Vertebral Column: Regions and Curvature

The adult spine contains 26 vertebrae distributed across five regions: seven cervical, twelve thoracic, five lumbar, and one each forming the sacrum and coccyx. Infants are born with 33 vertebrae, but nine bones in the sacral and coccygeal regions fuse after age 20, reducing the total count. This fusion occurs as part of normal skeletal maturation.

The vertebral column is subdivided into five regions: cervical (C-1 to C-7), thoracic (T-1 to T-12), lumbar (L-1 to L-5), sacral, and coccygeal. Vertebrae size gradually increases from the cervical to lumbar region, helping the spine distribute body weight effectively. Each region has distinct anatomical features and functions.

The characteristic S-shape results from four curvatures that increase the spine's strength, flexibility, and shock absorption capacity. The thoracic and sacral curvatures are primary curves present from birth, while cervical and lumbar curvatures develop later as infants learn to sit, stand, and walk. These curves allow the spine to spring back when weight is removed.

Primary curves are retained from the original fetal curvature and include the thoracic and sacrococcygeal curves, which are concave anteriorly. Secondary curves develop after birth as children learn postural control and include the cervical and lumbar curves, which are concave posteriorly. Both types contribute to spinal strength and flexibility.

The vertebral column is a flexible segmented structure that protects the spinal cord, supports the head and neck, and serves as an attachment site for the bones of the thoracic cage and muscles. It allows for movement of the head, neck, and body while maintaining structural integrity. The spine distributes body weight through progressively larger vertebrae.

Kyphosis involves excessive anterior concavity of the thoracic region, while lordosis involves excessive posterior concavity of the lumbar region. Scoliosis is characterized by an abnormal lateral curvature accompanied by twisting of the spine. These disorders disrupt the normal biomechanics and shock absorption capacity of the vertebral column.

Infants are born with 33 vertebrae, but nine bones in the sacral and coccygeal regions gradually fuse after age 20, reducing the adult count to 26. Additionally, secondary curvatures develop as infants grow and learn to sit upright, stand, and walk. The general structure of a vertebra remains consistent, but regional organization and fusion patterns change significantly.