Unlocking TPA’s Clinical and Sagittal Significance by Analyzing its Relation to Pelvic Tilt
Section snippets
Background context
TPA (T1 pelvic angle) is a valuable perioperative planning tool that accounts for both pelvic tilt (PT) and trunk inclination. While this parameter correlates with patient reported outcomes, it is limited as a standalone parameter because it does not distinguish patients’ ability to compensate with pelvic retroversion.
Purpose
Investigate the TPA and its close relation with pelvic tilt in order to assess patients HRQOL (health-related quality of life) with a given TPA and a varying PT.
Study design/setting
Retrospective cohort.
Patient sample
Single-center study of 230 patients (58.7±15.5 years old, 60% females) with full body radiographs, HRQOL forms and TPA≥10°.
Outcome measures
Sagittal spino-pelvic parameters including SVA, PT, PI-LL, and TPA, and the following health related quality of life questionnaires: ODI and EQ-5D.
Methods
Proportions of PT to TPA (PTp=PT/TPA) and T1SPi to TPA (T1SPip=T1SPi/TPA) were calculated and investigated against increased values of TPA. Then, two sub-groups of similar TPA were created (HighPT and LowPT) based on mean (PTp)±0.5 standard deviation. HighPT and LowPT were compared across the entire cohort using an unpaired T-test.
Results
Mean sagittal parameters included: PI-LL 12.3±16.3°, SVA 41±49mm, TPA 21.9±10.1° and PT 24.4±8.6°. The analysis of PTp distribution revealed a decrease in PT recruitment as TPA increases (137±39% for patients with TPA<15°, 87±15% for patients with TPA>40°). Comparing LowPT (n=57) with HighPT (n=69) revealed that for a similar TPA (24.1 vs 22.1°, p=0.308), patients with LowPT (and therefore little compensatory PT) had significantly worse HRQOL scores in terms of ODI (45 vs 32 in HighPT; p=0.002)
Conclusions
While TPA captures the severity of deformity, disability is a product of deformity severity and the inability to recruit compensatory mechanisms. TPA measures the severity of the thoracolumbar deformity separate from pelvic compensation. Therefore, to develop a complete picture of standing sagittal alignment, TPA should be considered in conjunction with PT to convey the full radiological and clinical picture. Failing to do so potentially results in inadequate assessment of a patient’s
FDA device/drug status
This abstract does not discuss or include any applicable devices or drugs.