The patient states she feels the pain “all the time now” but it has been “on and off” until it began worsening in the last few years. She also complains of weakness in her right leg when she stands and cannot stand on that leg for any length of time. This patient is an avid ballet student practicing 3-4 times per week and has difficulty moving her leg for ballet technique. She denies any trauma but does state that she had low back surgery as a bone-packed fusion of L4 and L5, five years ago for low back pain relief. She is not on any medication, does not smoke and has no children. She is retiring from her career in finance. This patient was advised to have a hip replacement because of mild iliofemoral joint space reduction.

Question: Based on this clinical history, what are some of the differential diagnoses you are considering?