Changes of the sacrum in severe spondylolisthesis: a possible key pathology of the disorder.

Deficient development of the posterior lumbosacral portion has been thought to be a possible etiology of severe spondylolisthesis. However, the precise causes of the deformity have yet to be revealed. To our knowledge, progression of the disorder has not been discussed in the light of sacral changes on magnetic resonance imaging (MRI). The objectives of the present study were to document changes of the sacrum on MRI scans in patients with severe spondylolisthesis and to discuss the relation of these changes to the progression of deformities. Roentgenograms and MRI scans of 13 patients (10 women and 3 men) with severe spondylolisthesis were retrospectively reviewed. Average age at first MRI examination was 20 years (range, 12 to 50 years). The MRI scans commonly showed a defect at the antero-superior portion of the sacrum. This lesion seems to appear during the period of progression of slipping associated with lumbosacral kyphosis. The defect of the sacrum was considered a unique feature to discriminate this type of olisthesis from others. Taking into consideration the present results, the deformity can be called kyphospondylolisthesis.