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Spino-Pelvic Parameters After Surgery Can be Predicted: A Preliminary Formula and Validation of Standing Alignment

Lafage, Virginie PhD; Schwab, Frank MD; Vira, Shaleen BA; Patel, Ashish MD; Ungar, Benjamin; Farcy, Jean-Pierre MD

doi: 10.1097/BRS.0b013e3181eb9469
Deformity

Study Design. Prospective and retrospective radiographic study of adult patients with spinal deformities.

Objective. Construct predictive models for pelvic tilt (PT) and global sagittal balance (sagittal vertical axis [SVA]) and evaluate the effectiveness of these predictive models against a group of patients after pedicle subtraction osteotomy.

Summary of Background Data. Spinal balance involves a complex interaction between the pelvis and vertebral column. In the setting of adult spinal deformity, prediction of postoperative alignment can be challenging.

Methods. The study included 219 adult patients treated for spinal deformity. Full-length standing films were available for all subjects. Multilinear models with a stepwise condition were used on the first group of patients (n 5 179) to predict PT and global sagittal balance (measured by the SVA). Prediction models were then applied on a second group of patients (n 5 40) to estimate postoperative radiographic parameters after pedicle subtraction osteotomy surgery. Differences between estimated parameters and real values were evaluated.

Results. Multilinear regression analysis applied on the first group of patients led to a predictive formula for PT (r 5 0.93, standard error = 4.4°) using the following parameters: pelvic incidence, maximal lordosis, and maximal kyphosis. These parameters with the addition of the predicted PT were then used to predict the SVA (r 5 0.89, standard error 5 32 mm). Validation of predictive models (second group of patients) used pelvic incidence and postoperative sagittal curves. Postoperative PT was predicted with a mean error of 4.3° (SD 3.5°) and postoperative SVA was predicted with a mean error of 29 mm (SD 5 23 mm).

Conclusion. This is the first study to develop and validate pragmatic predictive models for key spino-pelvic parameters (PT and SVA) in the setting of adult spinal deformity. Using a morphologic pelvic parameter (pelvic incidence) and spinal parameters modifiable through surgery (lumbar lordosis and thoracic kyphosis), postoperative sagittal alignment can be predicted.

Standing balance involves a complex interaction between the spinal column and pelvis. Using a morphologic pelvic parameter (pelvic incidence) and spinal parameters modifiable through surgery (regional sagittal curvatures), postoperative predictive formulas for pelvic version and global sagittal balance were constructed and validated on adult patients with spinal deformity.

From the NYU Hospital for Joint Diseases, New York, NY.

Address correspondence to Virginie Lafage, PhD, NYU Hospital for Joint Diseases, 380 2nd Ave, Ste 1001, New York, NY 10010; E-mail: virginie.lafage@gmail.com

Acknowledgment date: August 14, 2009. Revision date: April 19, 2010. Second revision date: May 10, 2010. Acceptance date: May 17, 2010.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

© 2011 Lippincott Williams & Wilkins, Inc.