Diagnosis of radiographically occult lumbar spondylolysis in young athletes by magnetic resonance imaging.

BACKGROUND: The early stages of spondylolysis are extremely difficult to diagnose on plain radiography. Although several studies have examined changes in active spondylolysis on magnetic resonance imaging (MRI), no studies to date have determined the onset frequency of active spondylolysis detectable on MRI but occult on plain radiography. Moreover, the clinical features of active spondylolysis described in the literature do not facilitate the differentiation of this condition from other causes of low back pain.

PURPOSE: This study aimed to evaluate the usefulness of MRI in diagnosing active spondylolysis early and in determining the prevalence of active spondylolysis in cases where findings were not detected on plain radiography. In addition, specific clinical features to aid in the early detection of active spondylolysis were evaluated.

STUDY DESIGN: Cohort study; Level of evidence, 3.

METHODS: Patients were 200 consecutive young athletes (144 boys and 56 girls; mean age, 14.1 ± 1.5 y) with low back pain. All patients were examined by plain radiography (188 with negative findings and 12 with unclear findings of spondylolysis) and MRI. Computed tomography (CT) was performed only for patients with high intensity changes of the pedicle observed on MRI. The presence or absence of low back pain was examined during lumbar spine extension and flexion. The Kemp test on the right and left sides and percussion of the vertebral spinous process were also performed.

RESULTS: Ninety-seven (48.5%) patients showed evidence of active spondylolysis on MRI, findings that had been missed by plain radiography. These pars defects were organized into the following categories based on CT findings: nonlysis stage, 52; very early stage, 37; late early stage, 22; progressive stage, 10; and terminal stage, 0. No significant physical examination factors were identified that could assist in the early detection of active spondylolysis.

CONCLUSION: The MRI results suggest a high rate of active spondylolysis in young athletes with low back pain who test negative for spondylolysis on plain radiography. Magnetic resonance imaging appears to be useful in the early diagnosis of active spondylolysis, especially as we found no significant physical examination factors that could assist in early detection.