Purpose <p>Isthmic spondylolysis Early-stage lumbar spondylolysis (ESS) is common in adolescents. The facet joint tropism has been reported to affect spondylolysis in two-dimensional analyses. However, more detailed 3D analyses of facet joint tropism in unilateral spondylolysis are not reported. Here, we sought to investigate the relationship between facet joint tropism, hand and foot dominance, and very early to early stage isthmic spondylolysis ESS using a three-dimensional (3D) bone model.</p> Methods <p>We studied 70 adolescent patients (55 males, 15 females) with unilateral very early spondylolysis using MRI and CT. We used CT images to create a 3D bone model and measured the intervertebral joint angles on an axial plane. We also examined hand and foot dominance, which were the affected sides of isthmic spondylolysis ESS. We used a paired t-test to determine differences between facet joint tropism, hand, foot dominance, and the affected side of isthmic spondylolysis ESS.</p> Results <p>No significant differences were observed in the facet joint angles between the right and left sides, affected and unaffected sides in patients with isthmic spondylolysis ESS or between the dominant and non-dominant hands or feet. The measurements revealed that these angles had similar values across the different factors, indicating that the facet joint angles did not vary significantly with these variables.</p> Conclusion <p>This study found that facet joint tropism was not a predisposing factor for isthmic spondylolysis ESS and was not associated with the dominant hand or foot. Predicting isthmic spondylolysis ESS based on morphological differences in the intervertebral joints and dominant hand, or foot is challenging.</p>