Back

The human back (a.k.a. dorsum), is the large posterior area of the body. It extends from the top of the buttocks to the back of the neck and shoulders, opposite to the chest and anterior abdominal wall. The height of the back is defined by the vertebral column (spine or backbone), while its breadth is supported by the ribcage and shoulders.

The back consist of various tissue layers, including the skin and fasciae (superficial and deep), underlying muscles, and a supportive bony framework. This framework comprises the vertebral column, rib cage, scapula, and posterior pelvic bones.

Like all other body regions, the superficial fascia of the back contains adipose tissue, contains cutaneous vessels, and nerves. The deep fascia is a dense fibrous tissue that attaches to the occipital bone, spinous processes of vertebrae, and iliac crest. It covers the skeletal muscles of the back, which can be categorized as superficial, intermediate, and deep.

The superficial and intermediate muscles in the back of the chest are extrinsic in nature. The superficial group of muscles include the trapezius, latissimus dorsi, levator scapulae, and rhomboids. They attach the scapula and the upper limb to the axial skeleton and assist in arm movement. The intermediate muscles include the serratus posterior superior and inferior. These lie in close approximation with the ribs and aid in respiration.

In the lower back (posterior abdomen), there are additional superficial structures, namely the quadratus lumborum muscle and thoracolumbar fascia.

The deeper intrinsic muscles of the back include the erector spinae and transversospinalis groups. The erector spinae comprises the iliocostalis, longissimus and spinalis muscles, while tranversospinalis group includes the semispinalis, multifidus, and rotatores muscles. These deep muscles play a crucial role in axial skeleton movements, such as flexion, extension, sideways bending, and rotation.

Numerous ligaments are present in the back region, including the interspinous ligament, ligamentum flavum, anterior and posterior longitudinal ligaments, and the ligamentum nuchae. Additionally, intervertebral discs located between successive vertebrae act as shock absorbers, providing support and flexibility for back movements.

The blood supply to the back originates from the posterior intercostal arteries, which branch from the descending thoracic aorta in the chest. The lower back receives blood supply from the descending abdominal aorta below the aortic hiatus. Other vessels in the back of the chest include the azygous and hemiazygos veins, situated anterior to the thoracic vertebrae. These veins receive the posterior intercostal veins on right and left sides, respectively.

The back is primarily innervated by the dorsal branches (posterior rami) of the spinal nerves.