The investigation of the role of the facet joint angle in the development of L5-S1 spondylolysis in young men.OBJECTIVES
 This study aims to evaluate facet tropism in younger patients with lumbar spondylolysis and to investigate the role of facet tropism in the development of spondylolysis.


 Between February 2013 and December 2015, a total of 102 male patients with bilateral L5 pars defect including 53 with spondylolysis and 49 control subjects were included in this case-control study.  The facet joint angles were measured bilaterally and axially at the level of L3-4, L4-5, L5-S1 using computed tomography (CT).  The classification was made as follows: A difference between two reciprocal facet joint angles of <6° indicated no tropism, 6°-12° indicated moderate tropism, and >12° indicated severe tropism.


 A total of 612 angles including 318 facet joint angles from 53 patients with spondylolysis and 294 facet joint angles from 49 control subjects were measured.  L3-4 measurements in the control group showed no tropism in 87.8% (n=43), moderate tropism in 12.2% (n=6), and severe tropism in 0% (n=0).  L4-5 measurements in control group showed no tropism in 79.6% (n=39), moderate tropism in 20.4% (n=10), and severe tropism in 0% (n=0).  L5-S1 measurements in the control group showed no tropism in 69.4% (n=34), moderate tropism in 28.6% (n=14), and severe tropism in 2.0% (n=1).  The mean facet joint angles in the spondylosis group were 32.9±5.1°, 37.5±5.4°, and 41.2±7.8° at the levels of L3-4, L4-5, and L5-S1, respectively.  The mean facet joint angles of the control group were 33.2±5.7°, 39.7±4.9°, and 42.2±4.9° at the levels of L3-4, L4-5, and L5-S1, respectively, indicating no significant difference between the right and left mean facet joint angles between the groups (p>0.05).  The frequency of facet tropism and the difference between right and left facet joint angles for all three levels were significantly higher in the spondylolysis group (p<0.05).  Facet tropism at the level of L5-S1 was significantly more frequent than facet tropism at L3-4 level (p<0.05).


 CONCLUSION
 Our study results show that the rate of facet joint tropism is higher in the patients with spondylolysis, suggesting that facet tropism seems to play a role in the etiology of spondylolysis as a predisposing factor.
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