Back injuries result from damage, wear, or trauma to the bones, muscles, or other tissues of the back. Common back injuries include sprains and strains, herniated discs, and fractured vertebrae. The lumbar spine is often the site of back pain. The area is susceptible because of its flexibility and the amount of body weight it regularly bears. It is estimated that low-back pain may affect as much as 80 to 90 percent of the general population in the United States. Classification Soft tissue graded system Muscle and soft tissue injuries can be classified using a graded system. Grade 1 muscle strain is the least severe with damage to few muscle fibers and little if any loss of function. Grade 2 muscle strain indicates a mild to moderate injury with appreciable tissue damage and some loss of function or strength. Grade 3 muscle strain is the most severe injury grade with the muscle being either completely torn or experiencing complete loss of function. AO spine injury classification system Spinal column or vertebral injuries can be classified using the AO spine injury classification system. The three categories - A, B, and C - are based on the location of damage on the vertebra (either on the anterior or posterior segment) and by the direction of the applied injurious force. Type A injuries are those associated with a compression force with damage to the vertebral bodies. Type B injuries are those associated with a distraction force resulting in structural damage to the posterior components of the vertebral column. Type C injuries are those associated with damage to both anterior and posterior aspects of the vertebral column resulting in displacement of the disconnected segments in any direction. This classification system can be used to classify injury to the cervical, thoracolumbar, and sacral regions of the spinal column. MSU classification for herniated discs Herniated discs can be graded based on the size and location of the herniation as seen on an MRI. Size The size of the herniation is the extent to which it protrudes into the vertebral foramen. The MSU Classification for herniated discs uses the proximity of the disc to the facet joint when measuring the size of a herniated disc. Using the MSU Classification, a grade of 1, 2 or 3 can be used to describe the size of a herniated disc with 1 being the least severe and 3 being the