Effect of Coronal and Sagittal Spinal Malalignment on Spinopelvic Mobility in Patients Undergoing Total Hip Replacement
Authors: Haffer Henryk , Wang Zhen , Hu Zhouyang , Muellner Maximilian , Hipfl Christian , Pumberger Matthias 
Published: March 2022

Study Design:
This was a prospective observational study.

Objective:
This investigation aimed (1) to determine the impact of sagittal spinal alignment with C7–sagittal vertical axis (SVA), pelvic incidence−lumbar lordosis (PI−LL) mismatch and Roussouly classification on individual segments of spinopelvic mobility represented by lumbar flexibility [∆lumbar lordosis (LL)], pelvic mobility [∆pelvic tilt (PT)], and hip motion [∆pelvic femoral angle (PFA)] and (2) to assess the influence of coronal spinal balance on the spinopelvic complex in patients undergoing total hip arthroplasty (THA) preoperatively and postoperatively.

Summary of Background Data:
Restricted spinopelvic mobility gained attention as a contributing factor for THA instability. However, it remains unclear what influence the coronal and sagittal spinal alignment has on spinopelvic mobility.

Materials and Methods:
A total of 197 THA patients were included in the investigation conducting biplanar stereoradiography in standing and sitting position preoperatively and postoperatively. Two independent investigators assessed C7–SVA (≤50 mm balanced, >50 mm imbalanced), PI−LL (≤10 degrees balanced, >10 degrees imbalanced), refounded Roussouly classification, coronal spinal balance with C7–central sacral vertical line, LL, pelvic incidence (PI), PT, PFA. Individual segments of spinopelvic mobility based on the change from standing to sitting were defined as ∆LL, ∆PT, and ∆PFA. Unpaired t test or Welch t test for comparison between groups of 2 was applied. Analysis of variance and post hoc analysis according to Bonferroni or Games-Howell was used to determine differences between groups of >2. The Spearman rank correlation coefficient was used to determine the interrater reliability of the radiographic measurements.

Results:
Significant differences were demonstrated for ∆LL (SVA balanced/imbalanced: 24.7 degrees/19.1 degrees, P=0.001; PI−LL balanced/imbalanced: 24.4 degrees/16.4 degrees, P<0.000), PT (SVA balanced/imbalanced: 12.5 degrees/15.2 degrees, P=0.029; PI−LL balanced/imbalanced: 10.8 degrees/20.5 degrees, P<0.000), PI (SVA balanced/imbalanced: 52.9 degrees/56.9 degrees, P=0.001; PI−LL balanced/imbalanced: 52.1 degrees/61.0 degrees, P<0.000), LL (SVA balanced/imbalanced: 54.8 degrees/47.8 degrees, P=0.029; PI−LL balanced/imbalanced: 55.3 degrees/42.6 degrees, P<0.000). The coronal spinal balance (central sacral vertical line) indicated no significant differences regarding spinopelvic mobility between positive, neutral, or negative balanced groups. Significant differences with decreased pelvic mobility (∆PT) and lumbar flexibility (∆LL) in low-grade PI types 1 and 2 compared with high-grade PI type 4 according to the Roussouly classification were observed.

Conclusions:
This is the first study to investigate spinal sagittal alignment using 3 different classifications in association to the spinopelvic complex in THA patients preoperatively and postoperatively. The significantly altered spinopelvic mechanics with decreased lumbar flexibility and increased pelvic retroversion in sagittal imbalanced patients clearly indicate the need for a separate consideration of the global spinal sagittal alignment. Our findings emphasize the importance of risk stratification for THA candidates in terms of sagittal imbalance attempting to mitigate the THA instability risk with accurate preoperative planning.

Level of Evidence:
Level III.