Relationship Between Lumbar Lordosis and Pelvic Incidence in the Adolescent Patient: Normal Cohort Analysis and Literature Comparison.

STUDY DESIGN: Retrospective review; literature comparison.

OBJECTIVES: To review the literature on the relationship between lumbar lordosis (LL) and pelvic incidence (PI) and evaluate this relationship in asymptomatic adolescents while testing the validity of previously reported adult correlation models between LL and PI in an adolescent population.

SUMMARY OF BACKGROUND DATA: Accurate understanding of the normal spinopelvic relationship is critical when considering surgical fusion of the lumbar spine. Many studies have reported relationships between pelvic measurements and LL in adult populations, but data in pediatric populations is lacking.

METHODS: A literature search was performed to identify previously reported relationships between pelvic parameters and LL in adults and pediatric patients. A cohort of 125 asymptomatic adolescent patients evaluated at our institution was evenly split into two cohorts for model development and validation. Linear regression between LL and PI was performed. The resultant regression model was tested in the validation cohort along with previously reported formulae with LL as a function of PI. Mean absolute error (MAE) was calculated and compared between prior models and the newly developed adolescent model using analysis of variance and post-hoc testing.

RESULTS: In our adolescent cohort (mean age: 13 ± 2), there was a strong correlation between PI and LL (r = 0.53). Regression analysis in the development cohort produced the following predictive model: LL = 0.66(PI) + 24.2. Testing in the validation cohort revealed a good correlation between predicted and actual LL (r = 0.51) and an MAE of 8.3. All but three previously reported models functioned with similar accuracy in the adolescent population, with only two methods having an MAE over 10.

CONCLUSIONS: The majority of previously published formulae for predicting LL as a function of PI developed in adults can be extrapolated to adolescent populations. These relationships are important in understanding how to surgically restore the sagittal alignment in adolescents with spinal deformity.

LEVEL OF EVIDENCE: Level IV.