Calf pain after L4-5 microdiscectomy

My husband had back surgery Sept 2010 and at first was relieved from most of the pain as soon as the procedure was over. But more recently, he has had severe cramps "charlie horses" in his left calf muscle that leave him almost in tears and truly unable to walk comfortably. When I rub the leg, I can definitely feel some type of knot or bulge and it is hard to the touch and causes him horrible pain with just the lightest touch. We cannot figure out if this is from the surgery and he is still healing or if he has aggravated the disc and caused more damage. He went to work 4 1/2 weeks after the surgery but has always been aware of his limitations. We are just trying to figure out if the severe pain in his calf muscle is because of the back surgery or something else. If anyone has had similar symptoms and could give us some advice, it would be much appreiciated.

Thank you