Does total hip arthroplasty restore native hip anatomy? three-dimensional reconstruction analysis

Abstract

Purpose: Component orientations and positions in total hip arthroplasty (THA) are important parameters in restoring hip function. However, measurements using plain radiographs and 2D computed tomography (CT) slices are affected by patient position during imaging. This study used 3D CT to determine whether contemporary THA restores native hip geometry.

Methods: Fourteen patients with unilateral THA underwent CT scan for 3D hip reconstruction. Hip models of the nonoperated side were mirrored with the implanted side to quantify the differences in hip geometry between sides.

Results: The study demonstrated that combined hip anteversion (sum of acetabular and femoral anteversion) and vertical hip offset significantly increased by 25.3° ± 29.3° (range, -25.7° to 55.9°, p = 0.003) and 4.1 ± 4.7 mm (range, -7.1 to 9.8 mm, p = 0.009) in THAs.

Conclusions: These data suggest that hip anatomy is not fully restored following THA compared with the contralateral native hip.

Fig. 1

a Three-dimensional models of the hip bone, femur, acetabular cup and femoral stem reconstructed from computed tomography (CT) scan data. b Models were split into implanted and native groups. c The contralateral native hip model was mirrored with respect to the sagittal plane. d The mirrored hipbone and femur were then best aligned with the implanted hipbone and the remaining femur of the implanted side

Fig. 2

a Origin of local pelvic coordinate system located at the midpoint of ASISs. The x axis is perpendicular to the frontal pelvic plane; x, y and z axes point anteriorly, superiorly and to the right. b Definitions of cup inclination and true (anatomical) anteversion. c Origin of femoral coordinate system at the centre of the femoral head. Y axis is parallel to the long axis of the best-fit cylinder to the femoral shaft; difference in femoral neck angles was quantified. The red dashed and yellow lines indicate the stem and native femoral neck axis, respectively. d X axis is perpendicular to the plane formed by the femoral long axis and origin; difference in femoral anteversion between implanted and native hips was measured

Fig. 3

True cup anteversion and inclination of implanted (red closed markers) and nonimplanted (blue open markers) hips. Measures of both hips of the same patient are noted using markers in the same shape