Collagen fibril structure of normal, aging, and osteoarthritic cartilage.
The collagen architecture in normal, aging, and osteoarthritic articular cartilage was studied optically using a new silver staining technique based on specimens from 50 autopsy cases, four amputated limbs, and six osteoarthritic knees. In the normal articular cartilage, the collagen fibrils in the superficial zone were compactly arranged into layers of decussating flat ribbons mostly parallel to the artificial split lines. The fibrils showed a tendency to condense into vertical arcade columns undergirded by tangential bundles in the intermediate zone. In the deep zone, the fibrils formed a random meshwork with a slight preponderance of vertical fibrils in the perilacunar region. Three types of early degradative lesions involving the collagen network were identified. Type I lesions consisted of focal superficial disruptions related to age and friction. Type II lesions consisted of focal disruptions of tangential fibrils in the intermediate zone leading to cyst formation, probably representing a form of local stress failure. Type III lesions were found in the patella and consisted of marked swelling of the superficial zone, the cause of which was unknown. Lesions of varying severity were seen within each of the three types; the morphological changes of the more severe lesions overlapped with those of clinically overt osteoarthritis.