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Spine (Phila Pa 1976). 2017 Oct 1;42(19):E1119-E1125. doi: 10.1097/BRS.0000000000002116.

Virtual Modeling of Postoperative Alignment After Adult Spinal Deformity Surgery Helps Predict Associations Between Compensatory Spinopelvic Alignment Changes, Overcorrection, and Proximal Junctional Kyphosis.

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*Spine Service, Hospital for Special Surgery, New York, NY †Spine Division, Department of Orthopedics, NYU Langone Medical Center, New York, NY ‡Department of Orthopedic Surgery, University of Louisville Medical Center, Louisville, KY §Department of Neurosurgery, San Francisco Medical Center, University of California, San Francisco, CA ¶Department of Orthopedic Surgery, University of Kansas Medical Center, Kansas City, KS ||Department of Orthopedic Surgery, Oregon Health Sciences University, Portland, OR **Department of Orthopedic Surgery, University of California, Davis, Sacramento, CA ††Rocky Mountain Hospital for Children Denver, Denver, CO ‡‡Department of Neurological Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL.



Retrospective review of a prospective multicenter database.


To develop a method to analyze sagittal alignment, free of the influence of proximal junctional kyphosis (PJK), and then compare PJK to non-PJK patients using this method.


PJK after adult spinal deformity (ASD) surgery remains problematic as it alters sagittal alignment. The present study proposes a novel virtual modeling technique that attempts to eliminate the confounding effects of PJK on postoperative spinal alignment.


A virtual spinal modeling technique was developed on a retrospective ASD cohort of patients with multilevel spinal fusions to the pelvis with at least 2-year postoperative follow-up. The virtual postoperative alignment (VIRTUAL) was created from the postoperative alignment of the instrumented segments and the preoperative alignment of the unfused segments. VIRTUAL was validated by comparisons to actual 2-year postoperative alignment (REAL) in non-PJK patients. Patients were then divided into two groups: PJK and non-PJK based on the presence/absence of PJK at 2 years postoperatively. PJK and non-PJK patients were compared using VIRTUAL and REAL.


A total of 458 patients (78F, mean 57.9 yr) were analyzed. The validation of VIRTUAL versus REAL demonstrated correlation coefficients greater than 0.7 for all measures except sagittal vertical axis (SVA; r = 0.604). At 2 years, REAL alignment in PJK patients demonstrated a smaller pelvic incidence minus lumbar lordosis and a larger thoracic kyphosis than non-PJK patients, but similar SVA, T1 pelvic angle, and pelvic tilt. An analysis of VIRTUAL demonstrated that patients with PJK had a smaller pelvic incidence minus lumbar lordosis, pelvic tilt, SVA, and T1 pelvic angle than non-PJK patients (P < 0.05).


This technique demonstrated strong correlations with actual postoperative alignment. Comparisons between REAL and VIRTUAL alignments revealed that postoperative PJK may develop partially as a compensatory mechanism to the overcorrection of sagittal deformities. Future research will evaluate the appropriate thresholds for deformity correction according to age and ASD severity.



[Indexed for MEDLINE]

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