Review Question - QID 4563

Flattened chondrocytes oriented parallel with the tidemark and collagen fibrils oriented parallel to the tidemark best describes the orientation of collagen fibrils in the superficial zone of articular cartilage.

The primary orientation of the collagen fibers in the superficial zone is parallel with the joint surface, in order to resist compressive and shear forces. This zone is the thinnest one, and it sometimes is referred to as the gliding zone. The surface layer, known as the lamina splendens, is cell-free and composed mainly of randomly oriented, flat bundles of fine collagen fibrils. Deep to the lamina splendens are more densely packed collagen fibers interspersed with elongated, oval chondrocytes oriented parallel to the articular surface.

Sophia Fox et al. in a review article state that the superficial zone comprises 10-20% of articular cartilage and is composed of mostly type II and IX collagen.

Illustration A displays that articular cartilage has four distinct zones: (1) a superficial (tangential) zone, (2) a middle (transitional) zone, (3) a deep (radial) zone, and (4) the calcified zone. Illustration B demonstrates the collagen orientation and chondrocyte appearance in the different articular cartilage layers.

Incorrect Answers:
Answer 1-4: None of these accurately describe the appearance of chondrocytes and orientation of collagen fibrils in the superficial zone of articular cartilage.