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  • The T1 Pelvic Angle (TPA), a Novel Radiographic Measure of Global Sagittal Deformity, Accounts for Both Pelvic Retroversion and Truncal Inclination and Correlates Strongly with HRQOL

    Final Number:

    Virginie Lafage PhD; Themistocles Protopsaltis MD; Frank Schwab MD, PhD; Nicolas Bronsard; Justin S. Smith MD PhD; Eric Klineberg MD; Gregory Mundis MD; Richard A. Hostin MD; Robert Hart MD; Douglas C. Burton MD; Christopher P. Ames MD; Christopher I. Shaffrey MD, FACS; Shay Bess MD; Thomas Errico; ISSG

    Study Design:
    Clinical Trial

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2013 Annual Meeting

    Introduction: Sagittal Vertical Axis (SVA) and Pelvic Tilt (PT) have been shown to correlate directly with Health Related Quality of Life (HRQOL) in adult spinal deformity (ASD). This study investigates the relationship of the T1 Pelvic Angle (TPA), a novel radiographic parameter of global sagittal deformity, and other established measures, correlating them with HRQOL. TPA accounts for both truncal inclination and pelvic retroversion, and it can be measured on a prone intraoperative long-cassette radiograph to gauge global correction, a function which is not possible with SVA or PT. Since the TPA is an angular and not a linear measure, it does not require calibration of the radiograph.

    Methods: Multicenter, prospective, analysis of consecutive ASD patients. Inclusion criteria: ASD, age>18, and any of the following: scoliosis Cobb angle >20 deg, SVA>5 cm, thoracic kyphosis>60 deg, and PT greater than 25 deg. Clinical measures of disability included ODI, SRS and SF36.

    Results: 559 ASD patients (mean age 52.5) were enrolled. TPA correlated most strongly with SVA (r=0.837) and PI-LL (r=0.889) and PT (0.933). Categorizing the patients by increasing TPA (<10; 10-20; 20-30; >30) revealed a significant and progressive worsening in HRQOL (all p<0.001). TPA and SVA correlated strongly with ODI (0.435, 0.457), SF36 PCS (-0.440, -0.465) SRS (-0.304, -0.360). Utilizing a linear regression analysis, the threshold for TPA of 19.8 was found to correspond to a severe disability (ODI>40). The meaningful change in TPA was 4.1, correlating it to an ODI change of 15.

    Conclusions: The TPA correlates strongly with HRQOL in patients with ASD. The TPA is related to both PT and SVA, but unlike SVA, it measures sagittal deformity independent of many postural compensatory mechanisms. It can be used as an intraoperative tool to measure global correction with a target TPA of less than 20.

    Patient Care: Improve our understanding of surgical treatment strategies for adults with spinal deformity.

    Learning Objectives: By the conclusion of this session, participants should be able to: (1) Understand how the T1 Pelvic Angle (TPA) is measured; (2) Appreciate that the TPA is a novel measurement of sagittal alignment that is less dependent on postural factors and accounts for both truncal inclination and pelvic retroversion; (3) Appreciate that the TPA can be measured based on intra-operative radiographs; (4) Appreciate that the TPA correlates strongly with measures of health-related quality of life.


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