Patients undergoing laminectomy and laminectomy with fusion have a 10-30% rate of continued or renewed low back pain (38). Causes of low back pain following surgery include degenerative facet or disc disease, recurrence of disc extrusion, infection, spinal stenosis, sacroiliitis, and pseudarthrosis (failure of fusion).
Pseudarthrosis is a common complication of spinal fusion procedures. Unfortunately, flexion-extension radiographs and CT are often inaccurate in the diagnosis of pseudarthrosis (39). SPECT bone scintigraphy appears to be promising in the diagnosis of pseudarthrosis in the early years following spinal surgery (40,41). Slizofski et al. studied painful pseudarthrosis following lumbar fusion using SPECT and planar bone scintigraphy (40). SPECT was superior to planar bone scintigraphy. SPECT bone scintigraphy had a sensitivity of 78% and a specificity of 83% in diagnosing pseudarthrosis in symptomatic patients. However, it also showed increased activity in the fusion mass of 6 of 11 asymptomatic patients. Exploratory surgery was not performed on the asymptomatic patients; therefore, the cause of the increased uptake is uncertain. The authors postulated that it may be due to painless pseudarthrosis.
SPECT bone scintigraphy is also useful in diagnosing early degenerative facet and disc disease related to changes in biomechanical stress on the spine following fusion surgery. Lusins et al. studied 25 patients with persistent low back pain following lumbar spine surgery and found that more extensive surgery was associated with a greater number of lesions identified in SPECT imaging (42). Patients with single level laminectomy had less extensive facet stress than those with multilevel laminectomy. Patients subjected to laminectomy and fusion had chronic facet stress above and below the fusion mass. This was attributed to transfer of biomechanical stresses to the segments above and below the fusion mass causing increased load on the facets at these levels. Even-Sapir et al. studied 33 patients with back pain after lumbar fusion surgery to determine the value of SPECT bone scintigra-phy in the assessment of pain occurring more than 4 yr after surgery (41). The most common findings were lesions in the facet joints and vertebral bodies in the free motion segments adjacent to the fused segments.
In the Even-Sapir study pseudarthrosis in the early years after surgery was associated with increased uptake in the fusion mass while pseudarthrosis in the late years after surgery showed no corresponding abnormalities in four of five patients. The authors hypothesized that the increased metabolic activity associated with pseudarthro-sis in the early years after surgery decreases with time.
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