Intra- and inter-operator variability in sagittal ratio values obtained from cervical radiographs of horses with neurological disease

Aims: To determine the intra- and inter-operator variability inintra- and inter-vertebral sagittal ratio value (SRV) measurementsmade from radiographs of horses with neurological disease fordiagnosis of cervical vertebral stenotic myelopathy (CVSM).Methods: For this retrospective study, archived digital cervicalradiographs, clinical history, serological and CSF analysis results,and myelographic and post mortem reports of horses withneurological disease were gathered from 4 veterinary hospitals.From 73 sets of radiographs in DICOM format, 42 were selectedfor inclusion in the study (horse age; 1'18 years, 33 male, 9female). Four operators experienced in examination of cervicalradiographs made measurements from all 42 radiograph sets andintra- and inter-vertebral SRVs were calculated for C2-C7 inclusiveto determine inter-operator variability. Ten sets of radiographswere randomly selected for re-measurement and calculation ofSRVs 2 weeks later for determination of intra-operator variability.For all radiographs, electronic calipers were used to makemeasurements. Operators were blinded to clinical and outcomedata of the cases. Bland Altman analyses were used to examine99Thursday 9th September 2010intra- and inter-operator agreement for each SRV.The degree ofvariation between 2 operators and within the same operator wasalso calculated as the percentage variation of the absolute SRVfor each vertebral site. Results: Intra-vertebral SRVs were morerepeatable and reproducible than inter-vertebral SRVs. Variationin inter-vertebral SRVs was greater for C2-3, C3-C4 and C4-C5than other sites. Variation in both intra- and inter-vertebral SRVswas greater between operators than within operators.Conclusions and practical significance: The lower repeatabilityfound with inter-vertebral SRVs, especially cranially, is of potentialclinical importance and could affect the accuracy of diagnosis andinfluence case management. Variability in SRVs betweenoperators has the potential to result in disagreement of diagnosisof CVSM. Acknowledgements: Funding was provided by theWellcome Trust. Professors David Hodgson and Steve Reed.