Saturday, April 5, 2008

Why Do My Bones Hurt?

Bone pain generally results in aching as well as pain and muscle spasm. For instance, in the case of arthritis, sensory fibers of the joint may respond to sympathetic activity due to inflammation. Most people know someone with arthritis. Sometimes the pain of arthritis is due to joint inflammation, but even this inflammatory response can cause bone pain.

Most body tissues, including bones, produce a number of chemicals and hormones that cause pain. Some examples are substance P, histamine and one class chemicals called prostaglandins. These are all associated with pain. Prostaglandins also play an important role in pain caused by bone metastases.

One of the most common reasons for bone pain is fracture due to trauma or osteoporosis. When normal bones are subjected to abnormal mechanical forces, a fracture can occur. Unfortunately in patients with osteoporosis, even normal mechanical stress can cause a fracture. This can result in disruption of the cortical bone and stimulation of the nociceptive (pain) nerve endings.

Although most people think of bone as a hard, unchanging tissue (like skeletons), our bones are living, active, changing organisms just like other organs. One reason fracture and other causes of bone pain hurt so much it of the exquisite nerve supply. Most of the nerves that cause pain appear to serve the periosteum.

The periosteum is the living, outer lining of bone that serves as a type of covering as well as a a type of anchor site for tendons and ligaments to attach to bone. When you pull a muscle or strain a ligament, much of the pain is associated with the stress on the periosteum and stimulation of the pain fibers there. This also is a factor in many forms of arthritis and the periosteum lines the bone up to the level of the joint.

As such, inflammation, fracture and even other pathological processes to which bone is subjected can result pressure changes which, in turn, results in bone pain. For example, during a bone marrow biopsy, a needle is placed into the marrow cavity and a sample obtained. This causes negative pressure (vacuum) that stimulates the pain fibers. In fact, this procedure is one of the most painful 'routine' medical procedures that we do. It's no surprise, therefore, that people with metastatic cancer or other bone pathology have so much pain.

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