Pelvic tilt in patients undergoing total hip arthroplasty: when does it matter?

Abstract

Pelvic tilt (PT) affects the functional anteversion and inclination of acetabular components in total hip arthroplasty (THA). One-hundred and thirty-eight consecutive patients who underwent unilateral primary THA were reviewed. Most cases had some degree of pre-operative PT, with 17% having greater than 10° of PT on standing pre-operative radiographs. There was no significant change in PT following THA. A computer model of a hemispheric acetabular component implanted in a range of anatomic positions in a pelvis with varying PT was created to determine the effects of PT on functional anteversion and inclination. Based on the study results, tilt-adjustment of the acetabular component position based on standing pre-operative imaging will likely improve functional component position in most patients undergoing THA.

Keywords: computer-assisted surgery; cup orientation; hip arthroplasty; navigation; preoperative planning.

Figure 1

A line representing the anterior pelvic plane (APP) is drawn in relation to the line representing the coronal plane in a pelvis with 15° of posterior pelvic tilt (PT).

Figure 2

Figure demonstrating position of acetabular shell with 30° anterior pelvic plane (APP) anteversion and 40° APP inclination with a) 0° of sagittal pelvic tilt and b) 20° of posterior pelvic tilt changing the functional anteversion to 44.2° and the functional inclination to 50.9°.

Figure 3

Plot of pre-operative versus post-operative pelvic tilt (PT). Pre-operative PT was strongly correlated with post-operative PT (r² = 0.88, p = 0.0001).

Figure 4

Plot of pelvic incidence versus change in pelvic tilt. Pelvic incidence does not appear to correlate with change in pelvic tilt (r² = −0.16, p = 0.06).

Figure 5

a) Plot of pelvic tilt versus anterior pelvic plane (APP) anteversion versus functional anteversion showing a relatively linear relationship throughout the range of tilt and acetabular component positions. b) Plot of pelvic tilt versus APP anteversion versus functional inclination showing a dramatic increase in effect of pelvic tilt on functional inclination as the APP anteversion is increased.