Novel tangent approximation formula to determine height loss in scoliosis patients through a trigonometric model

Study Design: Retrospective Study. Objective: To determine the effectiveness of a novel trigonometric method to calculate height loss in scoliosis patients. Background: The problem of predicting loss in body height due to scoliosis, especially in adolescent idiopathic scoliosis (AIS), has been investigated for over 50 years. The corrected height is required to make appropriate lung function and other anthropometry assessments. Most existing formulae estimate height loss through different regression models. Methods: A new trigonometric model was developed based on the Cobb angle (α) and the apical vertebral translation (AVT) in the coronal plane. By using this model, a formula was derived using the tangent of the triangle to estimate height loss in scoliosis. Height loss=2 * AVT ( ). As measurement of AVT is not commonly performed, a mean value was obtained from a series of patients reported by Şarlak et al . It was found that AVT is affected by the Cobb angle, which was significantly different between patients with a Cobb angle of ≥50 and <50 degrees. Results: Validation of this new Tangent formula was carried out with two data sets, one from Tyrakowski et al. 2014, and another from 58 operated Scoliosis patients in a local hospital. The mean bias was the lowest with this novel tangent formula compared with the Bjure, Kono, and Stokes formulae. The trigonometric approach has the advantage that it is valid over a larger range of Cobb angle, as most of the regression models cannot be extrapolated outside the range of available data points. Conclusions: The results indicate that using the Tangent formula with simple measurements and trigonometric calculations yields results comparable with other formulae used in the past to estimate height loss. The application of this new formula can prove useful in clinical settings to allow more accurate testing and better care for patients. The tangent formula is made available at this website: https://tangentformulae.scoliosisdevices.com/. Here, height loss can be estimated by inputting the Cobb angle. Level of Evidence: III.