A comparison of Cobb angle measurement on digitized radiographs using a computer pointing device(mouse): without endplate extrapolation versus with endplate extrapolation

Nakulan Nantha Kumar, Peter Alex Gilmer Torrie, Dylan Thomas, Hui Ling Kerr, Ian J. Harding


AIM: Advancements in technology have improved the reliability of Cobb angle measurements. Precision of new measurement techniques have to be quantified and established for their valid clinical application. In this study, we investigated the reliability and precision of commonly utilised semi-automatic techniques of Cobb angle measurement, with and without endplate extrapolation using PACS Synapse V4.

METHODS: 53 spinal curves on digitised radiographs, were measured without and with endplate extrapolation, by three assessors independently on two separate occasions. Reliability testing using Cronbach’s Alpha test was conducted for intra-observer reliability. ANOVA assessed the inter-observer correlate. All datasets were assessed for normality using D’Agostino and Pearson. Cobb angle techniques without and with extrapolation were compared using a two-way unpaired Students’ T-test. P<0.05 was accepted as significant.

RESULTS: All datasets passed normality testing. All intra-observer reliability was excellent (>0.9). The mean Cobb for all assessors, across both datasets, without extrapolation was 48.2° (95%CI 46.5-50.0) and with extrapolation was 48.1° (95%CI 46.4-49.8).

CONCLUSION: No significance (P=0.968) was observed in Cobb values measured between these semi-automatic techniques.  Both Cobb angle measurement techniques produces results that are not significantly different, highly reliable, precise and thus could be utilised interchangeably in clinical practice.


Cobb angle; Computer-assisted measurement; Scoliosis

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