Spinal pseudarthrosis complicating ankylosing spondylitis: comparison of CT and conventional tomography

Pseudarthrosis, a functional false joint, is an important mechanical complication of advanced ankylosing spondylitis. For correct determination of prognosis and therapy, the presence and extent of the abnormality must be assessed accurately. CT findings in 18 patients with 22 pseudarthroses were compared with the results of conventional tomography. The condition was confirmed by surgery in nine patients (50%). CT scans clearly characterized the pseudarthrosis, providing data not provided by conventional tomography in 17 (77%) of the 22 lesions. CT showed irregular diskovertebral osteolysis with reactive sclerosis and more frequently detected the vacuum phenomenon and paraspinal swellings. In all cases, CT showed either a fracture of mobile facet joints in the posterior elements and allowed clear differentiation between the two. In four cases, such differentiation was impossible on conventional tomograms. Associated spinal stenosis was suspected on conventional tomograms in three lesions, but it was shown clearly by CT in 10 lesions. Our results suggest that CT offers considerable advantages over conventional tomography in the investigation of spinal pseudarthrosis complicating ankylosing spondylitis.