[Structure and vascularization of the knee joint menisci].
BACKGROUND
The structural properties are important for the pathophysiology and healing of meniscus lesions.


METHODS
We analyzed the collagenous fiber texture of 44 menisci by scanning electron microscopy after exposure of the collagen fibrils with NaOH. The distribution of fibrocartilage and dense connective tissue is investigated by light microscopy. The vasculature of the menisci is demonstrated by injection techniques as well as by the immunohistochemical proof of laminin as a component of the basement membrane in the wall of blood vessels.


RESULTS
The meniscus surface is covered by a network of thin fibrils. Beneath the superficial network there is a layer of lamellar fiber bundles that intersect under various angles. The major part of the collagen fibrils is located in the central portion between the superficial layers and runs in a circular direction. In the external circumference the meniscus is composed of dense connective tissue that histologically resembles to tendon tissue. In the internal circumference and in the superficial layers the meniscus consists of fibrocartilage. Blood vessels enter the meniscus from the adjacent joint capsule. In the adult blood vessels are present only in a peripheral rim close to the joint capsule. The ligamentous anterior and posterior horns are completely vascularized regardless of age.


CONCLUSIONS
Our results allow the following conclusions. Reports from the literature, that describe an arcade-like collagenous fiber texture are incorrect. Our result show that there is a causal coherence between the circular orientation of the collagen fibers and the frequency of longitudinal meniscal tears. The occurrence of well vascularized dense connective tissue in the external circumference must be considered as cause for the well healing of peripheral meniscus lesions.
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003094:Collagen; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007719:Knee Joint / Q000033:anatomy & histology* / Q000098:blood supply* / Q000648:ultrastructure; D007797:Laminin / Q000032:analysis; D008297:Male; D008592:Menisci, Tibial / Q000033:anatomy & histology* / Q000098:blood supply* / Q000737:chemistry / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D008875:Middle Aged; D013314:Stress, Mechanical