How is quality of life after total hip replacement related to the reconstructed anatomy? A study with low-dose stereoradiography

•Pelvic incidence (the angle between a line perpendicular to the sacral plate at its midpoint and a line connecting the same point to the centre of the bicoxofemoral axis) is an indicator of quality of life in patients with hip arthroplasty.•Pelvic incidence seems to reflect adaptation capabilities of the hip after total hip arthroplasty.•Postoperative loss of femoral offset (distance from the centre of rotation of the femoral head to a line bisecting the long axis of the femur) negatively affects quality of life after total hip arthroplasty. The purpose of this study was to evaluate the relationships between the three-dimensional anatomy of operated hip in standing position using low-dose stereo-radiography imaging system and postoperative hip disability and osteoarthritis outcome score (HOOS) after total hip arthroplasty (THA). A total of 123 patients who underwent THA during a one-year period were included. There were 50 men and 73 women with a mean age of 67.3±13.6 (SD) years (range: 19–89 years). All patients underwent pre- and postoperative low-dose stereo-radiography examination and completed a HOOS form (score from 0 to 100, 100 for full satisfaction). We recorded 16 anatomical parameters before THA, and 15 after THA. After binary transformation of HOOS score using 70 as threshold value, outcome was assessed using logistic or generalised linear models. A total of 103 patients (103/123; 83.7%) had a HOOS score≥70 and were considered as the satisfied group. A significant difference in pelvic incidence (the angle between a line perpendicular to the sacral plate at its midpoint and a line connecting the same point to the centre of the bicoxofemoral axis) was found between the satisfied 56.4±10.4 (SD)° (range: 31–85°) and the unsatisfied group 48.7±8.9 (SD)° (range: 40–65) (P=0.006). The relative variation of offset (distance from the centre of rotation of the femoral head to a line bisecting the long axis of the femur) compared to the contralateral hip was −7% in the satisfied group and 7.2% in the unsatisfied group (P=0.01). Pelvic incidence, a parameter independent of the reconstructed anatomy, probably influences the quality of life of patients with THA, via pelvic compensatory capabilities. A loss of femoral offset negatively influences the satisfaction of patients.