The impact of preoperative cervical degeneration on proximal junctional kyphosis in adult spinal deformity surgery with an upper-thoracic upper instrumented vertebra.

OBJECTIVE: Preoperative cervical malalignment, including an increased cervical sagittal vertical axis and proximal junctional angle (PJA), has been associated with proximal junctional kyphosis (PJK) following thoracolumbar deformity correction. However, the influence of cervical disc degeneration on PJK risk remains unclear. This study evaluated whether preoperative MRI-based cervical degeneration predicts PJK following thoracolumbar deformity correction in patients with adult spinal deformity (ASD). METHODS: One hundred twenty-six patients with ASD and preoperative cervical MRI who underwent thoracolumbar deformity correction with fusion from an upper-thoracic upper instrumented vertebra (UIV; C7-T4) to the S1 vertebra and ilium with at least 2 years of follow-up were included. Cervical degeneration was graded using the MRI-based Miyazaki classification, with grade IV-V discs considered severely degenerated. PJK was defined as a PJA ≥ 10° and ≥ 10° greater than preoperatively. RESULTS: Patients without severe cervical degeneration had no significant increase in PJA and no cases of PJK at 2 years. From preoperatively to 2 years, PJA increased by 2.9° (p = 0.014), 4.0° (p = 0.002), and 4.1° (p = 0.04) in patients with 0, 1-2, and ≥ 3 severely degenerated discs, respectively, with corresponding PJK rates of 0%, 10.3%, and 40.6% (p < 0.0001). The posterior cranial vertical line to UIV screw head distance was greater in patients with minimal degeneration (15.8 mm) than those with 1-2 (2.8 mm) or ≥ 3 discs (6.0 mm; p < 0.0001). After adjusting for confounders, severe cervical degeneration independently predicted PJK (OR 3.01, p = 0.0004; area under the receiver operating characteristic curve = 0.90). CONCLUSIONS: Severe cervical degeneration on preoperative MRI strongly predicts PJK after thoracolumbar deformity correction with upper thoracic UIV and fusion to the S1 vertebra and ilium. Preoperative cervical MRI may identify high-risk patients and inform surgical planning for long thoracolumbar constructs.