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Updated: Jun 27, 2026
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Cone Beam Intraoperative Computed Tomography-based Image Guidance for Minimally Invasive Transforaminal Interbody Fusion
Published on: August 6, 2019
Identifying an X-Ray Threshold for Cage Subsidence After Single-Level Minimally Invasive Transforaminal Lumbar
Ahmet Kartal1, Gayle R Salama2, Lawrance K Chung1
1Department of Neurological Surgery, Och Spine at NewYork-Presbyterian Hospital, Weill Cornell Medicine, 525 East 68th Street, Box 99, New York, NY 10065, USA.
Journal of Clinical Medicine
|June 26, 2026
Summary
A 2.0 mm X-ray protrusion depth reliably detects early cage subsidence after lumbar fusion surgery. Intraoperative CT is specific but not sensitive for predicting later subsidence, requiring further risk stratification methods.
Area of Science:
- Spine surgery outcomes
- Minimally invasive spinal fusion
- Radiographic assessment of cage subsidence
Background:
- Cage subsidence after minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) increases revision rates and costs.
- Intraoperative computed tomography (CT) offers detailed visualization but isn't universally available.
- Plain X-ray is accessible but has lower resolution, necessitating a reliable method to identify subsidence.
Purpose of the Study:
- To establish the optimal X-ray protrusion depth threshold for identifying CT-confirmed early subsidence.
- To evaluate if intraoperative CT can predict late radiographic subsidence.
- To correlate early X-ray protrusion depth with intervertebral disc height (IVDH) and segmental lordosis (SL) loss.
Main Methods:
- Retrospective analysis of 100 patients undergoing MIS-TLIF (March 2015-July 2023).
- Subsidence defined as ≥2.0 mm endplate penetration on CT; X-ray measurements used parallax technique.
- Receiver operating characteristic (ROC) analysis determined the Youden-optimal X-ray cutoff; intraoperative CT compared to late subsidence.
Main Results:
- An X-ray protrusion depth of 1.90 mm was the Youden-optimal cutoff, showing 80.0% sensitivity and 97.4% specificity for CT-confirmed subsidence.
- Intraoperative CT predicted late subsidence with 45.8% sensitivity and 96.2% specificity.
- Each 1 mm of early X-ray depth correlated with 0.45 mm IVDH loss and 0.37° SL loss.
Conclusions:
- An X-ray protrusion depth of 2.0 mm serves as a reliable preliminary threshold for detecting early cage subsidence when CT is unavailable.
- Intraoperative CT is highly specific but lacks sensitivity for predicting late subsidence, indicating a need for additional predictive factors.
- Further prospective studies are warranted to validate these hypothesis-generating findings for improved surgical outcomes.
