Question
What are the diffences between L4 and L5?

Answer
Dear Mustafa,

Thank you for your question.

These are simply shorthand designations for the fourth and fifth lumbar vertebrae, or spinal bones.  Most often, there are five vertebrae in this region of the spine with the fifth being the lowermost.  For your reference, the lumbar portion of the spine is commonly referred to as the "small of the back."

I hope this helps you understand the terminology better.

Sincerely,
James W. Healey, DC