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A retrospective comparative study.To investigate the morphologic features of proximal vertebral fractures in adults following spinal deformity surgery using segmental pedicle screw instrumentation.Fractures above pedicle screw constructs are a clinical problem that warrants further investigation for prevention and treatment.Ten adult patients (6 lumbar scoliosis, 4 degenerative sagittal imbalance) who underwent segmental spinal instrumented fusion were analyzed. Patients were divided into 2 groups according to the features of vertebral fracture: upper instrumented vertebral collapse + adjacent vertebral subluxation (SUB group: n = 5), and adjacent vertebral fracture (Fracture group: n = 5).Both groups demonstrated a high frequency of osteopenia and all patients in the SUB group had comorbidities before surgery. The SUB group demonstrated a shorter interval between initial surgery and the fracture (subluxation: 3 ± 1.9 months; fracture: 33 ± 25.3 months, P < 0.05), and hypokyphosis (T5–T12) in the thoracic region before surgery (SUB: 13° ± 6.4°; fracture: 33° ± 15.6°). Both groups demonstrated severe global sagittal imbalance (SUB: 151 ± 62.8 mm; fracture: 94 ± 102.2 mm), and hypolordosis (T12–S1) in the lumbar spine (SUB: −19° ± 24.4°; fracture: −33° ± 22.7°) before surgery. Global sagittal imbalance in the SUB group was corrected to 8 ± 17.4 mm immediately postoperative (P < 0.05), but increased to 64 ± 19.9 mm after the junctional fractures (P < 0.05). The SUB group demonstrated a significantly higher wedging rate (SUB: 65% ± 12.4%; fracture: 36% ± 16.0%, P < 0.05) and greater local kyphosis (SUB: 42° ± 11.1°; fracture: 17° ± 4.1°, P < 0.05) after the fracture. Two of 5 patients in the SUB group demonstrated severe neurologic deficit from E to B after the fractures by a modified Frankel classification.Old age, osteopenia, preoperative comorbidities, and severe global sagittal imbalance were found to be frequent in patients with proximal junctional fracture. In addition, marked correction of sagittal malalignment might be considered as a risk factor of upper instrumented vertebra collapse followed by adjacent vertebral subluxation, which occurred in the first 6 months after corrective surgery with the potential for causing severe neurologic deficit because of the severe local kyphotic deformity.