What Causes Severe Pain And Swelling With Cracking Sound In The Toe Near Nail Bed?

I have had bad pain in the 2nd last toe on my left foot for the last month or so, near or in the joint - close to the nail bed. I didn't think too much of it - no other symptoms. Over this past weekend while walking down the steps I heard a loud crack and the pain intensified. I can walk and wear shoes although it's uncomfortable. It is now slightly swollen but not bruised. Any ideas as to the cause?