Abstract
PurposeAdolescent idiopathic scoliosis (AIS) patients are exposed to 9–10 times more radiation and a fivefold increased lifetime cancer risk. Radiation-free imaging alternatives are needed. Ultrasound imaging of spinal curvature was shown to be accurate, however, systematically underestimating the Cobb angle. The purpose of this study is to create and cross-validate an equation that calculates the expected Cobb angle using ultrasound spinal measurements of AIS patients.MethodsSeventy AIS patients with upright radiography and spinal ultrasound were split randomly in a 4:1 ratio to the equation creation (n = 54) or validation (n = 16) group. Ultrasound angles based on the spinous processes shadows were measured automatically by the ultrasound system (Scolioscan, Telefield, Hong Kong). For thoracic and lumbar curves separately, the equation: expected Cobb angle = regression coefficient × ultrasound angle, was created and subsequently cross-validated in the validation group.ResultsLinear regression analysis between ultrasound angles and radiographic Cobb angles (thoracic: R2 = 0.968, lumbar: R2 = 0.923, p < 0.001) in the creation group resulted in the equations: thoracic Cobb angle = 1.43 × ultrasound angle and lumbar Cobb angle = 1.23 × ultrasound angle. With these equations, expected Cobb angles in the validation group were calculated and showed an excellent correlation with the radiographic Cobb angles (thoracic: R2 = 0.959, lumbar: R2 = 0.936, p < 0.001). The mean absolute differences were 6.5°–7.3°. Bland–Altman plots showed good accuracy and no proportional bias.ConclusionThe equations from ultrasound measurements to Cobb angles were valid and accurate. This supports the implementation of ultrasound imaging, possibly leading to less frequent radiography and reducing ionizing radiation in AIS patients.
Highlights
Adolescent idiopathic scoliosis (AIS) is a complex threedimensional (3D) deformity of the spine and trunk with severe consequences for young patients in terms of pain, possible cardiopulmonary compromise, psycho-social burden and disturbed self-image [1]
Several authors described the use of ultrasound landmarks such as the spinous process (SP) and transverse process (TP) to measure the severity of the AIS curve, and goodto-excellent correlations were shown between ultrasound angles and radiographic Cobb angles [7,8,9,10,11]
There were no significant differences in age, sex, ultrasound angles and radiographic Cobb angles (Table 1)
Summary
Adolescent idiopathic scoliosis (AIS) is a complex threedimensional (3D) deformity of the spine and trunk with severe consequences for young patients in terms of pain, possible cardiopulmonary compromise, psycho-social burden and disturbed self-image [1]. Low-dose biplanar radiography (EOS imaging, Paris, France) is performed upright, but is not widely available and still utilizes ionizing radiation [6]. Because of these difficulties, other radiationfree methods to create a 3D image of the spine in upright position have been developed, like ultrasound imaging. The relationship between angles measured with ultrasound and radiography is described in earlier studies, but an equation to calculate the expected Cobb angle based on the ultrasound angle has not yet been properly cross-validated [9,10,11]. The purpose of the current study is to create and cross-validate an equation to calculate the expected Cobb angle of thoracic and lumbar curves based on the ultrasound angle of AIS patients
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