Spondylolysis is a defect in the pars interarticularis that may or may not be accompanied by forward translation of one vertebra relative to another (spondylolisthesis)

Patients with suspected spondylolysis should initially be evaluated with plain films - AP, lateral and oblique views. Lateral views are most sensitive and oblique views are most specific for detecting the pars defect.

Plain films- spondylolysis appears as a linear lucency in the pars interarticularis (see the images below). This lucency also can be seen on oblique radiographs.

Secondary signs on plain films - sclerosis of the contralateral pedicle and the presence of spina bifida occulta at the level of the lysis.

MRI, CT or SPECT bone imaging are other imaging options that should be considered for further evaluation or if plain radiographs are inconclusive.

MR imaging should be performed in thin sections at high resolution and in at least two planes - saggital and axial.

MRI - findings  vary depending on the timing of the examination -In acute stress reaction there is  increased signal on T2 images in the pars interarticularis representing marrow edema. On T1 images, there is decreased signal in the pars interarticularis.

In cases with an actual fracture of the pars interarticularis, there is discontinuity or fragmentation of the pars interarticularis best seen on sagittal T1 images. On T2 images, signal may be decreased in the pars if the process is chronic, indicating reactive sclerosis. If a pars defect is found with increased signal on T2 , this indicates a subacute process.

CT - linear lucency or defect extending through the pars interarticularis. Ocassionally, fragmentation of the pars interarticularis may be seen. Axial images will show absence of a complete bony ring at any given vertebral level.

Bone scintigraphy - increased activity in the pars interarticularis. These findings indicate an acute process.  This finding may imply the need for bracing.

If the bone scan is normal, it implies that the healing is complete and that bracing is of limited use in patient mangement.

Treatment is usually conservative. Physical therapy is an integral part of the patient's rehabilitation process. The most accepted protocol includes activity and exercise that reduces extension stress.