Prospective Analysis of Imaging Prediction of Pseudarthrosis After Anterior Cervical Discectomy and Fusion

Abstract

A threshold level of 4° of motion is commonly used to identify a pseudarthrosis. Our prospective study suggests that this value has a high PPV, but a low specificity and would miss many of the pseudarthroses that have angular motion less than 4° (sensitivity 23%). By lowering the threshold for angular motion to 1°, the sensitivity improves to 77%. CT scan has been touted as the gold standard, and it has a high positive predictive value of 100%. However, its NPV was slightly lower than using 1° of motion on QMA analyzed flexion-extension films (73% vs. 79%). In conclusion, although CT scan has long been regarded as the gold standard for determining a pseudarthrosis in the cervical spine, the interpretation is subjective and vulnerable to both type I and type II errors. Analysis of motion using Quantitative Motion Analysis is seemingly less subjective than CT and in our prospective study was more predictive of an operatively confirmed pseudarthrosis.

Diagnosing Pseudoarthrosis After Anterior Cervical Discectomy and Fusion

“…The Cobb angle measurement is closely associated with the instantaneous center of rotation while obtaining the dynamic cervical spine films, making an accurate and consistent angle measurement difficult. Although there is evidence that combining quantitative motion analysis software with dynamic radiographs may yield objective and reliable numbers compared to manual or subjective measurements, the limitation of specialized technology and software availability make this less useful [ 42 , 47 ]. The difficulty of consistently reproducing the Cobb angle measurement makes this a less appealing method to diagnose pseudoarthrosis for the authors.…”

“…Kim et al defined bony fusion as “fused with remodeling and trabeculae present” or “graft intact, not fully remodeled and incorporated, but no lucency present,” which is more of a general vague description of fusion status [ 48 ]. Other CT scan based parameters used the lack of motion in fused segments and at times no specific parameter was described for fusion assessment [ 14 , 28 , 29 , 37 , 47 , 55 ]. Song et al [ 18 ] first described the ExGBB and InGBB on CT scans to subcategorize the areas of achieved fusion in 2013.…”

“…It fails to assess for dynamic changes in the cervical spine during motion, which may leave out some cases of pseudoarthrosis seen only with movement. Also, the CT scan based fusion status is based on subjective interpretation compared to the objective measurement findings on standard films, which make the results more vulnerable to both type I and type II errors [ 47 ]. In addition, because of the imaging features of cortical allografts, the CT evaluation may actually omit the nonunion and overstate the fusion rates, particularly during the early post-operative follow-up period.…”

Pseudarthrosis due to galvanic corrosion presenting as subarachnoid hemorrhage

“…Previous studies have suggested that CT provides a higher sensitivity and positive predictive value in diagnosing the presence of successful fusion compared to using X-ray. [7] There are concerns about extraneous radiation from CT over X-ray, however, we still feel that CT should be a preferential modality for assessing arthrodesis status as demonstrated by this case.…”

Comparison of structural allograft and traditional autograft technique in occipitocervical fusion: radiological and clinical outcomes from a single institution

“…Discrepancies among imaging methods may further complicate the comparison of fusion rates among studies, and the results should be interpreted carefully. 11,31 …”