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T1 Pelvic Angle (TPA) Effectively Evaluates Sagittal Deformity and Assesses Radiographical Surgical Outcomes Longitudinally

Ryan, Devon J. BA*; Protopsaltis, Themistocles S. MD*; Ames, Christopher P. MD; Hostin, Richard MD; Klineberg, Eric MD§; Mundis, Gregory M. MD; Obeid, Ibrahim MD; Kebaish, Khaled MD**; Smith, Justin S. MD, PhD††; Boachie-Adjei, Oheneba MD‡‡; Burton, Douglas C. MD§§; Hart, Robert A. MD¶¶; Gupta, Munish MD§; Schwab, Frank J. MD*; Lafage, Virginie PhD*; International Spine Study Group

Spine:
doi: 10.1097/BRS.0000000000000382
Deformity
Abstract

Study Design. Retrospective review of a multicenter database of consecutive patients undergoing 3-column osteotomy for treatment of adult spinal deformity (ASD).

Objective. To rigorously develop a T1 pelvic angle (TPA) categorization paradigm and use it to assess the surgical management of patients with ASD.

Summary of Background Data. TPA, the angle between the hips-T1 line and hips-S1 endplate line, is a novel spinopelvic parameter that assesses the combined effect of a loss of lordosis on trunk inclination and pelvic retroversion.

Methods. A prospective, multicenter database of consecutive patients with ASD was queried to identify the severe deformity threshold and meaningful change values for TPA by correlation with Oswestry Disability Index. A separate multicenter, consecutive, retrospective database of patients with ASD treated with single lumbar 3-column osteotomy was then analyzed at baseline, 3-month, and 1-year follow-up. Subjects were classified into well-aligned or poorly aligned groups at 3 months on the basis of TPA. Patients “deteriorated” if they lost more than 1 meaningful change in TPA between 3 months and 1 year and had TPA more than deformity threshold at 1 year.

Results. The severe deformity threshold for TPA was 20° (Oswestry Disability Index > 40) and the meaningful change was 4.1° (Oswestry Disability Index change = 15). Review of the 3-column osteotomy database identified 179 patients with preoperative severe deformity; 63 were well-aligned (TPA < 15.9°) and 73 were poorly aligned (TPA > 20°) at 3-month follow-up. This newly developed TPA categorization mechanism grouped patients in a manner comparable with the Scoliosis Research Society-Schwab Classification. Subjects who were well-aligned at 3 months had less severe baseline deformity, but received more correction, than poorly aligned subjects. Four well-aligned patients and 13 poorly aligned patients deteriorated between 3 months and 1 year after surgery.

Conclusion. TPA accounts for sagittal vertical axis and pelvic tilt and shows great promise as a classification tool. Longitudinal analysis demonstrated undercorrection among patients with more severe preoperative deformity. We propose a surgical target of 10° for TPA.

Level of Evidence: 4

In Brief

T1 pelvic angle (TPA), the angle between the hips-T1 line and hips-S1 endplate line, is a novel spinopelvic parameter that assesses the combined effect of a loss of lordosis on trunk inclination and pelvic retroversion. TPA shows great promise in the assessment of sagittal deformity before and after surgery.

Author Information

*Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, NY

Department of Neurological Surgery, University of California, San Francisco, CA

Department of Orthopedic Surgery, Baylor Scoliosis Center, Plano, TX

§Department of Orthopaedic Surgery, University of California, Davis, Sacramento, CA

Department of Orthopaedic Surgery, San Diego Center for Spinal Disorders, La Jolla, CA

Department of Orthopaedic Surgery, Bordeaux University Hospital, Bordeaux, France

**Department of Orthopaedic Surgery, Johns Hopkins University, Baltimore, MD

††Department of Neurosurgery, University of Virginia, Charlottesville, VA

‡‡Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY

§§Department of Orthopedic Surgery, University of Kansas Medical Center, Kansas City, KS; and

¶¶Department of Orthopaedic Surgery, Oregon Health & Science University, Portland, OR.

Address correspondence and reprint requests to Themistocles S. Protopsaltis, MD, Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, 306 E 15th St, New York, NY 10003; E-mail: tprotopsaltis@gmail.com

Acknowledgment date: July 17, 2013. Revision date: January 17, 2014. Acceptance date: February 12, 2014.

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

International Study Group Foundation from DePuy Spine grant funds were received to support this work.

Relevant financial activities outside the submitted work: board membership, consultancy, payment for lectures, patents, royalties, stock/stock options, grants/grants pending, payment for manuscript preparation, payment for development of educational presentations, expert testimony, travel/accommodations/meeting expenses, and research support.

The International Spine Study Group (ISSG) is a consortium of 12 medical centers across the United States, specializing in the surgical treatment of spinal deformity. The centers are dedicated to pooling their outcome research data with appropriate IRB oversight and often within the context of prospective data collection. The common goal is to produce valuable outcome research to improve the surgical management of spinal deformity.

© 2014 by Lippincott Williams & Wilkins