40 - MRI vertebral bone quality correlates with interbody cage subsidence after anterior cervical discectomy and fusion

Friday, June 2, 2023

12:18 PM – 12:22 PM

Location: Salons 13-15

Co-Author(s)

JB

James Bernatz, MD

Orthopedic Spine Surgery Fellow
Mayo Clinic, Minnesota, United States
BG

Brian Goh, MD, PhD

Orthopedic Spine Surgery Fellow
Mayo Clinic, United States
ZP

Zachariah W. Pinter, MD

Resident
Mayo Clinic, United States
GM

Georgios Michalopoulos, MD

United States
MB

Mohamad Bydon, MD

Rochester, Minnesota, United States
AN

Ahmad Nassr, MD

Consultant
Mayo Clinic
Rochester, MN, United States
AS

Arjun S. Sebastian, MD

Consultant
Mayo Clinic, United States
BF

Brett A. Freedman, MD

Consultant
Mayo Clinic, United States

Submitter(s)

JB

James Bernatz, MD

Orthopedic Spine Surgery Fellow
Mayo Clinic, Minnesota, United States

Presenting Author (Person doing the Podium Present(s)

HL

Hannah A. Levy, n/a

Orthopaedic Resident
Mayo Clinic, United States

Introduction: Many risk factors have been reported for subsidence of interbody cages in anterior cervical discectomy and fusion (ACDF). MRI Vertebral Bone Quality (VQB) is a relatively new radiographic parameter that can be easily obtained from pre-operative MRI and has been shown to correlate with measurements of bone density such as DXA and CT Hounsfield Units.
Aims/

Objectives: The purpose of the study was to evaluate VBQ as a predictor of interbody subsidence and to determine threshold values that portend increased risk of subsidence.

Methods: We performed a retrospective review of patients who underwent one- to three-level ACDF using titanium interbodies with anterior plating between the years 2018 and 2020. VBQ was measured on pre-operative sagittal T1 MRI by two independent reviewers. Subsidence measurements were performed by two independent reviewers on CT scans obtained 6 months postoperatively. Subsidence was then classified as mild if subsidence into the inferior and superior endplate were both ≤2 mm, moderate if the worst subsidence into the inferior or superior endplate was between 2 to 4 mm, or severe if the worst subsidence into the inferior or superior endplate was ≥4 mm.

Results: Eight-five fusion levels in forty-four patients were included in the study. There were 32 levels with moderate subsidence and 12 levels with severe subsidence. The average VBQ score in those patients with severe subsidence was significantly higher than those without subsidence (3.80 vs 2.4, P < 0.01). A threshold value of 3.2 was determined to be optimal for predicting subsidence (AUC = 0.99) and had sensitivity of 100% and a specificity of 94.1% in predicting subsidence. Interobserver reliability of VBQ measurement was excellent with ICC=0.94 (95% CI: 0.89 – 0.97).

Conclusions: VBQ strongly correlates with subsidence of interbody grafts after ACDF. A threshold VBQ score value of 3.2 has excellent sensitivity and specificity for predicting subsidence. Spine surgeons can use VBQ as a readily available screening tool to identify patients at higher risk for subsidence.