Preoperative mid-cervical disc degeneration is associated with residual cervical kyphosis after surgery for adolescent idiopathic scoliosis.

Abstract

Persistent cervical kyphosis after surgery for adolescent idiopathic scoliosis (AIS) has been associated with inadequate restoration of thoracic kyphosis and low T1 slope. However, the influence of intrinsic cervical factors on postoperative cervical alignment remains unclear. This study aimed to determine whether preoperative cervical disc degeneration is associated with residual cervical kyphosis after AIS surgery. A retrospective cohort study was conducted in 72 patients with AIS Lenke type 1 or 2 who were followed for at least two years after surgery (mean follow-up, 5.1 years). Patients were categorized into a cervical kyphotic group (C2-7 angle < 0° at final follow-up; n = 42) and a non-kyphotic group (C2-7 angle ≥ 0°; n = 30). Radiographic parameters included C2-7 angle, T1 slope, thoracic kyphosis (TK), pelvic incidence, lumbar lordosis, PI-LL mismatch, sagittal vertical axis, and major Cobb angle. Preoperative cervical MRI was used to assess disc degeneration using the Pfirrmann classification and to calculate the signal intensity ratio (SIR) of cervical discs. Multivariable analyses were performed to identify factors independently associated with cervical kyphosis at final follow-up. The cervical kyphotic group demonstrated significantly smaller preoperative C2-7 angles and lower postoperative T1 slope and TK(5-12) compared with the non-kyphotic group. Mid-cervical disc degeneration (Pfirrmann grade ≥ 3) was significantly more frequent in the cervical kyphotic group. The SIR of mid-cervical discs also correlated with the C2-7 angle. In multivariable logistic regression, preoperative C2-7 angle and Pfirrmann grade ≥ 3 at the mid-cervical discs were independently associated with residual cervical kyphosis at final follow-up. In contrast, postoperative T1 slope and TK(5-12) were not significantly associated with cervical kyphosis. Preoperative mid-cervical disc degeneration and preoperative C2-7 angle are independently associated with residual cervical kyphosis after AIS surgery, highlighting the importance of intrinsic cervical structural factors in postoperative cervical sagittal alignment.