Bone weekness in Lumbar L4 region.

My mother age is 45 years. She is suffering with low back pain from many years in lumbar region. From many years she used to take rest and takes hot patch at pain area. If she do work, if she bent down she experiencing High pain in lumbar region. At present she consulted doctor he said that their is a bone week in L4 Junction. He prescribed medicines and he advised not to bent down for 15 days. She used the medicines the pain was reduced to 50% but again the pain was repeating even she is not doing any work. What is the parmanent solution for this problem?? Any operation is needed or orthopedic doctor is enough or we need to consult the spine doctor for this problem?? Please tell me the solution for this problem?? Their is no pain in legs, knees, foot.