Combined dysplastic and isthmic spondylolisthesis: possible etiology.

STUDY DESIGN: Four cases of combined dysplastic and higher-level isthmic spondylolisthesis were studied. OBJECTIVE: To attempt to understand the possible etiology of this unreported combination. SUMMARY OF BACKGROUND DATA: Dysplastic spondylolisthesis is thought to be hereditary. It is believed that isthmic spondylolisthesis, the more common type, is acquired. Multiple spondylolysis and spondylolisthesis have been reported, but no cases of combined dysplastic and isthmic spondylolisthesis. METHODS: The global and segmental Cobb angles of the lumbar vertebrae and sagittal vertical alignment were measured in four patients who presented with lower back pain and varying degrees of pain radiation to the lower limb. Posteroanterior and lateral radiographs were taken with patients standing barefooted. Three of the patients underwent surgery. The fourth patient refused surgery. RESULTS: The global and segmental Cobb angles were found significantly increased in these patients. Increased segmental extension angles were clearer at the levels above the dysplastic vertebrae and at the level of the isthmic defect. Large anterior translation of the thorax was noted in all cases. CONCLUSIONS: The authors believe that this unusual combination may have resulted from hyperlordosis occurring above the dysplastic vertebrae, which caused increased stresses that led to the isthmic defect. This combination should be investigated in patients with dysplastic spondylolisthesis and hyperlordosis.