Pars interarticularis defect is a fracture of the neural arch, the bony bridge between the upper and lower articular facets of a vertebrae. It most often affects the 5th lumbar vertebrae. The vertebrae may slip causing compression of the neural tissue and resulting in pain. This constitutes a spondylolisthesis. A pars defect can exist with no pain or symptoms. It may become symptomatic through excessive sport or trauma. It's existence should be considered where back pain is unresponsive to manual treatment and pain medication particularly in adolescence. Manual treatment such as vertebral manipulation and correction of muscle balance can resolve symptoms. Should symptoms not resolve the spine should be investigated with XRays and CT scan. Surgical intervention may be necessary to resolve the problem. This involves fusing the defect with screws.