Risk Factors for Postoperative Coronal Balance in Adult Spinal Deformity Surgery

Abstract

Study design: A retrospective case-control study.

Objectives: To determine factors influencing the ability to achieve coronal balance following spinal deformity surgery.

Methods: Following institutional ethics approval, the radiographs of 47 patients treated for spinal deformity surgery with long fusions to the pelvis, were retrospectively reviewed. The postoperative measurements included coronal balance, L4 tilt, and L5 tilt, levels fused, apical vertebral translation and maximum Cobb angle. L4 and L5 tilt angles were measured between the superior endplate and the horizontal. Sagittal parameters including thoracic kyphosis, lumbar lordosis, pelvic incidence, and sagittal vertical axis were recorded. Coronal balance was defined as the distance between the central sacral line and the mid body of C7 being ≤40 mm. Surgical factors, including levels fused, use of iliac fixation with and without connectors, use of S2A1 screws, interbody devices, and osteotomies. Statistical tests were performed to determine factors that contribute to postoperative coronal imbalance.

Results: Of the 47 patients reviewed, 32 were balanced after surgery and 14 were imbalanced. Coronal balance was 1.30 cm from center in the balanced group compared to 4.83 cm in the imbalanced group (P < .01). Both L4 and L5 tilt were statistically different between the groups. Gender and the use of transverse connectors differed between the groups but not statistically.

Conclusions: In adult spinal deformity patients undergoing primary fusions to the pelvis, the ability to level the coronal tilt of L4 and L5 had the greatest impact on the ability to achieve coronal balance in this small series. A larger prospective series can help validate this important finding.

Keywords: L4 tilt; L5 tilt; adult spinal deformity; coronal balance; pelvic fixation; sagittal balance.

Figure 1.

Artist’s rendering demonstrating a preoperative scoliotic spine (A). Note L4 in dark. Correcting the main curve without leveling L4 in the coronal plane leads to coronal imbalance (B) toward the convexity of the main curve. A temporary rod is used to distract L4 to S1 on the concave side of the fractional lumbosacral curve (arrows) while the pre-contoured rod is applied to the concave side of the main curve (C), reducing the deformity to the rod (D). The concave distraction of the fractional curve provides direct decompression of the foramens. Concave compression and convex distraction of the main curve is used to complete the correction of the main curve.

Figure 2.

Preoperative standing anteroposterior radiograph (A) demonstrating an L4 coronal tilt angle of 26°. Following placement of the pedicle screws, distraction is applied between L4-5 and L5-S1 on the lumboscaral concavity (right side) until the L4 pedicles screws appear in line with each other clinically. Following placement of the left rod and correction of the deformity, the temporary right rod is removed, and the permanent right rod is placed. Intraoperative radiographic assessment (B) shows significant improvement in the L4 tilt to 7°. Interbody implants were not required to achieve this correction.

Figure 3.

Preoperative standing anteroposterior (A) and lateral (B) radiographs of a 67-year-old patient with degenerative scoliosis with 17° of L4 tilt and 39 mm of coronal imbalance to the right. Close-up view of the distal lumbar spine (C) highlights the coronal tilt of L4 that is reduced to 4° (D) following correction of the deformity. Postoperative standing anteroposterior (E) and lateral (F) radiographs demonstrate correction of the coronal balance to 13 mm and a well-aligned sagittal plane.

Figure 4.

Preoperative standing anteroposterior (A) and lateral (B) radiographs of a 61-year-old patient with degenerative scoliosis with 22° of L4 tilt, and 62 mm of coronal imbalance to the left. Close-up view of the distal lumbar spine (C) highlights the coronal tilt of L4 at 22° that remains high at 19° (D) following correction of the deformity. Postoperative standing anteroposterior (E) radiographs show coronal imbalance of 63 mm to the left. Well-balanced alignment is seen on the lateral (F) radiograph.

Figure 5.

Preoperative standing anteroposterior (A) and lateral (B) radiographs of a 58-year-old patient with degenerative scoliosis with 29° of L4 tilt and 10 mm of coronal imbalance to the left. Anteroposterior radiographs following a T10 to pelvis construct shows persistent L4 tilt of 23° (C). Correction of the curve proximal to the tilted L4 resulted in coronal imbalance toward the convexity of 55 mm. Well-balanced alignment is seen on the lateral (D) radiograph.