Atrophy

I had a bad fall on my back around the age of 8-10.I landed hard on my back and it knocked the wind out of me.I just toughed it out  and forgot about it.In my high school years I started feeling clumsy.I have to keep my legs in a hyperextended position in order for me to walk.I have seen an orthopaedic Dr. that states my muscles are healthy there seems to be a neurological reason for this.I have a sharp pain that originated in my right lower lumbar.I have been through series of tests muscle biopsy,nerve conduction,spinal tap,and various blood tests.All test come out normal.I was tested for ms and im clean.I fell in 2007 because both my legs were bent in normal position and gave out on me.I broke my leg in3 places two different times due to my fall.I can lift 60 lbs with my legs in the down position,I can barely lift my legs in an up position.When there is range of motion my legs buckle and I fall.Could I have damaged nerves in my spine when I fell a long time ago.Can that cause bilateral atrophy in my quads?If so is there any cure?I cant walk up stairs or  curbs on the street.I just go down.Its like a light switch is turned off and I have no support.No matter how much exercise I do my quads and calves dont seem to get much stonger.