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T1 pelvic angle (TPA) effectively evaluates sagittal deformity and assesses radiographical surgical outcomes
Devon J Ryan1, Themistocles S Protopsaltis, Christopher P Ames
1*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.
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.
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