Acetabular cup positioning within the Lewinnek safe zone reduces the risk of complications related to prosthesis dislocation. However, it has been demonstrated that angles of abduction of the native acetabulum do not lie within this range, possibly leading to cup malpositioning. The purpose of this study was to determine whether the preoperative radiographic measurements of acetabular abduction correlate with those obtained intraoperatively with the use of an inclinometer.
Preoperative and intraoperative angles of abduction from 100 consecutive patients who underwent total hip arthroplasty between July 2007 and November 2008. An intraclass correlation coefficient (ICC) and its 95% confidence interval (95% CI) were calculated to determine the level of agreement between the preoperative and the intraoperative angles.
Mean preoperative angle of abduction was 48.9±6.1 degrees and mean intraoperative angle was 49±5.7 degrees. The mean difference between these angles was 0.06 degrees. Twenty-eight percent of patients had preoperative angles of abduction of>50 degrees. An ICC of 0.96 (95% CI: 0.94–0.97) was obtained. This indicates that preoperative and intraoperative measures of acetabular abduction are almost identical.
Preoperative and intraoperative measures of acetabular inclination are highly correlated. Measurements of acetabular inclination on preoperative plain anteroposterior radiographs of the pelvis should be considered for acetabular cup positioning during total hip arthroplasty. The systematic use of this simple, valid, and effective measurement might be useful.