Dynamic Disc Designs

Does facet joint morphology affect the development of spondylolysis?

Goal of the Study?

The goal of this study 1 is to better understand whether the morphology of the facet joint contributes to spondylolysis.


Why are they doing this study?

Lumbar spondylolysis is one of the most common sports injuries in adolescents. This is a condition in the lower back where there is a defect in the part of the vertebra known as the pars interarticularis, which is a part of the bone that connects the facet joints at the back of the spine. 

Existing research suggests that individuals with more coronally (frontal) oriented facets in the lower lumbar vertebrae, combined with facet tropism (growth or turning) are at a greater risk of developing spondylolysis at L5. However, to date, there are only a few studies looking at how the morphology (shape or arrangement) of the facet joint is associated with unilateral and bilateral spondylolysis in adolescents. 


What was done?

The participants for the study were 68 junior athletes who went to the Funabashi Orthopedic Hospital due to lower back pain between April 2012 and June 2014. 

All participants had computer tomography (CT) and MRI scans done to determine their grouping. From this, they were classified into three groups:

  1. Group B – 22 athletes (18 males and 4 females) with L5 bilateral spondylolysis
  2. Group U – 27 athletes (21 males and 6 females) with L5 unilateral spondylolysis
    1. Reclassified into two groups: one with a spondylolysis side (UL group) and the other with a normal side (UN group)
  3. Group C – 19 athletes (13 male, 6 female) without spondylolysis whose back pain eventually disappeared. 

Patients with multivertebral spondylolysis and previous lumbar surgery were excluded. 

Using CT, a researcher measured the sagittal alignment of the L4/L5 and L5/S1 facet joint angles from the axial sections. These angles were compared for differences among the groups. All of the measurements were repeated three times by the same person to increase validity.


What did they find?

The researchers found that for participants in groups B and UL, the L4/L5 facet joint angles were significantly more coronally oriented (more in the frontal plane) than those in group C. However, there were no significant differences found in L4/L5 facet joint angle between groups:

  • B and UL
  • B and UN, UL
  • UN and C

Additionally, there were no significant differences in L5/S1 facet joint angle were found among the groups.


L4 Tropism Spondylolysis
L4 Vertebra from the Professional LxH Dynamic Disc Model. Tropism


Why do these findings matter?

Compared to a normal orientation, a more coronal (frontal) orientation of the L4/L5 facet joint angle is likely to increase the stress on the vertebral arch of L5 during trunk extension. Therefore, if an adolescent athlete has a coronally oriented L4/L5 facet joint, they are more at risk of developing unilateral spondylolysis at L5. This knowledge can assist in identifying which young athletes are more likely to develop spondylolysis and help to implement appropriate prevention efforts by limiting certain activities in young athletes.