Measurements of Pelvic Flexion Angle Using Three-Dimensional Computed Tomography

Abstract

The purpose of the current study was to evaluate whether safe acetabular component position depends on differences in pelvic location between the supine, standing, and sitting positions. The subjects of the current study were 101 patients who had total hip arthroplasty. Anteroposterior radiographs of the pelvis with the patients in the supine, standing, and sitting positions were obtained preoperatively and 1 year after total hip arthroplasty. Computed tomography images of the pelvis were obtained preoperatively. Using image matching between the three-dimensional computed tomography model and anteroposterior radiograph, pelvic flexion angles with the patient in the supine, standing, and sitting positions were calculated. The mean preoperative pelvic flexion angle was 5 degrees +/- 9 degrees (range, -37 degrees -30 degrees ) in the supine position, 3 degrees +/- 12 degrees (range, -46 degrees -33 degrees ) in the standing position, and -29 degrees +/- 12 degrees (range, -62 degrees -10 degrees ) in the sitting position. Because there was much intersubject variability in pelvic flexion angle, it is not appropriate to determine orientation of the acetabular component from anatomic landmarks. In 90% of the cases, the difference in pelvic flexion angle between the supine and standing positions preoperatively was 10 degrees or less. In 90% of the cases, there was 20 degrees or greater extension of the pelvis from the supine position to the sitting position preoperatively, and the safe range of flexion of the hip from anterior prosthetic impingement in the sitting position was 20 degrees or greater than that in the supine position. Preoperative pelvic position in each case was almost completely maintained 1 year after total hip arthroplasty. It is reasonable to regard the pelvic position in the supine position as the functional pelvic position and proper pelvic reference frame in determining optimal orientation of the acetabular component in 90% of cases before and 1 year after total hip arthroplasty, although an adjustment of orientation of the acetabular component was needed for the remaining cases.

Pelvic Positioning Creates Error in CT Acetabular Measurements

“…Lembeck et al, in their cohort, observed a range of supine pelvic tilt from À17°to 3°, and standing pelvic tilt ranged from À27°to 3° [32]. Patients with hip disorders similarly have a wide range of individual pelvic tilt measurements [10], ranging greater than 60°in one study [39]. We (1) asked if acetabular anteversion measurements using the femoral head centers differed from those using the posterior ischia and (2) sought to understand the effects of changing obliquity, rotation, and tilt of a pelvis in a CT scanner on the measurement of acetabular variables.…”

Acetabular Morphology: Implications for Joint-preserving Surgery

“…Allocations of acetabular surface particularities or lesions were given either with reference to the acetabular incision [4,6,35,39,55,66] or in relation to the vertical axis of the patient as seen during surgery [30,38,58]. The individual acetabular tilt and variations in pelvic tilt [2,10,12,32,33,41,48,57] complicate comparison of these data.…”

“…Apart from variations in pelvic tilt [2,10,12,32,33,41,48,57], this can now be explained by variations of acetabular tilt, which influences spatial positions of peaks and depressions along the rim. The results of our measurements for version are comparable to other anatomical studies (Table 8).…”

Six Sigma Analysis of Minimally Invasive Acetabular Arthroplasty: A Preliminary Investigation

“…Imageless navigation referencing techniques do not appear to be process-capable using Six Sigma formulas and those findings held up in the current study. Although studies have shown pelvic tilt may be an equal factor determining functional acetabular component positioning, the goal of the current study was to assess the effectiveness of various methods to position the acetabular component with two degrees of freedom in relation to the APP [24,26,28]. In practice, the imageless CAS referencing technique currently uses a direct anatomic point matching method.…”