INTRODUCTION: The study aims were to identify the incidence of pelvic adduction during total hip arthroplasty (THA) in lateral decubitus and to determine, when aiming for 35° of apparent operative inclination (AOI), which of 3 operating table positions most accurately obtained a target radiographic inclination (RI) of 42°: (1) horizontal; (2) 7° head-down; (3) patient-specific position based on correction of pelvic adduction.
METHODS: With patients seated on a levelled theatre table, a ruler incorporating a spirit level was used to draw transverse pelvic lines (TPLs) on the skin overlying the pelvis and sacrum. Subsequently, when positioned in lateral decubitus these lines provided a measure of pelvic adduction. 270 participants were recruited, with 90 randomised to each group for operating table position. In all cases target AOI was 35°, aiming to achieve a target RI of 42°. The primary outcome measure was absolute (unsigned) deviation from the target RI of 42°.
RESULTS: 266/270 patients demonstrated pelvic adduction (overall mean 4.4°, range 0- 9.2°). No patients demonstrated pelvic abduction. There were significant differences in RI between each of the 3 groups. The horizontal table group displayed the highest mean RI. The patient specific table position group achieved the smallest absolute deviation from target RI of 42°.
DISCUSSION: In lateral decubitus, unrecognised pelvic adduction is common and is an important contributor to unexpectedly high RI. The use of preoperative TPLs helps identify pelvic adduction and its subsequent correction reduces variability in RI. Clinical Trial Protocol number: NCT01831401.