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. 2007 Oct;16(10):1587-92.
doi: 10.1007/s00586-007-0401-3. Epub 2007 Jun 5.

Inter- and intraobserver reliability assessment of the Cobb angle: manual versus digital measurement tools

Michaela Gstoettner  1 , Katrin Sekyra, Nadja Walochnik, Peter Winter, Roland Wachter, Christian M Bach
Affiliations

Inter- and intraobserver reliability assessment of the Cobb angle: manual versus digital measurement tools

Michaela Gstoettner et al. Eur Spine J. 2007 Oct.

Abstract

The objective of this study is to determine the intraobserver and interobserver reliability of end vertebra definition and Cobb angle measurement using printed and digital radiographs of 48 patients with scoliosis. The Cobb angle and the end vertebra were assessed by six observers in 48 patients with scoliosis using printed and digital radiographs. Definition of end vertebra and measurement of the Cobb angle was repeated three times with a 3 week interval. Intraclass correlation coefficients (ICC) were used to determine the interobserver and intraobserver reliabilities. 95% prediction limits for the errors in measurements are provided. For the Cobb angle a mean ICC of 0.97 was determined for intra- and interobserver reliability measurement of the printed radiographs. For the electronic radiographs a mean ICC value of 0.93 was determined for interobserver reliability and a mean ICC value of 0.96 for intraobserver reliability. Intraobserver ICC for definition of end vertebrae was 0.8 for both methods. Interobserver ICC was 0.83 for the manual and 0.74 in the digital method. One pitfall in angle measurement implies the Cobb method itself which measures in two dimensions. Until we develop a proper tri-dimensional measuring system an error is introduced. For the Cobb angle measurement the definition of end vertebrae introduces the main source of error. Digital radiography does not improve the measurement accuracy.

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Figures

Fig. 1
Fig. 1
Measuring the Cobb angle from the upper endplate of Th11 to the lower endplate of L3 results in an angle of 64.7°
Fig. 2
Fig. 2
Measuring the Cobb angle from the upper endplate of Th10 to the upper endplate of L3 results in an angle of 62.2°
Fig. 3
Fig. 3
Measuring the Cobb angle from the upper endplate of Th11 to the lower endplate of L4 results in an angle of 101°
Fig. 4
Fig. 4
Measuring the Cobb angle from the lower endplate of Th11 to the lower endplate of L4 results in an angle of 105.9°
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