Should Hurting The Knee After Patellofemoral Arthroplasty Be Taken Seriously?

hi, i am 46 years old 5'6" weight is 165. I had a right patellofemoral arthroplasty on Feb 10, 2011. Last sat I was sitting in a booth at a cafe and when sliding out of the booth I hit my knee on the metal leg under the table. I am worried if I hurt my knee.