[Features of pelvic parameters in adolescent idiopathic scoliosis and their relationships with spinal sagittal parameters].

OBJECTIVE: To explore the features of pelvic parameters in patients with adolescent idiopathic scoliosis (AIS) and the relationships with spinal sagittal parameters and evaluate their roles in sagittal balance.

METHODS: A total of 112 AIS patients from March 2007 to February 2011 were recruited. Six parameters were evaluated from lateral standing radiographs:pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), lumbar lordosis (LL), thoracic kyphosis (TK) and sagittal vertical axis (SVA). Pearson's correlation was used to determine the relationship between the above parameters and t-test applied to compare the differences between the subgroups: (1) by the major curve types in coronal plane (primary thoracic curve vs. primary lumbar curve); (2) by the value of SVA (positive vs. negative).

RESULTS: The values of PI and SS in our cohort were 47.2° and 39.4° and they were lower than those in Caucasians as previously reported. PI was correlated with SS, PT and LL (r = 0.562, 0.773 and 0.278 respectively); TK not correlated with pelvic parameters (PI, PT and SS). SVA correlated with both spinal (TK, LL) and pelvic parameters (PI, PT). In the subgroup analyses, the values of PI and SS were significantly higher in the primary thoracic curve subgroup than those in the primary lumbar curve subgroup (49.4° vs 45.1°, 41.0° vs 38.0°). The values of PI and PT were distinctively higher in the positive SVA subgroup than those in the negative SVA subgroup (54.6° vs 45.6°, 14.3° vs 6.2°).

CONCLUSION: Ethnic differences exist in the main pelvic parameters and their values are lower in Chinese than in Caucasians. There are also differences among different types of AIS. The values of main pelvic parameters are higher in AIS patients with a primary thoracic curve than in those with a primary lumbar curve. Pelvic parameters play an important role in maintaining a sagittal balance. The main pelvic parameters have influences on sagittal lumbar configuration but little on thoracic segment. A high PI value leads to a forward lean in torso with an increased PT as a result of compensation and vice versa. The alteration of PT is a major compensatory pattern of pelvis. The features of pelvic parameters should be considered during surgical planning.