Your back pain that has returned within about six months has a number of potential causes. One of the potential pain generators is a pseudoarthrosis (non-fusion). The next is another level that is causing pain. The third is some abnormality at the surgical level (bone spur or scar) and the last is a chronic radiculopathy.
AP and lateral X-rays (especially without flexion/extension films) are generally unhelpful to determine fusion status, especially with a lucency of a screw on a previous film. A lucency is a halo around a screw-a dark area around the “light” bone that could indicate cavitation-an indication of lack of fusion.
The most common symptom that indicates a lack of fusion is lower back pain at the three to six month mark after a fusion. A CT scan is the gold standard but these images have to be generated on a 64 (or above) slice scanner with one millimeter cuts and include sagittal and coronal reconstruction (front to back and side cuts).
The pain generated by the pseudoarthrosis is generally from the motion of the non-fusion interface. Pain could be generated from the screw-bone interface in a pseudoarthrosis but generally this is not the case. Now there are rare exceptions where you could have a solid fusion and still have some discomfort from the screw-bone interface. Removing the hardware in this particular case can be beneficial but I remind you this is a rare condition.
If you do have a loose screw, this would be an indicator of a lack of fusion as the screw would not be loose in a solid fusion. Thigh pain that returned sometime after surgery could be continued nerve irritation from a pseudoarthrosis, scar of the nerve root, another level not initially involved in the surgery or rarely a screw irritation of the nerve root.
The CT scan will be very helpful in determining the cause of continued pain.
Dr. Corenman
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.