High Preoperative T1 Slope Is a Marker for Global Sagittal Malalignment.

Area of Science:

• Spine surgery
• Orthopedics
• Radiographic analysis

Background:

• T1 slope (T1S) is linked to cervical deformity and quality of life.
• Establishing a threshold for "high" T1S is crucial for assessing global alignment.
• Full-spine imaging is not always performed, necessitating cervical radiograph parameters for thoracolumbar assessment.

Purpose of the Study:

• To determine T1 slope thresholds from cervical radiographs that correlate with thoracolumbar malalignment.
• To establish a definition for "high" T1 slope in adult spinal deformity (ASD).

Main Methods:

• Retrospective analysis of 226 adult spinal deformity patients' preoperative radiographs.
• Measurements included T1 slope (T1S), thoracic kyphosis (TK), sagittal vertical axis (SVA), T1-pelvic angle (TPA), pelvic tilt (PT), and pelvic incidence minus lumbar lordosis (PI-LL).
• Decision tree analysis identified T1S thresholds corresponding to established high alignment parameters.

Main Results:

• Higher T1S correlated with increased SVA, TPA, TK, and PT (P<0.001).
• A T1S threshold of 30 degrees was identified, with 50% of patients exceeding this.
• Patients with T1S >30 degrees demonstrated significantly worse global alignment parameters compared to those with T1S <30 degrees (P<0.05).

Conclusions:

• Elevated T1 slope is associated with poorer global spinal alignment, particularly thoracic kyphosis.
• A T1S of 30 degrees serves as a threshold indicating potential thoracolumbar malalignment.
• Consider full-spine imaging for patients with T1S >30 degrees on cervical radiographs.