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.