# Is flexion-extension imaging necessary for surgical decision-making in degenerative lumbar spondylolisthesis? Supine MRI and upright radiographs offer superior diagnostic value

## TL;DR

This study compares two imaging methods for diagnosing spinal instability in degenerative lumbar spondylolisthesis and finds that upright-supine imaging may be a better low-radiation alternative.

## Contribution

The study introduces upright-supine imaging as a potential alternative to flexion-extension radiographs for assessing spinal instability.

## Key findings

- Upright-supine imaging detected more patients with radiographic instability than flexion-extension radiographs.
- Dynamic slip angle was significantly higher in upright-supine imaging compared to flexion-extension imaging.
- Upright-supine imaging may offer a low-radiation alternative for preoperative assessment of spinal instability.

## Abstract

Degenerative lumbar spondylolisthesis (DLS) is a major indication for lumbar surgery. Surgical decision-making, particularly regarding the need for fusion, often depends on radiographic detection of segmental instability. Flexion–extension (FE) radiographs remain the reference standard but are limited by radiation exposure, motion-related discomfort, and poor reproducibility, whereas upright–supine (US) imaging - combining upright lateral radiographs with supine MRI - may offer a comparable, low-radiation alternative using routinely acquired images.

To compare segmental motion at L4/5 between FE and US imaging and evaluate their respective abilities to identify patients with radiographic signs of instability.

In this retrospective cross-sectional study, 128 patients surgically treated for isolated L4/5 DLS were included. Segmental motion was analyzed using FE and US imaging by determining relative slippage, dynamic slip angle, and radiographic instability, defined as sagittal translation ≥8% and/or a dynamic slip angle ≥10°.

Relative slippage was comparable between US and FE imaging (US: 7.43 ± 5.10%; FE: 7.29 ± 4.57%; p = 0.994). The dynamic slip angle was significantly higher in US imaging compared to FE imaging (US: 6.42 ± 4.20°; FE: 4.03 ± 2.98°; p < 0.001). US imaging identified more patients with radiographic signs of instability compared to FE imaging (US: n = 68, 53.1%; FE: n = 42, 32.8%; p < 0.001).

US imaging identified a higher proportion of patients meeting established thresholds for radiographic instability compared to FE radiographs. Although FE imaging remains the diagnostic standard, US imaging may offer a practical, low-radiation alternative for preoperative assessment. Prospective investigations are warranted to confirm its clinical utility.

•US imaging detected more patients with radiographic instability than FE radiographs.•Dynamic slip angle was significantly higher in US imaging than in FE imaging.•Relative slippage was comparable between US and FE imaging.•US imaging may provide a low-radiation approach for instability evaluation.

US imaging detected more patients with radiographic instability than FE radiographs.

Dynamic slip angle was significantly higher in US imaging than in FE imaging.

Relative slippage was comparable between US and FE imaging.

US imaging may provide a low-radiation approach for instability evaluation.