Foot drop or weakness can be caused from lower back problems, diabetic neuropathy, injury or trauma around the leg and many after knee surgeries. It can manifest itself in pain to the foot ankle or legs and has to be diagnosed correctly to see if it is treatable. It can cause instability in your gait as well difficulty with walking. Injections, imaging and nerve studies can aid in diagnosing your problem correctly so a procedure can be performed to correct the pain.