Periosteum [Greek peri = surrounding; osteon = bone] is a fibrous membrane that covers the outer surface of bones like an envelope 1,16.
Periosteum covers all bones, except the kneecap (patella) and certain small bones in the wrist, hand and foot, which are embedded within the tendons 16. Periosteum also does not cover the cartilaginous parts of the bones in the joints 17,35.
The outer, fibrous periosteal layer consists mainly of the dense irregular connective tissue, made of superficial collagen (type I) and deeper elastin fibers, and rare connective tissue cells (fibroblasts) 16. This layer also contains arteries, veins, lymphatic vessels and sensory nerves 16,31. The inner, cellular or osteogenic periosteal layer, also called cambium (which has got name from the cambium between the bark and wood of a tree) is in direct contact with the cortical bone; it consists of progenitor cells that develop into osteoblasts, which produce the bone tissue. The cambium layer is thickest in a newborn and thins with age 16,31.
In growing individuals, the periosteum of the long bones is 70-150 micrometers (0.07-0.15 millimeters) thick; it is thicker toward the ends of the bones, and it thins with age 38. Periosteum of the nasal bones is about 0.8-1.8 mm thick 32, and alveolar periosteum (under the gingiva) about 0.5 mm thick 39.
In periosteal reaction due to an irritating bone or systemic disorder, the periosteum can become several millimeters thick 20.
Endosteum is a lining that covers the inner surfaces of the long bones (the medullary cavity and hollow spaces in the spongy bone). It is mainly composed of progenitor cells that can develop into bone-producing cells (osteoblasts), and a small amount of connective tissue. Like periosteum, endosteum also participates in bone growth in width and bone repair 16,36. Endosteum is thinner than periosteum since it has very little fibers.
Sharpey’s perforating fibers run from the periosteum through the bone to the endosteum and firmly attach both membranes to the bone 34. They are thin (<40 micrometers) but strong fibers made mainly of collagen and elastin 34. They are especially abundant at the sites of ligament and tendon attachments to bones and in the alveolar bone, from which the teeth grow 34. Sharpey’s fibers become stronger with activity and weaker with lower blood estrogen levels 34.
Picture 1. The periosteum covers the outer surface of the bone, except
on the cartilaginous part, which is covered by the perichondreum.
1. Attachment Sites for the Muscle Tendons and Ligaments
Certain tendons (bands that connect muscles to bones) and ligaments (which connect the bones in the joints) attach to the periosteum at the insertion sites also called entheses or osteotendinous or osteoligamentous junctions 16,35. Some tendons and ligaments attach directly to the bones (not via periosteum) 35. In the joints, periosteum continues into articular cartilage and into the fibrous layer of the joint capsule 16.
2. Nourishment of the Bones and Muscles by Periosteal Arteries
Periosteum contains periosteal arteries, which run within the outer periosteal layer and supply blood to the periosteum and outer one third of the cortical bone 45. Larger periosteal arteries run above the periosteum and communicate (anastomose) with the muscle arteries and contribute to the blood supply of the part of muscles adjacent to bones 45. When periosteum is detached from the bone (injury, surgery, obtaining periosteal grafts), it does not affect the blood supply to the muscles and it only minimally affects the blood supply to the bone, because the bone also gets blood from the arteries that run inside the bone 45. Periosteum also contains veins, which collect the blood, and lymphatic vessels, which collect the lymph from the bones 1,16.
3. Bone Sensitivity (Innervation of Periosteum)
Sensory nerves in the outer, fibrous layer of the periosteum make periosteum sensitive to tension and tearing 1,17. Some nerve endings from periosteum penetrate into the bone canals and thus make bone sensitive to pain 44. Periosteum also contains cholinergic sympathetic nerves, called vasomotor nerves, which regulate the diameter of the periosteal arteries and thus the blood flow through periosteum 31.
Periosteum and Migraine
Nerve fibers in the periosteum or bones of the skull and in the dura mater (the outermost brain membrane) may be involved in migraine pain 54. Periosteal nerves contain substance P, which is involved in pain mediation 55.
4. Bone Growth and Repair
In children 1,16, osteoblasts in the inner layer of the periosteum (cambium) produce new bone and thus enable the growth of the bone in the width or periosteal or appositional bone growth 1,16. Periosteal bone growth, to some extent, probably also occurs in adults 31. After a bone fracture, the progenitor cells in the cambium develop into osteoblasts and chondroblasts that contribute to the bone repair and healing by forming a soft periosteal callus 1,16,48. The bone healing potential of the periosteum decreases with age and is greater in long bones, such as the tibia, than in flat bones, such as the skull bones 16. Periosteum may also contribute to bone wasting (resorption); for example, after a tooth loss, the alveolar bone under the gingiva shrinks 31.
Small bones, like wrist bones, that have only small amount of periosteum, have spherical growth plates inside them 16.
In growing males, low amounts of estrogens are needed for periosteal bone expansion m 61.
5. Periosteal Hinge
In certain fractures of long bones, the periosteum remains intact and acts as a hinge — it holds two pieces of the broken bone together rinks 50.
Pericranium is the periosteum that covers the outer surface of the skull bones.
Periosteum and Brain Membranes
The inner side of the skull bones is covered by the outermost brain membrane or meninge called the dura mater, which has the periosteal layer, which is firmly attached to the skull bones, and the inner meningeal layer. At certain points, the two layers separate and form canals called cerebral sinuses or dural venous sinuses through which the venous blood from the brain flows.
Meningeal arteries, which supply blood for the dura mater, run between the periosteal layer of the dura mater and the skull bones, in the so-called epidural space 42. A break of a meningeal artery, usually caused by a break of one of the skull bones, results in an epidural hematoma.
The periosteum in the eye orbit is continuous with the dura mater; 5 it is loosely attached to the bone, so surgeons often elevate it when removing tumors in the orbit to avoid damage of the eye content 47. A subperiosteal hematoma, usually in the orbit roof, can occur after a blunt trauma to the frontal area of the head (a fall or direct blow) 46.
Periosteum in the vertebrae is well innervated, which may be one of the reasons for pain during injection of anesthetic for epidural anesthesia ) 60.
Periosteal tear refers to detachment of a part of periosteum from the bone at the site where a ligament or tendon is attached to it 40. It commonly occurs in football or soccer players or runners when they suddenly twist a leg or foot. Symptoms include local tenderness, and pain during stretching the affected tendon 40. Periosteal tear can be detected by an X-ray, but this is usually not needed for diagnosis 40.
Subperiosteal Hematoma (Bruise, Contusion)
Periosteal bruise is a collection of blood between the periosteum and the bone, usually due to direct blow to the bone or bone fracture 18. Symptoms include local pain, a noticeable tender lump and skin bruise within minutes of injury 18.
Picture 1. X-ray of a periosteal reaction (long arrow)
triggered by an osteoid osteoma (short arrow)
in the right thighbone (femur) of the 7-month old girl
(source: springer.com, Creative Commons Licence)
Periostitis is inflammation of periosteum, and periosteal reaction refers to formation of new bone or bone hypertrophy under the periosteum in response to bone irritation 2,3,17. Both terms are often used as synonyms. Symptoms may include pain, tenderness and swelling of the affected limb, but sometimes there are no symptoms 21,41. Causes include shin splints, bone infection (osteomyelitis), vasculitis 26, benign tumors, fluorosis (especially in vertebrae) 20, cancer 21, chronic lung or liver disease, inflammatory bowel disease (IBD) 21. Main causes in infants include congenital syphilis and physiological periostitis 41. Diagnosis can be confirmed by an X-ray, CT or MRI 3.
Shin Splints or Medial Tibial Stress Syndrome (MTSS) or Periostalgia
Shin splints refers to an overuse injury of the shin area with pain in the lower two thirds of shins triggered by exercise 6,11. Mechanism may include inflammation of the tibial periosteum, periosteal edema, dysfunction of leg muscles, tendon tears and stress fractures of bones 11.
Periosteal ganglion is a ganglion cyst arising from the periosteum, for example, in the tibia, femur, iliac bone, radius or ulna, mostly in adults 12,13,14,15. It can cause local pain, for example, in the wrist 14 or shin 15. A periosteal ganglion can be associated with a ganglion cyst within the bone 15. It can be detected by a CT, MRI 12,13 or therapeutic ultrasound 15. Treatment is with surgical removal 15.
Periosteal necrosis can result, for example, from burns 57, contact with bone implants 58 or osteomyelitis 59.
Periosteal grafts can be used to treat defects in the connective tissue, bone, cartilage and muscles, because periosteal cells can differentiate into connective tissue cells (fibroblasts), bone cells (osteoblasts), cartilage cells (chondrocytes) or skeletal muscle cells (myocytes). Autologous periosteal graft, which is taken from the same person in whom the graft is used, for example a galea-periosteum graft from the scalp 49 or a graft from the shinbone (tibia) can be used to treat:
- Knee cartilage defects caused by osteochondritis, osteoarthritis or injuries 24,25,33.
- Muscle hernia, for example, anterior tibial muscle hernia 19
- Sternal clefts 23 or maxillary clefts 29 in infants
- The gingival recession defects in the gums 29
- Frontal sinus defects 49.
Periosteal hypertrophy or overgrowth is a common complication of periosteal grafts. If it occurs in the joint cartilage and if it causes symptoms it can be treated by an arthroscopic procedure called chondroplasty 51.
Certain physiotherapeutic techniques, such as deep transverse friction massage in combination with Mill’s joint manipulation can help reduce pain in tennis elbow (lateral epicondylalgia) 52,53.
Periosteal pecking is a form of dry needling (acupuncture) in which the needle touches the periost; it is used in treatment of shin splints 56.
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