INTRODUCTION: There is limited information on facet joint asymmetry in the sagittal plane in adolescents. To investigate the incidence of bidirectional lumbar facet tropism and its relationship with lumbar spine disease in adolescents.
METHODS: The orientation of all lumbar facet joints was measured in the bidirectional planes on computed tomographic images for 191 patients with low back pain. The patients were divided into four groups according to age (<15 or ≥15 years) and sex. The facet joint angle and tropism rate were compared among the groups. Facet tropism was defined as a difference in bilateral angle of >10° in the axial plane and >5° in the sagittal plane. The association of facet tropism with disease was investigated further by analyzing facet joint orientation and the incidence of facet tropism in 116 patients with single-level lumbar disease.
RESULTS: Facet tropism was observed in 8.7% of axial views and 7.5% of sagittal views. The incidence of axial facet tropism was significantly higher in male patients aged ≥15 years, especially at L4/5. Facet joint morphology in the axial plane was more coronal at L3/4 and L4/5 in male patients ≥15 years than in those <15 years. Facet joint morphology in the sagittal plane was unchanged at around 15 years of age in both sexes. Axial facet tropism was found at L4/5 in 55.6% of patients with herniated nucleus pulposus. There was a significant difference in sagittal facet orientation in patients with spondylolysis at L5. The facet angle was significant larger in patients with L5 spondylolysis at L3/4 and L4/5.
DISCUSSION: Most conclusions regarding facet tropism have been based on the results of studies that have evaluated this parameter only in the axial plane, or studies that have been performed in middle-aged or elderly patients. To the best of our knowledge, this is the first report to investigate facet tropism in both the axial and sagittal planes and to focus on the adolescent age group. The facet tropism rate in adolescents is similar in the axial and sagittal planes. It has been unclear in previous reports whether facet tropism is congenital or acquired. The results of our present study indicate that facet tropism may occur congenitally at the same frequency in the sagittal and axial planes, and acquired factors would also cause asymmetric facet joints with a particularly high frequency in the axial plane. Moreover, facet tropism and specific morphology may be related to lumbar disc herniation and spondylolysis in this age group. These findings may lead to a better understanding of the associations of facet morphology and tropism with various diseases of the lumbar spine.