Abnormality of the vertebral column Spondylolysis HP:0003304 UMLS:C0038018 The pars interarticularis is one of the bony bridges that connect the upper with the lower facet joints of the vertebra. Lumbar spondylolysis is a common cause of lower back pain. The vast majority of cases of spondylolysis occur at the L5 or L4 levels, and is usually diagnosed radiographically. Over half of patients affected by spondylolysis have associated spondylolisthesis. SNOMEDCT_US:240221008 Spondylolysis is an osseous defect of the pars interarticularis, thought to be a developmental or acquired stress fracture secondary to chronic low-grade trauma.