Deteriorating alignment in the nonfused vertebrae 5 years after surgery in patients with a T1 slope ≥ 40°

Correcting sagittal alignment is important in surgery for adult spinal deformity (ASD) surgery. T1 slope (TS) is a key parameter for evaluating whole spine alignment. Many patients with a large TS have thoracolumbar and cervical spine deformities. The aim of this study was to compare alignment changes before and after ASD surgery in two groups categorized by a preoperative TS of ≥ 40° or < 40°.

The authors included patients aged ≥ 40 years who underwent spinal correction surgery for ASD between 2010 and 2019 and had at least 5 years of follow-up. The patients were divided into two groups: the high TS group (group H, TS ≥ 40°) and the low TS group (group L, TS < 40°). Radiographic parameters and patient-reported outcome measures (PROMs) such as the Scoliosis Research Society-22 and Oswestry Disability Index were assessed preoperatively, postoperatively, and at the 2- and 5-year follow-ups.

There were 57 patients in group H and 161 in group L. Patients in group H had a higher upper instrumented vertebra (mean 8.1 vs 9.8, p < 0.001). Postoperative TS was reduced in both groups (mean 32.7° vs 24.2°). The sagittal vertical axis (SVA) improved in both groups immediately after surgery (51.9 mm vs 37.3 mm) but was higher in group H at 5 years (mean 85.3 mm vs 62.2 mm, p < 0.001). Thoracic kyphosis (TK) increased in both groups but remained significantly higher in group H (mean 38.2° to 46.2°) than in group L (mean 32.8° to 39.4°) (p < 0.001). The C2-7 SVA worsened in group H (18.5 mm to 31.4 mm) compared with group L (14.4 mm to 20.1 mm) (p < 0.001). Proximal junctional kyphosis (PJK) was more frequent in group H (36.8% vs 18.0%, p = 0.0058).

In ASD patients with TS ≥ 40°, initial alignment improvement was followed by significant deterioration in nonfused segments at 5 years. While PROMs showed no differences between the groups, higher PJK incidence warrants careful monitoring.