Time-dependent response of scoliotic curvature to orthotic intervention: when should a radiograph be obtained after putting on or taking off a spinal orthosis?

STUDY DESIGN A prospective study; 2-group design. OBJECTIVE This study aims to assess the time response of scoliotic spines to orthotic intervention using clinical ultrasound. SUMMARY OF BACKGROUND DATA Patients with moderate adolescent idiopathic scoliosis are generally advised orthotic treatment. However, the time to reach maximum correction after donning spinal orthosis or the time to return to pretreatment curvature after doffing spinal orthosis is not fully understood. METHOD Subjects were divided into 2 groups, the don-orthosis group and the doff-orthosis group where the time reaching maximum correction and the time returning to pretreatment curvature were investigated accordingly. To avoid excessive radiation exposure via obtaining repeated radiographs, a validated method of estimating Cobb angle using radiation-free clinical ultrasound was applied at an interval of every 30 minutes up to 180 minutes. The spinal flexibility (estimated from supine radiographs) and body mass index were collected from the subjects for analyses. RESULT Nine female patients with adolescent idiopathic scoliosis were recruited. There was no immediate change in the Cobb angles. A change of more than 5° could be observed in both groups only after 30 minutes and maximum change was found at/after 120 minutes. In the doff-orthosis group, the subject with the lowest body mass index took the longest time to increase more than 5° after doffing spinal orthosis. In the don-orthosis group, the subject with the highest body mass index took the longest time to achieve curve correction more than 5°. CONCLUSION This investigation demonstrated that there is a time lag between application of spinal orthosis and its effect on scoliotic curvature. This is likely due to the low-stiff and viscoelastic properties of the spine. The clinical relevance of this study is that for patients with scoliosis undergoing orthotic treatment, radiograph should not be obtained within 2 hours of putting on or taking off spinal orthosis because it may not show the maximum effect. LEVEL OF EVIDENCE 4.