Morphometrical Study of the Joint Surface and Capsule of the Lumbar Zygapophysial Joint with Special Reference to Their Laterality.

Abstract

Using 26 osteoligamentous lumbar vertebral columns (260 facets), we morphometrically investigated the cartilagenous joint surface, inner capsular surface and capsular thickness. We also examined whether the subcapsular pocket was present and, if present, how far it extended along the joint margin. The proportion of the inner capsular area in the total joint surface area in a facet (the capsular-joint surface ratio) was hypothesized to correspond to the potential looseness (or tightness) of the facet. The absolute data themselves seemed to be useful for better understanding of the joint morphology. However, further evaluations of the differences between segments, left/right differences, individual segmental fluctuation patterns and correlations between parameters provided a novel classification of specimens according to the hypothetical progress of joint degeneration. Criteria for the classification existed in 1) the laterality in parameters defined as more than 100% larger or smaller than the contralateral facet and 2) the drastic segmental difference in parameters over 50% larger or smaller than the adjacent segment. Consequently, three types were identified: 1) outside of the criteria in both area and thickness (-/- type, 9 of 26); 2) the criteria did not fit the area parameters but did fit the thickness parameters (-/+ type, 8); the criteria were filled in both categories of parameters (+/+ type, 9). Notably, in the +/+ types, the capsular thickness and capsular-joint surface ratio correlated significantly (p < 0.01), i.e., the hypothetical loose joint had a thick capsule. We speculated that early joint degeneration starts from the -/- type and advances via the -/+ type to the +/+ type. Considerating these results, we recommended using MR imaging for detailed identification of laterality in the capsular thickness for low-back pain patients to discriminate candidates for future severe degenerative changes of the articular cartilage in the lumbar spine.

Spinal Facet Joint Biomechanics and Mechanotransduction in Normal, Injury and Degenerative Conditions

“…Straining of the fibers in the facet capsule not only results from vertebral motion but also from the activation of the muscles that can occur during mechanical loading of the spine as the outer surface of the capsular ligament is covered by the surrounding paraspinal muscles [110]. As such, the individual fibers of the capsule can become stretched when the muscles that insert on it contract [83,88,110]. In fact, muscle insertions have been found to cover nearly 23% of the capsule area in the cervical spine with a nonuniform spatial distribution [110], which can give rise to unequal capsular strains and stresses in all the regions (posterior, anterior, lateral) of the capsule when different muscles are activated to stabilize the spine during loading.…”

“…For instance, the lumbar facet capsule has been reported to be 2.0 mm thick in the posterior region, and as much as 3.2 mm thick in the anterior region, whereas the superior and inferior regions are approximately 2.4 mm thick [83].The capsular ligament is comprised of dense collagen fiber bundles linked by proteoglycans, with elastin fibers and fibroblasts interspersed [18,84]. The collagen and elastin fibers extend between the laminae of adjacent vertebrae connecting to the ligamentum flavum both in the antero-and postero-medial regions of the facet joint, and completely surrounding the joint's articular surfaces in three dimensions.…”

Which Portion in a Facet is Specifically Affected by Articular Cartilage Degeneration with Aging in the Human Lumbar Zygapophysial Joint?

“…Why does the DC advance in the inferior process rather than the superior one? Sato et al (2002) reported that, in their recent morphometrical study, the superior articular surface was almost always larger than the complementary inferior surface. In general, a wide and curved surface can distribute a load to the entire surface depending on amount of the load, whereas a small flat surface tends to concentrate it on a point (Eckstein et al, 1995;Gries et al, 2000).…”

“…This discussion may be contraversial considering the high incidence of fibrillations in the superior articular process. Moreover, a high incidence of subcapsular pockets in the caudal margin of the inferior articular process (Sato et al, 2002) is likely to accelerate impingement of the capsule in extension. They may prevent DCs of the superior articular surface but seems to cause caudal capsular damage and following DCs in the caudal sector of the inferior articular process.…”

“…Gries et al (2000), using 29 cadavers (ages, 15-40 years), histologically described dorsal dominance in DCs in the lower lumbar facet. Data on localization of DCs in a facet are helpful for a discussion connected to the detailed morphometrical results of the joint surface and capsule such as that recently provided by Sato et al (2002). However, the few previous reports seem to be too general to use for such a discussion.…”