Grading method of spondylolisthesis
When spondylolysis involves the bilateral pars interarticularis at a particular vertebral level, it is commonly associated with a condition called spondylolisthesis, which is anterior translation of the involved vertebral body with respect to the more inferiorly located adjacent vertebral body. It is graded I through IV, based on the degree of anterior displacement. If it is displaced anteriorly less than 25% of the vertebral body’s anteroposterior dimension, it is considered to be grade I. Displacements of 25% to 50%, 50% to 75%, and greater than 75% constitute grades II, III, and IV, respectively. Its etiology can be congenital, traumatic, degenerative, or pathologic in nature such as from Paget’s disease or osteogenesis imperfecta.