Stress injuries of the pars interarticularis: radiologic classification and indications for scintigraphy.

Lumbar radiographs and scintigrams were compared in 24 patients with low back pain. Radiographs of the pars interarticularis were classified as type 0, normal; type 1, a stress fracture with an irregular lucent line in an area of sclerosis; type 2, an evolving or healed stress injury showing either sclerosis or narrowing; or type 3, a nonunited fracture with a large lucent defect and well defined margins. Radiographs and scintigrams were abnormal in 88% (21/24) and 54% (13/24) of patients, respectively. Scintigraphy was most often positive with type 1 (73% [11/15]) and negative with type 3 abnormalities (83% [10/12]). Findings suggest that in the proper clinical setting, identification of a type 1 abnormality is sufficient to diagnose acute pars injury. If a type 2 or 3 abnormality is present, scintigraphy is used to confirm recent injury. Finally, if no radiographic abnormality is present at the site of localized pain, scintigraphy should be used to exclude stress injury not radiographically apparent.