What is Dermatome you may ask? Dermatome is a fancy term for a group of muscles that a single nerve root is responsible for in terms of giving that area of the leg sensation.
Why is it important? It gives you an idea of which nerve root is pinched, compressed, inflamed, etc and targeting that specific region of the lumbar spine will hopefully get a step close to giving you relief.
I created a cheat sheet below. Keep in mind, various resources vary slightly which nerve does what and meant to be used as a guide, not the end all be all answer.
Lumbar Nerve Root: the area of the leg that this specific nerve root provides sensation to.
L2 : front of the thigh and or outer upper thigh
L3: inner knee
L4: inner calf and or inner ankle region
L5: outer calf region
S1: along the pinky side of the foot and heel
You can see which nerve root(s) are affected by performing a “light touch sensation test.” Here is how.
Have someone take a cotton ball and gentle touch (drawing line about 2 inches) the areas listed above while your eyes are close.
Compare the symptomatic leg versus the non symptomatic leg to see if similar area(s) of the leg feel the same or different. Also take notes of the area that you are having trouble feeling the cotton swab.