Can we use shorter constructs while maintaining satisfactory sagittal plane alignment for adult spinal deformity

OBJECTIVE Issues with spinopelvic fixation for adult spinal deformity (ASD) include loss of the physiological mobility of the entire lumbar spine, perioperative complications, and medical costs. Little is known about the factors associated with successful short fusion for ASD. The authors evaluated radiographic and clinical outcomes after shorter fusion for different subtypes of ASD at 2 years postoperatively and examined factors associated with successful short fusion. METHODS This was a single-center study of 37 patients who underwent short fusion and a minimum 2 years of follow-up for ASD in which lumbar kyphosis was the main deformity. The exclusion criteria were 1) age 20°, 5) scoliotic deformity with an upper end vertebra (UEV) above T12, and 6) concomitant Parkinson's disease or neurological disease. The surgical procedures, radiographic course, and Oswestry Disability Index (ODI) were assessed, and correlations between radiographic parameters and postoperative ODI at 2 years were analyzed. RESULTS A mean of 3.5 levels were fused. The mean radiographic parameters preoperatively, at 2 weeks, and at 2 years, respectively, were as follows: coronal Cobb angle: 22.9°, 11.5°, and 12.6°; lumbar lordosis (LL): 12.9°, 35.8°, and 32.2°; pelvic incidence (PI) minus LL: 35.5°, 14.7°, and 19.2°; pelvic tilt: 29.4°, 23.1°, and 25.0°; and sagittal vertical axis 85.3, 36.7, and 59.2 mm. Abnormal proximal junctional kyphosis occurred in 8 cases. Revision surgery was performed to extend the length of fusion from a lower thoracic vertebra to the pelvis in 2 cases. The mean ODI scores preoperatively and at 2 years were 50.7% and 24.1%, respectively. Patient age, number of fused intervertebral segments, and radiographic parameters were analyzed by the stepwise method to identify factors contributing to the ODI score at 2 years, preoperative PI, and sagittal vertical axis at 2 years. On receiver operating characteristic curve analysis of the minimal clinically important difference of ODI (15%) and preoperative PI, the cutoff value of the preoperative PI was 47° (area under the curve 0.75). CONCLUSIONS In terms of subtypes of ASD in which lumbar kyphosis is the main deformity, if the PI is < 47°, then the use of short fusion preserving mobile intervertebral segments can produce adequate LL for the PI, improving both postoperative global spinal alignment and quality of life.