What is the Ideal Zoom for Digital Lumbosacral Spine Radiographs to Detect Mild Instability?
Background: Often, lumbar spine radiographs are digitally printed in zoom [magnification] percentages smaller than 100% to cut down on the costs of a larger film! This might however, compromise cursory visual assessment of instability, particularly in low grade spondylolistheses. Present study aimed to assess accuracy of cursory visual assessment for radiological lumbar instability with varying zoom [magnification] percentages in digital radiographs in spondylolistheses <grade II.
Materials and Methods: Prospective trial carried out after IRB approval. Patients with complaints of low backache with/ without radiculopathy included. Patients with spondylolistheses> grade I, infections, trauma excluded. Pairs of flexion-extension radiographs of lumbar spine of all included patients printed in 25%, 50%, 75% and 100% zoom [magnification] on digital radiographic films. Each week, a set of radiographs of one zoom [magnification] level of every patient sentto practicing spine surgeons. Objective measurement of instability done by another observer using White and Panjabi’s criteria.
Results: Nineteen patients included. Ten practicing spine surgeons participated. Accuracy of assessment of instability was 53.4%[range:42%-74%], 54.8% [37%-68%], 60% [48%-68%] and 66.5% [48%-79%] in 25%, 50%, 75% and 100% zoom [magnification] percentages, respectively. This difference was statistically significant [p=0.01]. There was a decreasing trend of false positive values too, as the zoom [magnification] percentage increased [p=0.0066].
Conclusion: Though printing films in zoom [magnification] percentages less than 100% may cut down costs, it compromises cursory screening for lumbar radiological instability. This would be particularly relevant in high-volume surgical units wherein detailed objective assessment for every single patient may be impractical.
Keywords: lumbar spine, instability, radiological instability, dynamic radiographs
Citation: Pithwa YK, Sureja KB, Meka RB. “What is the Ideal Zoom for Digital Lumbosacral Spine Radiographs to Detect Mild Instability? ”. SVOA Orthopaedics 1:1 (2021) Pages 28-33.