Study design: The spatial distribution of fiber-forming collagens in the anulus fibrosus was investigated in the complete longitudinal and horizontal sections of human lumbar intervertebral discs of seven individuals.
Objectives: To obtain a more detailed structural definition of the anulus fibrosus because structural alterations of its collagen fiber network have been implicated in discal degeneration and other spinal pathologies.
Summary of background data: Prior biochemical or immunofluorescence studies permitted only limited conclusions concerning the spatial distribution of the fiber-forming collagens in relation to anatomic structures because they were based on intraoperative tissue specimens or performed on incomplete sections of human intervertebral discs.
Methods: Complete human intervertebral discs with their adjacent vertebral bodies were fixed, decalcified, and embedded in paraffin. The intervertebral disc and its adjacent structures were reviewed in their entirety on one histologic slide. Monoclonal antibodies against human Types I, II, and III collagen were used for immunohistochemistry. A comparative analysis based on both immunohistochemical and histologic evaluation was performed.
Results: Type I collagen was seen abundantly in the outer zone and outer lamellas of the inner zone of the anulus fibrosus. On longitudinal sections, the Type I collagen distribution took the shape of a wedge. On horizontal sections, the Type I collagen positive area took the shape of a ring that was wider anteriorly than posteriorly. This suggests that the three-dimensional shape of the Type I collagen-positive tissue in the anulus fibrosus can be described by a donut that is wider anteriorly than posteriorly. Type II collagen was present in the entire inner of the anulus fibrosus, but not in the outer zone. In addition, it was found in the cartilaginous endplates. Type III collagen showed some codistribution with Type II collagen, particularly in pericellular locations in areas of spondylosis, which was noted at the endplates, vertebral rim, and insertion sites of the anulus fibrosus.
Conclusions: These observations on the location of Types I and II collagen provide a more detailed structural definition of the anulus fibrosus, which may assist in further investigation of discal herniation.