Does facet joint morphology affect the development of spondylolysis?

[Purpose] This study aimed to clarify the contribution of the morphology of the facet joint in spondylolysis. [Participants and Methods] A total of 68 junior athletes with lower back pain were evaluated. They were classified into groups B (bilateral spondylolysis), U (unilateral spondylolysis), and C (without spondylolysis). The same observer measured the sagittal orientation of the L4/L5 and L5/S1 facet joint angles from the axial sections, using computed tomography. Facet joint angles were statistically compared for differences among groups B, UL (the spondylolysis side in group U), UN (the normal side in group U), and C. [Results] The L4/L5 facet joint angles were significantly more coronally oriented in groups B and UL than in group C, while the L5/S1 facet joint angles showed no significant differences among the four groups. [Conclusion] The results of this study suggest that a more coronal orientation of the L4/L5 facet joint may increase the point loading through the L5 pars interarticularis in extension and rotation. Therefore, if the L4/L5 facet joint is more coronally orientated, the patient may be at the risk of spondylolysis. This observation may aid in predicting patients with increased possibility of developing spondylolysis.