Presentation
Athlete with low back pain.
Patient Data
X-rays of the lumbar spine obtained at outside clinic were normal per report.
Bone scan performed using 20 mCi of Tc-99m MDP IV.
Whole body planar images obtained 3 hours after radiotracer injection show two foci of mild increased osteoblastic activity involving the posterior elements of L5.
Axial SPECT of the lumbrosacral area shows the abnormality with greater contrast. Uptake is greater on the right versus left.
Sagittal T2 and STIR weighted MRI images demonstrate increased signal intensity in the posterior elements of L5. This focally involves the pedicle and pars interarticularis on the left and more diffusely on the right where it extends into pars interarticularis and the adjacent vertebral body. No discrete fracture line was identified.
Edema is also present in the adjacent posterior paraspinous muscles.
Given the angled disk space technique, the findings are not well seen on the axial T2 weighted sequence.
Case Discussion
Injury of the pars interarticularis is a well-recognized cause of low back pain in adolescent athletes. It is a spectrum of findings including, in its earliest form, a bone stress injury, and progressing to spondyloysis (a non-displaced fracture of the pars interarticularis) and eventually spondylolisthesis (anterior subluxation of the effect vertebra in relation to the one below).
Bone scintigraphy is very sensitive for the detection of bone stress injuries. Bone stress, typically due to repetitive micro trauma, results in osseous remodeling and amplified osteoblastic activity, resulting in abnormally increased uptake of radiotracer.
Single photon emission computed tomography (SPECT) has been shown to have much better contrast than planar bone scintigraphy and is hence detection detection of a pars interarticularis bone stress injury, though it must be noted that once spondylolisthesis develops, the pars injury may no longer demonstrated abnormal uptake on bone scan.
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