Your spine has spaces in it for your spinal cord and the nerves that branch out from it. When those spaces shrink, bones can press against nerves. You might not even notice it, but any time nerves are messed with, you could have pain, tingling, or numbness, or your muscles might seem weak. Osteoarthritis is the most common cause of spinal stenosis. When it's severe, a surgeon goes in and makes more room for the nerves.