The results of this study support an association between lumbar lordosis and spondylolysis at L5, but can not imply causality of the defect.

A unifying factor of the mechanical and morphological theories associated with the genesis of spondylolysis is the need for a repetitive motion, such as hyperlordosis, to develop mechanical stress within the pars interarticularis [2,6,13]. It could therefore be argued that an increased lumbar lordosis may increase the risk of developing spondylolysis. Relatively few studies have been carried out to compare the lumbar lordosis of those with spondylolysis and the normal subjects.  The results of this study suggest that there is a strong association between the angle of lordosis and the presence of spondylolysis.

Roussouly [14] reviewed the sagittal alignment of the spine and pelvis radiographically in cases with L5 spondylolysis and spondylolisthesis of less than 50% displacement (grade 2 or less). These cases were compared to radiographs obtained from a cohort of asymptomatic adults (Average age 27. Range 18 – 48 years), assessed as normal on the basis of clinical history and plain radiographs. The spondylolysis group contained adolescents and adults (Average age 19 years. Range 15 – 44 years), about whom no gender statistics were provided. They found that the average angle of lumbar lordosis within the pars interarticularis fracture group was significantly greater than that in the controlled group. While these results agree with our own, no control is made for age or gender. To advance the understanding in this area of research, these are issue we have tried to address in our own study.

It has been demonstrated that there is a significant difference in the angle of lumbar lordosis between the genders in the normal population, with women having a greater lordosis [15]. The same study did not find a significant relationship between the angle of lumbar lordosis and age in the adult population reviewed. However, it has been shown that the angle of lumbar lordosis increases with age during childhood [16]. As our study includes children and adults, age and sex matched normal control cases were necessary for rigorous comparison.

Great care was taken to exclude cases with any potential cause for back pain seen on the MR examination.  This study therefore includes a highly selected cohort of patients with pars defects that do not represent the normal spectrum of associated findings.  The advantage of this is that any confounding causes of back pain, that might influence the lumbar lordosis, have been kept to a minimum.

The control group in this study were not normal controls.  Although the MR examinations were independently considered to be normal, all of the control group had presented with symptoms attributed to their lumbar spine.  Therefore the angle of lordosis in the case controls may not reflect a normal range.  However a previously reported study comparing the angle of lumbar lordosis in those with back pain and an asymptomatic control group found no significant difference between the groups [15]. This suggests that this limitation in the design of the study is probably not significant.

Line placement for the measurement of the constrained Cobb angle was performed manually on a PACS workstation. This technique is open to observer error, but the excellent inter-rater reliability measures indicate that this method was reliable. Another potential limitation of the study is that the observers measuring the endplate angle could not be blinded to the pars defects on the radiographs, providing a potential source of bias. 

Conclusion

There is a statistically significant association between lumbar lordosis and L5 pars interarticularis fractures.