T1 Pelvic and Lumbar Pelvic Angles Normative Values: A Prospective Cohort Study of 472 Asymptomatic Volunteers

Cross-sectional analysis of a prospectively enrolled cohort.

Determine the normative values of the T1 pelvic angle (TPA) and lumbar pelvic angle (LPA) in an asymptomatic cohort of volunteers.

The TPA and LPA have been introduced as sagittal spinopelvic parameters to guide correction of adult spinal deformity. Suggested values for these parameters were derived from linear regressions based on Oswestry disability index scores from adult spinal deformity patients. While a few studies have evaluated the normative value of TPA, none have evaluated the LPA in asymptomatic individuals.

TPA and LPA were measured on radiographs of 472 asymptomatic volunteers between 20 and 40 years old. TPA and LPA were calculated as originally described from the centroid of T1 and L1, respectively, to the center of the femoral head to the midpoint of the sacral endplate. TPA and LPA were also evaluated using the midpoint of the superior endpoint as a surrogate to the centroid of the vertebra to compare these two measurement techniques.

TPA and LPA normative values were, respectively, 7.3° (6.8-7.8) and 6.3° (5.9-6.7). There was no statistically significant difference between using the centroid of T1 or L1 versus using the midpoint of the superior endplate with respective results of 7.5° (7.0-8.0) ( P =0.55) and 6.1° (5.6-6.5) ( P =0.43). TPA was significantly different between Roussouly types 1, 2, 3, versus type 4 with respective results of of 6.7°, 7.2°, 6.5°, and 9.2° ( P <0.001). The same difference was observed for the LPA with normative results of 3.8°, 5.1°, 5.8°, and 9.3° ( P <0.001), respectively, for Roussouly types 1, 2, 3, and 4.

TPA and LPA normative values are 7° and 6°, respectively, and vary between Roussouly morphotypes 1, 2, and 3 versus type 4. Using the midpoint of the superior endplate of T1 and L1 versus the centroid yielded similar results and therefore could be easier to use intraoperatively.