Retroisthmic cleft of the vertebral arch
Handball player with back problems.
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Continuous dark sclerotic line in the right L5 vertebral arch with osteophytes, dorsal to the isthmus. This patient also had bilateral spondylolysis with minimal olisthesis.
Retroisthmic cleft is the least common of 6 types of posterior vertebral arch defects (including persistent fusion anomalies):
1 neurocentral synchondrosis
2 retrosomatic cleft
4 retroisthmic cleft
5 paraspinous cleft
6 spina bifida occulta
Other than isthmic spondylolysis, it lies dorsal to the inferior articular facet. Stress fracture from repetitive trauma is the most probable cause1.