Redefining physiological whole-body alignment according to pelvic incidence: normative values and prediction models

Area of Science:

• Spine biomechanics
• Radiographic analysis
• Orthopedic surgery

Background:

• Accurate spinopelvic alignment assessment is essential in clinical practice.
• Pelvic incidence (PI) is a key parameter influencing overall spinal alignment.
• Existing normative data may not adequately account for individual PI variations.

Purpose of the Study:

• To establish normative values for whole-body alignment parameters across different pelvic incidence (PI) groups.
• To develop predictive formulas for key spinopelvic parameters based on PI and age.
• To provide a foundation for more individualized assessment of spinal alignment.

Main Methods:

• A multicentric prospective study including 642 healthy volunteers.
• Full-body biplanar radiographs were analyzed using 3D reconstructions.
• Parameters including SVA, TPA, SSA, ODHA, pelvic parameters, SFA, KFA, AA, PSh, LL, TK, and CL were measured.
• Subjects were stratified into five groups based on PI for normative value derivation.
• Linear regression models were used to develop prediction formulas for PT, TPA, SSA, and SFA.

Main Results:

• Normative values for segmental, regional, and global alignment parameters were determined for each PI group.
• Lumbar lordosis (LL), pelvic tilt (PT), sacro-femoral angle (SFA), spino-sacral angle (SSA), and T1 pelvic angle (TPA) significantly correlated with PI and age.
• Prediction formulas were established: PT=-12.7+0.38*PI+0.14*Age, TPA=-16.9+0.34*PI+0.15*Age, SSA=109.8+0.58*PI-0.19*Age, SFA=173+0.39*PI+0.11*Age.
• ODHA, TK, CL, and lower limb parameters showed no association with PI.

Conclusions:

• Spino-sacral angle (SSA), pelvic tilt (PT), T1 pelvic angle (TPA), and sacro-femoral angle (SFA) should be interpreted relative to a patient's pelvic incidence (PI).
• The study provides essential normative data and predictive formulas incorporating age and PI for improved spinopelvic assessment.
• Pelvic incidence (PI) is not a determinant factor for thoracic and cervical curvatures.