Hello, Sciatica radiating to the lower limbs and long term lower back pain are very common problems, especially as age advances. It also depends on any history of accidents and long term heavy weight lifting during young age. This generally is caused by two processes. One is the wear and tear of the inter vertebral disc that may cause bulge which compresses the nerves around the vertebra. These nerves supply the lower back and legs leading to pain in these sites. Secondly, the vertebral bones also go through wear and tear which results in the growth of bony projections with further reduce blood supply to the intervertebral discs and may also directly compress nerves that are passing closely. Thirdly due to any momentary sprain in local muscles may also result in nerves being affected. This mechanism is how doctors try to treat sciatica and these are the problems that doctors try to identify in an investigation such as you got MRI. That is why MRI is very crucial after x-ray lumber spine. Once the problem is identified then the treatment is commenced accordingly. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Talal Hussain, General & Family Physician