I sent you a message as I needed to send you a link.
In a normal spine all sacral vertebrae fuse to form one bone. This is separated from the fifth lumbar vertebra by an intervertebral disc. Sometimes, the L5 becomes a part of the sacral bone. This is called sacralization of L5. In your case the L5 is fused with sacral bone but on left side it gives a picture of a false joint which is showing degenerative changes. This can cause spinal nerve compression, numbness and pain. Please consult your doctor regarding this. Take care!
The medical advice given should not be considered a substitute for medical care provided by a doctor who can examine you. The advice may not be completely correct for you as the doctor cannot examine you and does not know your complete medical history. Hence this reply to your post should only be considered as a guiding line and you must consult your doctor at the earliest for your medical problem.