Background: It is important to understand postoperative global sagittal spinal alignment after total hip arthroplasty (THA) to prevent not only the following hip complications but also progressing lumbar degeneration. The purpose of this study was to progress the analysis of the global sagittal spinal alignment between before and after THA in patients without large lower limbs discrepancy.
Subjects and methods: The subjects were 87 patients with bilateral hip osteoarthritis (OA) before unilateral primary THA. We measured sagittal vertical axis (SVA), lumbar lordotic angle, sacral slope, pelvic tilt (PT), and pelvic incidence (PI) and compared the postoperative change of those parameters. Excluded criteria were Crowe classification types II, III, and IV and more than 10 mm of leg length difference, spinal scoliosis (Cobb angle > 25°), and lumbar kyphosis.
Results: The correlation coefficient between preoperative factors and postoperative sagittal alignments revealed that postoperative SVA has correlation with age (r = 0.46, p < 0.008) and preoperative PT (r = 0.42, p = 0.015). Postoperative PT had a correlation with preoperative PI (r = 0.46, p = 0.007). The change of PT after operation had negative correlation to preoperative PT (r = -0.47, p < 0.01) and PI (r = -0.38, p = 0.03). Multiple regression analysis revealed that the change of PT = 4.979 - 0.235 × preoperative PT (p < 0.05). Therefore, when preoperative PT was less than 20°, the postoperative PT would become larger than the preoperative one.
Conclusion: (1) In patient with hip OA without large lower limbs discrepancy, the postoperative PT after THA correlated with PI. (2) The postoperative change of PT was influenced by preoperative PT.
Keywords: hip–spine syndrome; lower limbs discrepancy; osteoarthritis of the hip; sagittal spinal alignment; total hip arthroplasty.