Predictive formulae of ideal lumbar lordosis determined by individual pelvic incidence and thoracic kyphosis in asymptomatic adults

BACKGROUND:The precise prediction of ideal lumbar lordosis (LL) has become increasingly important in clinical practice. The aim of this study was to explore the regulatory mechanisms of sagittal spinopelvic alignment and to predict ideal LL based on individual pelvic incidence (PI) and thoracic kyphosis (TK) parameters in asymptomatic adults. METHODS:A total of 233 asymptomatic subjects older than 18 years were consecutively enrolled in our study between April 2017 and December 2019. A full-spine, standing X-ray was performed for each subject. The following parameters were measured in the sagittal plane: the apex of lumbar lordosis (LLA), the distance between the plumb line of the lumbar apex (LAPL) and the gravity plumb line, the inflection point (IP), LL, the upper arc and lower arc of lumbar lordosis (LLUA and LLLA, respectively), PI and TK. Stepwise multiple linear regressions were conducted, and the statistical significance level was P < 0.05. RESULTS:Both PI and TK were two important predictive variables for LLA, LAPL, IP and LL. In addition, the LLUA was mainly explained by TK, while the LLLA was explained by PI. The corresponding predictive models are listed as follows: LLA = 17.110 - 0.040∗PI + 0.023∗TK (R2 = 0.380), LAPL = 31.296 + 0.467∗PI - 0.126∗TK (R2 = 0.309), IP = 10.437 + 0.091∗TK - 0.029∗PI (R2 = 0.227), LL = 2.035 + 0.618∗PI + 0.430∗TK (R2 = 0.595), LLUA = 0.893 + 0.418∗TK (R2 = 0.598), LLLA = 3.543 + 0.576∗PI (R2 = 0.433). CONCLUSION:The specific sagittal lumbar profile should be regulated by both pelvic and thoracic morphology. Such predictive models for lumbar parameters determined by individual PI and TK parameters have been established, which are meaningful for surgeons to better understand the regulatory mechanisms of sagittal spinopelvic alignment and reconstruct a satisfactory lumbar alignment.