Elastic fibers in the anulus fibrosus of the dog intervertebral disc

A light microscopic investigation of the anulus fibrosus in cervical intervertebral discs of the dog was conducted to ascertain the arrangement and distribution of elastic fibers. Elastic fibers were observed in all lamellae of the anulus fibrosus. However, collagenous fibers were the predominant type of connective tissue fiber, and elastic fibers were randomly dispersed among them. Intralamellar (collagenous and elastic) fibers were vertically and obliquely oriented in both superficial and deep lamellae of the anulus fibrosus. All intralamellar fibers were densely and regularly arranged in superficial lamellae, but they were more loosely organized in deep lamellae. A narrow border of interlamellar, elastic fibers was observed between broader, contiguous lamellae in the superficial zone of the anulus fibrosus. Interlamellar elastic fibers were vertically and obliquely arranged in superficial lamellae however, they were radially oriented in deep lamellae. The deepest lamella of the anulus fibrosus consisted of a loose, three-dimensional network of intermeshing collagenous and elastic fibers. These observations suggest that elastic fibers are integral components of the articular and shock absorption mechanisms of the anulus fibrosus, and the cervical intervertebral disc of the dog is a suitable model for experimental investigation of the role of elastic fibers in intervertebral disc herniation.