Type I: dysplastic, with associated congenital abnormality of the upper sacrum and the arch of the lumbar vertebra.
Type II: isthmic, with a defect in the pars interarticularis that may be:
a) a fatigue fracture
b) an elongated but intact pars
c) an acute fracture
Type III: degenerative, due to long-standing intersegmental in stability (pseudospondylolisthesis)
Type IV: traumatic, due to a fracture in areas of the posterior elements other than the pars interarticularis
Type V: pathologic, due to generalized or localized bone disease
Osteoscintigraphy or a bone scan is the modality of choice when questioning the age of a spondylolysis. If the defect is an active stress fracture or a definite fracture the pars will demonstrate an increase in uptake of the radioisotope. The presence of a positive bone scan confirms the active nature of an existing defect or the presence of a developing stress fracture. This is a very important part of patient management, especially in the professional or highly motivated athlete. The increased uptake of the bone scan indicated there should be a reduction in the patient's physical activity. If there is a question of a developing or slight stress fracture, a special type of bone scan should be performed as it is more sensitive than the typical bone scan. It is called SPECT bone scintigraphy, or single-photon emission computed tomographic osteoscintigraphy. The major difference between SPECT and a regular bone scan is that a slice through the pars can be performed at smaller intervals, therefore allowing us to demonstrate the pars to best advantage. This ability will allow us to demonstrate even very subtle increases in uptake, which occurs with small developing stress fractures. If a subtle stress fracture is noted, the patient can modify and stop aggressive training to avoid a complete stress fracture through the pars. If given time, a recent stress fracture will heal and no spondylolysis develops.
Deborah Pate, DC, DACBR
San Diego, CA
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