Lower Extremity Dermatomes

Lower Extremity DermatomesThe term “dermatome” is a mix of two Ancient Greek words; “derma” suggesting “skin”, and “tome”, implying “cutting” or “thin segment”. It is an area of skin which is innervated by the posterior (dorsal) root of a single back nerve. As posterior roots are arranged in sections, dermatomes are too. This is why the term “dermatome” describes the segmental innervation of the skin.

Lower Extremity Dermatomes

Dermatome Anatomy Wikipedia – Dermatome anatomy Wikipedia

Surrounding dermatomes frequently, if not always overlap to some degree with each other, as the sensory peripheral branches representing one posterior root typically surpass the limit of their dermatome. The thin lines seen in the dermatome maps are more of a clinical guide than a real boundary. Lower Extremity Dermatomes

This indicates that if a single spine nerve is affected, there is most likely still some degree of innervation to that section of skin originating from above and below. For a dermatome to be totally numb, typically two or three neighboring posterior roots require to be affected. In addition, it’s important to note that dermatomes undergo a large degree of interindividual variation. A graphical representation of all the dermatomes on a body surface chart is described as a dermatome map. Lower Extremity Dermatomes

Dermatome maps

Dermatome maps depict the sensory distribution of each dermatome across the body. Clinicians can assess cutaneous feeling with a dermatome map as a way to localize lesions within central nervous tissue, injury to particular back nerves, and to identify the extent of the injury. A number of dermatome maps have been established for many years however are frequently conflicting.

The most commonly used dermatome maps in major textbooks are the Keegan and Garrett map (1948) which leans towards a developmental interpretation of this principle, and the Foerster map (1933) which associates much better with scientific practice. This post will evaluate the dermatomes using both maps, recognizing and comparing the significant distinctions in between them.

Why Are Dermatomes Important?

To understand dermatomes, it is important to understand the anatomy of the spinal column. The spine is divided into 31 sections, each with a set (right and left) of posterior and anterior nerve roots. The kinds of nerves in the anterior and posterior roots are different.

Anterior nerve roots are responsible for motor signals to the body, and posterior nerve roots receive sensory signals like pain or other sensory symptoms. The anterior and posterior nerve roots integrate on each side to form the spinal nerves as they exit the vertebral canal (the bones of the spine, or backbone).