Investigation of Cup Placement Position in Total Hip Arthroplasty with Cup-side Implant Placement in Computed Tomography Horizontal Sections.

The position attained in total hip arthroplasty (THA) is ideally in the center of the horizontal plane of the acetabulum. However, central placement is not always possible. We hypothesized that differences in approach result in individual differences in cup positioning; thus, we investigated the cup positions of 217 hips that underwent THA. The acetabulum's anteroposterior diameter was measured, and the cups placed within 2 mm of the line perpendicular to the center as a central placement (central). Of the 217 hips, 68, 114, and 35 hips were anterior, central, and posterior, respectively. In 21 hips, anteroposterior deviation was noted. Among patients operated using the anterolateral approach, 48, 93, and 30 hips were anterior, central, and posterior, respectively. Among those operated using the posterolateral approach, 16, 20, and 4 hips were anterior, central, and posterior, respectively. The cup position shifted either anteriorly or posteriorly to the acetabulum in approximately half of all hips operated using both approaches and tended to shift anteriorly in the hips operated using the posterolateral approach. During THA surgery, it is important to operate with awareness of the center of the acetabulum.