Abnormal sacrum morphology Dysplastic sacrum HP:0008455 A developmental defect of the sacrum characterized by partial or disordered development of the sacrum in which portions of the sacrum, which normally is formed by fusion of five sacral vertebrae S1-S5, fail to form or fail to form normally. Sacral dysgenesis Partial sacral agenesis UMLS:C1851305 dysgenesis of the fused sacrum