A disk becomes herniated when the outer layer of the disk becomes weak. This allows the soft tissue that makes up the inside of the disk to push against the weakened outer layer. As a result, a bulge forms in the side of the disk: the bulge becomes more prominent when the disk is under stress during lifting, or twisting of the spine. In turn, this bulge can place pressure on the nerves in the spinal canal.

Causes of herniated disk include:

• Arthritis
• Improper lifting
• Infection
• Osteomyelitis of the spine
• Injury
• Compression fracture of the spine
• Osteoporosis
• Stress or overuse injury
• Sports