LOS ANGELES (Reuters) – Pop star Lady Gaga said on Tuesday she was suffering from a severe inflammation of the joints that left her temporarily unable to walk, forcing her to postpone a handful of upcoming shows on the North American leg of her world tour. "I am completely devastated and heartsick. I've been hiding this injury and pain from my staff for a month, praying it would heal, but after last night's performance, I could not walk," the singer said in a statement. Her condition is called synovitis, an inflammation that sometimes follows a sprain, strain or injury. …