Position-related Change of Pelvic Incidence Depends on the Nonfused Sacroiliac Joint in Patients with Degenerative Spinal Diseases

Abstract

A retrospective cross-sectional study.Objective. This study aims to determine whether the sacroiliac (SI) joint motion correlated to pelvic incidence (PI) change from standing to supine position in patients with degenerative spinal diseases. Summary of Background Data. PI was found an unstable parameter after adolescence as the fixed nature of PI was challenged by several studies. The SI joint has been shown to have some motion, age-related degenerative changes of cartilage and SI ligaments contribute to SI joint instability. Methods. The study contains both specimen study and radiographic study. One human specimen was acquired, on which PI was measured with different sacrum-ilium positions. In radiographic study, patients with old thoracolumbar fracture, lumbar disc herniation, stenosis, and spondylolisthesis were included. Ankylosing spondylitis (AS) patients were also included as control group. PI was measured on standing x-rays and scanogram of computed tomography images in supine position.Results. Specimen study result revealed that SI motion would lead to the change of PI with fixed pelvic thickness. In radiographic study, 101 patients with different etiology and 30 AS patients were included. After stratifying into different age groups, standing PI was significantly larger than supine PI in each age groups (P ¼ 0.002, <0.001, and <0.001, respectively).In patients with degenerative diseases, PI was significantly larger on standing position than that on supine position. DPI showed no significant difference across etiologies. However, in AS patients, standing PI and supine PI revealed no significant difference (P ¼ 0.528). Conclusion.Mobile SI joint may be the cause of increased PI in the aging spine. The dynamic change of PI is etiologyindependent if the SI joint was not fused. Older patients have greater position-related change of PI.

Changes in Spinopelvic Parameters Between Standing and Sitting Postures

“…[36][37][38] It marks the sacral orientation in the sagittal plane in relation to the native hip joints and would only substantially alter in an individual due to sacroiliac diseases, hip disease with concomitant change in the location of hip center, and sacropelvic complex fractures/ osteotomies. [39][40][41] There is weak evidence to suggest a slight change in PI with age and after long segment spinal fusion surgeries which spares the sacroiliac joint. 42 However, the degree of angular change in the aforementioned situations was small (2.5-5.2 degrees) and likely insignificant.…”

“…PI is a marker of pelvic shape and remains largely constant at the end of skeletal maturity 36–38 . It marks the sacral orientation in the sagittal plane in relation to the native hip joints and would only substantially alter in an individual due to sacroiliac diseases, hip disease with concomitant change in the location of hip center, and sacropelvic complex fractures/ osteotomies 39–41 . There is weak evidence to suggest a slight change in PI with age and after long segment spinal fusion surgeries which spares the sacroiliac joint 42 .…”