The periosteum is a thin membrane of connective tissue composed of different layers covering the surface of a bone, providing structural integrity and contributing to growth and development as well as the repair of bone 1-3.
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Gross anatomy
The periosteum consists of different layers in particular an outer fibrous layer and an inner cambium layer 1,2 and a transparent undifferentiated layer in between the two 3,4. It invests most parts of bone except for those parts covered by articular cartilage, tendon insertions and the sesamoid bones 1,5,6.
Relations and/or Boundaries
The periosteum is tightly attached to the physis at the cartilaginous epiphysis just beyond the groove of Ranvier and more loosely to the bony cortex via Shapey fibers 1,2,7. It forms a membranous interface between muscle and bone.
Blood supply
The periosteal circulation consists of a rich plexus of periosteal, periosteal-cortical, musculo-periosteal and nutritive periosteal vessels and anastomoses mainly found in the fibrous layer of the periosteum providing at least one-third of the blood supply requirements of the cortical bone 2,3. Most of those vessels are located in the fibrous layer 2. This rich vascular plexus has been also called the ‘umbilical cord’ of bone 2,8.
Innervation
There are predominantly unmyelinated nerve fibers in the periosteum with free nerve endings possibly related to pain perception 3,6. In addition, bone metabolism seems to be least in part regulated by the adrenergic sympathetic nervous system that controls the bone formation and resorption via ß2-adrenergic receptors in the axial and appendicular skeleton 2.
Histology
Fibrous layer
The outer fibrous layer can be subdivided into two portions: a superficial and a deep portion. Both portions contain relatively few cells and a predominantly collagenous matrix:
The superficial portion is inelastic but highly vascularized and features the following 1-3:
small compact collagen bundles intermingled with elongated fibroblasts
few elastic fibers
many blood vessels
rich neural network
The deep fibroelastic portion has a significant elasticity and the following features 1:
many elastic fibers
not so many vessels
termination of periosteal tendon attachments
Cambium layer
The inner cambium layer or cellular layer has a relatively sparse collagenous matrix but with a large number of cells including the following cell types 1-4:
mesenchymal progenitor cells
osteogenic progenitor cells
osteoblasts
fibroblasts
It also features a rich vascular and neural sympathetic network located more in the periphery with intermingled endothelial pericytes 1.
Function
The roles of the periosteum are the following 1-5:
contribution to bone growth, modelling
contribution to the structural integrity of bone/physical protection of the bone
contribution to new bone formation, recovery and repair
bone nutrition
mechanosensor for detecting and measuring mechanical load
Radiographic features
The periosteum becomes visible in the setting of different periosteal reactions. Periosteal reactions can be roughly categorized by distribution (unifocal/multifocal) and then further classified in many different patterns. These patterns help to conclude the underlying pathology, particularly about its aggressiveness 6.
See also: periosteal reaction.
Ultrasound
The normal periosteum appears as a hypoechoic band immediately adjacent to the underlying cortical bone, it is thin and barely visible in adults and thicker in young children 9. At the level of physis, it is contiguous with the perichondrium 9. The normal periosteum should not show any Doppler signal except for perforating nutrient arteries 9.
Periosteal reactions in the setting of pathology may have different pathological patterns ranging from thickening of the periosteum to hyperemia on Doppler but should be interpreted in conjunction with other findings and using other imaging modalities 9.
Development
The cambium layer becomes progressively thinner with age being the thickest in the foetus 1,2. Vessel density and the number of periosteal fibroblasts also decrease with age and thus its overall osteoblastic potential. This loss of osteoblastic potential is greatest during childhood, although it can be stimulated and restarted later for example in the setting of a fracture although at a reduced speed of bone formation 1.
History and etymology
The word periosteum is derived from the greek language composed of the words 'peri' meaning surrounding and 'osteon' meaning bone. The French botanist chemist and engineer Henri Louis Duhamel (1700-1782) already noted in 1739 that silver wires implanted below the periosteum were associated with appositional growth and termed the inner layer cambium layer 1. Later the French surgeon Louis Leopold Ollier (1830-1900) could prove that the cambium layer is indeed capable of repairing and producing bone using a free periosteal graft in 1867 1,11.
Clinical importance
The periosteum plays an important role in bone healing. Conversely, its loss or destruction is associated with delayed bone healing or non-union. Due to its importance in bone repair and its regenerative capacity it has several surgical uses 2,3,5,12.
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