Nerve Function Tests for Evaluating Low Back Problems
The nerves that carry messages to and from your legs come from your low back. By checking your muscle strength, your reflexes, and your sensation (feeling), your doctor can tell whether there is pressure on a nerve root coming from your spinal column. He or she can often also tell which nerve root is involved.
Muscle strength tests can detect true muscle weakness, which is one sign of pressure on a nerve root. (Sometimes leg weakness is actually due to pain, not pressure on a nerve.) Most people who have herniated discs that cause symptoms also have some nerve root compression.
Specific muscles receive impulses from specific nerves, so finding out which muscles are weak shows your doctor where nerve roots are being compressed.
See a picture of the lumbosacral region, from which nerve root compression usually originates.
Muscle strength tests include:
Just as your muscles receive signals through certain nerves, other nerves carry signals back to your spinal cord from specific sections of your skin and other tissues. Testing your sense of feeling helps your doctor find out what nerve root may be compressed.
Your sense of feeling may be tested in several ways. Your doctor will probably ask you to close your eyes during this testing, because it's easy to imagine the feeling if you can see the test being done. Testing may include touching your skin lightly with a cotton ball or pricking your skin lightly with a pin.
Tendons attach the muscles to the bones. Reflexes are little movements of the muscle when the tendon is tapped. A reflex can be decreased or absent if there is a problem with the nerve supply. To test your reflexes, your doctor will use a rubber hammer to tap firmly on the tendon. If certain reflexes are decreased or absent, it will show what nerve might be compressed. Not all nerve roots have a reflex associated with them.
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