Predicting postoperative coronal alignment for adult spinal deformity: do lower-extremity factors matter?

Area of Science:

• Spine surgery
• Orthopedic surgery
• Adult spinal deformity

Background:

• Accurate prediction of postoperative coronal alignment is crucial for adult spinal deformity (ASD) surgery outcomes.
• Existing methods may not fully account for complex lower-extremity biomechanics influencing spinal alignment.

Purpose of the Study:

• To describe and validate an intraoperative method for predicting postoperative coronal alignment in ASD surgery.
• To assess the accuracy of this method up to 2 years postoperatively.
• To determine if lower-extremity parameters influence the choice of intraoperative measurement.

Main Methods:

• Developed an intraoperative method using prone radiographs with two reference lines: central sacral pelvic line (CSPL) and intraoperative central sacral vertical line (iCSVL).
• Compared measurements (C7-CSPL, iCVA) with immediate and 2-year postoperative coronal vertical axis (CVA).
• Categorized 108 ASD patients into four groups based on leg length discrepancy (LLD) and lower-extremity compensation (pelvic obliquity, knee bending, mechanical axis difference).

Main Results:

• The intraoperative method demonstrated high accuracy in predicting postoperative CVA for up to 2 years.
• For patients without LLD (Type 1 & 2), C7-CSPL showed minimal error (mean 0.5 cm).
• For patients with LLD (Type 3 & 4), iCVA was more accurate (mean error 0.4 cm).

Conclusions:

• The described intraoperative system accurately predicts postoperative coronal alignment in ASD patients.
• The method's accuracy is maintained up to 2 years post-surgery.
• Accounting for lower-extremity parameters (LLD, compensation) is essential for selecting the appropriate intraoperative measurement technique.