The Role of Bone SPECT/CT in Evaluation of Persistent or Recurrent Back Pain Following Spine Surgery

Low back pain is a common disorder, with international studies having found prevalence rates between 12% and 35% and life time prevalence rates ranging from 49% to 80%.

It is caused mainly by degenerative spinal disorders, such as spondylolisthesis, degenerative scoliosis, degenerative disc disease and recurrent disc herniations.

The management of low back pain varies from conservative to more invasive methods, such as spinal stabilization surgery that involves the placement of metallic screws, rods, plates or cages. Such surgery is increasingly performed to improve spinal stability in a variety of spine pathologies, including disc degeneration, spinal stenosis and spondylolisthesis.

On the other hand, spinal fusion surgery is performed in patients with severe chronic back pain when segmental instability is believed to cause the symptoms. The rationale for this is that pain relief will be achieved once the fusion restricts motion in the painful segments. For this purpose, a wide array of techniques has been proposed, including dorsal or dorsoventral spondylodesis, either in a one-step or two-step procedure.

It is estimated that more than 300,000 lumbar spinal fusion procedures are performed annually in the United States, and a continuously rising trend has also been observed in other parts of the world.

Unfortunately, recurrent pain after spinal surgery is a well known problem. It is reported that up to 10-20% of patients experience persistent/recurrent pain after lumbar spinal instrumentation and fusion , with studies estimating the surgical reintervention rate to be around 14% over a 4-year follow-up period and 19% over 11 years.

This may be related to loosening of the metallic implants or to a failure of a stably implanted graft to immobilize the fused segments. A further differential diagnosis is degenerative disease involving the spinal segments above or below the instrumented region. This so-called adjacent instability (AI) or adjacent level disease (ALD) may be precipitated by arthrodesis, as this procedure alters the biomechanics of the spine, thereby increasing motion of a mechanical load on the segments neighboring the graft. The differentiation between these conditions has therapeutic consequences as the treatment varies according to the cause.

Standard evaluation of patients with persistent or recurrent pain following spinal stabilization surgery includes clinical examination and conventional imaging using plain radiography, CT or MR imaging.

Conventional imaging is performed for the evaluation of hardware position (changes), hardware failure, fusion evolution, alignment of the vertebrae, possible pseudarthrosis and hardware loosening.

In general, because of the presence of nonspecific postoperative changes and metal-related imaging artifacts, the interpretation of CT images is often challenging and inconclusive. Thus, whether surgical reintervention is indicated based on conventional imaging may prove difficult to ascertain.

The value of bone scintigraphy with single-photon emission tomography/computed tomography (SPECT/CT) in patients with persistent or recurrent back pain after spine stabilization surgery has been addressed in a number of studies and the technique has been suggested to be a useful diagnostic tool for identification of postsurgical spine pathology.

Although most of these studies were based on a small sample size and lacked robust reference standards; it has been concluded that the use of SPECT/CT adds value in assessing patients following spinal surgery.