My Friend Had Back Surgery At L4-5 And Had A

My friend had back surgery at l4-5 and had a cage type to keep the levels apart. Now about 9 mos later she has no pain but her knees are giving way and she is falling. She says she has no pain. Has to use a walker and can barely stand up. Just got out of hopst for falling.all tests were normal..now going for emg. What is up with can't walk but hs no pain anywhere??