Pelvic rotation correction by using transverse acetabular ligament for acetabular component anteversion orientation in total hip arthroplasty

Abstract

Objective To investigate the effects of pelvic rotation on acetabular component placement by measuring the pelvic rotation intraoperively, and evaluate the accuracy and the correction of pelvic rotation by using transverse acetabular ligament for acetabular component anteversion orientation during total hip arthroplasty(THA) with posterolateral approach. Methods Forty patients (44 hips) undergoing primary THA in HeChi Third People’s Hospital from January 2015 to January 2016 were enrolled in this study. All the patients were positioned in the lateral decubitus position, THA was performed through posterolateral approach. A Steinmann pin (the sentinel pin) was inserted through the iliac crest at 90° to the floor to assess the degree of pelvic rotation with reference to the floor. The acetabulum and transverse acetabular ligament (TAL) were exposed, and the acetabular component anteversion were positioned with TAL orientation, in which the inferomedial rim of the cup had been positioned parallel to TAL intraoperatively. The degree of pelvic rotation during the operation was determined by the angle of Steinmann pin relative to the ground which was recorded with the camera. At the same time, the degree of operative anteversion relative to the long axis body was measured and recorded. CT scan was applied to measure radiographic cup anteversion and preoperative native acetabular anteversion. Acetabular component anteversion, operative acetabular anteversion, preoperative native acetabular anteversion were statistically analyzed by t test . Results In this study, pelvic rotation occurred in each case, the mean rotation angle was estimated (18±4) °. TAL was identified, the operative acetabular anteversion angle was (33±5) ° in average. The operative acetabular anteversion was larger than 24°, and in 93% of the cases (41 hip) it was larger than 25°(the upper limit of Lewinnek’s safe zone). No statistical difference was found between mean angle of acetabular component anteversion measured by CT scan (21±10)° and preoperative native acetabular anteversion (19±7) °(t=1.264, P >0.05). Conclusions Forward rotation of the patient will affect the accuracy of the acetabular component positioning during posterolateral approach to THA. TAL can be used as an anatomical landmark for anteversion orientation to correct pelvic rotation at the time of cup placement, and help the cup to be placed in a more precise orientation at the correct degree of anteversion. Key words: Arthroplasty; Acetabulum; Pelvis; Rotation; Anteversion; Ligament