الفهرس 
Acknowledgment.Only 14 pages are availabe for public view
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Abstract
Chronic low back pain is a serious medical and social problem, and one of the common causes responsible for disability. It is estimated that, in all populations, an individual has an 80% probability of having low back pain at some period during their life time, and about 18% of the population experiences low back pain at any given moment (Andersson , 1999) (Mooney , 1987).
DePalma et al 2011 found that the prevalence of zygapophysial joints, sacroiliac joints, and lumbar discs was 31%, 18%, and 42%, respectively. They confirmed the disc as the most common etiology of chronic low back pain in adults.
Protrusion of the lumbar intervertebral disc is a major cause of severe and chronic or chronic or recurrent LBP and leg pain. It is most likely to occur between the 4th and the 5th lumbar and the 5th and the 1st sacral vertebra (over 90% of the disc disease patients) and with lessening frequency between 3rd and 4th lumbar vertebra (7% of patients) (Hazlewood and Markov, 2006).
There are no typical characteristics of discogenic pain in the physical examination. Biphasic straightening from flexion is considered by some to be an indication of a discus complaint. Pain as a result of pressure on the processus spinosus is considered characteristic of discogenic low back pain (Schwarzer et al., 1995).
Imaging techniques such as CT and MRI are highly effective means of demonstrating detailed anatomical abnormalities in the vertebral column (Incorvaia et al., 1998).
This study was performed to establish the reliability of using ultrasound imaging to measure the thickness of the lumbar multifidus muscle and to establish the criterion validity of using thickness change as a measurement of muscle activation.
Lumbar paraspinal musculature plays a key role in providing stability during dynamic tasks; of particular interest recently has been study of the lumbar multifidus muscle. Altered characteristics of the lumbar multifidus identified in low back pain subjects include histological changes, girth changes, and deficits in motor control, recruitment, and endurance. Ultrasonography is an imaging technique utilizing high frequency sound waves to evaluate tissue properties such as thickness. Ultrasound examination is considered low risk. (Hodges et al., 2003).