Introduction and Aims: Vertical acetabular cup positioning is an important technical aspect in total hip arthroplasty. It has been reported that acetabular component malpositioning is associated with an increased risk of dislocation, limited range of motion and impingement. A high vertical acetabular angle is correlated positively with premature polyethylene wear, osteolysis and early aseptic loosening in metal-polyethylene and ceramic-ceramic interface.

Method: To evaluate the potential benefit of using an inclinometer in vertical acetabular cup positioning, 96 patients were randomised to have their acetabular cup insertions done with an inclinometer or by visuo-spatial perception alone. The surgeries were performed by five hip surgeons.

Results: The precision of the acetabular vertical angles averaged 43 degrees +/-6.7 by visuo-spatial perception alone and 44 degrees +/-6.8 with the inclinometer. With the inclinometer and by visuo-spatial perception respectively, 12.8% and 9.3% of the cups were outside a safe angle range of 35–54 degrees. The standard deviation was +/-4.9 degrees for the inclinometer and +/-4.7 degrees for the visuo spatial perception method.

Conclusion: The use of an inclinometer is as precise as the visuo spatial perception of a hip surgeon. Positioning the cup with the inclinometer did not reduce the variability or improve the precision of the vertical acetabular position during total hip arthroplasty, suggesting it is not an essential adjunct in the clinical practice of hip surgeons. However, the inclinometer might be a valuable tool for surgeons performing a low volume of hip surgery.