The human spine is designed for upright walking, but its design is not perfect. It arose through modifications of the spines of our four-legged ancestors and is not suited for modern living, especially things like stooping over computer keyboards and carrying excess weight in the belly. Because of this, injuries to the structures of the back are very common.

Strains are the most common cause of back pain. Also called a pulled muscle or tendon, a strain often occurs during heavy lifting or after a sudden awkward movement of the back. Another common cause of back pain is connective tissue injuries to the ligaments and soft tissues around the spine. All these types of injuries tend to cause acute pain that heals with time.

Nerve injury is another cause of back pain. The nerves that provide sensory information from the back must all pass through a small hole close to the site where each pair of vertebrae meets. In between each vertebra is a disk made of cartilage. One common back injury called a herniated or ruptured disc occurs when one of these discs is damaged and pushes into the small hole occupied by the nerve. When this type of injury occurs in a specific portion of the lower spine, it can pinch the sciatic nerve that goes down the leg, causing shooting pain through the buttock and back of the leg. Nerve pain may heal with time or it may require surgery to correct.

Bone and joint problems can also cause back pain. These include osteoarthritis, in which the vertebrae rub against each other and cause pain, and osteoporosis, which weakens bones to the point where the vertebrae can fracture easily. Abnormal spinal curvature such as scoliosis can also lead to back pain.

There are also some rare causes of back pain that can be very serious. These include a cancerous tumor in the spine that can press on a nerve causing back pain, an infection of the spine, or a blood clot in the protective membranes surrounding the spinal cord.