The spine is made up of bone segments called vertebrae. Vertebrae have two parts: 1) the cylinder-shaped vertebral bodies to the front; and 2) the boney bridges making up the facet joints at the back. Most of the spine is flexible enough to let people bend, stretch, and lift. Between the bones of the spine are small discs that are hard on the outside and soft and jelly-like on the inside. The spinal bones are connected by the facet joints at the back and by the discs at the front.
The nerves of the spinal cord run through the spinal canal, which is just behind the vertebral bodies, and separate into roots along the length of the spinal cord and at the tail end of the spine. Some of them pass through the pelvis to become the sciatic nerves, which pass down each leg. Problems with the vertebrae, joints, or discs can all cause back disorders. Back disorders can cause mild to very severe backache.
About 75% to 85% of Americans will develop back pain at some time in their lives. Though it hurts, back pain is rarely caused by a serious disease and usually disappears on its own. It often comes back, however, making it one of the most common reason people see doctors.
Most cases of back disorders aren't caused by underlying disease. They're usually caused by aging, wear and tear, and poor posture. Obesity and smoking are risk factors for back problems. There are a number of back disorders, each having a different cause.
Muscle spasms in the back can occur when any part of the back is irritated. Muscle spasms are often an attempt by the body to protect a sore back. Muscle spasms also occur when the spinal nerves are irritated or damaged. Joint pain occurs when the joints become worn by activity or by being twisted.
Disc trouble, also called discogenic back pain, can occur in two ways. The jelly-like material inside the disc either bulges out or bursts through the hard outer cartilage of the disc. When this material bulges out and presses on a nerve, it causes pain and is called a herniated or prolapsed disc. Disc pain usually gets worse over the course of a few days. It usually goes away after 4 to 6 weeks, but it may continue as a dull, nagging ache.
Anything that causes pressure on the sciatic nerve root causes sciatica. The most common cause of sciatica, which is characterized by buttock and leg pain, is a disc or bone spur pressing on spinal nerve. It usually gets worse over a period of days, and may last up to several weeks.
As people get older, they may develop a condition called spinal stenosis. Spinal stenosis is a narrowing of the canal holding the spinal cord. This can be due to bone spurs (osteophytes) sticking out into the canal or to hardening of
the bands of tissue that support the spine. Spinal stenosis can cause back and neck pain or numbness and weakness in the arms or legs.