Periostet

Periostet, commonly referred to as the periosteum in many languages, is a dense, vascularized membrane that covers the outer surface of most bones, excluding the articular cartilage of joints. It consists of two functional layers: an outer fibrous layer and an inner cambial (osteogenic) layer. The fibrous layer contains collagen fibers that blend with the connective tissues, tendons, and ligaments, providing a strong attachment to the bone. The cambial layer houses osteoprogenitor cells, osteoblasts, and a small amount of osteoclasts, which contribute to bone growth and repair.

Functions and significance include protection and nourishment of the underlying bone, as the periosteal blood vessels supply nutrients to the cortical bone. It serves as an attachment site for tendons and ligaments via Sharpey's fibers, which anchor the connective tissues into the bone. The periosteum is essential for appositional growth (growth in diameter) and plays a critical role in fracture healing, supplying osteogenic cells that participate in new bone formation. The periosteum is richly innervated, and its sensory nerves can make periosteal irritation particularly painful.

Anatomically, the periosteum lines most bones' surfaces, being thicker in some regions and thinner in others, and it remains intimately connected to the outer cortex through perforating fibers. It is supplied by periosteal vessels and is absent only where cartilage covers joint surfaces.

Clinical relevance includes periostitis, an inflammation of the periosteum that can follow infection, trauma, or repetitive stress, often associated with pain, swelling, and radiographic changes.