The anatomy of the back is complex, but the central feature is the spinal column, 33 vertebrae stacked atop one another, 26 of which are articulating and the remainder fused together to form the base of the spinal column known as the sacrum and coccyx. The bones of the spinal column are separated by intervertebral discs and lined with cartilage. Ligaments, tendons, and muscles that overlay the spine hold the spinal column together. The vertebrae are composed of the vertebral body, the vertebral arch, and the vertebral processes that form facet joints that allow the bones to articulate.
The spinal column bears most of the weight of the upper body and it also functions to protect the spinal cord. The spinal column begins with a uniquely shaped vertebra known as the atlas, which is a ring-like structure that connects to the skull with the second cervical vertebra known as the axis. There are 7 cervical vertebrae (neck region), 12 thoracic vertebra that demarcates the midback, and 5 lumbar vertebrae that compose the lower back or lumbar spine.
Intervertebral discs are soft tissue pads that cushion the bones of the spinal column from rubbing against one another, and the discs are composed of a rubbery annulus and a gel-like nucleus pulposus. Discs may degenerate with age, breaking at the annulus or extruding and pressing on the nerve roots of the spinal nerves, causing neurogenic pain. Neurogenic pain is felt in the area served by the particular nerve exiting the spinal canal from the spinal cord. Disc herniation may also be caused by injury or trauma, usually occurring in the cervical portion of the spine, or neck region, or in the lumbar (low back) region.
Overuse or injury of the muscles, ligaments and intervertebral discs that support the spinal column can all be causes of back pain in the upper back. One frequently seen cause of poor posture, which may result from a lack of core body strength, is slumping while standing or sitting.
Myofascial pain, or pain of the muscles and/or ligaments that connect bone to bone may cause pain in the upper back. Normal degenerative processes of aging include osteoarthritis, which causes the destruction of the cartilage that protects the joints of the vertebrae. In addition to causing pain as the cartilage wears down and bone rubs against bone, cartilage destruction can damage the bones themselves. Fractures may be caused by compression in people with demineralization of bone, such as occurs in osteoporosis, and this results in weakening of the bone and fracture with the collapse of the vertebral body. The fracture may also be the result of injuries from falls or motor vehicle collisions.
The spinal column has a natural curvature and when patients have spinal deformities, they may include scoliosis, a sideways deformity of spinal column alignment, which leads to pain caused by the uneven distribution of the weight borne by the vertebrae. Another deformity of the spinal column is known as kyphosis, or widow’s hump, which is characterized by a rounded hump of the upper back and may result in difficulty with lung expansion, resulting in respiratory problems. Some patients with kyphosis are unable to raise their heads.
Some degenerative diseases of the bones of the spine include spinal stenosis, which is a narrowing of the central space in the vertebra, caused by degenerative bony changes or thickening of the ligaments. When this occurs, there is pressure on the spinal cord and the nerve roots that exit the spinal column. This can cause burning or throbbing pain, sensory changes, feeling of heaviness and even weakness in the muscles served by the portion of the spinal cord with the affected nerve roots. Spondylolisthesis refers to slippage of one vertebra on top of the one below and can cause pressure on the spinal nerves or cord.
The most common cause of lower back pain is muscle strain from heavy lifting or trauma. This pain may radiate into the leg or foot if the large sciatic nerve that supplies the lower body is involved.
Many causes of back pain can resolve with conservative treatment that includes rest, non-steroidal anti-inflammatory pain medications, analgesics and physical therapy that may include heat, ultrasound, and massage, in addition, to exercise to strengthen the muscles that support the back. In some cases, a spinal epidural injection may be performed by your physician, using a corticosteroid to relieve inflammation around the spinal nerve roots.
Some cases of back pain may be more serious, such as metastatic cancer, and pain is often felt in the back from internal organs and blood vessels, including aortic dissection or kidney stones.
Whatever the cause, unexplained back pain that does not resolve after a few days of conservative treatment should be diagnosed by a physician, particularly new onset of pain after the age of 50.