Reliability of the Projection Area per Length Squared for Quantifying the Degree of Scoliosis on X-Ray Films

Abstract

Objectives: Precise measurement of spinal curvature is the cornerstone for assessment of and intervention for spinal scoliosis. This study provides an alternative and reliable approach for spinal curvature measurement. Design: This retrospective study was authorized and conducted in the Orthopedics and Traumatology Department of Ondokuz Mayis University, Turkey. Setting: Orthopedics and Traumatology Department, Faculty of Medicine, Ondokuz Mayis University, Samsun, Turkey. Subject: The anteroposterior digital X-rays of 46 patients diagnosed with idiopathic scoliosis were examined. The straight length between the superomedial and inferomedial corners of the upper and lower end vertebral bodies and the semilunar area on the concave side of the curvature were estimated using the planimetry technique. Intervention: The percentage of the semilunar area was estimated as the projection area per length squared (PAL). Measurements were taken on the radiographs twice by three observers independently using the PAL approach and the Cobb method. The diagnostic performance of the PAL method was tested against the Cobb method on the evaluation of the scoliotic deformity. Main Outcomes Measures: High correlation between the PAL estimations and Cobb angle measurements existed for the first and second sessions (r=0.840; P <0.001 and r=0.855; P <0.001, respectively). Results: The optimal cut-off values of the PAL were calculated as 5.53% and 9.67% corresponding to Cobb angles of 20 degrees and 40 degrees, respectively. Both methods showed high intra-observer and inter -observer reliability (all ICC values >0.929). Conclusion: The PAL method is more reliable than the Cobb method for measuring the degree of scoliosis and could replace the Cobb method, which showed a high degree of variability in the measurements. It could be used as an alternative and robust diagnostic criterion in the determination of the severity of scoliosis.