Preoperative pelvic axial rotation: a possible predictor for postoperative coronal decompensation in thoracolumbar/lumbar adolescent idiopathic scoliosis

Abstract

Background The pelvis as the biomechanical foundation of spine, plays an important role in the balance of the stance and gait through the multi-link spinal-pelvic system. If the pelvic axial rotation (PAR) exists in adolescent idiopathic scoliosis (AIS) patients, it should theoretically have some effects on the body balance. Purpose To explore the probable effects of preoperative PAR on the spinal balance in coronal plane in AIS patients with main thoracolumbar/lumbar (TL/L) curve after posterior spinal instrumentation. Methods Thirty-eight AIS patients (age: 15 ± 1.5 years) with main TL/L curve (51°± 6.2°) were recruited retrospectively into this study. The mean follow-up period was 27 months (24-36 months). Standing full spine posteroanterior radiographs were taken preoperatively, 3 month and 1 year postoperatively, and at last follow-up. The convex/concave ratio (CV/CC ratio) of the anterior superior iliac spine laterally and the inferior ilium at the sacroiliac joint medially was measured on posteroanterior radiographs. According to the preoperative CV/CC ratios, the patients were divided into two groups: normal group (N-group: 0.95 B CV/CC B 1.05); and the asymmetrical group (A-group: CV/CC \ 0.95, or [1.05). Results In all the patients, the 3-month-postoperative CV/ CC ratio (1.026 ± 0.087) was significantly different from the preoperative CV/CC ratio (0.969 ± 0.095, P \ 0.001), indicating that the pelvis had rotated in the opposite direction of the corrective derotation load applied to the TL/L spine after surgery. No significant change was found in the CV/CC ratio from 3-month-postoperative to the last follow-up (1.013 ± 0.103, P [ 0.05). There was no significant difference in the demographic, phenotypic, and treatment variables between the N-(n = 16) and A-groups (n = 22) (P [ 0.05). However, more coronal decompensation occurred in the A-group after surgery (36.4 vs. 0.0 %, P = 0.013): two patients having trunk translation, three having lower instrumented vertebra (LIV) translation, and one having LIV tilt; meanwhile, one patient having both LIV translation and LIV tilt, and one having both trunk translation and LIV tilt. Conclusions The present study confirmed the existence of PAR in AIS patients, and indicated that the pelvis would experience an active rebalancing in the transverse plane within 3 months after spinal correction, and since then, its position would remain stable. Moreover, TL/L-AIS patients with preoperative asymmetrical PAR probably had greater risk of coronal decompensation postoperatively.

Pelvic obliquity in adolescent idiopathic scoliosis planned for posterior spinal fusion: A preoperative analysis of 311 lower limb axis films

“…The pelvic axial rotation has been investigated by many authors. 6,7,[11][12][13] Gum et al concluded that the PR in the transverse plane was in the same direction of the apical thoracic vertebral rotation in major thoracic curves (Lenke 1, 2, and 3 curve types) and that Lenke 1 and 2 curve types without a compensatory thoracolumbar or lumbar curve did not have the predicted rotation. 6 Zhao et al 7 defined physiological PR as left/right ratio within the range of 1 + 0.1, whereas Lucas et al 12 defined the normal range of convex/concave ratio as from 0.95 to 1.05.…”

“…Qiu et al performed a retrospective study in 38 AIS patients with thoracolumbar/lumbar curve and found that in patients with pelvic axial rotation, there was a higher incidence of coronal decompensation. 13…”

“…Qiu et al performed a retrospective study in 38 AIS patients with thoracolumbar/lumbar curve and found that in patients with pelvic axial rotation, there was a higher incidence of coronal decompensation. 13 Abnormalities in the pelvis and hip geometry have also been associated with AIS. Tomasz reported that AIS patients had significant adduction range deficit of the right hip compared to normal subjects.…”

Maintenance of Derotation in Adolescent Idiopathic Scoliosis: a Novel Technique Measuring Postoperative Vertebral Rotation by Pedicle Screw Position

“…To ensure a proper orthogonal view, all radiographs were assessed on both views for adequacy. Orthogonal accuracy has previously been expressed as a comparative distance of ASIS to SI distance on either side [33]; however, this was not available for all patients. Instead, the distance from the S1 spinous process was measured to the most lateral aspect of the sciatic notch (S1–SN) as seen in Fig.…”

Factors affecting pelvic rotation in idiopathic scoliosis

“…It was found in another study [15] that preoperative PR might be related to postoperative loss of balance in the coronal plane. All these conclusions seem to suggest that axial balance may affect coronal balance, though more research is needed to elucidate the intrinsic association between them.…”