Part 7: THE BACK

The term back is used for the posterior part of the trunk, including skin, muscles, vertebral column, spinal cord, and various nerves and vessels. The vertebral column extends from the base of the skull down to the tip of the coccyx. In addition to protecting the spinal cord, the column supports the weight and transmits it to the pelvis and lower limbs. Because most of the weight is anterior to the column, the latter is supported posteriorly by numerous and powerful muscles attached to strong levers (the spinous and transverse processes). The presence of the spinal cord within the framework provided by the vertebral column results in frequently combined neural and skeletal manifestations in abnormal conditions, such as spina bifida.

The vertebral levels summarized below are useful. The spinous processes of the C6 and 7 and T1 vertebrae are usually visible in vivo when the neck is flexed. The apex of the lung and the cupola of the pleura extend to the C7 vertebral level. The spine of the scapula is commonly in line with the T3 vertebra, and the manubrium of the sternum is generally opposite T3 and 4 vertebrae. The trachea divides at the level of vertebrae T5 to 7 when a subject is in the erect position. The inferior angle of the scapula is frequently at the level of the spinous process of the T7 vertebra. The xiphisternal junction is approximately opposite the T10 vertebra. The spinal cord usually ends at the L1 or 2 vertebral level. The supracristal plane (through the highest points of the iliac crests), which is typically at the L4 vertebral level, is used as a landmark for lumbar puncture, and the aorta divides at this level. The anterior and posterior superior iliac spines (the latter being frequently marked by a dimple) are at the level of the second sacral segment.

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