I assume you got the information off of a report of an x-ray, CT scan, or MRI.
"1.WHAT IS LOSS OF LUMBAR CURVATURE" >> The lower part of the spine is called the lumbar region. The spine has a normal curvature to it when looked at from the side. The cervical portion (neck) has a lordotic curve (convex anterior, or the rounded portion is pointing to the front). The thoracic spine (chest) has a kyphotic curve (convex posterior, or rounded portion is pointing to the back). The lumbar spine (low back) has a lordotic curve. The amount of the curve is slightly different in every person, depending upon posture, body habitus, weight, etc.
"2.WHAT CAN CAUSE IT." >> Usually there are two reasons for loss of the lordotic curve in the lumbar region. The most common is positioning when a study is done. Since the study is done lying down, the curve straightens out some. This is normal.
If the study is a standing spot film x-ray and there is still loss of lordosis, then the cause is usually from spasms in the lumbar musculature.
"3. ANY AVAILABLE RELIEF." >> If it is just from positioning during the study, then nothing needs to be done about it. If it is due to spasm, then the spasm needs to be addressed. This can be done in many different way; massage, heat packs, hot tub, medicine, traction, etc.
"1-What is meant by L5 IS SACRALIZED ON RIGHT SIDE." >> There are five lumbar vertebra. Each of the lumbar vertebra is a separate bone. The sacrum, or lowest part of the spine, is actually part of the pelvic ring. The vertebral bones in the sacrum are all fused together, to make one solid mass.
Sometimes, during growth and development in utero, the vertebra of the lumbar region do not completely separate into individual bones. It is not uncommon to see the fifth lumbar vertebra fused to the sacrum. Some people even have an extra lumbar vertebra, L6. In some cases, the 5th lumbar vertebra fused to the sacrum and in other cases, the top sacral vertebra, S1, is a free separate bone.
In this case, the right side of L5 is fused to the sacrum, but the left side is not. The 5th lumbar vertebra just couldn't make up its mind as to whether or not it want to be a separate bone.
In the vast majority of cases, this is just a x-ray findings. In some patients, the partial separation can cause chronic low back pain. If this is the case, then usually, the rest of the vertebra is fused to the sacrum in a surgical procedure.
You should really discuss the results of any study with your physician. The findings on any study have to be correlated with the patient's history and physical examination.