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Scheuermann disease was initially described as a rigid kyphosis associated with wedged vertebral bodies occurring in late childhood. 37 The condition has been of significant orthopedic interest since that time, both because the condition is sometimes painful during its relative acute phase, and more importantly, because it causes significant truncal deformity that may be progressive. Sorensen subsequently described specific criteria for diagnosis in 1964, namely, that three adjacent vertebrae must be wedged at least 5° each. 40 Despite this, the specific criteria for the diagnosis of Scheuermann disease remain unclear in the subsequent literature. A spectrum of roundback has been described, going from postural roundback, to pre-Scheuermann disease, to classical Scheuermann disease. 45 Making these distinctions can be difficult, and the criteria on which diagnostic decisions are based are controversial.Most articles reference Sorensen’s criteria, 1,5,10,13,23,28 but others have used different criteria. These include increased thoracic kyphosis, disc space narrowing, and irregular endplates associated with a single-wedged vertebra, 3,7 kyphosis of greater than 45° with two or more wedged vertebra, 16 or “characteristic” radiographic findings (kyphosis, wedging of vertebral bodies, endplate irregularities, Schmorl’s nodes). 42,43 Bradford, in various studies over time, has changed his criteria for diagnosing Scheuermann kyphosis from thoracic kyphosis of greater than 35° and at least one wedged vertebra greater than 5°, 7 to the classic Sorenson criteria, 5 to most recently, a thoracic kyphosis of greater than 45° and at least one wedged vertebra. 36 Some consider any vertebral wedging to indicate Scheuermann disease, 7,43 while others have recommended making this distinction based on curve flexibility on a lateral hyperextension radiograph of the spine. 25 Measurement of vertebral wedging can be difficult, 45 particularly in skeletally immature patients when a significant portion of the vertebral body may be unossified, 30 and the reliability of intra- and interobserver measurements has not been established. Also, no study of normal adolescents has been done to assess the flexibility/rigidity of normal thoracic kyphosis, and although Scheuermann kyphosis is described as a rigid deformity, a considerable degree of flexibility may be noted on the hyperextension lateral film. 7 Thus, even the “pathognomonic” signs of Scheuermann disease remain somewhat controversial.This confusion points to the difficulty in defining pathologic deviations from normal with sagittal spinal alignment. Unlike scoliosis, where any significant lateral deviation in the coronal plane is abnormal, the sagittal alignment of the spine has a normal range of thoracic kyphosis. The Scoliosis Research Society has defined this range as being from 20° to 40° in the growing adolescent. 25,44,45 In a study of 316 healthy subjects with ages ranging from 2 to 27 years, the upper limit of normal kyphosis was noted to be 45°. In addition, it was noted that the average thoracic kyphosis increases with age, from 20° in childhood, to 25° in adolescents, to 40° in adults. 12 The lack of a consistent definition of Scheuermann kyphosis in the literature makes it difficult to compare studies as the inclusion criteria may be different; thus, making the distinction between the spectrum of upper normal thoracic kyphosis, severe adolescent roundback deformity, and Scheuermann disease may be impossible. Adding to the complexity are articles grouping Scheuermann disease together with spinal osteochondrosis, 41 and studies grouping patients diagnosed with abnormal juvenile kyphosis together with Scheuermann kyphosis patients when reporting the results of treatment. 16,43In defining Scheuermann kyphosis, the subgroup described as lumbar Scheuermann’s, type II Scheuermann’s, or “apprentice kyphosis” must be recognized.