The correlation between pelvic incidence and the sagittal spinopelvic balance in degenerative lumbar scoliosis

Objective To explore the correlation between pelvic incidence(PI) and the sagittal spinopelvic balance in degenerative lumbar scoliosis (DLS). Methods From Jan 2008 to Dec 2014, 136 cases of DLS were enrolled as experimental group, 120 healthy age-and gender-matched adults were enrolled as control group. All the participants were divided into three goups according to the PI value: low (PI less than 45° ), middle (PI between 45° and 60° ), and high PI group (PI more than 60° ). Sagittal balance was determined by measuring the sagittal vertical axis (SVA), thoracic kyphosis (TK), thoracolumbar junction (TLJ), lumbar lordosis (LL), PI, sacral slope (SS), pelvic tilt (PT) were measured at a full spine lateral radiograph, sagittal spinopelvic parametersr were compared between the DLS patients and asymptomatic adults in each PI group. The correlations between spinopelvic parameters were determined using the Pearson correlation coefficient. Results The number of DLS patients with low, middle, and high PI were 38 (27.9%), 50 (36.8%), and 48 (35.3%), respectively. In the Control group, the number of low, middle, and high PI patients were 52 (43.3%), 41 (34.2%), and 27 (22.5%), respectively. In the Experimental group, patients with high PI always presented with large LL, PT, SS and smaller SVA(all P values 0.05) and the PT was large in high PI than that in middle PI(P<0.01). In the control group and DLS group, PI determined pelvic orientation(PT, SS) and sagittal spinal patameters(LL, TLJ). In terms of correlation between SS and LL, between SS and TLJ, both DLS and control groups showed significant correlations(all P values<0.05). In terms of correlation between PT and SVA, only the DLS group showed a significant correlation(P<0.05). Compared with the asymptomatic adults, DLS patients showed a high PT and low SS as well as lumbar hypolordosis, thoracic hypokyphosis and decreased TLJ in all PI groups(all P values<0.01). Conclusions The compensatory mechanisms of the spine and pelvis in DLS patients depend on PI, the increased PT in high PI and the increased SS in low PI are often observed respectively, surgical planning and lumbar curve restoration should be also dependent on the value of PI. Key words: Scoliosis; Intervertebral disc degeneration; Radiography; Pelvis; Pelvic incidence