index) could serve as an index showing a functional aspect of a large or small capsule. Our results showed that the joint surface area increased significantly with increasing severity of DCs, according to Grogan’s classification. Facets with advanced DCs tended to have a small inner capsular surface. The capsule/facet index generally correlated positively with capsular thickness, especially the dorsal portion; however, this was not true for the ventral portion. The index also correlated negatively with DC progression. Thus, lumbar facet DCs were strongly linked to reconstructive alterations in capsular size, thickness, and looseness. The occurrence and progression of DCs narrowed the joint capsule, especially the dorsal portion, and this seemed to decrease the potential looseness of the joint. Conversely, these capsular alterations seemed to accelerate DC progression. A negative adaptation cycle seemed to occur.