1. The aetiology of a destructive lesion through a former interspace in a spine fused by ankylosing spondylitis is reviewed.

2. From the findings in three patients treated by anterior spinal fusion, evidence was obtained to show that a stress fracture, originating posteriorly between two fused spinous processes, leads to a pseudarthrosis between two vertebral bodies that may simulate a tuberculous lesion.

3. If spinal fusion is indicated, the anterior approach is recommended, both for direct observation of the lesion and to achieve sound union.