A unilateral or bilateral stress fracture of the narrow bridge between the upper and lower pars interarticularis (lumbar spondylolysis), is a common cause of low back pain (LBP) in adolescent athletes.The lifetime prevalence in those aged 11-17 years has been reported to be as high as 30.4% among adolescents participating in sports.

Repeated microtrauma is thought to be the cause of stress fracture of the pars interarticularis. Heredity also is believed to be a factor. Patients with spina bifida occulta have an increased risk for spondylolysis. Approximately 95% of cases of spondylolysis occur at the L5 level. Lyses can occur much less commonly at other lumbar or the thoracic levels. Involvement of multiple levels is rare. The process may be unilateral or bilateral

Patients with suspected spondylolysis should be evaluated initially with plain radiography. Other imaging methods used are CT, MRI and bone scintigraphy with SPECT

Plain radiography - linear lucency in the pars interarticularis on lateral views(most sensitive) and oblique views(most specific)

CT -linear lucency or defect extending through the pars interarticularis. In some patients, fragmentation of the pars interarticularis may be seen.

MRimaging- variable appearance that depends on the timing of the examination. In acute stress reaction, increased signal on T2 in the pars interarticularis representing marrow edema and decreased signal on T1. Signal may be decreased on T2 in the pars if the process is chronic, indicating reactive sclerosis.

Bone scan -increased activity in the pars interarticularis.This finding typically represents an acute stress reaction that radiographs of the lumbar spine will not reveal as a defect in the pars interarticularis.