Study of the human ligamentum flavum in old age: a histological and morphometric study

Ageing is associated with many changes in the ligamentum flavum (LF): ossification, diminish of the cross-sectional area of the elastic fibres, increase of the collagen fibres and change in its mineral and matrix elements. There are limited data about the influence of the ageing process on the structure of the LF at different spinal levels. The aim of the study was to clarify the effect of the ageing process on the LF at different spinal levels. This was done through histological study and morphometric analysis using the image analyser.

Vertebral column specimens were obtained from 10 human cadavers preserved in a mixture of formaldehyde and carbol. Their average age ranged 60-70 years. The vertebral blocks included 4 vertebrae at cervical level (C 3, 4, 5, 6), thoracic level (T 5, 6, 7, 8) and lumbar level (L 2, 3, 4, 5). Sections were stained with haematoxylin and eosin, Masson's trichrome, Orcein and Verhoeff stains. The morphometric measurements included the relative collagen area, relative elastic area, collagen area [%] and elastic area [%].

The relative elastic areas reduced in all the spinal levels. The relative collagen areas increased to become 46.1 ± 2.9 in the cervical region, 51.8 ± 1.3 in the thoracic region, and 49.7 ± 2.5 in the lumbar region. The average elastic area was highest in the cervical region, and lowest in the thoracic region. The ratio of elastic area to collagen area was 1.16:1 in the cervical region, 1.01:1 in the lumbar region and 0.93:1 in the thoracic region. The elastic fibres were regular, diffuse and organised in parallel order in the cervical and thoracic regions. Their orientations were craniocaudal with a variation of some fibres in the cervical region. Most of the elastic fibres in the lumbar region were regular and organized in parallel order. Nevertheless, rupture, fragmentation, and abnormal organization of the elastic fibres were discovered in a few specimens of the lumbar region. Increase of the vasculature and degeneration with abnormal body formations within the lumbar ligaments were observed. The LF midline gaps were present in the cervical, thoracic and lumbar regions. In 10% of lumbar specimens, the ligaments fused in the midline with absence of the midline gaps. Ossification was discovered in the thoracic and lumbar ligaments.

Structural differences have been observed among the LF at the different spinal levels, and all these changes were caused by the ageing process. Decrease of the relative elastic area, an increase of the relative collagen area and reduction of the elastic to collagen area ratio affected all the spinal levels of the ligaments. Many changes took place in the lumbar ligaments such as ossification, increase vasculature, degeneration with abnormal body formation, absence of the midline gaps, fragmentation and rupture of the elastic fibres.