How Reliable is the Assessment of Fusion Status Following ACDF Using Dynamic Flexion-Extension Radiographs?

Area of Science:

• Orthopedics
• Spine Surgery
• Radiology

Background:

• Radiographic assessment of non-union following anterior cervical discectomy and fusion (ACDF) lacks standardized criteria.
• Previous research suggested using interspinous process motion (ISPM) <1 mm on dynamic radiographs to diagnose non-union.
• The inter-observer reliability of ISPM measurements by practicing surgeons remains unclear.

Purpose of the Study:

• To evaluate the reliability of practicing spine surgeons in measuring ISPM on flexion-extension radiographs.
• To assess the accuracy of the <1 mm ISPM cutoff for diagnosing non-union after ACDF.
• To determine the agreement among surgeons regarding fusion status based on dynamic radiographs.

Main Methods:

• 29 spine surgeons measured ISPM across 19 ACDF levels in 9 patients.
• Surgeons used ISPM measurements to determine fusion status.
• Inter-observer correlation coefficients (ICC), standard error of measurement (SEM), and minimum detectable difference (MD) were calculated.
• Clerical errors were identified and removed by screening measurements deviating more than one standard deviation from the mean.

Main Results:

• The overall ICC for ISPM measurement was 0.76, with a SEM of 1 mm and MD of 2.76 mm.
• Agreement on fusion status was moderate (ICC = 0.6).
• After removing clerical errors, ISPM ICC improved to 0.82, SEM to 0.83 mm, and MD to 2.29 mm.
• High-performing reviewers (ICC > 0.9) achieved an ICC of 0.94, SEM of 0.45 mm, and MD of 1.26 mm.

Conclusions:

• The MD of 2.29 mm indicates that the <1 mm ISPM cutoff is insufficient as a sole criterion for diagnosing non-union after ACDF.
• Moderate agreement on fusion status highlights challenges in interpreting dynamic radiographs.
• More rigorous methods are needed to prevent misdiagnosis of non-union in clinical studies, potentially involving measurement auditing.