Calcium crystal deposition in the ligamentum flavum of the lumbar spine.

OBJECTIVE

To investigate the histological and immunohistochemical properties of the lumbar ligamentum flavum with calcium crystal deposition.

METHODS

We examined the histological characteristics of the ligamentum flavum of the lumbar spine containing calcium deposits, obtained from 16 surgical cases with symptomatic lumbar spinal stenosis. Sections of the ligaments were also immunostained for elastase, chymotrypsin and S-100 protein, and examined by energy dispensive X-ray microanalysis and scanning electron microscopy. The results were compared with those of ligaments without calcium deposits.

RESULTS

The elastic fibres of ligaments with calcium deposits showed marked degeneration (irregular arrangement and fragmentation of the fibre bundles) and nodular granulomatous lesions. Calcium crystal deposits were present in this area and in the nodular granulomatous areas. The calcified areas were surrounded by neutrophils and new small blood vessels. Immunostaining for elastase and chymotrypsin was positive in these areas, and S-100 protein-containing chondrocytes were detected around and within the calcified areas. Calcium pyrophosphate dihydrate crystals were identified in the calcified areas in all patients.

CONCLUSION

Nodular degeneration of the elastic fibres of the ligament is probably caused by the action of proteolytic enzymes. Degeneration results in small granulomatous areas that form the nidus for calcium crystal deposition. Accumulated neutrophils, and S-100 protein-containing chondrocytes appear to precipitate the deposition of calcium crystals in the granulomatous lesions of the degenerated lumbar ligamentum flavum.