The periosteum is a membranous tissue that covers the surfaces of your bones. The only areas it doesn’t cover are those surrounded by cartilage and where tendons and ligaments attach to bone.

The periosteum is made up of two distinct layers and is very important for both repairing and growing bones.

Periosteum function and anatomy

Inner layer

The inner layer of the periosteum is also referred to as the cambrium. It contains osteoblast cells.

Osteoblasts are bone-forming cells. They’re very important during the fetal and childhood phases of life when bone tissue is still developing. As a result, the inner layer of the periosteum is thick and rich in osteoblasts in the fetus and during early childhood.

The inner layer of the periosteum becomes thinner with age. This thinning begins in childhood and continues through adulthood. In many cases, the inner layer becomes so thin that it’s hard to distinguish from the outer layer of the periosteum.

If a fracture occurs in adult bone, osteoblasts can still be stimulated to repair the injury. But the rate of regeneration will be slower than it is in a child.

Outer layer

The outer layer of the periosteum is mostly made of elastic fibrous material, such as collagen. It also contains blood vessels and nerves.

The blood vessels of the periosteum contribute to the blood supply of the body’s bones. They can pass into the dense and compact layer of bone tissue below, called the bone cortex.

Blood vessels enter the bone through channels called Volkmann canals that lie perpendicular to the bone. From there, the blood vessels enter another group of channels called Haversian canals, which run along the length of the bone.

The nerves of the periosteum register pain when the tissue is injured or damaged. Some of the nerves of the periosteum travel alongside the blood vessels into the bone, although many remain in the outer layer of the periosteum.

Periosteum conditions

Periostitis

Periostitis is an inflammation of your periosteum. It’s caused by overuse or repetitive stress to muscles and connective tissue.

It’s often associated with shin splints, a painful condition that tends to affect runners and dancers. Shin splints can also happen when you start a new exercise program or increase the intensity of your usual workouts.

If you have periostitis, you may notice that you have pain or tenderness in the affected area. There may also be some swelling.

Your doctor can typically diagnose periostitis by a physical examination and going through your medical history. In some cases, they may use imaging tests, such as an X-ray, to rule out other conditions, such as stress fractures.

Treating periostitis may involve:

  • Resting the affected area. Take a break from any activities that cause pain or discomfort in the area affected by periostitis. Repeating activities that caused the condition could lead to a stress fracture, which can take much longer to heal. Try to focus your exercise routine on low-impact activities while you’re healing, such as swimming.
  • Applying ice to the area. Wrap an ice pack in a towel and apply it to the affected area several times a day for 15 to 20 minutes.
  • Taking over-the-counter pain medication. If pain or tenderness from your periostitis is bothering you, take an over-the-counter pain reliever, such as ibuprofen (Motrin, Advil) or acetaminophen (Tylenol).

You can slowly begin resuming your normal activities when the pain starts to decrease, usually within two to four weeks. Be sure to increase duration and intensity of your activities gradually to avoid reinjuring yourself.

Periosteal chondroma

Periosteal chondroma involves a noncancerous tumor in your periosteum. It’s a rare condition without any known causes. These tumors tend to occur in people under age 30 and affect males more often than females.

Symptoms of periosteal chondroma can include:

  • a dull pain or tenderness at or near the site of the tumor
  • a mass you can feel
  • a broken bone

The condition is typically diagnosed using imaging tests such as X-ray, CT scan, or MRI scan. If these don’t show much, your doctor may do a biopsy. This involves taking a small tissue sample and looking at it under a microscope.

Periosteal chondroma is usually treated by surgically removing the tumor. Once removed, these tumors rarely come back. The length of the recovery period will depend both on the location of the tumor and on its size. You’ll need to limit the use of the affected area while recovering and also gradually return to your normal activities.