Is the Sacro-Femoral-Pubic Angle Predictive for Pelvic Tilt in Adolescent Idiopathic Scoliosis Patients?

Study Design: This was a retrospective radiographic study. Objective: The aim of this study was to evaluate the correlation between pelvic tilt (PT) and the sacro-femoral-pubic angle (SFP angle) in AIS patients and to clarify whether the predictability of PT is affected by different curve patterns. Summary of Background Data: Pelvic retroversion is one of the compensatory mechanisms to maintain upright position and is also tied to health-related quality of life in patients with adolescent idiopathic scoliosis (AIS). However, measurement of spino-pelvic parameters including PT may not be accurate because of difficulty in visualizing femoral heads on lateral radiographs in some patients. Materials and Methods: In this study, 101 female AIS patients were recruited. The subjects were divided into 2 groups: thoracic scoliosis (TS) and lumbar scoliosis (LS) group. Long-cassette standing upright radiographs were obtained; PT and SFP angles were measured through digital analysis software (Surgimap Spine Software, New York, NY). The relations between PT and SFP angle were determined by the Pearson correlation coefficient (r). Linear regressions between PT and SFP angle were also performed. Results: The SFP angle was strongly correlated with PT in both groups, and PT could be estimated by the formulas: PT = 74.052 - 0.991 x SFP angle in the TS group and PT = 65.345 - 0.881 x SFP angle in the LS group. In the TS group, the SFP angle correlated with PT strongly with a Pearson coefficient of 0.65. Whereas in the LS group, the coefficient was weaker than that in the TS group (0.48 vs. 0.65); however, it still showed that PT was significantly associated with SFP. Conclusions: Given the high correlation between PT and SFP angle, the SFP angle should be considered a reliable alternative option to PT, which has routinely excellent visibility in coronal films in AIS patients. The predictability was more accurate for AIS patients with thoracic curves than with lumbar curves.