Facts about the spine

The vertebral column, also called the spine or backbone, is made up of multiple vertebrae that are separated by spongy disks and classified into 4 distinct areas. The cervical area consists of 7 bony parts in the neck; the thoracic spine consists of 12 bony parts in the back area; the lumbar spine consists of 5 bony segments in the lower back area; 5 sacral* bones; and 4 coccygeal* bones (the number of coccygeal bones can vary from 3 to 5).

(* By adulthood, the 5 sacral vertebrae fuse to form 1 bone, and the 4 coccygeal vertebrae fuse to form 1 bone.)

Facts about the pelvis

The pelvis is a basin-shaped structure that supports the spinal column and protects the abdominal organs. It contains the following:

• Sacrum. A spade-shaped bone that is formed by the fusion of 5 originally separate sacral vertebrae.

• Coccyx (also called the tail bone). This is formed by the fusion of 4 originally separated coccygeal bones.

• Pelvic (hip) bones. These are:

  • Ilium. This is the broad, flaring portion of the pelvis.

  • Pubis. This is the lower, anterior or front part of the pelvis.

  • Ischium. This is the part of the pelvis that forms the hip joint.

Facts about the shoulder

The shoulder is made up of several layers, including the following:

• Bones. These include the collarbone (clavicle), the shoulder blade (scapula), and the upper arm bone (humerus).

• Joints. These facilitate movement and include the following:

  • Sternoclavicular joint. This is where the clavicle meets the sternum.

  • Acromioclavicular (AC) joint. This is where the clavicle meets the acromion.

  • Shoulder joint (glenohumeral joint). A ball-and-socket joint that facilitates forward, circular, and backward movement of the shoulder.

• Ligaments. A white, shiny, flexible band of fibrous tissue that holds joints together and connects the various bones, including the following:

  • The joint capsule is a group of ligaments that connect the humerus to the socket of the shoulder joint on the scapula to stabilize the shoulder and keep it from dislocating.

  • Ligaments that attach the clavicle to the acromion

  • Ligaments that connect the clavicle to the scapula by attaching to the coracoid process

• Acromion. The roof (highest point) of the shoulder that is formed by a part of the scapula.

• Tendons. The tough cords of tissue that connect muscles to bones. The rotator cuff tendons are a group of tendons that connect the deepest layer of muscles to the humerus.

• Muscles. These help support and rotate the shoulder in many directions.

• Bursa. A closed space between 2 moving surfaces that has a small amount of lubricating fluid inside; located between the rotator cuff muscle layer and the outer layer of large, bulky muscles.

• Rotator cuff. Composed of tendons, the rotator cuff and associated muscles hold the ball tightly within the glenohumeral joint at the top of the upper arm bone (humerus).