How Does Bone Die?

Bone is a living tissue, so it requires a blood supply to have the nutrients it needs to stay alive and be healthy. However, there are times when the blood supply to a bone can be interrupted, which will cause the bone to die. This is called avascular necrosis or osteonecrosis. There is both primary and secondary avascular necrosis (bone death); primary has no cause for the bone death, but secondary avascular necrosis always has a cause for why the bone dies. There are many situations that can interrupt the blood supply to bone, some of these include:

  • Trauma or fracture
  • Sickle Cell Disease
  • Caisson Disease
  • Vasculitis
  • Cancer
  • Pregnancy
  • Medications, such as steroids
  • Alcoholism

These are just a few of the problems that may lead to secondary avascular necrosis, but avascular necrosis will be caused by anything that decreases or eliminates the bone’s blood supply.

The signs and symptoms of a patient with avascular necrosis will vary depending on location of bone death, and what caused the interruption of blood. Some patients may not have any symptoms whereas some patients may experience various degrees of joint pain; patients may have mild joint pain and may only be when exercising, whereas other patients may have excruciating joint pain even when resting. Besides pain, there are not many other signs and symptoms that a patient will have indicating that bone death has occurred. However, many signs of bone death can be seen on an x-ray. Some findings on x-rays may include:

  • Shrunken epiphysis (the epiphysis is the end of the bone)
  • Flat articular surface (the articular surface is the end of the bone that meets another bone)
  • The spaces between bones may be wider than normal
  • Some parts of the bone will be more white than other areas-this is called sclerosis and it is seen because the bone is hardening and becoming more dense (areas that are more dense show up more white on x-ray)
  • The bone may look deformed

There are four phases of bone death and each phase has different characteristics that will be seen on x-ray.

The most common site of avascular necrosis in the lower extremity is the hip, but the most common location in the foot is the second metatarsal (metatarsal is the bone the supports the toe bones). These sites are the most common because their blood supply is more easily damaged and there are fewer vessels carrying blood to the bone.

However, like stated previously, bone death can be caused in any bone due to the blood supply being destroyed. There are many types of avascular necrosis that impact different patient populations. Some more common types of avascular necrosis are:

  • Legg-Calve-Perthes Disease-avascular necrosis of the hip-affects males 5-7 years old
  • Frieberg’s Disease-avascular necrosis of second metatarsal-any age
  • Islen’s Disease-avascular necrosis of fifth metatarsal-any age
  • Blount’s Disease-avascular necrosis of the tibia (leg bone)-affects infants and children 8-15 years old
  • Trevor’s and Renandier’s Disease-avascular necrosis of the sesamoids (the two small pea size bones under the big toe)-affects patients who most commonly had an injury in the area of the big toe

Within two years of the onset of avascular necrosis, a patient will most likely be suffering from joint pain, so if you are having joint pain it is important to visit a doctor for evaluation and treatment. Treatment will partially depend on the x-ray findings, which will indicate the current phase of bone death, and the goal of the treatment will be to prevent further progression to complete bone death.

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