Influence of postoperative coronal malalignment following long-instrumented fusion in patients with adult spinal deformity: evaluation of clinical outcomes and mechanical complications.

Abstract

Achieving satisfactory sagittal alignment in patients with adult spinal deformity (ASD) is a major goal of deformity correction, which leads to high health-related quality. However, compared with the literature on sagittal alignment, studies on postoperative coronal malalignment in ASD are limited. This study aimed to investigate the impact of coronal malalignment on clinical outcomes and mechanical complications after corrective surgery for ASD. Retrospective observational study. Among patients who underwent deformity correction with ≥5-level fusion to the sacrum, this study focused on those who achieved optimal sagittal correction, defined as a pelvic incidence minus lumbar lordosis (PI-LL) of ≤10° postoperatively. Incidence of coronal malalignment; clinical outcomes using the visual analog scale (VAS), Oswestry disability index (ODI), and Scoliosis Research Society Outcomes Questionnaire-22 (SRS-22); and mechanical complications such as proximal junctional kyphosis (PJK), proximal junctional failure (PJF), and rod fracture. Coronal malalignment was evaluated using the coronal balance distance (CBD), defined as the horizontal distance between the C7 plumb line and the central sacral vertical line. Postoperative coronal malalignment was classified as CBD>3 cm. Patients were divided into two groups based on CBD as follows: the coronal balance (CB) group (balanced, CBD<3 cm) and the coronal imbalance (CI) group (imbalanced, CBD≥3 cm). Clinical outcomes and the incidence of mechanical complications were compared between the groups. This study included 112 patients, with a mean follow-up duration of 46.8 months. Among them, 24 patients (21.4%) were included in the CI group, with a mean CBD of 3.6±0.4 cm, whereas 88 patients comprised the CB group, with a mean CBD of 1.1±0.7 cm. The back pain VAS scores indicated that the CI group had significantly worse clinical outcomes than the CB group (52.5±19.8 vs. 40.1±24.0, p=.022). The appearance domain of the SRS-22 was also significantly lower in the CI group than in the CB group (2.8±0.6 vs. 3.4±0.9, p=.002). However, no significant differences in leg pain VAS scores, ODI scores, or other SRS-22 domains, except appearance, were observed between the two groups. The incidences of PJK, PJF, and rod fractures were similar between the groups. However, the rate of revision surgery for rod fractures was significantly higher in the CI group than in the CB group (5/5 in the CI group vs. 5/29 in the CB group, p<.001). After correction surgery for ASD, coronal malalignment demonstrated an association with increased back pain VAS scores and lower appearance scores on the SRS-22. The incidence of mechanical complications, including PJK, PJF, and rod fractures, was not influenced by coronal alignment. However, coronal malalignment significantly increased the risk of revision surgery for rod fractures.