Anatomical changes in lumbosacral vertebrae and their correlation with facet joint-derived low back pain in patients with hip osteoarthritis after total hip arthroplasty: a cohort study

BACKGROUND: Little is known about the anatomical changes in lumbosacral vertebrae and their correlation with facet joint-derived low back pain in patients with hip osteoarthritis (HOA) after total hip arthroplasty. METHODS: Seventy-four HOA patients with low back pain who underwent initial total hip arthroplasty were included. Their Harris Hip Score (HHS), Oswestry Disability Index (ODI), Visual Analogue Scale (VAS) and anatomical parameters were analyzed. Paired t-tests were used to compare the various index scores before and after surgery, and independent sample t-tests were used for the between-group comparisons. RESULTS: The HHS and ODI significantly changed at 3 and 6 months postoperatively [HHS: preoperative (43.56±4.34) vs. 3 months (80.34±5.23) vs. 6 months (84.37±4.78); ODI: preoperative (36.26±5.34) vs. 3 months (26.44±3.23) vs. 6 months (19.34±3.27); P<0.001]. At the first 3 months after surgery, the VAS low back pain score decreased from 5.24±1.21 to 2.89±1.03 (P<0.001), and the VAS hip pain score decreased from 7.45±1.32 to 2.34±1.12 (P<0.001). There was also a statistically significant difference between the preoperative and 1-month postoperative anatomical indices: lumbar lordosis (LL) increased significantly after surgery [preoperative (43.46°±13.89°) vs. 1 month (48.27°±14.42°), P=0.001], while slip angle (SA) decreased significantly [preoperative (89.20°±5.03°) vs. 1 month (84.45°±4.89°), P=0.010]. Sacral slope (SS) and radial abduction angle (RAA) showed significant postoperative changes compared with preoperative assessments; after surgery, SS increased significantly [preoperative (31.33°±8.23°) vs. 1 month (37.65°±8.19°), P=0.006), while RAA decreased significantly [preoperative (42.32°±8.12°) vs. 1 month (35.45°±7.67°), P=0.021]. Moreover, the increase of LL was both significantly correlated with the decrease of the VAS low back pain (P=0.009) and the VAS hip pain score (P=0.038). CONCLUSIONS: Total hip arthroplasty was associated with the anatomical changes in lumbosacral vertebrae.