Minimal radiation dose computed tomography for measurement of cup orientation in total hip arthroplasty.

We studied a computed tomography (CT) protocol with minimal radiation dose for measurements of cup orientation after total hip arthroplasty. Inclination and version angles were measured directly on cadaver pelvis fixed with an acetabular component. We performed the CT scanning on the phantom made of this model in 6 protocols as follows: tube current of 300, 100, 50, 30, 20, and 10 mA. The 30 mA protocol maintained good image quality for measurements with the smallest dose (1.1 millisievert), which corresponds to less than 2 times that of an anteroposterior radiograph of the pelvis. The differences of measured angles between direct and CT measurements on the phantom were less than 1 degrees. Measurements of cup orientation were possible by this protocol in 26 hips in 22 patients after total hip arthroplasty.