Introduction of the novel radiographic line (L5-kyphosis apex line) intended to evaluate scheuermann's disease and postural kyphosis progression on standard lateral X-rays

Study Design: Cross-sectional and follow-up nested study. Purpose: To assess the reliability of the L5-kyphosis apex line (L5-KAL) evaluation and determine the association between changes in L5-KAL, changes in radiological parameters, and changes in clinical symptoms. Overview of Literature: Scheuermann's disease is the most common cause of hyperkyphosis of the thoracolumbar and thoracic spine during adolescence. Scheuermann's disease patients usually show compensatory hyperlordosis of the lumbar spine, which is usually flexible, and express an anterior translation of the lumbar section. The L5-KAL was developed on the basis of our clinical experience, displaying the horizontal distance between the thoracic and lumbar curves. Methods: In the cross-sectional segment, 150 initial lateral X-rays of patients with Scheuermann's disease and postural kyphosis were analyzed, and 80 additional X-rays were analyzed in the follow-up segment. The data taken from the X-rays of the whole spinal column included the thoracic kyphosis angle, the C7 plumb line, and the L5-KAL. Clinical data included a numerical rating scale of self-perceived body image, pain, and a Scoliosis Research Society-22 questionnaire (SRS-22). Results: Significant positive associations were observed in a cross-sectional study between the L5-KAL and thoracic kyphosis, lumbar lordosis, C7 line, and self-perceived body image. In the follow-up nested study, in a mixed analysis of variance, the main effect of time was significant for the L5-KAL, kyphotic deformity and SRS-22, which indicated a change in these parameters after treatment of Scheuermann's disease patients. Significant positive associations were observed between the changes in L5-KAL and the changes in thoracic kyphosis. Conclusions: Our evidence suggests that the L5-KAL can serve as an indicator of the thoracic curve change in Scheuermann's disease and postural kyphosis patients and should be considered in clinical practice.