Inter/Intraobserver Reliability of T1 Pelvic Angle (TPA), a Novel Radiographic Measure for Global Sagittal Deformity

Area of Science:

• Orthopedics
• Radiography
• Spinal Biomechanics

Background:

• Existing literature suggests T1PA offers superior reliability for global sagittal alignment compared to traditional methods.
• Prior research primarily focused on postoperative spinal deformity patients.
• This study is the first to evaluate T1PA reliability in healthy subjects without spinal deformity.

Purpose of the Study:

• To assess the intra- and interobserver reliability of the T1 pelvic angle (T1PA) in healthy adults.
• To examine the relationship between T1PA measurements and pelvic position.
• To establish T1PA as a dependable radiographic measure for spinal sagittal alignment.

Main Methods:

• Seven orthopedic surgeons of varying experience measured T1PA in 50 healthy volunteers.
• Radiographs were taken in three pelvic positions: resting, maximal anterior rotation, and maximal posterior rotation.
• Intraclass correlation coefficients were used to determine intra- and inter-rater agreement.

Main Results:

• A very high level of agreement was observed for T1PA measurements (ICC = 0.98).
• Excellent intrarater reliability (>0.85) was achieved by all examiners across all pelvic positions.
• Inter-rater reliability demonstrated consistent T1PA measurements within ±2° of a gold standard, with T1PA varying based on pelvic rotation.

Conclusions:

• The T1 pelvic angle (T1PA) is a reproducible and reliable measure of global sagittal alignment.
• T1PA reliability is independent of the evaluator's training level.
• The influence of pelvic rotation on T1PA must be considered for accurate clinical application and correction targets.