The assessment of spine flexibility has been traditionally performed using lateral-bending radiograph obtained with the patient in the supine or standing position . In addition, push-prone radiograph in which the physician applies manual pressure on the apices of the curve [2, 3], fulcrum-bending radiograph which is made with patient lying on his or her side over a large radiolucent plastic cylinder [4–6], supine traction radiograph which is obtained by applying traction force using a standard cervical traction halter with a second individual applying countertraction on both lower extremities [7, 8], and suspension radiograph which was taken in lifting position by a axillary harness to create a spinal traction force resulting from the patient's own weight  are reported as stress radiographs to evaluate spinal flexibility in patients with idiopathic scoliosis. Further, some surgeons are employing general anesthesia to take supine traction radiograph for estimation of maximum curve flexibility just before surgery [10–12]. All of these stress radiographs are utilized as preoperative evaluation with the aim of predicting postoperative correction, planning fusion levels, and sparing patients anterior release surgery. At present, whereas, there is no report about stress radiographs for the patients with idiopathic scoliosis who are organized the conservative treatments. Because most idiopathic scoliosis patients subject to conservative treatments in daily clinical practice , it seems to be very important to develop an ideal method to evaluate the spinal flexibility for the patients who are indicated non-surgical treatments. In particular, it is so significant if the target angle corrected by brace will be able to set by some sort of stress radiographs for the idiopathic scoliosis patients since brace treatment is the most common and effective conservative treatment [14–16].
Immediate in-brace correction of scoliotic curve, 3D correction, and the absolute reduction of the Cobb angle are recognized to influence the treatments long-term effect . Orthotists frequently consider that approximately 50% initial correction in the Cobb angle is necessary to expect a positive outcome [22, 23]. Weiss et al  aim at an in-brace correction of more than 40% to make sure that for the patient the limitation of quality of life while brace wearing is worthwhile on the basis of the report from Landauer et al . Castro et al suggested that brace treatment was not recommended in patients whose curves did not correct at least 20% in a TLSO . The in-brace correction is dependent on curve pattern, age, sex, Cobb angle, and stiffness of the curve . Accordingly, not all curves can be corrected to the same extent. An appropriate in-brace angle is thought to be different in individual cases according to these various conditions. So we require any stress radiographs that simply calculate an indicative correction angle by brace wearing on each patient.
Castro et al stated a side-bending radiograph to assess curve flexibility may be cost effective in preventing TLSO application to patients, with rigid curves, unlikely to benefit from its use . However, all stress radiographs previously reported are not appropriate for evaluation of the patients who are performed conservative treatment since the mechanical force added to the spine of them is too much.
Then, we are routinely taking hanging total spine x-ray for the idiopathic scoliosis patients to assess if an appropriate correction by brace is achieved. HA were closely correlated with BA independent of curve patterns, except some curves in multiple curve patterns, and were useful for confirmation of adequate correction by brace.
In addition, we tried to find factors that affect the correction angle by OMC brace using main thoracic curve that is mostly common in idiopathic scoliosis. As the results of this investigation, maturity had some influence on the correlation between HA and BA. That is to say, in immature patients, HA tended to be larger than BA. In contrast, in mature patients, HA had a tendency to be smaller than BA.
Advantages of hanging total spine x-ray are as follows: it is easily taken in outpatient clinic without any expensive equipment, extra-time, and extra-workforce, the target angle corrected by OMC bracing can be estimated, and the condition of traction force stays constant because it depends just on the patient's own weight. Meanwhile, disadvantages of it are as follows: it is impossible to take for the patients who can not hang onto the bar, the force direction applied by this method is longitudinal which is not same as corrective force of OMC brace that is transverse, this method is not applied for some curves in multiple curve patterns, and some additional dosage of radiation can not be avoided.
Finally we have to supplementary say that the results of current study using the OMC brace do not always apply to those using other braces, especially braces of higher in-brace correction such as the Chêneau light brace [25, 26]. Another research must be provided to confirm if hanging total spine x-ray will helpful or not for the treatment of idiopathic scoliosis using other braces.