I had numbness in my leg BEFORE surgery caused by a ruptured lumbar disc pressing on the sciatic nerve. This nerve runs roughly down the back of the leg to the knee area where it crosses over and runs more toward the front of the leg between the knee and the foot. A myleogram will show if there is something pressing on the sciatic nerve. Or maybe the sciatic nerve was injured during surgery causing the numbness. Your mom should pursue this further with a neurologist. Be sure any doctor she sees is Board Certified in his/her specialty. Good luck.