Is Urine Retention Normal In An Infant Post Surgery For Tethered Cord?

My 14 month old grandson had surgery last week for tethered cord and a congenital dermis cyst. The surgery was a 6 hour very difficult surgery. Prior to surgery, he showed no symptoms of urinary problems or difficulty in walking. Now he cannot urinate. Is retention common after this surgery? What are his chances that normal bladder function will return?