Know Your Dermatomes For The USMLE

I won't attempt to cover them all, but I can give you a few pearls here.
It's something random that over the years have gotten me a bunch questions right without trying much.

• C6 includes your thumb and index finger (medial half)
• to remember this, make the number 6 with your left hand by touching your index finger to your thumb now look at your hand and say to yourself "C6"
• knowing this I can deduce C7 and C8 which I give C8 the lateral digit and half of the 4th while C7 just gets whats inbetween C6 and C8
  
• L5 vs S1 = very HY
  
• intervetebral discs commonly herniate at this level
• L5 affects the big toe
• I remember it by saying "L5 = Largest of the 5"
• L5 root is compressed by a herniated disc at the L4-L5 level
  
• S1 affects the smallest toe
• "S1 = the smallest one"
• S1 root is compressed at the L5-S1 level
• (If your toes don't follow this order you may need a different memory tool, sorry buddy.)
• L1 = Skin overlying the inguinal ligament
• L for ligament, 1 for 1nguinal
• S5 = Anus
• "S5 is the doodie hive"
  
• Other ones everyone probably knows but listed here just in case
• T10 = Umbilicus
• BellybuT-TEN
• L4 = Knee
• "L4 hits the floor" (when standing on your knees)

Remember that the above list isn't meant to be complete, and some dermatomes include more, but I hope this helps you to think of it in a way where you won't forget it! For exams knowing this usually gets me the point and when it comes to the USMLE, that is all I care about.