This is an excellent question. It has been my experience that useful and accurate second opinions can be obtained by obtaining the patient's history, all of their imaging studies, and speaking to them on the phone. If a patient does not have a diagnosis for their problem already, they should be skeptical of the outcome of an online second opinion. My son has had three lumber punctures and there was no fluid. They said they would try again in a few days.
People have to realize that doctors have very difficult jobs.
Many times, fluids are difficult to obtain for any number of reasons. I do not think that inability to get a positive puncture in any space in the body totally reflects a physician's capability. Adult scoliosis progresses at approximately one degree per year. Since you have already shown that your curve is progressive, there is a very high likelihood that it will continue to get larger. I would suggest you consult a spinal deformity expert because most progressive curves of this magnitude will require surgery for control.