Evaluation of a functional position for lateral radiograph acquisition in adolescent idiopathic scoliosis

Design. A retrospective examination of lateral spine radiographs of 50 patients with adolescent idiopathic scoliosis (AIS) was performed to evaluate the sagittal profile of patients in two different standing positions. Objectives. To evaluate segmental and global changes in the sagittal profile of the spine associated with two standing radiographic positions and determine if one position represents a more functional stance for accurate sagittal balance evaluation. Summary of Background Data. Studies of spinal sagittal balance during relaxed standing have indicated that the sagittal vertical axis (SVA), as determine by the horizontal displacement of a C7 plumb line from the posterior superior corner of the sacrum, is neutral or slightly positive. However, standing with the arms forward flexed to allow radiographic visualization of the spine results in a negative shift in SVA. Methods. Measurements were obtained from standing lateral radiographs in patients with AIS in two different standing positions: arms forward flexed to 45 with elbows fully extended versus elbows fully flexed with fists resting on clavicles. Sagittal plane parameters were analyzed using correlation analyses and repeated-measures analyses of variance with significance set at 0.005. Results. The study cohort included 25 patients who had undergone solely nonoperative treatment (without progression) and 25 patients who had undergone operative intervention for their scoliosis. In all patients, SVA was more negative (C7 shifted more posterior with respect to the sacrum) when the arms were in the forward flexed position compared to the fists on clavicles position (-4.2+/-2.5 cm vs. -1.3+/-2.4 cm, P<0.001). In operative patients, the shoulder forward flexed position was associated with relative posterior rotation of the pelvis represented by an average increase of 2.7 +/- 3.8 degrees in pelvic tilt (P=0.002) and an average decrease of 3.2 +/- 4.5 degrees in sacral slope (P=0.002). There was no correlation between the degree of arm forward flexion and changes in sagittal measures between the two positions. Conclusions. The fists on clavicles position for lateral radiograph acquisition has less negative shift in SVA, and in patients with spinal instrumentation, less compensatory posterior rotation of the pelvis. This position is more representative of a patient's functional balance while still allowing adequate lateral radiographic visualization of the spine.