abnormal vertebrae morphology abnormal sacral vertebrae morphology In humans, vertebrae S1-S5 are normally fused in maturity, with no intervertebral discs. In rodents, these vertebrae remain distinct in adulthood. MP:0003050 MPheno.ontology any structural anomaly of any or all of the bony segments of the spine located posterior to the lumbar vertebrae and anterior to the caudal vertebrae